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Sample records for alkali halide crystal

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

    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 $_{\\text{s}}$ for surface annihilation of dislocations and the pinning time $_{\\text{p}}$ 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.

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

    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)

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

    The elastico-mechanoluminescence (EML) intensity of X or γ-irradiated alkali halide crystals can be used in radiation dosimetry. The EML intensity of X or γ-irradiated alkali halide crystals increases linearly with the strain of the crystals, and when the crosshead of the testing machine deforming an X or γ-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 γ-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

  4. Study on growth of ternary alkali lead halide crystals for IR lasers

    Král, Robert

    Berlin : Polyprint GmbH, 2011, s. 146-147. [International Workshop on Crystal Growth Technology/5./. Berlin (DE), 26.06.2011-30.06.2011] R&D Projects: GA AV ČR KJB200100901 Institutional research plan: CEZ:AV0Z10100521 Keywords : interface s * vertical Bridgman method * ternary alkali lead halides * solid state lasers Subject RIV: BM - Solid Matter Physics ; Magnetism https://iwcgt5.ikz-berlin.de/index.php?id=18

  5. Mechanoluminescence produced during cleavage of γ-irradiated alkali halide crystals

    When g-irradiated alkali halide crystals are cleaved, then in their mechanoluminescence (ML) intensity versus time curve, two peak intensities Im1 and Im2 are observed at time tm1 and tm2 respectively. The ML intensity both beyond tm1 and tm2 decrease exponentially. It is shown that ML provides a new technique for determining the pinning time of dislocations and lifetime of the electrons in dislocation band. (author)

  6. Third-order elastic moduli for alkali-halide crystals possessing the sodium chloride structure

    Ray, U., E-mail: ray_ugrasen@yahoo.co [Department of Physics, Bhaktapur Multiple Campus, Tribhuvan University, Kathmandu (Nepal)

    2010-08-01

    The values of third-order elastic moduli for alkali halides, having NaCl-type crystal structure are calculated according to the Born-Mayer potential model, considering the repulsive interactions up to the second nearest neighbours and calculating the values of the potential parameters for each crystal, independently, from the compressibility data. This work presents the first published account of the calculation of the third-order elastic moduli taking the actual value of the potential parameter unlike the earlier works. Third-order elastic constants have been computed for alkali halides at 0 and 300 K. The results of the third-order elastic constants are compared with the available experimental and theoretical data. Very good agreement between experimental and theoretical third-order elastic constant data (except C{sub 123}) is found. We have also computed the values of the pressure derivatives of second-order elastic constants and Anderson-Grueneisen parameter for alkali halides, which agree reasonably well with the experimental values, indicating the satisfactory nature of our computed data for third-order elastic constants.

  7. Third-order elastic moduli for alkali-halide crystals possessing the sodium chloride structure

    The values of third-order elastic moduli for alkali halides, having NaCl-type crystal structure are calculated according to the Born-Mayer potential model, considering the repulsive interactions up to the second nearest neighbours and calculating the values of the potential parameters for each crystal, independently, from the compressibility data. This work presents the first published account of the calculation of the third-order elastic moduli taking the actual value of the potential parameter unlike the earlier works. Third-order elastic constants have been computed for alkali halides at 0 and 300 K. The results of the third-order elastic constants are compared with the available experimental and theoretical data. Very good agreement between experimental and theoretical third-order elastic constant data (except C123) is found. We have also computed the values of the pressure derivatives of second-order elastic constants and Anderson-Grueneisen parameter for alkali halides, which agree reasonably well with the experimental values, indicating the satisfactory nature of our computed data for third-order elastic constants.

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

    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 -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, 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.

  9. Rapid yet accurate first principle based predictions of alkali halide crystal phases using alchemical perturbation

    Solovyeva, Alisa

    2016-01-01

    We assess the predictive power of alchemical perturbations for estimating fundamental properties in ionic crystals. Using density functional theory we have calculated formation energies, lattice constants, and bulk moduli for all sixteen iso-valence-electronic combinations of pure pristine alkali halides involving elements $A \\in \\{$Na, K, Rb, Cs$\\}$ and $X \\in \\{$F, Cl, Br, I$\\}$. For rock salt, zincblende and cesium chloride symmetry, alchemical Hellmann-Feynman derivatives, evaluated along lattice scans of sixteen reference crystals, have been obtained for all respective 16$\\times$15 combinations of reference and predicted target crystals. Mean absolute errors (MAE) are on par with density functional theory level of accuracy for energies and bulk modulus. Predicted lattice constants are less accurate. NaCl is the best reference salt for alchemical estimates of relative energies (MAE $<$ 40 meV/atom) while alkali fluorides are the worst. By contrast, lattice constants are predicted best using NaF as a re...

  10. Skylab experiments on semiconductors and alkali halides. [single crystal growth

    Lundquist, C. A.

    1974-01-01

    The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.

  11. Crystal lattice properties fully determine short-range interaction parameters for alkali and halide ions

    Mao, Albert H; 10.1063/1.4742068

    2012-01-01

    Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-d...

  12. The Additive Coloration of Alkali Halides

    Jirgal, G. H.; and others

    1969-01-01

    Describes the construction and use of an inexpensive, vacuum furnace designed to produce F-centers in alkali halide crystals by additive coloration. The method described avoids corrosion or contamination during the coloration process. Examination of the resultant crystals is discussed and several experiments using additively colored crystals are…

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

    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

  14. Possible configuration of two-knot auto-localized exciton in strainless and deformed alkali halide crystals

    In the paper molecular component of two-knot auto-localized exciton (TALE) occupying centrosymmetric state in alkali halide crystal cubic lattice with local D2h symmetry is considered. In is suggested that the symmetry lowering of forming small radius auto-localized exciton (ALE) is realizing in order configuration transformation by the scenario: multi-knot continual ALE (with Oh symmetry)→six-halide ALE (with Oh symmetry)→TALE (with Oh symmetry) or by the scenario Oh→D2h. Then for TALE with local D2h symmetry normal molecular ion shifts are considered as well

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

    Aguado, Andrés; López, José 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 active clusters with 179 ions embedded in the surrounding crystalline lattice are considered in order to describe properly the lattice relaxation induced by the introduction of substitutional impurities. In all the cases considered, the lattice distortions imply the concerted movement of several shells of neighbors. The shell displacements are sm...

  16. Theoretical analysis of the kinetics of low-temperature defect recombination in alkali halide crystals

    Kuzovkov, V. N.; Popov, A. I.; Kotomin, E. A.; Moskina, A. M.; Vasilchenko, E.; Lushchik, A.

    2016-07-01

    We analyzed carefully the experimental kinetics of the low-temperature diffusion-controlled F, H center recombination in a series of irradiated alkali halides and extracted the migration energies and pre-exponential parameters for the hole H centers. The migration energy for the complementary electronic F centers in NaCl was obtained from the colloid formation kinetics observed above room temperature. The obtained parameters were compared with data available from the literature.

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

    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

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

    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

  19. Measurements of spin-lattice relaxation time in mixed alkali halide crystals

    Using magneto-optic techniques the ground state spin-lattice relaxation times (T1) of 'F' centers in mixed Alkali Halide cristals (KCl-KBr), was studied. A computer assisted system to optically measure short relaxation times (approx. = 1mS), was described. The technique is based on the measurement of the Magnetic Circular Dicroism (MCD) presented by F centers. The T1 magnetic field dependency at 2 K (up to 65 KGauss), was obtained as well as the MCD spectra for different relative concentration at the mixed matrices. The theory developed by Panepucci and Mollenauer for F centers spin-lattice relaxation in pure matrices was modified to explain the behaviour of T1 in mixed cristals. The Direct Process results (T approx. = 2.0 K) compared against that theory shows that the main relaxation mecanism, up to 25 KGauss, continues to be phonon modulation of the hiperfine iteraction between F electrons and surrounding nuclei. (Author)

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

    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 μs relative to the leading edge of a laser pulse), evaporation (after a further delay of 3-5 μs), 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)

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

    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 X1Σ+→a'3Σ+ 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)

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

    Dubinko, V. I.; Turkin, A.A.; Vainshtein, D.I.; Hartog, H.W. den

    2000-01-01

    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 ill 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 Vt centers (self-trapped ...

  3. Thermodynamic properties of Alkali Halides

    The method of moments of [1], developed by the authors in [2] for strongly and harmonic crystals with f.c.c. structure is used here to investigate the main thermodynamic properties of the potassium halides. Their analytic expressions as functions of temperature are obtained and the comparison between the theoretical results and the experimental data is made. (author). 22 refs., 5 tabs

  4. Alkali metal and alkali earth metal gadolinium halide scintillators

    Bourret-Courchesne, Edith; Derenzo, Stephen E.; Parms, Shameka; Porter-Chapman, Yetta D.; Wiggins, Latoria K.

