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Sample records for alkali halide crystal

  1. Energy determination from electron range in alkali-halide crystals

    International Nuclear Information System (INIS)

    The coloration of alkali-halide crystals was used to determine the electron energies <10 MeV. The coloration depth in a crystal - the visual range, was measured by using a lighted transparent ruler and an empirical relation was used to determine the extrapolated range. The sharpest edge of coloration was obtained in KBr crystals. The electron energy was calculated from a semi-empirical relation between the extrapolated range of electrons and their energy

  2. Self-trapped holes in alkali silver halide crystals

    International Nuclear Information System (INIS)

    ?-Ray irradiation at 77 K induces defects in M2AgX3 (M=Rb, K and NH4; X=Br and I) crystals. The irradiation induces self-trapped holes of the form of I0 in the case of alkali silver iodides, and (halogen)2- and (halogen)0 in the case of ammonium silver halides. The (halogen)0 is weakly coupled with the nearest alkali metal ion or ammonium ion. It is able to be denoted as RbI+, KI+, NH4I+ or NH4Br+. The directions of hole distribution of (halogen)2- and (halogen)0 were different in each case of the alkali silver iodides, ammonium silver halides and mixed crystal of them. The (halogen)0 decayed at 160 K in annealing process. The (halogen)2- was converted into another form of (halogen)2- at 250 K and this decayed at 310 K. A formation of metallic layers was observed on the crystal surface parallel with the c-plane of (NH4)2AgI3 irradiated at room temperature. (author)

  3. Dislocation unpinning model of acoustic emission from alkali halide crystals

    Indian Academy of Sciences (India)

    B P Chandra; Anubha S Gour; Vivek K Chandra; Yuvraj Patil

    2004-06-01

    The present paper reports the dislocation unpinning model of acoustic emission (AE) from alkali halide crystals. Equations are derived for the strain dependence of the transient AE pulse rate, peak value of the AE pulse rate and the total number of AE pulse emitted. It is found that the AE pulse rate should be maximum for a particular strain of the crystals. The peak value of the AE pulse rate should depend on the volume and strain rate of the crystals, and also on the pinning time of dislocations. Since the pinning time of dislocations decreases with increasing strain rate, the AE pulse rate should be weakly dependent on the strain rate of the crystals. The total number of AE should increase linearly with deformation and then it should attain a saturation value for the large deformation. By measuring the strain dependence of the AE pulse rate at a fixed strain rate, the time constant $\\tau_{\\text{s}}$ for surface annihilation of dislocations and the pinning time $\\tau_{\\text{p}}$ of the dislocations can be determined. A good agreement is found between the theoretical and experimental results related to the AE from alkali halide crystals.

  4. THEORY OF PLASTICO ML IN ?–IRRADIATED ALKALI HALIDE CRYSTALS

    Directory of Open Access Journals (Sweden)

    NAMITA RAJPUT

    2011-06-01

    Full Text Available The present paper reports the results of some theoretical approach made to the studies of mechanoluminescence (ML in coloured alkali halide crystals. It is shown that moving dislocations produced during plastic deformation of crystalline materials cause light emission due to several processes like mechanical or electrostatic interaction of dislocations with defect centres, the dielectric breakdown of adsorbed gaseous molecules by the surface accumulated dislocation charges, the generation of holes during decay of mobile dislocations on the surfaces of crystals, etc. On the basis of rate equations, expressions are derived for the rise and decay of ML intensity at a given strain rate. The estimated values of ML intensities for different crystals are found to be comparable with the experimentally observed values. The expression derived are able to explain the dependence of ML intensity on several parameters like strain-rate, defect centre density, temperature, applied stress, crystal- size etc.

  5. Energetics of substituted ion disordered alkali halide crystals

    International Nuclear Information System (INIS)

    A possibility of interstitial ion arrangement in vacant units of an opposite sublattice is theoretically considered by means of the variational simulation method, taking NaCl, KCl and NaBr alkali halide crystals as examples. Within the framework of the model chosen complex binding energies are calculated: ion vacancy of on and the same sign is the interstitial ion of the opposite sign. A possibility of anti-Schottky dipole rise, an anion component of which is placed in the cation vacancy, as well anti-Schottky dipole, a cation component of which is placed in the anion vacancy, is considered. Binding energies of such complexes are calculated. A possibility of interstitial ion arrangement in vacancy points of the oppopsite sublattice is established. A possibility of anti-Schottky dipole formation, whose component is placed in vacancy of an oppositely charged ion, is shown

  6. Transmission electron microscopy of weakly deformed alkali halide crystals

    International Nuclear Information System (INIS)

    Transmission electron microscopy (TEM) is applied to the investigation of the dislocation arrangement of [001]-orientated alkali halide crystals (orientation four quadruple slip) deformed into stage I of the work-hardenig curve. The investigations pertain mainly to NaCl - (0.1-1) mole-% NaBr crystals, because these exhibit a relatively long stage I. The time available for observing the specimens is limited by the ionization radiation damage occuring in the microscope. An optimum reduction of the damage rate is achieved by a combination of several experimental techniques that are briefly outlined. The crystals deform essentially in single glide. According to the observations, stage I deformation of pure and weakly alloyed NaCl crystals is characterized by the glide of screw dislocations, which bow out between jogs and drag dislocation dipoles behind them. In crystals with >= 0.5 mole-% NaBr this process is not observed to occur. This is attributed to the increased importance of solid solution hardening. (orig.)

  7. Simulation of X3- centers dissociation process in alkali halide crystals with accounting of crystalline surroundings

    International Nuclear Information System (INIS)

    For detailed elaboration of mechanisms both formation and destruction of X3- centers in irradiated alkali halide crystals by semi-empirical quantum-chemical method MNDO the decay process of X3- center in KCl and KI crystals is simulated. The applied method comes into MOPAC-7.21 program package. For study of these processes plane crystal structures of KCl and KI consisting of 18 cations and 18 anions with lattice parameters of KCl and KI were formed. It is determined, that X3- centers of irradiated alkali halide crystals at simulation with taking into accounting of surrounding are dissociating from singlet state on X20 and X- fragments

  8. Cu halide nanoparticle formation by diffusion of copper in alkali halide crystals

    Scientific Electronic Library Online (English)

    A., Pérez-Rodríguez; M., Flores-Acosta; R., Rodríguez-Mijangos; R., Pérez-Salas.

    2006-04-01

    Full Text Available Atomos de cobre han sido introducidos por difusión en cristales de NaCl, KCl y KBr a 500°C. Los cristales han sido analizados ópticamente con medidas de fotoluminiscencia y por microscopía electrónica de barrido. Los espectros de emisión y excitación, medidos a baja temperatura muestran el efecto de [...] confinamiento de exciton, indicando la formación de nanopartículas de CuX (X=Cl, Br), lo cual ha sido confirmado por imágenes de microscopía electrónica. Este método es propuesto como un método alternativo para obtener nanopartículas de CuX en cristales halogenuros alcalinos. Abstract in english Copper atoms have been introduced by diffusion in NaCl, KCl and KBr crystals at 500°C. The crystals have been optically analyzed with photoluminescence measurements and by scanning electron microscopy. The emission and excitation spectra measured at low temperatures show the exciton confinement effe [...] ct, indicating the formation of CuX (X=Cl, Br) nanoparticles, which has been confirmed by electron microscopy images. This is proposed as an alternative method to obtain CuX nanoparticles in alkali halides crystals.

  9. Irradiation-induced defects in alkali halide crystals

    International Nuclear Information System (INIS)

    Models are presented for the successive stages of aggregation and recombination of radiation-induced defects in alkali halides. The construction of the present models is assisted by the calculation of defect energies. Three main areas are discussed: firstly, initial aggregation of H centres is considered, where the formation of a weakly bound di-H centre which collapses into a neutral halogen molecule occupying an interstitial site is proposed. Secondly, the thermodynamics of formation of the interstitial loops detected in the electron microscope by Hobbs et al (Proc. R. Soc; A332; 167 (1973)) are considered. The previously proposed mechanism by which the loops are created is confirmed; this involves the displacement of lattice ions to dislocation loops by halogen molecules which occupy the vacancy pairs created. Thirdly, the mechanism of annealing of metal colloids is considered, and it is suggested that the vacancy-molecule complexes, which are created together with the dislocation loops, may play an important role. (author)

  10. Electronic States of F-Centers in Alkali Halide Crystals

    Science.gov (United States)

    Matsunaga, Katsuyuki; Narita, Nobutaka; Tanaka, Isao; Adachi, Hirohiko

    1996-08-01

    The electronic states of F-centers in alkali halides with NaCl-type structure have been investigated using the discrete variational (DV) Xα cluster method. The electronic transition accompanied by optical absorption is examined on the basis of Slater's transition state concept. The photo-absorption energies of F-centers computed for the compounds with relatively small anions agree well with experimental data, but those for iodides and bromides exhibit much lower values than the observed values. We have also investigated the change in the absorption energy by the atom displacement. By the inward displacement of 1st neighbor cations, the absorption energies are decreased to approach the experimental values. The relaxation of the 1st neighbors estimated from the computation exhibits fairly small values in fluorides, while large values in iodides and bromides. The effect of lattice relaxation around an F-center is discussed in connection with the bonding nature of the F-center level.

  11. Thermoluminescence response of a mixed ternary alkali halide crystals exposed to gamma rays

    International Nuclear Information System (INIS)

    Ionic crystals, mainly alkali halide crystals have been the subject of intense research for a better understanding of the luminescence properties of defects induced by ionizing radiation. The defects in crystals can be produced in appreciable concentration due to elastic stresses, radiation, and addition of impurities. These defects exhibit remarkable thermoluminescence properties. This work is concerned with the Tl properties of a ternary alkali halide crystal after being irradiated with gamma and beta rays. It has been found that the Tl glow peak of the crystal follows a rule of average associated to the Tl Temperatures of the components of the mixture, similarly to the response of europium doped binary mixed crystals KClxKBr1-x and KBrxRbBr1-x. (Author)

  12. Thermoluminescence response of a mixed ternary alkali halide crystals exposed to gamma rays

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez M, R.; Perez S, R. [Universidad de Sonora, Departamento de Investigacion en Fisica, Apdo. Postal 5-088, 83190 Hermosillo, Sonora (Mexico); Vazquez P, G.; Riveros, H. [UNAM, Instituto de Fisica, Apdo. Postal 20-364, 01000 Mexico D. F. (Mexico); Gonzalez M, P., E-mail: mijangos@cifus.uson.mx [ININ, Carretera Mexico-Toluca s/n, 52750 Ocoyoacac, Estado de Mexico (Mexico)

    2014-08-15

    Ionic crystals, mainly alkali halide crystals have been the subject of intense research for a better understanding of the luminescence properties of defects induced by ionizing radiation. The defects in crystals can be produced in appreciable concentration due to elastic stresses, radiation, and addition of impurities. These defects exhibit remarkable thermoluminescence properties. This work is concerned with the Tl properties of a ternary alkali halide crystal after being irradiated with gamma and beta rays. It has been found that the Tl glow peak of the crystal follows a rule of average associated to the Tl Temperatures of the components of the mixture, similarly to the response of europium doped binary mixed crystals KCl{sub x}KBr{sub 1-x} and KBr{sub x}RbBr{sub 1-x}. (Author)

  13. Luminescence of mono halide excitons and intraband luminescence in alkali-halide crystals

    International Nuclear Information System (INIS)

    Nanosecond electron beam pulses excite in RbCl, RbBr and KBr crystals the continuum of temperature of two-halide auto localized excitons, as well as weak rapid luminescence interference as luminescence of metastable monohalide auto localized excitons luminescence was performed for KBr crystal, excited by 6.6-7.7 and 14-20 eV photons

  14. Possibility of elastico-mechanoluminescence dosimetry using alkali halides and other crystals

    International Nuclear Information System (INIS)

    The elastico-mechanoluminescence (EML) intensity of X or ?-irradiated alkali halide crystals can be used in radiation dosimetry. The EML intensity of X or ?-irradiated alkali halide crystals increases linearly with the strain of the crystals, and when the crosshead of the testing machine deforming an X or ?-irradiated crystal is stopped, then the EML intensity decreases with time. The semilog plot of the EML intensity versus (t ? tc) (where tc is the time where the crosshead of the testing machine is stopped) indicates that, in the post-deformation region, the EML intensity initially decreases exponentially at a fast rate and later on it decreases exponentially at a slow rate. The EML intensity increases linearly with the density of the F-centres in the crystals. This fact indicates that elastico-ML can suitably be used for the radiation dosimetry. The EML spectra of X or ?-irradiated alkali halide crystals are similar to their thermoluminescence spectra. Based on the detrapping of electrons during the mechanical interaction between the dislocation segments and F-centres, an expression is derived, which indicates that the EML intensity should increase linearly with the density of F-centres in the crystals. The expression derived for the decay of EML indicates that the decay time for the fast decrease of EML should gives the pinning time of dislocation segments (lifetime of interacting F-centres), and the decay time for the slow decrease of EML intensity should gives the lifetime of electrons in the shallow traps. As the elastic deformation is non-destructive phenomenon and the EML intensity depends on the radiation dosage given to the alkali halide crystals, similar to the thermoluminescence and photo-stimulated luminescence, the EML of alkali halide crystals and other crystals may be used for the radiation dosimetry. In EML dosimetry, the same crystal can be used number of times because the elastic deformation does not cause permanent deformation in the crystals, and moreover, comparatively the devices needed for the EML measurements are of low cost and very simple. In recent years, a large number of elastico mechanoluminescent materials have been investigated, and the study of their suitability for the radiation dosimetry may be interesting. - Highlights: • Elastico-mechanoluminescence (EML) can be used in radiation dosimetry. • As EML occurs in the elastic region, the same sample can be used number of times. • The EML can be used for X-ray, ?-ray and ultraviolet dosimetry. • Mathematical approach verifies the possibility of EML dosimetry

  15. Acoustic and photon emissions during mechanical deformation of coloured alkali halide crystals

    International Nuclear Information System (INIS)

    Acoustic and photon emissions take place in the elastic and plastic as well as the fracture region of x-irradiated KBr, KCl and NaCl crystals. The rate of photon emission is linear with the strain rate: however, the RMS value of the acoustic emission is proportional to the square root of the strain rate. The acoustic emission is maximum for x-irradiated NaCl crystals; however, the photon emission is maximum for x-irradiated KBr crystals. From the similarity between the acoustic emission and the photon emission, it seems that mobile dislocations are responsible for the acoustic emission in coloured alkali halide crystals. (author)

  16. The process of colloidal centre formation in alkali halide crystals during irradiation

    International Nuclear Information System (INIS)

    In this paper are analysed the processes of electronic centre aggregation to colloidal alkali metal particles in alkali halide crystals under radiation. It is shown that the existing theories of particle coalescence do not describe the experimentally observed kinetics of radiolysis. A new model of radiation colloid formation in these systems is proposed in which the interaction between colloidal centres is taken into account. In the present model the experimentally observed dose and temperature dependences, as well as the size distribution of the electron products of radiolysis, are explained. (author)

  17. Helium irradiation of alkali halides

    International Nuclear Information System (INIS)

    An investigation has been made of radiation damage in alkali halide crystals induced by heavy bombardment of 1 MeV helium ions. The channeling technique has been employed and three processes have been monitored simultaneously to explain the apparent reduction of damage at high doses. It is shown that the initial rise and fall of the back-scattered yield from different alkali halides can be related to the Pooley mechanism coupled with the aggregation of interstitials to form dislocation loops through the intermediate stage of clusters

  18. Ga+, In+ and Tl+ Impurities in Alkali Halide Crystals Distortion Trends

    CERN Document Server

    Aguado, A

    2000-01-01

    A computational study of the doping of alkali halide crystals (AX: A = Na, K; X = Cl, Br) by ns2 cations (Ga+, In+ and Tl+) is presented. Active clusters of increasing size (from 33 to 177 ions) are considered in order to deal with the large scale distortions induced by the substitutional impurities. Those clusters are embedded in accurate quantum environments representing the surrounding crystalline lattice. The convergence of the distortion results with the size of the active cluster is analyced for some selected impurity systems. The most important conclusion from this study is that distortions along the (100) and (110) crystallographic directions are not independent. Once a reliable cluster model is found, distortion trends as a function of impurity, alkali cation and halide anion are identified and discussed. These trends may be useful when analycing other cation impurities in similar host lattices.

  19. Correlation between deformation bleaching and mechanoluminescence in coloured alkali halide crystals

    Indian Academy of Sciences (India)

    B P Chandra; M Ramrakhiani; P Sahu; A M Rastogi

    2000-02-01

    The present paper reports the correlation between deformation bleaching of coloration and mechanoluminescence (ML) in coloured alkali halide crystals. When the $F$-centre electrons captured by moving dislocations are picked up by holes, deep traps and other compatible traps, then deformation bleaching occurs. At the same time, radiative recombination of dislocation captured electrons with the holes gives rise to the mechanoluminescence. Expressions are derived for the strain dependence of the density of colour centres in deformed crystals and also for the number of colour centres bleached. So far as strain, temperature, density of colour centres, $E_{a}$ and volume dependence are concerned, there exists a correlation between the deformation bleaching and ML in coloured alkali halide crystals. From the strain dependence of the density of colour centres in deformed crystals, the value of coefficient of deformation bleaching is determined and it is found to be 1.93 and 2.00 for KCl and KBr crystals, respectively. The value of $(D + \\mathcal{X})$ is determined from the strain dependence of the ML intensity and it is found to be 2.6 and 3.7 for KCl and KBr crystals, respectively. This gives the value of coefficient of deformation generated compatible traps $\\mathcal{X}$ to be 0.67 and 1.7 for KCl and KBr crystals, respectively.

  20. Application of secondary ion mass spectrometer for measuring the diffusion profiles in alkali-halide crystals

    Science.gov (United States)

    Chernyavskii, A. V.; Kaz, M. S.

    2015-04-01

    Depth profiles of magnesium, fluorine and oxygen impurities was examined in the surface layers of alkali-halide KBr crystals using method of secondary ion mass spectrometry. Samples of potassium bromide, coated with a surface film of magnesium fluoride were subjected to isothermal diffusion annealing in air at various times. It is shown that the diffusion of O ions occurs from the ambient atmosphere besides the diffusion of Mg and F ions during annealing of KBr crystals. Accurate estimation of the diffusion coefficients of cationic impurity Mg requires taking into account the possible interaction of this impurity and oxygen.

  1. Defects in alkali halide crystals irradiated under applied stress

    International Nuclear Information System (INIS)

    Futher study of physical property alterations of dielectric crystals placed in different fields and subjected to irradiation is carried out. Mechanical, optical and thermal properties of NaCl, LiF, KCl crystals irradiated with p and n-p radiation in electric thermal and mechanical fields are presented. Crystal structural defects responsible for the property alteration are studied (point defects, their aggregates, dislocations, and their interactions). The irradiation of crystals in the stressed state allows one to change the defect spectrum which means the possibility to obtain materials with controllable properties

  2. Accidental birefringence and annealing effects in alkali halide single crystals

    International Nuclear Information System (INIS)

    Photoelasticity is used to explain the accidental birefringence patterns induced by thermal stresses in KCl and KBr-KCl crystals. It is shown that the residual stress and plastic deformations are essentially due to the variable temperature gradients. An optimal thermal treatment in order to eliminate the residual stresses is presented. (author)

  3. High-intensity ?-ray scattering from alkali halide crystals

    International Nuclear Information System (INIS)

    We have measured the fractional change F of the resonant photon fraction due to Bragg scattered from the (200), (400), and (600) planes of NaCl and NaF, as well as the (200) and (400) planes of LiF. Unlike previous measurements of this type, we have used well-collimated beams made possible by a high-intensity ?-ray source (?100 Ci). The values of F reflect loss in elastic intensity and are of importance since the crystals studied here are widely used as monochromating filters. We find a remarkably large fraction of the scattered radiation remains recoilless (>94%), even for the (600) reflection of NaCl, and a value of F=100.0(3%) for the (200) plane of LiF shows that this crystal is an excellent ?-ray monochromator and calibration for experiments with small F values. The F values can be expressed in terms of elastic and inelastic components, and as such provide information about the Debye-Waller factors of crystals

  4. A study of ion-photon emission in alkali-halide crystals

    International Nuclear Information System (INIS)

    Optical emission under bombardment of the NaCl, NaI, CsCl, and CsI crystals by Ar+ ions with an energy of 25 keV was studied, and the emission quantum yield of the sputtered alkaline-metal atoms is found to be higher for chlorides than for iodides. At the same time, the crystal luminescence reveals an inverse dependence. The assumption is made that population of the excited states of sputtered atoms is caused by electrons localized at the defect levels in the forbidden band. Studies of the energy distribution of the sputtered excited particles revealed the existence of a group of slow atoms emitting upon transitions from the highly-excited states. This fact testifies to the absence of substantial metallization of the surface under ionic bombardment of alkali-halide crystals. 20 refs., 3 figs., 1 tab

  5. An optical criterion to obtain miscible mixed crystals in alkali halides

    Scientific Electronic Library Online (English)

    R, Rodríguez-Mijángos; G, Vázquez-Polo; J.J., Palafox; R, Pérez-Salas.

    2008-11-01

    Full Text Available Este trabajo ofrece un nuevo criterio para predecir la formación de soluciones sólidas en halogenuros alcalinos cristalinos y discute algunos resultados obtenidos en el desarrollo de mezclas dieléctricas cristalinas miscibles de halogenuros alcalinos ternarias y cuaternarias. Estas mezclas son misci [...] bles en cualquier concentración de sus componentes. Tener el resultado de estas mezclas cristalinas está relacionado al centro F a través del comportamiento observado en la banda F de absorción en función de la constante de red de los halogenuros alcalinos donde el defecto fue formado (centro F). Dando un vistazo a la gráfica de Energía de banda F versus constante de red (ley de Mollwo-Ivey), se observa un conjunto de puntos, que dan la pauta (tal como KCl, KBr, RbCl), de posibles mezclas de materiales correspondientes a puntos adyacentes y una solución sólida podría formarse, significando un cristal de una sola fase, que dan por resultado cristales ternarios y cuaternarios. Así, la banda F de absorción nos permite tener un criterio numérico, basado en el porcentaje de cambio de la energía de la banda F que permite obtener soluciones sólidas. Encontramos información experimental, usando difractogramas de las mezclas cristalinas, se obtienen las constantes de red y se comparan con la obtenida teóricamente a través de la generalización de la Regla de Vegard, finalmente se discute la posibilidad de crecer cristales partiendo de cinco componentes, tomando cinco puntos consecutivos en la grafica de la Ley de Mollwo-Ivey. Abstract in english This work gives a novel criterion to predict the formation of alkali halide solid solutions and discusses some results obtained in the development of ternary and quaternary miscible crystalline dielectric mixtures of alkali halides. These mixtures are miscible in any concentration of their component [...] s. The miscibility of these mixed crystals is quite related to the F center through the behavior observed in the spectral position of the optical absorption F band as a function of the lattice constant of the alkali halide where the F center was formed. By inspection of an energy graph of the F band energy versus lattice constant (Mollwo-Ivey law), a set of points is observed corresponding to several pure alkali halides (such as KCl, KBr, RbCl), which gives a notion of possible mixed materials that would correspond to adjacent points and a solid solution could be obtained, meaning a single phase crystal, which result in ternary and quaternary mixed crystals. Thus, the optical absorption F band allows have a numerical criterion, based on the percentage respective of the F band energy, in order to predict possible solid solutions. We obtained experimental information using diffractograms of the mixed crystals, from which the lattice constant was obtained and compared with a theoretical calculus using a generalization of Vegard's law, finally it is discussed the case of a crystal growing, starting from five components, picking up five consecutive dots from the graph of Mollwo-Ivey's law.

  6. Efficiency of primary radiation-induced defects in alkali halide crystals

    International Nuclear Information System (INIS)

    Temperature dependences of F centers formation efficiency (FE) are measured by the method of pulse absorption spectrometry with nanosecond resolution with the aim of determination of the relative yield of decay reaction of electron excitations into primary pairs of structural defects in alkali halide crystals (LiF, NaF, NaCl, NaBr, KCl, KBr, KI, RbBr). It is shown that for all studied compounds FE of F centers increases in the temperature range from 100 up to 300 K. Activation energies of the primary defects storage process are determined. It is supposed that FE of primary defects is determined mainly by the ratio of exciton energy parameters of predissociated and predefect state as well as of energy, stored on defect

  7. New AIG method of growing alkali halide crystals and potential application to CZT

    International Nuclear Information System (INIS)

    The new AIG (Advance Interface Growth) method has been successfully applied to alkali halide scintillation crystals at PhotoPeak, Inc. for the last four years. It produces single, stress-free crystals having a low level of defects and has resulted in increasing the yield of usable CsI(Tl) crystals to 75-85%. Essentially it is a low gradient method but has the capability to adapt the gradient to that needed by an individual crystal for the most successful growth. High quality crystals have been supplied to national laboratories and the nuclear medicine market. For example, a blank CsI(Tl) crystal 2 in diameter and 2 in length was produced having a measured energy resolution of 6.5% at 662 keV on a 2 -diameter PMT having a standard blue bialkali photocathode. This far exceeds the best resolution, 8.5-9.5%, obtained for CsI(Tl) crystals grown by the conventional Bridgman method. It is expected that this method can be successfully applied to grow high quality CZT crystals with substantially higher yield, 25-35%, than the presently existing 5-10%. The reasons for the expected improved yield of CZT crystals are that the phase diagram of CZT material has a narrow range of stability and CZT crystals should benefit from growth in a low gradient environment. Since the AIG method does not involve any moving parts, the temperature control and stability are much higher than for the conventional Bridgman method. The experience with CsI crystals indicates that imperfections like twinning, sparks, and multiplicities can be substantially reduced or even eliminated in CZT crystals. The expected higher yield and improved spectroscopic quality of CZT should allow many commercial applications to become a reality

  8. Luminescent unit computerization to research spectral characteristics of fine film alkali halide crystal

    International Nuclear Information System (INIS)

    The fundamental optical absorption of ion crystals characterizes the creation of different free low energetic electronic excitation (the excitons and electron-hole pairs), but their straight registration is not possible because of incommensurable big absorption factor of alkali halide monocrystals. So to registration the spectrums of alkali halide monocrystal very fine layers are necessary. We have received fine films of Nal and KCl in system of KCl-Nal-KCl, KCl-KI-KCl on the base of universal vacuum post VUP-4, VUP-5 by thermal evaporation. A unique spectral unit has been created For this on the basic the SDL-2 complex. Complex consists of radiator, systems of condensers, monochromators MDR-12 and MDR-23, receivers of radiation, controller by unit. Connect and control of monochromators by means of IBM-compatible computer has been created. Kinematics schemes of monochromators provide consequent removing on output slot of monochromatic radiation in operating range of each diffraction lattice and indication its wavelength. The tumbling diffraction lattices is done the crossbar engines SHDR-711. For this special plate of control and block of reinforcement for crossbar engines in monochromators MDR-12 and MDR-23 are designed and constructed. Created controller of monochromators consists of double cascade preamplifier on transistors n-p-n type (815G) and logical scheme, constructed on summers and K555 series triggers. The preamplifier is used for reinforcement of signal to available amplifier on transistors KT837D. The logical scheme reduces the number of used categories of bidirectional port and enables unhooking the feeding to the windings of crossbar engine at conservation of previous combination of signals. The connection controller of monochromators is done through controller of port of computer with use the parallel interface. For installing computerized system of collection and data processing is provided marketed by means of modern object-oriented programming languages (Visual C++ 6.0, Visual Basic 6.0). As the result of the experiments it has been noted that the burning effect of own luminescence is in its maximum in the iodides of alkaline metals, for instance, in KI, NaI, RbI, and CsI crystals. From the point of the experimental equipment in order to registration the fundamental optical absorption of these crystals there is no necessity in such rare vacuum monochromators

  9. Electron-beam production of colour centres on alkali halide crystals and films

    International Nuclear Information System (INIS)

    In this article we analyze the production of localized colour centres on the surface of alkali halide crystals and films produced by electron beam radiations in the 10-30 keV range. It was found that the colour centre production is restricted to electron penetration (3-10 ?m depending on the material and electron energy) with a very intense local optical density (above 104 cm-1). As the refractive index variation calculated using the Kramers-Kroenig relations from the observed absorption bands should be enough for light confinement (10-3-10-2), electron beam generated colour centres should allow the production of light wave guides for several applications. Optical absorption bands can be created in ionic crystals anywhere from the ultraviolet to the infrared, preserving transparent regions of the spectrum. With an appropriate computer aided design (CAD) program and a microcomputer interface to the adapted micropositioning mechanical devices and shutter, it was possible to control an electron microprobe sample holder in order to draw precise patterns and have various controlled exposure times. (orig.)

  10. Ab Initio Calculation of the Lattice Distortions induced by Substitutional $Ag$- and $Cu$-Impurities in Alkali Halide Crystals

    CERN Document Server

    Aguado, A; Alonso, J A; Aguado, Andres; Lopez, Jose M.; Alonso, Julio A.

    2000-01-01

    An ab initio study of the doping of alkali halide crystals (AX: A=Li, Na, K,Rb; X=F, Cl, Br, I) by ns2 anions (Ag- and Cu-) is presented. Large activeclusters with 179 ions embedded in the surrounding crystalline lattice areconsidered in order to describe properly the lattice relaxation induced by theintroduction of substitutional impurities. In all the cases considered, thelattice distortions imply the concerted movement of several shells ofneighbors. The shell displacements are smaller for the smaller anion Cu-, asexpected. The study of the family of rock-salt alkali halides (excepting CsF)allows us to extract trends that might be useful at a predictive level in thestudy of other impurity systems. Those trends are presented and discussed interms of simple geometric arguments.

  11. Optical properties of alkali halide crystals from all-electron hybrid TD-DFT calculations

    International Nuclear Information System (INIS)

    We present a study of the electronic and optical properties of a series of alkali halide crystals AX, with A = Li, Na, K, Rb and X = F, Cl, Br based on a recent implementation of hybrid-exchange time-dependent density functional theory (TD-DFT) (TD-B3LYP) in the all-electron Gaussian basis set code CRYSTAL. We examine, in particular, the impact of basis set size and quality on the prediction of the optical gap and exciton binding energy. The formation of bound excitons by photoexcitation is observed in all the studied systems and this is shown to be correlated to specific features of the Hartree-Fock exchange component of the TD-DFT response kernel. All computed optical gaps and exciton binding energies are however markedly below estimated experimental and, where available, 2-particle Green’s function (GW-Bethe-Salpeter equation, GW-BSE) values. We attribute this reduced exciton binding to the incorrect asymptotics of the B3LYP exchange correlation ground state functional and of the TD-B3LYP response kernel, which lead to a large underestimation of the Coulomb interaction between the excited electron and hole wavefunctions. Considering LiF as an example, we correlate the asymptotic behaviour of the TD-B3LYP kernel to the fraction of Fock exchange admixed in the ground state functional cHF and show that there exists one value of cHF (?0.32) that reproduces at least semi-quantitatively the optical gap of this material

  12. Mobile interstitial model and mobile electron model of mechano-induced luminescence in coloured alkali halide crystals

    International Nuclear Information System (INIS)

    A theoretical study is made on the mobile interstitial and mobile electron models of mechano-induced luminescence in coloured alkali halide crystals. Equations derived indicate that the mechanoluminescence intensity should depend on several factors like strain rate, applied stress, temperature, density of F-centres and volume of crystal. The equations also involve the efficiency and decay time of mechanoluminescence. Results of mobile interstitial and mobile electron models are compared with the experimental observations, which indicated that the latter is more suitable as compared to the former. From the temperature dependence of ML, the energy gaps between the dislocation band and ground state of F-centre is calculated which are 0.08, 0.072 and 0.09 eV for KCl, KBr and NaCl crystals, respectively. The theory predicts that the decay of ML intensity is related to the process of stress relaxation in crystals. (author). 33 refs., 5 figs., 1 tab

  13. Effect of a magnetic field on the luminescent lifetime of Cu+ in alkali halide host crystals

    International Nuclear Information System (INIS)

    We have measured the change in the triplet emission lifetime of the Cu+ impurity in various alkali halide hosts at 4.2 K as a function of applied magnetic field. Pedrini [Phys. Status Solidi B 87, 273 (1978)] has proposed that the 3E/sub g/ emitting state is split into T/sub 1g/ and T/sub 2g/ spin-orbit components and has found that the emission lifetime depends sensitively on the splitting. We have utilized an external magnetic field to mix these spin-orbit levels. This produced a measurable decrease in the emission lifetime which we explained with Pedrini's model. We also diagonalized the d9s excited-state matrix to calculate independently the T/sub 1g/,T/sub 2g/ spin-orbit splitting and obtained reasonable agreement with our experimental results

  14. Optical surface breakdown of alkali halide crystals by microsecond pulses from a wide-aperture CO2 laser

    International Nuclear Information System (INIS)

    A study was made of the dynamics of temporal and spatial changes in the spectral characteristics of plasmas. A three-stage mechanism of the damage to surfaces of alkali halide crystals by microsecond pulses from a TEA CO2 laser was proposed: breakdown initiation (at a distance of 3-5 mm from the surface with a time delay up to 1 ?s relative to the leading edge of a laser pulse), evaporation (after a further delay of 3-5 ?s), and interaction of the adsorbates with a plasma jet and with the laser radiation, as well as heating and cracking of a crystal by the UV plasma radiation. (interaction of laser radiation with matter. laser plasma)

  15. EPR study of electron bombarded alkali- and alkaline-earth halide crystal surfaces

    Science.gov (United States)

    Fryburg, G. C.; Lad, R. A.

    1975-01-01

    An EPR study of electron bombarded LiF, NaCl, KCl, CaF2 and BaF2 polycrystalline surfaces has shown that small metal particles are formed on the surfaces of the crystals. Identification was made from CESR signals. The symmetric line-shape of the signals, even at 77 K, indicated that the particles were less than 0.5 micron in diameter. Signals due to F centers were observed in LiF but not in the other halides. Implications to metal deposition are considered.

  16. Ultraviolet optical absorption of alkali cyanides and alkali halide cyanides

    International Nuclear Information System (INIS)

    The ultraviolet absorption spectra of alkali cyanide and mixed alkali halide cyanide crystals were measured at temperatures ranging from 300K down to 4.2K. A set of small absorption peaks was observed at energies near 6 eV and assigned to parity forbidden X1?+?a'3?+ transitions of the CN- molecular ions. It was observed that the peak position depends on the alkali atom while the absorption cross section strongly depends on the halogen and on the CN- concentration of the mixed crystals. These effects are explained in terms of an interaction between the triplet molecular excitons and charge transfer excitons. The experimental data were fit with a coupling energy of a few meV. The coupling mechanism is discussed and it is found to be due to the overlap between the wave functions of the two excitations. (Author)

  17. Aging of alkali halide windows

    Science.gov (United States)

    Kennedy, Michael; Trung, D.; Meyer, Franz; Buth, T.; Ristau, Detlev; Schmidt, Holger; Korth, Joerg U.; Hamburg, K.

    1995-07-01

    The environmental effect on the aging behavior of NaCl and KCl windows was studied. Laser windows were aged at different relative humidities in a controlled climate-chamber. Degradation is monitored with a microscope inspection system equipped with a computer controlled image processing board. The temporal development of surface defect density under different atmospheric conditions was investigated with respect to optical absorption and damage thresholds of the windows at 10.6 micrometers . Laser windows coated with single layers of NaF deposited by an adapted IAD-technique were analyzed. The performance of the coated and uncoated laser windows is discussed under consideration of typical applications. In comparison to the bare samples, the coated windows show an improved resistivity against environmental influences. Accelerated testing theory is employed to model the aging behavior of the samples. An approach to deduce a qualified acceleration factor is made in order to extrapolate the lifetime of alkali halide laser window under normal conditions.

  18. Electron scattering from alkali halide molecules

    International Nuclear Information System (INIS)

    The low energy electron scattering from molecules belonging to alkali halide matrix is studied. The modified Born-Eikonal Series method is employed to calculate rotational excitation cross sections. The curves are plotted for the incident electron energy versus total cross section for each column of alkali halide matrix. The conclusion is drawn regarding dependence of the total cross section with the electron-negativity difference of the molecules. (author)

  19. Temperature dependence of pulse-induced mechanoluminescence excitation in coloured alkali halide crystals

    Indian Academy of Sciences (India)

    Namita Rajput; S Tiwari; B P Chandra

    2004-12-01

    In practice, the relative efficiencies of different crystals are often determined under identical conditions of temperature and excitation. If the temperature of a crystal is increased or decreased with respect to room temperature, luminescence efficiency may get increased or decreased according to the composition of the crystal. When coloured crystals of NaCl, NaBr, KCl and KBr are excited by pulse-induced excitation at different temperatures, the mechanoluminescence (ML) intensity increases with temperature. The ML intensity of first peak, ml, second peak, _m2 and the total ML intensity, T, initially increase with temperature and then tend to attain an optimum value for a particular temperature of crystals. The ratio, m2/ml, is found to increase with increasing temperature of the crystals. The expression derived on the basis of rate equations, are able to explain the temperature dependence of ML intensity on several parameters.

  20. The kinetics of diffusion-controlled annealing of Frenkel defects in alkali halide crystals

    International Nuclear Information System (INIS)

    The annealing kinetics of the strongly correlated (the so-called geminate) pairs of both neutral F,H centers as well as F, I centers entering secondary triplets (F..I..self-trapped hole) in KCl and KBr crystals is calculated. In this model diffusion of hole I and H centers and their annihilation with electron F centers at short relative distances stimulated by the elastic or Coulomb interaction are taken into account. It is demonstrated that F,H pairs are destroyed by tunneling recombination already at times ?10-4 s, i.e. much before the beginning of the thermostimulated experiments. A possible explanation of this contradiction is discussed. ((orig.))

  1. EPR and optical studies of Ge+ ions in alkali halide crystals

    International Nuclear Information System (INIS)

    By the method of EPR it is ascertained for the first time that X-ray irradiation of NaCl:Ce2+ and KCl:Ge2+ at 77 K results in the capture of an electron by Ge2+ ion and the formation of Ge+ ion. Two types of Ge+ centres are revealed Ge+ - centres with orthorhombic symmetry directly after irradiation; the nearest surrounding of these centres has a cation vacancy v sub(k) (Gesup(+)v sub(k) centres). When heating crystals up to 300 K, Gesup(+)v sub(k) - centres are transformed into Ge+ centres wth tetragonal symmetry (Gesup(+)v sub(k) centres) due to the drift of the cathion vacancy from Ge+ ion. Spin hamiltonan parameters are determined for Gesup(+)v sub(k) and Gesub(k)sup(+) centres. It is ascertained that cathion vacancy are primarily located in the nearest by (110) directions position from germanium ion. Absorption optical bands correspond to Gesub(k)sup(+) and Gesup(+)v sub(k) centres in 190-220 nm reg

  2. Temperature dependent dynamic ESD processes in alkali halides

    International Nuclear Information System (INIS)

    The effect of the sample temperature on angular-resolved kinetic-energy distributions of alkali and halogen atoms, electronically desorbed from single crystal alkali halides, has been measured. It was found that while the emission of particles with thermal energies increased by about a factor of 40 in the temperature range 90-300degC, the nonthermal halogen atom intensity decreased by about a factor of 3. From these temperature dependent measurements the activation energies for thermally assisted defect migration processes have been estimated. The results will be compared with the data available in the literature and the predictions of a recently proposed model for electron-stimulated desorption (ESD) of alkali halides. (orig.)

  3. Na+ and Rb+ tracer diffusion in alkali halides

    International Nuclear Information System (INIS)

    We have undertaken a fundamental study of heterodiffusion of foreign ions in pure single crystals. The present work describes measurements of the diffusion coefficient of monovalent cations in some alkali halides, namely Na+ and Rb+ into KCl, KBr, NaI and KI. Priority is given to the super-accuracy of the experimental data. The target is to test the validity of the existing theories for calculating the enthalpy and entropy of migration. (author)

  4. Optical radiation from electron sputtering of alkali halides

    International Nuclear Information System (INIS)

    Electron-surface collisions have been observed to result in the emission of optical radiation from excited atoms and molecules desorbed from alkali halide single crystal surfaces. The detected radiation included Na and Li resonance lines, hydrogen Balmer emission, and OH molecular radiation. Much previous experimental and theoretical effort has been devoted to electron stimulated desorption (ESD) of ground state neutrals and ions, and in particular from alkali halides. The few studies concerned with excited particles have dealt primarily with ejected metastable neutrals. In one case involving electron bombardment fluorescence of ice, a tentative identification has been made of OH molecular radiation. The results reported here include a) the first definitive work on optical radiation from electron bombardment induced emission of excited free substrate particles, and b) the first observations of characteristic radiation from previously adsorbed free atoms and molecules. (orig.)

  5. A simple formula for the fundamental optical absorption of alkali halide melts

    International Nuclear Information System (INIS)

    Significant similarities - with respect to absorption of ultraviolet - between the crystalline and liquid phases of the alkali halides are considered. It is shown that a simple formula which emerged from an earlier application of local electron transfer concepts to the fundamental absorption of the alkali halide crystals appears to apply equally well (i.e., within experimental error) to their melts. This formula fits the observations relating to the fundamental absorption of five molten alkali halides and yields predictions for all the others - which will, it is hoped, stimulate experimental activity. (author)

  6. Theory of the late stage of radiolysis of alkali halides

    International Nuclear Information System (INIS)

    Recent results on heavily irradiated natural and synthetic NaCl crystals give evidence for the formation of large vacancy voids, which were not addressed by the conventional Jain-Lidiard model of radiation damage in alkali halides. This model was constructed to describe metal colloids and dislocation loops formed in alkali halides during earlier stages of irradiation. We present a theory based on a new mechanism of dislocation climb, which involves the production of VF centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of excess H centers. Voids are shown to arise due to the reaction between F and VF centers at the surface of halogen bubbles. Critical parameters associated with the bubble-to-void transition are evaluated. Voids can grow to sizes exceeding the mean distance between colloids and bubbles, eventually absorbing them, and, hence, igniting a back reaction between the halogen gas and metal. The amount of radiation damage in alkali halides should be evaluated with account of void formation, which strongly affects the radiation stability of material

  7. Ground state properties of heavy alkali halides

    OpenAIRE

    Doll, Klaus; Stoll, Hermann

    1998-01-01

    We extend previous work on alkali halides by calculations for the heavy-atom species RbF, RbCl, LiBr, NaBr, KBr, RbBr, LiI, NaI, KI, and RbI. Relativistic effects are included by means of energy-consistent pseudopotentials, correlations are treated at the coupled-cluster level. A striking deficiency of the Hartree-Fock approach are lattice constants deviating by up to 7.5 % from experimental values which is reduced to a maximum error of 2.4 % by taking into account electron ...

  8. Study on influence of growth conditions on position and shape of crystal/melt interface of alkali lead halide crystals at Bridgman growth.

    Czech Academy of Sciences Publication Activity Database

    Král, Robert

    Ro?. 360 , S1 (2012), s. 162-166. ISSN 0022-0248. [5th International Workshop on Crystal Growth Technology (IWCGT). Berlin, 26.06.2011-30.06.2011] R&D Projects: GA AV ?R KJB200100901 Institutional research plan: CEZ:AV0Z10100521 Keywords : Interfaces * morphological stability * segregation * Bridgman technique * halides Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.552, year: 2012

  9. Thermoluminescence of alkali halides and its implications

    Energy Technology Data Exchange (ETDEWEB)

    Gartia, R.K., E-mail: rkgartia02@yahoo.in [Physics Department, Manipur University, Imphal 795003 (India); Rey, L. [Aerial-CRT-parc d' Innovation, B.P. 40443, F-67412 Illkirch Cedex (France); Tejkumar Singh, Th. [Physics Department, Manipur University, Imphal 795003 (India); Basanta Singh, Th. [Luminescence Dating Laboratory, Manipur University, Imphal 795003 (India)

    2012-03-01

    Trapping levels present in some alkali halides namely NaCl, KCl, KBr, and KI are determined by deconvolution of the thermoluminescence (TL) curves. Unlike most of the studies undertaken over the last few decades, we have presented a comprehensive picture of the phenomenon of TL as an analytical technique capable of revealing the position of the trapping levels present in the materials. We show that for all practical purposes, TL can be described involving only the three key trapping parameters, namely, the activation energy (E), the frequency factor (s), and the order of kinetics (b) even for complex glow curves having a number of TL peaks. Finally, based on these, we logically infer the importance of TL in development and characterization of materials used in dosimetry, dating and scintillation.

  10. Thermoluminescence of alkali halides and its implications

    International Nuclear Information System (INIS)

    Trapping levels present in some alkali halides namely NaCl, KCl, KBr, and KI are determined by deconvolution of the thermoluminescence (TL) curves. Unlike most of the studies undertaken over the last few decades, we have presented a comprehensive picture of the phenomenon of TL as an analytical technique capable of revealing the position of the trapping levels present in the materials. We show that for all practical purposes, TL can be described involving only the three key trapping parameters, namely, the activation energy (E), the frequency factor (s), and the order of kinetics (b) even for complex glow curves having a number of TL peaks. Finally, based on these, we logically infer the importance of TL in development and characterization of materials used in dosimetry, dating and scintillation.

  11. Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

    Energy Technology Data Exchange (ETDEWEB)

    Bory, Benjamin F.; Wang, Jingxin; Janssen, René A. J.; Meskers, Stefan C. J., E-mail: s.c.j.meskers@tue.nl [Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Gomes, Henrique L. [Instituto de Telecomunicações, Av. Rovisco, Pais 1, 1049-001 Lisboa, Portugal and Universidade do Algarve, Campus de Gambelas, 8005-139 Faro (Portugal); De Leeuw, Dago M. [Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany and King Abdulaziz University, Jeddah (Saudi Arabia)

    2014-12-08

    Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron–hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 10{sup 25}/m{sup 3}. The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics.

  12. Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

    International Nuclear Information System (INIS)

    Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron–hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 1025/m3. The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics

  13. Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

    Science.gov (United States)

    Bory, Benjamin F.; Wang, Jingxin; Gomes, Henrique L.; Janssen, René A. J.; De Leeuw, Dago M.; Meskers, Stefan C. J.

    2014-12-01

    Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron-hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 1025/m3. The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics.

  14. Electro-optic contribution to field-induced Raman scattering in alkali halides

    International Nuclear Information System (INIS)

    The electro-optic contribution to the field-induced first-order Raman scattering cross section in alkali halide crystals is calculated using measured values for hyperpolarizabilities. The electro-optic contribution is much larger than the previously reported atomic displacement contribution. The results cast some doubt on the accuracy of the reported hyperpolarizability values

  15. Quantum-chemical investigations of the electronic structure, mechanism of radiation defect production and recombination in alkali halide crystals

    International Nuclear Information System (INIS)

    The results of recent investigations of electronic and spatial structure as well as mechanism of radiation-induced production and tunneling recombination of defects in ionic crystals LiF and KCl are briefly summerized. The calculations have been performed in the framework of the semiempirical quantum- chemical method, which is the simplified version of the unrestricted Hartree-Fock-Rothaan method, and of a molecular cluster model

  16. Measurement of Surface Phonon Dispersion Curves of Alkali Halide Single Crystals by Time of Flight Spectroscopy of He Atom Beams

    Science.gov (United States)

    Toennies, J. Peter

    1982-01-01

    The development of highly expanded He nozzle beams with velocity half widths less than 1% has made it possible to observe the annihilation and creation of single surface phonons in time of flight spectra of the scattered atoms. Measurements have been carried out for a wide range of incident angles at a beam energy of about 20 meV for the following crystals and directions: LiF langle100rangle, LiF langle110rangle, NaF langle100rangle, KCl langle100rangle, NaCl langle100rangle, and MgO langle100rangle. In all cases the spectra show up to 5 sharp well resolved maxima. From the final angle and energy of each peak the parallel surface momentum component and frequency of the phonon is determined. The results show a predominant coupling with Rayleigh surface phonons with only a weak coupling with bulk phonons. Rayleigh dispersion curves have been measured out to the zone boundary for all crystals except LiF langle110rangle and MgO. There is also some evidence for excitation of modes of higher frequencies. Except for LiF langle100rangle at the zone boundary the results compare well with theoretical calculations. Benedek has been able to fit the new LiF He atom and previous neutron dispersion curves with a revised breathing shell model calculation.

  17. Lattice defect formation via exciton dissociation in ammonium halide crystals

    International Nuclear Information System (INIS)

    Peculiarities of lattice defect formation via exciton dissociations in ammonium halide crystals are investigated by means of optical and thermoactivation spectroscopy. Crystals were activated by ytterbium and europium bivalent ions and X-ray irradiated at liquid nitorgen temperature. Present experimental results and published data prove the formation diagram of lattice defects at exciton nonradiating dissociation-formation of stable Frenkel defects where Vk-center an NH30-center considered as electron center are initial ones. This formation diagram is suggested for alkali-halide crystals

  18. Energy transfer in alkali halide scintillators by electron-hole diffusion and capture

    International Nuclear Information System (INIS)

    Recent calculations and experiments dealing with charge transport and capture in activated alkali halide scintillators are reviewed. Both electrons and holes are captured at thallium sites in crystals such as KI(Tl) and NaI(Tl). The kinetics of charge transport is governed either by the diffusive motion of the self-trapped hole, or by the release of electrons from a thallium site. (U.S.)

  19. Alkali halide microstructured optical fiber for X-ray detection

    Energy Technology Data Exchange (ETDEWEB)

    DeHaven, S. L., E-mail: stanton.l.dehaven@nasa.gov, E-mail: russel.a.wincheski@nasa.gov; Wincheski, R. A., E-mail: stanton.l.dehaven@nasa.gov, E-mail: russel.a.wincheski@nasa.gov [NASA Langley Research Center, Hampton, VA 23681 (United States); Albin, S., E-mail: salbin@nsu.edu [Norfolk State University, Norfolk, VA 23504 (United States)

    2015-03-31

    Microstructured optical fibers containing alkali halide scintillation materials of CsI(Na), CsI(Tl), and NaI(Tl) are presented. The scintillation materials are grown inside the microstructured fibers using a modified Bridgman-Stockbarger technique. The x-ray photon counts of these fibers, with and without an aluminum film coating are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The photon count results show significant variations in the fiber output based on the materials. The alkali halide fiber output can exceed that of the CdTe detector, dependent upon photon counter efficiency and fiber configuration. The results and associated materials difference are discussed.

  20. Alkali halide microstructured optical fiber for X-ray detection

    International Nuclear Information System (INIS)

    Microstructured optical fibers containing alkali halide scintillation materials of CsI(Na), CsI(Tl), and NaI(Tl) are presented. The scintillation materials are grown inside the microstructured fibers using a modified Bridgman-Stockbarger technique. The x-ray photon counts of these fibers, with and without an aluminum film coating are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The photon count results show significant variations in the fiber output based on the materials. The alkali halide fiber output can exceed that of the CdTe detector, dependent upon photon counter efficiency and fiber configuration. The results and associated materials difference are discussed

  1. PLENARY SESSIONThermoluminescence and lattice defects in alkali halides

    OpenAIRE

    Alvarez Rivas, J.

    1980-01-01

    Recent developments in the study of the thermoluminescence of irradiated alkali halides indicate that many of the observed glow peaks are due to thermoluminescent processes related to the recombination of radiation induced lattice defects. There is a large amount of experimental results which supports that the F+H recombination is a rather common thermoluminescent process. Under some conditions it has been observed that the I + F, I + VK and H + ? recombinations can indirectly induce light em...

  2. Volcanic Origin of Alkali Halides on Io

    Science.gov (United States)

    Schaefer, L.; Fegley, B., Jr.

    2003-01-01

    The recent observation of NaCl (gas) on Io confirms our earlier prediction that NaCl is produced volcanically. Here we extend our calculations by modeling thermochemical equilibrium of O, S, Li, Na, K, Rb, Cs, F, Cl, Br, and I as a function of temperature and pressure in a Pele-like volcanic gas with O/S/Na/Cl/K = 1.518/1/0.05/0.04/0.005 and CI chondritic ratios of the other (as yet unobserved) alkalis and halogens. For reference, the nominal temperature and pressure for Pele is 1760 plus or minus 210 K and 0.01 bars based on Galileo data and modeling.

  3. Thermal conductivity of molten alkali halides and their mixtures

    International Nuclear Information System (INIS)

    Thermal conductivity of molten alkali halides and their mixtures with common anions is measured as a function of temperature. Use is made of the most reliable method of coaxial cylinders made of platinum, with radiation heat transfer being taken into account. It is found to vary directly with temperature. Expressions for its temperature dependence are derived from the experimental observations. Linear relations of the thermal conductivity to the molar volume are established for molten alkali fluorides, chlorides, bromides, iodides and their mixtures with common anions. Deviations from the additive quantities towards smaller values are observed in the case of the mixtures. They are in a good accordance with inverse deviations of their adiabatic compressibility. The heat conduction of ionic melts is semiquantitatively examined. Elementary quantities of heat transferred from cations to anions and vice versa are estimated. (author)

  4. Games people play with interstitials (in alkali halides)

    International Nuclear Information System (INIS)

    A survey is given of the various ways in which interstitial halogen atoms produced by ionising radiation can be trapped in alkali halides. First, the fundamental interstitial halogen atom center, the H-center, is discussed. Then, interstitial centers trapped by, or in the neighbourhood of, various impurities are presented. Particular attention is given to trapping by the following impurities: foreign halogen ions, foreign alkali ions or pairs of both. The discussion is limited to a description of the production and the models of these H-type centers and little is said about their sometimes interesting physical properties. A few speculations are offered why certain interstitial centers have not yet been observed. The models of a few paramagnetic diinterstitial centers are also presented

  5. Photoelectron spectroscopy of alkali halide clusters with excess electrons

    International Nuclear Information System (INIS)

    We have studied excess electrons in alkali halide clusters, using a combination of a laser vaporization source, time-of-flight mass spectrometer, and magnetic bottle photoelectron electron spectrometer. We have obtained photoelectron spectra of (NaCl)n-, (NaCl)nNa-, (NaCl)nNam- and (KI)3Km- cluster anions contain either a single excess electron, two excess electrons, or several excess electrons. In the spectra of (NaCl)n, our measured electron vertical binding energies are in excellent agreement with the calculated values. We found single excess electrons in the (NaCl)n- cluster anions are mostly localized, either occupying an anion vacancy as an F-center in solids, or neutralizing a Na+ ion. In a few case, electrons are delocalized on the surface of clusters. In the spectra of (NaCl)nNam-, we observed three distinct types of spectra, corresponding to three different electron accommodation modes. We suggest that in certain clusters, the excess electrons are spin paired, localizing in a single anion vacancy as an F'-center in solids or on a Na+ cation to form a Na-. In other clusters, the electrons separately occupy a pair of anion vacancies as a double F-center. In the spectra of (NaCl)3Nam- and (KI)3Km-, we found features of the spectra that resemble those seen in the spectra of pure alkali metal anions after m ? 2. We suggest that the metallic and ionic parts in these clusters are separated, analogous to the metal and nonmetal phase separation in alkali-alkali halide metals

  6. Epitaxial growth of alkali halides on stepped metal surfaces

    International Nuclear Information System (INIS)

    We present a growth study of the alkali halides NaCl and KCl on the stepped metal surfaces Cu(311) and Cu(221) using high resolution low energy electron diffraction. For all systems studied it was found that the alkali halide deposit forms (100)-terminated epitaxial layers which have essential structural features in common: The interfacial arrangement between the ionic adlayer and the stepped metal substrate is characterized by an alignment of the polar in-plane Cl ion rows parallel and perpendicular to the intrinsic Cu steps. For low coverages (?1 ML) the Cl ions are in registry with the intrinsic substrate steps causing uniaxial strain in the direction perpendicular to the steps. In contrast, parallel to the steps the Cl ions are free to adjust their optimum Cl-Cl spacing. For coverages >3 ML, the strain perpendicular to the intrinsic Cu steps is accommodated which suggests the incorporation of monoatomic Cu defect steps at the interface in this regime of higher coverage

  7. Response of alkali halide scintillators to neutrons from 5 to 100 MeV

    International Nuclear Information System (INIS)

    The response of three alkali halide scintillator's to neutrons in the range 5 to 100 MeV was investigated with the spallation neutron source at LAMPF/WNR. Scintillating crystals were Nal(Tl), Kl(Tl) and Csl(Tl), each 2.5 cm in diameter and 1.2 cm thick. Pulse shapes that depend on particle type were observed for Nal(Tl) and Csl(Tl) but not for Kl(Tl). Pulse height spectra for are reported as a function of neutron energy, and, where pulse shape discrimination was observed, for individual charged-particle groups

  8. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

    Science.gov (United States)

    Brendel', V. M.; Bukin, V. V.; Garnov, Sergei V.; Bagdasarov, V. Kh; Denisov, N. N.; Garanin, Sergey G.; Terekhin, V. A.; Trutnev, Yurii A.

    2012-12-01

    A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation.

  9. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

    International Nuclear Information System (INIS)

    A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation. (laser technologies)

  10. Theory of freezing of alkali halides and binary alloys

    International Nuclear Information System (INIS)

    Using the basic equations of classical statistical mechanics relating the singlet densities rho1 and rho2 of a binary system to the three partial direct correlation functions csub(ij), a theory of freezing is developed. Though the theory is set up for arbitrary concentration, we focus on the freezing of the alkali halides. In particular, we show that periodic solutions of the equations for rho1 and rho2 can coexist with homogeneous solutions. The difference in free energy between periodic and homogeneous phases is built up in terms of (i) the volume difference and (ii) the Fourier components of rho1, rho2 and csub(ij). To lowest order, it is stressed that the freezing transition is determined by the charge-charge structure factor at the principal peak and by the compressibility. (author)

  11. Solution enthalpies of alkali metal halides in water and heavy water mixtures with dimethyl sulfoxide

    International Nuclear Information System (INIS)

    Solution enthalpies of CsF, LiCl, NaI, CsI and some other halides of alkali metals and tetrabutylammonium have been measured by the method of calorimetry. Standard solution enthalpies of all alkali metals (except rubidium) halides in water and heavy water mixtures with dimethylsulfoxide at 298.15 K have been calculated. Isotopic effects in solvation enthalpy of the electrolytes mentioned in aqueous solutions of dimethylsulfoxide have been discussed. 29 refs., 2 figs., 4 tabs

  12. Charge-charge liquid structure factor and the freezing of alkali halides

    International Nuclear Information System (INIS)

    The peak height of the charge-charge liquid structure factor Ssub(QQ) in molten alkali halides is proposed as a criterion for freezing. Available data on molten alkali chlorides, when extrapolated to the freezing point suggests Ssub(QQ)sup(max) approximately 5. (author)

  13. Formation of structured nanophases in halide crystals.

    Czech Academy of Sciences Publication Activity Database

    Kulveit, Jan; Demo, Pavel; Polák, Karel; Sveshnikov, Alexey; Kožíšek, Zden?k

    2013-01-01

    Ro?. 5, ?. 6 (2013), s. 561-564. ISSN 2164-6627 R&D Projects: GA ?R GAP108/12/0891 Institutional support: RVO:68378271 Keywords : halide crystals * nucleation Subject RIV: BM - Solid Matter Physics ; Magnetism http://www.aspbs.com/asem.html#v5n6

  14. Aggregating of mercury-like rare-earth ions in the alkali halide crystals as model of clusterization in lava-like fuel-containing materials

    International Nuclear Information System (INIS)

    On the basis of results of spectral-luminescent characteristics research for dielectric crystals of different structure, activated by lead ions, possibility of creation of lead-containing nanocrystals is shown, that can model mechanism and reasons of creation of different crystalline inclusions into lava-like fuel-containing materials. Mechanical destruction of lava under influence of alpha-, beta-, gamma-rays may promote going out of lava the crystalline inclusions

  15. Physics and nanofriction of alkali halide solid surfaces at the melting point

    Science.gov (United States)

    Zykova-Timan, T.; Ceresoli, D.; Tartaglino, U.; Tosatti, E.