    2016-08-02

    The present invention provides for a composition comprising an inorganic scintillator comprising a gadolinium halide, optionally cerium-doped, having the formula A.sub.nGdX.sub.m:Ce; wherein A is nothing, an alkali metal, such as Li or Na, or an alkali earth metal, such as Ba; X is F, Br, Cl, or I; n is an integer from 1 to 2; m is an integer from 4 to 7; and the molar percent of cerium is 0% to 100%. The gadolinium halides or alkali earth metal gadolinium halides are scintillators and produce a bright luminescence upon irradiation by a suitable radiation.

  5. Cohesive Energy-Lattice Constant and Bulk Modulus-Lattice Constant Relationships: Alkali Halides, Ag Halides, Tl Halides

    Schlosser, Herbert

    1992-01-01

    In this note we present two expressions relating the cohesive energy, E(sub coh), and the zero pressure isothermal bulk modulus, B(sub 0), of the alkali halides. Ag halides and TI halides, with the nearest neighbor distances, d(sub nn). First, we show that the product E(sub coh)d(sub 0) within families of halide crystals with common crystal structure is to a good approximation constant, with maximum rms deviation of plus or minus 2%. Secondly, we demonstrate that within families of halide crystals with a common cation and common crystal structure the product B(sub 0)d(sup 3.5)(sub nn) is a good approximation constant, with maximum rms deviation of plus or minus 1.36%.

  6. Influence of small dozes ultra-violet radiation on motion of dislocation in alkali-halide crystals

    Victor; A.; Feodorov; Tatjana.; N.; Plushnikova; Andrey; V.; Chivanov; Margarita; V.Chemerkina; Roman; A.; Kirillov.

    2005-01-01

    The purpose of this work was research into influence of ultra-violet radiation on size of run of regional and screw dislocations in beams of dislocation sockets, formed at indentation surface of alkali-halide crystals. In experiments it was used crystals NaCl, with the quantitative maintenance of impurity 10-2 -10-3weight%, the wave length of UV-radiation λ=250 nanometers, the sizes of samples 10mm× 20mm× 2mm,temperature of samples was constant T=290 K.It is established that indentation and the simultaneous irradiation of samples a ultraviolet is increases size of run of head dispositions in dislocation sockets..It is marked, that influence UV-radiation nonequivalence for various times of an exposition. At small times (till 5 minutes) the size of run grows. The length of beams increases on ~ 50 %. At the further increase in time of influence of a ultraviolet the length of beams is reduced till the sizes corresponding stressing without an irradiation (Figs. 1, 2, 3). The effect is observed on dislocation beams of regional and screw orientations and most expressed at small loadings (in our experiments-10 grams) (Fig. 3).Observable effects are explained from positions dislocation-exciton interactions. At UV-radiation exciton cooperates with the charged step on a disposition, causing movement of a step along a disposition on one internuclear distance. Due to this interaction overcoming by a disposition of a grid of stoppers is facilitated.Big times of endurance cause a relaxation of pressure directly in a print that provides convertible movement of dispositions in area of a print and as consequence, reduction of length of beams of dislocation sockets.

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

    Dubinko, V.I.; Turkin, A.A.; Vainshtein, D.I.; Hartog, H.W. den

    2000-01-01

    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 ill alkali halides. This model was constructed to describe metal colloids and dislocati

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

    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.

  9. Solid-solution hardening in kbr-kcl alkali halide single crystals

    Temperature and concentration dependences of the critical resolved shear stress (CRSS) of KBr-KCI solid- solution crystals containing 8 to 41 mol% KCI in the temperature range 77 to 230 K have been analysed within the frame work of the KPN mode of plastic flow in solid- solution crystals. It is found that CRSS tow decreases with the increase in temperature T in accord with the model relation In tow= A -BT, where A and B are positive constants. The CRSS tow at a given temperature depends on solute concentration c as tow alpha c/sup row/, where exponent p has a value between 0.5 and 1 depending on the temperature at which deformation is carried out. The model parameter W/sub o/, i.e. binding energy between the edge-dislocation segment involved in the unit activation process and the solute atoms close to it ( T --+ OK), increases with solute concentration c monotonically upto a critical value Cm = 35 mol% KCI, as predicted by the model. However, W/sub o/ decreases with increase in c beyond cm, which indicates somewhat ordered distribution of solute in the host lattice of concentrated solid-solutions with c > cm. (author)

  10. Large resonance enhanced second order susceptibilities in alkali halide crystals due to FA color centers

    Model calculation of second order susceptibilities for FA color centers in wide band gap materials is reported. The second order optical nonlinearity in KCL:Li crystals due to FA color centers evaluated theoretically. The density matrix formalism is employed and the equation of motion is solved by second order perturbation to evaluate the nonlinear optical susceptibility for second harmonic generation as well as frequency mixing. It is found that the system shows large resonance-enhanced second order susceptibilities (≅10-16 mV-1) for color center concentration of ≅1023 m-3. A scheme of phase matching in terms of anomalous dispersion of the centers and coherent length are discussed (Author)

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

    Král, Robert

    2012-01-01

    Roč. 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 ČR KJB200100901 Institutional research plan: CEZ:AV0Z10100521 Keywords : Interface s * morphological stability * segregation * Bridgman technique * halides Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.552, year: 2012

  12. Thermoluminescence of alkali halides and its implications

    Gartia, R. K.; Rey, L.; Tejkumar Singh, Th.; Basanta Singh, Th.

    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.

  13. Method of Gaussian quadrature in the calculation of optical absorption and magnetic circular dichroism spectra of s2 ions in alkali halide crystals: application to KBr:In+

    The problem of calculating the lineshape functon for optical absorption and magnetic circular dichroism due to ionic impurities with the ns2 outer electron configuraton, incorporated substitutionally in alkali halide crystals, has been reformulated. The complete energy matrix has been diagonalized directly. Integration over the interaction mode coordinates of E sub(g) and T sub(2g) symmetry has been carried out numerically using Gaussian quadrature formulae; the interaction with the A sub(1g) mode has been taken into account by the usual convolution procedure. The method has been applied to KBr:In+. The calculated lineshape functions for optical absorption at temperatures ranging from 4 to 300 K and, for MCD at 5 K, are in good agreement with the experimentally determined lineshapes. Moreover, the theory accounts very well for the observed variation of the effective g tensor for the A band with temperature. The calculated values for the moments of the absorption and MCD lineshape functions are in reasonably satisfactory agreement with those deduced from the observed spectra. (author)

  14. Graphitic cage transformation by electron-beam-induced catalysis with alkali-halide nanocrystals

    Fujita, Jun-ichi; Tachi, Masashi; Ito, Naoto; Murakami, Katsuhisa; Takeguchi, Masaki

    2016-05-01

    We found that alkali-halide nanocrystals, such as KCl and NaCl, have strong catalytic capability to form graphitic carbon cages from amorphous carbon shells under electron beam irradiation. In addition to the electron beam irradiation strongly inducing the decomposition of alkali-halide nanocrystals, graphene fragments were formed and linked together to form the final product of thin graphitic carbon cages after the evaporation of alkali-halide nanocrystals. The required electron dose was approximately 1 to 20 C/cm2 at 120 keV at room temperature, which was about two orders of magnitude smaller than that required for conventional beam-induced graphitization. The “knock-on” effect of primary electrons strongly induced the decomposition of the alkali-halide crystal inside the amorphous carbon shell. However, the strong ionic cohesion quickly reformed the crystal into thin layers inside the amorphous shell. The bond excitation induced by the electron beam irradiation seemed to enhance strongly the graphitization at the interface between the outer amorphous carbon shell and the inner alkali-halide crystal.

  15. A new polarizable force field for alkali and halide ions

    We developed transferable potentials for alkali and halide ions which are consistent with our recent model of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. Following the approach used for the water potential, we applied Gaussian charge distributions, exponential repulsion, and r−6 attraction. One of the two charges of the ions is fixed to the center of the particle, while the other is connected to this charge by a harmonic spring to express polarization. Polarizability is taken from quantum chemical calculations. The repulsion between different species is expressed by the combining rule of Kong [J. Chem. Phys. 59, 2464 (1972)]. Our primary target was the hydration free energy of ions which is correct within the error of calculations. We calculated water-ion clusters up to 6 water molecules, and, as a crosscheck, we determined the density and internal energy of alkali-halide crystals at ambient conditions with acceptable accuracy. The structure of hydrated ions was also discussed

  16. Laser-synchrotron studies of the dynamics of UV-photon-stimulated desorption in alkali halides

    Laser-synchrotron studies of neutral alkali emission from alkali halide crystals are yielding new insights into the dynamics of energy absorption, energy localization and bond-breaking in photon-stimulated desorption. The ground-state neutral desorption is triggered by the thermal diffusion of photon-induced electronic defects; however, the excited-state neutral alkalis are formed in a surface-specific process on an extremely short time scale. In addition, there is new evidence for a surface overlayer which retards substrate desorption, thus suggesting a new approach to the optical damage problem at ultraviolet wavelengths. 8 references

  17. Laser-synchrotron studies of the dynamics of UV-photon-stimulated desorption in alkali halides

    Laser-synchrotron studies of neutral alkali emission from alkali halide crystals are yielding new insights into the dynamics of energy absorption, energy localization and bond-breaking in photon-stimulated desorption. The ground-state neutral desorption is triggered by thermal diffusion of photon-induced electronic defects; however, the excited-state neutral alkalis are formed in a surface-specific process on an extremely short time scale. In addition, there is new evidence for a surface overlayer which retards substrate desorption, thus suggesting a new approach to the optical damage problem at ultraviolet wavelengths

  18. A new mechanism for radiation damage processes in alkali halides

    Dubinko, V.I.; Turkin, A.A.; Vainshtein, D.I.; Hartog, H.W. den

    1999-01-01

    We present a theory of radiation damage formation in alkali halides 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 H centers of dislocation lines. We consider the evolution o

  19. Alkali Halide Microstructured Optical Fiber for X-Ray Detection

    DeHaven, S. L.; Wincheski, R. A.; Albin, S.

    2014-01-01

    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

    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. Volcanic Origin of Alkali Halides on Io

    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.

  2. A new mechanism for radiation damage processes in alkali halides

    Dubinko, V. I.; Turkin, A.A.; Vainshtein, D.I.; Hartog, H.W. den

    1999-01-01

    We present a theory of radiation damage formation in alkali halides 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 H centers of dislocation lines. We consider the evolution of all experimentally observed extended defects: metal colloids, gas bubbles, and vacancy voids. Voids are shown to arise and grow large due to the reaction between F and VF centers at the surface o...

  3. A new mechanism for radiation damage processes in alkali halides

    Dubinko, V. I.; Turkin, A. A.; Vainshtein, D. I.; den Hartog, H. W.

    1999-12-01

    We present a theory of radiation damage formation in alkali halides 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 H centers of dislocation lines. We consider the evolution of all experimentally observed extended defects: metal colloids, gas bubbles, and vacancy voids. Voids are shown to arise and grow large due to the reaction between F and VF centers at the surface of halogen bubbles. Voids can ignite a back reaction between the radiolytic products resulting in decomposition of the irradiated material.

  4. Analysis and modeling of alkali halide aqueous solutions

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

    2016-01-01

    calculations for various electrolyte properties of alkali halide aqueous solutions such as mean ionic activity coefficients, osmotic coefficients, and salt solubilities. The model covers highly nonideal electrolyte systems such as lithium chloride, lithium bromide and lithium iodide, that is, systems that are...... very soluble in water, for example, up to more than 30 mol kg-1. Phase behaviors for the systems are analyzed at concentrations of salt up to the solubility in water at temperatures between 273 and 373 K by comparing calculated results with available experimental data and available models....

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

    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

  6. Structure and Bonding in Small Neutral Alkali-Halide Clusters

    Aguado, A; López, J M; Alonso, J A

    1997-01-01

    The structural and bonding properties of small neutral alkali-halide clusters (AX)n, with n less than or equal to 10, A=Li, Na, K, Rb and X=F, Cl, Br, I, are studied using the ab initio Perturbed Ion (aiPI) model and a restricted structural relaxation criterion. A trend of competition between rock-salt and hexagonal ring-like isomers is found and discussed in terms of the relative ionic sizes. The main conclusion is that an approximate value of r_C/r_A=0.5 (where r_C and r_A are the cationic and anionic radii) separates the hexagonal from the rock-salt structures. The classical electrostatic part of the total energy at the equilibrium geometry is enough to explain these trends. The magic numbers in the size range studied are n= 4, 6 and 9, and these are universal since they occur for all alkali-halides and do not depend on the specific ground state geometry. Instead those numbers allow for the formation of compact clusters. Full geometrical relaxations are considered for (LiF)n (n=3-7) and (AX)_3 clusters, an...

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

    Zykova-Timan, T.; Ceresoli, D.; 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: ...

  8. Modeling and investigation of heavy oxide and alkali-halide scintillators for potential use in neutron and gamma detection systems

    Cadiente, Jeremy S.

    2015-01-01

    Approved for public release; distribution is unlimited Heavy inorganic oxide and alkali-halide crystals, which previous experimental research has indicated to have fast neutron detection efficiencies well over 40%, were investigated for potential use as highly efficient gamma-neutron radiation detectors. The Monte Carlo N-Particle radiation transport code (MCNP) was used to characterize the radiation interactions in a candidate set of crystals, including Bismuth Germanate (BGO), Lead Tungs...

  9. Strong Turbulence in Alkali Halide Negative Ion Plasmas

    Sheehan, Daniel

    1999-11-01

    Negative ion plasmas (NIPs) are charge-neutral plasmas in which the negative charge is dominated by negative ions rather than electrons. They are found in laser discharges, combustion products, semiconductor manufacturing processes, stellar atmospheres, pulsar magnetospheres, and the Earth's ionosphere, both naturally and man-made. They often display signatures of strong turbulence^1. Development of a novel, compact, unmagnetized alkali halide (MX) NIP source will be discussed, it incorporating a ohmically-heated incandescent (2500K) tantulum solenoid (3cm dia, 15 cm long) with heat shields. The solenoid ionizes the MX vapor and confines contaminant electrons, allowing a very dry (electron-free) source. Plasma densities of 10^10 cm-3 and positive to negative ion mass ratios of 1 Fusion 4, 91 (1978).

  10. Theory of freezing of alkali halides and binary alloys

    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. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

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

    2012-12-31

    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)

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

    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.

  13. Efficient destruction of CF4 through in situ generation of alkali metals from heated alkali halide reducing mixtures.

    Lee, Myung Churl; Choi, Wonyong

    2002-03-15

    Perfluorocarbons (PFCs) are the most potent green house gases that are very recalcitrant at destruction. An effective way of converting PFCs using hot solid reagents into safe products has been recently introduced. By investigating the thermal reductive destruction of tetrafluoromethane (CF4) we provided new insight and more physicochemical consideration on this novel process. The complete destruction of CF4was successfully achieved by flowing the gas through a heated reagent bed (400-950 degrees C) that contained powder mixtures of alkali halides, CaO, and Si. The silicon acted as a reducing agent of alkali halides for the in-situ production of alkali metals, and the calcium oxide played the role of a halide ion acceptor. The absence of any single component in this ternary mixture drastically reduced the destruction efficiency of CF4. The CF4 destruction efficiencies with the solid reagent containing the alkali halide, MX, increased in the order of Li approximately Na < K < Cs for alkali cations and I < Br < Cl < F for halide anions. This trend agreed with the endothermicity of the alkali metal generation reaction: the higher the endothermicity, the lower the destruction efficiency. Alkali metal generation was indirectly detected by monitoring H2 production from its reaction with water. The production of alkali metals increased with NaF, KF, and CsF in this order. The CsF/CaO/Si system exhibited the complete destruction of CF4 at as low as 600 degrees C. The solid product analysis by X-ray diffraction (XRD) showed the formation of CaF2 and the depletion of Si with black carbon particles formed in the solid reagent residue. No CO/CO2 and toxic HF and SiF4 formation were detected in the exhaust gas. PMID:11944694

  14. Famed Bulgarian physicists. I. St. Petroff's Goettingen research of the photostimulated interconversions of color centers in alkali halides: the discovery of the photostimulated aggregation

    Georgiev, Mladen

    2008-01-01

    This essay tells briefly of the life and work of one of the most successful scientists originating from a Balkan settlement whose name and popularity have greatly exceeded its realm. The word is of a discovery during WWII of the photostimulated aggregation of the F centers (else alkali atoms) dissolved from the vapor into an alkali halide crystal. Using optical absorption techniques while a grantee of Humboldt's Foundation in Goettingen, Germany between 1943-1944, he found new absorption band...