    2006-09-01

    Alkali halide (1 0 0) surfaces are anomalously poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(1 0 0) within a simple (BMHFT) model potential. Calculations of the solid-vapor, solid-liquid and liquid-vapor free energies showed that solid NaCl(1 0 0) is a nonmelting surface, and that the incomplete wetting can be traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid-solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface, reducing in particular its entropy much below that of solid NaCl(1 0 0). Presently, we are making use of the nonmelting properties of this surface to conduct case study simulations of hard tips sliding on a hot stable crystal surface. Preliminary results reveal novel phenomena whose applicability is likely of greater generality.

  16. Ab initio perspective on the Mollwo-Ivey relation for F centers in alkali halides

    Science.gov (United States)

    Tiwald, Paul; Karsai, Ferenc; Laskowski, Robert; Gräfe, Stefanie; Blaha, Peter; Burgdörfer, Joachim; Wirtz, Ludger

    2015-10-01

    We revisit the well-known Mollwo-Ivey relation that describes the "universal" dependence of the absorption energies of F-type color centers on the lattice constant a of alkali-halide crystals, Eabs?a-n. We perform both state-of-the-art ab initio quantum chemistry and post-DFT calculations of F-center absorption spectra. By "tuning" independently the lattice constant and the atomic species we show that the scaling with the lattice constant alone (keeping the elements fixed) would yield n =2 in agreement with the "particle-in-the-box" model. Keeping the lattice constant fixed and changing the atomic species enables us to quantify the ion-size effects which are shown to be responsible for the exponent n ?1.8 .

  17. Why Are Alkali Halide Solid Surfaces Not Wetted By Their Own Melt?

    CERN Document Server

    Zykova-Timan, T; Tartaglino, U; Tosatti, E

    2005-01-01

    Alkali halide (100) crystal surfaces are anomalous, being very poorly wetted by their own melt at the triple point. We present extensive simulations for NaCl, followed by calculations of the solid-vapor, solid-liquid, and liquid-vapor free energies showing that solid NaCl(100) is a nonmelting surface, and that its full behavior can quantitatively be accounted for within a simple Born-Meyer-Huggins-Fumi-Tosi model potential. The incomplete wetting is traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid-solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface. The latter is pursued in detail, and it is shown that surface short-range charge order acts to raise the surface tension because incipient NaCl molecular formation anomalously reduces the surface entropy of liquid NaCl much below that of solid NaCl(100).

  18. Physics and Nanofriction of Alkali Halide Solid Surfaces at the Melting Point

    CERN Document Server

    Zykova-Timan, T; Tartaglino, U; Tosatti, E

    2006-01-01

    Alkali halide (100) surfaces are anomalously poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(100) within a simple (BMHFT) model potential. Calculations of the solid-vapor, solid-liquid and liquid-vapor free energies showed that solid NaCl(100) is a nonmelting surface, and that the incomplete wetting can be traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid-solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface, reducing in particular its entropy much below that of solid NaCl(100). Presently, we are making use of the nonmelting properties of this surface to conduct case study simulations of hard tips sliding on a hot stable crystal surface. Preliminary results reveal novel phenomena whose applicability is likely of greater generality.

  19. Role of water in alkali halide heterogeneous chemistry relevant to the atmosphere: A surface science study

    Science.gov (United States)

    Ghosal, Sutapa

    2001-05-01

    Water is a ubiquitous atmospheric constituent. The interaction of water in its various forms (vapor, liquid, ice) with other atmospheric constituents has a significant impact on the chemistry of the atmosphere. Another class of compounds that are of considerable importance in atmospheric chemistry are alkali halide salts such as sea salt particles. Heterogeneous reactions of alkali halides with gas phase pollutants are believed to be an important source of halogens in the troposphere. There is an increasing amount of evidence that the presence of water plays an important role in the heterogeneous chemistry of alkali halide particles. It is the goal of this dissertation to contribute to the understanding of the interaction of water with alkali halide surfaces and its atmospheric implications. Surface processes are of fundamental importance in heterogeneous atmospheric chemistry, but they are often difficult to study because of their inherent complexity. As this dissertation shows, the use of modern surface science techniques offer valuable insights into these complex processes and as such offer complementary alternatives to the traditional atmospheric chemistry experiments. The surface science techniques used in this dissertation are X-ray photoelectron spectroscopy (XPS), scanning polarization force microscopy (SPFM) and scanning electron microscopy (SEM). Presented here are the results of the XPS and SEM studies undertaken to determine the nature and content of surface adsorbed water on NaCl as a function of surface defects. The details of HNO3 uptake on NaCl and the effect of surface adsorbed water on this uptake are also discussed. Our results show that the amount of ``strongly adsorbed water'' (SAW) on the surface of NaCl particles depends on the particle size and hence, on the concentration of surface defects. Unlike the (100) single crystal the more defective surfaces show dissociative water uptake at room temperature upon exposure to water vapor well below the deliquescence point of NaCl. The binding energy and temperature dependence characteristics of the SAW related oxygen signal on the NaCl particles are consistent with OH- like species. We also show that the dissociative adsorption of HNO3(g) on NaCl to form NaNO3(s) and HCl(g) follows single-site Langmuir adsorption behavior. The dissociative adsorption accompanied by water-induced recrystallization of the NaNO3 product on the NaCl surface gives rise to the experimentally observed HNO3 pressure dependence of the reactive sticking coefficient for reaction under steady-state reaction conditions. Surface segregation of bromine in bromide doped NaCl single crystals has been studied using XPS, SEM and SPFM. Our results show, for the first time, that substantial segregation of Br- to the surface of NaCl samples with low level Br- dopant concentrations occurs under conditions of water vapor exposure. The segregation phenomenon is likely to play an important role in atmospheric phenomena involving surface reactions of sea salt particles and aerosols.

  20. The electronic structure of the F-center in alkali-halides-The Bethe cluster - lattice

    International Nuclear Information System (INIS)

    The electronic structure of the F-center in alkali-halides with the NaCl structure has been studied using the Bethe Cluster lattice method. The central cluster has been taken as constituted by the vacancy and the nearest- and second-neighbors to it, respectively cations and anions. The optical transitions have been calculated and compared to experimental data on the location of the peak of the F-absorption band. The agreement obtained indicates that this method may be used to study properties of this defect in alkali halides. (Author)

  1. Cluster-Bethe lattice calculation for the electronic structure of hydrogen centers in alkali-halides

    International Nuclear Information System (INIS)

    The Cluster-Bethe lattice (CBL) method to calculate the electronic structure of the hydrogen centers U, U1, U2, U3 in alkali-halides has been used. The results show the adequacy of the CBL in the interpretation of the nature of the optical transitions. (author)

  2. Luminescent decay and spectra of impurity-activated alkali halides under high pressure

    International Nuclear Information System (INIS)

    The effect of high pressure on the luminescence of alkali halides doped with the transition-metal ions Cu+ and Ag+ and the heavy-metal ions In+ and Tl+ was investigated to 140 kbar. Measurement of spectra allowed the prediction of kinetic properties, and the predictions agree with lifetime data

  3. Epitaxial Growth of a Methoxy-Functionalized Quaterphenylene on Alkali Halide Surfaces

    DEFF Research Database (Denmark)

    Balzer, Frank; Sun, Rong; Parisi, Jürgen; Rubahn, Horst-Günter; Lützen, Arne; Schiek, Manuela

    The epitaxial growth of the methoxy functionalized para-quaterphenylene (MOP4) on the (001) faces of the alkali halides NaCl and KCl and on glass is investigated by a combination of lowenergy electron diffraction (LEED), polarized light microscopy (PLM), atomic force microscopy (AFM), and X...

  4. Angular dependence of static and kinetic friction on alkali halide surfaces

    Science.gov (United States)

    Steiner, Pascal; Roth, Raphael; Gnecco, Enrico; Baratoff, Alexis; Meyer, Ernst

    2010-11-01

    The angular dependence of the lateral forces acting on an atomically sharp tip slowly pulled by an elastic spring along a crystal surface with square symmetry is investigated in the framework of a separable two-dimensional tip-surface interaction potential. In the stick-slip regime kinetic friction is proportional to (cos?+|sin?|) , ? being the angle between the scan direction and a particular symmetry axis. For a high enough normal force, static friction is proportional to 1/cos? , whereas for intermediate loads it shows a ? -dependent spread of possible values. Continuous sliding with ultralow friction sets in below a load-dependent corrugation amplitude. Numerical simulations help interpret those analytic results in terms of the zigzag motion of a friction force microscope tip sliding on the (001) surface of a rocksalt crystal. The influence of the offset between the start of a scan and the center of the corresponding unit cell, in particular, for scans along ?100? directions is also elucidated. The predicted ratio of kinetic friction along the ?100? and ?110? directions agrees best with values measured on alkali halides with similar cation and anion radii. This ratio, as well as the angular dependence of the static friction may be used to determine fine details of the lateral tip-sample interaction.

  5. Surface tension of molten alkali metal halides as a function of ion sizes

    International Nuclear Information System (INIS)

    The analysis of the experimental data on the surface tension of the liquid/vapor interphase boundary of the molten alkali metal halides MX (M Li-Cs, X = F-I) near the melting temperature, accounting for the cation and anion dimensional differences, is presented. The main attention is focused at the manifestation of the effects of the interphase boundary of the effects of the interphase boundary thickness and twofold electric layer. It is shown, that the experimental data on the whole MX series may be represented in the form of the electrocapillary curve on the graph of the surface tension dependence on the degree of the halides dimensional asymmetry

  6. Physics of solid and liquid alkali halide surfaces near the melting point

    Science.gov (United States)

    Zykova-Timan, Tatyana; Ceresoli, Davide; Tartaglino, Ugo; Tosatti, Erio

    2006-03-01

    NaCl (and other alkali halide) crystal surfaces have the peculiar property of repelling their own melt. As a result they let themselves be wetted only partially by their own liquid at the melting point TM. We recently investigated the physical reasons for this unusual behavior. We found them through theory and molecular dynamics simulation to stem from the conspiracy of three factors. First, the solid NaCl(100) surface is exceptionally anharmonic,but also exceptionally stable. It can in fact survive even well above the melting point, for unlike most other surfaces it does not spontaneously melt. Second, the solid-liquid interface is very costly, due to a 27% density difference between solid and liquid. Third, the surface tension of liquid NaCl is relatively high. This last feature is due to an unexpected entropy deficit, that can in turn be traced to incipient molecular charge order in the outermost regions of the molten salt surface[1,2].[1] T. Zykova-Timan, D. Ceresoli, U. Tartaglino, E. Tosatti, Phys. Rev. Lett. 94, 176105 (2005) [2] T. Zykova-Timan, D. Ceresoli, U. Tartaglino, E. Tosatti, J. Chem. Phys. 123, 164701 (2005)

  7. A study on the electrochemical behaviour of polypyrrole films in concentrated aqueous alkali halide electrolytes

    DEFF Research Database (Denmark)

    Jafeen, M. J. M.; Careem, M.A.; Skaarup, Steen

    2014-01-01

    difference. In highly concentrated aqueous electrolytes, the mass of the PPy/DBS film at the end of each redox cycle is found to drift, which can be controlled by changing the concentration of the electrolyte. The PPy/DBS films were also cycled at different scan rates in various alkali halide aqueous...... electrolytes of concentrations 0.1 and 1 M to determine the effective diffusion coefficients of alkali ions in the films. The effective diffusion coefficients were found to increase with the concentration of the electrolytes and decrease with the increase in size of cations....

  8. Physics and Nanofriction of Alkali Halide Solid Surfaces at the Melting Point

    OpenAIRE

    Zykova-Timan, T.; Ceresoli, D.; Tartaglino, U.; Tosatti, E

    2006-01-01

    Alkali halide (100) surfaces are anomalously poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(100) within a simple (BMHFT) model potential. Calculations of the solid-vapor, solid-liquid and liquid-vapor free energies showed that solid NaCl(100) is a nonmelting surface, and that the incomplete wetting can be traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad...

  9. Estimation of the critical temperatures and densities of molten alkali metal halides

    International Nuclear Information System (INIS)

    The critical temperatures and densities of the alkali halides MX (M Li-Cs; X = F-I) are calculated on the basis of the Rykov, Goldhammer and Philippov equations for estimating the liquids density. The modified Philippov equation is recommended as the equation for describing the experimental data on the density of the these melts in the temperature area Tmelt-Tc with the relative error of 0.1-0.2%

  10. A refinement of the Mollwo-Ivey rule for F-centres in alkali halides

    International Nuclear Information System (INIS)

    The simple formula is a very good fit for the detailed variation of the F-center peak absorption energy, for the 16 alkali halides with NaCl structure, excluding CsF. The first term arises from incoherent photon scattering leading to electronic level transitions. The second term is a diffraction term, arising from the coherent scattering of photons from relaxed ionic aggregates around F-centers separated on the average by distances of the order of optical wavelengths

  11. Lifetime of Eu2+ luminescence in alkali halides. Dependence on the host matrix

    International Nuclear Information System (INIS)

    Luminescence and decay time measurements of Eu2+ were performed under excitation at 337 nm (N2-pulsed laser) for a number of alkali halides such as NaCl, KCl, RbCl, KBr, RbBr, and KI as host matrices. Room temperature emission spectra for quenched samples and luminescence decay time plots are given and discussed. The results can be explained on the basis of the peak position of emission and the refractive index of the corresponding host matrix

  12. Experimental studies of photon-surface interaction dynamics in the alkali halides

    International Nuclear Information System (INIS)

    We describe recent measurements which have provided, in unprecedented detail, insights into the electronic mechanisms through which energy carried into a material by photon irradiation is absorbed, localized and rechanneled to produce desorption, surface modification, erosion and damage. The specific object of these studies has been desorption induced by electronic transition in alkali halide crystals, with particular emphasis on the dynamics of changes in the surface and near-surface regions. In our experiments, the irradiating ultraviolet photons are provided by a synchrotron storage ring, and the dynamical information about desorption products is obtained from optical measurements of the quantum states, yields and velocity distributions of neutral ground-state and excited-state atoms ejected from the surface of the irradiating material. These studies have shown that the dominant exit channels in photon-induced particle emission are those producing ground-state and excited-state neutral atoms. Using dynamical information about these desorbing neutral species, obtained, for example, by laser-induced fluorescence and laser Doppler spectroscopy, we are generating an increasingly comprehensive picture of the dynamics of electronic energy flow into and out of pure crystalline surfaces in these prototypical dielectrics. We are also beginning to be able to relate desorption dynamics to specific materials properties, and to discriminate between pure surface and near-surface effects in these materials. Applications of these techniques to the problem of photon-induced surface damage and to analysis of surface dynamics in dielectric materials are discussed, and the relationships between these nearly ideal model materials and the non-crystalline, covalently bonded materials more typical of real optical elements are pointed out. 19 refs., 13 figs

  13. Observation of nuclear wave packets in the excited state of the F-center in alkali halides

    International Nuclear Information System (INIS)

    Oscillations of nuclear wave packets (NWPs) in the excited state of the F-center in four alkali halides, potassium chloride (KCl), potassium bromide (KBr), potassium iodide (KI), and rubidium chloride (RbCl), are investigated. In KCl, the dominant mode is the LO mode near the zone center in the Brillouin zone. In KBr, the NWP oscillation consists mainly of the LO mode near the zone center and the LA modes near the singularity points in the [1 0 0] and/or [1 1 0] crystal directions. In KI, the totally symmetric local mode is dominant in the NWP oscillation. In RbCl, the LO mode near the zone boundary [1 0 0] predominantly forms the NWP oscillation. We comprehensively elucidate correspondences and differences between the present results and the resonance Raman spectra by considering the spatial extension of the electronic wave function and the perturbed phonon density of states.

  14. Negative photoplastic effect due to the relaxed excited state of the F-center in alkali halides

    International Nuclear Information System (INIS)

    To make clear the mechanism of the photoplastic effect (PPE) in alkali halides containing F-centers, on the basis of the photochemical reaction of the F-center, temperature dependence of the PPE in KCl, and KBr and NaCl was studied from 95 K up to RT. The characteristic critical points thetasub(t)s in colored KCl and KBr were determined to be 110 and 190 K, respectively. Below thetasub(t) the sign of the PPE in both crystals was negative, i.e., decrement of the flow stress during light illumination was observed. Moreover, the thetasub(t)s were in good agreement with the temperature where the photoconductivities show remarkable increase in the course of the measurements. The negative PPE is explained in terms of the rotation of the principal strain axis of the relaxed state of the F-center having tetragonarity as to relax the stress around the edge dislocation coming closely. (author)

  15. Examination of the double layer contribution to the surface tension of alkali metal halides

    International Nuclear Information System (INIS)

    Analysis of surface tension on the liquid-vapor interface for alkali metal halides MX (M=Li-Cs; X=F-I) was made using microscopic theory, influence of the appearing double electric layer on the characteristic mentioned both for cationic and anionic substitutions was discussed. It is shown that for most MX salts the dependence of surface tension near melting point on the size difference of cation and anion can be adequately described using a model of mean-spheric approximation and parametrized density profile

  16. Evidence for New Excess Electron Localization Sites in NanFn-1 Alkali-Halide Clusters

    International Nuclear Information System (INIS)

    This Letter examines new types of localization sites for an excess electron in finite alkali-halide clusters resulting from defects on cuboidal structures, namely open-quotes edge states,close quotes R center, and other surface defects. We present theoretical calculations on NanF n-1 clusters with one excess electron. Comparisons with experimental results are presented for different cluster sizes (n=17 , 23, 28, and 29). Structures with edge or surface defects are relevant for n=23 , 28, and 29. copyright 1997 The American Physical Society

  17. Thermoluminescence in alkali halides irradiated at 80K

    International Nuclear Information System (INIS)

    The thermoluminescence, the thermally stimulated currents and the thermal stability of the F centres induced in pure NaCl and KC1 crystals by X irradiation at 80K have been studied in detail, in the range between 80 and 300K. The thermoluminescent processes induced by illumination at 80K with F light in samples previously irradiated at room temperature has also been studied. It has been clearly observed the existence of thermoluminescent processes due to electrons and holes thermally released from traps, in which the F centres are not involved. The existence of hole-F centre recombination has not been observed. There are several thermoluminescent processes in both materials which are scribed to the recombination of F centres with mobile interstitial halogen atoms thermally released from traps, which are likely monovalent impurities in this temperature interval. The light emitting stage in these processes is originated by the formation of self trapped excitons. (Author) 66 refs

  18. Electron- and photon-stimulated desorption of excited hydrogen atoms from alkali halide surfaces

    International Nuclear Information System (INIS)

    This dissertation presents the first extensive investigation of electronically-stimulated desorption of excited hydrogen atoms from alkali halide surfaces. Such desorption is observed in fluorescence spectra from alkali halide compounds which are irradiated by electrons or photons in the presence of H2. The fundamental adsorbate-surface interactions which lead to the emission of excited hydrogen atoms has long been an open question. This treatise addresses the nature of this surface bond, its bonding site, and the bond-breaking processes involved in the desorption of excited hydrogen atoms from these surfaces. To this end, the desorption yields of excited hydrogen atoms from the surfaces of KCl, KBr, NaCl, NaF and LiF have been measured as a function of incident photon and electron energy and flux, time of irradiation, dosing pressure of H2 and sample temperature. Under electron or photon bombardment, halogen atoms are preferentially desorbed leaving a metal-rich surface. The results of this study indicate that the desorption yields of H* follow the time evolution of this excess metal and its subsequent evaporation as the substrate is heated. Energy dependent yields of H* exhibit a prominent resonance at threshold when irradiated by photons. This is the first observation of a selective bondbreaking process leading to desorption of neutral hydrogen atoms from a surface. Resonant yields stimulated from compounds which contain the same alkali metal occur energetically at the same incident photon energies. The energy thresholds of electron bombardment studies are also correlated to the alkali component of the substrate

  19. A comparative study of semi-empirical interionic potentials for alkali halides - II

    International Nuclear Information System (INIS)

    A comprehensive study of some semi-empirical interionic potentials is carried out through the calculation of the cohesive energy, relative stability and pressure induced solid-solid phase transformations in alkali halides. The theoretical values of these properties of the alkali halides are obtained using a new set of van der Waals coefficients and zero-point energy in the expression for interionic potential. From the comparison of the present calculations with some previous sophisticated ab-initio quantum-mechanical calculations and other semi-empirical approaches, it is concluded that the present calculations in the simplest central pairwise interaction description with the new values of the van der Waals coefficients and zero-point energy are in better agreement with the experimental data than the previous calculations. It is also concluded that in some cases the better choice of the interionic potential alone in the simplest semi-empirical picture of interaction gives an agreement of the theoretical predictions with the experimental data much superior to the ab-initio quantum mechanical approaches. (author)

  20. Molecular dispersion energy parameters for alkali and halide ions in aqueous solution

    Energy Technology Data Exchange (ETDEWEB)

    Reiser, S.; Deublein, S.; Hasse, H., E-mail: hans.hasse@mv.uni-kl.de [Laboratory of Engineering Thermodynamics, University of Kaiserslautern, 67663 Kaiserslautern (Germany); Vrabec, J. [Thermodynamics and Energy Technology, University of Paderborn, 33098 Paderborn (Germany)

    2014-01-28

    Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li{sup +}, Na{sup +}, K{sup +}, Rb{sup +}, Cs{sup +}, F{sup ?}, Cl{sup ?}, Br{sup ?}, and I{sup ?}. The employed ion force fields consist of one Lennard-Jones (LJ) site and one concentric point charge with a magnitude of ±1 e. The SPC/E model is used for water. The LJ size parameter of the ion models is taken from Deublein et al. [J. Chem. Phys. 136, 084501 (2012)], while the LJ energy parameter is determined in the present study based on experimental self-diffusion coefficient data of the alkali cations and the halide anions in aqueous solutions as well as the position of the first maximum of the radial distribution function of water around the ions. On the basis of these force field parameters, the electric conductivity, the hydration dynamics of water molecules around the ions, and the enthalpy of hydration is predicted. Considering a wide range of salinity, this study is conducted at temperatures of 293.15 and 298.15 K and a pressure of 1 bar.

  1. Oxidizing agents produced by radiolysis of alkali-metal halide melts

    International Nuclear Information System (INIS)

    The principal short-lived products from the radiolysis of alkali-metal halide melts are solvated electrons (e/sub s/-), which are particles with the F-center type structure, and molecular anion-radicals of the halogen (GAMMA2-); these are formed in the reactions: (1)GAMMA- ? GAMMA0 + e-; (2) e- ? e/sub s/-; (3) GAMMA0 + GAMMA- ? GAMMA2-. Solvated electrons are strong reducing agents, and they disappear almost completely in rections with the metal cations. Here we are presenting results from a study of the properties of the oxidizer products GAMMA2-, by means of a pulse radiolysis method. The optical spectra of the oxidizer components of radiolysis of alkali-metal halide melts, the molecular anion-radicals GAMMA2-, are similar to the spectra of the corresponding species in aqueous solutions. Rate constants have been measured for the disappearance of GAMMA2-, which goes forward mainly in the reaction of GAMMA2- with the reduced form of the cation. In the presence of alkaline-earth metal cations, owing to the fast disproportionation of their reduced form, there is a greater contribution from the relatively slow reaction of disproportionation of GAMMA2-, leading to an observed retardation of the rate of GAMMA2- disappearance and an increase in the yield of molecular halogen

  2. Calculation of the melting point of alkali halides by means of computer simulations

    CERN Document Server

    Aragones, J L; Valeriani, C; Vega, C; 10.1063/1.4745205

    2012-01-01

    In this manuscript we study the liquid-solid coexistence of NaCl-type alkali halides, described by interaction potentials such as Tosi-Fumi (TF), Smith-Dang (SD) and Joung-Cheatham (JC), and compute their melting temperature (Tm) at 1 bar via three independent routes: 1) liquid/solid direct coexistence, 2) free-energy calculations and 3) Hamiltonian Gibbs-Duhem integration. The melting points obtained by the three routes are consistent with each other. The calculated Tm of the Tosi-Fumi model of NaCl is in good agreement with the experimental value as well as with other numerical calculations. However, the other two models considered for NaCl, SD and JC, overestimate the melting temperature of NaCl by more than 200 K. We have also computed the melting temperature of other alkali halides using the Tosi-Fumi interaction potential and observed that the predictions are not always as close to the experimental values as they are for NaCl. It seems that there is still room for improvement in the area of force-fields...

  3. Formation of structured nanophases in halide crystals.

    Czech Academy of Sciences Publication Activity Database

    Kulveit, J.; Demo, Pavel; Polák, Karel; Sveshnikov, Alexey; Kožíšek, Zden?k

    2011-01-01

    Ro?. 134, ?. 14 (2011), 144504/1-144504/7. ISSN 0021-9606 R&D Projects: GA AV ?R IAA100100806 Institutional research plan: CEZ:AV0Z10100521 Keywords : nanophase * halides * nucleation * spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.333, year: 2011

  4. Infrared Vibrational Fluorescence and Persistent Spectral Hole Burning from Negatively Charged Cyanogen Molecules in Alkali Halides.

    Science.gov (United States)

    Spitzer, Ronnie Claudette

    1988-12-01

    The union of IR semiconductor diode laser and Fourier transform interferometric methods has produced two new spectroscopic probes for investigating the dynamics of matrix isolated molecules: vibrational fluorescence and persistent spectral hole burning. In this thesis, we investigate a single system, CN^- doped ionic crystals, with both low power techniques. High resolution measurements of the IR vibrational fluorescence from CN^- molecules matrix isolated in alkali halide hosts at low temperatures reveal an up-the-ladder cascade of remarkable range. The CN^- fundamental absorption line is pumped with a CW tunable diode laser near 5 ?m and the vibrational fluorescence analyzed with the high resolution (0.04 cm^{ -1}) interferometer. We find high-lying vibrational levels of CN^- (up to v = 16) are populated at 1.7 K by an electric dipole mediated V-V energy transfer process. At our high resolution, new aspects of the system emerge. Emission features from defect centers composed of a CN^- molecule associated with another nearby impurity ion dominate the spectrum at high CN^- concentrations. The most important center is the CN^- pair defect. At elevated temperatures population of the CN^- pair defect vibrational levels in the ground electronic state have been observed at ultraviolet energies for all hosts. Our results show that energy preferentially accumulates at the pair defect because one member of the pair is always in the ground state ready to accept an excitation from a neighboring center. By using the diode laser as a high brightness probe, a new photophysical hole burning mechanism has been identified. Persistent spectral holes form during laser excitation of the Na^+:CN ^- defect's vibrational mode, when the CN ^- molecule occasionally reorients by 180^circ to an inequivalent lattice orientation generated by the nearby Na ^+ ion. A lattice barrier to reorientation blocks relaxation back to the original ground state at low temperatures. By combining persistent spectral hole burning with broadband FT spectroscopy, the CN ^- dynamics are identified. A solid state linear vibrational Stark effect, observed here for the first time, probes the local lattice configuration.

  5. Potential differences between chlorine and bromine electrode and between chlorine and iodine electrode in melts of the corresponding alkali-metal halides

    International Nuclear Information System (INIS)

    Halogen electrodes, according to the authors, are the most convenient electrodes for thermodynamic studies of reactions involving halogens in molten alkali metal halides when the emf method is used. The authors measured the potential differences between the chlorine and bromine electrode and between the chlorine and iodine electrode in cells described here. From the results of measurements at different temperatures, the authors generalized interpolation relations between the potentials of the bromine and iodine electrode in molten alkalimetal bromides and iodides and their mixtures relative to the chlorine electrode in chlorides of the same metals, on one hand, and the temperature and cation's crystal radius on the other hand

  6. From unexpected reactions to a new family of ionic co-crystals: the case of barbituric acid with alkali bromides and caesium iodide

    OpenAIRE

    Gobetto, Roberto; CHIEROTTI, Michele Remo

    2010-01-01

    Pressing solid barbituric acid with KBr to prepare samples for IR spectroscopy leads to the formation of an ionic co-crystal, in which the co-former is a classical ionic salt; co-crystal formation is also obtained with the other alkali bromides (LiBr, NaBr, RbBr and CsBr) and with caesium iodide. The simultaneous presence of alkali and halide ions affects the dissolution properties of barbituric acid in water.

  7. Chemistry of alkali cation exchanged faujasite and mesoporous NaX using alkyl halides and phosphates

    Science.gov (United States)

    Lee, Min-Hong

    The purpose of this work was to increase the reactivity of Faujasite X (NaX) zeolite toward the reactive decontamination of materials subject to nucleophilic attack by means of zeolite cation optimization and by means of the synthesis of mesoporous Faujasite X. Primary alkyl halides and trialkyl phosphates have been the test materials on which the cation-optimized and mesoporous zeolites have been tested. In the alkali cation optimization work, reactions of methyl iodide and 1-chloropropane with alkali metal cation exchanged Faujasite zeolite X were investigated at room temperature. The reactivity of the framework and the product formation were shown to depend on zeolite framework counter-cation. A quantitative study of zeolite product formation has been carried out, primarily using solid-state NMR spectroscopy. Large alkali cations showed preference toward substitution chemistry. In contrast, alkyl halide exposed LiX and NaX zeolites underwent both substitution and elimination. Subsequently introduced water molecules led to hydrolysis of framework species that was sensitive to framework counter-cation. The mesoporous NaX zeolites work undertakes to test whether an improvement in surface chemical reactivity can be achieved by introducing mesopores into the already reactive nucleophilic microporous NaX zeolite. Incorporation of the polydiallyl dimethyl ammonium chloride (PDADMAC) template and the formation of mesopores in Faujasite X zeolite (NaX) were successful and well-characterized. The mesopores are proposed to have occurred from incorporation of the cationic PDADMAC polymer into the zeolite by compensating zeolite framework charge. Subsequent sodium cation exchange of calcined mesoporous NaX was shown to restore the chemical reactivity characteristic of as-synthesized NaX. Trialkyl organophosphorous compounds underwent substitution reactions. The reactivity of both microporous and mesoporous Faujasite zeolite X and the product formation was shown to depend on the length of the alkyl chain. Although introduced mesopores alleviated the limited reagent diffusion to reactive sites due to the microporosity of the NaX zeolites, no marked improvement in the product yields was achieved with either the 1-chloroalkanes or the trialkyl phosphates test compounds, regardless of alkyl chain length. The disappointing results have been attributed to lack of substantial net increase in the numbers of zeolite nucleophilic sites accompanying mesopore introduction.

  8. N ,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) on alkali halide (001) surfaces

    Science.gov (United States)

    Fendrich, Markus; Lange, Manfred; Weiss, Christian; Kunstmann, Tobias; Möller, Rolf

    2009-05-01

    The growth of N ,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) (DiMe-PTCDI) on KBr(001) and NaCl(001) surfaces has been studied. Experimental results have been achieved using frequency modulation atomic force microscopy at room temperature under ultrahigh vacuum conditions. On both substrates, DiMe-PTCDI forms molecular wires with a width of 10nm, typically, and a length of up to 600nm at low coverages. All wires grow along either the [110] direction (or [11¯0] direction, respectively) of the alkali halide (001) substrates. There is no wetting layer of molecules: atomic resolution of the substrates can be achieved between the wires. The wires are mobile on KBr but substantially more stable on NaCl. A p(2×2) superstructure in a brickwall arrangement on the ionic crystal surfaces is proposed based on electrostatic considerations. Calculations and Monte Carlo simulations using empirical potentials reveal possible growth mechanisms for molecules within the first layer for both substrates, also showing a significantly higher binding energy for NaCl(001). For KBr, the p(2×2) superstructure is confirmed by the simulations; for NaCl, a less dense, incommensurate superstructure is predicted.

  9. Heavy ion passive dosimetry with silver halide single crystals

    Science.gov (United States)

    Childs, C. B.; Parnell, T. A.

    1972-01-01

    A method of detecting radiation damage tracks due to heavy particles in large single crystals of the silver halides is described. The tracks, when made visible with a simple electrical apparatus, appear similar to tracks in emulsions. The properties of the crystals, the technique of printing out the tracks, and evidence concerning the threshold energy for registering particles indicates that this method may find application in heavy ion dosimetry. The method has been found to be sensitive to stopping He nuclei and relativistic M group cosmic rays. Some impurities strongly influence the printout of the tracks, and the effects of these impurities are discussed.

  10. Physics of Solid and Liquid Alkali Halide Surfaces Near the Melting Point

    CERN Document Server

    Zykova-Timan, T; Tartaglino, U; Tosatti, E

    2005-01-01

    This paper presents a broad theoretical and simulation study of the high temperature behavior of crystalline alkali halide surfaces typified by NaCl(100), of the liquid NaCl surface near freezing, and of the very unusual partial wetting of the solid surface by the melt. Simulations are conducted using two-body rigid ion BMHFT potentials, with full treatment of long-range Coulomb forces. After a preliminary check of the description of bulk NaCl provided by these potentials, which seems generally good even at the melting point, we carry out a new investigation of solid and liquid surfaces. Solid NaCl(100) is found in this model to be very anharmonic and yet exceptionally stable when hot. It is predicted by a thermodynamic integration calculation of the surface free energy that NaCl(100) should be a well ordered, non-melting surface, metastable even well above the melting point. By contrast, the simulated liquid NaCl surface is found to exhibit large thermal fluctuations and no layering order. In spite of that, ...

  11. Calculation of intraband electron and band-to-band hole luminescence spectra of some alkali halide crystals under pulse excitation by dense electron and laser beams of nano- and picosecond duration

    International Nuclear Information System (INIS)

    Theoretical calculation of spectra of two new types of fundamental radioluminescence of dielectrics - intraband electron and band-to-band hole ones - was conducted. These types of radioluminescence were revealed and studied experimentally due to the use of two high-power nano- and picosecond radiation sources for dielectric excitation - high-current electron accelerators and lasers with generators of ultraviolet harmonics. Satisfactory agreement of calculated spectra with ones, measured experimentally, was achieved. Correlation of calculation results with experimental data enabled to determine some important parameters of electron spectrum and specifically the upper boundary of passive region for conduction band ionization for CsI crystals. 27 refs., 8 figs

  12. H2O- center in alkali halides with OH-: properties and formation kinetics-destruction after radiation damage

    International Nuclear Information System (INIS)

    In order to understand the basic mechanisms that are responsible for the thermal formation and thermal destruction of the primary and secondary defects after low energy radiation damage in alkali halide crystals doped with OH-, the production of defects by pulse annealing in KCl:OH- and KBr:OH- was studied. These thermal processes were studied over a wide range of temperatures (52-300 K), and the several hydrogen reaction products were identified by their characteristic electronic absorption (visible-ultraviolet). Besides the well known substitucional and interstitial H0 sub(i) and H- defects, a new hydrogen defect, U2 sub(x) center, was discovered after the thermal destruction of the U2 centers. It is characterized by a new structureless eletronic absorption band (UV) at 45000 cm-1 in KCl and 40000 cm-1 in KBr. From this experimental observations it was proposed that the U2 sub(x) center is constituted by one H0 sub(i) center trapped by a substitucional OH-, without disturbing the electronic transition of the OH-. H2O- centers in KCl or H2O- and U centers in KBr are produced by thermal destruction of the U2 sub(x) centers. Furthermore, it was observed that thermal desctruction of H2O- centers produced: F(15%), U(60%) and OH- (25%) centers in KCl and F (approximated 100%) in KBr. At the end of this thermal process (at 300 K), 90 to 95% of the iitial OH- centers were restored at the expenses of F and U centers. Several new properties of the H2O- defect were found and studied. (Author)

  13. Photodissociation comprehensive study of OH- on alkali halides and their interaction with colour centers

    International Nuclear Information System (INIS)

    This work shows that the OH- defect induces changes in the electronics processes of the alkali halides such as in radiation damage and optical cycles of colour centers. Two cases were considered: with the presence of an OH- ion in the (1) excited state and (2) in the ground state; 1) the comprehensive study of resonant OH- photodissociation in several hosts showed that deep traps (for electrons) can be produced from the OH- dissociation. These traps can be effective for the capture of electrons produced in the radiation damage of the lattice as well as for trapping electrons from ionized color centers. It was observed a second channel (new) for the de-excitation of the (OH-)* molecule in KI and RbI. This effect can be effective only when the lattice around the molecule holds a large enough interstitial space. This new mechanism is responsible for the strong production at LNT of F centers and OH0 molecules at the expenses of OH- defects. Considering the complete investigation of the full cycle it was proposed a phenomenological model that would explain the observed behaviour when one covers a wide variation of lattice parameters (KCl -> RbI); 2) It was verified that the OH- ion present in the lattice induces strong changes in the de-excitation processes of electronic defects with a spread out wave function (like F centers). A change in the reorientation behaviour of excited F2 and F+2 centers was also verified. Two main effects should be mentioned: A) The induced de-excitation is very fast and non-radiative on F centers. B) Another type of system investigated (F2 and F+2) has shown an intense increase of the speed of reorientation of the F2 and F+2 excited centers. (autor)

  14. Low-Energy Grazing Ion-Scattering from Alkali-Halide Surfaces: A Novel Approach to C-14 Detection

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, Fred W [ORNL; Galutschek, Ernst [ORNL; Hotchkis, Michael [Australian Nuclear Science and Technology Organization

    2009-01-01

    Carbon-14 labeled compounds are widely used in the pharmaceutical industry, e.g., as tracers to determine the fate of these compounds in vivo. Conventional accelerator mass spectrometry (AMS) is one approach that offers sufficiently high sensitivity to avoid radiological waste and contamination issues in such studies, but requires large, expensive facilities that are usually not solely dedicated to this task. At the ORNL Multicharged Ion Research Facility (MIRF) we are exploring a small size, low cost alternative to AMS for biomedical 14C tracer studies that utilizes ECR-ion-source-generated keV-energy-range multicharged C beams grazingly incident on an alkali halide target, where efficient negative ion production by multiple electron capture takes place. By using C ion charge states of +3 or higher, the molecular isobar interference at mass 14, e.g. 12CH2 and 13CH, is eliminated. The negatively charged ions in the beam scattered from the alkali halide surface are separated from other scattered charge states by two large acceptance ({approx}15 msr) stages of electrostatic analysis. The N-14 isobar interference is thus removed, since N does not support a stable negative ion. Initial results for C-14 detection obtained using C-14 enriched CO2 from ANSTO will be described.

  15. Low-Energy Grazing Ion-Scattering from Alkali-Halide Surfaces: A Novel Approach to C-14 Detection

    International Nuclear Information System (INIS)

    Carbon-14 labeled compounds are widely used in the pharmaceutical industry, e.g., as tracers to determine the fate of these compounds in vivo. Conventional accelerator mass spectrometry (AMS) is one approach that offers sufficiently high sensitivity to avoid radiological waste and contamination issues in such studies, but requires large, expensive facilities that are usually not solely dedicated to this task. At the ORNL Multicharged Ion Research Facility (MIRF) we are exploring a small size, low cost alternative to AMS for biomedical 14C tracer studies that utilizes ECR-ion-source-generated keV-energy-range multicharged C beams grazingly incident on an alkali halide target, where efficient negative ion production by multiple electron capture takes place. By using C ion charge states of +3 or higher, the molecular isobar interference at mass 14, e.g. 12CH2 and 13CH, is eliminated. The negatively charged ions in the beam scattered from the alkali halide surface are separated from other scattered charge states by two large acceptance (?15 msr) stages of electrostatic analysis. The N-14 isobar interference is thus removed, since N does not support a stable negative ion. Initial results for C-14 detection obtained using C-14 enriched CO2 from ANSTO will be described.

  16. Low-Energy Grazing Ion-Scattering From Alkali-Halide Surfaces: A Novel Approach To C-14 Detection

    Science.gov (United States)

    Meyer, F. W.; Galutschek, E.; Hotchkis, M.

    2009-03-01

    Carbon-14 labeled compounds are widely used in the pharmaceutical industry, e.g., as tracers to determine the fate of these compounds in vivo. Conventional accelerator mass spectrometry (AMS) is one approach that offers sufficiently high sensitivity to avoid radiological waste and contamination issues in such studies, but requires large, expensive facilities that are usually not solely dedicated to this task. At the ORNL Multicharged Ion Research Facility (MIRF) we are exploring a small size, low cost alternative to AMS for biomedical 14C tracer studies that utilizes ECR-ion-source-generated keV-energy-range multicharged C beams grazingly incident on an alkali halide target, where efficient negative ion production by multiple electron capture takes place. By using C ion charge states of +3 or higher, the molecular isobar interference at mass 14, e.g. 12CH2 and 13CH, is eliminated. The negatively charged ions in the beam scattered from the alkali halide surface are separated from other scattered charge states by two large acceptance (˜15 msr) stages of electrostatic analysis. The N-14 isobar interference is thus removed, since N does not support a stable negative ion. Initial results for C-14 detection obtained using C-14 enriched CO2 from ANSTO will be described.

  17. Low-Energy Grazing Ion-Scattering From Alkali-Halide Surfaces: A Novel Approach To C-14 Detection

    International Nuclear Information System (INIS)

    Carbon-14 labeled compounds are widely used in the pharmaceutical industry, e.g., as tracers to determine the fate of these compounds in vivo. Conventional accelerator mass spectrometry (AMS) is one approach that offers sufficiently high sensitivity to avoid radiological waste and contamination issues in such studies, but requires large, expensive facilities that are usually not solely dedicated to this task. At the ORNL Multicharged Ion Research Facility (MIRF) we are exploring a small size, low cost alternative to AMS for biomedical 14C tracer studies that utilizes ECR-ion-source-generated keV-energy-range multicharged C beams grazingly incident on an alkali halide target, where efficient negative ion production by multiple electron capture takes place. By using C ion charge states of +3 or higher, the molecular isobar interference at mass 14, e.g. 12CH2 and 13CH, is eliminated. The negatively charged ions in the beam scattered from the alkali halide surface are separated from other scattered charge states by two large acceptance (?15 msr) stages of electrostatic analysis. The N-14 isobar interference is thus removed, since N does not support a stable negative ion. Initial results for C-14 detection obtained using C-14 enriched CO2 from ANSTO will be described.

  18. Photography: enhancing sensitivity by silver-halide crystal doping

    International Nuclear Information System (INIS)

    The physical chemistry of the silver photography processes, exposure, development and fixing, is briefly summarized. The mechanism of the autocatalytic development by the developer of the clusters produced in silver bromide crystals during the exposure which is controlled by the critical nuclearity of these clusters was understood from pulse radiolysis studies. The effective quantum yield PHIeff of photoinduced silver cluster formation in silver halide microcrystals is usually much lower than the photoionization theoretical limit PHItheor=1 electron-hole pair per photon absorbed, owing to a subsequent very fast intra-crystal recombination of a part of the electron-hole pairs. In order to inhibit this recombination and favor the silver reduction by photo-electrons, the AgX crystals were doped with the formate HCO2- as a specific hole scavenger. First, the dopant scavenges the photoinduced hole, thus enhancing the electron escape from the pair recombination. Second, the CO2·- radical so formed transfers an electron to another silver cation, so that the PHIeff limit may be of 2Ag0 per photon. This Photoinduced Bielectronic Transfer mechanism is strictly proportional to the light quanta absorbed and induces an exceptional efficiency for enhancing the radio- or photographic sensitivity insofar as it totally suppresses the electron-hole recombination

  19. Viscometric and thermodynamic studies of interactions in ternary solutions containing sucrose and aqueous alkali metal halides at 293.15, 303.15 and 313.15 K

    Indian Academy of Sciences (India)

    Reena Gupta; Mukhtar Singh

    2005-05-01

    Viscosities and densities of sucrose in aqueous alkali metal halide solutions of different concentrations in the temperature range 293.15 to 313.15 K have been measured. Partial molar volumes at infinite dilution ($V_{2}^{0}$) of sucrose determined from apparent molar volume ($\\phi_v$) have been utilized to estimate partial molar volumes of transfer ($V^{0}_{2,tr}$) for sucrose from water to alkali metal halide solutions. The viscosity data of alkali metal halides in purely aqueous solutions and in the presence of sucrose at different temperatures (293.15, 303.15 and 313.5 K) have been analysed by the Jones-Dole equation. The nature and magnitude of solute-solvent and solute-solute interactions have been discussed in terms of the values of limiting apparent molar volume ($\\phi^{0}_{v}$), slope ($S_{v}$) and coefficients of the Jones-Dole equation. The structuremaking and structure-breaking capacities of alkali metal halides in pure aqueous solutions and in the presence of sucrose have been ascertained from temperature dependence of $\\phi^{0}_{v}$.

  20. Dependences of molar volumes in solids, partial molal and hydrated ionic volumes of alkali halides on covalent and ionic radii and the golden ratio.

    Czech Academy of Sciences Publication Activity Database

    Heyrovská, Raji

    2007-01-01

    Ro?. 436, ?. 1-3 (2007), s. 287-293. ISSN 0009-2614 R&D Projects: GA MŠk(CZ) LC06035 Institutional research plan: CEZ:AV0Z50040702 Keywords : alkali halides * ionic hydration * golden ratio Subject RIV: BO - Biophysics Impact factor: 2.207, year: 2007

  1. Cu halide nanoparticle formation by diffusion of copper in alkali halide crystals

    Directory of Open Access Journals (Sweden)

    A. Pérez-Rodríguez

    2006-01-01

    Full Text Available Atomos de cobre han sido introducidos por difusión en cristales de NaCl, KCl y KBr a 500±C. Los cristales han sido analizados óptimamente con medidas de fotoluminiscencia y por microscopía electrónica de barrido. Los espectros de emisión y excitación, medidos a baja temperatura muestran el efecto de confinamiento de exciton, indicando la formación de nanopartículas de CuX (X=Cl, Br, lo cual ha sido confirmado por imágenes de microscopía electrónica. Este método es propuesto como un método alternativo para obtener nanopartículas de CuX en cristales halogenuros alcalinos.

  2. Effect of replacing calcium oxide with calcium halide on crystallization and some physical properties of calcium vanadium phosphate glass ceramics

    International Nuclear Information System (INIS)

    The effect of halide ions on density, electrical, magnetic and crystallization kinetics for (20X-50P2O5-30V2O5) mole% has been investigated, where X=CaO, CaF2, CaCl2 and CaBr2. Halide ions reduce the glass transition temperature, crystallization temperature and activation energy of crystallization. Density, electrical conductivity and magnetic susceptibility increase while molar volume, glass thermal stability and interatomic distance between transition metal ions decrease as the halide ions replace the oxygen ions in these glasses. -- Research Highlights: ? Replacing oxygen ions by halide ions decreases glass transition temperature and thermal stability. ? Replacing oxygen ions by halide ions increases electrical conductivity and decreases activation energy. ? Replacing oxygen ions by halide ions enhances the tendency of glass ceramic and decreases the crystallization activation energy.

  3. An Investigation of Ion-Pairing of Alkali Metal Halides in Aqueous Solutions Using the Electrical Conductivity and the Monte Carlo Computer Simulation Methods

    Science.gov (United States)

    Gujt, Jure; Bešter-Rogač, Marija; Hribar-Lee, Barbara

    2013-01-01

    The ion pairing is, in very dilute aqueous solutions, of rather small importance for solutions’ properties, which renders its precise quantification quite a laborious task. Here we studied the ion pairing of alkali halides in water by using the precise electric conductivity measurements in dilute solutions, and in a wide temperature range. The low-concentration chemical model was used to analyze the results, and to estimate the association constant of different alkali halide salts. It has been shown that the association constant is related to the solubility of salts in water and produces a ’volcano relationship’, when plotted against the difference between the free energy of hydration of the corresponding individual ions. The computer simulation, using the simple MB+dipole water model, were used to interprete the results, to find a microscopic basis for Collins’ law of matching water affinities. PMID:24526801

  4. Ca-Fe and Alkali-Halide Alteration of an Allende Type B CAI: Aqueous Alteration in Nebular or Asteroidal Settings

    Science.gov (United States)

    Ross, D. K.; Simon, J. I.; Simon, S. B.; Grossman, L.

    2012-01-01

    Ca-Fe and alkali-halide alteration of CAIs is often attributed to aqueous alteration by fluids circulating on asteroidal parent bodies after the various chondritic components have been assembled, although debate continues about the roles of asteroidal vs. nebular modification processes [1-7]. Here we report de-tailed observations of alteration products in a large Type B2 CAI, TS4 from Allende, one of the oxidized subgroup of CV3s, and propose a speculative model for aqueous alteration of CAIs in a nebular setting. Ca-Fe alteration in this CAI consists predominantly of end-member hedenbergite, end-member andradite, and compositionally variable, magnesian high-Ca pyroxene. These phases are strongly concentrated in an unusual "nodule" enclosed within the interior of the CAI (Fig. 1). The Ca, Fe-rich nodule superficially resembles a clast that pre-dated and was engulfed by the CAI, but closer inspection shows that relic spinel grains are enclosed in the nodule, and corroded CAI primary phases interfinger with the Fe-rich phases at the nodule s margins. This CAI also contains abundant sodalite and nepheline (alkali-halide) alteration that occurs around the rims of the CAI, but also penetrates more deeply into the CAI. The two types of alteration (Ca-Fe and alkali-halide) are adjacent, and very fine-grained Fe-rich phases are associated with sodalite-rich regions. Both types of alteration appear to be replacive; if that is true, it would require substantial introduction of Fe, and transport of elements (Ti, Al and Mg) out of the nodule, and introduction of Na and Cl into alkali-halide rich zones. Parts of the CAI have been extensively metasomatized.

  5. Thermodynamics of small alkali metal halide cluster ions: comparison of classical molecular simulations with experiment and quantum chemistry.

    Science.gov (United States)

    Vlcek, Lukas; Uhlik, Filip; Moucka, Filip; Nezbeda, Ivo; Chialvo, Ariel A

    2015-01-22

    We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali metal halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge nonpolarizable SPC/E, (ii) Drude point charge polarizable SWM4-DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ion hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas-phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties. PMID:25513841

  6. Conductometric study of some alkali metal halides in (dimethyl sulfoxide + acetonitrile) at T = 298.15 K

    Energy Technology Data Exchange (ETDEWEB)

    Roy, Mahendra Nath [Department of Chemistry, North Bengal University, Darjeeling 734013 (India)], E-mail: mahendraroy2002@yahoo.co.in; Banerjee, Ashis; Das, Rajesh Kumar [Department of Chemistry, North Bengal University, Darjeeling 734013 (India)

    2009-11-15

    Electrolytic conductivities of some alkali metal halides, MX (M{sup +} = Li{sup +}, Na{sup +}, and K{sup +}; X{sup -} = Cl{sup -}, Br{sup -}, and I{sup -}), NaBPh{sub 4} and Bu{sub 4}NBr have been investigated in (20, 40, and 60) mass% {l_brace}dimethyl sulfoxide (DMSO) in DMSO + acetonitrile{r_brace} at T = 298.15 K. The conductance results have been analyzed by the Fuoss-conductance-concentration equation in terms of the limiting molar conductance {lambda}{sup o} the association constant K{sub A} and the association diameter R. The ionic contributions to the limiting molar conductance have been estimated using Bu{sub 4}NBPh{sub 4} as the 'reference electrolyte'. The association constant K{sub A} tends to increase in the order mass percent 20 < 40 < 60 DMSO in (DMSO + acetonitrile) which is explained by the thermodynamic parameter {delta}G{sup o} and Walden product {lambda}{sup o}{eta}. The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvents.

  7. Tunable Crystal-to-Crystal Phase Transition in a Cadmium Halide Chain Polymer

    Directory of Open Access Journals (Sweden)

    Ulli Englert

    2011-07-01

    Full Text Available The chain polymer [{Cd(μ-X2py2}1∞] (X = Cl, Br; py = pyridine undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and can be confirmed for the bulk by powder diffraction. The transition temperature can be adjusted by tuning the composition of the mixed-halide phase: Transition temperatures between 175 K up to the decomposition of the material at ca. 350 K are accessible. Elemental analysis, ion chromatography and site occupancy refinements from single-crystal X-ray diffraction agree with respect to the stoichiometric composition of the samples.

  8. A study on the electrochemical behaviour of polypyrrole films in concentrated aqueous alkali halide electrolytes

    DEFF Research Database (Denmark)

    Jafeen, M. J. M.; Careem, M.A.; Skaarup, Steen

    2014-01-01

    The electrochemical behaviour of polypyrrole films doped with dodecyl benzene sulfonate (PPy/DBS) in LiCl aqueous electrolytes has been investigated in order to find the electrolyte concentration suitable for the operation of PPy/DBS-based soft actuators. For this investigation, PPy/DBS films deposited on gold-coated quartz crystals by electropolymerization and simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance techniques were used. During the first redox cycle, whil...

  9. Coloration of cadmium halide crystals due to reactor irradiation at low temperature

    International Nuclear Information System (INIS)

    The optical absorption spectra and ESR spectra of cadmium halide crystals were measured after the reactor irradiation at low temperature to study the coloration. The irradiated neutron dose was about 5 x 1017 n/cm2. In the measurement of ESR spectra, the crystal was rotated around the v-axis (the two-fold axis) in the magnetic field of fixed direction. The optical absorption spectra showed that the Cd3+ center was generated. From the analysis of the angular dependence of ESR spectra, the centers of C(2h) symmetry and the centers of D(3d) symmetry were considered to be generated. The models of these centers were considered, and the angular dependence was analyzed. It can be concluded from the present experiment that the coloration of cadmium halide crystals is recognized as the results of the reactor irradiation at low temperature. (Kato, T.)

  10. Evidence for New Excess Electron Localization Sites in Na{sub {ital n}}F{sub {ital n}{minus}1 } Alkali-Halide Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Durand, G.; Spiegelmann, F. [Laboratoire de physique quantique (UMR 5626 CNRS-UPS), IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F31062 Toulouse Cedex 4 (France); Labastie, P.; LHermite, J.; Poncharal, P. [Laboratoire CAR (UMR 5589 CNRS-UPS), IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F31062 Toulouse cedex 4 (France)

    1997-07-01

    This Letter examines new types of localization sites for an excess electron in finite alkali-halide clusters resulting from defects on cuboidal structures, namely {open_quotes}edge states,{close_quotes} R center, and other surface defects. We present theoretical calculations on Na{sub n}F {sub n{minus}1} clusters with one excess electron. Comparisons with experimental results are presented for different cluster sizes (n=17 , 23, 28, and 29). Structures with edge or surface defects are relevant for n=23 , 28, and 29. {copyright} {ital 1997} {ital The American Physical Society}

  11. Effect of alkali and alkaline earth metal oxides on crystal growth rate of wollastonite crystals in melt

    International Nuclear Information System (INIS)

    The effect of oxide additions of alkali (Li, Na, K) and alkaline earth (Mg, Sr, Ba) metals on growth rate of wollastonite CaSiO3 crystals in melt is studied. It has been found that low oxide additions of alkali and alkaline earth metals in melt can increase as well as decrease the wollastonite crystals growth

  12. Structure and molar refraction and its wavelength dependence at different alkali and ammonium halides

    International Nuclear Information System (INIS)

    The wavelength dependence of the molar refraction of AB-compounds, crystallizing in the NaCl- or CsCl-structure type, is analysed by use of a two-term Sellmeier dispersion formula. In the range of the validity of a single-oscillator model a clear distinction between series with NaCl or CsCl structure is possible on the base of the influence of the parameters lambda1, the resonance wavelength of the electronic absorption, and n/sub eff/, the effective number of electrons involved in the elctron transition, on the molar refraction and its slope. The Sellmeier model is compared with the dispersion model of Wemple. (author)

  13. Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces

    Directory of Open Access Journals (Sweden)

    Laurent Nony

    2012-03-01

    Full Text Available We investigated the adsorption of 4-methoxy-4?-(3-sulfonatopropylstilbazolium (MSPS on different ionic (001 crystal surfaces by means of noncontact atomic force microscopy. MSPS is a zwitterionic molecule with a strong electric dipole moment. When deposited onto the substrates at room temperature, MSPS diffuses to step edges and defect sites and forms disordered assemblies of molecules. Subsequent annealing induces two different processes: First, at high coverage, the molecules assemble into a well-organized quadratic lattice, which is perfectly aligned with the directions of the substrate surface (i.e., rows of equal charges and which produces a Moiré pattern due to coincidences with the substrate lattice constant. Second, at low coverage, we observe step edges decorated with MSPS molecules that run along the direction. These polar steps most probably minimize the surface energy as they counterbalance the molecular dipole by presenting oppositely charged ions on the rearranged step edge.

  14. Thermoluminescence in alkali halides irradiated at 80K; Termoluminiscencia en haluros alcalinos irradiados a 80K

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez de Castro, M.

    1978-07-01

    The thermoluminescence, the thermally stimulated currents and the thermal stability of the F centres induced in pure NaCl and KC1 crystals by X irradiation at 80K have been studied in detail, In the range between 80 and 300K. The thermoluminescent processes induced by illumination at 80K with F light in samples previously irradiated at room temperature has also been studied. It has been clearly observed the existence of thermoluminescent processes due to electrons and holes thermally released from traps, in which the F centres are not involved. The existence of hole-F centre recombination has not been observed. There are several thermoluminescent processes in both materials which are scribed to the recombination of F centres with mobile interstitial halogen atoms thermally released from traps, which are likely monovalent impurities in this temperature interval. The light emitting stage in these processes is originated by the formation of self trapped excitons. (Author) 66 refs.

  15. Differential calorimeter and temperature controller for stored energy measurements in irradiated alkali halides

    International Nuclear Information System (INIS)

    The design and performance of a simple temperature-controlled differential calorimeter are presented. This system allows to measure radiation-induced stored energy in insulators, above room temperature with a differential thermal analysis method. With platelets of KC1 single crystals, the base lines obtained for T2 T1 (with T2: irradiated sample temperature and T1: reference sample temperature) show a smooth drift less of 0,2 degree centigree in the interval from 25 to 400 degree centigree. The discrepancy between two consecutive base lines is less than ± 0,02 degree centigree which implies a calorimeter sensitivity of about ±0,004 cal/g. This sensitivity allows to measure stored energy release in samples with a color center concentration low enough to be directly measured with a spectrophotometer so that a search for correlations among the features of the stored energy spectrum and the color center annealing can be made. (Author) 13 refs

  16. A generalized rule of average for glow peak temperature of ternary alkali halide systems

    Scientific Electronic Library Online (English)

    G., Moroyoqui-Estrella; R., Pérez-Salas; R., Rodriguez-Mijangos.

    2011-04-01

    Full Text Available Se estudia la dependencia de la temperatura en la curva de brillo con la composición de los aniones en mezclas cristalinas impurificadas con Europio: KCl0.50KBr0.25RbX0.25:Eu2+ (X = Cl, Br). Cada material muestra una curva de brillo termoluminiscente consistente en dos picos de brillo principales co [...] n temperatura entre la del KCl:Eu2+ y la del KBr:Eu2+. El pico más intenso está relacionado con la destrucción del centro F, como ocurre en el caso de cristales de KCl:Eu2+ y su temperatura característica depende fuertemente de la composición del halogeno. El comportamiento confirma que la temperatura de la recombinación de los centros F-H en este tipo de materiales depende en gran medida de la proporción de los aniones. De estos resultados se propone una regla generalizada para obtener la temperatura, promediando la temperatura característica en función de la composición. Abstract in english The anion composition dependence of the characteristic glow peak temperature of europium doped KCl0.50KBr0.25RbX0.25:Eu2+ (X=Cl, Br) mixed crystals are studied. Each material shows a thermoluminescence glow curve consisting of two main glow peaks with a temperature is between KCl:Eu2+ and KBr:Eu2+. [...] The most intense is related to the F center destruction as occur in the case of KCl:Eu2+ crystals and its characteristic temperature depends strongly on the halogen composition. This behavior confirms that the temperature of the F-H centers recombination in this type of materials depends more on the proportion of anions. From these results, a generalized rule to obtain the temperature from averaging the characteristic temperature as function of the composition is discussed.