  15. Ion Segregation and Deliquescence of Alkali Halide Nanocrystals on SiO2

    Arima, Kenta; Jiang, Peng; Lin, Deng-Sung; Verdaguer, Albert; Salmeron, Miquel

    2009-08-11

    The adsorption of water on alkali halide (KBr, KCl, KF, NaCl) nanocrystals on SiO{sub 2} and their deliquescence was investigated as a function of relative humidity (RH) from 8% to near saturation by scanning polarization force microscopy. At low humidity, water adsorption solvates ions at the surface of the crystals and increases their mobility. This results in a large increase in the dielectric constant, which is manifested in an increase in the electrostatic force and in an increase in the apparent height of the nanocrystals. Above 58% RH, the diffusion of ions leads to Ostwald ripening, where larger nanocrystals grow at the expense of the smaller ones. At the deliquescence point, droplets were formed. For KBr, KCl, and NaCl, the droplets exhibit a negative surface potential relative to the surrounding region, which is indicative of the preferential segregation of anions to the air/solution interface.

  16. A two-accelerator facility and its use for radiation damage studies in alkali halides

    An experimental system is described in which heavy ions, of energies 50-100 MeV, and light ions of energies 0.5-2 MeV, may be transported alternately from different accelerators into a common scattering chamber. The beam-transport and scattering-chamber details are described, the latter being designed to make in-beam studies of different modes of radiation damage in the target material. Experimental studies are described of simultaneous detection of back-scattered helium ions, X-rays and optical absorption in single-crystal alkali halide samples, done during continuous irradiation by a 1 MeV He beam; also back-scattered protons following intermittent irradiation by a 60 MeV oxygen beam. Analysis of the relative damage by these two beams is discussed in relation to a damage mechanism due to Pooley

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

    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)

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

    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

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

    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...

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

    Balzer, Frank; Sun, Rong; Parisi, Jürgen;

    2015-01-01

    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...

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

    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

  2. Excess-electron and excess-hole states of charged alkali halide clusters

    Honea, Eric C.; Homer, Margie L.; Whetten, R. L.

    1990-12-01

    Charged alkali halide clusters from a He-cooled laser vaporization source have been used to investigate two distinct cluster states corresponding to the excess-electron and excess-hole states of the crystal. The production method is UV-laser vaporization of an alkali metal rod into a halogen-containing He flow stream, resulting in variable cluster composition and cooling sufficient to stabilize weakly bound forms. Detection of charged clusters is accomplished without subsequent ionization by pulsed-field time-of-flight mass spectrometry of the skimmed cluster beam. Three types of positively charged sodium fluoride cluster are observed, each corresponding to a distinct physical situation: NanF+n-1 (purely ionic form), Nann+1F+n-1 (excess-electron form), and NanF+n (excess-hole form). The purely ionic clusters exhibit an abundance pattern similar to that observed in sputtering and fragmentation experiments and are explained by the stability of completed cubic microlattice structures. The excess-electron clusters, in contrast, exhibit very strong abundance maxima at n = 13 and 22, corresponding to the all-odd series (2n + 1 = jxkxl;j,k,l odd). Their high relative stability is explained by the ease of Na(0) loss except when the excess electron localizes in a lattice site to complete a cuboid structure. These may correspond to the internal F-center state predicted earlier. A localized electron model incorporating structural simulation results as account for the observed pattern. The excess-hole clusters, which had been proposed as intermediates in the ionization-induced fragmentation of neutral AHCs, exhibit a smaller variation in stability, indicating that the hole might not be well localized.

  3. Famed Bulgarian physicists. I. St. Petroff's Goettingen research of the photostimulated interconversions of color centers in alkali halides: the discovery of the photostimulated aggregation

    Georgiev, Mladen

    2008-01-01

    This essay tells briefly of the life and work of one of the most successful scientists originating from a Balkan settlement whose name and popularity have greatly exceeded its realm. The word is of a discovery during WWII of the photostimulated aggregation of the F centers (else alkali atoms) dissolved from the vapor into an alkali halide crystal. Using optical absorption techniques while a grantee of Humboldt's Foundation in Goettingen, Germany between 1943-1944, he found new absorption bands pertaining to small-size F center aggregates and followed their interconversions. A primary photochemical solid state reaction was evidenced for the first time leading to nanoscale products.

  4. Reactions between cold methyl halide molecules and alkali-metal atoms

    We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH3X (X = F, Cl, Br, I) and alkali-metal atoms A (A = Li, Na, K, Rb) using high-level ab initio calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, CH3X + A → CH3 + AX. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow

  5. Reactions between cold methyl halide molecules and alkali-metal atoms

    Lutz, Jesse J

    2013-01-01

    We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH$_{3}X$ ($X$ = F, Cl, Br, I) and alkali-metal atoms $A$ ($A$ = Li, Na, K, Rb) using high-level {\\it ab initio} calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, ${\\rm CH}_{3}X+A\\rightarrow{\\rm CH}_{3}+AX$. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

  6. Correlations for calculating the surface tension and enthalpies of sublimation of alkali halides

    The capability of a new model on predicting the surface tension of molten alkali halides is described. A relationship, with a simple form of calculation, exists between the surface tension (γ) at the melting point, molar volume (V), inter-nuclear distance (D) and the enthalpy of sublimation (Es). The basic idea results from the assumption that all the parameters are constants that are usually easy to acquire. Moreover, two previous models (Furth and Schytil equations) were also checked and applied for calculating surface tension of molten salts. The three formulas have been examined for 20 salts and showed remarkable agreement between calculated and experimental data with a difference of less than 10% for most of the salts studied. The heats of sublimation of alkali halides were, theoretically, calculated and compared to literature values.

  7. Temperature Dependence of Interatomic Separation and Bulk Modulus for Alkali Halides

    Liu, Quan

    2016-07-01

    The values of interatomic separation r with the change of temperature T for seven alkali halides have been investigated with the help of an isobaric equation of state. The calculated results are used to predict the values of bulk modulus at different temperatures. The results are compared with the available experimental data and other theoretical results and are further discussed in view of recent research in the field of high temperature physics.

  8. Trap spectroscopy in alkali halides at synchronous measurements of exoelectron emission and luminescence by fractional glow technique. [X radiation

    Tale, I. (Latvijskij Gosudarstvennyj Univ., Riga (USSR)); Kortov, V.; Popov, V. (Ural' skij Politekhnicheskij Inst., Sverdlovsk (USSR))

    1982-12-16

    A fractional heating technique in spectroscopy of electron traps in the conditions of synchronous registration of exoemission and luminescence is used for the first time. LiF and KCl:Tl monocrystals excited by X-rays are investigated. Based on the equality of the TSE and TSL activation energy and frequency factors, the identity of traps giving rise to the appearance of these peaks in the temperature intervals of the hole and electron trap devastation is found. The important role of the bulk charge appearing at X-ray irradiation in the TSE of dielectrics is proved experimentally. The TSE from the bulk traps in alkali halides is shown to be an emission of 'hot electrons' which is insensitive to the value of the crystal electron affinity.

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

    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

  10. Mass and orientation effects in dissociative collisions between rare gas atoms and alkali halide molecules

    The collision induced dissociation of alkali halide molecules to ion pairs upon impact with hyperthermal rare gas atoms has been investigated using the crossed molecular beam method. Relative total cross sections for the dissociation of CsI, CsBr, RbI, and KI to ion pairs upon collision with xenon and krypton have been measured over a relative collision energy range from threshold to 10 and 8 eV, respectively. In addition, complete angular and energy distributions of both dissociated ions from Xe+CsI, CsBr, and RbI collisions and from Kr+CsI and CsBr collisions have been obtained at several collision energies within the above energy range. Mass, collision orientation, and energy dependence effects observed throughout this work define two limiting case dissociation mechanisms for the Xe(Kr)+MX→Xe(Kr)+M++X- processes. The dominant dissociation configuration consists of the rare gas atom incident on the light atom end of the alkali halide molecule in a near collinear collision. The less preferred dissociation mechanism results when the rare gas atom is incident in a near collinear configuration on the heavy atom end of the alkali halide molecule. Experimental measurements of the percentage of energy transfer from the relative kinetic energy between Xe(Kr) and MX to the relative motion of M+--X- range as high as 95%; these percentage energy transfers correlate well with the predictions of an impulsive collision model. Three-dimensional classical trajectory calculations using realistic interaction potentials have been performed and they verify the dynamical interpretation suggested by the experiments

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

    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 liquid-solid adhe...