  17. Energy Transfer Processes Involving Cyanide Ion Defects and F Center/cyanide Ion Pairs in Alkali Halides

    Science.gov (United States)

    Dierolf, Volkmar Rudolf Gunter

    1992-01-01

    The association of F centers to CN^ - substitutional molecular defects in alkali halides forms so-called "F_{rm H} (CN^-)" complexes. Under excitation of their electronic absorption in the visible, vibrational excitation and IR luminescence (~ 5mum) of long life-time ( ~10ms) is produced by a very efficient electronic to vibrational (E-V) energy transfer. The population of excited vibrational states of the CN ^- next to the F center can be measured by vibrational luminescence and by anti-Stokes resonance Raman techniques. The E-V transfer and the relaxation kinetics in CsCl, CsBr and RbCl are studied with low intensity pulses and the primary relative E-V transfer efficiencies ( eta_{rm EV(v)}) for the various v-levels have been determined. The maximum of the eta_{rm EV(v)} distribution is found to be at v = 4 and/or 3 depending on the hosts. The relaxation from the v-levels between v = 2 and v = 6 occurs radiatively at low concentrations, but with decay-rates that are fast compared to the isolated CN^- defect. For the v = 1 level a nonradiative decay-channel caused by vibrational-vibrational (V-V) transfer into the isolated CN^- system is found. A secondary E-V transfer was studied using high intensity pulses, causing F_ {rm H} center re-excitation long before full vibrational relaxation is achieved. By this transfer higher excited v-levels (v > 6) become populated, which exhibit fast nonradiative decay -rates. The overall kinetics are explained by phenomenological models, which suggest that besides the E-V transfer a (V -E) energy transfer process from the higher (v > 6) excited vibrational states to electronic excited state occurs. The F_{rm H} (CN^-) relaxation and V-V transfer allow, for higher CN^- concentrations, an excitation of the abundant isolated CN^- molecules and can therefore be used as a pump source of this molecular system. This system exhibits excitation energy migration, trapping and energy accumulation in certain molecules (up to v = 24). The dynamics of these processes is studied experimentally and is compared to a simple model. It turns out that the fixed distribution of the pump sources and the isolated molecules have to be taken into account to explain the experiments.

  18. Solution growth of single crystal methylammonium lead halide perovskite nanostructures for optoelectronic and photovoltaic applications.

    Science.gov (United States)

    Fu, Yongping; Meng, Fei; Rowley, Matthew B; Thompson, Blaise J; Shearer, Melinda J; Ma, Dewei; Hamers, Robert J; Wright, John C; Jin, Song

    2015-05-01

    Understanding crystal growth and improving material quality is important for improving semiconductors for electronic, optoelectronic, and photovoltaic applications. Amidst the surging interest in solar cells based on hybrid organic-inorganic lead halide perovskites and the exciting progress in device performance, improved understanding and better control of the crystal growth of these perovskites could further boost their optoelectronic and photovoltaic performance. Here, we report new insights on the crystal growth of the perovskite materials, especially crystalline nanostructures. Specifically, single crystal nanowires, nanorods, and nanoplates of methylammonium lead halide perovskites (CH3NH3PbI3 and CH3NH3PbBr3) are successfully grown via a dissolution-recrystallization pathway in a solution synthesis from lead iodide (or lead acetate) films coated on substrates. These single crystal nanostructures display strong room-temperature photoluminescence and long carrier lifetime. We also report that a solid-liquid interfacial conversion reaction can create a highly crystalline, nanostructured MAPbI3 film with micrometer grain size and high surface coverage that enables photovoltaic devices with a power conversion efficiency of 10.6%. These results suggest that single-crystal perovskite nanostructures provide improved photophysical properties that are important for fundamental studies and future applications in nanoscale optoelectronic and photonic devices. PMID:25871732

  19. Advances in the growth of alkaline-earth halide single crystals for scintillator detectors

    Energy Technology Data Exchange (ETDEWEB)

    Boatner, Lynn A [ORNL; Ramey, Joanne Oxendine [ORNL; Kolopus, James A [ORNL; Neal, John S [ORNL; Cherepy, Nerine [Lawrence Livermore National Laboratory (LLNL); Payne, Stephen A. [Lawrence Livermore National Laboratory (LLNL); Beck, P [Lawrence Livermore National Laboratory (LLNL); Burger, Arnold [Fisk University, Nashville; Rowe, E [Fisk University, Nashville; Bhattacharya, P. [Fisk University, Nashville

    2014-01-01

    Alkaline-earth scintillators such as strontium iodide and other alkaline-earth halides activated with divalent europium represent some of the most efficient and highest energy resolution scintillators for use as gamma-ray detectors in a wide range of applications. These applications include the areas of nuclear nonproliferation, homeland security, the detection of undeclared nuclear material, nuclear physics and materials science, medical diagnostics, space physics, high energy physics, and radiation monitoring systems for first responders, police, and fire/rescue personnel. Recent advances in the growth of large single crystals of these scintillator materials hold the promise of higher crystal yields and significantly lower detector production costs. In the present work, we describe new processing protocols that, when combined with our molten salt filtration methods, have led to advances in achieving a significant reduction of cracking effects during the growth of single crystals of SrI2:Eu2+. In particular, we have found that extended pumping on the molten crystal-growth charge under vacuum for time periods extending up to 48 hours is generally beneficial in compensating for variations in the alkaline-earth halide purity and stoichiometry of the materials as initially supplied by commercial sources. These melt-pumping and processing techniques are now being applied to the purification of CaI2:Eu2+ and some mixed-anion europium-doped alkaline-earth halides prior to single-crystal growth by means of the vertical Bridgman technique. The results of initial studies of the effects of aliovalent doping of SrI2:Eu2+ on the scintillation characteristics of this material are also described.

  20. New halides of neodymium and their crystal structures

    International Nuclear Information System (INIS)

    The crystal structures of the peritectic phases NdClsub(2.27) (t-phase) and NdClsub(2.37) (rh-phase) were determined. The structure of the rh-phase was solved, from the t-phase only the elementary cell could be determined because no single crystals of sufficient quality were obtained. Jutting out feature of the rh-phase which has to be formulated as Nd14Cl32O is a polyeder cluster of 6 quadratic antiprisms the inner cubo octahedric cavity of which is occupied by an oxygen atom. The linkage of these polyeder cluster ensues only under each other along the triple axis of the rhomboedric system over 3 upper and 3 lower common borders each. Therewith for the first time a superlattice of the fluorite-type was found in which this unit exclusively occurs. The type of linkage of polyeder clusters causes the occurrence of an exceptional polyeder around the twovalent Nd ions which can be looked at as a zwitter polyeder of icosahedron and cube and therefore coordinates tenfold the twovalent neodymium. The strict order of chemically and crystallografically clearly differentiated cations is expressed by a hexagonal-rhomboedric superstructure of the fluorite-aristotyp with a doubled c-axis. The phase diagram of the system Nd-NdBr3 was determined and a structure proposition was worked out for the first Vernier phase in there with n=4 of the series Lnsub(n)Xsub(2n+1). (SPI)

  1. Photofragmentation of metal halides

    International Nuclear Information System (INIS)

    The author deals with photodissociation of molecules of alkali halides. It is shown that the total absorption cross section consists of two contributions arising from transitions to excited states of total electronic angular momentum ?=0+ and ?=1. From the inversion of the absorption continua potential energy curves of the excited states can be constructed in the Franck-Condon region. It is found that for all alkali halides the 0+ state is higher in energy than the ?=1 state. Extensive studies are reported on three thallium halides, TlI, TlBr and TlCl at various wavelengths covering the near ultraviolet region. (Auth.)

  2. Interaction of dislocations with radiation defects in alkaline-halide crystals

    International Nuclear Information System (INIS)

    The studies on interaction of dislocations with point defects in the alkaline-halide crystal are carried out with the purpose of clarifying the nature of the deformation-stimulated luminescence (DSL) and radiation strengthening mechanism. The KCl monocrystals were irradiated by the gamma-quanta (the absorbed dose is of 2 MGy). The information on the hole centers is obtained by analysis of the thermostimulated luminescence curves within the temperature range of 300-540 K. The load on the sample was registered simultaneously with studying the DSL luminescence intensity. It is established that at the room temperature of the DSL crystals the KCl is conditioned by the Vz and V2 hole centers. Dislocations destroy the Vz and V2 centers, which results in the VF- and H-centers, recombining with the F-type centers formation. Thus, the DSL is the consequence of destroying the V2 and Vz hole centers

  3. Potential Advantage of Multiple Alkali Metal Doped KNbO3 Single Crystals

    OpenAIRE

    Hideo Kimura; Hongyang Zhao; Rumi Tanahashi; Lei Guo; Tingting Jia; Qiwen Yao; Zhenxiang Cheng

    2014-01-01

    Potassium niobate crystal KNbO3 (KN) is a well-known crystal for lead free piezoelectric or nonlinear optical applications. The KN crystal has been studied in both single crystal form and in thin film form which has resulted in many review articles being published. In order to exceed the KN crystal, it is important to study KN phase forming and doping effects on the K site. This article summarizes the authors’ study towards a multiple alkali metal doped KN crystal and related single crystals ...

  4. Energetic aspects of water radiolysis on surface of alkali-halogen crystals

    International Nuclear Information System (INIS)

    It is established that radiolysis rate of water adsorbed with alkali-halogen crystals depends on the nature of salt, adsorbate concentration and crystal sizes. It is shown that water decomposition on the surface of potassium and rubidium iodides results from the interaction with components of electron-hole pairs. Assumption of diffusive sink of thermalized electrons and holes to the surface from crystal volume of 0.1-1 mm depth was suggested

  5. Neutron inelastic scattering investigation of phonons in alkali-halides and a neutron small-angle scattering study of voids in creep-deformed steel

    International Nuclear Information System (INIS)

    Studies on lattice dynamics in alkali-halides have been performed on RbBr and NaCl using inelastic scattering of thermal neutrons. Anharmonic properties of RbBr have been examined by measuring phonon peaks at the three temperatures 80, 290 and 370 K. In NaCl a three dimensional phonon dispersion map has been obtained. 72 phonon frequencies in off-symmetry directions have been determined. In creep-deformed alloy 800 the void radius distribution was obtained using neutron small-angle scattering. Six samples with different creep-times were studied. As these samples also contain carbides and ?'-precipitates the measured intensity is in principle due to scattering from three kinds of particles. Transmission electron microscopy measurements show that the scattering by the carbides is negligible, however. The relative radius distribution of ?'-particles, calculated for each sample individually, has an average radius of approximately 25 A. Because of experimental difficulties the void radius distribution could be determined only for samples with 5 and 10% creep. The voids appear to have a broad distribution around 300 A and the volume fraction of voids shows an increase of 7% between these two samples. (Auth.)

  6. Band-structure calculations of noble-gas and alkali halide solids using accurate Kohn-Sham potentials with self-interaction correction

    International Nuclear Information System (INIS)

    The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP

  7. Electron-hole recombination limited by ion processes in ionic crystals

    International Nuclear Information System (INIS)

    The complex of electrical, optical and other thermostimulated characteristics of wide-gap ionic crystals (halides of alkali, alkali-earth metals and silver) excited by radiation is investigated. Various mechanisms of two-stage ion-electron processes of thermostimulated relaxation of these crystals are discussed

  8. Surface and zeta-potentials of silver halide single crystals: pH-dependence in comparison to particle systems

    International Nuclear Information System (INIS)

    We have carried out surface and zeta-potential measurements on AgCl and AgBr single crystals. As for particle systems we find that, surprisingly and previously unnoted, the zeta-potential exhibits pH-dependence, while the surface potential does not. A possible interpretation of these observations is the involvement of water ions in the interfacial equilibria and in particular, stronger affinity of the hydroxide ion compared to the proton. The pH-dependence of the zeta-potential can be suppressed at sufficiently high silver concentrations, which agrees with previous measurements in particle systems where no pH-dependence was found at high halide ion concentrations. The results suggest a subtle interplay between the surface potential determining the halide and silver ion concentrations, and the water ions. Whenever the charge due to the halide and silver ions is sufficiently high, the influence of the proton/hydroxide ion on the zeta-potential vanishes. This might be related to the water structuring at the relevant interfaces which should be strongly affected by the surface potential. Another interesting observation is accentuation of the assumed water ion effect on the zeta-potential at the flat single crystal surfaces compared to the corresponding silver halide colloids. Previous generic MD simulations have indeed predicted that hydroxide ion adsorption is accentuated on flat/rigid surfaces. A thermodynamic model for AgI single crystals was developed to describe the combined effects of iodide, silver and water ions, based on two independently previously published models for AgI (that only consider constituent and background electrolyte ions) and inert surfaces (that only consider water and background electrolyte ions). The combined model correctly predicts all the experimentally observed trends. (paper)

  9. Alkali metals

    International Nuclear Information System (INIS)

    The discussion is presented under the following section headings: introduction; effect of contaminants; reactions of alkali metals with oxygen and nitrogen (sections on Li, Na, K, Rb, Cs); reactions of alkali metals with hydrogen; sample storage; sampling (sections on liquid metals in dynamic and static syystems and solid metals; methods for determination of oxygen (amalgamation, alkyl halide, fluorination, methanol solution and Karl Fischer titration, liquid ammonia for oxygen in lithium, distillation, plugging meter, electrochemical oxygen meter, freezing-point depression, resistivity, activation analysis); methods for determination of hydrogen (diffusion gasometric procedure, vacuum fusion and similar methods, amalgamation, isotope dilution, and miscellaneous); and,determination of nitrogen. (105 references.) (U.S.)

  10. Manipulating Crystallization of Organolead Mixed-Halide Thin Films in Antisolvent Baths for Wide-Bandgap Perovskite Solar Cells.

    Science.gov (United States)

    Zhou, Yuanyuan; Yang, Mengjin; Game, Onkar S; Wu, Wenwen; Kwun, Joonsuh; Strauss, Martin A; Yan, Yanfa; Huang, Jinsong; Zhu, Kai; Padture, Nitin P

    2016-01-27

    Wide-bandgap perovskite solar cells (PSCs) based on organolead (I, Br)-mixed halide perovskites (e.g., MAPbI2Br and MAPbIBr2 perovskite with bandgaps of 1.77 and 2.05 eV, respectively) are considered as promising low-cost alternatives for application in tandem or multijunction photovoltaics (PVs). Here, we demonstrate that manipulating the crystallization behavior of (I, Br)-mixed halide perovskites in antisolvent bath is critical for the formation of smooth, dense thin films of these perovskites. Since the growth of perovskite grains from a precursor solution tends to be more rapid with increasing Br content, further enhancement in the nucleation rate becomes necessary for the effective decoupling of the nucleation and the crystal-growth stages in Br-rich perovskites. This is enabled by introducing simple stirring during antisolvent-bathing, which induces enhanced advection transport of the extracted precursor-solvent into the bath environment. Consequently, wide-bandgap planar PSCs fabricated using these high quality mixed-halide perovskite thin films, Br-rich MAPbIBr2, in particular, show enhanced PV performance. PMID:26726763

  11. Study of growth conditions influence on shape and position of crystal/melt interface during crystal growth of ternary halides by vertical bridgman method.

    Czech Academy of Sciences Publication Activity Database

    Cihlá?, Antonín; Král, Robert

    Bratislava : Slovak Expert Group of Solid State Chemistry and Physics, 2011 - (Koman, M.; Jorík, V.), 32-33 ISBN 978-80-8134-002-4. [Joint Seminar – Development of materials science in research and education(DMRSE)/21.th./. Kežmarské Žlaby (SK), 29.08.2011-02.09.2011] R&D Projects: GA AV ?R KJB200100901 Institutional research plan: CEZ:AV0Z10100521 Keywords : crystal growth * growth conditions * vertical Bridgman method * crystal melt interface * ternary halid Subject RIV: BM - Solid Matter Physics ; Magnetism

  12. Introducing alkali impurities into BaFBr:Eu2+ crystals and their effect on photo-stimulated luminescence

    International Nuclear Information System (INIS)

    In alkali doped BaFBr:Eu2+ a considerable increase of photostimulated luminescence (PSL) intensity is observed. Upon Na doping the intensity of the PSL is increased by a factor of 15 in contrast to undoped samples. Moreover, the PSL peak shifted on 0.08 eV in the red region of spectrum upon Na doping. The potassium and rubidium doping results in the same effects, but with less efficiency. We prepared undoped BaFBr:Eu2+ crystals and those doped with varied concentrations of NaF, KF, RbF. The concentrations of alkali, which we doped before growth, were in the region of 0.1-5%. Atomic-Emission Analysis shows that the real alkali concentrations in the crystals are 0.0002-0.0025%. However, even such a small alkali doping concentration in BaFBr:Eu2+ influences effectively the PSL process

  13. Electrolytic systems and methods for making metal halides and refining metals

    Energy Technology Data Exchange (ETDEWEB)

    Holland, Justin M.; Cecala, David M.

    2015-05-26

    Disclosed are electrochemical cells and methods for producing a halide of a non-alkali metal and for electrorefining the halide. The systems typically involve an electrochemical cell having a cathode structure configured for dissolving a hydrogen halide that forms the halide into a molten salt of the halogen and an alkali metal. Typically a direct current voltage is applied across the cathode and an anode that is fabricated with the non-alkali metal such that the halide of the non-alkali metal is formed adjacent the anode. Electrorefining cells and methods involve applying a direct current voltage across the anode where the halide of the non-alkali metal is formed and the cathode where the non-alkali metal is electro-deposited. In a representative embodiment the halogen is chlorine, the alkali metal is lithium and the non-alkali metal is uranium.

  14. Structural systematic and crystal chemistry of novel borates with REE, Pb, Sr, and alkali metals

    Energy Technology Data Exchange (ETDEWEB)

    Belokoneva, E.L. [Moscow State Univ., Moscow (Russian Federation). Dept. of Crystallography and Crystal Chemistry

    2013-11-01

    Crystal structures of novel borates with REE, Pb, Sr and alkali metals were analyzed using classical fundamental buildings blocks approach. It is demonstrated that hexa-, penta-, tetra-, tri- and diborates subdivisions in systematic are real families of structures with the common peculiarities. According to the symmetrical way and the degree of FBB condensation structural-generic rows exist in every of subdivisions. Mega- or polyborates subdivision is valid for the structures with the different types of simplest FBB. In all new complex borates it is possible to separate FBB of equal or different types which are presented in isolated form or are connected into chains, layers or frameworks, and to find unexpected correlation between structures. The possibility to recognize and to visualize in this approach the polarity or non-polarity of the structural units and correspondingly the polarity or nonpolarity of the structures in the whole is very important for the conclusion on structure-properties relation. (orig.)

  15. Spectral-luminescence properties of the halide-cesium crystals with the impurity of the tetrahedral molecular anions

    International Nuclear Information System (INIS)

    Absorption, excitation (PLE) and emission (PL) spectra as well as infrared absorption spectra and Raman spectra of the tetrahedral molecular anions (MA) CrO42-. MoO42-, ReO4- in the halide-cesium crystals (CsHal) CsCl, CsBr, CsI have been studied in the temperature range of 4.2 K to 300 K. Impure MA in crystals CsHal is characterized by complicated structure of the infrared absorption and Raman spectra. The structure of the spectra is due to the splitting of the degenerate vibration ?2(E), ?3(F2), ?4(F2) of the impure MA as a result of the decreasing of their local symmetry from Td to C3v, C2v or Cs because of the formation of the complexes of the several types. Such molecular complexes are formed with anion or cation vacancies or with metal cations Me+(Na+, K+, Rb+, Tl+) and Me2+(Mg2+, Ca2+, Sr2+, Ba2+) which have been doped to the crystals for the charge compensation of the impure MA. Observed structure of the vibrational spectra has been identified by the calculation of the MA vibration, decreased the local symmetry in the formed complexes and by the computer optimisation of the theoretical and observed data of the vibrational frequency of MA in crystals. Luminescence of the crystals CsHal with the impure MA CrO42-, MoO4-, ReO4- can be observed only at low temperature. Impure complexes with different structure and symmetry which are formed by the same tetrahedral MA are characterized by different value of the electron-phonon interaction that may be seen in the structure of the absorption, PL and PLE spectra or in the character of the temperature dependence of the emission quantum yield. The parameters of spin orbit and spin lattice interactions in the impure complexes has been received. (author)

  16. Preparation and Single-Crystal X-Ray Structures of Four Related Mixed-Ligand 4-Methylpyridine Indium Halide Complexes

    Science.gov (United States)

    Hepp, Aloysius F.; Clark, Eric B.; Schupp, John D.; Williams, Jennifer N.; Duraj, Stan A.; Fanwick, Philip E.

    2013-01-01

    We describe the structures of four related indium complexes obtained during synthesis of solid-state materials precursors. Indium adducts of halides and 4-methylpyridine, InX3(pic)3 (X = Cl, Br; pic = 4-methylpyridine) consist of octahedral molecules with meridional (mer) geometry. Crystals of mer-InCl3(pic)3 (1) are triclinic, space group P1(bar) (No. 2), with a = 9.3240(3), b = 13.9580(6), c = 16.7268 (7) A, alpha = 84.323(2), beta = 80.938(2), gamma = 78.274(3)Z = 4, R = 0.035 for 8820 unique reflections. Crystals of mer-InBr3(pic)3 (2) are monoclinic, space group P21/n (No. 14), with a = 15.010(2), b = 19.938(2), c = 16.593(3), beta = 116.44(1)Z = 8, R = 0.053 for 4174 unique reflections. The synthesis and structures of related compounds with phenylsulfide (chloride) (3) and a dimeric complex with bridging hydroxide (bromide) (4) coordination is also described. Crystals of trans-In(SC6H5)Cl2(pic)3 (3) are monoclinic, space group P21/n (No. 14), with a = 9.5265(2), b = 17.8729(6), c = 13.8296(4), beta = 99.7640(15)Z = 4, R = 0.048 for 5511 unique reflections. Crystals of [In(mu-OH)Br2(pic)22 (4) are tetragonal, space group = I41cd (No. 110) with a = 19.8560(4), b = 19.8560(4), c = 25.9528(6), Z = 8, R = 0.039 for 5982 unique reflections.

  17. Radiation-induced aggregation of Frenkel defects in binary ionic crystals with isoelectronic impurities

    International Nuclear Information System (INIS)

    In the work possibility for receiving of fractal distribution of nano-dimensional defects concentration in alkali-halide crystal is obtained. Experimental data for crystals KBr-Li and KBr-Na with different concentration in wide temperature range (4.2-300 K) irradiation are obtained

  18. Retrograde solubility of formamidinium and methylammonium lead halide perovskites enabling rapid single crystal growth

    KAUST Repository

    Saidaminov, Makhsud I.

    2015-10-20

    Here we show the retrograde solubility of various hybrid perovskites through the correct choice of solvent(s) and report their solubility curves. Retrograde solubility enables to develop inverse temperature crystallization of FAPbX3 (FA = HC(NH2)2+, X = Br−/I−). FAPbI3 crystals exhibit a 1.4 eV bandgap – considerably narrower than their polycrystalline counterparts.

  19. Role of the crystallization substrate on the photoluminescence properties of organolead mixed halides perovskites

    OpenAIRE

    Michele Bastiani; Valerio D’Innocenzo; Samuel D. Stranks; Henry J. Snaith; Annamaria Petrozza

    2014-01-01

    We have fabricated CH3NH3PbI3-xCl x perovskite thin films crystallized in situ on substrates of different natures (e.g., porosity, wettability) and investigated their photoluminescence properties. We observe that the crystallization time and thin film structure are strongly influenced by the chemical nature and porosity of the substrate. Moreover, we find that the mesoporous scaffold can tune the emissive properties of the semiconducting compound both in terms of spectral region and dynamics....

  20. Retrograde solubility of formamidinium and methylammonium lead halide perovskites enabling rapid single crystal growth.

    Science.gov (United States)

    Saidaminov, Makhsud I; Abdelhady, Ahmed L; Maculan, Giacomo; Bakr, Osman M

    2015-12-01

    Here we show the retrograde solubility of various hybrid perovskites through the correct choice of solvent(s) and report their solubility curves. Retrograde solubility enables to develop inverse temperature crystallization of FAPbX3 (FA = HC(NH2)2(+), X = Br(-)/I(-)). FAPbI3 crystals exhibit a 1.4 eV bandgap - considerably narrower than their polycrystalline counterparts. PMID:26511771

  1. Photoluminescence and EPR studies on gamma irradiated Ce3+ doped potassium halide single crystals

    International Nuclear Information System (INIS)

    Electron Paramagnetic Resonance(EPR), Photoluminescence(PL), Thermoluminescence (TL) and other optical studies of ?-irradiated KBr, KCl:Ce3+ single crystals. Cerium when doped into the KBr, KCl is found to enter the host lattice in its trivalent state and act as electron trap during ?-irradiation, thereby partially converting itself to Ce2+. The Photoluminescence(PL) spectra of both KCl and KBr crystals doped with Ce exhibit the strong blue emissions of Ce corresponding to 5d(2D)?2F5/2 and 5d(2D)?2F7/2 transitions. The defect centers formed in the Ce3+ doped KBr and KCl. Crystals are studied using the technique of EPR. A dominant TL glow peak at 374, 422 K and KCl:Ce3+ at 466, 475 K is observed in the crystal. EPR studies indicate the presence at two centers at room temperature. Spectral distribution under the thermoluminescence emission(TLE) and optically stimulated emission(OSL) support the idea that defect annihilation process to be due to thermal release of F electron in KBr, KCl:Ce3+ crystals. Both Ce3+ and Ce2+ emissions were observed in the thermoluminescence emission of the crystals.

  2. Structural morphology of analbite: the influence of the substitution of K by Na on the crystal morphology of alkali feldspars

    International Nuclear Information System (INIS)

    The habit of the theoretical growth form of monoclinic high sanidine (KAlSi3O8) calculated from the attachment energies in an electrostatic point charge model is most similar to that of the alpine vein potassium feldspar called adularia. The effect on the crystal growth of alkali feldspar due to the substitution of K by Na has been investigated by the calculation of the attachment energies of analbite (NaAlSi3O8), which is triclinic with a disordered Si/Al distribution. The theoretical growth form of analbite consists of {110}, {1anti 10}, {001}, {010} and, as additional minor forms, {021} and {0anti 21}. Hence other habits than the Adularia type cannot be explained by the crystal structure of disordered alkali feldspars. Either ordering of Si and Al during the growth or external factors, such as impurities or supersaturation, must be examined as possible habit modifiers. They must be responsible for the platy Finisterre, the elongated Baveno or the thick prismatic Carlsbad habit of many alkali feldspar crystals

  3. The radiation defect accumulation in scintillative crystals of caesium halides under intense electron beam irradiation

    CERN Document Server

    Galiy, P V

    1999-01-01

    The characteristics of defect accumulation and radiolysis at CsI crystals under mean energies of electron irradiation at wide dose rates and ranges of doses have been investigated by such methods: thermostimulated exoelectron emission (TSEE), Auger electron spectroscopy (AES) and optical absorption spectroscopy (OAS). The limit dose rates and absorbed doses of electron irradiation that lead to defects accumulation at room temperature in crystals volume and also surface stoichiometry violation have been evaluated. The doses of electron irradiation that lead to CsI radiolysis, with caesium coagulation in metallic phase have been determined. Some quasi periodic connection of such process with irradiation dose was observed.

  4. Crystallization and halide phasing of the C-terminal domain of human KIN17

    International Nuclear Information System (INIS)

    Expression, purification, crystallization and phasing procedure are reported for the C-terminal domain of human KIN17. Here, the crystallization and initial phasing of the C-terminal domain of human KIN17, a 45 kDa protein mainly expressed in response to ionizing radiation and overexpressed in certain tumour cell lines, are reported. Crystals diffracting to 1.4 Å resolution were obtained from 10% ethylene glycol, 27% PEG 6000, 500 mM LiCl and 100 mM sodium acetate pH 6.3 in space group P212121, with unit-cell parameters a = 45.75, b = 46.31, c = 60.80 Å and one molecule in the asymmetric unit. Since this domain has a basic pI, heavy-atom derivatives were obtained by soaking the crystals with negatively charged ions such as tungstate and iodine. The replacement of LiCl by KI in the cryosolution allowed the determination of phases from iodide ions to give an interpretable electron-density map

  5. Systematic hardness measurements on single crystals and polycrystalline blanks of cesium halides

    Indian Academy of Sciences (India)

    D B Sirdeshmukh; P Geeta Krishna; K G Subhadra

    2002-06-01

    Vickers and knoop hardness measurements were carried out on CsBr and CsI single crystals. Polycrystalline blanks of CsCl, CsBr and CsI were prepared by melting and characterized by X-ray diffraction. Vickers hardness measurements were carried out on these blanks. The hardness values were correlated with the lattice constant and the Schottky defect formation energy.

  6. Characterization of an Alkali- and Halide-Resistant Laccase Expressed in E. coli: CotA from Bacillus clausii

    DEFF Research Database (Denmark)

    Brander, Søren; Mikkelsen, Jørn Dalgaard; Kepp, Kasper Planeta

    2014-01-01

    . subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine......H, but not up to 500–700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ,20 minutes half-life at 80uC, less than the ,50 minutes at 80uC for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH,8, the cotA from B...

  7. Ionic conductivity in gem-quality single-crystal alkali feldspar from the Eifel: temperature, orientation and composition dependence

    Science.gov (United States)

    El Maanaoui, Hamid; Wilangowski, Fabian; Maheshwari, Aditya; Wiemhöfer, Hans-Dieter; Abart, Rainer; Stolwijk, Nicolaas A.

    2016-01-01

    We measured the ion conductivity of single-crystal alkali feldspar originating from two different locations in the Eifel/Germany, named Volkesfeld and Rockeskyller sanidine and having potassium site fractions C_K of 0.83 and 0.71, respectively. The dc conductivities resulting from electrochemical impedance spectroscopy over the temperature range of 300-900° C show a weak composition dependence but pronounced differences between the b-direction [perp (010) ] and c^{*} -direction [perp (001) ] of the monoclinic feldspar structure. Conductivity activation energies obtained from the observed linear Arrhenius plots are close to 1.2 eV in all cases, which is closely similar to the activation energies of the ^{22}Na tracer diffusivity in the same crystals. Taking into account literature data on K tracer diffusion and diffusion correlation effects, the present results point to a predominance of the interstitialcy mechanism over the vacancy mechanism in mass and charge transport on the alkali sublattice in potassium-rich alkali feldspar.

  8. Alkali Metal Ion Templated Transition Metal Formate Framework Materials : Synthesis, Crystal Structures, Ion Migration, and Magnetism

    DEFF Research Database (Denmark)

    Eikeland, Espen; Lock, Nina

    2014-01-01

    Four transition metal formate coordination polymers with anionic frameworks, namely, Na[Mn(HCOO)(3)], K[Mn(HCOO)(3)], Na-2[Cu-3(HCOO)(8)], and K-2[Cu-5(HCOO)(12)], were synthesized using a mild solution chemistry approach. Multitemperature single-crystal (100-300 K) and powder Xray diffraction studies of the compounds reveal structures of large diversity ranging from cubic chiral Na-Mn formate to triclinic Na-Cu formate. The structural variety is caused by the nature of the transition metals, the alkali metal ion templation, and the versatility of the formate group, which offers metal metal coordination through three different O-C-O bridging modes (syn-syn, syn-anti, anti-anti) in addition to metal metal bridging via a single oxygen atom. The two manganese(II) compounds contain mononuclear, octahedrally coordinated moieties, but the three-dimensional connectivity between the manganese octahedra is very different in the two structures. The two copper frameworks, in contrast, consist of binuclear and mononuclear moieties (Na-Cu formate) and trinuclear and mononuclear moieties (K-Cu formate), respectively. Procrystal electron density analysis of the compounds indicates one-dimensional K+-ion conductivity in K-Mn and K-Cu, and the nature of the proposed potassium ion migration is compared with results from similar analysis on known Na+ and K+ ion conductors. K-Mn and Na-Mn were tested as cathode materials, but this resulted in poor reversibility due to low conductivity or structural collapse. The magnetic properties of the compounds were studied by vibrating sample magnetometric measurements, and their thermal stabilities were determined by thermogravimetric analysis and differential thermal analysis. Despite structural differences, the metal formates that contain the same transition metal have similar magnetic properties and thermal decomposition pathways, that is, the nature of the transition metal controls the compound properties.

  9. Alkali-ions diffusion, mullite formation, and crystals dissolution during sintering of porcelain bodies: Microstructural approach

    DEFF Research Database (Denmark)

    Leonelli, C.; Kamseu, E.; Boccaccini, Dino; Sglavo, V.M.; Pellacani, G.C.

    2009-01-01

    composition (amount of alkali and alumina) between the two types of porcelain studied influenced the final microstructure: density, pore size and shape, and mullite content. Quartz dissolution was more important in soft porcelain where the mullitization was limited by the low amount of alumina compared to...... hard porcelain. Replacing the feldspar by alkali-silicate glassy matrices with similar chemical composition, the amount of secondary mullite and mechanical properties increased in both soft and hard compositions....

  10. Characterization of an Alkali- and Halide-Resistant Laccase Expressed in E. coli: CotA from Bacillus clausii

    DEFF Research Database (Denmark)

    Brander, SØren; Mikkelsen, JØrn Dalgaard

    2014-01-01

    The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ,0.5–2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s21 at pH 6 and 5 s21 at pH 8 in contrast to 6 s21 at pH 6 and 2 s21 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher forB. subtilis cotA at pHopt. While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500–700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ,20 minutes half-life at 80uC, less than the ,50 minutes at 80uC for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH,8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization.

  11. Nonmetal-metal transition in molten potassium-potassium halide solutions

    International Nuclear Information System (INIS)

    It is suggested, in the light of the available experimental evidence, that the nonmetal-to-metal transition in solutions of potassium in molten potassium halides may be viewed as a volume-percolation transition. The critical concentration is estimated and differences between alkali-alkali halide and metal-ammonia solutions are discussed. (author)

  12. Metal halide reduction with molten sodium/potassium alloy

    International Nuclear Information System (INIS)

    A method of obtaining a desired metal, selected from the group consisting of titanium, aluminium, iron, manganese, hafnium, zirconium, tantalum, vanadium, uranium and tungsten, which comprises reacting a halide of the desired metal with an alkali metal reducing agent at temperature at which the reducing agent is molten, in order to produce the desired metal and halide of the metal reducing agent

  13. Theory of Distinct Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs the Specific Role of Alkalis

    CERN Document Server

    Michel, K H

    2000-01-01

    The polymer phases of AC60 form distinct crystal structures characterized by the mutual orientations of the (C60-)n chains. We show that the direct electric quadrupole interaction between chains always favors the orthorhombic structure Pmnn with alternating chain orientations. However the specific quadrupolar polarizability of the alkali metal ions leads to an indirect interchain coupling which favors the monoclinic structure I2/m with equal chain orientations. The competition between direct and indirect interactions explains the structural difference between KC60 and RbC60, CsC60.

  14. Crystal structures of five 1-alkyl-4-aryl-1,2,4-triazol-1-ium halide salts

    OpenAIRE

    Guino-o, Marites A.; Talbot, Meghan O.; Slitts, Michael M.; Pham, Theresa N.; Audi, Maya C.; Daron E. Janzen

    2015-01-01

    To investigate the predominant inter­molecular inter­actions in 1-alkyl-4-aryl-1,2,4-triazol-1-ium halide salts, five salts were prepared and crystallographically characterized. The halide ions generally inter­act with the H atoms of the triazolium cation forming extended sheets. When the aryl ring lies on the plane of the triazolium cation, the cationic core formed two-dimensional networks that lead into layer-like assembled structures. The triazolium core exhibits ?–? inter­actions with the...

  15. Complexing in binary molten halide systems with a common anion, containing sodium halides

    International Nuclear Information System (INIS)

    Analysis of meltability diagrams of binary halide systems with a common anion published in literature permitted studying the interaction in sodium halide melts NaX (X = F-I) and halides of alkali, alkaline-earth, transition and rare earth elements, as well as uranium and thorium. It was ascertained that in most systems enhancement of polarizing effect of cation in the melt involves intensification of complexing. Transition from ideal to non-ideal eutectic systems and further to systems with incongruently and congruently melting compounds was pointed out, as well

  16. Differential calorimeter and temperature controller for stored energy measurements in irradiated alkali halides; Calorimetro diferencial y controlador de temperatura para medidas de energia almacenada en haluros alcalinos irradiados

    Energy Technology Data Exchange (ETDEWEB)

    Delgado Martinez, L.

    1977-07-01

    The design and performance of a simple temperature-controlled differential calorimeter are presented. This system allows to measure radiation-induced stored energy in insulators, above room temperature with a differential thermal analysis method. With platelets of KC1 single crystals, the base lines obtained for T{sub 2} T{sub 1} (with T{sub 2}: irradiated sample temperature and T{sub 1}: reference sample temperature) show a smooth drift less of 0,2 degree centigree in the interval from 25 to 400 degree centigree. The discrepancy between two consecutive base lines is less than {+-} 0,02 degree centigree which implies a calorimeter sensitivity of about {+-}0,004 cal/g. This sensitivity allows to measure stored energy release in samples with a color center concentration low enough to be directly measured with a spectrophotometer so that a search for correlations among the features of the stored energy spectrum and the color center annealing can be made. (Author) 13 refs.

  17. Stability diagrams for fourfold coordination of polyvalent metal ions in molten mixtures of halide salts

    International Nuclear Information System (INIS)

    The stability of local fourfold coordination for divalent and trivalent metal ions in liquid mixtures of polyvalent metal halides and alkali halides is classified by means of structural coordinates obtained from properties of the elements. In parallel with earlier classifications of compound crystal structures and molecular shapes, the elemental properties are taken from first-principles calculations of valence electron orbitals in atoms, in the form of (i) the nodal radii of Andreoni, Baldereschi and Guizzetti or (ii) the pseudopotential radii or Zunger and Cohen. As a third alternative a classification based on Pettifor's phenomenological chemical scale of the elements is also considered. The alternative structural classification schemes that are developed from these elemental properties are generally successfully in distinguishing molten mixtures in which the available experimental evidence indicates long-lived fourfold coordination of polyvalent metal ions. In addition, Pettifor's chemical scale scheme is useful in sorting out finer details of local coordination in the liquid state. 3 figs., 71 refs

  18. Crystal Dynamics from Neutron Spectrometry

    International Nuclear Information System (INIS)

    This paper reviews investigations carried out at Chalk River on the lattice dynamics of various crystals including lead, sodium, alkali halides, semi-conductors, and other more complex compounds. Analysis of the low temperature results (-?100oK) gives considerable insight into the nature of the interatomic forces. In sodium, a simple metal, the interatomic forces are very nearly derivable from a potential. Lead, a more complicated metal, has extremely long range forces accompanied by strong electronic effects. At higher temperatures anharmonic effects are very pronounced in both metals, especially in lead. The alkali halide results can be interpreted on a ''shell'' model, with polarizable ions. Even at low temperature neutron groups corresponding to the longitudinal optical modes. (author)

  19. Synthesis, characterization and computational studies of zinc(ii)-halide complexes with a bidentate Schiff base ligand (2,5-MeO-ba)2En: the crystal structure of (2,5-MeO-ba)2En.

    Czech Academy of Sciences Publication Activity Database

    Khalaji, A.D.; Mighani, H.; Gholinejad, M.; Grivani, G.; Jalali Akerdi, S.; Fejfarová, Karla; Dušek, Michal

    2013-01-01

    Ro?. 54, ?. 4 (2013), s. 766-773. ISSN 0022-4766 Institutional research plan: CEZ:AV0Z10100521 Keywords : zinc(II) halides * Schiff base * crystal structure * density functional theory Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.501, year: 2013

  20. Thermally stimulated luminescence and lattice defects in crystals of alkali metal borate LiB3O5 (LBO)

    International Nuclear Information System (INIS)

    The recombination processes and lattice defects in crystals of alkali metal borate LiB3O5 (LBO) were studied by the means of the thermally stimulated luminescence (TL) and electron spin resonance (ESR) techniques. The glow curves, the spectra of the LBO recombination luminescence, and the angular variations of ESR-spectra of the O- center in three different planes were measured in the temperature range from 80 to 400 K. The luminescence bands were assigned to the electron (Em=4.0 eV) and hole (Em=4.2 eV) recombination processes. The model of the trapped hole center O- was proposed. The processes responsible for the formation of localised electronic excitations in LBO were discussed and compared with those taking place in other wide-gap oxides

  1. Crystal structures of five 1-alkyl-4-aryl-1,2,4-triazol-1-ium halide salts.

    Science.gov (United States)

    Guino-O, Marites A; Talbot, Meghan O; Slitts, Michael M; Pham, Theresa N; Audi, Maya C; Janzen, Daron E

    2015-06-01

    The asymmetric units for the salts 4-(4-fluoro-phen-yl)-1-isopropyl-1,2,4-triazol-1-ium iodide, C11H13FN3 (+)·I(-), (1), 1-isopropyl-4-(4-methyl-phen-yl)-1,2,4-triazol-1-ium iodide, C12H16N3 (+)·I(-), (2), 1-isopropyl-4-phenyl-1,2,4-triazol-1-ium iodide, C11H14N3 (+)·I(-), (3), and 1-methyl-4-phenyl-1,2,4-triazol-1-ium iodide, C9H10N3 (+)·I(-), (4), contain one cation and one iodide ion, whereas in 1-benzyl-4-phenyl-1,2,4-triazol-1-ium bromide monohydrate, C15H14N3 (+)·Br(-)·H2O, (5), there is an additional single water mol-ecule. There is a predominant C-H?X(halide) inter-action for all salts, resulting in a two-dimensional extended sheet network between the triazolium cation and the halide ions. For salts with para-substitution on the aryl ring, there is an additional ?-anion inter-action between a triazolium carbon and iodide displayed by the layers. For salts without the para-substitution on the aryl ring, the ?-? inter-actions are between the triazolium and aryl rings. The melting points of these salts agree with the predicted substituent inductive effects. PMID:26090137

  2. Crystal structures of five 1-alkyl-4-aryl-1,2,4-triazol-1-ium halide salts

    Directory of Open Access Journals (Sweden)

    Marites A. Guino-o

    2015-06-01

    Full Text Available The asymmetric units for the salts 4-(4-fluorophenyl-1-isopropyl-1,2,4-triazol-1-ium iodide, C11H13FN3+·I?, (1, 1-isopropyl-4-(4-methylphenyl-1,2,4-triazol-1-ium iodide, C12H16N3+·I?, (2, 1-isopropyl-4-phenyl-1,2,4-triazol-1-ium iodide, C11H14N3+·I?, (3, and 1-methyl-4-phenyl-1,2,4-triazol-1-ium iodide, C9H10N3+·I?, (4, contain one cation and one iodide ion, whereas in 1-benzyl-4-phenyl-1,2,4-triazol-1-ium bromide monohydrate, C15H14N3+·Br?·H2O, (5, there is an additional single water molecule. There is a predominant C—H...X(halide interaction for all salts, resulting in a two-dimensional extended sheet network between the triazolium cation and the halide ions. For salts with para-substitution on the aryl ring, there is an additional ?–anion interaction between a triazolium carbon and iodide displayed by the layers. For salts without the para-substitution on the aryl ring, the ?–? interactions are between the triazolium and aryl rings. The melting points of these salts agree with the predicted substituent inductive effects.

  3. Dynamics of defects in x-ray irradiated alkali chloride crystals studied by positron annihilation

    International Nuclear Information System (INIS)

    Data on the time dependence of positron-electron annihilation characteristics in single crystals of the homologous series NaCl, KCl, RbCl, and CsCl after large doses of x irradiation are reported. A new instrument, the ?-radian coincidence apparatus (PICA), recorded the coincidence count rate P of the two 0.5-MeV annihilation #betta# rays emerging 1800 apart from the crystal during isothermal and isochronal heating conditions. In most crystals an initial rapid increase of P to a maximum followed by a slow decline toward the coincidence count rate corresponding to the pre-irradiation state of the crystal was observed. Positron-annihilation data were completed by independent measurements of the optical absorption in KCl and NaCl crystals after various durations of isothermal heating. Absorption spectrophotometry revealed enhancement of the M band in KCl, of the R and N bands in NaCl, at the expense of the F band during the interpretation that positrons are trapped by radiation-induced color centers in which they annihilate with a higher P than in the bulk of the crystal. The dynamics associated with the incipient rise of P during the initial heating period is attributable to the agglomeration of F centers into aggregate centers. The rise times of P give access to the diffusion rates for agglomeration. At equal temperatures, a strong dependence of the rate of defect diffusion on the size of the cation was observed. The data must be corrected for the effects of decoloration of the crystals by the positrons during the measurements. Activation energies for defect diffusion annealing are extracted

  4. Dynamics of Defects in X-Ray Irradiated Alkali Chloride Crystals Studied by Positron Annihilation.

    Science.gov (United States)

    Stern, Stanley Hy.

    This thesis reports first data on the time dependence of positron-electron annihilation characteristics in single crystals of the homologous series NaCl, KCl, RbCl, and CsCl after large doses of x irradiation. A new instrument, the (pi)-radian coincidence apparatus (PICA), recorded the coincidence count rate P of the two 0.5-MeV annihilation (gamma) rays emerging 180(DEGREES) apart from the crystal during isothermal and isochronal heating conditions. In most crystals one observes an initial rapid increase of P to a maximum followed by a slow decline toward the coincidence count rate corresponding to the pre-irradiation state of the crystal. Positron-annihilation data were completed by independent measurements of the optical absorption in KCl and NaCl crystals after various durations of isothermal heating. Absorption spectrophotometry revealed enhancement of the M band in KCl, of the R and N bands in NaCl, at the expense of the F band during the interval of increasing P. The PICA results are consistent with the interpretation that positrons are trapped by radiation-induced color centers in which they annihilate with a higher P than in the bulk of the crystal. The dynamics associated with the incipient rise of P during the initial heating period is attributable to the agglomeration of F centers into aggregate centers. The rise times of P give access to the diffusion rates for agglomeration. At equal temperatures, we observe a strong dependence of the rate of defect diffusion on the size of the cation. For example, it is 100 times faster in CsCl than in NaCl at 120(DEGREES)C. The data must be corrected for the effects of decoloration of the crystals by the positrons during the measurements. Activation energies for defect diffusion annealing are extracted. They test the hypotheses underlying the theories of macroscopic transport properties in these crystals in that they are indicative of the dominant microscopic lattice processes and their dependence on the crystal composition.

  5. Dislocations in SmS single crystals

    International Nuclear Information System (INIS)

    Single crystals of SmS with NaCl structure are grown by zone melting in a sealed molybdenum tube. Dislocations introduced during cleaving the crystal are investigated by transmission electron microscopy. The dislocations have Burgers vector of 1/2 and their glide plane is (11-bar0), i.e. the slip system is (11-bar0) as in alkali-halide NaCl-type crystals. The slip seems to be governed by the Peierls mechanism for the screw dislocation. (author)

  6. Synthesis and crystal structure of alkali metal diamido dioxosilicates M2SiO2(NH2)2 with M corresponds to K, Rb and Cs

    International Nuclear Information System (INIS)

    SiO2 - ?-quartz - reacts with alkali metal amides MNH2 (M corresponds to K, Rb, and Cs) in molar ratios from 1:2 to 1:10 at 450 C ? T ? 600 C and P(NH3) = 6 kbar in autoclaves to diamidodioxosilicates M[SiO2(NH2)2]. Crystals of the colourless compounds which hydrolyze rapidly were investigated by X-ray methods. (orig.)

  7. Dislocation Dynamics in a Crystal Lattice (Peierls-Nabarro) Relief

    OpenAIRE

    Petukhov, B. V.

    2007-01-01

    The theory of the dislocation motion in the periodic potential relief of the crystal lattice (the Peierls-Nabarro barriers) is reviewed. On the basis of the kink mechanism the temperature dependence of the flow stress is described for a wide class of materials. The theory of quantum mechanical dislocation tunnelling through the Peierls-Nabarro barriers is extended and compared with experimental data on the plasticity of alkali halides, BCC and HCP metals at low temperatures. The behavior of t...

  8. Radiation-induced processes and defects in alkali and alkaline-earth borate crystals

    International Nuclear Information System (INIS)

    The paper presents the results of a study of the radiation-induced processes and defects in nonlinear optical crystals Li2B4O7 (LTB), LiB3O5 (LBO), CsLiB6O10, KB5O8·4H2O, ?-BaB2O4. It was revealed that a pulsed electron beam irradiation at 290 K forms the radiation-induced pairs of the 'vacancy--interstitial atom' defects in the cation sublattice of these crystals. This gives rise to a creation of metastable electronic (interstitial atom) and hole (small-radius polaron near the cation vacancy) centers in high concentrations. Optical hole-transitions from the local level of the trapped hole centers to the valence band states are responsible for the transient optical absorptions (TOA) of borates in the visible and UV spectral ranges. A sublattice of the weakly bound mobile lithium cations in LTB and LBO favors a spatial separation of the radiation-induced pair defects 'hole polaron near Li-vacancy--mobile interstitial Li0 atom'. Their decay rated by the electron-hole nonradiative tunnel recombination determines a peculiar feature of the TOA decay kinetics in LTB and LBO

  9. Nitrate (chloride) melts as media for crystal growth of complex phosphates of alkali and trivalent metals

    Science.gov (United States)

    Livitska, Oksana; Strutynska, Nataliia; Zatovsky, Igor; Slobodyanik, Nikolai; Odinets, Eugen

    2016-01-01

    The interaction in the molten systems MIPO3-MIII2O3-MINO3 (MICl) (MI - Na, K; MIII - Al, Fe, Y, Bi) was investigated at molar ratios P/MIII=1 or 3 at the temperatures 400 °C (for MINO3) or 810 °C (for MICl). Formation conditions of complex phosphates MI3MIII2(PO4)3 and MI3MIII(PO4)2 (MI - Na, K; MIII - Al, Fe, Bi) were established. It was shown that the crystal size of obtained phosphates can be controlled by using different salt melts. The synthesized compounds were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, Optical microscopy and Scanning electron microscopy with Energy-dispersive X-ray spectroscopy. Differential thermal data for Na3Bi(PO4)2 and Na3Fe(PO4)2 showed congruent and incongruent melting, respectively.

  10. Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs and Alkali-mediated Interactions

    CERN Document Server

    Verberck, B; Nikolaev, A V

    2002-01-01

    Starting from a model of rigid interacting C60 polymer chains on an orthorhombic lattice, we study the mutual orientation of the chains and the stability of the crystalline structures Pmnn and I2/m. We take into account i) van der Waals interactions and electric quadrupole interactions between C60 monomers on different chains as well as ii) interactions of the monomers with the surrounding alkali atoms. The direct interactions i) always lead to an antiferrorotational structure Pmnn with alternate orientation of the C60 chains in planes (001). The interactions ii) with the alkalis consist of two parts: translation-rotation (TR) coupling where the orientations of the chains interact with displacements of the alkalis, and quadrupolar electronic polarizability (ep) coupling, where the electric quadrupoles on the C60 monomers interact with induced quadrupoles due to excited electronic d states of the alkalis. Both interactions ii) lead to an effective orientation-orientation interaction between the C60 chains and ...

  11. Thermoluminescence studies of gamma irradiated mixed crystals

    International Nuclear Information System (INIS)

    In the present work we have grown (KCl)x(KI)y-x(KBr)x-y ternary alkali halide crystals with MgCl2 dopant for various values of x and y by the melt method and physically characterized. We have studied the thermoluminescence (TL) spectra of ?-irradiated KCl-KI-KBr ternary mixed crystals containing MgCl2 as the dopant. Two peaks were detected for the low heating rate and one for the high heating rate. The chief cause of the differences between the parameters of the TL peaks is the difference between the topography of distribution of the F and FH pairs. (author)

  12. He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth

    International Nuclear Information System (INIS)

    Investigations in this laboratory have focused on the surface structure and dynamics of ionic insulators and on epitaxial growth onto alkali halide crystals. In the later the homoepitaxial growth of NaCl/NaCl(001) and the heteroepitaxial growth of KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been studied by monitoring the specular He scattering as a function of the coverage and by measuring the angular and energy distributions of the scattered He atoms. These data provide information on the surface structure, defect densities, island sizes and surface strain during the layer-by-layer growth. The temperature dependence of these measurements also provides information on the mobilities of the admolecules. He atom scattering is unique among surface probes because the low-energy, inert atoms are sensitive only to the electronic structure of the topmost surface layer and are equally applicable to all crystalline materials. It is proposed for the next year to exploit further the variety of combinations possible with the alkali halides in order to carry out a definitive study of epitaxial growth in the ionic insulators. The work completed so far, including measurements of the Bragg diffraction and surface dispersion at various stages of growth, appears to be exceptionally rich in detail, which is particularly promising for theoretical modeling. In addition, because epitaxial growth conditions over a wide range of lattice mismatches is possible with these materials, size effects in growth processes can be explored in great depth. Further, as some of the alkali halides have the CsCl structure instead of the NaCl structure, we can investigate the effects of the heteroepitaxy with materials having different lattice preferences. Finally, by using co-deposition of different alkali halides, one can investigate the formation and stability of alloys and even alkali halide superlattices

  13. Halide Adsorption on Single-crystal Silver Substrates: Dynamic Simulations and ab-initio Density-functional Theory

    OpenAIRE

    Mitchell, S. J.; Wang, Sanwu; Rikvold, P. A.

    2001-01-01

    We investigate the static and dynamic behaviors of a Br adlayer electrochemically deposited onto single-crystal Ag(100) using an off-lattice model of the adlayer. Unlike previous studies using a lattice-gas model, the off-lattice model allows adparticles to be located at any position within a two-dimensional approximation to the substrate. Interactions with the substrate are approximated by a corrugation potential. Using Density Functional Theory (DFT) to calculate surface b...

  14. Metal-halide mixtures for latent heat energy storage

    Science.gov (United States)

    Chen, K.; Manvi, R.

    1981-01-01

    Alkali metal and alkali halide mixtures are identified which may be suitable for thermal energy storage at temperatures above 600 C. The use of metal-halides is appropriate because of their tendency to form two immiscible melts with a density difference, which reduces scale formation and solidification on heat transfer surfaces. Also, the accumulation of phase change material along the melt interface is avoided by the self-dispersing characteristic of some metal-halides, in particular Sr-SrCl2, Ba-BaCl2, and Ba-BaBr2 mixtures. Further advantages lie in their high thermal conductivities, ability to cope with thermal shock, corrosion inhibition, and possibly higher energy densities.

  15. Crystallization and preliminary X-ray study of a family 10 alkali-thermostable xylanase from alkalophilic Bacillus sp. strain NG-27

    International Nuclear Information System (INIS)

    A family 10 alkali-thermostable xylanase from Bacillus sp. NG-27 has been crystallized. A diffraction data set has been collected to 2.2 Å resolution. Xylanases (EC 3.2.1.8) catalyze the hydrolysis of ?-1,4-glycosidic linkages within xylan, a major hemicellulose component in the biosphere. The extracellular endoxylanase (XylnA) from the alkalophilic Bacillus sp. strain NG-27 belongs to family 10 of the glycoside hydrolases. It is active at 343 K and pH 8.4. Moreover, it has attractive features from the point of view of utilization in the paper pulp, animal feed and baking industries since it is an alkali-thermostable protein. In this study, XylnA was purified from the native host source and crystallized by the hanging-drop vapour-diffusion method. The crystals belong to the monoclinic space group C2, with unit-cell parameters a = 174.5, b = 54.7, c = 131.5 Å, ? = 131.2°, and diffract to better than 2.2 Å resolution

  16. Halide Adsorption on Single-crystal Silver Substrates Dynamic Simulations and ab-initio Density-functional Theory

    CERN Document Server

    Mitchell, S J; Rikvold, P A; Wang, Sanwu

    2002-01-01

    We investigate the static and dynamic behaviors of a Br adlayer electrochemically deposited onto single-crystal Ag(100) using an off-lattice model of the adlayer. Unlike previous studies using a lattice-gas model, the off-lattice model allows adparticles to be located at any position within a two-dimensional approximation to the substrate. Interactions with the substrate are approximated by a corrugation potential. Using Density Functional Theory (DFT) to calculate surface binding energies, a sinusoidal approximation to the corrugation potential is constructed. A variety of techniques, including Monte Carlo and Langevin simulations, are used to study the behavior of the adlayer. The lateral root-mean-square (rms) deviation of the adparticles from the binding sites is presented along with equilibrium coverage isotherms, and the thermally activated Arrhenius barrier-hopping model used in previous dynamic Monte Carlo simulations is tested.

  17. Analysis of the physical atomic forces between noble gas atoms, alkali ions and halogen ions

    Science.gov (United States)

    Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

    1986-01-01

    The physical forces between atoms and molecules are important in a number of processes of practical importance, including line broadening in radiative processes, gas and crystal properties, adhesion, and thin films. The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base for the dispersion forces is developed from the literature based on evaluations with the harmonic oscillator dispersion model for higher order coefficients. The Zener model of the repulsive core is used in the context of the recent asymptotic wave functions of Handler and Smith; and an effective ionization potential within the Handler and Smith wave functions is defined to analyze the two body potential data of Waldman and Gordon, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

  18. NMR spectra of alkali and halogen nuclei in alkali and halogen salts

    International Nuclear Information System (INIS)

    NMR signals of 7Li, 23Na, 35Cl, 39K, 79Br, 87Rb and 127I have been measured in various alkali and halogen salt powders relative to well defined aqueous solutions. With the known shielding constants of some of these solutions the nuclear magnetic shielding constants of the alkali and values of the shielding constants in alkali halides do not agree even in the order of magnitude with the experimental ones in some cases. For 23Na first-order and second-order quadrupole patterns have been observed and the quadrupole coupling constants are given. (orig.) 891 WBU

  19. Persistent infrared spectral hole burning of NO - 2 ions in potassium halide crystals. I. Principle and satellite hole generation

    Science.gov (United States)

    Ambrose, W. P.; Sethna, J. P.; Sievers, A. J.

    1991-12-01

    New features are resolved within the internal vibrational mode spectra of NO-2 defects in KCl, KBr, and KI crystals at low temperatures using high-resolution Fourier transform spectroscopy and persistent infrared spectral hole (PIRSH) burning separately and together. With interferometry it has been discovered that the vibrational linewidths of the different modes range over a factor of 300—from 0.01 cm-1 to ˜3 cm-1 and, with PIRSH burning, it has been demonstrated that the narrowest lines are inhomogeneously broadened while the broadest ones are homogeneously broadened. PIRSH's have been found in some internal modes and combination bands of the NO-2 molecule when pumped with low-intensity single-mode lead salt diode lasers; however, detectable persistent holes are not produced in all of the modes because of a competition between hole production and relaxation by tunneling at low temperatures. This competition results in a hole burning intensity, below which hole relaxation overwhelms hole production and only small holes may be produced. The most unusually shaped absorption features are the V-shaped notches in the reorientational tunneling fine structure at the NO-2 bending mode frequency in KCl and KBr. Of all the internal modes that do show pronounced PIRSH burning, these V-notched absorption bands exhibit the most striking behavior. Multiple satellite PIRSH's are detected at frequencies away from the single-mode laser burn frequency with a broadband probe beam produced by a high-resolution Fourier transform interferometer. An explanation for these satellite holes is derived from temperature, plastic deformation, and uniaxial stress dependence measurements on the KCl: NO-2 absorption spectrum. We find that the inhomogeneous broadening of the KCl: NO-2 ?2 reorientational tunneling fine structure is dominated by degenerate rotor level splitting produced by random crystal strains. Degenerate perturbation theory of the rotor level splitting in the strain field is found to match very closely the V-shaped inhomogeneous distribution of levels associated with the KCl: NO-2 reorientational tunneling fine structure. The general conclusion is that whenever strain splitting of a doubly degenerate level dominates the inhomogeneous broadening, then the absorption spectrum displays zero strength in the distribution at zero splitting and a linear increase in absorption coefficient away from this frequency generating the observed V-shaped notch in the absorption profile.

  20. Molten alkali metal nitrate flux to well-crystallized and homogeneous La0.7Sr0.3MnO3 nanocrystallites

    International Nuclear Information System (INIS)

    Nanocrystalline La0.7Sr0.3MnO3 (LSO) has been synthesized by an alkali metal nitrate flux process at a relatively low temperature of 600 deg. C. Scanning electron and transmission electron microscopic images show that LSMO grains are of good crystallization and uniform size distribution. Inductively coupled plasma and elemental analyses indicate that the content of K+ is no more than 0.6% in all the samples and the stoichiometry of La, Sr and Mn is very close to the expected value. A significant enhanced magnetoresistance is observed in the nanosized LSMO especially at low temperatures. By improving grain crystallization, the surface spin-glass behavior disappears, and the blocking temperature corresponding to the super-paramagnetic transformation shifts to a higher temperature

  1. Alkali Metal/Salt Thermal-Energy-Storage Systems

    Science.gov (United States)

    Phillips, Wayne W.; Stearns, John W.

    1987-01-01

    Proposed thermal-energy-storage system based on mixture of alkali metal and one of its halide salts; metal and salt form slurry of two immiscible melts. Use of slurry expected to prevent incrustations of solidified salts on heat-transfer surfaces that occur where salts alone used. Since incrustations impede heat transfer, system performance improved. In system, charging heat-exchanger surface immersed in lower liquid, rich in halide-salt, phase-charge material. Discharging heat exchanger surface immersed in upper liquid, rich in alkali metal.

  2. Crystal preferred orientations of minerals from mantle xenoliths in alkali basaltic rocks form the Catalan Volcanic Zone (NE Spain)

    Science.gov (United States)

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2015-04-01

    Mantle xenoliths in alkali basaltic rocks from the Catalan Volcanic Zone, associated with the Neogene-Quaternary rift system in NE Spain, are formed of anhydrous spinel lherzolites and harzburgites with minor olivine websterites. Both peridotites are considered residues of variable degrees of partial melting, later affected by metasomatism, especially the harzburgites. These and the websterites display protogranular microstructures, whereas lherzolites show continuous variation between protogranular, porphyroclastic and equigranular forms. Thermometric data of new xenoliths indicate that protogranular harzburgites, lherzolites and websterites were equilibrated at higher temperatures than porphyroclastic and equigranular lherzolites. Mineral chemistry also indicates lower equilibrium pressure for porphyroclastic and equigranular lherzolites than for the protogranular ones. Crystal preferred orientations (CPOs) of olivine and pyroxenes from these new xenoliths were determined with the EBSD-SEM technique to identify the deformation stages affecting the lithospheric mantle in this zone and to assess the relationships between the deformation fabrics, processes and microstructures. Olivine CPOs in protogranular harzburgites, lherzolites and a pyroxenite display [010]-fiber patterns characterized by a strong point concentration of the [010] axis normal to the foliation and girdle distribution of [100] and [001] axes within the foliation plane. Olivine CPO symmetry in porphyroclastic and equigranular lherzolites varies continuously from [010]-fiber to orthorhombic and [100]-fiber types. The orthorhombic patterns are characterized by scattered maxima of the three axes, which are normal between them. The rare [100]-fiber patterns display strong point concentration of [100] axis, with normal girdle distribution of the other two axes, which are aligned with each other. The patterns of pyroxene CPOs are more dispersed than those of olivine, especially for clinopyroxene, but there is good correlation between the [100] olivine axis and the [001] pyroxene axis in most protogranular peridotites. However, the [001] axes of the three silicates are parallel in equigranular and some porphyroclastic lherzolites. CPOs and misorientation axes indicate deformation by dislocation creep accommodated mainly by the [100](010) slip system for olivine and the [001](100), [001](010) for orthopyroxene. Also, subsidiary slip systems for olivine are [100]{0kl}, [001](100), [100](001) in porphyroclastic and equigranular lherzolites. The fabric strength of the three main silicates are consistent, all of them decreasing with grain size reduction. These results indicate that the lithospheric mantle in this area was affected by several deformation stages that took place at decreasing temperature and pressure. An earlier stage is preserved in protogranular peridotites and a pyroxenite, with olivine [010]-fiber patterns and consistent deformation of pyroxenes. It could be related to axial shortening, transpression and/or subsequent recovery and annealing. Later deformation stages would be recorded by most porphyroclastic and equigranular lherzolites characterized by orthorhombic and [100]-fiber patterns for olivine, and transitions between them and with the [010]-fiber one. These samples would come most likely from an active shear zone at shallower upper mantle depth, where deformation at higher strain rates would explain the olivine [100]-fiber symmetry. Transient deformation patterns for olivine, grain size reduction along with weakening of the fabric strength could be due to dynamic recrystallization through grain boundary migration and subgrain rotation mechanisms.

  3. Theoretical and experimental study of the Stark effect in the ground state of alkali atoms in helium crystals

    OpenAIRE

    Ulzega, Simone; Weis, Antoine

    2007-01-01

    This thesis work describes a detailed study of the Stark interaction in the ground state of cesium atoms trapped in a solid helium matrix. The motivation for the investigation of electric field effects on alkali species implanted in solid helium is related to the original main goal of our experimental activities, i.e., the measurement of a permanent atomic electric dipole moment (EDM). The existence of an atomic EDM simultaneously violates the discrete symmetries of time reversal (T) and pari...

  4. Thermal emf of alkali metal--molten salt mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, K.E. (Univ. of Regina, Saskatchewan, Canada); Sime, S.J.

    1977-09-01

    The thermal emf of alkali metal--alkali halide mixtures is calculated on the basis of two models, the Pitzer model which suggests that the metal is completely dissociated to cation and electron, and the Rice model which assumes no dissociation. The Rice model gives surprisingly good agreement with the only available datum, that for Cs in CsAu. It is suggested that these systems will show a significant improvement in the figure of merit over simple molten salt mixtures. 3 tables.

  5. Influence of PbCl2 content in PbI2 solution of DMF on the absorption, crystal phase, morphology of lead halide thin films and photovoltaic performance in planar perovskite solar cells

    Science.gov (United States)

    Wang, Mao; Shi, Chengwu; Zhang, Jincheng; Wu, Ni; Ying, Chao

    2015-11-01

    In this paper, the influence of PbCl2 content in PbI2 solution of DMF on the absorption, crystal phase and morphology of lead halide thin films was systematically investigated and the photovoltaic performance of the corresponding planar perovskite solar cells was evaluated. The result revealed that the various thickness lead halide thin film with the small sheet-like, porous morphology and low crystallinity can be produced by adding PbCl2 powder into PbI2 solution of DMF as a precursor solution. The planar perovskite solar cell based on the 300-nm-thick CH3NH3PbI3-xClx thin film by the precursor solution with the mixture of 0.80 M PbI2 and 0.20 M PbCl2 exhibited the optimum photoelectric conversion efficiency of 10.12% along with an open-circuit voltage of 0.93 V, a short-circuit photocurrent density of 15.70 mA cm-2 and a fill factor of 0.69.

  6. Bio-conventional bleaching of kadam kraft-AQ pulp by thermo-alkali-tolerant xylanases from two strains of Coprinellus disseminatus for extenuating adsorbable organic halides and improving strength with optical properties and energy conservation.

    Science.gov (United States)

    Lal, Mohan; Dutt, Dharm; Tyagi, C H

    2012-04-01

    Two novel thermo-alkali-tolerant crude xylanases namely MLK-01 (enzyme-A) and MLK-07 (enzyme-B) from Coprinellus disseminatus mitigated kappa numbers of Anthocephalus cadamba kraft-AQ pulps by 32.5 and 34.38%, improved brightness by 1.5 and 1.6% and viscosity by 5.75 and 6.47% after (A)XE(1) and (B)XE(1)-stages, respectively. The release of reducing sugars and chromophores was the highest during prebleaching of A. cadamba kraft-AQ pulp at enzyme doses of 5 and 10 IU/g, reaction times 90 and 120 min, reaction temperatures 75 and 65°C and consistency 10% for MLK-01 and MLK-07, respectively. MLK-07 was more efficient than MLK01 in terms of producing pulp brightness, improving mechanical strength properties and reducing pollution load. MLK-01 and MLK-07 reduced AOX by 19.51 and 42.77%, respectively at 4% chlorine demands with an increase in COD and colour due to removal of lignin carbohydrates complexes. A. cadamba kraft-AQ pulps treated with xylanases from MLK-01 to MLK-07 and followed by CEHH bleaching at half chlorine demand (2%) showed a drastic reduction in brightness with slight improvement in mechanical strength properties compared to pulp bleached at 4% chlorine demand. MLK-01 reduced AOX, COD and colour by 43.83, 39.03 and 27.71% and MLK-07 by 38.34, 40.48 and 30.77%, respectively at half chlorine demand compared to full chlorine demand (4%). pH variation during prebleaching of A. cadamba kraft-AQ pulps with strains MLK-01 and MLK-07 followed by CEHH bleaching sequences showed a decrease in pulp brightness, AOX, COD and colour with an increase in mechanical strength properties, pulp viscosity and PFI revolutions to get a beating level of 35 ± 1 °SR at full chlorine demand. PMID:22805918

  7. Binary technetium halides

    Science.gov (United States)

    Johnstone, Erik Vaughan

    In this work, the synthetic and coordination chemistry as well as the physico-chemical properties of binary technetium (Tc) chlorides, bromides, and iodides were investigated. Resulting from these studies was the discovery of five new binary Tc halide phases: alpha/beta-TcCl3, alpha/beta-TcCl 2, and TcI3, and the reinvestigation of the chemistries of TcBr3 and TcX4 (X = Cl, Br). Prior to 2009, the chemistry of binary Tc halides was poorly studied and defined by only three compounds, i.e., TcF6, TcF5, and TcCl4. Today, ten phases are known (i.e., TcF6, TcF5, TcCl4, TcBr 4, TcBr3, TcI3, alpha/beta-TcCl3 and alpha/beta-TcCl2) making the binary halide system of Tc comparable to those of its neighboring elements. Technetium binary halides were synthesized using three methods: reactions of the elements in sealed tubes, reactions of flowing HX(g) (X = Cl, Br, and I) with Tc2(O2CCH3)4Cl2, and thermal decompositions of TcX4 (X = Cl, Br) and alpha-TcCl 3 in sealed tubes under vacuum. Binary Tc halides can be found in various dimensionalities such as molecular solids (TcF6), extended chains (TcF5, TcCl4, alpha/beta-TcCl2, TcBr 3, TcI3), infinite layers (beta-TcCl3), and bidimensional networks of clusters (alpha-TcCl3); eight structure-types with varying degrees of metal-metal interactions are now known. The coordination chemistry of Tc binary halides can resemble that of the adjacent elements: molybdenum and ruthenium (beta-TcCl3, TcBr3, TcI 3), rhenium (TcF5, alpha-TcCl3), platinum (TcCl 4, TcBr4), or can be unique (alpha-TcCl2 and beta-TcCl 2) in respect to other known transition metal binary halides. Technetium binary halides display a range of interesting physical properties that are manifested from their electronic and structural configurations. The thermochemistry of binary Tc halides is extensive. These compounds can selectively volatilize, decompose, disproportionate, or convert to other phases. Ultimately, binary Tc halides may find application in the nuclear fuel cycle and as precursors in inorganic and organometallic chemistry.

  8. Self-Trapped Excitons in Ionic-Covalent Silver Halide Crystals and Nanostructures: High-Frequency EPR, ESE, ENDOR and ODMR Studies

    OpenAIRE

    P. G. Baranov; Romanov, N. G.; Poluektov, O. G.; Schmidt, J.

    2010-01-01

    Silver halides have unique features in solid state physics because their properties are considered to be of borderline nature between ionic and covalent bonding. In AgCl, the self-trapped hole (STH) is centered and partly trapped in the cationic sublattice, forming an Ag2+ ion inside of a (AgCl6)4? complex as a result of the Jahn–Teller distortion. The STH in AgCl can capture an electron from the conduction band forming the self-trapped exciton (STE). Recent results of a study of STE by means...

  9. Exciton-relaxation dynamics in lead halides

    OpenAIRE

    Iwanaga, Masanobu; Hayashi, Tetsusuke

    2002-01-01

    We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of s...

  10. Process for oxidation of hydrogen halides to elemental halogens

    Science.gov (United States)

    Lyke, Stephen E. (Middleton, WI)

    1992-01-01

    An improved process for generating an elemental halogen selected from chlorine, bromine or iodine, from a corresponding hydrogen halide by absorbing a molten salt mixture, which includes sulfur, alkali metals and oxygen with a sulfur to metal molar ratio between 0.9 and 1.1 and includes a dissolved oxygen compound capable of reacting with hydrogen halide to produce elemental halogen, into a porous, relatively inert substrate to produce a substrate-supported salt mixture. Thereafter, the substrate-supported salt mixture is contacted (stage 1) with a hydrogen halide while maintaining the substrate-supported salt mixture during the contacting at an elevated temperature sufficient to sustain a reaction between the oxygen compound and the hydrogen halide to produce a gaseous elemental halogen product. This is followed by purging the substrate-supported salt mixture with steam (stage 2) thereby recovering any unreacted hydrogen halide and additional elemental halogen for recycle to stage 1. The dissolved oxygen compound is regenerated in a high temperature (stage 3) and an optical intermediate temperature stage (stage 4) by contacting the substrate-supported salt mixture with a gas containing oxygen whereby the dissolved oxygen compound in the substrate-supported salt mixture is regenerated by being oxidized to a higher valence state.

  11. Studies of EPR theory and trigonal distortion of the (NiX 6) 4- clusters (X = halide ion) in the series of perovskite crystals AMX 3 (A = Rb, Cs; M = Cd, Mg; X = halide ion)

    Science.gov (United States)

    Wang, Huai-Qian; Kuang, Xiao-Yu; Li, Hui-Fang

    2008-07-01

    A theoretical method is shown to yield a detailed explanation of numerous EPR parameters for d 8 configuration ion in trigonal ligand field. On the basis of the complete energy matrix, the local lattice structures of the octahedral (NiX 6) 4- clusters in the series of perovskite crystals AMX 3 (A = Rb, Cs; M = Cd, Mg; X = Cl, Br, I) with D3 d site symmetry have been studied by simulating the EPR and optical spectra. Moreover, the influences of the local lattice structure parameters R and ? as well as the spin-orbit coupling coefficient ? on the ZFS parameter D from different systems are discussed.

  12. Kinetics of aggregation and annealing of defects in heavily X-irradiated alkali chloride crystals studied by positron annihilation

    International Nuclear Information System (INIS)

    Using the positron as a microscopic probe, the authors have measured rates and activation energies for the kinetics of F-center aggregation and anneal in single crystals of NaCl, KCl, RbCl, and CsCl. The crystals were colored to F-center concentrations of approximately 1018 cm-3 by X-rays of average energy 11 keV at a dose rate approximately 5 Mrad/h at 200C to a total dose of 80 Mrad. Isothermal and isochronal measurements were performed in a ?-radian coincidence apparatus (PICA) for recording the two 0.5 MeV positron-electron annihilation #betta# rays emerging from the crystals. (Auth.)

  13. Crystal-structural study of zirconium chelates with alkali metals of composition A2[Zr(Nta)2]·xH2O (A=Li, Na, K, Rb, Cs or CH3H6)

    International Nuclear Information System (INIS)

    Some zirconium complexes with nitrile triacetate and with alkali metal in the external sphere were studied crystalostructurally. Packing of complexes and extra-sphere cations was studied. Plane or slightly corrugated anion layers of two essentially different types arranged according to the principle of trigonal and square grids represent the standard element of crystal structure. Water molecules are located both in anion and cation layers. CN and coordination polyhedron of cations are different even in case of stereotype nature of reasons of their location in the interlayer space. In Cs-, Rb- and K- compounds polyhedrons of alkali metal form specific doubled chains. These compounds are not isomorphous ones and are characterized by a specific way of water molecule location. Structure of sodium compound differs fundamentally from other ones. Ionic conductivity may be expected in crystals. 4 refs., 6 figs., 2 tabs

  14. Properties of mixed alkali germanate glasses

    Science.gov (United States)

    Ashton-Patton, Melissann Marie

    There is little data in the literature pertaining to mixed alkali germanate glasses. The majority of the data exists for the sodium-potassium-germanate glasses, and focuses on the density, glass transition temperature and vibrational spectra. This study explores three of the ten possible mixed alkali germanate glass systems: the lithium-cesium-germanium ternary, the sodium-potassium-germanium ternary, and the potassium-rubidium-germanium ternary. The mixed alkali effect was examined at two different concentrations of germania (85 and 90 mol %). To examine the mixed alkali effect on the germanate anomaly, the alkali oxides were held in a ratio of 1:1 and the germanium was varied from 100 to 75 mol %. The glass transition temperature and densities behavior of the mixed alkali germanate glasses in this study behaved as expected, exhibiting a maximum in Tg and no mixed alkali effect in density. The glasses with a 1:1 ratio of alkali exhibited properties between the end member glasses. The infrared spectra from this study show that the hydroxyl content increases as the amount of alkali in the glass increases. The cation identity does effect the band positions and intensities. The infrared bands between 1500 and 4000 cm-1 are shown to be a result of water. Electrical conductivity of mixed alkali germanate glasses exhibited unique behavior. Small additions of alkali (? 5 mol %) result in a positive or a linear deviation from additivity, in both the lithium-cesium-germanate system and the sodium-potassium-germanate system. With 10 mol % alkali oxide addition the deviation from additivity increases as the radius ratio of the cations increases. However, with 15 mol % alkali oxide addition, the greater the difference in the radius ratio of the cations, the smaller the deviation from additivity. A Kissinger study on the lithium-cesium-germanate glasses, yields activation energies consistent with crystallization studies in the literature for other mixed alkali germanate glasses. Glasses with a 1:1 ratio of cesium oxide to lithium oxide, or more cesium oxide than lithium oxide, crystallize into cesium germanium oxide crystals, however if there is more lithium the glasses crystallize into an unknown phase.

  15. Phase separation of crystal surfaces a lattice gas approach

    CERN Document Server

    Shore, J D; Shore, Joel D; Bukman, Dirk Jan

    1994-01-01

    We consider both equilibrium and kinetic aspects of the phase separation (``thermal faceting") of thermodynamically unstable crystal surfaces into a hill--valley structure. The model we study is an Ising lattice gas for a simple cubic crystal with nearest--neighbor attractive interactions and weak next--nearest--neighbor repulsive interactions. It is likely applicable to alkali halides with the sodium chloride structure. Emphasis is placed on the fact that the equilibrium crystal shape can be interpreted as a phase diagram and that the details of its structure tell us into which surface orientations an unstable surface will decompose. We find that, depending on the temperature and growth conditions, a number of interesting behaviors are expected. For a crystal in equilibrium with its vapor, these include a low temperature regime with logarithmically--slow separation into three symmetrically--equivalent facets, and a higher temperature regime where separation proceeds as a power law in time into an entire one-...

  16. Copper doped alkali halides for computed radiography and digital imaging

    OpenAIRE

    Chakrabarti, K; Bandyopadhyay, P. K.; Barkyoumb, J. H.

    1998-01-01

    We report here the results of our x-ray fluorescence, photostimulated luminescence, and time resolved laser spectroscopy studies in KCI:Cu. This material seems to possess some desirable properties for being used as an imaging plate in computed radiography.

  17. Analysis and modeling of alkali halide aqueous solutions

    DEFF Research Database (Denmark)

    Kim, Sun Hyung; Anantpinijwatna, Amata; Kang, Jeong Won; Gani, Rafiqul

    2016-01-01

    A new model is proposed for correlation and prediction of thermodynamic properties of electrolyte solutions. In the proposed model, terms of a second virial coefficient-type and of a KT-UNIFAC model are used to account for a contribution of binary interactions between ion and ion, and water and i...

  18. Cold ablation driven by localized forces in alkali halides.

    Science.gov (United States)

    Hada, Masaki; Zhang, Dongfang; Pichugin, Kostyantyn; Hirscht, Julian; Kochman, Micha? A; Hayes, Stuart A; Manz, Stephanie; Gengler, Regis Y N; Wann, Derek A; Seki, Toshio; Moriena, Gustavo; Morrison, Carole A; Matsuo, Jiro; Sciaini, Germán; Miller, R J Dwayne

    2014-01-01

    Laser ablation has been widely used for a variety of applications. Since the mechanisms for ablation are strongly dependent on the photoexcitation level, so called cold material processing has relied on the use of high-peak-power laser fluences for which nonthermal processes become dominant; often reaching the universal threshold for plasma formation of ~1 J cm(-2) in most solids. Here we show single-shot time-resolved femtosecond electron diffraction, femtosecond optical reflectivity and ion detection experiments to study the evolution of the ablation process that follows femtosecond 400 nm laser excitation in crystalline sodium chloride, caesium iodide and potassium iodide. The phenomenon in this class of materials occurs well below the threshold for plasma formation and even below the melting point. The results reveal fast electronic and localized structural changes that lead to the ejection of particulates and the formation of micron-deep craters, reflecting the very nature of the strong repulsive forces at play. PMID:24835317

  19. Temperature jump induction of isomerization dynamics of alkali halide clusters

    International Nuclear Information System (INIS)

    The time resolved dynamics of diffusionless cube?ring isomerization of the Na4Cl4 cluster was interrogated by constant energy molecular dynamics simulations, utilizing the first passage time method. The nonreactive isomerization induced by nonselective vibrational excitation is well accounted for in terms of the statistical RRK theory, opening avenues for experimental exploration of time-resolved cluster isomerization dynamics. (orig.)

  20. Dynamics of early stage defect production in irradiated alkali halides

    International Nuclear Information System (INIS)

    The growth of F, HD and V2m centres in X-irradiated KCl (0.01 mol% SrCl2) has been studied as a function of temperature in the range 140 K to 185 K. The results show a dynamic, temperature-dependent saturation concentration of HD centres, which decreases with increasing temperature of irradiation and partially recovers on re-irradiation at a lower temperature. The growth of F and V2m centres has a temperature dependence quite different from that obtained for irradiations performed at higher temperatures. The model of Comins and Carragher is in good agreement with the experimental results and accounts in detail for the complex, interrelated defect growth. Analysis of the rate equations of the model shows that in the limit of sufficiently high temperature the form of solution F(t)= sum i?i(1-e-?it) is obtained; this has been used in the past to provide empirical fits to F centre growth curves and demonstrates an overall unity in the approaches used. ((orig.))

  1. Impact of the organic halide salt on final perovskite composition for photovoltaic applications

    KAUST Repository

    Moore, David T.

    2014-08-01

    The methylammonium lead halide perovskites have shown significant promise as a low-cost, second generation, photovoltaic material.Despite recent advances, however, there are still a number of fundamental aspects of their formation as well as their physical and electronic behavior that are not well understood. In this letter we explore the mechanism by which these materials crystallize by testing the outcome of each of the reagent halide salts. We find that components of both salts, lead halide and methylammonium halide, are relatively mobile and can be readily exchanged during the crystallization process when the reaction is carried out in solution or in the solid state. We exploit this fact by showing that the perovskite structure is formed even when the lead salt\\'s anion is a non-halide, leading to lower annealing temperature and time requirements for film formation. Studies into these behaviors may ultimately lead to improved processing conditions for photovoltaic films. © 2014 Author(s).

  2. Impact of the organic halide salt on final perovskite composition for photovoltaic applications

    Directory of Open Access Journals (Sweden)

    David T. Moore

    2014-08-01

    Full Text Available The methylammonium lead halide perovskites have shown significant promise as a low-cost, second generation, photovoltaic material. Despite recent advances, however, there are still a number of fundamental aspects of their formation as well as their physical and electronic behavior that are not well understood. In this letter we explore the mechanism by which these materials crystallize by testing the outcome of each of the reagent halide salts. We find that components of both salts, lead halide and methylammonium halide, are relatively mobile and can be readily exchanged during the crystallization process when the reaction is carried out in solution or in the solid state. We exploit this fact by showing that the perovskite structure is formed even when the lead salt's anion is a non-halide, leading to lower annealing temperature and time requirements for film formation. Studies into these behaviors may ultimately lead to improved processing conditions for photovoltaic films.

  3. Characteristics of the fast electron emission produced during the cleavage of crystals

    Indian Academy of Sciences (India)

    B P Chandra; N L Patel; S S Rahangdale; R P Patel; V K Patle

    2003-01-01

    The present paper reports the fast electron emission produced during the cleavage of alkali halide crystals and models the dynamics of the process. The mechano-emission arises as a result of the ionization of surface traps at the expense of the energy which is released in the annihilation of the defects which are formed during cleavage. The slow electrons which appear upon the ionization of surface traps are subsequently accelerated in the ?eld of negatively charged segment of the freshly cleaved surface. Considering the basic mechanism of fast electron emission, expressions are derived which are able to explain satisfactorily the temporal, thermal, charge, surface, coloration, water adsorption and other characteristics of the fast electron emission produced during the cleavage of crystals. The decay time of the charges on the newly created surfaces, and the velocity of cracks can be determined from the measurements of fast electron emission produced during the cleavage of crystals. It is shown that two types of diffusing centres are responsible for the charge relaxation and thereby for the emission of fast electrons produced during the cleavage of alkali halide crystals.

  4. Halide laser glasses

    International Nuclear Information System (INIS)

    Energy storage and energy extraction are of prime importance for efficient laser action and are affected by the line strengths and linewidths of optical transitions, excited-state lifetimes, nonradiative decay processes, spectroscopic inhomogeneities, nonlinear refractive index, and damage threshold. These properties are all host dependent. To illustrate this, the spectroscopic properties of Nd3+ have been measured in numerous oxide, oxyhalide, and halide glasses. A table summarizes the reported ranges of stimulated emission cross sections, peak wavelengths, linewidths, and radiative lifetimes associated with the 4F/sub 3/2/ ? 4I/sub 11/2/ lasing transition

  5. Making and Breaking of Lead Halide Perovskites.

    Science.gov (United States)

    Manser, Joseph S; Saidaminov, Makhsud I; Christians, Jeffrey A; Bakr, Osman M; Kamat, Prashant V

    2016-02-16

    A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as organic metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compounds can be processed at low temperature (typically in the range 80-150 °C) and readily self-assemble from the solution phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chemical and structural stability, undergoing rapid degradation in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphology, manipulation of the stoichiometry and chemistry of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degradation mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degradation under operating conditions. This Account provides insight into the lifecycle of organic-inorganic lead halide perovskites, including (i) the nature of the precursor solution, (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chemistry, and thus the lead halide charge-transfer complexes present in solution, crystallization kinetics can be tailored to yield improved thin film homogeneity. Because degradation of the as-formed perovskite film is in many ways analogous to its initial formation, the same suite of monitoring techniques reveals the moisture-induced transformation of low band gap methylammonium lead iodide (CH3NH3PbI3) to wide band gap hydrate compounds. The rate of degradation is increased upon exposure to light. Interestingly, the hydration process is reversible under certain conditions. This facile formation and subsequent chemical lability raises the question of whether CH3NH3PbI3 and its analogues are thermodynamically stable phases, thus posing a significant challenge to the development of transformative perovskite photovoltaics. Adequately addressing issues of structural and chemical stability under real-world operating conditions is paramount if perovskite solar cells are to make an impact beyond the benchtop. Expanding our fundamental knowledge of lead halide perovskite formation and degradation pathways can facilitate fabrication of stable, high-quality perovskite thin films for the next generation of photovoltaic and light emitting devices. PMID:26789596

  6. Making and Breaking of Lead Halide Perovskites

    KAUST Repository

    Manser, Joseph S.

    2016-02-16

    A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as organic metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compounds can be processed at low temperature (typically in the range 80–150 °C) and readily self-assemble from the solution phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chemical and structural stability, undergoing rapid degradation in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphology, manipulation of the stoichiometry and chemistry of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degradation mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degradation under operating conditions. This Account provides insight into the lifecycle of organic–inorganic lead halide perovskites, including (i) the nature of the precursor solution, (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chemistry, and thus the lead halide charge-transfer complexes present in solution, crystallization kinetics can be tailored to yield improved thin film homogeneity. Because degradation of the as-formed perovskite film is in many ways analogous to its initial formation, the same suite of monitoring techniques reveals the moisture-induced transformation of low band gap methylammonium lead iodide (CH3NH3PbI3) to wide band gap hydrate compounds. The rate of degradation is increased upon exposure to light. Interestingly, the hydration process is reversible under certain conditions. This facile formation and subsequent chemical lability raises the question of whether CH3NH3PbI3 and its analogues are thermodynamically stable phases, thus posing a significant challenge to the development of transformative perovskite photovoltaics. Adequately addressing issues of structural and chemical stability under real-world operating conditions is paramount if perovskite solar cells are to make an impact beyond the benchtop. Expanding our fundamental knowledge of lead halide perovskite formation and degradation pathways can facilitate fabrication of stable, high-quality perovskite thin films for the next generation of photovoltaic and light emitting devices.

  7. Alkali metal intercalates of molybdenum disulfide.

    Science.gov (United States)

    Somoano, R. B.; Hadek, V.; Rembaum, A.

    1973-01-01

    Study of some of the physicochemical properties of compounds obtained by subjecting natural molybdenite and single crystals of molybdenum disulfide grown by chemical vapor transport to intercalation with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Reported data and results include: (1) the intercalation of the entire alkali metal group, (2) stoichiometries and X-ray data on all of the compounds, and (3) superconductivity data for all the intercalation compounds.

  8. Effect of the nature of alkali and alkaline-earth oxides on the structure and crystallization of an alumino-borosilicate glass developed to immobilize highly concentrated nuclear waste solutions

    International Nuclear Information System (INIS)

    A complex rare-earth rich alumino-borosilicate glass has been proved to be a good candidate for the immobilization of new high level radioactive wastes. A simplified seven-oxides composition of this glass was selected for this study. In this system, sodium and calcium cations were supposed in other works to simulate respectively all the other alkali (R+ = Li+, Rb+, Cs+) and alkaline-earth (R2+ = Sr2+, Ba2+) cations present in the complex glass composition. Moreover, neodymium or lanthanum are used here to simulate all the rare-earths and actinides occurring in waste solutions. In order to study the impact of the nature of R+ and R2+ cations on both glass structure and melt crystallization tendency during cooling, two glass series were prepared by replacing either Na+ or Ca2+ cations in the simplified glass by respectively (Li+, K+, Rb+, Cs+) or (Mg2+, Sr2+, Ba2+) cations. From these substitutions, it was established that alkali ions are preferentially involved in the charge compensation of (AlO4)- entities in the glass network comparatively to alkaline-earth ions. The glass compositions containing calcium give way to the crystallization of an apatite silicate phase bearing calcium and rare-earth ions. The melt crystallization tendency during cooling strongly varies with the nature of the alkaline-earth. (authors)

  9. The Raman effect in crystals

    Science.gov (United States)

    Loudon, R.

    2001-11-01

    A review is given of progress in the theoretical and experimental study of the Raman effect in crystals during the past ten years. Attention is given to the theory of those properties of long-wavelength lattice vibrations in both cubic and uniaxial crystals which can be studied by Raman scattering. In particular the phenomena observed in the Raman scattering from crystals which lack a centre of inversion are related to the theory. The angular variations of the scattering by any type of lattice vibration in a crystal having any symmetry can be easily calculated using a complete tabulation of the Raman tensor. Recent measurements of first-order lattice vibration spectra are listed. A discussion of Brillouin scattering is included. The relation of second-order Raman spectra to critical points in the lattice vibration density of states is discussed, and measurements of the second-order spectra of diamond and the alkali halides are reviewed. The theory and experimental results for Raman scattering by electronic levels of ions in crystals are examined, and proposals for Raman scattering by spin waves, electronic excitations across the superconductive gap and by plasmons are collected together. Finally, the prospects for applying lasers as sources for Raman spectroscopy are discussed, and progress in the new technique of stimulated Raman scattering is reviewed.

  10. Actinide halide complexes

    Energy Technology Data Exchange (ETDEWEB)

    Avens, L.R.; Zwick, B.D.; Sattelberger, A.P.; Clark, D.L.; Watkin, J.G.

    1991-02-07

    A compound of the formula MX{sub n}L{sub m} wherein M = Th, Pu, Np,or Am thorium, X = a halide atom, n = 3 or 4, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is 3 or 4 for monodentate ligands or is 2 for bidentate ligands, where n + m = 7 or 8 for monodentate ligands or 5 or 6 for bidentate ligands, a compound of the formula MX{sub n} wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant, are provided.

  11. Combustion synthesis of nano-sized tungsten carbide powder and effects of sodium halides

    International Nuclear Information System (INIS)

    The synthesis of nano-size tungsten carbide powder has been investigated with a WO3 + Mg + C + carbonate system using alkali halides. The effects of different types of alkali halides on combustion temperature and tungsten carbide formation were discussed. Sodium fluoride had a notable effect on the particle size of the product and the degree of transformation from the initial mixture. A small amount of ammonium carbonate activated the carburization of tungsten carbide by the gas phase carbon transportation. X-ray diffraction data and particle analysis showed that the final product synthesized from a WO3-Mg-C-(NH4)2CO3-NaF system contains pure-phase tungsten carbide with a particle size of 50-100 nm.

  12. Specificity of structure of zinc(2) halides with cyclic tetraaminne ligands. Crystal structures of ZnCyclamX2, X=Cl, Br, I

    International Nuclear Information System (INIS)

    Crystal structure of ZnCyclamX2, X=Cl, Br, I, Cyclam(C10H24N4)=1,4,8,11-tetraazacyclotetradecane, was defined. The complexes are monomer tetragonally-bipyramid structures with meso-planar conformation Cyclam. Metal atoms is statistically shifted from equatorial plane by 0.24 A in case X=Cl; 0.33 A - X=Br; and 0.40 A - X=I. Secondary (elongated) axial bonds are nonequilibrium: Zn-Cl 2.424(8) and 2.0905(8) A, Zn-Br 2.555(4) and 3.214(4) A; Zn-I 2.753(1) and 3.543(1) A. Judging by geometry of the complexes and 13C[1H]NMR data statistical shift of Zn is dynamic character. The assumption is made that intramolecular motion increases stability of the complexes and characterizes specific type of binding, inherent of d10-metal complexes. It is shown that antibate correlation in the lengths of equatorial and axial bonds ascertained for slightly distorted octahedral complexes is just both for pyramid and bipyramid complexes with axial long-range action

  13. Nickel(II) complexes of N2S2 donor set ligand and halide/pseudohalides: Synthesis, crystal structure, DNA and bovine/human serum albumin interaction

    Indian Academy of Sciences (India)

    Animesh Patra; Biplab Mondal; Buddhadeb Sen; Ennio Zangrando; Pabitra Chattopadhyay

    2015-11-01

    A series of neutral hexacoordinated nickel(II) complexes of formula [NiII (L)X2] (where L = 3,4-bis(2-pyridylmethylthio)toluene with tetradentate N2S2 donor set and X = chloride (1), azide (2), cyanate (3) and isothiocyanate anion (4)) have been synthesized and isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods along with detailed structural characterization of 1,2 and 3 by single crystal X-ray diffraction analyses. The structural study showed that the nickel(II) ion has a distorted octahedral geometry being chelated by the tetradentate N2S2 ligand and bound to cis- located choride or pseudohalide anions. In dimethylformamide solution the complexes showed quasi-reversible NiII/NiIII redox couples in cyclic voltammograms with E1/2 values of +0.723, +0.749, +0.768 and +0.868 V for 1, 2, 3 and 4, respectively. The study of interaction of the complexes with calf thymus DNA, bovine serum albumin (BSA) and human serum albumin (HSA) using spectroscopic and physicochemical tools clearly indicates that the complexes interact with DNA via groove binding mode.

  14. Efficiency of energy transfer from ?-irradiated ammonium halides in aqueous iodide and nitrate solutions

    International Nuclear Information System (INIS)

    It is well known that ammonium halide (NH4X) crystals, on ?-exposure, store energy in the form of primary and secondary radiolytic products. Such crystals on dissolution in aqueous iodide and nitrate solutions result in oxidation of iodide and reduction of nitrate, respectively. The yields of iodine and nitrite are determined by chemical methods under varying conditions of the amount, dose and particle size of the irradiated ammonium halide salts. The maximum values of the efficiency of energy transfer for oxidation and reduction processes for ammonium halide salts correspond to 40% and 10%, respectively. At low doses, an empirical relation proposed between the percent efficiency of energy transfer and the absorbed dose is valid. The concentrations of inherent oxidizing and reducing species initially present are 7.0*1018 and 1.0*1018 per mol of ammonium halide, respectively. (author) 21 refs.; 7 figs.; 2 tabs

  15. Actinide halide complexes

    Science.gov (United States)

    Avens, Larry R. (Los Alamos, NM); Zwick, Bill D. (Santa Fe, NM); Sattelberger, Alfred P. (Los Alamos, NM); Clark, David L. (Los Alamos, NM); Watkin, John G. (Los Alamos, NM)

    1992-01-01

    A compound of the formula MX.sub.n L.sub.m wherein M is a metal atom selected from the group consisting of thorium, plutonium, neptunium or americium, X is a halide atom, n is an integer selected from the group of three or four, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is an integer selected from the group of three or four for monodentate ligands or is the integer two for bidentate ligands, where the sum of n+m equals seven or eight for monodentate ligands or five or six for bidentate ligands, a compound of the formula MX.sub.n wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant, are provided.

  16. Coprecipitation of alkali metal ions with calcium carbonate

    International Nuclear Information System (INIS)

    The coprecipitation of alkali metal ions Li+, Na+, K+ and Rb+ with calcium carbonate has been studied experimentally and the following results have been obtained: (1) Alkali metal ions are more easily coprecipitated with aragonite than with calcite. (2) The relationship between the amounts of alkali metal ions coprecipitated with aragonite and their ionic radii shows a parabolic curve with a peak located at Na+ which has approximately the same ionic radius as Ca2+. (3) However, the amounts of alkali metal ions coprecipitated with calcite decrease with increasing ionic radius of alkali metals. (4) Our results support the hypothesis that (a) alkali metals are in interstitial positions in the crystal structure of calcite and do not substitute for Ca2+ in the lattice, but (b) in aragonite, alkali metals substitute for Ca2+ in the crystal structure. (5) Magnesium ions in the parent solution increase the amounts of alkali metal ions (Li+, Na+, K+ and Rb+) coprecipitated with calcite but decrease those with aragonite. (6) Sodium-bearing aragonite decreases the incorporation of other alkali metal ions (Li+, K+ and Rb+) into the aragonite. (author)

  17. Research Update: Physical and electrical characteristics of lead halide perovskites for solar cell applications

    Directory of Open Access Journals (Sweden)

    Simon A. Bretschneider

    2014-04-01

    Full Text Available The field of thin-film photovoltaics has been recently enriched by the introduction of lead halide perovskites as absorber materials, which allow low-cost synthesis of solar cells with efficiencies exceeding 16%. The exact impact of the perovskite crystal structure and composition on the optoelectronic properties of the material are not fully understood. Our progress report highlights the knowledge gained about lead halide perovskites with a focus on physical and optoelectronic properties. We discuss the crystal and band structure of perovskite materials currently implemented in solar cells and the impact of the crystal properties on ferroelectricity, ambipolarity, and the properties of excitons.

  18. Infrared Spectroscopic Study of Vibrational Modes in Methylammonium Lead Halide Perovskites.

    Science.gov (United States)

    Glaser, Tobias; Müller, Christian; Sendner, Michael; Krekeler, Christian; Semonin, Octavi E; Hull, Trevor D; Yaffe, Omer; Owen, Jonathan S; Kowalsky, Wolfgang; Pucci, Annemarie; Lovrin?i?, Robert

    2015-08-01

    The organic cation and its interplay with the inorganic lattice underlie the exceptional optoelectronic properties of organo-metallic halide perovskites. Herein we report high-quality infrared spectroscopic measurements of methylammonium lead halide perovskite (CH3NH3Pb(I/Br/Cl)3) films and single crystals at room temperature, from which the dielectric function in the investigated spectral range is derived. Comparison with electronic structure calculations in vacuum of the free methylammonium cation allows for a detailed peak assignment. We analyze the shifts of the vibrational peak positions between the different halides and infer the extent of interaction between organic moiety and the surrounding inorganic cage. The positions of the NH3(+) stretching vibrations point to significant hydrogen bonding between the methylammonium and the halides for all three perovskites. PMID:26267180

  19. Liquid + liquid equilibrium in mixtures of lithium fluoride with potassium and rubidium halides

    International Nuclear Information System (INIS)

    Highlights: ? We measured electrical conductivity of the dissolving melts of LiF with KBr, KI, RbBr, and RbI along the saturation line. ? We studied a transient layer between the coexisting phases. ? The difference between the conductivities of phases increases as the radius of ion grows. ? An essential reorganisation of the light phase was found near the critical solution point. - Abstract: The liquid + liquid phase equilibrium of molten mixtures of lithium fluoride with potassium and rubidium halides was investigated over an extended temperature range in the two-phase region along the saturation line by the electrical conductivity method. In the overwhelming majority of mixtures, the electrical conductivity for coexisting equilibrium phases increased when the temperature increased. For mixtures with only potassium bromide, it decreased because of the extensive solubility of potassium bromide in lithium fluoride. The electrical conductivity for the light phase was half the value of the conductivity of the pure lithium fluoride. The electrical conductivity of the heavy phase did not differ enough from the conductivity of the pure heavy alkali halides. At the same time, the solubility of the heavy component in LiF was many times less than the lithium fluoride solubility in the lower phase. This contradiction points to essential reorganisation of the structure of the light phase. The difference between the conductivities of the coexisting phases at equal temperatures increased as the radius of the halide anion or alkali cation grew. The temperature growth led to the increase in the conductivity difference along the saturation line for mixtures of LiF with RbI. For mixtures of LiF with lighter alkali halides, it decreased up to zero at the critical mixing point for LiF + KBr mixtures as the temperature increased. Between the coexisting equilibrium phases, a transient layer was revealed, where a conductivity gradient exists. The thickness of this layer decreased as the temperature decreased and the sum of the ionic radii of the mixtures increased.

  20. Development of Halide and Oxy-Halides for Isotopic Separations

    Energy Technology Data Exchange (ETDEWEB)

    Leigh R. Martin; Aaron T. Johnson; Jana Pfeiffer; Martha R. Finck

    2014-10-01

    The goal of this project was to synthesize a volatile form of Np for introduction into mass spectrometers at INL. Volatile solids of the 5f elements are typically those of the halides (e.g. UF6), however fluorine is highly corrosive to the sensitive internal components of the mass separator, and the other volatile halides exist as several different stable isotopes in nature. However, iodide is both mono-isotopic and volatile, and as such presents an avenue for creation of a form of Np suitable for introduction into the mass separator. To accomplish this goal, the technical work in the project sought to establish a novel synthetic route for the conversion NpO2+ (dissolved in nitric acid) to NpI3 and NpI4.

  1. The first alkali metal hydroxide-ammoniate, cesium hydroxide-ammoniate (1:1), CsOH·NH3, synthesis and crystal structure

    International Nuclear Information System (INIS)

    Cesium hydroxide-ammoniate (1:1), CsOH·NH3, was obtained as a side product in the reaction of cesium hydride, CsH and telluric acid, Te(OH)6 in liquid ammonia at ?38 °C. The compound crystallizes as colorless crystals in the monoclinic space group P21/c with Z = 8, a = 4.391(9) Å, b = 18.593(4) Å, c = 8.141 (16) Å, ? = 90.37(3)°, and V = 664.6(24) Å3. The crystal structure was solved from single crystal X-ray data. The structure contains a three-dimensional network built up by contacts between cesium cations and hydroxide anions and ammonia molecules, which in turn are connected by O–H···N and N–H···O hydrogen bonds. (author)

  2. Solution-Phase Synthesis of Cesium Lead Halide Perovskite Nanowires.

    Science.gov (United States)

    Zhang, Dandan; Eaton, Samuel W; Yu, Yi; Dou, Letian; Yang, Peidong

    2015-07-29

    Halide perovskites have attracted much attention over the past 5 years as a promising class of materials for optoelectronic applications. However, compared to hybrid organic-inorganic perovskites, the study of their pure inorganic counterparts, like cesium lead halides (CsPbX3), lags far behind. Here, a catalyst-free, solution-phase synthesis of CsPbX3 nanowires (NWs) is reported. These NWs are single-crystalline, with uniform growth direction, and crystallize in the orthorhombic phase. Both CsPbBr3 and CsPbI3 are photoluminescence active, with composition-dependent temperature and self-trapping behavior. These NWs with a well-defined morphology could serve as an ideal platform for the investigation of fundamental properties and the development of future applications in nanoscale optoelectronic devices based on all-inorganic perovskites. PMID:26181343

  3. Melting and liquid structure of polyvalent metal halides

    International Nuclear Information System (INIS)

    A short review is given of recent progress in determining and understanding liquid structure types and melting mechanisms for halides of polyvalent metals. The nature of the preferred local coordination for the polyvalent metal ion in the melt can usually be ascertained from data on liquid mixtures with halogen-donating alkali halides. The stability of these local coordination states and the connectivity that arises between them in the approach to the pure melt determines the character of its short-range and possible medium-range order. A broad classification of structural and melting behaviours can be given on the basis of measured melting parameters and transport coefficients for many compounds, in combination with the available diffraction data on the liquid structure of several compounds. Correlations have been shown to exist with a simple indicator of the nature of the chemical bond and also with appropriate parameters of ionic models, wherever the latter are usefully applicable for semiquantitative calculations of liquid structure. Consequences on the mechanisms for valence electron localization in solutions of metallic elements into strongly structured molten salts are also briefly discussed. (author). 46 refs, 4 figs, 2 tabs

  4. New ternary alkali oxides and quaternary alkali oxy-nitrides of molybdenum and tungsten

    OpenAIRE

    Arumugam, Nachiappan

    2005-01-01

    This work has focused on exploring the synthesis and characterization of new alkali oxides and oxynitrides of molybdenum and tungsten. In particular, the synthetic approach via the azide/nitrate route, which was developed recently, should be evaluated and extended to the oxides of the heavy group VI elements. For characterization, the crystal structures have been determined by using X-ray diffraction data by means of single crystal or powder methods, and TGA/DTA, DSC and specific heat me...

  5. DEVELOPMENT AND EVALUATION OF METHODS FOR TOTAL ORGANIC HALIDE AND PURGEABLE ORGANIC HALIDE IN WASTEWATER

    Science.gov (United States)

    This report describes a series of studies involving the use of 'surrogate' methods for the determination of total organic halides (TOX), purgeable organic halides (POX), and solvent extractable organic halides (EOX), in wastewater and solid wastes. A pyrolysis/microcoulometric sy...

  6. Effect of alkali metal- and ammonium dichromates on solubility of boric acid

    International Nuclear Information System (INIS)

    Boric acid solubility in aqueous solutions of alkali metal and ammonium dichromates has been studied. It is established that the salts studied salt out boric acid. The value of lyotropic effect decreases in the series of NH4+, K+, Na+, Li+ cations. The sequence is the reciprocal to the one, observed in alkali metal chromates, and it is the same as in the case of halides and nitrates. It is conditioned by the character of cation hydration in acid medium. The negative sign of lyotropic effect is related to the absence of local interaction of boric acid with dimeric anions Cr2O72-, which is confirmed by the data of electron spectroscopy

  7. Alkali and Halogen Chemistry in Volcanic Gases on Io

    CERN Document Server

    Schaefer, L

    2004-01-01

    We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10^-6 to 10^+1 bars) ranges, which overlap the nominal conditions at Pele (T = 1760 K, P = 0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. We predict the major alkali and halogen species in a Pele-like volcanic gas and the major alklai and halogen condensates. We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observation...

  8. HF Adducts of alkali metal acid salts containing hydrogen bonds of the F-H-O type: synthesis and crystal structures

    International Nuclear Information System (INIS)

    Crystal adducts of acid oxysalts with hydrogen fluoride, i.e. CsH2PO3·HF (1) and Cs4(SeO4)(HSeO4)2·HF (2) were synthesized. By the method of X-ray diffraction analysis of monocrystals at 180 K crystal structure of compounds 1 and 2 was determined respectively: 1 - a = 5.581 (2), b = 4.863 (2), c = 18.400 (7) A, ? = 92.09 (3) deg, sp.gr. P21/c; 2 - a = 25.413 (5), b = 12.718 (3), c = 10.819 (2) A, ? 107.57 (3) deg, sp.gr. C2/c. Besides hydrogen bonds of used type O-H-O shorter bonds F-H-O, their length 2.36-2.44 A, were discovered in the structures studied

  9. Cs7Sm11[TeO3]12Cl16 and Rb7Nd11[TeO3]12Br16, the new tellurite halides of the tetragonal Rb6LiNd11[SeO3]12Cl16 structure type

    Science.gov (United States)

    Charkin, Dmitri O.; Black, Cameron; Downie, Lewis J.; Sklovsky, Dmitry E.; Berdonosov, Peter S.; Olenev, Andrei V.; Zhou, Wuzong; Lightfoot, Philip; Dolgikh, Valery A.

    2015-12-01

    Two new rare-earth - alkali - tellurium oxide halides were synthesized by a salt flux technique and characterized by single-crystal X-ray diffraction. The structures of the new compounds Cs7Sm11[TeO3]12Cl16 (I) and Rb7Nd11[TeO3]12Br16 (II) (both tetragonal, space group I4/mcm) correspond to the sequence of [MLn11(TeO3)12] and [M6X16] layers and bear very strong similarities to those of known selenite analogs. We discuss the trends in similarities and differences in compositions and structural details between the Se and Te compounds; more members of the family are predicted.

  10. New sulfido antimonates of the heavy alkali metals. Synthesis, crystal structure and chemical bonding of (K/Rb/Cs)3SbS3 and Cs3SbS4 . H2O

    International Nuclear Information System (INIS)

    The new sulfido antimonates(III) (Rb/Cs)3SbS3 were prepared from the alkali metal sulfides Rb2S/Cs2S2 and elemental antimony and sulfur or Sb2S3 at reaction temperatures of about 700 C. The known isotypic potassium compound was similarly synthesized from the elements. The structures of the light-yellow crystals were refined using single-crystal X-ray data. Both compounds are isotypic to the respective Na salt forming the Na3AsS3 structure type (cubic, space group P213, K/Rb/Cs: a = 947.21(7)/982.28(5)/1025.92(5) pm, Z = 4, R1 = 0.0159/0.0560/0.0582). The ?-tetrahedral SbS33- anions with Sb-S bond lengths of 242 pm are arranged in a cubic face centered packing, in which the three crystallographically different A+ cations occupy the tetrahedral and octahedral voids, overall exhibiting a distorted octahedral sulfur coordination. The chemical bonding and the characteristics of the stereochemically active lone electron pair have been investigated by means of FP-LAPW band structure calculations. Needle-shaped crystals of the monohydrate of the antimony(V) salt Cs3SbS4 . H2O were obtained from a suspension of Sb2O3, CsOH and elemental sulfur. Cs3SbS4 . H2O crystallizes in a new structure type (monoclinic, space group P21/c, a = 987.17(10), b = 994.83(7), c = 1600.46(14) pm, ? = 126.895(8) , Z = 4, R1 = 0.0234). As expected, the Sb-S distances (233.1-234.7 pm) in the nearly ideally tetrahedral anion SbS43- are considerably shorter than in the antimonates(III) but match the bond lengths in the anhydrous sulfido antimonate(V) Cs3SbS4. Due to their similar fcc-like anion packing and the stereochemically active lone electron pair of Sb in the antimonates(III), the whole series of compounds A3SbIII,VS3/4 shows a uniform structure relation, which is elucidated using crystallographic group-subgroup relations. (orig.)

  11. Dehydrated rare earth halides and production process

    International Nuclear Information System (INIS)

    Rare earth chlorides, bromides or iodides containing less than 1 wt% water and less than 3 wt% oxyhalide are dehydrated by a gas flow of hydrogen halide through the halide bed. Structural water can interfer in some applications for instance metal preparation by chemical or electrochemical reduction

  12. ALKALI RESISTANT CATALYST

    DEFF Research Database (Denmark)

    alkali metal and/or alkali-earth compounds which process comprises using a catalyst combined of (i) a formed porous superacidic support, said superacidic support having an Hammett acidity stronger than Ho=-12, and (ii) a metal oxide catalytic component deposited on said superacidic support selected from......The present invention concerns the selective removal of nitrogen oxides (NOx) from gasses. In particular, the invention concerns a process, a catalyst and the use of a catalyst for the selective removal of nitrogen oxides in the presence of ammonia from gases containing a significant amount of...

  13. Alkali metal ion battery with bimetallic electrode

    Energy Technology Data Exchange (ETDEWEB)

    Boysen, Dane A; Bradwell, David J; Jiang, Kai; Kim, Hojong; Ortiz, Luis A; Sadoway, Donald R; Tomaszowska, Alina A; Wei, Weifeng; Wang, Kangli

    2015-04-07

    Electrochemical cells having molten electrodes having an alkali metal provide receipt and delivery of power by transporting atoms of the alkali metal between electrode environments of disparate chemical potentials through an electrochemical pathway comprising a salt of the alkali metal. The chemical potential of the alkali metal is decreased when combined with one or more non-alkali metals, thus producing a voltage between an electrode comprising the molten the alkali metal and the electrode comprising the combined alkali/non-alkali metals.

  14. Chlor-Alkali Technology.

    Science.gov (United States)

    Venkatesh, S.; Tilak, B. V.

    1983-01-01

    Chlor-alkali technology is one of the largest electrochemical industries in the world, the main products being chlorine and caustic soda (sodium hydroxide) generated simultaneously by the electrolysis of sodium chloride. This technology is reviewed in terms of electrochemical principles and manufacturing processes involved. (Author/JN)

  15. Spectra of alkali atoms

    International Nuclear Information System (INIS)

    Emission spectra of alkali atoms has been determined by using spectrometer at the ultraviolet to infra red waves range. The spectra emission can be obtained by absorption spectrophotometric analysis. Comparative evaluations between experimental data and data handbook obtained by spark method were also presented. (author tr.)

  16. Local structure of alkalis in mixed-alkali borate glass to elucidate the origin of mixed-alkali effect

    Directory of Open Access Journals (Sweden)

    Yomei Tokuda

    2015-12-01

    Full Text Available We report the structural analysis of Na+ and Cs+ in sodium cesium borate crystals and glasses using 23Na and 133Cs magic-angle spinning nuclear magnetic resonance (MAS NMR spectroscopy. The composition dependence of NMR spectra of the borate was similar to that of the silicate: (1 the peak position of cesium borate crystals shifted to upfield for structures with larger Cs+ coordination numbers, (2 the MAS NMR spectra of xNa2O-yCs2O-3B2O3 (x = 0, 0.25, 0.5, 0.75, 1.0, x + y = 1 glass showed that the average coordination number (CN of both the alkali cations decreases with increasing Cs+/(Na+ + Cs+ ratio. However, the degree of decrement in borates is much smaller than that in silicates. We have considered that the small difference in CN is due to 4-coordinated B, because it is electrically compensated by the alkali metal ions resulting in the restriction of having various coordinations of O to alkali metal.

  17. Oscillatory rule in the energy spectrum of traps in KCl and NaI crystals

    CERN Document Server

    Gumenyuk, A F; Stanovyi, O P; Pashchenko, V G; Tomylko, S V

    2010-01-01

    The thermoluminescence (TL) method is used for the investigation of the energy spectrum of traps in KCl and NaI crystals in the temperature range 80-500 K. It is shown that the thermal activation energies of traps in KCl and NaI form one oscillatory series E=hwn with vibrational quantum energies of 0.121 eV in KCl and 0.061 eV in NaI. In this case, the quantum number n assumes half-integer and integer values. Based on the generalized data on the investigated alkali-halide crystals (AHC), we confirmed the earlier proposed model of TL in AHCs. It is assumed that, in addition to the nonradiative H-F recombination, there exists the two-stage recombination of H-centers at anion vacancies resulting in the radiative recombination of a hole at an F-center. The energy of a quantum in the oscillatory rule corresponds to a local vibrational mode of an X2 halide molecule.

  18. Fullerenes doped with metal halides

    International Nuclear Information System (INIS)

    The cage-like structure of fullerenes is a challenge to every experimental to put something inside - to dope the fullerenes. In fact, the research team that first identified C60 as a football-like molecule quickly succeeded in trapping metal atoms inside and in shrinking the cage around this atom by photofragmentation. In this paper we report the results of ''shrink-wrapping'' the fullerenes around metal halide molecules. Of special interest is the critical size (the minimum number of carbon atoms) that can still enclose the dopant. A rough model for the space available inside a carbon cage gives good agreement with the measured shrinking limits. (author). 8 refs, 6 figs

  19. Crystal structure, IMT and superconducting transitions in solids under high pressure

    International Nuclear Information System (INIS)

    Band structure methods have reached a high level of sophistication enabling us to calculate a wide variety of physical properties of solids. In this paper, the high pressure behaviour of Ni3(Al,Nb), LaFeO3, AgGaS2 and some of the alkali halide systems have been discussed. The crystal structural transformation in Ni3(Al,Nb) system and the magnetic as well as insulator-metal transition in La2FeO3 systems are studied by calculating their total energies as a function of volume. The question as to whether ionic solids will become superconductors under pressure is also discussed. The band structure calculations are made using the TBLMTO method. (author)

  20. ICES studies on sup(99m)Tc-halide complexes: formation, hydrolysis and ligand exchange

    Energy Technology Data Exchange (ETDEWEB)

    Fiser, M.; Brabec, V.; Dragoun, O.; Kovalik, A.; Rysavy, M.; Dragounova, N.

    1988-01-01

    The Internal Conversion Electron Spectroscopy (ICES) method was employed to study the products of reduction of no-carrier-added (sup(99m)Tc)pertechnetate by concentrated hydrochloric, hydrobromic and hydroiodic acids. The reductions were carried out in vacuum with subsequent evaporation of the solution to dryness. In the solid deposits, containing /similar to/ 10/sup -9/ g Tc, chemical shifts of sup(99m)Tc electron binding energies were measured and the results were compared with known data of x-ray photoelectron spectroscopy for defined technetium compounds. It was evidenced that all reduction/evaporation procedures yielded sup(99m)Tc(IV)-halide complexes. Another technique of reduction by vapours of halogen acids was proposed to prepare thin radioactive sources for physics studies. The reduction power of alkali halides in absence of acids was examined and a partial reduction of pertechnetate by iodide was found. The product was a hydrolysed species. The hydrolysis of halide complexes yielded the same product. In the absence of acids, dissolved species were partly oxidised to Tc(VII) by air. Oxidation was most apparent for the chloride and negligible for the iodide system. Ligand exchange of chloro and bromo complexes to chelate with DTPA at pH 3 was found to be uncomplete. Tc(IV) hydrolysed species, Tc(IV)DTPA and Tc(VII) were evidenced. Tc(V)DTPA was also observed which arises from partially oxidised products.