  12. Thermoluminescence in alkali halides irradiated at 80K

    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

  13. Off-center impurity in alkali halides: reorientation, electric polarization and pairing to F center. III. Numerical calculations

    Baldacchini, G; Grassano, U M; Scacco, A; Petrova, P; Mladenova, M; Ivanovich, M; Georgiev, M

    2007-01-01

    We carried out numerical calculations by an extended-Hueckel program in order to check the analytical results reported in the preceding Part I and Part II. We typically consider alkali halide clusters composed of some tens of constituent atoms to calculate electronic energies under static conditions or versus the displacements of particular atoms. Among other things, the off-center displacement of substitutional Li+ impurity in most alkali halides is evidenced. The trigonometric profile of the rotational barriers is also confirmed for KCl.

  14. Enthalpic Interaction for α-Amino Acid with Alkali Metal Halides in Water

    LU,Yan(卢雁)

    2004-01-01

    The studies of the enthalpic interaction parameters, hxy, hxyy and hxxv, of alkali metal halides with glycine,α-alanine and α-aminobutyric acid were published. Synthetic considering of the results of the studies, some interesting behaviors of the interaction between alkali metal halides and the α-amino acids have been found. The values of hxy will increase with the increase of the number of carbon atoms in alkyl side chain of amino acid molecules and decrease with the increase of the radius of the ions. The increasing of the salt's effect on the hydrophobic hydration structure as the radii of anion is more obvious than as that of cation. The value of hxxy will regularly decrease with the increase of the number of carbon atoms in the alkyl chain of amino acids and linear increase with the increase of the radius. But the relation of hxxy with the radius of cations is not evident. The value of hxyy will increase with the increase of the radii of the ions. As the increase of the number of carbon atoms of amino acids, hxyy is decreas for the ions which have lager size and there is a maximum value at α-alanine for the ions which have small size. The behaviors of the interaction mentioned above were further discussed in view of electrostatic and structural interactions.

  15. Study on growth of lead halides single crystals for solid-state lasers in mid-IR

    Král, Robert; Cihlář, Antonín

    Bratislava: N, 2009 - (Koman, M.; Mikloš, D.), s. 38-39 ISBN 978-80-89088-81-2. [Development of Materials Science in Research and Education - DMS -RE 2009 /19./. Závažná Poruba (SK), 31.08.2009-04.09.2009] R&D Projects: GA AV ČR KJB200100901 Institutional research plan: CEZ:AV0Z10100521 Keywords : ternary alkali lead halides * crystal growth * Bridgman method * laser mid-IR Subject RIV: BM - Solid Matter Physics ; Magnetism

  16. Two-electron F' centers in alkali halides: a saddle point approach. I. General and semicontinuum analyses

    Georgiev, Mladen

    2006-01-01

    The F' center in an alkali halide forms when an anion vacancy traps two electrons which is the prerequisite of a diatomic molecule. Indeed, the center may displace left or right along in a (110) plane, due to its coupling to the B_{1u} vibrational mode of polarization respectively. On jumping from the initial position to the final position the F' center passes through a saddle point which configuration is molecule-like being conformed by two neighboring semi-vacancies along . Each semi-vaca...

  17. Nonradiative DKR processes: revisiting the theory. IV. On the controversy over a polaron state bound to an F center in alkali halides

    Georgiev, Mladen

    2007-01-01

    We are commenting on an earlier hypothesis of polaron states bound to F centers in alkali halides. These states increasing the effective size of the color centers, they play an active role in concentration-dependent phenomena, such as the observed quenching of F center luminescence. Our record shows only one related study on NaBr and NaI which has also been aimed at checking the bound polaron hypothesis. Further studies of the concentration quenching in other alkali halide hosts whould eventu...

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

    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. Photography: enhancing sensitivity by silver-halide crystal doping

    Belloni, Jacqueline

    2003-06-01

    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 PHI{sub eff} of photoinduced silver cluster formation in silver halide microcrystals is usually much lower than the photoionization theoretical limit PHI{sub theor}=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 HCO{sub 2}{sup -} as a specific hole scavenger. First, the dopant scavenges the photoinduced hole, thus enhancing the electron escape from the pair recombination. Second, the CO{sub 2}{sup {center_dot}}{sup -} radical so formed transfers an electron to another silver cation, so that the PHI{sub eff} limit may be of 2Ag{sup 0} 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.

  20. Temperature-dependent solubilities and mean ionic activity coefficients of alkali halides in water from molecular dynamics simulations.

    Mester, Zoltan; Panagiotopoulos, Athanassios Z

    2015-07-28

    The mean ionic activity coefficients of aqueous KCl, NaF, NaI, and NaCl solutions of varying concentrations have been obtained from molecular dynamics simulations following a recently developed methodology based on gradual insertions of salt molecules [Z. Mester and A. Z. Panagiotopoulos, J. Chem. Phys. 142, 044507 (2015)]. The non-polarizable ion models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)], Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)], Reiser et al. [J. Chem. Phys. 140, 044504 (2014)], and Joung and Cheatham [J. Phys. Chem. B 112, 9020 (2008)] were used along with the extended simple point charge (SPC/E) water model [Berendsen et al., J. Phys. Chem. 91, 6269 (1987)] in the simulations. In addition to the chemical potentials in solution used to obtain the activity coefficients, we also calculated the chemical potentials of salt crystals and used them to obtain the solubility of these alkali halide models in SPC/E water. The models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)] and Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)] provide excellent predictions of the mean ionic activity coefficients at 298.15 K and 1 bar, but significantly underpredict or overpredict the solubilities. The other two models generally predicted the mean ionic activity coefficients only qualitatively. With the exception of NaF for which the solubility is significantly overpredicted, the model of Joung and Cheatham predicts salt solubilities that are approximately 40%-60% of the experimental values. The models of Reiser et al. [J. Chem. Phys. 140, 044504 (2014)] make good predictions for the NaCl and NaI solubilities, but significantly underpredict the solubilities for KCl and NaF. We also tested the transferability of the models to temperatures much higher than were used to parametrize them by performing simulations for NaCl at 373.15 K and 1 bar, and at 473.15 K and 15.5 bar. All models overpredict the drop in the values of mean ionic

  1. 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

    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 $\\phi^{0}_{v}$.

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

    Heyrovská, Raji

    2007-01-01

    Roč. 436, č. 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

  3. Organometallic halide perovskite single crystals having low deffect density and methods of preparation thereof

    Bakr, Osman M.

    2016-02-18

    The present disclosure presents a method of making a single crystal organometallic halide perovskites, with the formula: AMX3, wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, and Eu, and X is a halide. The method comprises the use of two reservoirs containing different precursors and allowing the vapor diffusion from one reservoir to the other one. A solar cell comprising said crystal is also disclosed.

  4. Sensitivity of alkali halide scintillating calorimeters with particle identification to investigate the DAMA dark matter detection claim

    Nadeau, Patrick; Di Stefano, P C F; Lanfranchi, J -C; Roth, S; von Sivers, M; Yavin, Itay

    2014-01-01

    Scintillating calorimeters are cryogenic detectors combining a measurement of scintillation with one of phonons to provide particle identification. In view of developing alkali halide devices of this type able to check the DAMA/LIBRA claim for the observation of dark matter, we have simulated detector performances to determine their sensitivity by two methods with little model-dependence. We conclude that if performance of the phonon channel can be brought in line with those of other materials, an exposure of 10 kg-days would suffice to check the DAMA/LIBRA claim in standard astrophysical scenarios. Additionally, a fairly modest array of 5 kg with background rejection would be able to directly check the DAMA/LIBRA modulation result in 2 years.

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

    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.

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

    Assem, E.E., E-mail: e_assem_2000@sci.kfs.edu.e [Physics Department, Faculty of Science, Kafrelsheikh University, Kafrelsheikh (Egypt)

    2011-02-01

    The effect of halide ions on density, electrical, magnetic and crystallization kinetics for (20X-50P{sub 2}O{sub 5}-30V{sub 2}O{sub 5}) mole% has been investigated, where X=CaO, CaF{sub 2}, CaCl{sub 2} and CaBr{sub 2}. 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: {yields} Replacing oxygen ions by halide ions decreases glass transition temperature and thermal stability. {yields} Replacing oxygen ions by halide ions increases electrical conductivity and decreases activation energy. {yields} Replacing oxygen ions by halide ions enhances the tendency of glass ceramic and decreases the crystallization activation energy.

  7. Solubility of alkali metal halides in the ionic liquid [C4C1im][OTf].

    Kuzmina, O; Bordes, E; Schmauck, J; Hunt, P A; Hallett, J P; Welton, T

    2016-06-28

    The solubilities of the metal halides LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbCl, CsCl, CsI, were measured at temperatures ranging from 298.15 to 378.15 K in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4C1im][OTf]). Li(+), Na(+) and K(+) salts with anions matching the ionic liquid have also been investigated to determine how well these cations dissolve in [C4C1im][OTf]. This study compares the influence of metal cation and halide anion on the solubility of salts within this ionic liquid. The highest solubility found was for iodide salts, and the lowest solubility for the three fluoride salts. There is no outstanding difference in the solubility of salts with matching anions in comparison to halide salts. The experimental data were correlated employing several phase equilibria models, including ideal mixtures, van't Hoff, the λh (Buchowski) equation, the modified Apelblat equation, and the non-random two-liquid model (NRTL). It was found that the van't Hoff model gave the best correlation results. On the basis of the experimental data the thermodynamic dissolution parameters (ΔH, ΔS, and ΔG) were determined for the studied systems together with computed gas phase metathesis parameters. Dissolution depends on the energy difference between enthalpies of fusion and dissolution of the solute salt. This demonstrates that overcoming the lattice energy of the solid matrix is the key to the solubility of inorganic salts in ionic liquids. PMID:27264676

  8. Ion partitioning at the liquid/vapor interface of a multicomponent alkali halide solution: A model for aqueous sea salt aerosols

    Ghosal, S.; Brown, M. A.; Bluhm, H.; Krisch, M. J.; Salmeron, M.; Jungwirth, Pavel; Hemminger, J. C.

    2008-01-01

    Roč. 112, č. 48 (2008), s. 12378-12384. ISSN 1089-5639 R&D Projects: GA ČR GA203/07/1006; GA MŠk LC512 Grant ostatní: NSF(US) CHE0431312 Institutional research plan: CEZ:AV0Z40550506 Keywords : photoelectron spectroscopy * molecular dynamics * water surface * alkali halides Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.871, year: 2008

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

    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.

  10. Alkali atoms, dimers, exciplexes and clusters in 4He crystals

    this effect to the formation of an entangled diatomic bubble state. The doped region of the He crystal has a bluish color that originates from Mie scattering by alkali clusters, the size distribution of which can be inferred from the extinction spectrum. When the doped He crystal is molten by lowering the He pressure, the doped (column-shaped) region remains solid at pressures, where pure He is superfluid. We present experimental support for our hypothesis that this new form of solid He is an amorphous or crystalline ionic structure formed by snowballs (nanoscopic solid He structures formed around positive ions) and electron bubbles. (author)

  11. Electrohydrodynamic emission of positive and negative ions from alkali-metal halide melts

    The characteristics of electrohydrodynamic (EHD) emission of positive and negative ions from melts of alkali-metal metals are presented. The angular current density is 3-4 μA/sr with emission currents of 0.1-0.5 μA. The salt EHD sources which have been developed yield stable currents of K+, Rb+, Cs+, F-, Cl-, and I- ions for several tens of hours. 10 refs., 4 figs., 1 tab

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

    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.

  13. Photostimulated luminescence in alkali halides induced by excitation with ionizing radiation

    The photostimulated luminescence (PSL) phenomenon induced in copper-doped sodium chloride (NaCl : Cu) and europium-doped potassium chloride (KCl : Eu) phosphor crystals by excitation with ionizing radiation such as X-rays is studied. The emission mechanism of the PSL in both phosphor crystals is discussed in terms of the recombination of electrons optically stimulated from the radiation-induced F centers with the luminescence centers such as Cu2+ in NaCl and Eu3+ ions in KCl. The potentiality of both phosphor crystals as a material for two-dimensional X-ray imaging sensors utilizing the PSL phenomenon is also discussed. ((orig.))

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

    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.)

  15. Effect of halides addition on the ligand field of chromium in alkali borate glasses

    Hassan, M.A., E-mail: moukhtar_hassan@yahoo.com

    2013-10-15

    Highlights: •The 10 KM–64.7 B{sub 2}O{sub 3}–25 Na{sub 2}O–0.3 Cr{sub 2}O{sub 3} (M = Cl, Br and I) glassy system was prepared by a quenching method. •Optical basicity, ligand field theory optical band gap energy, refractive index, ESR and IR were studied. •The electronegativity plays an important role in deforming the crystal field around the transition metal ions. •The crystal-field sites of KCl or KBr sample are very strong compared to the very weak one in the KI sample. -- Abstract: Borate oxide glass system of composition 10 KM–64.7 B{sub 2}O{sub 3}–25 Na{sub 2}O–0.3 Cr{sub 2}O{sub 3} (M = Cl, Br and I) was prepared by conventional melt quenching technique. The amorphous nature of the investigated glasses was checked by the X-ray diffraction (XRD) technique. The optical basicity of the system has been calculated, and was found to increase by going from KCl to KBr and to KI. Optical absorption spectra were recorded in the UV–visible range. Through a careful analysis of the data, the ligand field parameters (crystal field strength Dq, Racah parameters B and nephelauxetic functions h) and the optical parameters (optical band gap, Urbach tail band width, and refractive index) have been estimated. The obtained results reveal a strong correlation between that ligand field parameters and the type of halogen atom; the crystal-field strength of KCl or KBr samples are very pronounced but it is rather weak in the KI sample. Electron spin resonance (ESR) has been used to probe the valency of the Chromium ions. The resulting ESR parameters revealed that chromium ions are predominantly in the trivalent state with traces of hexavalent state. Using Infrared spectroscopy (IR) information on the boron structural units has been obtained. The N{sub 4} ratio increases by replacing the KCl by KBr or KI, and it was found that the tetrahedral coordination of Cr{sup +} ions becomes preferential in the host glasses with increasing the optical basicity.

  16. Effect of homologous impurities on primary radiation defect accumulation in alkali halides

    To clarify the mechanism of the effect of anion and cation homologous impurities on the primary radiation-induced defect accumulation, the transient absorption of H and F centers was studied in KCl and KBr crystals. Pulse electron accelerator technique was used. Pure and doped crystals were investigated. It was obtained that the cation homologue Na in the concentration range from 0 to 0.5 m. % in 10-8-10-6 s post-irradiation time has no effect on the defect accumulation efficiency at low temperature and increases the latter at high temperature. At large post-irradiation time and at high temperatures the rise of efficiency at low Na concentration and decrease of it at high Na concentrations were observed. The conclusion was made that Na does not affect the generation process. The anion homologous impurities (I and Br) lead to a significant increase of the accumulation efficiency due to the formation of more stable F-H pair at self-trapped exciton decay on anion impurities compared with that formed in perfect lattice. Some assumptions are advanced to explain the effect

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

    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

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

    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.

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

    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.

  20. Intrinsic femtosecond charge generation dynamics in a single crystal organometal halide perovskite

    Valverde-Chávez, David A.; Ponseca Jr., Carlito; Stoumpos, Constantinos; Yartsev, Arkady; Kanatzidis, Mercouri G.; Sundström, Villy; Cooke, David G.

    2015-01-01

    Hybrid metal-organic perovskite solar cells have astounded the solar cell community with their rapid rise in efficiency over the past three years. Despite this success, the basic processes governing the photogeneration of free charges, particularly their dynamics and efficiency, remain unknown. Here we use ultrabroadband pulses of THz frequency light to see the intrinsic photophysical properties of single crystal lead halide perovskite just femtoseconds after a photon is first absorbed. Our s...

  1. New halides of neodymium and their crystal structures

    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)

  2. Photofragmentation of metal halides

    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 Ω=0+ and Ω=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 Ω=1 state. Extensive studies are reported on three thallium halides, TlI, TlBr and TlCl at various wavelengths covering the near ultraviolet region. (Auth.)

  3. Mass spectrometry of oligopeptides in the presence of large amounts of alkali halides using desorption/ionization induced by neutral cluster impact.

    Portz, André; Baur, Markus; Gebhardt, Christoph R; Dürr, Michael

    2016-06-01

    Oligopeptides in the presence of large amounts of salt were desorbed and ionized using desorption/ionization induced by neutral clusters (DINeC) for further analysis by means of mass spectrometry (MS). Using oligopeptides in alkali halide solutions as a model system, DINeC was shown to yield clear and fragmentation free mass spectra of the biomolecules even from environments with a large excess of salt. The results were traced back to a phase separation between salt and biomolecules during sample preparation. The ratio between alkali metal complexes [M+A](+) and bare biomolecules [M+H](+) was controlled using different preparation schemes. DINeC was applied to the products of a tryptic digest of bovine serum albumin in the presence of sodium chloride; the results of a mass fingerprint analysis did not show a major difference for the spectra with and without salt in the original solution. The metal-ion/peptide interaction was further investigated by means of tandem-MS. PMID:26825286

  4. A different view of structure-making and structure-breaking in alkali halide aqueous solutions through x-ray absorption spectroscopy.