  1. ICES studies on 99mTc-halide complexes: formation, hydrolysis and ligand exchange

    International Nuclear Information System (INIS)

    The Internal Conversion Electron Spectroscopy (ICES) method was employed to study the products of reduction of no-carrier-added [99mTc]pertechnetate by concentrated hydrochloric, hydrobromic and hydroiodic acids. The reductions were carried out in vacuum with subbsequent evaporation of the solution to dryness. In the solid deposits, containing ? 10-9 g Tc, chemical shifts of 99mTc electron binding energies were measured and the results were compared with known data of x-ray photoelectron spectroscopy for defined technetium compounds. It was evidenced that all reduction/evaporation procedures yielded 99mTc(IV)-halide complexes. Another technique of reduction by vapours of halogen acids was proposed to prepare thin radioactive sources for physics studies. The reduction power of alkali halides in absence of acids was examined and a partial reduction of pertechnetate by iodide was found. The product was a hydrolysed species. The hydrolysis of halide complexes yielded the same product. In the absence of acids, dissolved species were partly oxidised to Tc(VII) by air. Oxidation was most apparent for the chloride and negligible for the iodide system. Ligand exchange of chloro and bromo complexes to chelate with DTPA at pH 3 was found to be uncomplete. Tc(IV) hydrolysed species, Tc(IV)DTPA and Tc(VII) were evidenced. Tc(V)DTPA was also observed which arises from partially oxidised products. (author)

  2. The effect of doses, irradiation temperature, and doped impurities in the thermoluminescence response of NaCl crystals

    International Nuclear Information System (INIS)

    The interactions between ionizing gamma-radiation and two alkali halide single crystals, NaCl doped with Cd2+ (0.5 mol %) or Mn2+ (0.087 mol %), were analyzed for their possible use as low dose dosimeters. For that purpose, two irradiation temperatures (298 K and 77 K) and different doses at a fix dose rate were studied. The irradiated crystals were analyzed using their thermoluminescence and optical absorption properties. The F-centers formed in these crystals were measured as a function of the dose. The production of irradiation defects in the solid were correlated with the glow curve. Bleaching the F-centers produced a decrease in the peak of the glow curve, suggesting that F centers are intimately involved in the production of the thermoluminescence phenomenon. For the NaCl crystals doped with Cd, the area under the peak observed in the glow curves (associated to very deep traps) changes uniformly in the 1.15–13.8 Gy dose intervals, making this crystal a candidate for use as a dosimeter in low dose intervals. -- Highlights: ? The gamma irradiation of single crystals of NaCl doped with Cd or Mn were studied. ? The bleaching of the F-centers produced a decrease of the peak of the glow curve. ? Crystals of NaCl:Cd can be use as a dosimeter at low radiation doses

  3. Halide Ion Enhancement of Nitrate Ion Photolysis

    Science.gov (United States)

    Richards, N. K.; Wingen, L. M.; Callahan, K. M.; Tobias, D. J.; Finlayson-Pitts, B. J.

    2009-12-01

    Nitrate ion photochemistry is an important source of NOx in the polar regions. It is uncertain whether coexisting ions such as halides play a role in nitrate photochemistry. The effect of halides on NO3 photolysis was investigated using photolysis experiments in 230 L Teflon chambers that contain deliquesced aerosols of NaBr:NaNO3, KBr:KNO3 and ternary mixtures of NaCl:NaBr:NaNO3. Gas phase NO2 and gaseous halogen products were measured as a function of photolysis time using long path FTIR, NOx chemiluminescence and API-MS (atmospheric pressure ionization mass spectrometry). Experiments were conducted with NO3- held at a constant 0.5 M and with the amount of total halide concentration varying from 0.25 M to 4 M. Studies on NaBr:NaNO3 mixtures suggest that as the bromide ion to nitrate ion ratio increases, there is an enhancement in the rate of production of NO2 in the nitrate-bromide mixtures over that formed in the photolysis of NaNO3. Molecular dynamic (MD) simulations provide molecular level insight into the ions near the air-water interface in the aqueous halide-nitrate mixtures. These studies suggest that the presence of sodium halides at the air-water interface may encourage some nitrate ions to approach the top layers of water, allowing for more efficient escape of photoproducts than is seen in the absence of halides. Experiments on mixtures of KBr:KNO3 are being conducted to determine potential cation effects. In addition, ternary mixtures of NaCl:NaBr:NaNO3 are being examined to determine the effects of mixtures of halides on production of NO2 and gaseous halogen products. The implications of this photochemistry for tropospheric chemistry will be discussed.

  4. Double-Diffusive Convection During Growth of Halides and Selenides

    Science.gov (United States)

    Singh, N. B.; Su, Ching-Hua; Duval, Walter M. B.

    2015-01-01

    Heavy metal halides and selenides have unique properties which make them excellent materials for chemical, biological and radiological sensors. Recently it has been shown that selenohalides are even better materials than halides or selenides for gamma-ray detection. These materials also meet the strong needs of a wide band imaging technology to cover ultra-violet (UV), midwave infrared wavelength (MWIR) to very long wavelength infrared (VLWIR) region for hyperspectral imager components such as etalon filters and acousto-optic tunable filters (AO). In fact AOTF based imagers based on these materials have some superiority than imagers based on liquid crystals, FTIR, Fabry-Perot, grating, etalon, electro-optic modulation, piezoelectric and several other concepts. For example, broadband spectral and imagers have problems of processing large amount of information during real-time observation. Acousto-Optic Tunable Filter (AOTF) imagers are being developed to fill the need of reducing processing time of data, low cost operation and key to achieving the goal of covering long-wave infrared (LWIR). At the present time spectral imaging systems are based on the use of diffraction gratings are typically used in a pushbroom or whiskbroom mode. They are mostly used in systems and acquire large amounts of hyperspectral data that is processed off-line later. In contrast, acousto-optic tunable filter spectral imagers require very little image processing, providing new strategies for object recognition and tracking. They are ideally suited for tactical situations requiring immediate real-time image processing. But the performance of these imagers depends on the quality and homogeneity of acousto-optic materials. In addition for many systems requirements are so demanding that crystals up to sizes of 10 cm length are desired. We have studied several selenides and halide crystals for laser and AO imagers for MWIR and LWIR wavelength regions. We have grown and fabricated crystals of several materials such as mercurous chloride, mercurous bromide, mercurous iodide, lead chloride lead bromide, lead iodide, thallium arsenic selenide, gallium selenide, zince sulfide zinc selenide and several crystals into devices. We have used both Bridgman and physical vapor transport (PVT) crystal growth methods. In the past have examined PVT growth numerically for conditions where the boundary of the enclosure is subjected to a nonlinear thermal profile. Since past few months we have been working on binary and ternary materials such as selenoiodides, doped zinc sulfides and mercurous chloro bromide and mercurous bromoiodides. In the doped and ternary materials thermal and solutal convection play extremely important role during the growth. Very commonly striations and banding is observed. Our experiments have indicated that even in highly purified source materials, homogeneity in 1-g environment is very difficult. Some of our previous numerical studies have indicated that gravity level less than 10-4 (?-g) helps in controlling the thermosolutal convection. We will discuss the ground based growth results of HgClxBr(1-x) and ZnSe growth results for the mm thick to large cm size crystals. These results will be compared with our microgravity experiments performed with this class of materials. For both HgCl-HgBr and ZnS-ZnSe the lattice parameters of the mixtures obey Vagard's law in the studied composition range. The study demonstrates that properties are very anisotropic with crystal orientation, and performance achievement requires extremely careful fabrication to utilize highest figure of merit. In addition, some parameters such as crystal growth fabrication, processing time, resolution, field of view and efficiency will be described based on novel solid solution materials. It was predicted that very similar to the pure compounds solid solutions also have very large anisotropy, and very precise oriented and homogeneous bulk and thin film crystals is required to achieve maximum performance of laser or imagers. Some of the parameters controlling the homogeneity su

  5. Alkali oxide-tantalum oxide and alkali oxide-niobium oxide ionic conductors

    Science.gov (United States)

    Roth, R. S.; Parker, H. S.; Brower, W. S.; Minor, D.

    1974-01-01

    A search was made for new cationic conducting phases in alkali-tantalate and niobate systems. The phase equilibrium diagrams were constructed for the six binary systems Nb2O5-LiNbO3, Nb2O5-NaNbO3, Nb2O5-KNbO3, Ta2O5-NaTaO3, Ta2O5-LiTaO3, and Ta2O5-KTaO3. Various other binary and ternary systems were also examined. Pellets of nineteen phases were evaluated (by the sponsoring agency) by dielectric loss measurements. Attempts were made to grow large crystals of eight different phases. The system Ta2O5-KTaO3 contains at least three phases which showed peaks in dielectric loss vs. temperature. All three contain structures related to the tungsten bronzes with alkali ions in non-stoichiometric crystallographic positions.

  6. Harmonic dynamical behaviour of thallous halides

    Indian Academy of Sciences (India)

    Sarvesh K Tiwari; L J Shukla; K S Upadhyaya

    2010-05-01

    Harmonic dynamical behaviour of thallous halides (TlCl and TlBr) have been studied using the new van der Waals three-body force shell model (VTSM), which incorporates the effects of the van der Waals interaction along with long-range Coulomb interactions, three-body interactions and short-range second neighbour interactions in the framework of rigid shell model (RSM). Phonon dispersion curves (PDC), variations of Debye temperature with absolute temperature and phonon density of state (PDS) curves have been reported for thallous halides using VTSM. Comparison of experimental values with those of VTSM and TSM are also reported in the paper and a good agreement between experimental and VTSM values has been found, from which it may be inferred that the incorporation of van der Waals interactions is essential for the complete harmonic dynamical behaviour of thallous halides.

  7. Effect of temperature on non-destructive wave propagation in potassium halides

    International Nuclear Information System (INIS)

    Temperature dependence of ultrasonic attenuation is investigated for potassium halides in the temperature range 100-400 K. These calculations are done for KCl, KBr and KI for longitudinal and shear waves along the ?1 1 1? direction. The non-linearity coupling parameters and thermal relaxation time have also been obtained for these crystals. In the present investigation, it has been found that phonon-phonon interaction is the dominant cause for ultrasonic attenuation.

  8. Syntheses, crystal structures, magnetic properties and vibrational spectra of nitridoborate-halide compounds Sr2[BN2]Br and Eu2[BN2]X (X = Br, I) with isolated [BN2]3- units

    International Nuclear Information System (INIS)

    The title compounds Sr2[BN2]Br (1), Eu2[BN2]Br (2) and Eu2[BN2]I (3) were obtained from reactions of mixtures of Sr3[BN2]2 and SrBr2 (1) and the binaries EuN, h-BN and EuX2 (X = Br, I) (2, 3), respectively. The crystal structure of Sr2[BN2]Br was solved from X-ray powder diffraction data and those of the europium compounds from X-ray single crystal data. Sr2[BN2]Br and Eu2[BN2]Br are isotypic crystallizing in the rhombohedral space group R anti 3m (No. 166, Pearson code: hR18; Z = 3; a = 4.11692(2) A, c = 26.4611(2) A (1); a = 4.0728(3) A, c = 26.589(3) A (2)). The crystal structures are built up by layers of condensed edge-sharing [B - N - B] rate at Eu6 and [Br] rate at Eu6 trigonal antiprisms, which are alternately stacked along [001]. Eu2[BN2]I - isotypic to Sr2[BN2]I - crystallizes in the monoclinic space group P21/m (No. 11, Pearson code: mP24; Z = 4; a = 10.2548(6) A, b = 4.1587(3) A, c = 13.1234(9) A, ? = 91.215(4) ). The crystal structure is characterized by slightly puckered layers formed by condensed edge sharing I rate at Eu6 octahedra which are separated by isolated [BN2]3- units. The bond lengths for the strictly linear [BN2]3- anions in (1) and (2) are d(B-N) = 1.351(4) A and 1.356(8) A, respectively. In Eu2[BN2]I two crystallographically distinct [BN2]3- anions are present with d(B1-N) = 1.32(4) A, 1.37(4) A and d(B2-N) = 1.30(4) A, 1.34(4) A, respectively. Their bond angles vary slightly: angle (N - B1 -N) = 179(3) and angle (N - B2 - N) = 177(3) . The magnetic susceptibility data of the europium compounds (2) and (3) indicate that the Eu ions are divalent with 4f7 configuration. Vibrational spectra were measured and interpreted based on the D?h symmetry of the discrete linear [N - B - N]3- moieties, considering the site symmetry reduction and the presence of two distinct [BN2]3- groups in (3). (orig.)

  9. New ternary transplutonium compounds: chalcogenide halides

    International Nuclear Information System (INIS)

    Although chalcogenide halides have been identified in almost all groups of the Periodic Table, they were previously unknown in the case of the actinide elements. Based on the known lanthanide chalcogenide halides, they focused their investigation on the sulfur-based compounds. Consistent with the scarcity of transplutonium elements, they developed an original microscale preparation of the ternary compounds AnSI (An = 242Pu, 243Am, 248Cm). The reaction scheme is: An2O3 (or AnO2) ? AnBr3 ?AnI3 ? AnSI. All products are examined by X-ray powder diffraction and solid state spectroscopy

  10. Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites

    Science.gov (United States)

    Yakunin, Sergii; Protesescu, Loredana; Krieg, Franziska; Bodnarchuk, Maryna I.; Nedelcu, Georgian; Humer, Markus; de Luca, Gabriele; Fiebig, Manfred; Heiss, Wolfgang; Kovalenko, Maksym V.

    2015-08-01

    Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcrystalline, thin-film and bulk single-crystalline metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from ~10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temperature optical amplification can be obtained in the entire visible spectral range (440-700 nm) with low pump thresholds down to 5+/-1 ?J cm-2 and high values of modal net gain of at least 450+/-30 cm-1. Two kinds of lasing modes are successfully observed: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals.

  11. Theory of Hydrogen Migration in Organic-Inorganic Halide Perovskites.

    Science.gov (United States)

    Egger, David A; Kronik, Leeor; Rappe, Andrew M

    2015-10-12

    Solar cells based on organic-inorganic halide perovskites have recently been proven to be remarkably efficient. However, they exhibit hysteresis in their current-voltage curves, and their stability in the presence of water is problematic. Both issues are possibly related to a diffusion of defects in the perovskite material. By using first-principles calculations based on density functional theory, we study the properties of an important defect in hybrid perovskites-interstitial hydrogen. We show that differently charged defects occupy different crystal sites, which may allow for ionization-enhanced defect migration following the Bourgoin-Corbett mechanism. Our analysis highlights the structural flexibility of organic-inorganic perovskites: successive iodide displacements, combined with hydrogen bonding, enable proton diffusion with low migration barriers. These findings indicate that hydrogen defects can be mobile and thus highly relevant for the performance of perovskite solar cells. PMID:26073061

  12. Electric field effects on alanine tripeptide in sodium halide solutions.

    Science.gov (United States)

    Astrakas, Loukas G; Gousias, Christos; Tzaphlidou, Margaret

    2015-12-01

    The electric field effects on conformational properties of trialanine in different halide solutions were explored with long-scale molecular dynamics simulations. NaF, NaCl, NaBr and NaI solutions of low (0.2?M) and high (2?M) concentrations were exposed to a constant electric field of 1000?V/m. Generally, the electric field does not disturb trialanine's structure. Large structural changes appear only in the case of the supersaturated 2.0?M NaF solution containing NaF crystals. Although the electric field affects in a complex way, all the ions-water-peptide interactions, it predominantly affects the electroselectivity effect, which describes specific interactions such as the ion-pair formation. PMID:25006865

  13. Theory of Hydrogen Migration in Organic–Inorganic Halide Perovskites**

    Science.gov (United States)

    Egger, David A; Kronik, Leeor; Rappe, Andrew M

    2015-01-01

    Solar cells based on organic–inorganic halide perovskites have recently been proven to be remarkably efficient. However, they exhibit hysteresis in their current–voltage curves, and their stability in the presence of water is problematic. Both issues are possibly related to a diffusion of defects in the perovskite material. By using first-principles calculations based on density functional theory, we study the properties of an important defect in hybrid perovskites—interstitial hydrogen. We show that differently charged defects occupy different crystal sites, which may allow for ionization-enhanced defect migration following the Bourgoin–Corbett mechanism. Our analysis highlights the structural flexibility of organic–inorganic perovskites: successive iodide displacements, combined with hydrogen bonding, enable proton diffusion with low migration barriers. These findings indicate that hydrogen defects can be mobile and thus highly relevant for the performance of perovskite solar cells. PMID:26073061

  14. Band gap expansion, shear inversion phase change behaviour and low-voltage induced crystal oscillation in low-dimensional tin selenide crystals.

    Science.gov (United States)

    Carter, Robin; Suyetin, Mikhail; Lister, Samantha; Dyson, M Adam; Trewhitt, Harrison; Goel, Sanam; Liu, Zheng; Suenaga, Kazu; Giusca, Cristina; Kashtiban, Reza J; Hutchison, John L; Dore, John C; Bell, Gavin R; Bichoutskaia, Elena; Sloan, Jeremy

    2014-05-28

    In common with rocksalt-type alkali halide phases and also semiconductors such as GeTe and SnTe, SnSe forms all-surface two atom-thick low dimensional crystals when encapsulated within single walled nanotubes (SWNTs) with diameters below ?1.4 nm. Whereas previous density functional theory (DFT) studies indicate that optimised low-dimensional trigonal HgTe changes from a semi-metal to a semi-conductor, low-dimensional SnSe crystals typically undergo band-gap expansion. In slightly wider diameter SWNTs (?1.4-1.6 nm), we observe that three atom thick low dimensional SnSe crystals undergo a previously unobserved form of a shear inversion phase change resulting in two discrete strain states in a section of curved nanotube. Under low-voltage (i.e. 80-100 kV) imaging conditions in a transmission electron microscope, encapsulated SnSe crystals undergo longitudinal and rotational oscillations, possibly as a result of the increase in the inelastic scattering cross-section of the sample at those voltages. PMID:24637546

  15. The influence of Halide and pseudo-Halide antioxidants in Fenton-like reaction systems

    OpenAIRE

    Malesic, J.; Kolar, J.; Strlic, M.; Polanc, S.

    2006-01-01

    An application of the N,N'-(5-nitro-1,3-phenylene) bisglutaramide (NPG) hydroxylation assay for spectrophotometric determination of the rate of oxidising species generation in Fenton-like systems in the presence of halide and pseudo-halide antioxidants was evaluated. Using ion chromatography it was demonstrated that the concentration of antioxidants did not decrease during the course of the experiment. Although the stoichiometry was not constant, determination of the rate constant of NPG hydr...

  16. Reactivity of perfluoroalkyl halides towards nucleophiles

    International Nuclear Information System (INIS)

    The method of cyclic voltammetry was employed for the study and comparative evaluation of reactivity of perfluoroalkyl iodides and arylperfluoroalkyliodonium salts towards nucleophiles in various solvents. The method suggested can be used for predicting the reactivity of perfluoroalkyl halides in reactions proceeding according to the SRN1 mechanism. 16 refs., 3 figs., 4 tabs

  17. Unraveling halide hydration: A high dilution approach

    International Nuclear Information System (INIS)

    The hydration properties of halide aqua ions have been investigated combining classical Molecular Dynamics (MD) with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Three halide-water interaction potentials recently developed [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)], along with three plausible choices for the value of the absolute hydration free energy of the proton (?Ghyd?[H+]), have been checked for their capability to properly describe the structural properties of halide aqueous solutions, by comparing the MD structural results with EXAFS experimental data. A very good agreement between theory and experiment has been obtained with one parameter set, namely LE, thus strengthening preliminary evidences for a ?Ghyd?[H+] value of ?1100 kJ mol?1 [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)]. The Cl?, Br?, and I? ions have been found to form an unstructured and disordered first hydration shell in aqueous solution, with a broad distribution of instantaneous coordination numbers. Conversely, the F? ion shows more ordered and defined first solvation shell, with only two statistically relevant coordination geometries (six and sevenfold complexes). Our thorough investigation on the effect of halide ions on the microscopic structure of water highlights that the perturbation induced by the Cl?, Br?, and I? ions does not extend beyond the ion first hydration shell, and the structure of water in the F? second shell is also substantially unaffected by the ion

  18. Compounds of alkali metal anions

    Energy Technology Data Exchange (ETDEWEB)

    Dye, J.L.

    1979-01-01

    Anions of sodium, potassium, rubidium, and cesium are stable both in suitable solvents and in crystalline solids. The latter can be prepared either by cooling a saturated solution or by rapid solvent evaporation. Thermodynamic arguments show that alkali metal anions can probably exist in saturated solutions of the alkali metals in any compatible solvent, but that below saturation, dissociation into the cation and solvated electrons is favored in highly polar solvents such as ammonia. The key to solvent-free salts of the alkali metal anions is stabilization of the cation by incorporation into a suitable crown or cryptand complex. By using such complexes it also appears possible to produce electride salts in which the charge of the complexed cation is balanced by a trapped electron. The chemical, electrical, and optical properties of salts of the alkali metal anions and electrides could provide useful applications. 83 references.

  19. Synthesis, characterization and thermal properties of small R 2 R '2N+ X --type quaternary ammonium halides

    International Nuclear Information System (INIS)

    Twenty-one R 2 R '2N+ X - -type (R=methyl or ethyl, R '=alkyl, X=Br or I) quaternary ammonium (QA) halides have been prepared by using a novel one-pot synthetic route in which a formamide (dimethyl-, diethylformamide, etc.) is treated with alkyl halide in the presence of sodium or potassium carbonate. The formation of QA halides was verified with 1H-NMR, 13C-NMR, MS and elemental analysis. The crystal structures of four QA halides (two bromide and two iodide) were determined using X-ray single crystal diffraction, and the powder diffraction method was used to study the structural similarities between the single crystal and microcrystalline bulk material. The thermal properties of all compounds were studied using TG/DTA and DSC methods. The smallest compounds decomposed during or before melting. The decreasing trend of melting points was observed when the alkyl chain length was increased. The liquid ranges of 120-180 deg. C were observed for compounds with 5-6 carbon atoms in the alkyl chain. The low melting points and wide liquid ranges suggest potential applicability of these compounds for example as ionic liquids precursors

  20. Barium halide nanocrystals in fluorozirconate based glass ceramics for scintillation application

    International Nuclear Information System (INIS)

    Europium (Eu)-activated barium halide nanocrystals in fluorozirconate based glass ceramics represent a promising class of Xray scintillators. The scintillation in these glass ceramics is mainly caused by the emission of divalent Eu incorporated in hexagonal BaCl2 nanocrystals which are formed in the glass matrix upon appropriate annealing. Experiments with cerium (Ce)-activated fluorozironate glass ceramics showed that Ce is an interesting alternative. In order to get a better understanding of the scintillation mechanism in Eu- or Ce-activated barium halide nanocrystals, an investigation of the processes in the corresponding bulk material is essential. The objective of this thesis is the investigation of undoped, Eu-, and Ce-doped barium halides by X-ray excited luminescence (XL), pulse height, and scintillation decay spectra. That will help to figure out which of these crystals has the most promising scintillation properties and would be the best nanoparticles for the glass ceramics. Furthermore, alternative dopants like samarium (Sm) and manganese (Mn) were also investigated. Besides the above-mentioned optical investigation electron paramagnetic resonance (EPR) and Moessbauer measurements were carried out in order to complete the picture of Eu-doped barium halides. The EPR data of Eu-doped BaI2 is anticipated to yield more information about the crystal field and crystal structure that will help to understand the charge carrier process during the scintillation process. The main focus of the Moessbauer investigations was set on the Eu-doped fluorochlorozirconate glass ceramics. The results of this investigation should help to improve the glass ceramics. The Eu2+/Eu3+ ratio in the glass ceramics should be determined and optimize favor of the Eu2+. We also want to distinguish between Eu2+ in the glass matrix and Eu2+ in the nanocrystals. For a better understanding of Moessbauer spectroscopy on Eu also measurements on Eu in a CaF2 host lattice were carried out. (orig.)

  1. Thermodynamic properties of pure and dilute alkali cyanides: short range order effects

    International Nuclear Information System (INIS)

    The alkali-cyanides NaCN and KCN, both pure and mixed in alkali-halides are studied, in the low temperature phases (paraelectric and antiferroelectric). Experimental results on the dielectric properties of these systems indicate that short-range order effects are important. These effects are investigated using the Kikuchi method in the limit of the pair correlation approximation (Bethe approximation). The results for the temperature dependence of the dielectric constant, for the pure systems, are adjusted to the experimental data available to obtain the three relevant parameters of the model: coordination number, coupling interaction and electric dipole moment of the CN- molecular ion. This parametrization is used in the study of the dielectric constants of the mixed systems and the critical temperature as a function of the CN- dipole concentration is obtained. The results are in good qualitative agreement with the experimental ones. (Author)

  2. New hypodiphosphates of the alkali metals: Synthesis, crystal structure and vibrational spectra of the hypodiphosphates(IV) M{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] (M=Rb and Cs)

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Peng [Institut fuer Anorganische und Analytische Chemie der TU Clausthal, Paul-Ernst-Strasse 4, D-38678 Clausthal-Zellerfeld (Germany); Wiegand, Thomas; Eckert, Hellmut [Institut fuer Physikalische Chemie and Graduate School of Chemistry, Westfaelische Wilhelms-Universitaet Muenster, Corrensstr. 28/30, D-48149 Muenster (Germany); Gjikaj, Mimoza, E-mail: mimoza.gjikaj@tu-clausthal.de [Institut fuer Anorganische und Analytische Chemie der TU Clausthal, Paul-Ernst-Strasse 4, D-38678 Clausthal-Zellerfeld (Germany)

    2012-10-15

    The new hypodiphosphates(IV) Rb{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] (1) and Cs{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] (2) were synthesized by soft chemistry reactions from aqueous solutions of hypophosphoric acid and the corresponding heavy alkali-metal carbonates. Their crystal structures were determined by single crystal X-ray diffraction. Both compounds crystallize isotypic in the triclinic space group P-1 with one formula unit in the unit cell. The structures are built up by discrete (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) units in staggered conformation for the P{sub 2}O{sub 6} skeleton and the corresponding alkali-metal cations. In the (H{sub 2}P{sub 2}O{sub 6}){sup 2-} ion the hydrogen atoms are in a 'trans-trans' conformation. O{center_dot}H-O hydrogen bonds between the (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) groups consolidate the structures into a three-dimensional network. The FT-Raman and {sup 31}P and {sup 1}H and MAS NMR spectra of the title compounds have been recorded and interpreted, especially with respect to their assignment to the (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) groups. Thermogravimetric data of 2 have been interpreted in terms of a thermal decomposition model. - Graphical Abstract: The layered compounds Rb{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] and Cs{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] have been synthesized and investigated. Both crystallize isotypic. The structures are built up by discrete (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) units and the corresponding alkali-metal cations. Highlights: Black-Right-Pointing-Pointer Synthesis and single-crystal structure of new alkali hypodiphosphates. Black-Right-Pointing-Pointer Structures are characterized by [(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})]{sup 2-} units and M{sup +} cations. Black-Right-Pointing-Pointer (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) units are linked by short hydrogen bonds. Black-Right-Pointing-Pointer Both compounds are characterized by {sup 31}P MAS-NMR spectra.

  3. A generalized rule of average for glow peak temperature of ternary alkali halide systems

    Directory of Open Access Journals (Sweden)

    G. Moroyoqui-Estrella

    2011-01-01

    Full Text Available Se estudia la dependencia de la temperatura en la curva de brillo con la composición de los aniones en mezclas cristalinas impurificadas con Europio: KCl0.50KBr0.25RbX0.25:Eu2+ (X = Cl, Br. Cada material muestra una curva de brillo termoluminiscente consistente en dos picos de brillo principales con temperatura entre la del KCl:Eu2+ y la del KBr:Eu2+. El pico más intenso está relacionado con la destrucción del centro F, como ocurre en el caso de cristales de KCl:Eu2+ y su temperatura característica depende fuertemente de la composición del halogeno. El comportamiento confirma que la temperatura de la recombinación de los centros F-H en este tipo de materiales depende en gran medida de la proporción de los aniones. De estos resultados se propone una regla generalizada para obtener la temperatura, promediando la temperatura característica en función de la composición.

  4. Nearest neighbors EPR superhyperfine interaction in divalent iridium complexes in alkali halide host lattice

    International Nuclear Information System (INIS)

    Further splitting of chlorine superhyperfine lines on the EPR spectrum of the [Ir (CN)4 Cl2]4- molecular species in NaCl latice indicates a super-superhyperfine interaction with the nearest neighbors sodium atoms. (Author)

  5. Reduction of Methylene Blue and related dyes by gamma-irradiated alkali halides

    International Nuclear Information System (INIS)

    A spectrophotometric study is reported of the reduction of some dyes with methylene blue structure used in bacteriological staining. The reduction is effected by the species liberated during the dissolution of γ-irradiated sodium chloride. The G values for the two modes of the reduction are compared and the effects of radical scavengers on the reactions are studied. Results are found to be similar to the chemically and biologically induced reduction. The dyes studied include, in addition to Methylene Blue, Janus Green B and Nile Blue sulfate. (author) 9 refs.; 5 figs.; 2 tabs

  6. Inelastic light scattering of the VK- and H-centre in alkali halides

    OpenAIRE

    Goovaerts, E.; De Schepper, L.; Schoemaker, D.

    1980-01-01

    The inelastic light scattering of the VK-centre was measured in LiF, KCl and RbCl. The spectra consist of a single peak at 437 cm-1 of the laser frequency in LiF, at 241 cm-1 in KCl and at 244 cm-1 in RbCl [1]. The raman active fundamental mode of the X-2 molecule (X- : halogen ion) induces the inelastic light scattering, as is seen by comparison with calculated data on the free X-2 molecules [2] as well as with measured frequencies of analogous systems. A tentative calculation of the frequen...

  7. Interaction of the model alkyltrimethylammonium ions with alkali halide salts: an explicit water molecular dynamics study

    Directory of Open Access Journals (Sweden)

    M. Druchok

    2013-01-01

    Full Text Available We present an explicit water molecular dynamics simulation of dilute solutions of model alkyltrimethylammonium surfactant ions (number of methylene groups in the tail is 3, 5, 8, 10, and 12 in mixture with NaF, NaCl, NaBr, and NaI salts, respectively. The SPC/E model is used to describe water molecules. Results of the simulation at 298 K are presented in form of the radial distribution functions between nitrogen and carbon atoms of CH2 groups on the alkyltrimethylammonium ion, and the counterion species in the solution. The running coordination numbers between carbon atoms of surfactants and counterions are also calculated. We show that I- counterion exhibits the highest, and F- the lowest affinity to "bind" to the model surfactants. The results are discussed in view of the available experimental and simulation data for this and similar solutions.

  8. Role of Farben centers in electron- and photon-stimulated desorption from alkali halides

    International Nuclear Information System (INIS)

    Measurements of the time history of ground-state neutral lithium desorption from LiF during pulsed electron irradiation have resulted in a new model for the lithium-desorption mechanism. We show that the slow diffusion to the surface of bulk Farben (F) centers created by the electron-beam is the rate-controlling factor responsible for most of the time history of the lithium desorption rather than the thermal evaporation of the metal from the surface. Comparison between theoretical and experimental time dependencies yields values for the F center diffusion constant and its activation energy

  9. Structure and electric resistivity of dilute solutions of potassium halides in molten potassium

    International Nuclear Information System (INIS)

    The change in electric resistivity due to the addition of potassium halides to liquid potassium is calculated at high dilution within the Faber-Ziman scheme. The relevant structure factors of the dilute solution are evaluated by an electron-ion plasma model previously developed for the liquid alkali metals and their alloys. The halogen ion is found to form a rather well-define co-ordination shell of potassium ions, and these ''clusters'' are an important source of extra resistivity in the solution. Another sizeable contribution arises from the change in density relative to the pure metal. The numerical results for the change in resistivity are in good agreement with experimental data, and in particular, its observed dependence on the size of the halogen ion is reproduced by the theory. (author)

  10. Structure and bonding in metal-rich compounds: pnictides, chalcides and halides

    International Nuclear Information System (INIS)

    The subject is reviewed under the following headings: introduction (compounds included in the review; purpose of the review); MX compounds with M = transition metal and X = O,N,S or P; sulfides and selenides of the transition metals; transition-metal phosphides; alkali oxides; transition-metal oxides and nitrides with X/M < 1; metal-rich halides; conclusion. The references number 238. Compounds of the following principal elements of nuclear interest are included in the tables and text: Am, Ce, Cs, Eu, Gd, Hf, La, Mo, Np, Nb, Pu, Pr, Pa, Re, Ru, Sc, Ta, Tb, Th, W, U, V, Y, Zr. The information in the tables is presented under: structure type, space group, lattice parameters and remarks. (U.K.)

  11. Factors affecting alkali jarosite precipitation

    Science.gov (United States)

    Dutrizac, J. E.

    1983-12-01

    Several factors affecting the precipitation of the alkali jarosites (sodium jarosite, potassium jarosite, rubidium jarosite, and ammonium jarosite) have been studied systematically using sodium jarosite as the model. The pH of the reacting solution exercises a major influence on the amount of jarosite formed, but has little effect on the composition of the washed product. Higher temperatures significantly increase the yield and slightly raise the alkali content of the jarosites. The yield and alkali content both increase greatly with the alkali concentration to about twice the stoichiometric requirement but, thereafter, remain nearly constant. At 97 °C, the amount of product increases with longer retention times to about 15 hours, but more prolonged reaction times are without significant effect on the amount or composition of the jarosite. Factors such as the presence of seed or ionic strength have little effect on the yield or jarosite composition. The amount of precipitate augments directly as the iron concentration of the solution increases, but the product composition is nearly independent of this variable. A significant degree of agitation is necessary to suspend the product and to prevent the jarosite from coating the apparatus with correspondingly small yields. Once the product is adequately suspended, however, further agitation is without significant effect. The partitioning of alkali ions during jarosite precipitation was ascertained for K:Na, Na:NH4, K:NH4, and K:Rb. Potassium jarosite is the most stable of the alkali jarosites and the stability falls systematically for lighter or heavier congeners; ammonium jarosite is slightly more stable than the sodium analogue. Complete solid solubility among the various alkali jarosite-type compounds was established.

  12. Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies.

    Science.gov (United States)

    Bekenstein, Yehonadav; Koscher, Brent A; Eaton, Samuel W; Yang, Peidong; Alivisatos, A Paul

    2015-12-30

    Anisotropic colloidal quasi-two-dimensional nanoplates (NPLs) hold great promise as functional materials due to their combination of low dimensional optoelectronic properties and versatility through colloidal synthesis. Recently, lead-halide perovskites have emerged as important optoelectronic materials with excellent efficiencies in photovoltaic and light-emitting applications. Here we report the synthesis of quantum confined all inorganic cesium lead halide nanoplates in the perovskite crystal structure that are also highly luminescent (PLQY 84%). The controllable self-assembly of nanoplates either into stacked columnar phases or crystallographic-oriented thin-sheet structures is demonstrated. The broad accessible emission range, high native quantum yields, and ease of self-assembly make perovskite NPLs an ideal platform for fundamental optoelectronic studies and the investigation of future devices. PMID:26669631

  13. Properties of Ce-activated alkali-lutetium double phosphate scintillators

    Energy Technology Data Exchange (ETDEWEB)

    Wi?niewski, D. [Institute of Physics, Nicolaus Copernicus University, Toru?, Poland; Wojtowicz, A. J. [Institute of Physics, Nicolaus Copernicus University, Toru?, Poland; Boatner, Lynn A [ORNL

    2010-01-01

    The scintillation properties of Ce-activated alkali-lutetium double phosphate single crystals that vary with the alkali ion type and activation level are summarized and compared. The materials investigated here have been identified as fast and efficient scintillators for the detection of x-ray and radiation, and in case of Li3Lu(PO4)2:Ce, for thermal neutron detection as well.

  14. Computer calculations of stability of C{sub 70} fullerene intercalated by alkali metals

    Energy Technology Data Exchange (ETDEWEB)

    Fabianski, R.; Kuchta, B. [Politechnika Wroclawska, Wroclaw (Poland). Inst. Chemii Fizycznej i Teoretycznej; Firlej, L. [Groupe de Dynamique des Phases Condensees, Universite Montpellier II, Montpellier (France)

    2000-03-01

    Calculations of the energy of alkali atoms placed in tetrahedral and octahedral voids in the fcc crystal lattice of C{sub 70} are presented. A comparison of stabilities of intercalated C{sub 60} and C{sub 70} has been done. An existence of the off-centre positions in the octahedral voids has been shown and discussed. A path of diffusion of alkali atoms (ions) into C{sub 70} structure has been proposed. (orig.)

  15. Computational Screening of Mixed Metal Halide Ammines

    DEFF Research Database (Denmark)

    Jensen, Peter Bjerre; Lysgaard, Steen

    Metal halide ammines, e.g. Mg(NH3)6Cl2 and Sr(NH3)8Cl2, can reversibly store ammonia, with high volumetric hydrogen storage capacities. In this project we are searching for improved mixed materials with optimal desorption temperature and kinetics. We apply DFT calculations on mixed compounds selected by a Genetic Algorithm (GA), relying on biological principles of natural selection. The GA is evolving from an initial (random) population and selecting those with highest fitness, e.g. stability, release temperature and storage capacity. The search space includes all alkaline, alkaline earth, 3d and 4d metals and the four lightest halides, giving in total almost two million combinations.

  16. Unraveling halide hydration: A high dilution approach

    Energy Technology Data Exchange (ETDEWEB)

    Migliorati, Valentina, E-mail: valentina.migliorati@uniroma1.it; Sessa, Francesco; D’Angelo, Paola, E-mail: p.dangelo@uniroma1.it [Dipartimento di Chimica, Università di Roma “La Sapienza”, P. le A. Moro 5, 00185 Roma (Italy); Aquilanti, Giuliana [Sincrotrone Trieste S.C.p.A s.s. 14, km 163.5, I-34149 Basovizza, Trieste (Italy)

    2014-07-28

    The hydration properties of halide aqua ions have been investigated combining classical Molecular Dynamics (MD) with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Three halide-water interaction potentials recently developed [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)], along with three plausible choices for the value of the absolute hydration free energy of the proton (?G{sub hyd}{sup ?}[H{sup +}]), have been checked for their capability to properly describe the structural properties of halide aqueous solutions, by comparing the MD structural results with EXAFS experimental data. A very good agreement between theory and experiment has been obtained with one parameter set, namely L{sub E}, thus strengthening preliminary evidences for a ?G{sub hyd}{sup ?}[H{sup +}] value of ?1100 kJ mol{sup ?1} [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)]. The Cl{sup ?}, Br{sup ?}, and I{sup ?} ions have been found to form an unstructured and disordered first hydration shell in aqueous solution, with a broad distribution of instantaneous coordination numbers. Conversely, the F{sup ?} ion shows more ordered and defined first solvation shell, with only two statistically relevant coordination geometries (six and sevenfold complexes). Our thorough investigation on the effect of halide ions on the microscopic structure of water highlights that the perturbation induced by the Cl{sup ?}, Br{sup ?}, and I{sup ?} ions does not extend beyond the ion first hydration shell, and the structure of water in the F{sup ?} second shell is also substantially unaffected by the ion.

  17. Electrical conductivity of supercooled halide melts.

    Czech Academy of Sciences Publication Activity Database

    Sveshnikov, Alexey; Demo, Pavel; Kožíšek, Zden?k; Nitsch, Karel; Rodová, Miroslava

    Praha : MAXDORF s.r.o., 2002 - (Nitsch, K.; Rodová, M.), s. 51-52 ISBN 80-85912-85-8. [Joint Seminar "Development of Materials Science in Research and Education " /12./. Praha (CZ), 10.09.2002-12.09.2002] R&D Projects: GA AV ?R IAA1010010; GA ?R GA203/00/1423 Institutional research plan: CEZ:AV0Z1010914 Keywords : supercooled halide metals * electrical conductivity Subject RIV: BM - Solid Matter Physics ; Magnetism

  18. Computational screening of mixed metal halide ammines

    DEFF Research Database (Denmark)

    Jensen, Peter Bjerre; Lysgaard, Steen

    Metal halide ammines, e.g. Mg(NH3)6Cl2 and Sr(NH3)8Cl2, can reversibly store ammonia, with high volumetric hydrogen storage capacities. The storage in the halide ammines is very safe, and the salts are therefore highly relevant as a carbon-free energy carrier in future transportation infrastructure. In this project we are searching for improved mixed materials with optimal desorption temperatures and kinetics, optimally releasing all ammonia in one step. We apply Density Functional Theory, DFT, calculations on mixed compounds selected by a Genetic Algorithm (GA), relying on biological principles of natural selection. The GA is evolving from an initial (random) population and selecting those with highest fitness, a function based on e.g. stability, release temperature and storage capacity. The search space includes all alkaline, alkaline earth, 3d and 4d metals and the four lightest halides. In total the search spaces consists of millions combinations, which makes a GA ideal, to reduce the number of necessarycalculations. We are screening for a one step release from either a hexa or octa ammine, and we have found promising candidates, which will be further investigated ? both computationally and experimentally.

  19. Cerium doped lanthanum halides: fast scintillators for medical imaging

    International Nuclear Information System (INIS)

    This work is dedicated to two recently discovered scintillating crystals: cerium doped lanthanum halides (LaCl3:Ce3+ and LaBr3:Ce3+).These scintillators exhibit interesting properties for gamma detection, more particularly in the field of medical imaging: a short decay time, a high light yield and an excellent energy resolution. The strong hygroscopicity of these materials requires adapting the usual experimental methods for determining physico-chemical properties. Once determined, these can be used for the development of the industrial manufacturing process of the crystals. A proper comprehension of the scintillation mechanism and of the effect of defects within the material lead to new possible ways for optimizing the scintillator performance. Therefore, different techniques are used (EPR, radioluminescence, laser excitation, thermally stimulated luminescence). Alongside Ce3+ ions, self-trapped excitons are involved in the scintillation mechanism. Their nature and their role are detailed. The knowledge of the different processes involved in the scintillation mechanism leads to the prediction of the effect of temperature and doping level on the performance of the scintillator. A mechanism is proposed to explain the thermally stimulated luminescence processes that cause slow components in the light emission and a loss of light yield. Eventually the study of afterglow reveals a charge transfer to deep traps involved in the high temperature thermally stimulated luminescence. (author)

  20. Short-arc metal halide lamp suitable for projector application

    Science.gov (United States)

    Kawai, Kouji; Matsumoto, Masayuki

    1995-04-01

    Recently, progress has been made in the development of projectors used for large screen displays. Projection systems employing high luminous efficiency Metal Halide Lamps as a light source demonstrate unique and desirable features. For example, compared to conventional lamps, a Metal Halide Lamp has longer life, higher luminous efficiency, the shortest arc length possible, and higher color-rendering characteristics, resulting in an overall superior performance. Several lamps, including Metal Halide, Xenon, and Halogen lamps, are used in HDTV (High Definition Television). Recently, Metal Halide Lamps have become accepted as the light source of choice. The reason for this is the high brightness, color balance, and long life of the Metal Halide Lamp. The fundamental operating principal for Metal Halide Lamps is almost the same as that of Mercury lamps. A Metal Halide Lamp has very different characteristics in that, the spectrum of illumination can be varied by varying the mixture of Metal Halide generated in the lamp. For these lamps, we have improved the electrode, the chemical composition of the Metal Halide, and the glass envelope. We have achieved a longer average life (greater than 2500 hours) for a compact, single-bulb, projection-type lamp.

  1. Lanthanide doped strontium-barium cesium halide scintillators

    Science.gov (United States)

    Bizarri, Gregory; Bourret-Courchesne, Edith; Derenzo, Stephen E.; Borade, Ramesh B.; Gundiah, Gautam; Yan, Zewu; Hanrahan, Stephen M.; Chaudhry, Anurag; Canning, Andrew

    2015-06-09

    The present invention provides for a composition comprising an inorganic scintillator comprising an optionally lanthanide-doped strontium-barium, optionally cesium, halide, useful for detecting nuclear material.

  2. Corrosion by the Alkali Metals

    International Nuclear Information System (INIS)

    This is a review of the state of the art of corrosion testing of materials by the alkali metals, the models proposed to explain the observed corrosion results, and the status of materials selection for application in alkali metal-cooled systems. Corrosion of structural and fuel cladding materials by liquid Na and NaK has been studied intensively, but intermittently for the last 18 years. These studies and the liquid-metal-cooled reactors in operation demonstrate that stainless steels can be considered for structural and cladding applications below 650°C. Above this temperature increased corrosion and radiation-induced embrittlement make them unsatisfactory. Corrosion models are reviewed and their inability to explain all the experimental observations discussed. An alternate model is proposed which qualitatively is in agreement with experimental observations. In this model, the rate-controlling step is either the surface reaction of Fe with ''available oxygen'' (dissolved Na2O) to form an Fe-O-Na complex or the rate at which ''available oxygen'' can reach the surface to form the complex; which process is rate controlling depends on the temperature, Na velocity and oxygen concentration in the Na. The solution chemistry of oxygen, carbon and alkali metal-oxygen-transition metal complexes dissolved in the alkali metals is reviewed. ''Molecular'' complexes appear unlikely to exist in solution in the alkali metals, although the thermodynamic tendencies for them to form suggest that stable bonds exist in solution between oxygen, the transition and the alkali metals. The insolubility of carbon in ''oxygen-free'' sodium indicates that carbon transfer may be associated with oxygen in sodium down to very low oxygen levels, although experimental data do not generally confirm this postulate. Corrosion of refractory metals by boiling alkali metals at temperatures above 1000°C is markedly affected by impurities in either the liquid or refractory metal; the addition of Ti, Zr or Hf as ''getters'' to the refractory alloys and proper heat treatment to make the 'getter' addition react with oxygen, nitrogen, carbon and hydrogen in the alloys are required to prevent their corrosion by the alkali metals at these temperatures. (author)

  3. Origin of the 330 nm absorption band and effect of doping Yb in LiYF4 crystals

    International Nuclear Information System (INIS)

    The electronic structures of LiYF4 (YLF) crystals containing F color center (YLF-F) and Yb doped YLF crystals (Yb3+:YLF, Yb2+:YLF) are systematically studied within the framework of the density functional theory. The calculated results indicate that the 330 nm absorption band originates from the F center in YLF crystals. Thus the doping of Yb3+ can weaken the 330 nm absorption band by competing with F vacancies in capturing free electrons arising after ?-irradiation and change to Yb2. By analyzing the lattice relaxation and the electronic structure of YLF containing Yb2+, we can reasonably believe that once Yb2+ is formed in YLF crystal, its compensating hole will turn out to be shared by two F- nearest to Yb2+ forming a diatomic fluoride molecular ion (F2-) perturbed by Yb2+, or to say VF color center. According to the molecular-orbital linear combination of atomic orbital (MO-LCAOs) theory, compared to the alkali halides, e.g. LiF, the F2- in VF center in LiYF4 peaks at about 340 nm, which is in agreement with the experimental results.

  4. Origin of the 330 nm absorption band and effect of doping Yb in LiYF{sub 4} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yin Jigang [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China); Hang Yin, E-mail: yhang@siom.cn.co [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhang Lianhan [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhao Chengchun; Xiong Jing; Hu Pengchao [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China)

    2010-08-15

    The electronic structures of LiYF{sub 4} (YLF) crystals containing F color center (YLF-F) and Yb doped YLF crystals (Yb{sup 3+}:YLF, Yb{sup 2+}:YLF) are systematically studied within the framework of the density functional theory. The calculated results indicate that the 330 nm absorption band originates from the F center in YLF crystals. Thus the doping of Yb{sup 3+} can weaken the 330 nm absorption band by competing with F vacancies in capturing free electrons arising after {gamma}-irradiation and change to Yb{sup 2}. By analyzing the lattice relaxation and the electronic structure of YLF containing Yb{sup 2+}, we can reasonably believe that once Yb{sup 2+} is formed in YLF crystal, its compensating hole will turn out to be shared by two F{sup -} nearest to Yb{sup 2+} forming a diatomic fluoride molecular ion (F{sub 2}{sup -}) perturbed by Yb{sup 2+}, or to say V{sub F} color center. According to the molecular-orbital linear combination of atomic orbital (MO-LCAOs) theory, compared to the alkali halides, e.g. LiF, the F{sub 2}{sup -} in V{sub F} center in LiYF{sub 4} peaks at about 340 nm, which is in agreement with the experimental results.

  5. Probing the Catalytic Mechanism of Copper Amine Oxidase from Arthrobacter globiformis with Halide Ions.

    Science.gov (United States)

    Murakawa, Takeshi; Hamaguchi, Akio; Nakanishi, Shota; Kataoka, Misumi; Nakai, Tadashi; Kawano, Yoshiaki; Yamaguchi, Hiroshi; Hayashi, Hideyuki; Tanizawa, Katsuyuki; Okajima, Toshihide

    2015-09-18

    The catalytic reaction of copper amine oxidase proceeds through a ping-pong mechanism comprising two half-reactions. In the initial half-reaction, the substrate amine reduces the Tyr-derived cofactor, topa quinone (TPQ), to an aminoresorcinol form (TPQamr) that is in equilibrium with a semiquinone radical (TPQsq) via an intramolecular electron transfer to the active-site copper. We have analyzed this reductive half-reaction in crystals of the copper amine oxidase from Arthrobacter globiformis. Anerobic soaking of the crystals with an amine substrate shifted the equilibrium toward TPQsq in an "on-copper" conformation, in which the 4-OH group ligated axially to the copper center, which was probably reduced to Cu(I). When the crystals were soaked with substrate in the presence of halide ions, which act as uncompetitive and noncompetitive inhibitors with respect to the amine substrate and dioxygen, respectively, the equilibrium in the crystals shifted toward the "off-copper" conformation of TPQamr. The halide ion was bound to the axial position of the copper center, thereby preventing TPQamr from adopting the on-copper conformation. Furthermore, transient kinetic analyses in the presence of viscogen (glycerol) revealed that only the rate constant in the step of TPQamr/TPQsq interconversion is markedly affected by the viscogen, which probably perturbs the conformational change. These findings unequivocally demonstrate that TPQ undergoes large conformational changes during the reductive half-reaction. PMID:26269595

  6. Lanthanum halide scintillators for time-of-flight 3-D pet

    Science.gov (United States)

    Karp, Joel S. (Glenside, PA); Surti, Suleman (Philadelphia, PA)

    2008-06-03

    A Lanthanum Halide scintillator (for example LaCl.sub.3 and LaBr.sub.3) with fast decay time and good timing resolution, as well as high light output and good energy resolution, is used in the design of a PET scanner. The PET scanner includes a cavity for accepting a patient and a plurality of PET detector modules arranged in an approximately cylindrical configuration about the cavity. Each PET detector includes a Lanthanum Halide scintillator having a plurality of Lanthanum Halide crystals, a light guide, and a plurality of photomultiplier tubes arranged respectively peripherally around the cavity. The good timing resolution enables a time-of-flight (TOF) PET scanner to be developed that exhibits a reduction in noise propagation during image reconstruction and a gain in the signal-to-noise ratio. Such a PET scanner includes a time stamp circuit that records the time of receipt of gamma rays by respective PET detectors and provides timing data outputs that are provided to a processor that, in turn, calculates time-of-flight (TOF) of gamma rays through a patient in the cavity and uses the TOF of gamma rays in the reconstruction of images of the patient.

  7. ACCUMULATION OF ALKALIS IN THE RECYCLING FILTRATE OF THE PHOSPHOGYPSUM PULPS

    Directory of Open Access Journals (Sweden)

    ANTANAS KAZILIUNAS

    2011-12-01

    Full Text Available Sodium and potassium combinations existing in phosphogypsum are highly soluble and remain in the filtrate, their amount increasing with each recycle. It has been determined that the amount of alkalis in the recycling filtrate depends on an amount of alkalis in uncleaned phosphogypsum, a number of recycles in the filtrate, the technology of the phosphogypsum pulp preparation and an amount of soluble phosphates. New phosphate formations composed in an acid medium (pH = 4.5-5 are well crystalized crystals. They do not alter the filtrability of the phosphogypsum pulp. The new combinations formed in an alkaline medium (pH = 7-11 are colloidal. They settle down on the surface of the hard particles and make the filtration of the phosphogypsum pulp complicated. The filtrated phosphogypsum is more humid which causes the growth of the amount of alkalis carried out together with moisture and thus the lower alkali concentration is observed in the recycling filtrate. In the discussed case, the larger amount of soluble phosphates of uncleaned phosphogypsum is formed the larger amount of the colloidal particles in the neutralized phosphogypsum pulp which results in complicated filtration. In all the cases, the alkali concentration in the recycling filtrate approaches the maximum degree which would take place if alkalis existing in uncleaned phosphogypsum were thawed in humidity of cleaned phosphogypsum.

  8. The coacervation of aqueous solutions of tetraalkylammonium halides

    International Nuclear Information System (INIS)

    The coacervation of aqueous solutions of tatraalkylammonium halides in the presence of not of inorganic halides and acids has been studied, considering thermodynamic and spectroscopic aspects. The importance of dispersion forces as well as forces resulting from hydrophobic hydration has been assessed. The analogy between these systems and anionic ion exchange resins has been shown especially for Uranium VI extraction

  9. Growth and characterization of polycrystalline lanthanide halide scintillators

    International Nuclear Information System (INIS)

    We are exploring a novel time- and cost-efficient approach to produce robust, large-volume polycrystalline lanthanide halide scintillators using a hot wall evaporation (HWE) technique. To date, we have fabricated LaBr3:Ce and LaCl3:Ce films (slabs) measuring up to 7 cm in diameter and 7+ mm in thickness (20-25 cm3 in volume) on quartz substrates. These polycrystalline scintillators exhibit very bright emissions approaching those exhibited by their melt-grown crystal counterparts. Scanning electron micrographs (SEMs) and X-ray diffraction analysis confirm polycrystalline growth with columnar structures, both of which help in light piping, thereby contributing to the observed high light yields. The new scintillators also exhibit good energy resolution for γ-rays over the tested range of 60 keV (241Am) to 662 keV (137Cs), although they have not yet reached that of the corresponding crystals. The measured response linearity over the same energy range is comparable for both our HWE synthesized films and melt-grown commercially-available reference crystals. Similar consistency in response is also observed in terms of their decay time and afterglow behaviors. The data collected so far demonstrate that our HWE technique permits the rapid creation of scintillators with desired structural and compositional characteristics, without the introduction of appreciable defects, and yields material performance equivalent to or approaching that of crystals. Consequently, the deposition parameters may be manipulated to tailor the physical and scintillation performance of the resulting structures, while achieving a cost per unit volume that is substantially lower than that of crystals. In turn, this promises to allow the use of these novel scintillation materials in such applications as SPECT, PET, room-temperature radioisotope identification and homeland security, where large volumes of materials in a wide variety of shapes and sizes are needed. This paper describes our growth and testing of polycrystalline LaBr3:Ce scintillators and provides comparative characterizations of their performance with crystals.

  10. Water Content of Lunar Alkali Fedlspar

    Science.gov (United States)

    Mills, R. D.; Simon, J. I.; Wang, J.; Alexander, C. M. O'D.; Hauri, E. H.

    2016-01-01

    Detection of indigenous hydrogen in a diversity of lunar materials, including volcanic glass, melt inclusions, apatite, and plagioclase suggests water may have played a role in the chemical differentiation of the Moon. Spectroscopic data from the Moon indicate a positive correlation between water and Th. Modeling of lunar magma ocean crystallization predicts a similar chemical differentiation with the highest levels of water in the K- and Th-rich melt residuum of the magma ocean (i.e. urKREEP). Until now, the only sample-based estimates of water content of KREEP-rich magmas come from measurements of OH, F, and Cl in lunar apatites, which suggest a water concentration of water content of the magma ocean would have water contents of 320 ppm for the bulk Moon and 1.4 wt % for urKREEP from plagioclase in ferroan anorthosites. Results and interpretation: NanoSIMS data from granitic clasts from Apollo sample 15405,78 show that alkali feldspar, a common mineral in K-enriched rocks, can have approx. 20 ppm of water, which implies magmatic water contents of approx. 1 wt % in the high-silica magmas. This estimate is 2 to 3 orders of magnitude higher than that estimated from apatite in similar rocks. However, the Cl and F contents of apatite in chemically similar rocks suggest that these melts also had high Cl/F ratios, which leads to spuriously low water estimates from the apatite. We can only estimate the minimum water content of urKREEP (+ bulk Moon) from our alkali feldspar data because of the unknown amount of degassing that led to the formation of the granites. Assuming a reasonable 10 to 100 times enrichment of water from urKREEP into the granites produces an estimate of 100-1000 ppm of water for the urKREEP reservoir. Using the modeling of and the 100-1000 ppm of water in urKREEP suggests a minimum bulk silicate Moon water content between 2 and 20 ppm. However, hydrogen loss was likely very significant in the evolution of the lunar mantle. Conclusions: Lunar granites crystallized between 4.3-3.8 Ga from relatively wet melts that degassed upon crystallization. The formation of these granites likely removed significant amounts of water from some mantle source regions, e.g. later mare basalts predicting derivation from a mantle with water. However, this would have been a heterogeneous pro-cess based on K distribution. Thus some, if not most of the mantle may not have been devolatilized by this process; as seen by water in volcanic glasses and melt inclusions.

  11. Color separation in metal halide lamps

    Science.gov (United States)

    Stoffels, W. W.; Nimalasuriya, T.; Flikweert, A. J.; Brok, W. J. M.; Mullen, J. J. A. M.; Kroesen, G. M. W.; Haverlag, M.

    2006-10-01

    Metal halide discharge lamps are efficient lighting sources. However their widespread application is hindered by several problems. One problem is color separation. This is caused by a non-homogeneous distribution of radiating species within the lamp. It is believed to be the result of a complex interplay between diffusion and convection processes. In this contribution convection in the lamp is varied by placing the lamp in a rotating centrifuge. The resulting centrifugal force of up to ten times the normal gravitational force enhances the convection within the lamp and allows studying its effect on the color separation.

  12. Novel Ultra-Violet/Blue Optoelectronic Materials and Devices Based on Copper Halides (CuHa)

    OpenAIRE

    Cowley, A.J.

    2011-01-01

    Considerable research is being carried out in the area of wide band gap semiconductor materials for light emission applications in the UV/Blue (300-400 nm) spectral range. This project explores the novel use of the Copper Halides (CuHa), specifically γ-CuCl and γ-CuBr, I–VII wide band gap mixed ionic–electronic semiconducting materials with light emitting properties suitable for novel UV/blue light applications. This project details novel research carried out towards achieving single crystal...

  13. Mesoporous zeolite single crystals for catalytic hydrocarbon conversion

    DEFF Research Database (Denmark)

    Schmidt, I.; Christensen, C.H.; Hasselriis, Peter; Kustova, Marina; Nielsen, Michael Brorson; Dahl, Søren; Johannsen, K.; Christensen, Claus H.

    Recently, mesoporous zeolite single crystals were discovered. They constitute a novel family of materials that features a combined micropore and mesopore architecture within each individual crystal. Here, we briefly summarize recent catalytic results from cracking and isomerization of alkalies, a...

  14. Effect of alkali and heat treatments for bioactivity of TiO{sub 2} nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seo young, E-mail: mast6269@nate.com [Dept. of Dental Biomaterials and Institute of Bio degradable material, Institute of Oral Bioscience and BK21 plus project, School of Dentistry, Chonbuk National University, Jeonju, 561-756 (Korea, Republic of); Kim, Yu kyoung, E-mail: yk0830@naver.com [Dept. of Dental Biomaterials and Institute of Bio degradable material, Institute of Oral Bioscience and BK21 plus project, School of Dentistry, Chonbuk National University, Jeonju, 561-756 (Korea, Republic of); Park, Il song, E-mail: ilsong@jbnu.ac.kr [Division of Advanced Materials Engineering, Research Center for Advanced Materials Development and Institute of Biodegradable Materials, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Jin, Guang chun, E-mail: jingc88@126.com [Oral Medical College, Beihua University, Jilin City 132013 (China); Bae, Tae sung, E-mail: bts@jbnu.ac.kr [Dept. of Dental Biomaterials and Institute of Bio degradable material, Institute of Oral Bioscience and BK21 plus project, School of Dentistry, Chonbuk National University, Jeonju, 561-756 (Korea, Republic of); Lee, Min ho, E-mail: mh@jbnu.ac.kr [Dept. of Dental Biomaterials and Institute of Bio degradable material, Institute of Oral Bioscience and BK21 plus project, School of Dentistry, Chonbuk National University, Jeonju, 561-756 (Korea, Republic of)

    2014-12-01

    Highlights: • TiO{sub 2} nanotubes formed via anodization were treated by alkali and heat. • The surface roughness was increased after alkali treatment (p < 0.05). • After alkali and heat treatment, the wettability was better than before treatment. • Alkali treated TiO{sub 2} nanotubes were shown higher HAp formation in SBF. • Heat treatment affected on the attachment of cells for alkali treated nanotubes. - Abstract: In this study, for improving the bioactivity of titanium used as an implant material, alkali and heat treatments were carried out after formation of the nanotubes via anodization. Nanotubes with uniform length, diameter, and thickness were formed by anodization. The alkali and heat-treated TiO{sub 2} nanotubes were covered with the complex network structure, and the Na compound was generated on the surface of the specimens. In addition, after 5 and 10 days of immersion in the SBF, the crystallized OCP and HAp phase was significantly increased on the surface of the alkali-treated TiO{sub 2} nanotubes (PNA) and alkali and heat-treated TiO{sub 2} nanotubes (PNAH) groups. Cell proliferation was decreased due to the formation of amorphous sodium titanate (Na{sub 2}TiO{sub 3}) layer on the surface of the PNA group. However, anatase and crystalline sodium titanate were formed on the surface of the PNAH group after heat treatment at 550 °C, and cell proliferation was improved. Thus, PNA group had higher HAp forming ability in the simulated body fluid. Additional heat treatment affected on enhancement of the bioactivity and the attachment of osteoblasts for PNA group.

  15. Effect of alkali and heat treatments for bioactivity of TiO2 nanotubes

    International Nuclear Information System (INIS)

    Highlights: • TiO2 nanotubes formed via anodization were treated by alkali and heat. • The surface roughness was increased after alkali treatment (p < 0.05). • After alkali and heat treatment, the wettability was better than before treatment. • Alkali treated TiO2 nanotubes were shown higher HAp formation in SBF. • Heat treatment affected on the attachment of cells for alkali treated nanotubes. - Abstract: In this study, for improving the bioactivity of titanium used as an implant material, alkali and heat treatments were carried out after formation of the nanotubes via anodization. Nanotubes with uniform length, diameter, and thickness were formed by anodization. The alkali and heat-treated TiO2 nanotubes were covered with the complex network structure, and the Na compound was generated on the surface of the specimens. In addition, after 5 and 10 days of immersion in the SBF, the crystallized OCP and HAp phase was significantly increased on the surface of the alkali-treated TiO2 nanotubes (PNA) and alkali and heat-treated TiO2 nanotubes (PNAH) groups. Cell proliferation was decreased due to the formation of amorphous sodium titanate (Na2TiO3) layer on the surface of the PNA group. However, anatase and crystalline sodium titanate were formed on the surface of the PNAH group after heat treatment at 550 °C, and cell proliferation was improved. Thus, PNA group had higher HAp forming ability in the simulated body fluid. Additional heat treatment affected on enhancement of the bioactivity and the attachment of osteoblasts for PNA group

  16. Silver nanoparticles from silver halide photography to plasmonics

    CERN Document Server

    Tani, Tadaaki

    2015-01-01

    This book provides systematic knowledge and ideas on nanoparticles of Ag and related materials. While Ag and metal nanoparticles are essential for plasmonics, silver halide (AgX) photography relies to a great extent on nanoparticles of Ag and AgX which have the same crystal structure and have been studied extensively for many years. This book has been written to combine the knowledge of nanoparticles of Ag and related materials in plasmonics and AgX photography in order to provide new ideas for metal nanoparticles in plasmonics. Chapters 1–3 of this book describe the structure and formation of nanoparticles of Ag and related materials. Systematic descriptions of the structure and preparation of Ag, Au, and noble-metal nanoparticles for plasmonics are followed by and related to those of nanoparticles of Ag and AgX in AgX photography. Knowledge of the structure and preparation of Ag and AgX nanoparticles in photography covers nanoparticles with widely varying sizes, shapes, and structures, and formation proce...

  17. Synthetic and structural chemistry of amidinate-substituted boron halides.

    Science.gov (United States)

    Hill, Nicholas J; Findlater, Michael; Cowley, Alan H

    2005-10-01

    The following new amidinate-substituted boron halides are reported: [PhC{N(SiMe(3))}(2)]BCl(2)(6), [MeC{NCy}(2)]BCl(2)(10), [Mes*C{NCy}(2)]BCl(2)(11), [MeC{N(i)Pr}(2)]BCl(2)(12), and [FcC{NCy}(2)]BBr(2)(13). Compound 6 was prepared via the trimethylsilyl chloride elimination reaction of BCl(3) with N,N,N'-tris(trimethylsilyl)benzamidine, and compounds 10-12 were prepared by salt metathesis between the lithium amidinates [RC(NR')(2)]Li and BX(3). Compound 13 was prepared via the insertion of 1,3-dicyclohexylcarbodiimide into the B-C bond of ferrocenyldibromoborane FcBBr(2). The molecular structures of 6, 10, 11, 13 and the known compound [PhC{N(SiMe(3))}(2)]BBr(2)(1) were established by single-crystal X-ray diffraction. PMID:16172649

  18. On-line alkali monitoring - Part 1

    International Nuclear Information System (INIS)

    As a consequence of the increased knowledge of the environmental impact of combustion based heat and power generation, the use of renewable biofuels will be increased. An obstacle associated to biofuel combustion compared to other fuels is the large release of alkali. Alkali compounds in flue gases are known to cause severe operational problems. Three of the major problems are; fouling of superheating tubes (causing reduced heat transfer and possibly corrosion), agglomeration of the bed material in fluidized beds, and poisoning of SCR catalysts. Yet another alkali related problem arises when, in order to increase the electric efficiency of combustion power plants, combined-cycle technology is used. Alkali vapour present in the fuel gas for the gas turbine is condensed to particles which increase corrosion and erosion of the turbine blades. The research on ash related operational problems has to be extended in order to ensure future use of biofuels in heat and power generation. In all successful research, adequate tools are necessary. To investigate ash related problems the key issue is to be able to perform continuous alkali measurements. This pilot study has investigated the need of continuous alkali measurements, which alkali species are harmful in the different applications and also available instrumentation capable of measuring the specific alkali species. The report gives a short summary presenting alkali related operational problems. In addition a schematic overview is given, showing the alkali species that possibly can exist in various parts of the power plant. 48 refs, 13 figs, 4 tabs

  19. Barium halide nanocrystals in fluorozirconate based glass ceramics for scintillation application

    Energy Technology Data Exchange (ETDEWEB)

    Selling, J.

    2007-07-01

    Europium (Eu)-activated barium halide nanocrystals in fluorozirconate based glass ceramics represent a promising class of Xray scintillators. The scintillation in these glass ceramics is mainly caused by the emission of divalent Eu incorporated in hexagonal BaCl{sub 2} nanocrystals which are formed in the glass matrix upon appropriate annealing. Experiments with cerium (Ce)-activated fluorozironate glass ceramics showed that Ce is an interesting alternative. In order to get a better understanding of the scintillation mechanism in Eu- or Ce-activated barium halide nanocrystals, an investigation of the processes in the corresponding bulk material is essential. The objective of this thesis is the investigation of undoped, Eu-, and Ce-doped barium halides by X-ray excited luminescence (XL), pulse height, and scintillation decay spectra. That will help to figure out which of these crystals has the most promising scintillation properties and would be the best nanoparticles for the glass ceramics. Furthermore, alternative dopants like samarium (Sm) and manganese (Mn) were also investigated. Besides the above-mentioned optical investigation electron paramagnetic resonance (EPR) and Moessbauer measurements were carried out in order to complete the picture of Eu-doped barium halides. The EPR data of Eu-doped BaI{sub 2} is anticipated to yield more information about the crystal field and crystal structure that will help to understand the charge carrier process during the scintillation process. The main focus of the Moessbauer investigations was set on the Eu-doped fluorochlorozirconate glass ceramics. The results of this investigation should help to improve the glass ceramics. The Eu{sup 2+}/Eu{sup 3+} ratio in the glass ceramics should be determined and optimize favor of the Eu{sup 2+}. We also want to distinguish between Eu{sup 2+} in the glass matrix and Eu{sup 2+} in the nanocrystals. For a better understanding of Moessbauer spectroscopy on Eu also measurements on Eu in a CaF{sub 2} host lattice were carried out. (orig.)

  20. Theoretical study on RbCl crystal with M\\"{o}bius inverse potentials

    CERN Document Server

    Shen, Y; Chen, N; Shen, Yue; Zhang, Shuo; Chen, Nan-xian

    2003-01-01

    The alkali halides have been studied very frequently for their simple structures and interesting properties, for example, the high-pressure induced transition$^1$. There are several successful models that can be employed. The most famous model of them is the Tosi-Fumi interionic potential$^2$ which is an empirical potential derived from the experimental data. Whereas, here we developed a new potential model based on the M\\"{o}bius lattice inversion method$^{3,4}$, which can be derived directly from the cohesive energy curve without any experimental data and is more effective than the ab initial calculation. With the M\\"{o}bius interionic potentials, we calculated the structural and elastic properties of RbCl crystal. The results are in good agreement with experiments. We also studied the high-pressure induced B1-B2 transition of RbCl crystal and estimated approximately the transition-point which is about 1.09GPa. Further more, we used this potential model to simulate the RbCl melting with molecular dynamics. ...

  1. Mutual effect of elements in coprecipitation. Influence of alkali metals on cocrystallization of rare earths with alkaline earth metal sulfates

    International Nuclear Information System (INIS)

    Coprecipitation of rare earths with Sr, Ca and Ba sulfates in the presence of alkali metals in a wide range of component concentration variation has been studied to establish reciprocal effect of elements during cocrystallization in such systems. The degree of rare earths coprecipitation is determined radiometrically, and the composition of the phases formed - using X-ray phase analysis and ESR method. Cocrystallization of rare earths (3) with calcium, strontium and barium sulfates in the presence of alkali metals is realized depending on conditions as to mechanisms resulting in the formation of solid phases, different in composition and structure. When rare earths are included in crystal lattice alkali metals manifest a compensating effect, the character of which is determined by the process mechanism. Cocrystallization is the most energetically profitable in the case when metal is included in the composition of solid phase, and in particular, under crystallization conditions of double sulfates of alkali and alkaline earth metals

  2. Liquid alkali metals and alkali-based alloys as electron-ion plasmas

    International Nuclear Information System (INIS)

    The article reviews the theory of thermodynamic and structural properties of liquid alkali metals and alkali-based alloys, within the framework of linear screening theory for the electron-ion interactions. (author)

  3. New alkali metal diphosphates how materials to preserve the security of the environment: CsNaCu(P2O7), Rb2Cu(P2O7) and CsNaCo(P2O7) synthesis and crystal structure determination

    Science.gov (United States)

    Chernyatieva, Anastasiya; Filatova, Alyona; Spiridonova, Dariya; Krivovichev, Sergey

    2013-04-01

    In this work we describe preliminary results of the synthesis and of a crystal-chemical study of synthetic phosphates with transition metals. Due to the increasing requirements for environmental safety specialists from various industries, we are searching for sustainable forms of immobilization of hazardous waste during storage. We are also developing a component-based waste for new materials. In our continued exploratory synthesis of compounds containing transition-metals, we were able to produce the new diphosphate phases CsNaCu(P2O7), Rb2Cu(P2O7) and CsNaCo(P2O7). A crystal chemical study has allowed us to identify new phosphates. Crystals of CsNaCu(P2O7) (Phase 1) is orthorhombic, crystallizes in space group Pmn21, with a = 5.147(8), b = 15.126(2), c = 9.717(2) Å, V = 756.20 Å3, R1 = 0.066 and Rb2Cu(P2O7) (Phase 2) is orthorhombic as well, crystallizes in space group Pmcn, with a = 5.183(8), b = 10.096(1), c = 15.146(3) Å, V = 793.55 Å3, R1 = 0.063, they have been obtained by high-temperature reaction of RbNO3, CsNO3, Cu(NO3)2, NaOH and (NH4)4P2O7. Synthetic crystals of the phosphate of copper and rubidium were studied in detail by us on the structures of Rb2Cu(P2O7) and Rb2Cu3(P2O7)2 - new alkali metal copper diphosphates (CHERNYATIEVA et al., 2008). Here we report the synthesis, the structure and the properties of the title compounds and we compare these phases with the previously discovered K2CuP2O7 (ELMAADI et al., 1995) and CsNaMnP2O7 (HUANG et al., 1998). These structures crystallize in other space groups, although their structures are also based on 2-D layers, formed by P2O7 groups combined with polyhedra of the transition metals (CHERNYATIEVA et al., 2012). A crystal chemical study has allowed us to identify even new diphosphates CsNaCu(P2O7) (Phase 3). Crystals of CsNaCoP2O7 is monoclinic, space group P 21/n, with a = 7,424(2), b = 7,648(1), c = 12,931(3)Å, ? = 90,71(2)° , V = 734.2(3) Å3 and R1 = 0.060. The structure is based framework of Co tetrahedra and P2O7 groups. The structure of the [Co(P2O7)]2-framework in more detail. The phosphate groups and tetrahedra coordinate cobalt ions form topology. This is a unique 4-coordination topology, where Co and P2O7 groups in the structure are topologically equivalent. References CHERNYATIEVA, A. P., KRIVOVICHEV, S. V., SPIRIDONOVA, D. V. (2008): International conference «Inorganic Materials» Dresden (2008) P3 - 143. CHERNYATIEVA, A. P, SPIRIDONOVA, D. V., KRIVOVICHEV, S. V. The crystal structures of two new synthetic compounds CsNaCu(P2O7) and Rb2Cu(P2O7), Acta Mineralogica-Petrographica (2012) Vol.7, p.25 EL MAADI, A., BOUKHARI, A., HOLT, E.M. (1995) Journal of Alloys Compounds, 223: 13-17. HUANG, Q., HWU, S. J., MO, X. H. (2001): Angewandte Chemie - International Edition, 40: 1690-1693.

  4. Performance of Alkali Activated Slag with Various Alkali Activators

    Directory of Open Access Journals (Sweden)

    D.V.S.P.RAJESH

    2013-02-01

    Full Text Available The need to meet a sustainable development is now an important challenge to the cement industry. The production of OPC is responsible for about 7% of the world?s CO2 emission, a major contributor to the green house effect which is implicated in global warming and climatic changes, lead to the search for more environmentally viable alternative to cement. One of those alternative material is alkali activated slag (AAS where ground granulated blast furnace slag is used not as partial replacement to cement but also as a sole binder in the production of concrete. The overall aim of the study was to investigate the potential of alkali activated slag as a sole binder in producing concrete.The performance of alkali-activated slag concrete with sodium silicate, sodium hydroxide, sodium carbonate as activator are used at 4% Na2O(by weight of slag and 4% of hydrated lime by total weight of solid binder content if used as a retarder. The scope of the work covered four mixes: - Normal OPC mix and three alkali activated slag mixesof the same binder content and the same water binder ratio. The fresh concrete properties studied were setting time and workability and the Engineering properties studied are compressive strength was measured in 1,7,28 days, split tensile strength was measured in 7,28 days and flexure, punching shear strength was compared in 12 days only. The AAS concrete with different activators investigated was found to achieve good workability comparable with that of OPC. Sodium silicate, sodium hydroxide activated slag mixes sets very quickly. AAS concrete is much more sensitive to curing where if there is no addition of retarder (hydrated lime to the mix. Among AAS mix sodium silicate was the best; sodium carbonate was the second; and sodium hydroxide was third in terms of compressive, split tensile strengths and in terms of flexure strength and punching shear strength sodium hydroxide was best; sodium carbonate was second; sodium silicate (water glass was third.

  5. Paramagnetic SO3- radicals in alkali-borate and alkali-silicate glasses

    International Nuclear Information System (INIS)

    Alkali-silicate and alkali-borate glasses with sulphur include sulphite ion compounds, whose formation is promoted by alkali-metal oxides. Gamma irradiation effect gives rise to paramagnetic SO3- radicals, which are responsible for the EPR signal in the range of g=2.004

  6. Topological insulator phase in halide perovskite structures

    Science.gov (United States)

    Jin, Hosub; Im, Jino; Freeman, Arthur J.

    2012-09-01

    Topological insulators are a novel quantum state of matter that reveals their properties and shows exotic phenomena when combined with other phases. Hence, priority has been given to making a good quality topological insulator interface with other compounds. From the applications point of view, the topological insulator phase in perovskite structures could be important to provide the various heterostructure interfaces with multifunctional properties. Here, by performing a tight-binding analysis and first-principles calculations, we predict that cubic-based CsPbI3 and CsSnI3 perovskite compounds under reasonable hydrostatic pressure are feasible candidates for three-dimensional topological insulators. Combined with cubic symmetry, the spin and total angular momentum doublets forming the valence and conduction bands result in a prototype of a continuum model, representing three-dimensional isotropic Dirac fermions, and govern the topological phase transition in halide perovskite materials.

  7. Colloquium: The unexpected properties of alkali metal iron selenide superconductors

    Science.gov (United States)

    Dagotto, Elbio

    2013-04-01

    The iron-based superconductors that contain FeAs layers as the fundamental building block in the crystal structures have been rationalized in the past using ideas based on the Fermi surface nesting of hole and electron pockets when in the presence of weak Hubbard U interactions. This approach seemed appropriate considering the small values of the magnetic moments in the parent compounds and the clear evidence based on photoemission experiments of the required electron and hole pockets. However, recent results in the context of alkali metal iron selenides, with generic chemical composition AxFe2-ySe2 (A=alkali metal element), have challenged those previous ideas since at particular compositions y the low-temperature ground states are insulating and display antiferromagnetic order with large iron magnetic moments. Moreover, angle-resolved photoemission studies have revealed the absence of hole pockets at the Fermi level in these materials. The present status of this exciting area of research, with the potential to alter conceptually our understanding of the iron-based superconductors, is here reviewed, covering both experimental and theoretical investigations. Other recent related developments are also briefly reviewed, such as the study of selenide two-leg ladders and the discovery of superconductivity in a single layer of FeSe. The conceptual issues considered established for the alkali metal iron selenides, as well as several issues that still require further work, are discussed.

  8. The unexpected properties of alkali metal iron selenide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Dagotto, Elbio R [ORNL

    2013-01-01

    The iron-based superconductors that contain FeAs layers as the fundamental building block in the crystal structures have been rationalized in the past using ideas based on the Fermi surface nesting of hole and electron pockets when in the presence of weak Hubbard U interactions. This approach seemed appropriate considering the small values of the magnetic moments in the parent compounds and the clear evidence based on photoemission experiments of the required electron and hole pockets. However, recent results in the context of alkali metal iron selenides, with generic chemical composition AxFe2ySe2 (A alkali metal element), have challenged those previous ideas since at particular compositions y the low-temperature ground states are insulating and display antiferromagnetic order with large iron magnetic moments. Moreover, angle-resolved photoemission studies have revealed the absence of hole pockets at the Fermi level in these materials. The present status of this exciting area of research, with the potential to alter conceptually our understanding of the ironbased superconductors, is here reviewed, covering both experimental and theoretical investigations. Other recent related developments are also briefly reviewed, such as the study of selenide two-leg ladders and the discovery of superconductivity in a single layer of FeSe. The conceptual issues considered established for the alkali metal iron selenides, as well as several issues that still require further work, are discussed.

  9. Characterization of Waste Poly(Ethylene-Terephthalate after Alkali Treatment

    Directory of Open Access Journals (Sweden)

    Rešček, A.

    2011-07-01

    Full Text Available Poly(ethylene terephthalate, PET, recycling represents one of the most successful and widespread examples of polymer recycling. This material is fully recyclable and may be used for manufacturing new products in many industrial areas. Nevertheless, the excellent properties of PET needed for its many applications are also responsible for the difficult degradation of PET and an accumulation of polymer waste, which in turn creates serious environmental problems connected to littering and illegal landfilling or incineration. The main goal of this study was to examine the effect of alkali pretreatment on the properties of PET flakes. PET flakes were washed at twotemperatures, 70 °C and 75 °C and in various time intervals of 15, 18, 21, 25, and 30 min. All samples were characterized by FTIR spectroscopy, differential scanning calorimetry and by contact angle measurements. The results showed that during the alkali treatment the partial depolymerization of PET was obtained, which resulted in the formation of various types of oligomers with hydroxyl and carboxyl end groups, which were the result of loss of high molecular structure. Decrease of intensity of characteristic vibrational bands (CO at 1717, COO at 1265 and CH2 at 722 cm-1 with extended time was observed (Figs. 1 and 2. Further on, the formation of hydroxyl groups at ṽ = 3428 cm-1 was also observed as a result of PET depolimerization during the alkali treatment, which behaviour was better visible for samples washed at 75 °C and with extended washing time (Fig 2b. During the DSC thermal analysis, multiple melting peaks were observed in some studied samples which could be linked to partial melting and re-crystallization of PET or to the occurrence of new polymer fractions of lower molecular mass (Figs. 3 and 4. It is evident that the contact angle of PET samples (Fig. 5 decreases in comparison to the PET 0, which points to the changes on the PET surface during the alkali treatment. Decrease in contact angle (which is measured with water indicates an increase in surface hydrophilicity and increase in the number of present polar -OH and -COOH groups formed during the partial degradation. Also, the values of total surface energies and their polar and dispersive components indicate that during the alkali treatment the surface characteristics of PET flakes were slightly changed due to depolymerization (Table 3. Generally, it can be concluded that partial depolymerization of PET flakes occurs during the alkali treatment but the material retains its good properties and it is appropriate for the further recycling process.

  10. Alkali burns from wet cement.

    OpenAIRE

    Peters, W. J.

    1984-01-01

    When water is added to the dry materials of Portland cement calcium hydroxide is formed; the wet cement is caustic (with a pH as high as 12.9) and can produce third-degree alkali burns after 2 hours of contact. Unlike professional cement workers, amateurs are usually not aware of any danger and may stand or kneel in the cement for long periods. As illustrated in a case report, general physicians may recognize neither the seriousness of the injury in its early stages nor the significance of a ...

  11. Optimized spatial frequency response in silver halide sensitized gelatin

    OpenAIRE

    Fimia Gil, Antonio; Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto

    1991-01-01

    Silver halide sensitized gelatin processing is optimized to increase the spatial frequency response in Agfa-Gevaert 8E75 HD emulsion; therefore a diffraction efficiency of 55% in reflection gratings of 5000 lines/mm is achieved.

  12. Single Cesium Lead Halide Perovskite Nanocrystals at Low Temperature: Fast Single-Photon Emission, Reduced Blinking, and Exciton Fine Structure.

    Science.gov (United States)

    Rainò, Gabriele; Nedelcu, Georgian; Protesescu, Loredana; Bodnarchuk, Maryna I; Kovalenko, Maksym V; Mahrt, Rainer F; Stöferle, Thilo

    2016-02-23

    Metal-halide semiconductors with perovskite crystal structure are attractive due to their facile solution processability, and have recently been harnessed very successfully for high-efficiency photovoltaics and bright light sources. Here, we show that at low temperature single colloidal cesium lead halide (CsPbX3, where X = Cl/Br) nanocrystals exhibit stable, narrow-band emission with suppressed blinking and small spectral diffusion. Photon antibunching demonstrates unambiguously nonclassical single-photon emission with radiative decay on the order of 250 ps, representing a significant acceleration compared to other common quantum emitters. High-resolution spectroscopy provides insight into the complex nature of the emission process such as the fine structure and charged exciton dynamics. PMID:26771336

  13. Structural analysis of alkali cations in mixed alkali silicate glasses by 23Na and 133Cs MAS NMR

    Directory of Open Access Journals (Sweden)

    T. Minami

    2014-12-01

    Full Text Available We report the structural analysis of Na+ and Cs+ in sodium cesium silicate glasses by using 23Na and 133Cs magic-angle spinning nuclear magnetic resonance (MAS NMR spectroscopy. In the NMR spectra of cesium silicate crystals, the peak position shifted to higher magnetic field for structures with larger Cs+ coordination numbers and to lower magnetic field for smaller Cs+ coordination numbers. The MAS NMR spectra of xNa2O-yCs2O-2SiO2 (x = 0, 0.2, 0.33, 0.5, 0.66, 0.8, 1.0; x + y = 1 glass reveal that the average coordination number of both the alkali cations decreases with increasing Cs+/(Na+ + Cs+ ratio. In addition, the coordination number of Na+ in xNa2O-yCs2O-2SiO2 glass is smaller than that of Cs+. This difference between the average coordination numbers of the alkali cations is considered to be one structural reason of the mixed alkali effect.

  14. Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

    OpenAIRE

    Satoshi Kamiguchi; Sayoko Nagashima; Teiji Chihara

    2014-01-01

    Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the clu...

  15. Investigation of doped cuprous halides for photovoltaic and display applications

    OpenAIRE

    Vijayaraghavan, Rajani

    2011-01-01

    The thesis mainly focuses on the growth and optoelectronic characterisation of the doped cuprous halides (CuX) with high UV/blue emission properties and the light harvesting in the CuBr/Si based heterojunction photovoltaic (PV) cells. Since cuprous halides are short wavelength emitters with high excitonic binding energies, growth of lower resistivity, highly luminescent p and n-type films are essential for the development of the future excitonic based light emitting devices with these materia...

  16. Role of microstructure in the electron-hole interaction of hybrid lead halide perovskites

    Science.gov (United States)

    Grancini, Giulia; Srimath Kandada, Ajay Ram; Frost, Jarvist M.; Barker, Alex J.; de Bastiani, Michele; Gandini, Marina; Marras, Sergio; Lanzani, Guglielmo; Walsh, Aron; Petrozza, Annamaria

    2015-10-01

    Organic-inorganic metal halide perovskites have demonstrated high power conversion efficiencies in solar cells and promising performance in a wide range of optoelectronic devices. The existence and stability of bound electron-hole pairs in these materials and their role in the operation of devices with different architectures remains a controversial issue. Here we demonstrate, through a combination of optical spectroscopy and multiscale modelling as a function of the degree of polycrystallinity and temperature, that the electron-hole interaction is sensitive to the microstructure of the material. The long-range order is disrupted by polycrystalline disorder and the variations in electrostatic potential found for smaller crystals suppress exciton formation, while larger crystals of the same composition demonstrate an unambiguous excitonic state. We conclude that fabrication procedures and morphology strongly influence perovskite behaviour, with both free carrier and excitonic regimes possible, with strong implications for optoelectronic devices.

  17. Energy transfer by borate and cyanide additives in gamma radiolytic decomposition of alkali metal nitrates

    International Nuclear Information System (INIS)

    Oxyanions are well known to form radical species after gamma irradiation and so the alkali halides (and even pseudohalides) from colour centres. Effect of borate and cyanide additives on the gamma radiolytic decomposition of sodium and potassium nitrates has shown enhancement in G(NO2-) calculated on the basis of electron fraction of the nitrate salt. Studies over a concentration range of 0.5 to 90 mol% of the additives and at different doses upto 1 MGy have shown maximum enhancement upto two orders of magnitude. It is proposed that energy transfer via radical species may be the main cause of enhancement in the radiolytic decomposition process. (author). 7 refs., 2 figs., 1 tab

  18. A complete series of uranocene(III) halides :braceUCp''2Xbracesub(n): :X=F, Cl, Br, or I; Cp'' = eta-C5H3(SiMe3)2]; Single-crystal x-ray structure determinations of the chloride and bromide (n=2 for X-=?-Cl- or ?-Br-)

    International Nuclear Information System (INIS)

    Reduction of [UCp''2X2] [Cp''=eta-C5H3(SiMe3)2; X=Cl, Br, or l: or :braceUCp''2(?-BF4)(?-F)brace2: with Na/Hg in toluene yields the lipophilic (and n.m.r. characterisable) compounds :braceUCp''2Xbracesub(n): (X=F, Cl, Br, or l), which are versatile precursors to uranocene (III or IV) compounds; X-ray data on the chloro- and bromo-derivatives reveal them to be the first uranocene(III) halide dimers (i.e., n=2, with ?-X-). (author)

  19. Novel, inorganic composites using porous, alkali-activated, aluminosilicate binders

    Science.gov (United States)

    Musil, Sean

    Geopolymers are an inorganic polymeric material composed of alumina, silica, and alkali metal oxides. Geopolymers are chemical and fire resistant, can be used as refractory adhesives, and are processed at or near ambient temperature. These properties make geopolymer an attractive choice as a matrix material for elevated temperature composites. This body of research investigated numerous different reinforcement possibilities and variants of geopolymer matrix material and characterized their mechanical performance in tension, flexure and flexural creep. Reinforcements can then be chosen based on the resulting properties to tailor the geopolymer matrix composites to a specific application condition. Geopolymer matrix composites combine the ease of processing of polymer matrix composites with the high temperature capability of ceramic matrix composites. This study incorporated particulate, unidirectional fiber and woven fiber reinforcements. Sodium, potassium, and cesium based geopolymer matrices were evaluated with cesium based geopolymer showing great promise as a high temperature matrix material. It showed the best strength retention at elevated temperature, as well as a very low coefficient of thermal expansion when crystallized into pollucite. These qualities made cesium geopolymer the best choice for creep resistant applications. Cesium geopolymer binders were combined with unidirectional continuous polycrystalline mullite fibers (Nextel(TM) 720) and single crystal mullite fibers, then the matrix was crystallized to form cubic pollucite. Single crystal mullite fibers were obtained by the internal crystallization method and show excellent creep resistance up to 1400°C. High temperature flexural strength and flexural creep resistance of pollucite and polycrystalline/single-crystal fibers was evaluated at 1000-1400°C.

  20. Method of handling radioactive alkali metal waste

    International Nuclear Information System (INIS)

    Radioactive alkali metal is mixed with particulate silica in a rotary drum reactor in which the alkali metal is converted to the monoxide during rotation of the reactor to produce particulate silica coated with the alkali metal monoxide suitable as a feed material to make a glass for storing radioactive material. Silica particles, the majority of which pass through a 95 mesh screen or preferably through a 200 mesh screen, are employed in this process, and the preferred weight ratio of silica to alkali metal is 7 to 1 in order to produce a feed material for the final glass product having a silica to alkali metal monoxide ratio of about 5 to 1

  1. Tellurite glass as a waste form for mixed alkali-chloride waste streams: Candidate materials selection and initial testing

    Energy Technology Data Exchange (ETDEWEB)

    Riley, Brian J., E-mail: brian.riley@pnnl.gov [Pacific Northwest National Laboratory, Richland, WA 99352 (United States); Rieck, Bennett T. [Washington State University, Pullman, WA 99164 (United States); McCloy, John S.; Crum, Jarrod V. [Pacific Northwest National Laboratory, Richland, WA 99352 (United States); Sundaram, S.K. [Alfred University, Alfred, NY 14802 (United States); Vienna, John D. [Pacific Northwest National Laboratory, Richland, WA 99352 (United States)

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer We provide the first standardized chemical durability test on tellurite glasses. Black-Right-Pointing-Pointer The glasses we studied showed a wide variety of chemical durability. Black-Right-Pointing-Pointer The best-performing glass showed good halide retention following melting and durability testing. Black-Right-Pointing-Pointer These glasses have very high densities resulting in high volumetric waste loading ability. - Abstract: Tellurite glasses have historically been shown to host large concentrations of halides. They are here considered for the first time as a waste form for immobilizing chloride wastes, such as may be generated in the proposed molten alkali salt electrochemical separations step in nuclear fuel reprocessing. Key properties of several tellurite glasses are determined to assess acceptability as a chloride waste form. TeO{sub 2} glasses with other oxides (PbO, Al{sub 2}O{sub 3} + B{sub 2}O{sub 3}, WO{sub 3}, P{sub 2}O{sub 5}, or ZnO) were fabricated with and without 10 mass% of a simulated (non-radioactive) mixed alkali, alkaline-earth, and rare earth chloride waste. Measured chemical durability is compared for the glasses, as determined by the product consistency test (PCT), a common standardized chemical durability test often used to validate borosilicate glass waste forms. The glass with the most promise as a waste form is the TeO{sub 2}-PbO system, as it offers good halide retention, a low sodium release (by PCT) comparable with high-level waste silicate glass waste forms, and a high storage density.

  2. About alkali metal dicyanamides. Syntheses, single-crystal structure determination, DSC/TG and vibrational spectra of KCs[N(CN)2]2 and NaRb2[N(CN)2]3 . H2O

    International Nuclear Information System (INIS)

    Transparent colorless crystals of KCs[N(CN)2]2 and NaRb2[N(CN)2]3 . H2O were obtained by blending aqueous solutions of Na[N(CN)2] and RbF or KF, respectively. After evaporation of the water, the remaining solid was extracted with absolute ethanol and the solvent was allowed to evaporate at r. t. KCs[N(CN)2]2 crystallizes in the space group C2/c (no. 15) with the cell parameters a = 1382.7(2), b = 998.1(1) and c = 1455.4(2) pm, and ? = 118.085(4) . The structure of NaRb2[N(CN)2]3 . H2O is exhibiting the P63/m (no. 176) with the cell parameters a = 705.98(7) and c = 1462.89(12) pm. Single-crystalline ?-K[N(CN)2] was obtained while attempting to synthesize 'NaK2[N(CN)2]3', corroborating the results of previous X-ray powder diffraction experiments. Vibrational spectra and DSC/TGA analyses complete our results.

  3. Alteration of alkali reactive aggregates autoclaved in different alkali solutions and application to alkali-aggregate reaction in concrete

    International Nuclear Information System (INIS)

    Surface alteration of typical aggregates with alkali-silica reactivity and alkali-carbonate reactivity, i.e. Spratt limestone (SL) and Pittsburg dolomitic limestone (PL), were studied by XRD and SEM/EDS after autoclaving in KOH, NaOH and LiOH solutions at 150 deg. C for 150 h. The results indicate that: (1) NaOH shows the strongest attack on both ASR and ACR aggregates, the weakest attack is with LiOH. For both aggregates autoclaved in different alkali media, the crystalline degree, morphology and distribution of products are quite different. More crystalline products are formed on rock surfaces in KOH than that in NaOH solution, while almost no amorphous product is formed in LiOH solution; (2) in addition to dedolomitization of PL in KOH, NaOH and LiOH solutions, cryptocrystalline quartz in PL involves in reaction with alkaline solution and forms typical alkali-silica product in NaOH and KOH solutions, but forms lithium silicate (Li2SiO3) in LiOH solution; (3) in addition to massive alkali-silica product formed in SL autoclaved in different alkaline solutions, a small amount of dolomite existing in SL may simultaneously dedolomitize and possibly contribute to expansion; (4) it is promising to use the duplex effect of LiOH on ASR and ACR to distinguish the alkali-silica reactivity and alkali-carbonate reactivity of aggregate when both ASR and ACR might coexist

  4. High Pressure Electrochemistry: Application to silver halides

    Science.gov (United States)

    Havens, K.; Kavner, A.

    2007-12-01

    Electron and ion charge transfer processes help govern electrical conductivity and diffusive mass and heat transport properties in deep Earth minerals. In an attempt to understand how pressure influences charge transfer behavior, the halide silver bromide (AgBr) was studied under the influence of an electric potential difference applied across two electrodes in a diamond anvil cell. This study follows our previous work on AgI, which was found to dissociate to molecular iodine and silver metal due to pressure and voltage influences. We performed two sets of experiments on AgBr at high pressure in a diamond anvil cell: electrochemical dissociation and electrical resistance measurements. In our study, we were able to electrochemically dissociate AgBr at pressures of 0.25-1.6 GPa by applying a voltage across the electrodes in the diamond cell sample chamber. Ag metal grew visibly on the negatively-charged electrode when voltages varying from 0.1 V to 5 V were applied. Additionally, a dark blue color appeared in low pressure areas of the diamond cell and grew darker from both voltage application and light exposure, indicating photochemical effects. We found that the reaction area and growth rate of both metal and dark blue color strongly increased as voltage increased, but tended to decrease with greater pressure. The resistance across the cell was observed to be influenced by both pressure and light exposure. As the AgBr sample was exposed to visible light, the resistance dropped instantaneously, and after the light was turned off, the resistance increased on a timescale of 10's of seconds to minutes. Notably, at higher pressures, the AgBr showed less photosensitivity. Exploration of these metal halide systems has many potential applications. First, these experiments explore the pressure-dependence of photochemical and photovoltaic processes, and may spur development of pressure-tuned microscale electronic devices. Second, these experimental results can be used to constrain thermodynamic models of pressure-dependent electrochemical behavior of materials, which may then be applied to the high temperature, high pressure mineral phases of the deep Earth and planets.

  5. Oxygen mobility in alkali feldspars

    International Nuclear Information System (INIS)

    The oxygen mobility is shown from oxygen atoms exchange between potassic and sodic feldspars and 18 oxygen enriched water. Exchanges are carried out in autoclaves between 400 and 800 deg. C under a water pressure between 300 and 800 bars. The oxygen is extracted from silicate by a ClF3 attack. Two distinct mechanisms may be found. The first one is auto-diffusion; for adularia we have: D = 9.10-7 exp(-32000/RT) (cm2.s-1), for albite: D 4.5.10-5 exp(-37000/RT) (cm2.s-1). The second one, more rapid, is associated with alkali atoms exchanges. These results are applied to the order-disorder problem in feldspars and to the oxygen geochemistry. (author)

  6. EPR and optical absorption studies on manganese ion doped in mixed alkali cadmium phosphate glasses

    International Nuclear Information System (INIS)

    Electron paramagnetic resonance (EPR) spectra of Mn(II) ions in cadmium phosphate glasses are presented with mixed alkali variation as xLi2O + (20 - x) Na2O + 20 CdO + 59.5 P2O5 + 0.5 MnO glass system with 5 ? x ? 15 mol%. The EPR spectra of Mn(II) ions doped samples exhibit a sextet centered at g = 2·0. The optical absorption spectrum at room temperature shows three bands for Mn(II) ions in octahedral symmetry. The crystal field (Dq) and Racah parameters (B and C) are evaluated. From EPR and optical spectral studies reveals the nature of the bonding is dominantly ionic and its site symmetry is octahedral. At equal composition of alkali content, i.e. for x = 10 the glass system shows the mixed alkali effect.

  7. High effective silica fume alkali activator

    Indian Academy of Sciences (India)

    Vladimír Živica

    2004-04-01

    Growing demands on the engineering properties of cement based materials and the urgency to decrease unsuitable ecologic impact of Portland cement manufacturing represent significant motivation for the development of new cement corresponding to these aspects. One category represents prospective alkali activated cements. A significant factor influencing their properties is alkali activator used. In this paper we present a new high effective alkali activator prepared from silica fume and its effectiveness. According to the results obtained this activator seems to be more effective than currently used activators like natrium hydroxide, natrium carbonate, and water glass.

  8. A Bismuth-Halide Double Perovskite with Long Carrier Recombination Lifetime for Photovoltaic Applications.

    Science.gov (United States)

    Slavney, Adam H; Hu, Te; Lindenberg, Aaron M; Karunadasa, Hemamala I

    2016-02-24

    Despite the remarkable rise in efficiencies of solar cells containing the lead-halide perovskite absorbers RPbX3 (R = organic cation; X = Br(-) or I(-)), the toxicity of lead remains a concern for the large-scale implementation of this technology. This has spurred the search for lead-free materials with similar optoelectronic properties. Here, we use the double-perovskite structure to incorporate nontoxic Bi(3+) into the perovskite lattice in Cs2AgBiBr6 (1). The solid shows a long room-temperature fundamental photoluminescence (PL) lifetime of ca. 660 ns, which is very encouraging for photovoltaic applications. Comparison between single-crystal and powder PL decay curves of 1 suggests inherently high defect tolerance. The material has an indirect bandgap of 1.95 eV, suited for a tandem solar cell. Furthermore, 1 is significantly more heat and moisture stable compared to (MA)PbI3. The extremely promising optical and physical properties of 1 shown here motivate further exploration of both inorganic and hybrid halide double perovskites for photovoltaics and other optoelectronics. PMID:26853379

  9. Genetic Control of Methyl Halide Production in Arabidopsis

    Science.gov (United States)

    Rhew, R. C.; Ostergaard, L.; Saltzman, E. S.; Yanofsky, M. F.

    2003-12-01

    Methyl chloride and methyl bromide are the primary carriers of natural chlorine and bromine to the stratosphere where they catalyze the destruction of ozone, whereas methyl iodide influences aerosol formation and ozone loss in the troposphere. Methyl bromide is also an agricultural fumigant whose use is scheduled to be phased out by international agreement. Despite the economic and environmental importance of these methyl halides, their natural sources and biological production mechanisms are poorly understood. Currently identified sources include oceans, biomass burning, industrial and agricultural use, fuel combustion, salt marshes, wetlands, rice paddies, certain terrestrial plants and fungi, and abiotic processes. We demonstrate that the model plant Arabidopsis thaliana produces and emits methyl halides and that the enzyme primarily responsible for the production is encoded by the HARMLESS TO OZONE LAYER (HOL) gene located on chromosome II. In mutant plants that have a disruption of the HOL gene, methyl halide production is largely eliminated. A phylogenetic analysis using the HOL gene suggests that the ability to produce methyl halides is widespread among vascular plants. This approach provides a genetic basis for understanding and predicting patterns of methyl halide production by plants.

  10. Alkali metal for ultraviolet band-pass filter

    Science.gov (United States)

    Mardesich, Nick (inventor); Fraschetti, George A. (inventor); Mccann, Timothy A. (inventor); Mayall, Sherwood D. (inventor); Dunn, Donald E. (inventor); Trauger, John T. (inventor)

    1993-01-01

    An alkali metal filter having a layer of metallic bismuth deposited onto the alkali metal is provided. The metallic bismuth acts to stabilize the surface of the alkali metal to prevent substantial surface migration from occurring on the alkali metal, which may degrade optical characteristics of the filter. To this end, a layer of metallic bismuth is deposited by vapor deposition over the alkali metal to a depth of approximately 5 to 10 A. A complete alkali metal filter is described along with a method for fabricating the alkali metal filter.

  11. Phonon Dispersion Relations in Alkali Metals

    International Nuclear Information System (INIS)

    It has been shown in this paper that the phonon dispersion curves of sodium in the [100], [110] and [111] symmetry directions can be explained well on the basis of a simple model, where one has to consider only central force constants between nearest and next nearest neighbours. The tangential force constant between the nearest neighbours is very much smaller as compared to the radial force constant, while for the next nearest neighbours the radial and tangential force constants are comparable. The calculation is carried out on the basis of the model suggested by de Launay, where it is shown that the conduction electrons exert a volume force for longitudinal modes. The stiffness constant of the electron gas is its bulk modulus which in de Launay's model is equal to the Cauchy discrepancy (C12-C14) for the cubic crystals. The three force constants ?1, ?2 and ?1' can be determined from the measured elastic constants and the secular equation can be solved to give the dispersion curves. The dispersion curves have also been obtained using the calculated values of the bulk modulus of the electron gas after considering not only the exchange and correlation energies but also the Fermi kinetic energy. These also agree fairly well with experiment. The measured elastic constants as well as calculated bulk modulus of the electron gas indicate that the Cauchy relation C12 = C44 holds good approximately in alkali metals. This result is rather surprising as it requires that the interaction between the atoms be central in nature in spite of the metallic binding. A justification for this has been given by Cochran. A model with four force constants is being worked out. They can be determined from the three elastic constants and calculated bulk modulus of the electron gas. (author)

  12. Dissolution Process of Palladium in Hydrochloric Acid: A Route via Alkali Metal Palladates

    Science.gov (United States)

    Kasuya, Ryo; Miki, Takeshi; Morikawa, Hisashi; Tai, Yutaka

    2015-12-01

    To improve the safety of the Pd recovery processes that use toxic oxidizers, dissolution of Pd in hydrochloric acid with alkali metal palladates was investigated. Alkali metal palladates were prepared by calcining a mixture of Pd black and alkali metal (Li, Na, and K) carbonates in air. Almost the entire amount of Pd was converted into Li2PdO2 after calcination at 1073 K (800 °C) using Li2CO3. In contrast, PdO was obtained by calcination at 1073 K (800 °C) using Na and K carbonates. Our results indicated that Li2CO3 is the most active reagent among the examined alkali metal carbonates for the formation of palladates. In addition, dissolution of the resulting Li2PdO2 in HCl solutions was evaluated under various conditions. In particular, Li2PdO2 rapidly dissolved in diluted (0.1 M) HCl at ambient temperature. Solubility of Pd of Li2PdO2 was found to be 99 pct or larger after dissolution treatment at 353 K (80 °C) for 5 minutes; in contrast, PdO hardly dissolved in 0.1 M HCl. The dissolution mechanism of Li2PdO2 in HCl was also elucidated by analysis of crystal structures and particulate properties. Since our process is completely free from toxic oxidizers, the dissolution process via alkali metal palladates is much safer than currently employed methods.

  13. DELIGNIFICATION OF SUGARCANE BAGASSE WITH ALKALI AND PERACETIC ACID AND CHARACTERIZATION OF THE PULP

    Directory of Open Access Journals (Sweden)

    Ting Zhang

    2010-06-01

    Full Text Available Sugarcane bagasse was delignified with alkali and peracetic acid in a two-stage process to obtain pulps with high yield and low kappa number. The experimental results indicated that alkali pretreatment prior to peracetic acid (PAA delignification could significantly reduce PAA loading by partially removing lignin and swelling the fibers. An optimum condition for the two-stage delignification was obtained for pulping of sugarcane bagasse. The pulps were further characterized by chemical composition analysis, strength property tests, Fourier Transform Infrared Spectroscopy (FTIR, X-Ray Diffraction (XRD, and Thermal Gravimetric Analysis (TGA. It was found that the alkali-PAA process could be conducted under milder conditions with resulting higher pulping selectivity, higher degree of polymerization (DP, and superior mechanical properties of pulps, compared to the kraft pulping process. Both kraft pulps and alkali-PAA pulp had similar FTIR spectra, XRD spectra, and TGA (DTG curves. However, further analysis indicated that the alkali-PAA pulp had higher infrared crystallization index and cellulose crystallinity.

  14. Dissolution Process of Palladium in Hydrochloric Acid: A Route via Alkali Metal Palladates

    Science.gov (United States)

    Kasuya, Ryo; Miki, Takeshi; Morikawa, Hisashi; Tai, Yutaka

    2015-08-01

    To improve the safety of the Pd recovery processes that use toxic oxidizers, dissolution of Pd in hydrochloric acid with alkali metal palladates was investigated. Alkali metal palladates were prepared by calcining a mixture of Pd black and alkali metal (Li, Na, and K) carbonates in air. Almost the entire amount of Pd was converted into Li2PdO2 after calcination at 1073 K (800 °C) using Li2CO3. In contrast, PdO was obtained by calcination at 1073 K (800 °C) using Na and K carbonates. Our results indicated that Li2CO3 is the most active reagent among the examined alkali metal carbonates for the formation of palladates. In addition, dissolution of the resulting Li2PdO2 in HCl solutions was evaluated under various conditions. In particular, Li2PdO2 rapidly dissolved in diluted (0.1 M) HCl at ambient temperature. Solubility of Pd of Li2PdO2 was found to be 99 pct or larger after dissolution treatment at 353 K (80 °C) for 5 minutes; in contrast, PdO hardly dissolved in 0.1 M HCl. The dissolution mechanism of Li2PdO2 in HCl was also elucidated by analysis of crystal structures and particulate properties. Since our process is completely free from toxic oxidizers, the dissolution process via alkali metal palladates is much safer than currently employed methods.

  15. Density of mixed alkali borate glasses: A structural analysis

    International Nuclear Information System (INIS)

    Density of mixed alkali borate glasses has been correlated with the glass structure. It is assumed that in such glasses each alkali oxide associates with a proportional quantity of B2O3. The number of BO3 and BO4 units related to each type of alkali oxide depends on the total concentration of alkali oxide. It is concluded that in mixed alkali borate glasses the volumes of structural units related to an alkali ion are the same as in the corresponding binary alkali borate glass. This reveals that each type of alkali oxide forms its own borate matrix and behaves as if not affected with the presence of the other alkali oxide. Similar conclusions are valid for borate glasses with three types of alkali oxide

  16. Density of mixed alkali borate glasses: A structural analysis

    Energy Technology Data Exchange (ETDEWEB)

    Doweidar, H. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt)]. E-mail: hdoweidar@mans.edu.eg; El-Damrawi, G.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt); Moustafa, Y.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt); Ramadan, R.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt)

    2005-05-15

    Density of mixed alkali borate glasses has been correlated with the glass structure. It is assumed that in such glasses each alkali oxide associates with a proportional quantity of B{sub 2}O{sub 3}. The number of BO{sub 3} and BO{sub 4} units related to each type of alkali oxide depends on the total concentration of alkali oxide. It is concluded that in mixed alkali borate glasses the volumes of structural units related to an alkali ion are the same as in the corresponding binary alkali borate glass. This reveals that each type of alkali oxide forms its own borate matrix and behaves as if not affected with the presence of the other alkali oxide. Similar conclusions are valid for borate glasses with three types of alkali oxide.

  17. Improved alkali-metal/silicate binders

    Science.gov (United States)

    Schutt, J.

    1978-01-01

    Family of inorganic binders utilizes potassium or sodium oxide/silicate dispersion and employs high mole ratio of silicon dioxide to alkali-metal binder. Binders are stable, inexpensive, extremely water resistant, and easy to apply.

  18. “On water” sp3–sp2 cross-couplings between benzylic and alkenyl halides†

    OpenAIRE

    Krasovskaya, Valeria; Krasovskiy, Arkady; Bhattacharjya, Anish; Lipshutz, Bruce H.

    2011-01-01

    Organic-solvent-free cross-couplings between benzylic and alkenyl halides have been developed. Various alkenyl halides can be effciently benzylated by combining the precursor halides in the presence of Zn dust and a Pd catalyst at room temperature, in water as the only medium.

  19. Chemistry of gaseous lower-valent actinide halides

    International Nuclear Information System (INIS)

    The objective of this program is to provide accurate thermochemical information for the uranium and thorium halide and oxyhalide systems, two of the key actinide systems, so that the basic factors underlying the chemical bonding and chemical reactivity in these systems can be elucidated in a systematic way. A complete characterization of the uranium and thorium systems will serve as a reliable base for modeling the behavior of the heavier actinides, which will be much more difficult to study because of sample size and safety restrictions. Our principal focus is on the the gaseous halides, mainly the lower-valent halides, because these molecular species largely will define the high-temperature chemistry in the nuclear applications of interest. 2 refs., 1 tab

  20. Slow relaxation, confinement, and solitons

    CERN Document Server

    Schulman, L S; Scardicchio, A; Facchi, P; Nikl, M; Polák, K; Gaveau, B

    2002-01-01

    Millisecond crystal relaxation has been used to explain anomalous decay in doped alkali halides. We attribute this slowness to Fermi-Pasta-Ulam solitons. Our model exhibits confinement of mechanical energy released by excitation. Extending the model to long times is justified by its relation to solitons, excitations previously proposed to occur in alkali halides. Soliton damping and observation are also discussed.

  1. Solutions of hydrogen in liquid alkali metals

    International Nuclear Information System (INIS)

    The paper reviews work carried out on solutions of hydrogen in liquid alkali metals. Phase diagrams for the lithium-hydrogen system are described, and equilibrium hydrogen pressure data for solutions in lithium, sodium, potassium, rubidium, caesium and sodium-potassium, are summarized. Solubility data for hydrogen in lithium, sodium, potassium, sodium-potassium, rubidium and caesium, are discussed. Finally, thermodynamic data for the alkali metal hydrides are given. (U.K.)

  2. Unconventional Superconductivity in electron-doped layered metal nitride halides $M$N$X$ ($M$ = Ti, Zr, Hf; $X$ = Cl, Br, I)

    OpenAIRE

    Kasahara, Yuichi; Kuroki, Kazuhiko; Yamanaka, Shoji; Taguchi, Yasujiro

    2014-01-01

    In this review, we present a comprehensive overview of superconductivity in electron-doped metal nitride halides $M$N$X$ ($M$ = Ti, Zr, Hf; $X$ = Cl, Br, I) with layered crystal structure and two-dimensional electronic states. The parent compounds are band insulators with no discernible long-range ordered state. Upon doping tiny amount of electrons, superconductivity emerges with several anomalous features beyond the conventional electron-phonon mechanism, which stimulate th...

  3. Halide-Dependent Electronic Structure of Organolead Perovskite Materials

    KAUST Repository

    Buin, Andrei

    2015-06-23

    © 2015 American Chemical Society. Organometal halide perovskites have recently attracted tremendous attention both at the experimental and theoretical levels. These materials, in particular methylammonium triiodide, are still limited by poor chemical and structural stability under ambient conditions. Today this represents one of the major challenges for polycrystalline perovskite-based photovoltaic technology. In addition to this, the performance of perovskite-based devices is degraded by deep localized states, or traps. To achieve better-performing devices, it is necessary to understand the nature of these states and the mechanisms that lead to their formation. Here we show that the major sources of deep traps in the different halide systems have different origin and character. Halide vacancies are shallow donors in I-based perovskites, whereas they evolve into a major source of traps in Cl-based perovskites. Lead interstitials, which can form lead dimers, are the dominant source of defects in Br-based perovskites, in line with recent experimental data. As a result, the optimal growth conditions are also different for the distinct halide perovskites: growth should be halide-rich for Br and Cl, and halide-poor for I-based perovskites. We discuss stability in relation to the reaction enthalpies of mixtures of bulk precursors with respect to final perovskite product. Methylammonium lead triiodide is characterized by the lowest reaction enthalpy, explaining its low stability. At the opposite end, the highest stability was found for the methylammonium lead trichloride, also consistent with our experimental findings which show no observable structural variations over an extended period of time.

  4. Unconventional superconductivity in electron-doped layered metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I)

    International Nuclear Information System (INIS)

    In this review, we present a comprehensive overview of superconductivity in electron-doped metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) with layered crystal structure and two-dimensional electronic states. The parent compounds are band insulators with no discernible long-range ordered state. Upon doping tiny amount of electrons, superconductivity emerges with several anomalous features beyond the conventional electron–phonon mechanism, which stimulate theoretical investigations. We will discuss experimental and theoretical results reported thus far and compare the electron-doped layered nitride superconductors with other superconductors

  5. Halide-Free Synthesis of Hydrochalcogenide Ionic Liquids of the Type [Cation][HE] (E=S, Se, Te).

    Science.gov (United States)

    Finger, Lars H; Sundermeyer, Jörg

    2016-03-14

    We present the synthesis and thorough characterization of ionic liquids and organic salts based on hydrochalcogenide HE(-) (E=S, Se, Te) anions. Our approach is based on halide-, metal-, and water-free decarboxylation of methylcarbonate precursors under acidic conditions, resulting from the easily dissociating reagents H2 E. The compounds were characterized by elemental analysis, multinuclear NMR spectroscopy, thermal and single-crystal XRD analyses. The hydrosulfide salts were investigated with respect to their ability to dissolve elemental sulfur in varying stoichiometry. Thus-prepared polysulfide ILs were also analyzed by UV/Vis spectroscopy and cyclic voltammetry. PMID:26879604

  6. Unconventional superconductivity in electron-doped layered metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I)

    Science.gov (United States)

    Kasahara, Yuichi; Kuroki, Kazuhiko; Yamanaka, Shoji; Taguchi, Yasujiro

    2015-07-01

    In this review, we present a comprehensive overview of superconductivity in electron-doped metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) with layered crystal structure and two-dimensional electronic states. The parent compounds are band insulators with no discernible long-range ordered state. Upon doping tiny amount of electrons, superconductivity emerges with several anomalous features beyond the conventional electron-phonon mechanism, which stimulate theoretical investigations. We will discuss experimental and theoretical results reported thus far and compare the electron-doped layered nitride superconductors with other superconductors.

  7. Thallous and cesium halide materials for use in cryogenic applications

    International Nuclear Information System (INIS)

    Certain thallous and cesium halides, either used alone or in combination with other ceramic materials, are provided in cryogenic applications such as heat exchange material for the regenerator section of a closed-cycle cryogenic refrigeration section, as stabilizing coatings for superconducting wires, and as dielectric insulating materials. The thallous and cesium halides possess unusually large specific heats at low temperatures, have large thermal conductivities, are nonmagnetic, and are nonconductors of electricity. They can be formed into a variety of shapes such as spheres, bars, rods, or the like and can be coated or extruded onto substrates or wires. (author)

  8. Ultrafast time-resolved spectroscopy of lead halide perovskite films

    Science.gov (United States)

    Idowu, Mopelola A.; Yau, Sung H.; Varnavski, Oleg; Goodson, Theodore

    2015-09-01

    Recently, lead halide perovskites which are organic-inorganic hybrid structures, have been discovered to be highly efficient as light absorbers. Herein, we show the investigation of the excited state dynamics and emission properties of non-stoichiometric precursor formed lead halide perovskites grown by interdiffusion method using steady-state and time-resolved spectroscopic measurements. The influence of the different ratios of the non-stoichiometric precursor solution was examined. The observed photoluminescence properties were correlated with the femtosecond transient absorption measurements.

  9. Layered structures of organic/inorganic hybrid halide perovskites

    OpenAIRE

    Huan, Tran Doan; Tuoc, Vu Ngoc; Minh, Nguyen Viet

    2015-01-01

    Organic/inorganic hybrid halide perovskites, formed by substituting the cations A of ABX$_3$ halide perovskites with certain organic cations, may be used for solar thermoelectric applications. In this work, we systematically study three lead-free hybrid perovskites, i.e., methylammonium tin iodide CH$_3$NH$_3$SnI$_3$, ammonium tin iodide NH$_4$SnI$_3$, and formamidnium tin iodide HC(NH$_2$)$_2$SnI$_3$, by first-principles calculations. We find that in addition to the commonl...

  10. Reactivity of halide and pseudohalide ligands in transition metal complexes

    International Nuclear Information System (INIS)

    The review generalizes experimental material on reactions of coordinated halide ligands, as well as cyanide, azide, thiocyanate and cyanate ligands in transition metal (Mo, W, Ru, etc.) complexes. It is shown that transformation of the intrasphere pseudohalide ligands is a very important method of directed synthesis of coordination compounds. The tendency of halide and pseudohalide ions to the formation of low-soluble salts or strong complexes can be widely used in preparation coordination chemistry for the ''forced'' introduction of solvent molecules into the complexes

  11. Facile Preparation of Silver Halide Nanoparticles as Visible Light Photocatalysts

    OpenAIRE

    Cui, Linfan; Jiao, Tifeng; Zhang, Qingrui; Zhou, Jingxin; Peng, Qiuming

    2015-01-01

    In this study, highly efficient silver halide (AgX)-based photocatalysts were successfully fabricated using a facile and template-free direct-precipitation method. AgX nanoparticles, which included silver chloride (AgCl), silver bromide (AgBr) and silver iodide (AgI), were synthesized using different potassium halides and silver acetate as reactive sources. The size distribution of the AgX nanopar? ticles was determined by the reaction time and ratio of the reagents, which were monitored by U...

  12. Excitons versus free charges in organo-lead tri-halide perovskites

    Science.gov (United States)

    D'Innocenzo, Valerio; Grancini, Giulia; Alcocer, Marcelo J. P.; Kandada, Ajay Ram Srimath; Stranks, Samuel D.; Lee, Michael M.; Lanzani, Guglielmo; Snaith, Henry J.; Petrozza, Annamaria

    2014-04-01

    Excitonic solar cells, within which bound electron-hole pairs have a central role in energy harvesting, have represented a hot field of research over the last two decades due to the compelling prospect of low-cost solar energy. However, in such cells, exciton dissociation and charge collection occur with significant losses in energy, essentially due to poor charge screening. Organic-inorganic perovskites show promise for overcoming such limitations. Here, we use optical spectroscopy to estimate the exciton binding energy in the mixed-halide crystal to be in the range of 50?meV. We show that such a value is consistent with almost full ionization of the exciton population under photovoltaic cell operating conditions. However, increasing the total photoexcitation density, excitonic species become dominant, widening the perspective of this material for a host of optoelectronic applications.

  13. Raman study of the charge transfer C 60 complexes with tetraphenylphosphonium halides

    Science.gov (United States)

    Sauvajol, J. L.; Graja, A.; Firlej, L.; Król, S.

    1997-12-01

    Raman spectra are presented for single crystal charge-transfer complexes of fullerene and tetraphenylphosphonium halides, (Ph 4P) 2C 60Y (Y = Cl, Br, I). The Raman spectrum is found to be insensitive to the halogen ion indicating the intrinsic character of this spectrum. The spectra of complexes excited at 514.5 nm look very different from those excited at 647.1 nm; especially the low-frequency modes are stronger in the Raman spectrum excited at 647.1 nm. The 1469 cm -1 pentagonal pinch mode of C 60 is shifted and split in these complexes, a double-peak structure with components at 1462 and 1452 cm -1 is observed. All these results are understood as due to the presence of C -60 in crystalline sites of low symmetry.