    Waluyo, Iradwikanari; Nordlund, Dennis; Bergmann, Uwe; Schlesinger, Daniel; Pettersson, Lars G M; Nilsson, Anders

    2014-06-28

    X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl(-) and Br(-) are shown to have insignificant effect on the structure of water while I(-) locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na(+) and the effect on the liquid as similar to an increase in temperature. PMID:24985653

  5. Metallotropic liquid crystals formed by surfactant templating of molten metal halides.

    Martin, James D; Keary, Cristin L; Thornton, Todd A; Novotnak, Mark P; Knutson, Jeremey W; Folmer, Jacob C W

    2006-04-01

    Liquid crystals consist of anisotropic molecular units, and most are organic molecules. Materials incorporating metals into anisotropic molecules, described as metallomesogens, have been prepared. Anisotropic structures such as one-dimensional chains and two-dimensional layers are frequently observed in solid-state inorganic materials, however, little is understood about structural organization in melts of such materials. Achieving liquid-crystalline behaviour in inorganic fluids should be possible if the anisotropic structure can be retained or designed into the molten phase. We demonstrated the ability to engineer zeolite-type structures into metal halide glasses and liquids. In this work we have engineered lamellar, cubic and hexagonal liquid-crystalline structure in metal-halide melts by controlling the volume fraction and nature of the inorganic block (up to 80 mol%) with respect to alkylammonium surfactants. The high metal content of these liquid-crystalline systems significantly advances the field of metallomesogens, which seeks to combine magnetic, electronic, optical, redox and catalytic properties common to inorganic materials with the fluid properties of liquid crystals. PMID:16547520

  6. Growth of high quality mercurous halide single crystals by physical vapor transport method for AOM and radiation detection applications

    Amarasinghe, Priyanthi M.; Kim, Joo-Soo; Chen, Henry; Trivedi, Sudhir; Qadri, Syed B.; Soos, Jolanta; Diestler, Mark; Zhang, Dajie; Gupta, Neelam; Jensen, Janet L.; Jensen, James

    2016-09-01

    Single crystals of mercurous halide were grown by physical vapor transport method (PVT). The orientation and the crystalline quality of the grown crystals were determined using high resolution x-ray diffraction (HRXRD) technique. The full width at half maximum (FWHM) of the grown mercurous bromide crystals was measured to be 0.13 degrees for (004) reflection, which is the best that has been achieved so far for PVT grown mercurous halide single crystals. The extended defects of the crystals were also analyzed using high resolution x-ray diffraction topography. Preliminary studies were carried out to evaluate the performance of the crystals on acousto-optic modulator (AOM) and gamma-ray detector applications. The results indicate the grown mercurous halide crystals are excellent materials for acousto-optic modulator device fabrication. The diffraction efficiencies of the fabricated AOM device with 1152 and 1523 nm wavelength lasers polarizing parallel to the acoustic wave were found to be 35% and 28%, respectively. The results also indicate the grown crystals are a promising material for gamma-ray detector application with a very high energy resolution of 1.86% FWHM.

  7. An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

    The synthesis of large-area monolayer tungsten disulphide (WS2) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS2 crystals using tungsten hexachloride (WCl6) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl6 in ethanol was drop-casted on SiO2/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS2 single crystalline monolayer can be grown using the WCl6 precursor. Our finding shows an easier and effective approach to grow WS2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction

  8. An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

    Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap, E-mail: kalita.golap@nitech.ac.jp; Tanemura, Masaki [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)

    2016-02-01

    The synthesis of large-area monolayer tungsten disulphide (WS{sub 2}) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS{sub 2} crystals using tungsten hexachloride (WCl{sub 6}) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl{sub 6} in ethanol was drop-casted on SiO{sub 2}/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS{sub 2} crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS{sub 2} single crystalline monolayer can be grown using the WCl{sub 6} precursor. Our finding shows an easier and effective approach to grow WS{sub 2} monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.

  9. An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

    Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap; Tanemura, Masaki

    2016-02-01

    The synthesis of large-area monolayer tungsten disulphide (WS2) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS2 crystals using tungsten hexachloride (WCl6) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl6 in ethanol was drop-casted on SiO2/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS2 single crystalline monolayer can be grown using the WCl6 precursor. Our finding shows an easier and effective approach to grow WS2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.

  10. Characterization of an alkali- and halide-resistant laccase expressed in E. coli: CotA from Bacillus clausii.

    Søren Brander

    Full Text Available 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 (K(M but to pH dependence of catalytic turnover: The k(cat of B. clausii cotA was 1 s⁻¹ at pH 6 and 5 s⁻¹ at pH 8 in contrast to 6 s⁻¹ at pH 6 and 2 s⁻¹ at pH 8 for of B. subtilis cotA. Overall, k(cat/K(M was 10-fold higher for B. subtilis cotA at pH(opt. 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 80°C, less than the ~50 minutes at 80°C 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. Quasicharacteristic radiation of relativistic electrons at orientation motion in lithium halides crystals along charged planes and axes

    Maksyuta, N. V.; Vysotskii, V. I.; Efimenko, S. V.

    2016-07-01

    The paper deals with the investigation of the orientation motion of relativistic electrons in charged (111) planes and charged [110] axes of lithium halides ionic crystals of LiF, LiCl, LiBr and LiI. On the basis of these investigations the spectra of quasicharacteristic radiation for the electron beams with various Lorentz-factors both in planar and axial cases have been calculated numerically.

  12. Reaction rate approach to dipolar relaxation in alkali halides: Adiabaticity versus classical, activated-tunneling, and quantal dipoles

    Medrano, C; Georgiev, M.

    2007-01-01

    This paper is aimed at presenting a simple vibronic model for describing the dipolar reorientation in crystals by means of reaction rate theory. The Hamiltonian of an isolated dipole is simplified so as to render the problem solvable. Depending on the crossover splitting the dipoles may reorientate adiabatically with a high electron-transfer expectancy or exhibit low reorientation rates due to low expectancy. An important quantity to distinguish between adiabatic dipoles behaving classically ...

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

    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

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

    Cihlář, 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 ČR 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

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

    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.

  16. Preparation of cerium halide solvate complexes

    Vasudevan, Kalyan V; Smith, Nickolaus A; Gordon, John C; McKigney, Edward A; Muenchaussen, Ross E

    2013-08-06

    Crystals of a solvated cerium(III) halide solvate complex resulted from a process of forming a paste of a cerium(III) halide in an ionic liquid, adding a solvent to the paste, removing any undissolved solid, and then cooling the liquid phase. Diffusing a solvent vapor into the liquid phase also resulted in crystals of a solvated cerium(III) halide complex.

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

    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.)

  18. Radiation processes in crystal solid solutions

    Gladyshev, Gennadi

    2012-01-01

    This is a monograph explaining processes occurring in two classes of crystal solids (metal alloys and doped alkali halide) under irradiation by various types of radiation (alpha, beta, gamma, X-radiations, ions). This e-book is a useful reference for advanced readers interested in the physics of radiation and solid state physics.

  19. Stability diagrams for complexes in molten mixtures of halide salts

    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 pseudo-potential radii of Zunger and Cohen. As a third alternative we also consider a classification based on Pettifor's phenomenological chemical scale of the elements. The alternative structural classification schemes that are developed from these elemental properties are very successful in distinguishing molten mixtures in which the available experimental evidence indicates stability of ''complexes'', i.e. long-lived fourfold coordination of polyvalent metal ions. (author). 55 refs, 3 figs

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

    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.

  1. Purification, crystallization and halide phasing of a Streptococcus agalactiae backbone pilin GBS80 fragment

    Vengadesan, Krishnan; Ma, Xin; Dwivedi, Prabhat; Ton-That, Hung; Narayana, Sthanam V. L

    2010-01-01

    The C-terminal fragment of Streptococcus agalactiae (group B streptococcus) major (backbone) pilin GBS80 was purified and crystallized in two different space groups. Single-wavelength anomalous dispersion (SAD) data collected to 2.0 Å resolution on a iodide (NaI) derivative crystal using the home source were used to obtain initial phases.

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

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

    2016-05-01

    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.

  3. The role of oxygen containing impurities in defects formation in cesium halide crystals

    Hud, I.; Garapyn, I.; Pavlyk, B.