  14. Synthesis, crystal structure, and properties of the rhombohedral modification of the thiospinel CuZr1.86(1)S4

    International Nuclear Information System (INIS)

    The rhombohedral modification of the thiospinel, CuZr1.86(1)S4, has been synthesized by the reaction of the constituent elements in an alkali metal halide flux and structurally characterized by single crystal X-ray diffraction techniques. The title compound crystallizes in the rhombohedral space group D3d5-R3-barm (no. 166, a=7.3552(2) A, c=35.832(2) A, V=1678.76(13) A3, Z=12, and R/wR=0.0239/0.0624). The structure is composed of close packed S layers, with a stacking order of ...ABCBCABABCACAB....along the c axis. The Zr and Cu atoms occupy the octahedral and tetrahedral holes between S layers, respectively. Three different kinds of S-M-S layers exist in the structure: layer I has fully occupied Zr and Cu sites, layer II has fully occupied Zr sites but no Cu, and layer III has partially occupied Zr and fully occupied Cu sites. Transport and optical properties indicate that the title compound is a small band gap (1.26 eV) n-type semiconductor. - Graphical abstract: The projected view of the rhombohedral modification, CuZr1.86(1)S4, down the [100] direction. Large letters denote the packing sequence of the S atoms (yellow circles) along the c axis. Zr (black circles) and Cu (red circles) atoms occupy the octahedral and tetrahedral holes, respectively, between close packed S layers.

  15. Thermoluminescence and F centers of manganese doped NaCl and NaCl-CKl crystals exposed to gamma radiation

    Energy Technology Data Exchange (ETDEWEB)

    Somera, L.; Cruz Z, E.; Roman L, J. [UNAM, Instituto de Ciencias Nucleares, Circuito Exterior, Ciudad Universitaria, 04510 Mexico D. F. (Mexico); Hernandez A, J. M.; Murrieta S, H., E-mail: ecruz@nucleares.unam.mx [UNAM, Instituto de Fisica, Circuito Exterior, Ciudad Universitaria, 04510 Mexico D. F. (Mexico)

    2015-10-15

    Alkali halides crystals doped with rare earths or transition metals have been widely studied due to the luminescence properties. In particular, NaCl and KCl single crystals present thermally stimulated luminescence (Tl) after gamma irradiation. The NaCl and the NaCl KCl mixed crystal doped with manganese (MnCl{sub 2}) impurity were grown by using the Czochralski method. The emission characteristic of Mn{sup 2+} was observed at 543 nm. The crystals were exposed between 0.02 and 10 kGy gamma dose from {sup 60}Co irradiator. Optical absorption at room temperature shows the peaked band at 452 nm corresponding to the manganese impurity. The F bands, was ascribed to the electron trapped in the anion vacancy in the lattice, were obtained at 452 nm and 455 nm belonging to NaCl:Mn and NaCl KCl:Mn, respectively. The F band increases as the doses increase and it was bleaching by the UV light at 470 nm. The glow curves of the samples show the first glow peak between 92-103 degrees C, while the second main peak was observed at 183 degrees C for the undoped NaCl and at 148 and 165 degrees C for the NaCl:Mn and NaCl-KCl:Mn, respectively. The main peak was slowly bleaching when the irradiated sample was illuminated with F (470 nm) light. Optical bleaching confirms that the F center has an important participation in the thermoluminescent response. The glow curves structure from the thermal bleaching suggests the participation of different kind of traps. Also, the kinetics parameters such as activation energy (E), frequency factor (s) and the kinetic order (b) were investigated. (Author)

  16. Thermoluminescence and F centers of manganese doped NaCl and NaCl-CKl crystals exposed to gamma radiation

    International Nuclear Information System (INIS)

    Alkali halides crystals doped with rare earths or transition metals have been widely studied due to the luminescence properties. In particular, NaCl and KCl single crystals present thermally stimulated luminescence (Tl) after gamma irradiation. The NaCl and the NaCl KCl mixed crystal doped with manganese (MnCl2) impurity were grown by using the Czochralski method. The emission characteristic of Mn2+ was observed at 543 nm. The crystals were exposed between 0.02 and 10 kGy gamma dose from 60Co irradiator. Optical absorption at room temperature shows the peaked band at 452 nm corresponding to the manganese impurity. The F bands, was ascribed to the electron trapped in the anion vacancy in the lattice, were obtained at 452 nm and 455 nm belonging to NaCl:Mn and NaCl KCl:Mn, respectively. The F band increases as the doses increase and it was bleaching by the UV light at 470 nm. The glow curves of the samples show the first glow peak between 92-103 degrees C, while the second main peak was observed at 183 degrees C for the undoped NaCl and at 148 and 165 degrees C for the NaCl:Mn and NaCl-KCl:Mn, respectively. The main peak was slowly bleaching when the irradiated sample was illuminated with F (470 nm) light. Optical bleaching confirms that the F center has an important participation in the thermoluminescent response. The glow curves structure from the thermal bleaching suggests the participation of different kind of traps. Also, the kinetics parameters such as activation energy (E), frequency factor (s) and the kinetic order (b) were investigated. (Author)

  17. Magnetic studies on alkali metal uranates(V) MUO3 with the perovskite structure

    International Nuclear Information System (INIS)

    The magnetic properties of alkali metal uranates(V) MUO3 (M, alkali metal) with the perovskite structure have been studied. In this study RbUO3 (cubic perovskite structure) was prepared and its magnetic susceptibility was measured from 4.2 K to room temperature. It was found that a magnetic anomaly (magnetic transition) occurred at about 27 K. As a result of the U5+ ion in the paramagnetic state, the electron paramagnetic resonance spectrum was not observed even at 4.2 K. The magnetic susceptibility results and the optical absorption spectrum were analysed on the basis of an octahedral crystal field model. The magnetic transition temperatures and crystal field parameters determined for MUO3 (M triple bond Li, Na, K, Rb) are compared and discussed. (orig.)

  18. Mutual effect of elements during coprecipitation. Cocrystallization of rare earths in conditions of formation of double sulfates of alkali and alkaline earth metals

    International Nuclear Information System (INIS)

    Effect of solution composition on the coprecipitation of rare earths with double sulphates of alkali and alkali earth metals is studied. A principle possibility of the use of these crystal precipitates as collectors for selective rare earths concentrating out of solutions is shown. A possibility of rare earths determination after their concentrating at double salts by X-ray fluorescence, atom-emission and neutron-activation methods

  19. Methyl halide emission estimates from domestic biomass burning in Africa

    Science.gov (United States)

    Mead, M. I.; Khan, M. A. H.; White, I. R.; Nickless, G.; Shallcross, D. E.

    Inventories of methyl halide emissions from domestic burning of biomass in Africa, from 1950 to the present day and projected to 2030, have been constructed. By combining emission factors from Andreae and Merlet [2001. Emission of trace gases and aerosols from biomass burning. Global Biogeochemical Cycles 15, 955-966], the biomass burning estimates from Yevich and Logan [2003. An assessment of biofuel use and burning of agricultural waste in the developing world. Global Biogeochemical Cycles 17(4), 1095, doi:10.1029/2002GB001952] and the population data from the UN population division, the emission of methyl halides from domestic biomass usage in Africa has been estimated. Data from this study suggest that methyl halide emissions from domestic biomass burning have increased by a factor of 4-5 from 1950 to 2005 and based on the expected population growth could double over the next 25 years. This estimated change has a non-negligible impact on the atmospheric budgets of methyl halides.

  20. Halide glass containing trivalent uranium ions and its fabrication process

    International Nuclear Information System (INIS)

    This halide glass, showing an optical attenuation -1 in the near infrared from 2.2 to 304 micrometers, is prepared with a glass containing uranium ions as U4+ and/or U5+ reduced by ionizing radiations in U3+. Application is made to the fabrication of optical fibers and lasers doped with trivalent uranium

  1. Method for calcining nuclear waste solutions containing zirconium and halides

    International Nuclear Information System (INIS)

    A reduction in the quantity of gelatinous solids which are formed in aqueous zirconium-fluoride nuclear reprocessing waste solutions by calcium nitrate added to suppress halide volatility during calcination of the solution while further suppressing chloride volatility is achieved by increasing the aluminum to fluoride mole ratio in the waste solution prior to adding the calcium nitrate

  2. Solubility of alkali and alkaline earth metal sulfates in anhydrous hydrogen peroxide

    International Nuclear Information System (INIS)

    Solubility of alkali and alkaline earth metals sulfates is determined by isothermal method in anhydrous hydrogen method. Sodium sulfated of anhydrous hydrogen peroxide are crystallized in form of Na2SO4x2H2O2 solvates. Presence of peroxosolvates in the rest of solvates was not determined. Solubility of fluorides and perchlorates in hydrogen peroxide was also considered. 9 refs., 1 fig

  3. Silica enigma and ignorance in alkali

    International Nuclear Information System (INIS)

    Si migration and K, Na alterations are two key problems for understanding the whole process of hydrothermal metallogenesis, but they have not attracted sufficient attention of geologists for a long time. It is impossible for us to know hydrothermal metallogenetic regularity actually without studying dequartzfication and alkali-introduction. Being distinct from common habitual thinking, it is considered that ore-forming elements are micro-amount, passive subordinate components in the flow of hydrothermal matter movement, and there is no metallogenesis for a certain element in nature. Except that the ore source is controlled by the uneven distribution ore-forming elements in the mantle and crust the same metallogenesis may almost lead to the formation of deposits of all elements. Principal active components in the hydrothermal matter system include alkali, silica and acid volatiles. The ternary system has determined the fate of release, activation, migration, precipitaion and concentration of ore-forming elements. Each member of the ternary system plays a different role in metallogenesis, having marvellous functional division of work. of these three members main control factor is alkali metal, whereas silica and acid are constrained by alkali. Acidic matter (including silica) and ore-forming elements are derivatives from activities of alkali metals

  4. Study of the point defect creation and of the excitonic luminescence in alkali halides irradiated by swift heavy ions

    International Nuclear Information System (INIS)

    The aim of this experimental thesis is to study the excitonic mechanisms and of the defect creation, in NaCl and KBr, under dense electronic excitations induced by swift heavy ion irradiations. In the first part, we present the main features of the interaction of swift heavy ions with solid targets, and after we review the well known radiolytic processes of the defect creation during X-ray irradiation. In the second chapter, we describe our experimental set-up. In the chapter III, we present our results of the in-situ optical absorption measurements. This results show that defect creation is less sensitive to the temperature than during a classical irradiation. Besides, we observe new mechanisms concerning the defect aggregation. In the chapter IV, we present the results of excitonic luminescence induced by swift by swift heavy ions. We observe that the luminescence yields only change with the highest electronic stopping power. In the chapter V, we perform thermal spike and luminescence yields calculations and we compare the numerical results to the experiments presented in the chapter IV. (author). 121 refs., 65 figs., 30 tabs

  5. Molecular Simulation of Aqueous Electrolyte Solubility. 3. Alkali-halide Salts and Their Mixtures in Water and in Hydrochloric Acid.

    Czech Academy of Sciences Publication Activity Database

    Mou?ka, F.; Lísal, Martin; Smith, W. R.

    2012-01-01

    Ro?. 116, ?. 18 (2012), s. 5468-5478. ISSN 1520-6106 R&D Projects: GA ?R GA203/08/0094; GA MŠk LH12020 Grant ostatní: NSERC(CA) OGP1041; EC(XE) COST TD0802 Institutional research plan: CEZ:AV0Z40720504 Keywords : molecular simulations * electrolyte hydrates * oemc simulations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.607, year: 2012

  6. N,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) on alkali halide(001) surfaces

    OpenAIRE

    Fendrich, Markus; Lange, Manfred; WEISS, CHRISTIAN; Kunstmann, Tobias; Moeller, Rolf

    2008-01-01

    The growth of N,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) (DiMe-PTCDI) on KBr(001) and NaCl(001) surfaces has been studied. Experimental results have been achieved using frequency modulation atomic force microscopy at room temperature under ultra-high vacuum conditions. On both substrates, DiMe-PTCDI forms molecular wires with a width of 10 nm, typically, and a length of up to 600 nm at low coverages. All wires grow along the [110] direction (or [1$\\bar{1}$0] direction...

  7. Alkali subhalides: high-pressure stability and interplay between metallic and ionic bonds.

    Science.gov (United States)

    Saleh, G; Oganov, A R

    2016-01-20

    The application of high pressure (hundreds of gigapascals) to materials, besides modifying their properties, changes dramatically their reactivity. Consequently, new compounds are formed, which violate the chemical paradigms known to date. In fact, it was recently discovered (Zhang et al., Science, 2013) that sodium subchlorides (NaxCl, x > 1) become stable at high pressure. In this work, we carry out a thorough study of these compounds as well as of other alkali subhalides by means of evolutionary crystal structure prediction calculations combined with an in-depth analysis of their crystal and electronic structures. The results of our investigation are threefold. We present an updated phase diagram of NaxCl, including one new compound (Na4Cl3) and two previously undiscovered phases of Na3Cl. We demonstrate the appearance of remarkable features in the electronic structure of sodium subchlorides, such as chlorine atoms acquiring a -2 oxidation state. Most importantly, we derive a model which enables one to rationalize the stability of alkali subhalides at high pressure. The predictive ability of our model was validated by the results of crystal structure prediction calculations we carried out on alkali subhalides A3Y (A = Li, Na, K; Y = F, Cl, Br). Moreover, we show how the stability of recently reported high-pressure compounds can be rationalized on the basis of the insights gained in the present study. PMID:26728327

  8. Second virial coefficients of alkali vapours

    International Nuclear Information System (INIS)

    Based on the ab initio calculations of Bertoncini et al, (J. Chem. Phys.; 52:5112 (1970)), on the triplet state of LiNa, the present authors proposed a Sato-type anti-Morse potential for the alkali dimers and used this in the calculation of Bsup((3))(T) [the triplet state contribution to the second virial coefficient] of alkali vapours. In this note the potential is compared with those of other workers in the calculation of Bsup((3))(T) and the second virial coefficients of all the alkali vapours are calculated over a wide range of temperature using the Morse and Rydberg potentials for the ground state and the anti-Morse potential for the triplet state of the dimers. (U.K.)

  9. Photoluminescence of Au - formed in 12CaO · 7Al 2O 3 single crystal by Au +-implantation

    Science.gov (United States)

    Miyakawa, M.; Kamioka, H.; Hirano, M.; Kamiya, T.; Hosono, H.

    2006-09-01

    Au + ion implantation with fluences from 1 × 10 14 to 3 × 10 16 cm -2 into 12CaO · 7Al 2O 3 (C12A7) single crystals was carried out at a sample temperature of 600 °C. The implanted sample with the fluence of 1 × 10 15 cm -2 exhibited photoluminescence (PL) bands peaking at ˜3.1 and ˜2.3 eV at ?150 K when excited by He-Cd laser (325 nm). This was the first observation of PL from C12A7. These two PL bands are possibly due to intra-ionic transitions of an Au - ion having the electronic configuration of 6 s2, judged from their similarities to those reported on Au - ions in alkali halides. However, when the concentration of the implanted Au ions exceeded the theoretical maximum value of anions encaged in C12A7 (˜2.3 × 10 21 cm -3), surface plasmon absorption appeared in the optical absorption spectrum, suggesting Au colloids were formed at such high fluences. These observations indicate that negative gold ions are formed in the cages of C12A7 by the Au + implantation if an appropriate fluence is chosen.

  10. Photoluminescence of Au- formed in 12CaO . 7Al2O3 single crystal by Au+-implantation

    International Nuclear Information System (INIS)

    Au+ ion implantation with fluences from 1 x 1014 to 3 x 1016 cm-2 into 12CaO . 7Al2O3 (C12A7) single crystals was carried out at a sample temperature of 600 deg. C. The implanted sample with the fluence of 1 x 1015 cm-2 exhibited photoluminescence (PL) bands peaking at ?3.1 and ?2.3 eV at ?150 K when excited by He-Cd laser (325 nm). This was the first observation of PL from C12A7. These two PL bands are possibly due to intra-ionic transitions of an Au- ion having the electronic configuration of 6s 2, judged from their similarities to those reported on Au- ions in alkali halides. However, when the concentration of the implanted Au ions exceeded the theoretical maximum value of anions encaged in C12A7 (?2.3 x 1021 cm-3), surface plasmon absorption appeared in the optical absorption spectrum, suggesting Au colloids were formed at such high fluences. These observations indicate that negative gold ions are formed in the cages of C12A7 by the Au+ implantation if an appropriate fluence is chosen

  11. Alkali metal vapors - Laser spectroscopy and applications

    Science.gov (United States)

    Stwalley, W. C.; Koch, M. E.

    1980-01-01

    The paper examines the rapidly expanding use of lasers for spectroscopic studies of alkali metal vapors. Since the alkali metals (lithium, sodium, potassium, rubidium and cesium) are theoretically simple ('visible hydrogen'), readily ionized, and strongly interacting with laser light, they represent ideal systems for quantitative understanding of microscopic interconversion mechanisms between photon (e.g., solar or laser), chemical, electrical and thermal energy. The possible implications of such understanding for a wide variety of practical applications (sodium lamps, thermionic converters, magnetohydrodynamic devices, new lasers, 'lithium waterfall' inertial confinement fusion reactors, etc.) are also discussed.

  12. Matrix isolation infrared spectra of hydrogen halide and halogen complexes with nitrosyl halides

    Science.gov (United States)

    Allamandola, Louis J.; Lucas, Donald; Pimentel, George C.

    1982-01-01

    Matrix isolation infrared spectra of nitrosyl halide (XNO) complexes with HX and X2 (X = Cl, Br) are presented. The relative frequency shifts of the HX mode are modest (ClNO H-Cl, delta-nu/nu = -0.045; BrNO H-Br, delta-nu/nu = -0.026), indicating weak hydrogen bonds 1-3 kcal/mol. These shifts are accompanied by significant shifts to higher frequencies in the XN-O stretching mode (CIN-O HCl, delta-nu/nu = +0.016; BrN-O HBr, delta-nu/nu = +0.011). Similar shifts were observed for the XN-O X2 complexes (ClN-O Cl2, delta-nu/nu = +0.009; BrN-O-Br2, delta-nu/nu = +0.013). In all four complexes, the X-NO stretching mode relative shift is opposite in sign and about 1.6 times that of the NO stretching mode. These four complexes are considered to be similar in structure and charge distribution. The XN-O frequency shift suggests that complex formation is accompanied by charge withdrawal from the NO bond ranging from about .04 to .07 electron charges. The HX and X2 molecules act as electron acceptors, drawing electrons out of the antibonding orbital of NO and strengthening the XN-O bond. The implications of the pattern of vibrational shifts concerning the structure of the complexes are discussed.

  13. Lighter Alkali hydride and deuteride 1: Electronic properties of pure solids

    International Nuclear Information System (INIS)

    The properties of lighter alkali hydrides of metals which crystallize in the rock-salt structure are discussed. First, the properties of pure crystals which are dominated by the electrons, in particular the energy levels and the eigenstates of the electrons in the absence of lattice defects are considered. After that, the optical properties of the solids excited at photon energies larger than those appropriate to lattice vibration and dominated by the transition of electron from the occupied core and valence levels to the normally empty conduction states, are discussed. 127 refs, 29 figs, 17 tabs

  14. Effect of alkali and heat treatments for bioactivity of TiO2 nanotubes

    Science.gov (United States)

    Kim, Seo young; Kim, Yu kyoung; Park, Il song; Jin, Guang chun; Bae, Tae sung; Lee, Min ho

    2014-12-01

    In this study, for improving the bioactivity of titanium used as an implant material, alkali and heat treatments were carried out after formation of the nanotubes via anodization. Nanotubes with uniform length, diameter, and thickness were formed by anodization. The alkali and heat-treated TiO2 nanotubes were covered with the complex network structure, and the Na compound was generated on the surface of the specimens. In addition, after 5 and 10 days of immersion in the SBF, the crystallized OCP and HAp phase was significantly increased on the surface of the alkali-treated TiO2 nanotubes (PNA) and alkali and heat-treated TiO2 nanotubes (PNAH) groups. Cell proliferation was decreased due to the formation of amorphous sodium titanate (Na2TiO3) layer on the surface of the PNA group. However, anatase and crystalline sodium titanate were formed on the surface of the PNAH group after heat treatment at 550 °C, and cell proliferation was improved. Thus, PNA group had higher HAp forming ability in the simulated body fluid. Additional heat treatment affected on enhancement of the bioactivity and the attachment of osteoblasts for PNA group.

  15. Solvent-free MALDI investigation of the cationization of linear polyethers with alkali metals.

    Science.gov (United States)

    Hortal, Ana R; Hurtado, Paola; Martínez-Haya, Bruno; Arregui, Andrés; Bañares, Luis

    2008-07-24

    The MALDI technique with solvent-free sample preparation has been applied to evaluate relative gas-phase affinities of polyether chain polymers with alkali metal cations. The study is performed on poly(ethylene glycol) and poly(propylene glycol) polymers of different lengths (PEG600, PEG1000, PPG425, PPG750) and the alkali metal cations Li(+), Na(+), K(+), and Cs(+). The experiments show that the lattice energy of the alkali metal salts employed as cation precursors can have a strong influence on the outcome of conventional MALDI measurements. With the solvent-free method, these crystal binding effects can be made negligible by combining in the same sample alkali metal salts with different counterions. The recorded MALDI spectra show that the polyether-cation aggregation efficiencies decrease systematically with growing cation size. This cation size selectivity is considerably enhanced for the polymers with the shorter chains, which can be attributed to the reduced ability of the polymer to build a coordination shell around the larger cations. The steric effects introduced by the side CH3 group of propylene glycol with respect to ethylene glycol also enhance the preference for cationization of the polymer by the smaller cations. These observations correct some qualitative trends derived from previous studies, which did not account for lattice energy effects of the cation precursors. PMID:18582106

  16. 40 CFR 721.4660 - Alcohol, alkali metal salt.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alcohol, alkali metal salt. 721.4660... Substances § 721.4660 Alcohol, alkali metal salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as alcohol, alkali metal salt (PMN P-91-151)...

  17. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Science.gov (United States)

    2010-07-01

    ..., alkali salt. 721.5278 Section 721.5278 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.5278 Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical... as a substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to reporting...

  18. 40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.

    Science.gov (United States)

    2010-07-01

    ..., alkali salt. 721.8900 Section 721.8900 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.8900 Substituted halogenated pyridinol, alkali salt. (a) Chemical... as substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and P-88-1272) are subject...

  19. Synthesis and Characterization of Novel Ternary and Quaternary Alkali Metal Thiophosphates

    KAUST Repository

    Alahmary, Fatimah S.

    2014-05-01

    The ongoing development of nonlinear optical (NLO) crystals such as coherent mid-IR sources focuses on various classes of materials such as ternary and quaternary metal chalcophosphates. In case of thiophosphates, the connection between PS4-tetrahedral building blocks and metals gives rise to a broad structural variety where approximately one third of all known ternary (A/P/S) and quaternary (A/M/P/S) (A = alkali metal, M = metal) structures are acentric and potential nonlinear optical materials. The molten alkali metal polychalcophosphate fluxes are a well-established method for the synthesis of new ternary and quaternary thiophosphate and selenophosphate compounds. It has been a wide field of study and investigation through the last two decades. Here, the flux method is used for the synthesis of new quaternary phases containing Rb, Ag, P and S. Four new alkali metal thiophosphates, Rb4P2S10, RbAg5(PS4), Rb2AgPS4 and Rb3Ag9(PS4)4, have been synthesized successfully from high purity elements and binary starting materials. The new compounds were characterized by single crystal and powder X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet-visible (UV-VIS), Raman spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). These compounds show interesting structural variety and physical properties. The crystal structures feature 3D anionic framework built up of PS4 tetrahedral units and charge balanced by Ag and alkali metal cations. All prepared compounds are semiconductors with band gap between 2.3 eV to 2.6 eV and most of them are thermally stable up to 600ºC.

  20. Lanthanum halide scintillators: Properties and applications

    International Nuclear Information System (INIS)

    BrilLanCe[reg]-350 and BrilLanCe[reg]-380, Saint-Gobain Crystals' trade-names for LaCl3:Ce and LaBr3:Ce are being brought to market under exclusive license to Delft and Bern Universities. We are reporting the properties of crystals produced with commercially viable processes and find they match others' observations. These scintillators are bright (60,000 photons/MeV for LaBr3:Ce) and have very linear response, a combination that leads to very good energy resolution (3:Ce). The materials also have fast scintillation decay times (3:Ce). These excellent properties are retained at high temperature with only moderate light loss (138 and Ac227, the latter having been substantially reduced in recent processing. BrilLanCe[reg]-350 is now available in detectors up to 51 mm diameter while 38 mm diameter is available for BrilLanCe[reg]-380. Larger sizes are expected

  1. Alkali resistant optical coatings for alkali lasers and methods of production thereof

    Science.gov (United States)

    Soules, Thomas F; Beach, Raymond J; Mitchell, Scott C

    2014-11-18

    In one embodiment, a multilayer dielectric coating for use in an alkali laser includes two or more alternating layers of high and low refractive index materials, wherein an innermost layer includes a thicker, >500 nm, and dense, >97% of theoretical, layer of at least one of: alumina, zirconia, and hafnia for protecting subsequent layers of the two or more alternating layers of high and low index dielectric materials from alkali attack. In another embodiment, a method for forming an alkali resistant coating includes forming a first oxide material above a substrate and forming a second oxide material above the first oxide material to form a multilayer dielectric coating, wherein the second oxide material is on a side of the multilayer dielectric coating for contacting an alkali.

  2. Analysis of Melting for Alkali Earth and Alkali Oxides Based on the Diffusional Force Theory

    Science.gov (United States)

    Liu, Quan; Chen, Li-Rong

    An analysis of the melting alkali earth and alkali oxides is presented using the concept of diffusional force. The calculations are performed by developing an ionic model based on Harrison's quantum mechanical treatment of overlap repulsive potential which takes into account the interactions up to second neighbors. Van der Waals dipole-dipole and dipole-quadrupole interactions calculated by more accurate methods are also included in the model. Using the formula by Fang, derived on the basis of thermodynamic analysis, the values of interionic distances for 8 alkali earth and alkali oxides at melting have been obtained. A simple model for melting is developed based on the diffusional force models. The values of Tm thus obtained are found to show fairly good agreement with experimental values of melting temperatures.

  3. Positronium impact ionization of Alkali atoms

    CERN Document Server

    Ghosh, D

    2015-01-01

    Target ionization processes of alkali atoms by Positronium impact are investigated. Calculations are performed in the frame work of model potential formalism using the Coulomb distorted eikonal approximation. Interesting qualitative features are noted both in the scattered Ps and the ejected electron distributions in differential as well as double differential levels of the collision cross sections.

  4. Corrosion and compatibility in liquid alkali metals

    International Nuclear Information System (INIS)

    The literature dealing with liquid alkali metal corrosion of vanadium and its alloys is reviewed in the following subsections. Attention is given to both lithium and sodium data. Preceding this review, a brief outline of the current state of understanding of liquid metal corrosion mechanisms is provided

  5. Contributions to the mixed-alkali effect in molecular dynamics simulations of alkali silicate glasses

    OpenAIRE

    Lammert, Heiko; Heuer, Andreas

    2005-01-01

    The mixed-alkali effect on the cation dynamics in silicate glasses is analyzed via molecular dynamics simulations. Observations suggest a description of the dynamics in terms of stable sites mostly specific to one ionic species. As main contributions to the mixed--alkali slowdown longer residence times and an increased probability of correlated backjumps are identified. The slowdown is related to the limited accessibility of foreign sites. The mismatch experienced in a forei...

  6. Nonlinear lattice relaxation of photoexcited diplatinum-halide chain compounds

    CERN Document Server

    Ohara, J; Ohara, Jun; Yamamoto, Shoji

    2006-01-01

    In order to reveal the relaxation mechanism of photogenerated charge-transfer excitations in quasi-one-dimensional halogen-bridged diplatinum complexes, we calculate the low-lying adiabatic potential energy surfaces of a one-dimensional extended Peierls-Hubbard model. High-energy excitations above the electron-hole continuum may relax into polarons, while excitons pumped within the optical gap are self-localized and then either decay by luminescence or divide into solitons. Neutral solitons, charged solitons, and polarons may be simultaneously photogenerated in a diplatinum-halide chain, which has never been observed in any conventional platinum-halide chain. Optical conductivity is also simulated along the decay paths for experimental verification.

  7. He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth

    Science.gov (United States)

    Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.

  8. He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth

    International Nuclear Information System (INIS)

    Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves

  9. Organic-inorganic hybrid photovoltaics based on organometal halide perovskites

    OpenAIRE

    Lee, Michael M.; Henry J. Snaith

    2013-01-01

    This thesis details the development of a novel photovoltaic device based on organometal halide perovskites. The initial focus of this thesis begins with the study of lighttrapping strategies in solid-state dye-sensitised solar cells (detailed in chapter 3). While I report enhancement in device performance through the application of near and far-?eld light-trapping techniques, I ?nd that improvements remain step-wise due to fundamental limitations currently employed in dye-sensitised ...

  10. Study of methyl halide fluxes in temperate and tropical ecosystems

    OpenAIRE

    Blei, Emanuel

    2010-01-01

    CH3Br and CH3Cl (methyl halides) are the most abundant natural vectors of bromine and chlorine into the stratosphere and play an important role in stratospheric ozone destruction. The current knowledge of their respective natural sources is incomplete leading to large uncertainties in their global budgets. Beside the issue of quantification, characterisation of possible sources is needed to assist modelling of future environmental change impacts on these sources and hence the s...

  11. Silver halide sensitized gelatin derived from BB-640 holographic emulsion

    OpenAIRE

    Neipp lópez, Cristian; Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto

    1998-01-01

    Silver halide sensitized gelatin (SHSG) is one of the most interesting techniques for the production of holographic optical elements, achieving relatively high sensitivity of photographic material with a low scattering of dichromated gelatin. Here we present experimental results for SHSG derived from the novel BB-640, a red-sensitive ultra-fine-grain emulsion from Holographic Recording Technologies (Steinau, Germany). The material is characterized before recording and after processing, and in...

  12. Influence of the Print Run on Silver Halide Printing Plates

    Directory of Open Access Journals (Sweden)

    Tomislav Cigula

    2010-09-01

    Full Text Available The most common printing technique today is lithography. The difference between printing and nonprinting areason a printing plate is accomplished by opposite physical and chemical properties of those areas (MacPhee, 1998.The printing areas are made of photoactive layer that attracts oil and chemical substances with oil solvent – printinginks. The nonprinting areas are made of aluminium-oxide which attracts water based substances – the fountainsolution.There are many of various types of photoactive layer which are used for production of offset printing plates, amongothers is silver halide layer. The usage of the silver halide technology in the graphic reproduction is not a novelty.The filmmaking phase is based on the usage of the silver halide as the photographically active ingredient, for instance,AgBr (silver bromide. The new, digital plate making technology (Computer to Plate, CtP eliminates thefilmmaking phase and therefore enables control of the printing plate’s exposure made by computer. CtP technologyeliminates the filmmaking phase, but it also results with the reduction of needed material quantities and requiredtime for the production (Limburg, 1994; Seydel, 1996.In this paper the basis of the graphic reproduction by using the silver halide digital printing plates was described.The changes of the AgX copying layer and the surface of the aluminium base in the printing process have beenobserved. The surface characteristics were determined by measuring the relevant surface roughness parameters. Inaddition, measurements of coverage values on the prints, detailed at smaller print run, were conducted.Results showed that surface changes on the printing plate are changing during printing process and that thesechanges influence transfer of the printing ink on the printing substrate. These measurements proved to be of greatinterest in the graphic reproduction as they enable us to determine consistency of the printing plates during theprinting process, to predict the endurance as well as to define the print run which will result with optimal qualityprints.

  13. Silver halide sensitized gelatin as a holographic storage medium

    OpenAIRE

    Fimia Gil, Antonio; Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto

    1988-01-01

    Silver halide sensitized gelatin is one of the most promising techniques for the manufacturing of transmission holographic optical elements. These techniques combine the relatively high sensitivity of photographic material with the low scattering and high light-stability of dichromated gelatin. The influences of the developer and the bleaching in the diffraction efficiency and noise is analyzed starting with Agfa 8E75 HD plates.

  14. Reflection holographic optical elements in silver-halide sensitized gelatin

    OpenAIRE

    Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto; Fimia Gil, Antonio

    1991-01-01

    Silver halide sensitized gelatin has proven to be an alternative to dichromated gelatin as a recording material in the production of transmission holographic optical elements (HOEs). In this paper we discuss the possible applications of this process to the production of reflection HOEs as well as the possible use of one of them in the construction of a hybrid refraction- diffraction system that could be used to copy transmission HOEs using partially coherent light.

  15. Silver halide sensitized gelatin holograms using Slavich PFG-01 emulsion

    OpenAIRE

    Pascual Villalobos, Inmaculada; Neipp lópez, Cristian; Beléndez Vázquez, Augusto

    1999-01-01

    Silver halide sensitized gelatin (SHSG) is an interesting technique for the production of holographic optical elements. It combines the high sensitivity of photographic emulsions with the well-known low scattering and high diffraction efficiency corresponding to dichromated gelatin. In this paper we present a comparative study of SHSG holograms recorded on both Slavich PFG-01 and Agfa 8E75 HD emulsions. We will show that real high diffraction efficiencies can be obtained (as high as 93% allo...

  16. Silver halide sensitized gelatin as a holographic recording material

    OpenAIRE

    Fimia Gil, Antonio; Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto

    1994-01-01

    Silver halide sensitized gelatin (SHSG) has proven to be a good alternative to dichromated gelatin and bleached emulsions in the production of volume phase holographic optical elements. In the present paper, the processing procedure for SHSG derived from Agfa-Gevaert holographic plates is reviewed and the holographic characteristics of the processed SHSG are experimentally measured and analysed. Several important aspects related to the influence of the developer and the bleach bath, the noise...

  17. Halide-bridged binuclear HX-splitting catalysts.

    Science.gov (United States)

    Powers, David C; Hwang, Seung Jun; Zheng, Shao-Liang; Nocera, Daniel G

    2014-09-01

    Two-electron mixed-valence compounds promote the rearrangement of the two-electron bond photochemically. Such complexes are especially effective at managing the activation of hydrohalic acids (HX). Closed HX-splitting cycles require proton reduction to H2 and halide oxidation to X2 to be both accomplished, the latter of which is thermodynamically and kinetically demanding. Phosphazane-bridged Rh2 catalysts have been especially effective at activating HX via photogenerated ligand-bridged intermediates; such intermediates are analogues of the classical ligand-bridged intermediates proposed in binuclear elimination reactions. Herein, a new family of phosphazane-bridged Rh2 photocatalysts has been developed where the halide-bridged geometry is designed into the ground state. The targeted geometries were accessed by replacing previously used alkyl isocyanides with aryl isocyanide ligands, which provided access to families of Rh2L1 complexes. H2 evolution with Rh2 catalysts typically proceeds via two-electron photoreduction, protonation to afford Rh hydrides, and photochemical H2 evolution. Herein, we have directly observed each of these steps in stoichiometric reactions. Reactivity differences between Rh2 chloride and bromide complexes have been delineated. H2 evolution from both HCl and HBr proceeds with a halide-bridged Rh2 hydride photoresting state. The H2-evolution efficiency of the new family of halide-bridged catalysts is compared to a related catalyst in which ligand-bridged geometries are not stabilized in the molecular ground state, and the new complexes are found to more efficiently facilitate H2 evolution. PMID:25137532

  18. Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

    Directory of Open Access Journals (Sweden)

    Satoshi Kamiguchi

    2014-04-01

    Full Text Available Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the cluster framework is retained up to 350–450 °C. One of the active sites is a Brønsted acid resulting from a hydroxo ligand that is produced by the elimination of hydrogen halide from the halogen and aqua ligands. The other active site is a coordinatively unsaturated metal, which can be isoelectronic with the platinum group metals by taking two or more electrons from the halogen ligands. In the case of the rhenium chloride cluster Re3Cl9, the cluster framework is stable at least up to 300 °C under inert atmosphere; however, it is reduced to metallic rhenium at 250–300 °C under hydrogen. The activated clusters are characterized by X-ray diffraction analyses, Raman spectrometry, extended X-ray absorption fine structure analysis, thermogravimetry–differential thermal analysis, infrared spectrometry, acid titration with Hammett indicators, and elemental analyses.

  19. Reaction of mesophase pitch and semicoke with halogens and halides

    Energy Technology Data Exchange (ETDEWEB)

    Preiss, H. (Academy of Sciences of the GDR, Berlin. Central Institute of Physical Chemistry)

    1989-10-01

    The reaction of both mesophase pitch and semicoke with halogens and halides has been studied. Absorption of chlorine and bromine, and subsequent desorption indicate the existence of both loosely- and strongly-held halogens in the pyrolysed pitch. The absorbed halogen concentration decreases when the pyrolysis temperature of the pitch increases. The total concentration of absorbed bromine in mesophase pitch is three times higher than that in stage 2 bromine graphite, however, no X-ray evidence for intercalation has been found. The mechanism of fixation of the strongly-held halogen atoms is discussed in view of the content of C-H groups. Mesophase pitch absorbs non-oxidizing halides (e.g. AsCl{sub 3}, SbCl{sub 3}) without any indication of interlayer intercalate ordering. Oxidizing halides (e.g. SbCl{sub 5}, PCl{sub 5}) react with mesophase pitches and semi-cokes, forming halogenated pitches with a halogen content ranging from about 30-50 wt%. 20 refs., 5 figs., 2 tabs.

  20. Methyl halide emissions from greenhouse-grown mangroves

    Science.gov (United States)

    Manley, Steven L.; Wang, Nun-Yii; Walser, Maggie L.; Cicerone, Ralph J.

    2007-01-01

    Two mangrove species, Avicennia germinans and Rhizophora mangle, were greenhouse grown for nearly 1.5 years from saplings. A single individual of each species was monitored for the emission of methyl halides from aerial tissue. During the first 240 days, salinity was incrementally increased with the addition of seawater, and was maintained between 18 and 28‰ for the duration of the study. Exponential growth occurred after 180 days. Methyl halide emissions normalized to leaf area were measured throughout the study and varied dramatically. Emission rates normalized to land area (mg m-2 y-1), assuming a LAI = 5, yielded 82 and 29 for CH3Cl, 10 and 1.6 for CH3Br, and 26 and 11 for CH3I, for A. germinans and R. mangle, respectively. From these preliminary determinations, only CH3I emissions emerge as being of possible global atmospheric significance. This study emphasizes the need for field studies of methyl halide emissions from mangrove forests.

  1. Sample preparation and crystal growth for solid state actinide research

    International Nuclear Information System (INIS)

    The authors review the latest developments in the preparation of actinide samples for solid state physics investigations. Metallothermic reduction of the actinide halides, oxides and carbides in the preparation of actinide metals is discussed. Various methods of refining the metals are presented. Then the synthesis of actinide compounds is considered. Finally the various methods of crystal growth are reviewed. (Auth.)

  2. Anionic halide···alcohol clusters in the solid state.

    Science.gov (United States)

    Gushchin, Pavel V; Kuznetsov, Maxim L; Haukka, Matti; Kukushkin, Vadim Yu

    2014-10-01

    The cationic (1,3,5-triazapentadiene)Pt(II) complexes [1](Cl)2, [2](Cl)2, [3](Br)2, and [4](Cl)2, were crystallized from ROH-containing systems (R = Me, Et) providing alcohol solvates studied by X-ray diffraction. In the crystal structures of [1-4][(Hal)2(ROH)2] (R = Me, Et), the Hal(-) ion interacts with two or three cations [1-4](2+) by means of two or three or four contacts thus uniting stacked arrays of complexes into the layers. The solvated MeOH or EtOH molecules occupy vacant space, giving contacts with [1-4](2+), and connects to the Hal(-) ion through a hydrogen bridge via the H(1O)O(1S) H atom forming, by means of the Hal(-)···HOR (Hal = Cl, Br) contact, the halide-alcohol cluster. Properties of the Cl(-)···HO(Me) H-bond in [1][(Cl)2(MeOH)2] were analyzed using theoretical DFT methods. PMID:25192004

  3. The etching process of boron nitride by alkali and alkaline earth fluorides under high pressure and high temperature

    Energy Technology Data Exchange (ETDEWEB)

    Guo, W., E-mail: guowei1982cry@163.com [College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Ma, H.A.; Jia, X. [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China)

    2014-03-01

    Graphical abstract: - Highlights: • Appropriate etch processes of hBN and cBN under HPHT are proposed. • The degree of the crystallization of hBN was decreased. • A special cBN growth mechanism with a triangular unit is proposed. • Plate-shape cBN crystals with large ratio of length to thickness were obtained. • A strategy provides useful guidance for controlling the cBN morphology. - Abstract: Some new etching processes of hexagonal boron nitride (hBN) and cubic boron nitride (cBN) under high pressure and high temperature in the presence of alkali and alkaline earth fluorides have been discussed. It is found that hBN is etched distinctly by alkali and alkaline earth fluorides and the morphology of hBN is significantly changed from plate-shape to spherical-shape. Based on the “graphitization index” values of hBN, the degree of the crystallization of hBN under high pressure and high temperature decreases in the sequence of LiF > CaF{sub 2} > MgF{sub 2}. This facilitates the formation of high-quality cBN single crystals. Different etch steps, pits, and islands are observed on cBN surface, showing the strong etching by alkali and alkaline earth fluorides and the tendency of layer-by-layer growth. A special layer growth mechanism of cBN with a triangular unit has been found. Furthermore, the morphologies of cBN crystals are apparently affected by a preferential surface etching of LiF, CaF{sub 2} and MgF{sub 2}. Respectively, the plate-shape and tetrahedral cBN crystals can be obtained in the presence of different alkali and alkaline earth fluorides.

  4. The etching process of boron nitride by alkali and alkaline earth fluorides under high pressure and high temperature

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Appropriate etch processes of hBN and cBN under HPHT are proposed. • The degree of the crystallization of hBN was decreased. • A special cBN growth mechanism with a triangular unit is proposed. • Plate-shape cBN crystals with large ratio of length to thickness were obtained. • A strategy provides useful guidance for controlling the cBN morphology. - Abstract: Some new etching processes of hexagonal boron nitride (hBN) and cubic boron nitride (cBN) under high pressure and high temperature in the presence of alkali and alkaline earth fluorides have been discussed. It is found that hBN is etched distinctly by alkali and alkaline earth fluorides and the morphology of hBN is significantly changed from plate-shape to spherical-shape. Based on the “graphitization index” values of hBN, the degree of the crystallization of hBN under high pressure and high temperature decreases in the sequence of LiF > CaF2 > MgF2. This facilitates the formation of high-quality cBN single crystals. Different etch steps, pits, and islands are observed on cBN surface, showing the strong etching by alkali and alkaline earth fluorides and the tendency of layer-by-layer growth. A special layer growth mechanism of cBN with a triangular unit has been found. Furthermore, the morphologies of cBN crystals are apparently affected by a preferential surface etching of LiF, CaF2 and MgF2. Respectively, the plate-shape and tetrahedral cBN crystals can be obtained in the presence of different alkali and alkaline earth fluorides

  5. A study of the influence of slag alkali level on the alkali-silica reactivity of slag concrete

    OpenAIRE

    Hester, David; McNally, Ciaran; Richardson, Mark G.

    2005-01-01

    Ground granulated blast furnace slag (ggbs), can reduce the alkali load in concrete, despite its relatively high alkali content. Most research has been devoted to the efficacy of slag with an alkali content of less than 1.0% and this is reflected in guidance documents. A comparative assessment was made of the effect, if any, of the alkali level of ggbs on potential alkali-silica reactivity. Expansion tests were performed on a matrix of concrete mixes using Irish normal Portland cement, two sl...

  6. Superconductivity in room-temperature stable electride and high-pressure phases of alkali metals.

    Science.gov (United States)

    Hosono, Hideo; Kim, Sung-Wng; Matsuishi, Satoru; Tanaka, Shigeki; Miyake, Atsushi; Kagayama, Tomoko; Shimizu, Katsuya

    2015-03-13

    S-band metals such as alkali and alkaline earth metals do not undergo a superconducting transition (SCT) at ambient pressure, but their high-pressure phases do. By contrast, room-temperature stable electride [Ca24Al28O64](4+)?4e(-) (C12A7:e(-)) in which anionic electrons in the crystallographic sub-nanometer-size cages have high s-character exhibits SCT at 0.2-0.4?K at ambient pressure. In this paper, we report that crystal and electronic structures of C12A7:e(-) are close to those of the high-pressure superconducting phase of alkali and alkaline earth metals and the SCT of both materials is induced when electron nature at Fermi energy (EF) switches from s- to sd-hybridized state. PMID:25666076

  7. Preparation of lithium manganese oxides in molten alkali hydroxides and their electrochemical properties

    Energy Technology Data Exchange (ETDEWEB)

    Katayama, K.; Higuchi, M.; Azuma, Y. [Tokai Univ., Kanagawa (Japan). Dept. of Industrial Chemistry; Yukawa, M.; Suhara, M. [Seimi Chemical Co., Ltd., Chigasaki (Japan)

    2002-07-01

    Lithium manganese oxides, which are used as cathode materials in lithium rechargeable batteries, were prepared by using molten alkali hydroxides, and the electrochemical properties of these oxide powders were evaluated. The composition of alkali hydroxides and heating period altered the composition and crystal structure of the powders, with the shorter period being the more favorable in this preparation method. The cathode performance of the batteries prepared using these powders was evaluated as satisfactory. This method was also applied to the preparation of doped lithium manganese oxide powders with a composition of LiMn{sub 0.9}M{sub 0.1}O{sub 2}(M: Co, Ni, Cr, Al, Ag, Fe), which also showed promising properties for use as cathode materials in rechargeable lithium batteries. These results indicated that this simple and quick method was promising for the preparation of cathode powders. (orig.)

  8. Time-resolved photoemission study of the electronic structure and dynamics of chemisorbed alkali atoms on Ru(0001)

    Science.gov (United States)

    Zhang, Shengmin; Wang, Cong; Cui, Xuefeng; Wang, Yanan; Argondizzo, Adam; Zhao, Jin; Petek, Hrvoje

    2016-01-01

    We investigate the electronic structure and photoexcitation dynamics of alkali atoms (Rb and Cs) chemisorbed on transition-metal Ru(0001) single-crystal surface by angle- and time-resolved multiphoton photoemission. Three- and four-photon photoemission (3PP and 4PP) spectroscopic features due to the σ and π resonances arising from the n s and n p states of free alkali atoms are observed from ˜2 eV below the vacuum level in the zero-coverage limit. As the alkali coverage is increased to a maximum of 0.02 monolayers, the resonances are stabilized by formation of a surface dipole layer, but in contrast to alkali chemisorption on noble metals, both resonances form dispersive bands with nearly free-electron mass. Density functional theory calculations attribute the band formation to substrate-mediated interaction involving hybridization with the unoccupied d bands of the substrate. Time-resolved measurements quantify the phase and population relaxation times in the three-photon photoemission (3PP) process via the σ and π resonances. Differences between alkali-atom chemisorption on noble and transition metals are discussed.

  9. Nanostructured Lanthanum Halides and CeBr3 for Nuclear Radiation and Detection

    Energy Technology Data Exchange (ETDEWEB)

    Paul Guss, Sanjoy Mukhopadhyay, Ron Guise, Ding Yuan

    2010-06-09

    Scintillator materials are used to detect, and in some cases identify, gamma rays. Higher performance scintillators are expensive, hard to manufacture, fragile, and sometimes require liquid nitrogen or cooling engines. But whereas lower-quality scintillators are cheap, easy to manufacture, and more rugged, their performance is lower. At issue: can the desirable qualities of high-and low-performance scintillators be combined to achieve better performance at lower cost? Preliminary experiments show that a LaF{sub 3}:Ce oleic acid-based nanocomposite exhibits a photopeak when exposed to {sup 137}Cs source gamma-radiation. The chemical synthesis of the cerium-doped lanthanum halide nanoparticles are scalable and large quantities of material can be produced at a time, unlike typical crystal growth processes such as the Bridgeman process. Using a polymer composite (Figure 1), produced by LANL, initial measurements of the unloaded and 8% LaF{sub 3}:Ce-loaded sample have been made using {sup 137}Cs sources. Figure 2 shows an energy spectrum acquired for CeF{sub 3}. The lighter plot is the measured polymer-only spectrum and the black plot is the spectrum from the nanocomposite scintillator. As the development of this material continues, the energy resolution is expected to improve and the photopeak-to-Compton ratio will become greater at higher loadings. These measurements show the expected Compton edge in the polymer-only sample, and the Compton edge and photo-peak expected in the nanophosphor composites that LANL has produced. Using a porous VYCORR with CdSe/ZnS core shell quantum dots, Letant has demonstrated that he has obtained signatures of the 241Am photopeak with energy resolution as good at NaI (Figure 3). We begin with the fact that CeBr{sub 3} crystals do not have a self-activity component as strong as the lanthanum halides. The radioactive 0.090% {sup 138}La component of lanthanum leads to significant self-activity, which will be a problem for very large detector volumes. Yet a significant strength of the nanostructure detector concept is the ability to create extremely large detector volumes by mixing nanoparticles into a transparent matrix. This would argue for use of nanoparticles other than lanthanum halides. Nanocomposites are easy to prepare; it is much less costly to use nanocomposites than to grow large whole crystals of these materials. The material can be fabricated at an industrial scale, further reducing cost. This material potentially offers the performance of $300/cc material (e.g., lanthanum bromide) at a cost of $1/cc. Because the material acts as a plastic, it is rugged and flexible, and can be made in large sheets, increasing the sensitivity of a detector using it. It would operate at ambient temperatures. Very large volumes of detector may be produced at greatly reduced cost, enhancing the non-proliferation posture of the nation for the same dollar value.

  10. Nanostructured Lanthanum Halides and CeBr3 for Nuclear Radiation and Detection

    International Nuclear Information System (INIS)

    Scintillator materials are used to detect, and in some cases identify, gamma rays. Higher performance scintillators are expensive, hard to manufacture, fragile, and sometimes require liquid nitrogen or cooling engines. But whereas lower-quality scintillators are cheap, easy to manufacture, and more rugged, their performance is lower. At issue: can the desirable qualities of high-and low-performance scintillators be combined to achieve better performance at lower cost? Preliminary experiments show that a LaF3:Ce oleic acid-based nanocomposite exhibits a photopeak when exposed to 137Cs source gamma-radiation. The chemical synthesis of the cerium-doped lanthanum halide nanoparticles are scalable and large quantities of material can be produced at a time, unlike typical crystal growth processes such as the Bridgeman process. Using a polymer composite (Figure 1), produced by LANL, initial measurements of the unloaded and 8% LaF3:Ce-loaded sample have been made using 137Cs sources. Figure 2 shows an energy spectrum acquired for CeF3. The lighter plot is the measured polymer-only spectrum and the black plot is the spectrum from the nanocomposite scintillator. As the development of this material continues, the energy resolution is expected to improve and the photopeak-to-Compton ratio will become greater at higher loadings. These measurements show the expected Compton edge in the polymer-only sample, and the Compton edge and photo-peak expected in the nanophosphor composites that LANL has produced. Using a porous VYCORR with CdSe/ZnS core shell quantum dots, Letant has demonstrated that he has obtained signatures of the 241Am photopeak with energy resolution as good at NaI (Figure 3). We begin with the fact that CeBr3 crystals do not have a self-activity component as strong as the lanthanum halides. The radioactive 0.090% 138La component of lanthanum leads to significant self-activity, which will be a problem for very large detector volumes. Yet a significant strength of the nanostructure detector concept is the ability to create extremely large detector volumes by mixing nanoparticles into a transparent matrix. This would argue for use of nanoparticles other than lanthanum halides. Nanocomposites are easy to prepare; it is much less costly to use nanocomposites than to grow large whole crystals of these materials. The material can be fabricated at an industrial scale, further reducing cost. This material potentially offers the performance of $300/cc material (e.g., lanthanum bromide) at a cost of $1/cc. Because the material acts as a plastic, it is rugged and flexible, and can be made in large sheets, increasing the sensitivity of a detector using it. It would operate at ambient temperatures. Very large volumes of detector may be produced at greatly reduced cost, enhancing the non-proliferation posture of the nation for the same dollar value.

  11. Effect of alkali lignins with different molecular weights from alkali pretreated rice straw hydrolyzate on enzymatic hydrolysis.

    Science.gov (United States)

    Li, Yun; Qi, Benkun; Luo, Jianquan; Wan, Yinhua

    2016-01-01

    This study investigated the effect of alkali lignins with different molecular weights on enzymatic hydrolysis of lignocellulose. Different alkali lignins fractions, which were obtained from cascade ultrafiltration, were added into the dilute acid pretreated (DAP) and alkali pretreated (AP) rice straws respectively during enzymatic hydrolysis. The results showed that the addition of alkali lignins enhanced the hydrolysis and the enhancement for hydrolysis increased with increasing molecular weights of alkali lignins, with maximum enhancement being 28.69% for DAP and 20.05% for AP, respectively. The enhancement was partly attributed to the improved cellulase activity, and filter paper activity increased by 18.03% when adding lignin with highest molecular weight. It was found that the enhancement of enzymatic hydrolysis was correlated with the adsorption affinity of cellulase on alkali lignins, and the difference in surface charge and hydrophobicity of alkali lignins were responsible for the difference in affinity between cellulase and lignins. PMID:26496216

  12. Photoluminescence of Au{sup -} formed in 12CaO . 7Al{sub 2}O{sub 3} single crystal by Au{sup +}-implantation

    Energy Technology Data Exchange (ETDEWEB)

    Miyakawa, M. [Frontier Collaborative Research Center, Tokyo Institute of Technology, Mail Box S2-13, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)]. E-mail: m-miyakawa@lucid.msl.titech.ac.jp; Kamioka, H. [ERATO-SORST, Japan Science and Technology Agency, in Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Hirano, M. [ERATO-SORST, Japan Science and Technology Agency, in Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Kamiya, T. [ERATO-SORST, Japan Science and Technology Agency, in Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Hosono, H. [Frontier Collaborative Research Center, Tokyo Institute of Technology, Mail Box S2-13, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); ERATO-SORST, Japan Science and Technology Agency, in Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)

    2006-09-15

    Au{sup +} ion implantation with fluences from 1 x 10{sup 14} to 3 x 10{sup 16} cm{sup -2} into 12CaO . 7Al{sub 2}O{sub 3} (C12A7) single crystals was carried out at a sample temperature of 600 deg. C. The implanted sample with the fluence of 1 x 10{sup 15} cm{sup -2} exhibited photoluminescence (PL) bands peaking at {approx}3.1 and {approx}2.3 eV at {<=}150 K when excited by He-Cd laser (325 nm). This was the first observation of PL from C12A7. These two PL bands are possibly due to intra-ionic transitions of an Au{sup -} ion having the electronic configuration of 6s {sup 2}, judged from their similarities to those reported on Au{sup -} ions in alkali halides. However, when the concentration of the implanted Au ions exceeded the theoretical maximum value of anions encaged in C12A7 ({approx}2.3 x 10{sup 21} cm{sup -3}), surface plasmon absorption appeared in the optical absorption spectrum, suggesting Au colloids were formed at such high fluences. These observations indicate that negative gold ions are formed in the cages of C12A7 by the Au{sup +} implantation if an appropriate fluence is chosen.

  13. Removal of Retired Alkali Metal Test Systems

    Energy Technology Data Exchange (ETDEWEB)

    Brehm, W. F.; Church, W. R.; Biglin, J. W.

    2003-02-26

    This paper describes the successful effort to remove alkali metals, alkali metal residues, and piping and structures from retired non-radioactive test systems on the Hanford Site. These test systems were used between 1965 and 1982 to support the Fast Flux Test Facility and the Liquid Metal Fast Breeder Reactor Program. A considerable volume of sodium and sodium-potassium alloy (NaK) was successfully recycled to the commercial sector; structural material and electrical material such as wiring was also recycled. Innovative techniques were used to safely remove NaK and its residues from a test system that could not be gravity-drained. The work was done safely, with no environmental issues or significant schedule delays.

  14. Alkali metal containing battery grid lead alloy

    Energy Technology Data Exchange (ETDEWEB)

    Vikram Rao, M.; Foerster, G.S.; Hebbar, R.K.

    1979-07-03

    A lead alloy containing alkali metal and with low antimony content, characterized by improved ductility for use as an electric storage battery grid or in acidic environments, suitably contains from 0.5% to 3.0% Sb, 0.01% to 0.7% As, 0.001% to 0.7% Sn, 0.001% to 0.15% Cu, 0.001% to 0.015% S or 0.001% to 0.05% Se or admixtures thereof, and 0.001% to 0.05% of an alkali metal. Battery grids made from the alloy are resistant to electrochemical corrosion, gassing, and grid growth, and exhibit improved bend ductility. 3 tables.

  15. Geopolymers and Related Alkali-Activated Materials

    Science.gov (United States)

    Provis, John L.; Bernal, Susan A.

    2014-07-01

    The development of new, sustainable, low-CO2 construction materials is essential if the global construction industry is to reduce the environmental footprint of its activities, which is incurred particularly through the production of Portland cement. One type of non-Portland cement that is attracting particular attention is based on alkali-aluminosilicate chemistry, including the class of binders that have become known as geopolymers. These materials offer technical properties comparable to those of Portland cement, but with a much lower CO2 footprint and with the potential for performance advantages over traditional cements in certain niche applications. This review discusses the synthesis of alkali-activated binders from blast furnace slag, calcined clay (metakaolin), and fly ash, including analysis of the chemical reaction mechanisms and binder phase assemblages that control the early-age and hardened properties of these materials, in particular initial setting and long-term durability. Perspectives for future research developments are also explored.

  16. Structural characterization of alkali metal 3-nitrobenzoates

    Science.gov (United States)

    ?wis?ocka, R.; Oleksi?ski, E.; Regulska, E.; Kalinowska, M.; Lewandowski, W.

    2007-05-01

    In this paper, the influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of the 3-nitrobenzoic acid was studied. The vibrational (FT-IR, FT-Raman) and NMR ( 1H and 13C) spectra for 3-nitrobenzoic acid and its alkali metal salts were recorded. The changes of chemical shifts of protons ( 1H NMR) and carbons ( 13C NMR) in the series of studied alkali metal 3-nitrobenzoates were observed too. Optimized geometrical structures of studied compounds were calculated by B3PW91 method using 6-311++G ?? and 6-311++G basis sets. Geometric aromaticity indices, dipole moments and energies were also calculated. The theoretical wavenumbers and intensities of IR spectra were obtained at B3PW91/6-311++G level. The calculated parameters were compared to experimental characteristic of studied compounds.

  17. Transmission of alkali aerosols through sampling systems

    Energy Technology Data Exchange (ETDEWEB)

    Kowalski, T.; Judex, J.; Schildhauer, T.J.; Ludwig, C. [Paul Scherrer Institut, General Energy Department, Villigen (Switzerland)

    2011-01-15

    In biomass gasification, particles such as condensed alkali salts pose a threat on equipment. Due to high loads of condensable tars in the gases, sampling of these particles to liquids and subsequent analysis of the liquid is frequently the method of choice for measuring the alkali concentration in the gas. However, little is known about the collection efficiency of liquid sampling devices. By measuring the aerosol transmission using a surface ionization detector, two continuous sampling systems are compared with conventional impinger bottles. A low collection efficiency for the latter was found, but down to nearly zero transmission for the continuous sampling systems. The main mechanisms for mass transfer from gas to liquid are discussed with emphasis on particle removal in gas slugs in two-phase flow inside tubes of the sampling system. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Influence of alkali and alkaline earth ions on the -alkylation of the lower rim phenolic-OH groups of -tert-butyl-calix[4]arene to result in amide-pendants: Template action of K+ and the structure of K+ bound tetra-amide derivative crystallized with a -tert-butylcalix[4]arene anion

    Indian Academy of Sciences (India)

    Amjad Ali; Chebrolu P Rao; Philippe Guionneau

    2008-03-01

    Role of alkali and alkaline earth ions on the formation of calix[4]arene-amide derivatives through -alkylation of the lower rim phenolic-OH groups in general and template action of K+ in particular have been explored. Na+ and K+ ions among alkali, and Ca2+ and Sr2+ ions among alkaline earth have shown tetra-amide derivatives bound to metal ion species. Among all these, potassium salts act as template and yields a K+ bound tetra-amide derivative where the charge is counter balanced by a calix[4] arene-monoanion and the product is crystallographically characterized. Change in the amide precursor used in these -alkylation reactions has no effect on the type of the amide derivative formed. Also demonstrated is a direct one-step reaction for the preparation of 1,3-di-amide derivative in high yield and low reaction period using CsHCO3.

  19. Mesoscopic photosystems for solar light harvesting and conversion: facile and reversible transformation of metal-halide perovskites.

    Science.gov (United States)

    Harms, Hauke Arne; Tétreault, Nicolas; Pellet, Norman; Bensimon, Michaël; Grätzel, Michael

    2014-01-01

    Recently, hybrid organic-inorganic metal halide perovskites have gained prominence as potent light harvesters in thin film solid-state photovoltaics. In particular the solar-to-electric power conversion efficiency (PCE) of devices using CH(3)NH(3)PbI(3) as sensitizer has increased from 3 to 20.1% within only a few years. This key material can be prepared by solution processing from PbI(2) and CH(3)NH(3)I in one step or by sequential deposition. In the latter case an electron capturing support such as TiO(2) is first covered with PbI(2), which upon exposure to a CH(3)NH(3)I solution is converted to the perovskite. Here we apply for the first time quartz crystal microbalance (QCMD) measurements in conjunction with X-ray diffraction and scanning electron microscopy to analyse the dynamics of the conversion of PbI(2) to CH(3)NH(3)PbI(3). Employing 200 nm thick PbI(2) films as substrates we discover that the CH(3)NH(3)I insertion in the PbI(2) is reversible, with the extraction into the solvent isopropanol occurring on the same time scale of seconds as the intercalation process. This offers an explanation for the strikingly rapid and facile exchange of halide ions in CH(3)NH(3)PbX(3) by solution processing at room temperature. PMID:25643832

  20. A simple alkali metal ion gun

    International Nuclear Information System (INIS)

    An easily constructed alkali-metal-ion gun with a large metal-zeolite reservoir is described. The gun provides ion-beam currents from 100 eV to 5 keV in excess of 10 ?A with a wide range of focal lengths. The ion trajectories of the extraction, acceleration, and focusing have been computed using the program simion. A versatile three-electrode extraction geometry that provides ion trajectories which emulate the planar diode is described

  1. Pulse radiolysis of alkali metal fluorides melts

    International Nuclear Information System (INIS)

    The melts of alkali metal fluoride mixtures are investigated by the method of pulse radiolysis with optical recording. Parameters of optical spectra and radiochemical yields of solveted electrons in these systems are close to the halogenides. Optical absorption of radiolysis oxydizing component is established, the parameters of this component differ significantly from those in the melts of chlorides, bromides and iodides which seems to be related to fast reaction of F3-

  2. Seasonal variations in halides in marine brown algae from Porbandar and Okha coasts (NW coast of India)

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, Ch.K; Singbal, S.Y.S.

    Seasonal variation of halides and their ratios were estimated in three brown algae, namely Cystoseira indica, Sargassum tenerrimum) and S. johnstonii from Porbandar and Okha Coasts. Halides were found to be higher in early stages of growth. The Br...

  3. Radiation studies of aqueous alkali-metal hydroxide systems at low temperatures

    International Nuclear Information System (INIS)

    This investigation initially involves the study of electron trapping in gamma-irradiated alkali-metal hydroxide aqueous glasses. The study was conducted using electron spin resonance (esr) and optical spectroscopy techniques at about 77K. The hydroxides of lithium, sodium and potassium were looked at briefly as these have been covered in previous work. Rubidium and caesium hydroxides have been investigated in more detail, and results presented here clearly show that a second electron trapped centre exists for gamma-irradiated Rb aqueous glasses. Results for irradiated CsOH aqueous glasses are less conclusive, but certainly show divergence from the pattern established in lithium, sodium and potassium systems. Other systems studied are the aqueous hydroxide glasses of sodium, potassium, rubidium and caesium (by pulse-radiolysis) irradiated aqueous glasses containing halide salts (by esr and optical spectroscopy), irradiated aqueous hydroxide glasses of caesium or rubidium mixed with sodium or potassium (esr spectroscopy), gamma-irradiated glasses of mixed ammonia-water systems at 77K (esr and optical spectroscopy) and gamma irradiated KOH pellets at 77K (esr spectroscopy). (UK)

  4. An efficient transformation of primary halides into nitriles through palladium-catalyzed hydrogen transfer reaction.

    Science.gov (United States)

    Zou, Tao; Yu, Xiaoqiang; Feng, Xiujuan; Bao, Ming

    2015-07-01

    Two-step one-pot transformation of primary halides into corresponding nitriles is successfully achieved. Nucleophilic substitution of primary halides with sodium azide and subsequent palladium-catalyzed hydrogen transfer proceeds smoothly in the presence of sterically bulky ligand dicyclohexyl(2',4',6'-triisopropylbiphenyl-2-yl)phosphine (XPhos) in acetone to produce nitriles in satisfactory to good yields. PMID:26050994

  5. Gamma radiolytic decomposition of solid binary mixtures of potassium nitrate with halides

    International Nuclear Information System (INIS)

    Gamma-ray induced decomposition of solid binary mixtures of KNO3 with halides viz. KCl, KBr and KI was studied at room temperature. G(NO2-) values were found to vary with absorbed dose. Size and electronegativity of anions and molar composition of halides are the other factors influencing radiolysis. (author) 23 refs.; 4 figs

  6. Crystallization In High Level Waste (HLW) Glass Melters: Operational Experience From The Savannah River Site

    International Nuclear Information System (INIS)

    processing strategy for the Hanford Tank Waste Treatment and Immobilization Plant (WTP). The basis of this alternative approach is an empirical model predicting the crystal accumulation in the WTP glass discharge riser and melter bottom as a function of glass composition, time, and temperature. When coupled with an associated operating limit (e.g., the maximum tolerable thickness of an accumulated layer of crystals), this model could then be integrated into the process control algorithms to formulate crystal tolerant high level waste (HLW) glasses targeting higher waste loadings while still meeting process related limits and melter lifetime expectancies. This report provides a review of the scaled melter testing that was completed in support of the Defense Waste Processing Facility (DWPF) melter. Testing with scaled melters provided the data to define the DWPF operating limits to avoid bulk (volume) crystallization in the un-agitated DWPF melter and provided the data to distinguish between spinels generated by K-3 refractory corrosion versus spinels that precipitated from the HLW glass melt pool. This report includes a review of the crystallization observed with the scaled melters and the full scale DWPF melters (DWPF Melter 1 and DWPF Melter 2). Examples of actual DWPF melter attainment with Melter 2 are given. The intent is to provide an overview of lessons learned, including some example data, that can be used to advance the development and implementation of an empirical model and operating limit for crystal accumulation for WTP. Operation of the first and second (current) DWPF melters has demonstrated that the strategy of using a liquidus temperature predictive model combined with a 100 °C offset from the normal melter operating temperature of 1150 °C (i.e., the predicted liquidus temperature (TL) of the glass must be 1050 °C or less) has been successful in preventing any detrimental accumulation of spinel in the DWPF melt pool, and spinel has not been observed in any of the pour stream glass samples. Spinel was observed at the bottom of DWPF Melter 1 as a result of K-3 refractory corrosion. Issues have occurred with accumulation of spinel in the pour spout during periods of operation at higher waste loadings. Given that both DWPF melters were or have been in operation for greater than 8 years, the service life of the melters has far exceeded design expectations. It is possible that the DWPF liquidus temperature approach is conservative, in that it may be possible to successfully operate the melter with a small degree of allowable crystallization in the glass. This could be a viable approach to increasing waste loading in the glass assuming that the crystals are suspended in the melt and swept out through the riser and pour spout. Additional study is needed, and development work for WTP might be leveraged to support a different operating limit for the DWPF. Several recommendations are made regarding considerations that need to be included as part of the WTP crystal tolerant strategy based on the DWPF development work and operational data reviewed here. These include: Identify and consider the impacts of potential heat sinks in the WTP melter and glass pouring system; Consider the contributions of refractory corrosion products, which may serve to nucleate additional crystals leading to further accumulation; Consider volatilization of components from the melt (e.g., boron, alkali, halides, etc.) and determine their impacts on glass crystallization behavior; Evaluate the impacts of glass REDuction/OXidation (REDOX) conditions and the distribution of temperature within the WTP melt pool and melter pour chamber on crystal accumulation rate; Consider the impact of precipitated crystals on glass viscosity; Consider the impact of an accumulated crystalline layer on thermal convection currents and bubbler effectiveness within the melt pool; Evaluate the impact of spinel accumulation on Joule heating of the WTP melt pool; and Include noble metals in glass melt experiments because of their potential to act as nucleation site

  7. Alkali depletion and ion-beam mixing in glasses

    International Nuclear Information System (INIS)

    Ion-implantation-induced alkali depletion in simple alkali-silicate glasses (12M2O.88SiO2) has been studied for implantations at room temperature and near 77K. Results are consistent with a mechanism for alkali removal, by heavy ion bombardment, based on radiation-enhanced migration and preferential removal of alkali from the outermost layers. Similar results were obtained for mixed-alkali glasses ((12-x)Cs2.O.xM2O.88SiO2) where, in addition, a mixed-alkali effect may also be operative. Some preliminary experiments with ion implantation through thin Al films on SiO2 glass and on a phosphate glass show that inter-diffusion takes place and suggest that this ion-mixing technique may be a useful method for altering the physical properties of glass surfaces

  8. Modeling of Lead Halide Perovskites for Photovoltaic Applications

    OpenAIRE

    Jishi, Radi A.; Ta, Oliver B.; Sharif, Adel A.

    2014-01-01

    We report first-principles calculations, using the full potential linear augmented plane wave method, on six lead halide semiconductors, namely, CH3NH3PbI3, CH3NH3PbBr3, CsPbX3 (X=Cl, Br, I), and RbPbI3. Exchange is modeled using the modified Becke-Johnson potential. With an appropriate choice of the parameter that defines this potential, an excellent agreement is obtained between calculated and experimental band gaps of the six compounds. We comment on the possibility that ...

  9. Inelastic low-energy electron collisions with hydrogen halides

    Science.gov (United States)

    Horá?ek, J.

    2000-02-01

    Inelastic low-energy electron collisions with hydrogen halides HCl, HBr, DBr and HI are studied theoretically on the basis of the nonlocal resonance model of Domcke and Mündel. The model takes account of the dependence of the dipole-modified threshold exponent on the internuclear distance and of the precise form of the long-range part of the negative ion potential. Cross sections for vibrational excitation, dissociative attachment and associative detachment have been calculated. For all three collision processes, the cross sections calculated are in better agreement with experiment than previous calculations.

  10. Iron Halide Species Produced by Laser-Evaporation

    International Nuclear Information System (INIS)

    Iron halide species were produced by the reaction of laser-evaporated iron atoms with halogen-containing reactant gas, and isolated in low-temperature matrices to obtain their Moessbauer spectra. Iron fluoride (Fe2F6, FeF3 and Fe2F4) and iron iodide (FeI2 and Fe2I4) were produced by the reaction of laser-evaporated iron atoms with sulfur hexafluoride SF6 and methyl iodide CH3I, respectively. The yields of the products varied depending on the concentration of reactant gas in the Ar matrix. Molecular orbital calculations were performed in order to confirm their assignments.

  11. Application of electrogenerated iodine(1) for successive determination by halides

    International Nuclear Information System (INIS)

    Conditions have been studied for electrogeneration of iodine at a platinum electrode in RI (R=CH3, C2H5, C3H7, C4H9) solutions in glacial acetic acid containing 0.2 M HClO4. At potentials from 1.8 to 2.3 V (vs Ag/AgCl electrode) RI is oxidized to iodine (1) to give the quantitative current yield. The real redox potential of the I(I)/RI system has been measured. A method has been developed of successive coulometric titration of halide ions in their mixtures

  12. Evaluation of field test equipment for halide and DOP testing

    International Nuclear Information System (INIS)

    The Nucon Testing Services Department, field testing at power reactor sites, has performed tests using R-11, R-12, and R-112 in conjunction with gas chromatographs and direct reading halide detectors. The field operational experience with these detector systems, thus sensitivity, precision, and manner of field calibration, are presented. Laboratory experiments regarding 3H-tagged methyl iodide for in place leak testing of adsorber systems indicate a low hazard, high reliability process for leak testing in facilities where atmospheric cross contamination occurs. (U.S.)

  13. The Oxidation State of Europium in Halide Glasses

    OpenAIRE

    Weber, J. K. R.; Vu, M.; Paßlick, C.; Schweizer, S.; Brown , D E; C. E. Johnson; Johnson, J. A.

    2011-01-01

    The luminescent properties of divalent europium ions can be exploited to produce storage phosphors for x-ray imaging applications. The relatively high cost and limited availability of divalent europium halides makes it desirable to synthesize them from the readily available trivalent salts. In this work, samples of pure EuCl3 and fluoride glass melts doped with EuCl3 were processed at 700-800 °C in an inert atmosphere furnace. The Eu oxidation state in the resulting materials was determined u...

  14. New route for the synthesis of tricyclopentadienyluranium halides

    International Nuclear Information System (INIS)

    A facile synthetic route for UCp4, UCp3, U(COT)2, and other related organoactinides has been achieved by the direct reaction of a fresh reactive uranium powder from electrolytic amalgamation with respective organic substrates. In this work we further demonstrate the applicability of the uranium powder method to the simple synthesis of UCp3X, where X = Cl, Br, and I, respectively. The uranium powder was reacted with cyclopentadiene and alkyl halides simultaneously under a mild condition to obtain the respective complexes

  15. Thermal Isomerization in Isolated Cesium-Halide Clusters

    International Nuclear Information System (INIS)

    We have used photoelectron spectroscopy to observe thermal isomerization in cesium-halide cluster anions. In many of the (CsX)nCsm- (X=Cl,Br,I; n=27; m=0,1) systems we have studied, small changes in the source nozzle temperature produce dramatic changes in the distribution of cluster isomers. When specific isomers are selectively photodepleted, isomer interconversion quickly reestablishes the thermal isomer distribution, even though the clusters are isolated in a cluster beam. copyright 1996 The American Physical Society

  16. Thermalization of different alkali and alkali-earth elements at the TRI?P facility

    International Nuclear Information System (INIS)

    Radioactive isotopes produced by the in-flight method are converted into low-energy ions with a thermal ionizer (TI) ion catcher, the operation of which is based on a hot cavity ion source. The extraction efficiency of the TI for different alkali and alkali-earth elements has been studied and compared to a model based on diffusion only. The model describes the stationary limit, i.e. the extraction efficiency, as well as the dynamic response of the TI output when the primary beam is switched on and off.

  17. Thermalization of different alkali and alkali-earth elements at the TRI{mu}P facility

    Energy Technology Data Exchange (ETDEWEB)

    Shidling, P.D., E-mail: P.Shidling@rug.n [Kernfysisch Versneller Instituut, University of Groningen, Zernikelaan 25, 9747 AA Groningen (Netherlands); Giri, G.S.; Hoek, D.J. van der; Jungmann, K.; Kruithof, W.L.; Onderwater, C.J.G.; Santra, B.; Sohani, M.; Versolato, O.O.; Willmann, L.; Wilschut, H.W. [Kernfysisch Versneller Instituut, University of Groningen, Zernikelaan 25, 9747 AA Groningen (Netherlands)

    2010-10-01

    Radioactive isotopes produced by the in-flight method are converted into low-energy ions with a thermal ionizer (TI) ion catcher, the operation of which is based on a hot cavity ion source. The extraction efficiency of the TI for different alkali and alkali-earth elements has been studied and compared to a model based on diffusion only. The model describes the stationary limit, i.e. the extraction efficiency, as well as the dynamic response of the TI output when the primary beam is switched on and off.

  18. Contributions to the mixed-alkali effect in molecular dynamics simulations of alkali silicate glasses

    CERN Document Server

    Lammert, H; Lammert, Heiko; Heuer, Andreas

    2005-01-01

    The mixed-alkali effect on the cation dynamics in silicate glasses is analyzed via molecular dynamics simulations. Observations suggest a description of the dynamics in terms of stable sites mostly specific to one ionic species. As main contributions to the mixed--alkali slowdown longer residence times and an increased probability of correlated backjumps are identified. The slowdown is related to the limited accessibility of foreign sites. The mismatch experienced in a foreign site is stronger and more retarding for the larger ions, the smaller ions can be temporarily accommodated. Also correlations between unlike as well as like cations are demonstrated that support cooperative behavior.

  19. Alkali-aggregate reactions, strengthening or total collaps?

    DEFF Research Database (Denmark)

    Nielsen, Anders

    2000-01-01

    Alkali-aggregate reactions (AAR) can have many different effects, ranging from nothing happening to total cracking of the structure. The reason for this is related to the fact that chemistry and mechanics interfere with each other in the reactions. So, factors such as the concrete composition, the...... development. As a case study a road bridge is analysed according to the principles presented. Keywords: Alkali-aggregate reactions, alkali-silica reactions, bridges, concrete structures, dams, repair decision, time development....

  20. Quadrupolar deformation of the electronic charge cloud and the lattice mechanics of LiH-LiD crystals

    International Nuclear Information System (INIS)

    As the deformable shell model incorporates both scalar and dipolar deformation, it is natural to expect that the quadrupolar deformation may be important in the case of lithium hydride, where the unstable hydrogen ion with its extremely loose bound outermost electron (compared to alkali halides) appears to be a plausible candidate for such deformation. Quadrupolar deformation in an ion in crystal may arise because of the variation of the electric field produced by o,.her ions over the extent of the charge cloud or due to a shortrange overlap effect of nearest neighbours. The second effect is much stronger than the first and this alone is considered in the present investigation. A method has been developed to obtain the relevant equations and evaluate all the lattice sums appropriate for the structure on the basis of an extended deformable shell model which incorporates scalar, dipolar and quadrupolar deformation. The quadrupolar deformation is found to have quite a considerable effect both on the dynamic and static properties of LiH-LiD crystals. The resulting model not only removes the discrepancies mentioned above but has also been successful in correlating the specific properties namely, the static lattice structure, the cohesive energy, the second order elastic constants, the dielectric properties and the lattice dynamics with a single set of parameters used for all of them. Only the shortrange overlap effect of the nearest neighbours has been taken into account and not that due to the variation of the electric field produced by other ions over the extent of charge cloud, since the former effect is much stronger than the latter one. (K.B.)

  1. Formation and evolution of point defects created in alkali halogen compounds irradiated by heavy ions

    International Nuclear Information System (INIS)

    The goal of this study was to achieve a better understanding of the heavy-ion material interaction. Alkali halogen crystals were chosen since the color centers produced by heavy ions can be distinguished easier from those generated by X rays. Measurements on KI irradiated at low temperature showed that the usual process of non radiative de-excitation of self-captured exciton is not prevailing. As the main objective of this work was the exact determination of the defects created by accelerated heavy ions, an important effort was dedicated to the spectrum deconvolution. Due to the high quality of the obtained spectra the V band analyse was possible. The defect stability was found to have the same nature in all the cubical alkali halogens and depend essentially on the crystal type. The defect evolution after irradiation is related to the diffusion coefficients corresponding to each mobile species and to the crystal lattice in which they move. Based on measurements made at different temperatures a simple modeling of the recombination kinetics was proposed. This effect was found to be specific to irradiation by heavy ions. It is difficult to determine the initial processes from the fossil defects, so, the defect history must be known as the described investigation methods do not permit to establish the transient aspect of defect creation. The important role of impurities should be stressed as the third intruder in the ion/crystal configuration; it can modify significantly the final state of the irradiated crystal, as it was found in KI, for instance. The open problems underlined in this study will probably be solved by using the atomic force microscopy and diffraction or on-line Raman measurements in ISOC chamber to avoid the passage to ambient conditions of the crystals irradiated at low temperatures

  2. Organic-inorganic hybrid lead halide perovskites for optoelectronic and electronic applications.

    Science.gov (United States)

    Zhao, Yixin; Zhu, Kai

    2016-02-01

    Organic and inorganic hybrid perovskites (e.g., CH3NH3PbI3), with advantages of facile processing, tunable bandgaps, and superior charge-transfer properties, have emerged as a new class of revolutionary optoelectronic semiconductors promising for various applications. Perovskite solar cells constructed with a variety of configurations have demonstrated unprecedented progress in efficiency, reaching about 20% from multiple groups after only several years of active research. A key to this success is the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of hybrid perovskites. The rapid progress in material synthesis and device fabrication has also promoted the development of other optoelectronic applications including light-emitting diodes, photodetectors, and transistors. Both experimental and theoretical investigations on organic-inorganic hybrid perovskites have enabled some critical fundamental understandings of this material system. Recent studies have also demonstrated progress in addressing the potential stability issue, which has been identified as a main challenge for future research on halide perovskites. Here, we review recent progress on hybrid perovskites including basic chemical and crystal structures, chemical synthesis of bulk/nanocrystals and thin films with their chemical and physical properties, device configurations, operation principles for various optoelectronic applications (with a focus on solar cells), and photophysics of charge-carrier dynamics. We also discuss the importance of further understanding of the fundamental properties of hybrid perovskites, especially those related to chemical and structural stabilities. PMID:26645733

  3. Halide salts accelerate degradation of high explosives by zerovalent iron

    International Nuclear Information System (INIS)

    Zerovalent iron (Fe0, ZVI) has drawn great interest as an inexpensive and effective material to promote the degradation of environmental contaminants. A focus of ZVI research is to increase degradation kinetics and overcome passivation for long-term remediation. Halide ions promote corrosion, which can increase and sustain ZVI reactivity. Adding chloride or bromide salts with Fe0 (1% w/v) greatly enhanced TNT, RDX, and HMX degradation rates in aqueous solution. Adding Cl or Br salts after 24 h also restored ZVI reactivity, resulting in complete degradation within 8 h. These observations may be attributed to removal of the passivating oxide layer and pitting corrosion of the iron. While the relative increase in degradation rate by Cl- and Br- was similar, TNT degraded faster than RDX and HMX. HMX was most difficult to remove using ZVI alone but ZVI remained effective after five HMX reseeding cycles when Br- was present in solution. - The addition of halide ions promotes the degradation of high explosives by zerovalent iron

  4. Sodium-metal halide and sodium-air batteries.

    Science.gov (United States)

    Ha, Seongmin; Kim, Jae-Kwang; Choi, Aram; Kim, Youngsik; Lee, Kyu Tae

    2014-07-21

    Impressive developments have been made in the past a few years toward the establishment of Na-ion batteries as next-generation energy-storage devices and replacements for Li-ion batteries. Na-based cells have attracted increasing attention owing to low production costs due to abundant sodium resources. However, applications of Na-ion batteries are limited to large-scale energy-storage systems because of their lower energy density compared to Li-ion batteries and their potential safety problems. Recently, Na-metal cells such as Na-metal halide and Na-air batteries have been considered to be promising for use in electric vehicles owing to good safety and high energy density, although less attention is focused on Na-metal cells than on Na-ion cells. This Minireview provides an overview of the fundamentals and recent progress in the fields of Na-metal halide and Na-air batteries, with the aim of providing a better understanding of new electrochemical systems. PMID:24953300

  5. Isomorphism in the structural chemistry of two-coordinate adducts of diphenyl(2-formylphenyl)phosphine and triphenylphosphine with gold(I) halides

    Science.gov (United States)

    Dunstan, Samuel P. C.; Healy, Peter C.; Sobolev, Alexandre N.; Tiekink, Edward R. T.; White, Allan H.; Williams, Michael L.

    2014-08-01

    Single crystal X-ray structure determinations are recorded for diphenyl(2-formylphenyl)phosphine gold(I) halides [Ph2(Ph-CHO)PAuX], X = Cl, Br and I, and for redeterminations of enhanced precision for triphenylphosphine gold(I) halides [Ph3PAuX], X = Cl, Br, I, and SCN0.91Br0.09. These complexes, other than [Ph2(Ph-CHO)PAuCl], together with a diverse array of other structures, crystallize as an isomorphous series in the orthorhombic space group P212121a = 9.804(1)-11.906(3), b = 11.771(2)-12.996(3) and c = 12.871(1)-14.169(3) Å. In these complexes, introduction of the formyl group results in only minor differences between the conformations of the two phosphine ligands and the corresponding Au-P, Au-X, and Au-P-X bond lengths and angles. The crystal packings of [Ph3PAuX] for X = Cl, Br, I and of [Ph2(Ph-CHO)PAuX] for X = Br and I show that, while these structures are isomorphous, different supramolecular synthons may be present, suggesting global packing considerations are all-important rather than specific supramolecular interactions. This is borne out by the different packing found for the centrosymmetric [Ph2(Ph-CHO)PAuCl] structure. Crystallization of the mixed anion structure [Ph3PAuSCN0.91Br0.09] in the above P212121 lattice rather than the P21/c lattice reported for pure [Ph3PAuSCN] suggests that co-crystallization with bromide may impose constraints on packing considerations which favor crystallization in the P212121 lattice.

  6. Superconductivity in Room Temperature Stable electride and high-pressure phases of alkali metals

    OpenAIRE

    hosono, Hideo; Kim, Sung-Wng; Matsuishi, Satoru; Tanaka, Shigeki; Miyake, Atsushi; Kagayama, Tomoko; Shimizud, Katsuya

    2015-01-01

    S-band metals such as alkali and alkaline earth metals do not undergo a superconducting transition (SCT) at an ambient pressure, but their high-pressure phases do. In contrast, room temperature stable electride electride (C12A7:e-) in which anionic electrons in the crystallographic sub-nanometer-size cages have high s-character exhibits SCT at 0.2-0.4K at an ambient pressure. In this paper we report that crystal and electronic structure of C12A7:e- are close to those of the ...

  7. Structural and spectroscopic studies on the alkali borohydrides MBH4 (M=Na,K,Rb,Cs)

    OpenAIRE

    Renaudin, Guillaume; Gomes, Sandrine; Hagemann, Hans-Rudolf; Keller, L.; Yvon, Klaus

    2004-01-01

    Alkali borohydrides MBH[4] and their deuterides have been investigated by X-ray and neutron powder diffraction (M=K,Rb,Cs) and by infrared and Raman spectroscopy (M=Na,K,Rb,Cs). At room temperature the compounds crystallize with a cubic high temperature (HT) structure having FM[3]M symmetry in which the [BH4][?] complexes are disordered. At low temperature (LT) the potassium compound transforms into a tetragonal low temperature structure having P4[2]/n mc symmetry in which the [BH4][?] comple...

  8. The influence of different parameters on the hydration process of binders based on alkali activated slag

    OpenAIRE

    DARKO KRIZAN; MIROSLAV KOMLJENOVIC; BRANISLAV ZIVANOVIC

    2005-01-01

    The influence of certain types of activators (water glass Na2O·nSiO2 and sodium-metasilicate Na2SiO3·5H2O) on the hydration process of alkali activated slag was investigated in this study. The influence of activator concentration, specific surface area of the slag and the modulus n of the water glass (mass ratio between SiO2 and Na2O) on the kinetics of the hydration process i.e., the change of compressive strength were also investigated. Poorly crystallized low base calcium silicate hydrate ...

  9. Cathode architectures for alkali metal / oxygen batteries

    Science.gov (United States)

    Visco, Steven J; Nimon, Vitaliy; De Jonghe, Lutgard C; Volfkovich, Yury; Bograchev, Daniil

    2015-01-13

    Electrochemical energy storage devices, such as alkali metal-oxygen battery cells (e.g., non-aqueous lithium-air cells), have a cathode architecture with a porous structure and pore composition that is tailored to improve cell performance, especially as it pertains to one or more of the discharge/charge rate, cycle life, and delivered ampere-hour capacity. A porous cathode architecture having a pore volume that is derived from pores of varying radii wherein the pore size distribution is tailored as a function of the architecture thickness is one way to achieve one or more of the aforementioned cell performance improvements.

  10. Alternative alkali resistant deNOx catalysts

    DEFF Research Database (Denmark)

    Putluru, Siva Sankar Reddy; Kristensen, Steffen Buus; Due-Hansen, Johannes; Riisager, Anders; Fehrmann, Rasmus

    2012-01-01

    Alternative alkali resistant deNOx catalysts were prepared using three different supports ZrO2, TiO2 and Mordenite zeolite. The majority of the catalysts were prepared by incipient wetness impregnation of a commercial support, with vanadium, copper or iron precursor, one catalyst was prepared by onepot sol–gel method. All catalysts were characterized by BET, XRPD and NH3-TPD. Initial SCR activities of 8 out of 9 catalysts showed higher NO conversion at least at one temperature in the temperature...

  11. Alkali?silica reaction (ASR) – Performancetesting

    OpenAIRE

    Lindgård, Jan

    2013-01-01

    Whether or not concrete prism tests developed for assessment of alkali?silica reactivity of aggregates is suitable for general ASR performance testing of concrete has been evaluated. The work has been part of the Norwegian COIN program (2007?2014), and has been performed in co?operation with the "performance testing" task group of RILEM TC 219?ACS. Thus, the RILEM aggregate concrete prism tests (CPTs) form the basis for the laboratory program. As a foundation for the experimental work, an int...

  12. Pulse radiolysis of alkali metal nitrates

    International Nuclear Information System (INIS)

    Absorption spectra of alkali metal nitrate monocrystals irradiated by pulses of accelerated electrons with 200 keV energy and 5-8 kGy pulse dose were measured. Absorption bands of separate centers were distinguished, their identification was conducted and temperature dependence of efficiency of their formation and death was studied. It is shown that in 200-250 K region sudden change of kinetic characteristics of processes of formation and death of intermediate radiolysis products conditioned by structural changes of matrix lattices is observed

  13. The structure of alkali silicate gel by total scattering methods

    International Nuclear Information System (INIS)

    The structure of the alkali silicate gel (ASR) collected from the galleries of Furnas Dam in Brazil was determined by a pair distribution function (PDF) analysis of high energy X-ray diffraction data. Since this method is relatively new to concrete structure analysis a detailed introduction on the PDF method is given for glassy SiO2. The bulk amorphous structure of the dam material is confirmed as no Bragg peaks are observed in the scattered intensity. The real space results show that the local structure of the amorphous material is similar to kanemite (KHSi2O5:3H2O) however the long range layer structure of the crystal is broken up in the amorphous state, so that ordering only persists of the length scale of a few polyhedra. The silicate layer structure is a much more disordered than predicted by molecular dynamics models. The X-ray results are consistent with the molecular dynamics model of Kirkpatrick et al. (2005) [1] which predicts that most of the water resides in pores within the amorphous network rather than in layers. The total scattering data provide a rigorous basis against which other models may also be tested.

  14. The structure of alkali silicate gel by total scattering methods

    KAUST Repository

    Benmore, C.J.

    2010-06-01

    The structure of the alkali silicate gel (ASR) collected from the galleries of Furnas Dam in Brazil was determined by a pair distribution function (PDF) analysis of high energy X-ray diffraction data. Since this method is relatively new to concrete structure analysis a detailed introduction on the PDF method is given for glassy SiO2. The bulk amorphous structure of the dam material is confirmed as no Bragg peaks are observed in the scattered intensity. The real space results show that the local structure of the amorphous material is similar to kanemite (KHSi2O5:3H2O) however the long range layer structure of the crystal is broken up in the amorphous state, so that ordering only persists of the length scale of a few polyhedra. The silicate layer structure is a much more disordered than predicted by molecular dynamics models. The X-ray results are consistent with the molecular dynamics model of Kirkpatrick et al. (2005) [1] which predicts that most of the water resides in pores within the amorphous network rather than in layers. The total scattering data provide a rigorous basis against which other models may also be tested. © 2010.

  15. Synthesis, structural and spectral studies of five- and six-coordinate adducts of organotin(IV) halides containing dibenzylsulfoxide (DBSO) as ligand. The crystal structures of fac-[MeSnCl{sub 3}(dbso){sub 2}] and trans-[Ph{sub 2}SnCl{sub 2}(dbso){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Sousa, Gerimario F. de [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Quimica], e-mail: gfreitas@unb.br; Sabino, Jose R.; Vencato, Ivo [Universidade Federal do Goias (UFGO), Goiania, GO (Brazil). Inst. de Fisica; Filgueiras, Carlos A. L. [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Quimica; Ardisson, Jose D. [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil). Lab. de Fisica Aplicada

    2009-07-01

    The reaction of the ambidentate ligand dibenzylsulfoxide (dbso) with Me{sub 2}SnCl{sub 2} in 1:1 molar ratio leads to the formation of the five-coordinate adduct [Me{sub 2}SnCl{sub 2}(dbso)], whereas the same reaction conditions with Ph{sub 2}SnCl{sub 2} provide the six-coordinate adduct trans-[Ph{sub 2}SnCl{sub 2}(dbso){sub 2}]. On the other hand, the reaction with {sup {pi}}Bu{sub 2}SnCl{sub 2} forms the dimeric adduct [{l_brace}{sup {pi}}Bu{sub 2}SnCl{sub 2}(dbso){r_brace}{sub 2}], which probably possesses octahedral tin(IV) nuclei and bridging chlorides. The adducts [MeSnCl{sub 3}(dbso){sub 2}] and [Ph{sub 3}SnCl(dbso)] were also prepared and included in the study. All complexes were studied by microanalysis and IR, NMR ({sup 1}H, {sup 13}C and {sup 119}Sn) and Moessbauer spectroscopies to investigate their structural properties. The six-coordinate species fac-[MeSnCl{sub 3}(dbso){sub 2}] and trans-[Ph{sub 2}SnCl{sub 2}(dbso){sub 2}] were also studied by single crystal X-ray diffractometry. These compounds crystallize in the orthorhombic, Pbcn, and monoclinic space group P2{sub 1}/c, respectively, as discrete neutral molecules with the tin(IV) atom in a distorted octahedral geometry and the two dbso ligands in cis and trans positions, respectively. (author)

  16. Synthesis and thermal stability of perovskite alkali metal strontium borohydrides.

    Science.gov (United States)

    Møller, Kasper T; Ley, Morten B; Schouwink, Pascal; ?erný, Radovan; Jensen, Torben R

    2015-12-22

    Three new perovskite-type bimetallic alkali metal strontium borohydride compounds, ?-MSr(BH4)3 (M = K, Rb, Cs), have been synthesized and investigated by in situ synchrotron radiation powder X-ray diffraction, thermal analysis combined with mass spectrometry and Sievert's measurements. The bimetallic borohydrides were synthesized via an addition reaction between Sr(BH4)2 and MBH4 (M = K, Rb, Cs) by mechanochemical treatment. The Sr(BH4)2-NaBH4 system, which was treated in a similar manner, did not undergo reaction. All three ?-MSr(BH4)3 compounds crystallize in the orthorhombic crystal system at room temperature: KSr(BH4)3 (P21cn), a = 7.8967(6), b = 8.2953(7), and c = 11.508(1) Å (V = 753.82(12) Å(3)). RbSr(BH4)3 (Pbn21), a = 8.0835(3), b = 8.3341(4), and c = 11.6600(5) Å (V = 785.52(6) Å(3)). CsSr(BH4)3 (P22121), a = 8.2068(9), b = 8.1793(9), and c = 6.0761(4) Å (V = 407.87(7) Å(3)). All three compounds are perovskite-type 3D framework structures built from distorted [Sr(BH4)6] octahedra. High-temperature polymorphs are identified to form at 258, 220 and 150 °C for MSr(BH4)3, M = K, Rb and Cs, respectively. The new compounds are thermally stable and decompose at T > 360 °C into SrB6, SrH2 and MBH4 (M = K, Rb, Cs). PMID:26646319

  17. Dispersion coefficients for alkali-metal diatoms

    Energy Technology Data Exchange (ETDEWEB)

    Dalgarno, A.; Marinescu, M.; Sadeghpour, H.R. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)

    1993-05-01

    The knowledge of the long-range interaction between atoms and molecules is of fundamental importance for low-energy and low-temperature collisions. The electrostatic interaction between the charge distributions of two ground-state alkali-metal atoms can be expanded in powers of 1/R, the internuclear distance. The coefficients corresponding to the expansion powers of R{sup -6}, R{sup -8}, and R{sup -10} are calculated exactly using a numerical technique originally developed for determining resonance profile near an absorption line. These coefficients are evaluated by integrating the dynamic electric multipole polarizabilities at imaginary frequencies which are in turn obtained by solving two coupled inhomogeneous differential equations. Highly accurate one-electron model potentials are developed to represent the motion of the valence electron in the field of the closed alkali positive ion core. The numerical results for the constants C{sub 6}, C{sub 8}, and C{sub 10} for the homo- and hetero-nuclear alkai diatoms are compared with other calculations.

  18. Durability of Alkali Activated Blast Furnace Slag

    Science.gov (United States)

    Ellis, K.; Alharbi, N.; Matheu, P. S.; Varela, B.; Hailstone, R.

    2015-11-01

    The alkali activation of blast furnace slag has the potential to reduce the environmental impact of cementitious materials and to be applied in geographic zones where weather is a factor that negatively affects performance of materials based on Ordinary Portland Cement. The scientific literature provides many examples of alkali activated slag with high compressive strengths; however research into the durability and resistance to aggressive environments is still necessary for applications in harsh weather conditions. In this study two design mixes of blast furnace slag with mine tailings were activated with a potassium based solution. The design mixes were characterized by scanning electron microscopy, BET analysis and compressive strength testing. Freeze-thaw testing up to 100 freeze-thaw cycles was performed in 10% road salt solution. Our findings included compressive strength of up to 100 MPa after 28 days of curing and 120 MPa after freeze-thaw testing. The relationship between pore size, compressive strength, and compressive strength after freeze-thaw was explored.

  19. Induced Spin-Currents in Alkali-Films

    CERN Document Server

    Bergmann, G; Garrett, D; Bergmann, Gerd; Song, Funing; Garrett, Doug

    2004-01-01

    In sandwiches of FeK and FeCs the conduction electrons in the alkali metals have a large mean free path. The experiments suggest that the specular reflection for spin up and down electrons is different at the interface yielding a spin current in the alkali film. The spin current is detected by the anomalous Hall effect of Pb surface impurities.

  20. High-Order Dispersion Coefficients for Alkali-metal Atoms

    International Nuclear Information System (INIS)

    High-order dispersion coefficients C9, C11, C12, and C13 for the ground-state alkali-metals were calculated by combining the l-dependent model potential of alkali-metal atoms and linear variation method based on B-spline basis functions. The results were compared. (atomic and molecular physics)

  1. Recovery of alkali metal constituents from catalytic coal conversion residues

    Science.gov (United States)

    Soung, Wen Y. (Houston, TX)

    1984-01-01

    In a coal gasification operation (32) or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by contacting them (46, 53, 61, 69) with water or an aqueous solution to remove water-soluble alkali metal constituents and produce an aqueous solution enriched in said constituents. The aqueous solution thus produced is then contacted with carbon dioxide (63) to precipitate silicon constituents, the pH of the resultant solution is increased (81), preferably to a value in the range between about 12.5 and about 15.0, and the solution of increased pH is evaporated (84) to increase the alkali metal concentration. The concentrated aqueous solution is then recycled to the conversion process (86, 18, 17) where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst.

  2. Energetics of the ruthenium-halide bond in olefin metathesis (pre)catalysts

    KAUST Repository

    Falivene, Laura

    2013-01-01

    A DFT analysis of the strength of the Ru-halide bond in a series of typical olefin metathesis (pre)catalysts is presented. The calculated Ru-halide bond energies span the rather broad window of 25-43 kcal mol-1. This indicates that in many systems dissociation of the Ru-halide bond is possible and is actually competitive with dissociation of the labile ligand generating the 14e active species. Consequently, formation of cationic Ru species in solution should be considered as a possible event. © 2013 The Royal Society of Chemistry.

  3. Energetics of the ruthenium-halide bond in olefin metathesis (pre)catalysts.

    Science.gov (United States)

    Falivene, Laura; Poater, Albert; Cazin, Catherine S J; Slugovc, Christian; Cavallo, Luigi

    2013-05-28

    A DFT analysis of the strength of the Ru-halide bond in a series of typical olefin metathesis (pre)catalysts is presented. The calculated Ru-halide bond energies span the rather broad window of 25-43 kcal mol(-1). This indicates that in many systems dissociation of the Ru-halide bond is possible and is actually competitive with dissociation of the labile ligand generating the 14e active species. Consequently, formation of cationic Ru species in solution should be considered as a possible event. PMID:23235534

  4. Energetics of the ruthenium-halide bond in olefin metathesis (pre)catalysts

    OpenAIRE

    Falivene, Laura; Poater Teixidor, Albert; Cazin, Catherine S. J.; Slugovc, Christian; Cavallo, Luigi

    2013-01-01

    A DFT analysis of the strength of the Ru-halide bond in a series of typical olefin metathesis (pre)catalysts is presented. The calculated Ru-halide bond energies span the rather broad window of 25-43 kcal mol(-1). This indicates that in many systems dissociation of the Ru-halide bond is possible and is actually competitive with dissociation of the labile ligand generating the 14e active species. Consequently, formation of cationic Ru species in solution should be considered as a possible event

  5. Electrowinning of metallic tungsten, molybdenum and their carbides from low-distillation halide-oxide melts

    International Nuclear Information System (INIS)

    Cyclic voltametry, potentiostatic and galvanic electrolysis were used for the investigation into electrochemical deposition of metallic tungsten and molybdenum as well as their carbides from halide-oxide melts at 550 Deg C. Conditions of mutual electroreduction of tungsten and molybdenum fluorine-oxide complexes with carbon dioxide as well as with nickel and cobalt ions in halide-oxide melts at 550 Deg C were found. Optimal conditions for the metallic tungsten and molybdenum separation, tungsten (molybdenum) carbides, binary tungsten carbides with nickel (cobalt) from oxide-halide melts were determined

  6. Photophysical behavior and fluorescence quenching by halides of quinidine dication: Steady state and time resolved study

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, Neeraj Kumar; Tewari, Neeraj; Arora, Priyanka; Rautela, Ranjana; Pant, Sanjay [Photophysics Laboratory, Department of Physics, DSB Campus, Kumaun University, Nainital 263002, Uttarakhand (India); Joshi, Hem Chandra, E-mail: hem_sup@yahoo.co.uk [Institute for Plasma Research, Laser Diagnostics Division, Bhat, Near Indira Bridge, Gandhinagar 382428, Gujarat (India)

    2015-02-15

    The fluorescence quenching of quinidine in acidified aqueous solution by various halides (Cl{sup ?}, Br{sup ?} and I{sup ?}) was studied using steady state and time resolved fluorescence techniques. The quenching process was characterized by Stern–Volmer (S–V) plots. Possibility of conformers (one is not quenched by halide and the other is quenched) is invoked to explain the observed results. - Highlights: • Fluorescence quenching of quinidine in acidified aqueous solution by halides. • Various quenching parameters have been estimated. • Possibility of conformers is invoked to explain the observed results.

  7. Neutron Activation Analysis of Lead Halide Pollution Aerosols

    International Nuclear Information System (INIS)

    Iodine, bromine and chlorine have been determined by neutron activation analysis in atmospheric samples of both natural and pollution origin, and a comparison of the two sources provides the basis of a technique described in this paper for determining the composition and possible source of lead halide pollution aerosols. The activation analysis procedure employed consists of reactor neutron irradiation of aqueous samples and comparators for 20 min followed by radiochemical separation of iodine, bromine and chlorine and automatic counting of beta radioactivity from solid silver halide sources. Determination of lead by anodic stripping voltammetry (inverse polarography) consists of deposition of Pb++ from the solution onto a composite paraffin- impregnated graphite and mercury electrode at -1.00 V versus the standard calomel electrode, and then stripping by increasing the potential continuously. A significant question of public health interest in the air chemistry of lead is the source of the lead. Ethyl fluid, a mixture of organic lead, bromine and chlorine compounds, burns to form inorganic lead halide particles with Cl/Pb = 0.34 and Br/Pb = 0.39 by weight. In Cambridge, Massachusetts, analyses of cascade impactor aerosols were compared with similarly collected samples from the unpolluted air of Hawaii. The pollution bromine component ranged from 0.4 to 0.1 or less of the lead concentration, indicating in most cases either automotive lead with a bromine deficiency or a mixture of lead from automotive and other sources. In Fairbanks, Alaska, during winter, atmospheric conditions favour high local concentrations of air pollutants. Aerosols collected by Millipore filters show that pollution chlorine averages very nearly the value predicted from the observed lead and the known composition of ethyl fluid, and the automotive source for both chlorine and lead is strongly indicated. Pollution bromine, however, was less than predicted, and the bromine deficiency was about the same in Fairbanks and in Cambridge. These results imply that ethyl fluid combustion is the major source of atmospheric lead in Cambridge as well as in Fairbanks, and the observed pollution bromine and chlorine come predominantly from the same source. (author)

  8. Group separation method for radioactive alkali scrubber liquid wastes

    International Nuclear Information System (INIS)

    Radioactive alkali scrubber liquid wastes generated in a reprocessing facility are at first neutralized by nitric acid, and precipitates are removed from filtrates. The filtrates are processed by oxalic acid, hydrogen fluoride, iodic acid or ammonium, and rare earth elements are precipitated and removed as insoluble salts. Further, after increasing the valency of TRU elements in the filtrates by an electrolytic method, the TRU elements are adsorbed and solidified by cationic ion exchange resins, and removed from the filtrates. Further, alkali and alkaline earth metals contained in the filtrates processed by the cation exchange resins are evaporated to dryness and stabilized. In this way, platinum elements, rare earth elements, TRU element and alkali/alkaline earth metal elements dissolved in the radioactive alkali scrubber liquid wastes are separated into four groups. Since radioactive alkali liquid wastes are thus converted to solid wastes, entire amount of the radioactive wastes can be reduced. (T.M.)

  9. Ion Partitioning at the liquid/vapor interface of a multi-component alkali halidesolution: A model for aqueous sea salt aerosols

    Energy Technology Data Exchange (ETDEWEB)

    Ghosal, Sutapa; Brown, Matthew A.; Bluhm, Hendrik; Krisch, Maria J.; Salmeron, Miquel; Jungwirth, Pavel; Hemminger, John C.

    2008-12-22

    The chemistry of Br species associated with sea salt ice and aerosols has been implicated in the episodes of ozone depletion reported at Arctic sunrise. However, Br{sup -} is only a minor component in sea salt, which has a Br{sup -}/Cl{sup -} molar ratio of {approx}0.0015. Sea salt is a complex mixture of many different species, with NaCl as the primary component. In recent years experimental and theoretical studies have reported enhancement of the large, more polarizable halide ion at the liquid/vapor interface of corresponding aqueous alkali halide solutions. The proposed enhancement is likely to influence the availability of sea salt Br{sup -} for heterogeneous reactions such as those involved in the ozone depletion episodes. We report here ambient pressure x-ray photoelectron spectroscopy studies and molecular dynamics simulations showing direct evidence of Br{sup -} enhancement at the interface of an aqueous NaCl solution doped with bromide. The experiments were carried out on samples with Br{sup -}/Cl{sup -} ratios in the range 0.1% to 10%, the latter being also the ratio for which simulations were carried out. This is the first direct measurement of interfacial enhancement of Br{sup -} in a multi-component solution with particular relevance to sea salt chemistry.

  10. Reactivity of mercury(II) halides with the unsymmetrical phosphorus ylide Ph2PCH2CH2PPh2=C(H)C(O)Ph: Crystal structure of {HgI2 [PPh2CH2CH2PPh2=C(H)C(O)Ph]}n

    OpenAIRE

    Ebrahim, Mothi Mohamed; Stoeckli-Evans, Helen; Panchanatheswaran, Krishnaswamy

    2009-01-01

    The unsymmetrical phosphorus ylide, Ph2PCH2CH2PPh2=C(H)C(O)Ph is shown to react with Hg(II) halides to form polymeric products with the composition {HgX2 [PPh2CH2CH2PPh2C(H)C(O)Ph]}n, where X = Cl (1), Br (2), I (3). The complexes have been characterized by elemental analysis, IR, 1H, 31P NMR spectra as well as by ESI mass spectra. In product 1 the ylide exhibits a P, C-bridging mode of coordination, while in 2 and 3 it shows a monodentate P-coordination with the dangling ylide. The structur...

  11. Synthesis, structural and spectral studies of five- and six-coordinate adducts of organotin(IV) halides containing dibenzylsulfoxide (dbso) as ligand. The crystal structures of fac-[MeSnCl3(dbso)2] and trans-[Ph2SnCl2(dbso)2

    Scientific Electronic Library Online (English)

    Gerimário F. de, Sousa; José R., Sabino; Ivo, Vencato; Carlos A. L., Filgueiras; José D., Ardisson.

    Full Text Available A reação do ligante ambidentado dibenzilsulfóxido (dbso) com Me2SnCl2 na proporção molar 1:1 leva à formação do produto pentacoordenado [Me2SnCl2(dbso)], enquanto Ph2SnCl2 leva à formação do complexo hexacoordenado trans-[Ph2SnCl2(dbso)2], utilizando as mesmas condições de reação. Por outro lado, a [...] reação com nBu2SnCl2 forma o produto bimetálico [{nBu2SnCl2(dbso)}2], o qual provavelmente possui núcleos de estanho(IV) octaédricos e cloretos em ponte. Os complexos [MeSnCl3(dbso)2] e [Ph3SnCl(dbso)] também foram preparados. Todos os produtos foram estudados por análise elementar e por espectroscopias no IV, RMN (¹H, 13C, 119Sn) e Mössbauer. As espécies hexacoordenadas fac-[MeSnCl3(dbso)2] e trans-[Ph2SnCl2(dbso)2] foram também estudadas por difratometria de raios X; as determinações estruturais revelaram que estes compostos cristalizam-se nos sistemas cristalinos ortorrômbico, Pbcn, e monoclínico, P2(1)/c, respectivamente. As moléculas possuem átomos de estanho(IV) numa geometria octaédrica distorcida, com os dois ligantes dbso em posições cis e trans, respectivamente. Abstract in english The reaction of the ambidentate ligand dibenzylsulfoxide (dbso) with Me2SnCl2 in 1:1 molar ratio leads to the formation of the five-coordinate adduct [Me2SnCl2(dbso)], whereas the same reaction conditions with Ph2SnCl2 provide the six-coordinate adduct trans-[Ph2SnCl2(dbso)2]. On the other hand, the [...] reaction with nBu2SnCl2 forms the dimeric adduct [{nBu2SnCl2(dbso)}2], which probably possesses octahedral tin(IV) nuclei and bridging chlorides. The adducts [MeSnCl3(dbso)2] and [Ph3SnCl(dbso)] were also prepared and included in the study. All complexes were studied by microanalysis and IR, NMR (¹H, 13C and 119Sn) and Mössbauer spectroscopies to investigate their structural properties. The six-coordinate species fac-[MeSnCl3(dbso)2] and trans-[Ph2SnCl2(dbso)2] were also studied by single crystal X-ray diffractometry. These compounds crystallize in the orthorhombic, Pbcn, and monoclinic space group P2(1)/c, respectively, as discrete neutral molecules with the tin(IV) atom in a distorted octahedral geometry and the two dbso ligands in cis and trans positions, respectively.

  12. Two-photon pumped lead halide perovskite nanowire lasers

    CERN Document Server

    Gu, Zhiyuan; Sun, Wenzhao; Li, Jinakai; Liu, Shuai; Song, Qinghai; Xiao, Shumin

    2015-01-01

    Solution-processed lead halide perovskites have shown very bright future in both solar cells and microlasers. Very recently, the nonlinearity of perovskites started to attract considerable research attention. Second harmonic generation and two-photon absorption have been successfully demonstrated. However, the nonlinearity based perovskite devices such as micro- & nano- lasers are still absent. Here we demonstrate the two-photon pumped nanolasers from perovskite nanowires. The CH3NH3PbBr3 perovskite nanowires were synthesized with one-step solution self-assembly method and dispersed on glass substrate. Under the optical excitation at 800 nm, two-photon pumped lasing actions with periodic peaks have been successfully observed at around 546 nm. The obtained quality (Q) factors of two-photon pumped nanolasers are around 960, and the corresponding thresholds are about 674?J=cm2. Both the Q factors and thresholds are comparable to conventional whispering gallery modes in two-dimensional polygon microplates. Ou...

  13. Mechanical properties of silver halide core/clad IR fibers

    Science.gov (United States)

    Shalem, Shaul; German, Alla; Moser, Frank; Katzir, Abraham

    1996-04-01

    We have developed core/clad polycrystalline silver halide optical fibers with a loss of roughly 0.3 dB/m at 10.6 micrometers. Such fibers, with core diameters 0.3 - 0.6 mm and lengths of 1 to 2 meters are capable of continuously delivering output power densities as high as 14 KW/cm2. The fibers were repetitively bent in the plastic and elastic regimes and the optical transmission monitored during bending. The mechanical properties of the core/clad fibers and of the core only fibers are similar. It was also demonstrated that the 'bending' properties of the core/clad fibers are determined by the cladding material. Our investigations suggest that proper design of the core/clad structure may give significant improvement in mechanical properties such as more cycles to optical failure. This will be very important especially for endoscopic laser surgery and other medical applications.

  14. Inorganic Halide Perovskites for Efficient Light-Emitting Diodes.

    Science.gov (United States)

    Yantara, Natalia; Bhaumik, Saikat; Yan, Fei; Sabba, Dharani; Dewi, Herlina A; Mathews, Nripan; Boix, Pablo P; Demir, Hilmi Volkan; Mhaisalkar, Subodh

    2015-11-01

    Lead-halide perovskites have transcended photovoltaics. Perovskite light-emitting diodes (PeLEDs) emerge as a new field to leverage on these fascinating semiconductors. Here, we report the first use of completely inorganic CsPbBr3 thin films for enhanced light emission through controlled modulation of the trap density by varying the CsBr-PbBr2 precursor concentration. Although pure CsPbBr3 films can be deposited from equimolar CsBr-PbBr2 and CsBr-rich solutions, strikingly narrow emission line (17 nm), accompanied by elongated radiative lifetimes (3.9 ns) and increased photoluminescence quantum yield (16%), was achieved with the latter. This is translated into the enhanced performance of the resulting PeLED devices, with lower turn-on voltage (3 V), narrow electroluminescence spectra (18 nm) and higher electroluminescence intensity (407 Cd/m(2)) achieved from the CsBr-rich solutions. PMID:26722972

  15. Silver Halide Sensitized Gelatin Derived from BB-640 Holographic Emulsion

    Science.gov (United States)

    Neipp, Cristian; Pascual, Inmaculada; Beléndez, Augusto

    1999-03-01

    Silver halide sensitized gelatin (SHSG) is one of the most interesting techniques for the production of holographic optical elements, achieving relatively high sensitivity of photographic material with a low scattering of dichromated gelatin. Here we present experimental results for SHSG derived from the novel BB-640, a red-sensitive ultra-fine-grain emulsion from Holographic Recording Technologies (Steinau, Germany). The material is characterized before recording and after processing, and information about the thickness, absorption, and refractive-index modulation of the final holograms is obtained. The influence of the developer is analyzed, and diffraction efficiencies as great as 96.2% (after allowing for reflections) with a transmission of 1% and absorption and scatter losses of 2.8% are obtained with AAC developer. Our investigations reveal that high-quality SHSG transmission holograms may be obtained with the new BB-640 plates.

  16. Recent progress and challenges of organometal halide perovskite solar cells

    Science.gov (United States)

    Yang, Liyan; Barrows, Alexander T.; Lidzey, David G.; Wang, Tao

    2016-02-01

    We review recent progress in the development of organometal halide perovskite solar cells. We discuss different compounds used to construct perovskite photoactive layers, as well as the optoelectronic properties of this system. The factors that affect the morphology of the perovskite active layer are explored, e.g. material composition, film deposition methods, casting solvent and various post-treatments. Different strategies are reviewed that have recently emerged to prepare high performing perovskite films, creating polycrystalline films having either large or small grain size. Devices that are constructed using meso-superstructured and planar architectures are summarized and the impact of the fabrication process on operational efficiency is discussed. Finally, important research challenges (hysteresis, thermal and moisture instability, mechanical flexibility, as well as the development of lead-free materials) in the development of perovskite solar cells are outlined and their potential solutions are discussed.

  17. Electrodeposition of tungsten and tungsten carbide from molten halide

    International Nuclear Information System (INIS)

    The behaviour of tungstate ion, such as its reduction potentials and dissociation equilibria in several molten halide systems, has been investigated, and using these data, electrodeposition of tungsten and tungsten carbide has been conducted. The reduction potentials of tungstate ion in a molten LiF-KF eutectic system at 973K were about 0.8V and 0.3V (vs. Li,K/Li/sup +/, K/sup +/). And dissociation constant K of the reaction; WO/sub 4//sup 2-/K/sup / = W(VI) + 40/sup 2-/ was K = 5(+- 1) x 10/sup -12/ (mole fraction unit). Taking these data into consideration, tungsten and tungsten carbide have been electrodeposited from both molten fluoride and chloride. The electro-deposit from the fluoride was dumpy or mossy

  18. Solvation structures of lithium halides in methanol-water mixtures

    Science.gov (United States)

    Sarkar, Atanu; Dixit, Mayank Kumar; Tembe, B. L.

    2015-02-01

    The potentials of mean force (PMFs) for the ion pairs, Li+sbnd Cl-, Li+sbnd Br- and Li+sbnd I- have been calculated in five methanol-water compositions. The results obtained are verified by trailing the trajectories and calculating the ion pair distance residence times. Local structures around the ions are studied using the radial distribution functions, density profiles, orientational correlation functions, running coordination numbers and excess coordination numbers. The major change in PMF is observed as the methanol mole fraction (xmethanol) is changed from 1.0 to 0.75. The stable contact ion pair occurring for xmethanol = 1.0 becomes unstable at and below xmethanol = 0.75. The preferential solvation data show that the halide ions are always preferentially solvated by water molecules. Although the lithium ion is preferentially solvated by methanol molecules, there is significant affinity towards water molecules as well.

  19. Phase-resolved response of a metal-halide lamp

    International Nuclear Information System (INIS)

    The metal-halide (MH) lamp sometimes shows unwanted colour segregation, caused by a combination of convection and diffusion. In the past we investigated the lamp, running on a switched dc ballast of 120 Hz, using a dc approximation for the distribution of the radiating species. Here we present phase-resolved intensity measurements to verify this approximation. The MH lamp contains Hg as buffer gas and DyI3 as salt additive; we measure the light emitted by Dy and by Hg atoms. An intensity fluctuation of ∼25% close to the electrodes is found only. The observed fluctuations are explained by the cataphoresis effect and temperature fluctuations; the time scales are in the same order. Furthermore, measurements at higher gravity in a centrifuge (up to 10g) show that the effect becomes smaller at increasing gravity levels. From these results it is concluded that a dc approximation, which is generally assumed by lamp developers, is allowed for this MH lamp.

  20. Versatile, isotopically specific hydrogen halide TEA pin laser

    International Nuclear Information System (INIS)

    A practical, easily constructed design for a laboratory hydrogen/deuterium halide chemical TEA laser is presented. Typical output energies in excess of 50 mJ/pulse broadband and 5 mJ/pulse on single lines are easily obtained. Isotopically specific oscillation on the v=1?0 band of single isotopes of H35Cl--H37Cl, D35Cl--D37Cl, H79Br--H81Br, and D79Br--D81Br is demonstrated. The ease of conversion from one laser species to the next and the flexible design provide a highly versatile device for laboratory problems in chemical and physical dynamics. Major advances in the development of laboratory HCl and HBr chemical TEA lasers are also reviewed