    2003-01-01

    The dependence of defect formation efficiency in CsI single crystals both on the type of oxygen containing impurities and the value of the absorbed irradiation dose was studied. Correlative results were obtained under investigation by methods of ionic thermocurrent (ITC), thermostimulated exoemission (TSEE), electrical conductivity and optical spectroscopy. The peculiarities of defect formation in gamma-irradiated CsI-CO3(SO4, OH) and X-irradiated CsI-OH single crystals are discussed.

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

    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.

  5. Intensity distributions of reflected surface channeling protons scattered on surfaces of electron-bombarded alkali halide crystals

    Fukazawa, Y., E-mail: yukofu@cc.osaka-kyoiku.ac.jp; Kihara, K.; Iwamoto, K.; Susuki, Y.

    2013-11-15

    We have examined the surface-channeling of 550 keV protons on electron-bombarded KBr(0 0 1) surfaces at grazing incidence. On the surface, electron-stimulated desorption (ESD) resulting from the irradiation of 5 keV electrons changes the surface morphology. In order to investigate the change of the surface morphology, the luminous intensity distributions observed on a fluorescent screen (scattering patterns) of the reflected protons under the surface-channeling conditions are measured. Normalized specular intensity of the protons oscillates, and the results of computer simulations show that the period of the intensity oscillation agrees with the period of layer-by-layer desorption. The measured period of the oscillation is comparable to the simulated one, i.e., the period of the desorption, however, the measured amplitude of the oscillation is weak. This shows that the layer-by-layer desorption of the experimental surface is observed but is not as remarkable as that of the perfect surface introduced in the simulation.

  6. Mechanochemical synthesis in copper(II) halide/pyridine systems: single crystal X-ray diffraction and IR spectroscopic studies.

    Bowmaker, Graham A; Di Nicola, Corrado; Pettinari, Claudio; Skelton, Brian W; Somers, Neil; White, Allan H

    2011-05-14

    Whereas complexes of divalent metal halides (X = Cl, Br, I) with/from pyridine commonly crystallise as trans-[M(py)(4)X(2)]·2py, M on a site of 222 symmetry in space group Ccca, true for CuCl(2) and CuBr(2) in particular, the copper(II) iodide adduct is of the form [Cu(py)(4)I]I·2py, Cu on a site of mm2 symmetry in space group Cmcm, and five-coordinate (square-pyramidal), the same cationic species also being found in 2[Cu(py)(4)I](I(3))·[(py)(2)Cu(μ-I)(2)Cu(py)(2)] (structurally defined). Bromide or N-thiocyanate may be substituted for the unbound iodide ion in the solvated salt, resulting in complexes which crystallize in space group Ccca, but with both anions and the metal atom disordered. In [Cu(py)(4)(I(3))(2)], a pair of long Cu···I contacts approach a square-planar Cu(py)(4) array. Assignments of the ν(CuN) and ν(CuX) (X = Br, I, SCN) bands in the far-IR spectra are made, the latter with the aid of analogous assignments for [Cu(py)(2)X(2)] (X = Cl, Br), which show a dependence of ν(CuX) on the Cu-X bond length that is very similar to that determined previously for copper(i) halide complexes. The structure of the adventitious complex [(trans-)(H(2)O)(py)(4)CuClCu(py)(4)](I(3))(3)·H(2)O is also recorded, with six- and five-coordinate copper atoms; rational synthesis provides [{Cu(py)(4)}(2)(μ-Cl)](I(3))(3)·H(2)O with one water molecule less. In [{Cu(py)(4)Cl}((∞|∞))](I(3))·3py, square pyramidal [Cu(py)(4)Cl](+) cations, assisted by Cl···Cu interactions, stack to give rise to infinite polymeric strings. Several of these compounds were prepared mechanochemically, illustrating the applicability of this method to syntheses involving redox reactions as well as to complex syntheses involving up to five components. The totality of results demonstrates that the [Cu(II)(py)(4)] entity can be stabilized in an unexpectedly diverse range of mononuclear and multinuclear complexes through the presence of lattice pyridine molecules, the bulky triiodide

  7. Role of the crystallization substrate on the photoluminescence properties of organo-lead mixed halides perovskites

    Michele De Bastiani

    2014-08-01

    Full Text Available We have fabricated CH3NH3PbI3−xClx 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. In particular, perovskite crystallites grown in the nanometre size porous scaffold present a shorter-living and blue-shifted emission with respect to the perovskite crystals which are free to grow without any constraints.

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

    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.

  9. Oxidation of hydrogen halides to elemental halogens

    Rohrmann, Charles A.; Fullam, Harold T.

    1985-01-01

    A process for oxidizing hydrogen halides having substantially no sulfur impurities by means of a catalytically active molten salt is disclosed. A mixture of the subject hydrogen halide and an oxygen bearing gas is contacted with a molten salt containing an oxidizing catalyst and alkali metal normal sulfates and pyrosulfates to produce an effluent gas stream rich in the elemental halogen and substantially free of sulfur oxide gases.

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

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

    2009-01-01

    The effect of alkali-silicate glassy matrix as replacement for feldspar in soft and hard porcelain compositions was studied. SEM and X-ray diffraction analysis were used to evidence phase evolution. For each composition, the influence of soaking time was evaluated. The difference in chemical comp...

  11. Broad Wavelength Tunable Robust Lasing from Single-Crystal Nanowires of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I).

    Fu, Yongping; Zhu, Haiming; Stoumpos, Constantinos C; Ding, Qi; Wang, Jue; Kanatzidis, Mercouri G; Zhu, Xiaoyang; Jin, Song

    2016-08-23

    Lead halide perovskite nanowires (NWs) are emerging as a class of inexpensive semiconductors with broad bandgap tunability for optoelectronics, such as tunable NW lasers. Despite exciting progress, the current organic-inorganic hybrid perovskite NW lasers suffer from limited tunable wavelength range and poor material stability. Herein, we report facile solution growth of single-crystal NWs of inorganic perovskite CsPbX3 (X = Br, Cl) and their alloys [CsPb(Br,Cl)3] and a low-temperature vapor-phase halide exchange method to convert CsPbBr3 NWs into perovskite phase CsPb(Br,I)3 alloys and metastable CsPbI3 with well-preserved perovskite crystal lattice and NW morphology. These single crystalline NWs with smooth end facets and subwavelength dimensions are ideal Fabry-Perot cavities for NW lasers. Optically pumped tunable lasing across the entire visible spectrum (420-710 nm) is demonstrated at room temperature from these NWs with low lasing thresholds and high-quality factors. Such highly efficient lasing similar to what can be achieved with organic-inorganic hybrid perovskites indicates that organic cation is not essential for light emission application from these lead halide perovskite materials. Furthermore, the CsPbBr3 NW lasers show stable lasing emission with no measurable degradation after at least 8 h or 7.2 × 10(9) laser shots under continuous illumination, which are substantially more robust than their organic-inorganic counterparts. The Cs-based perovskites offer a stable material platform for tunable NW lasers and other nanoscale optoelectronic devices. PMID:27437566

  12. Magnetoplastic effect in irradiated NaCl and LiF crystals

    Impact of low doses of X-ray radiation on magnetoplastic effect is alkali-halide crystals, consisting in detachment of dislocations from paramagnetic centers under effect of external magnetic field is studied. The measurements of LiF crystals and three types of NaCl crystals, differing in the admixture content were conducted. Dependence of the dislocations medium run on the sample rotation frequency in the magnetic field proved to be especially sensitive to low doses

  13. Crystal growth and evaluation of scintillation properties of Eu and alkali-metal co-doped LiSrAlF6 single crystals for thermal neutron detector

    In recent work, Na co-doping have found to improve the light output of Eu doped LiCaAlF6 (Eu:LiCAF) for thermal neutron scintillator. We grew Eu 2% and alkali metal 1% co-doped LiSAF crystals by Micro-Pulling down method to understand the effect of alkali metal co-doping on scintillation properties and mechanism compared with LiCAF. In photo- and α-ray induced radio-luminescence spectra of the all grown crystals, the emissions from d-f transition of Eu2+ were observed. Without relation to excitation source, decay times of co-doped LiSAF were longer than Eu only doped one. The light yield of Na, K and Cs co-doped LiSAF under 252Cf neutron excitation were improved. Especially, K co-doped Eu:LiSAF reached 33200 ph/n, which outperformed Eu only doped one by approximately 20% (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    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

  15. 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

    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.

  16. Evolution of an alkali basalt-trachyte suite from Jebel Marra volcano, Sudan, through assimilation and fractional crystallization

    The suite of alkali basalts and differentiates (hawaiites, mugearites and trachytes) erupted at Jebel Marra volcano, Sudan, provides an excellent opportunity to examine the differentiation theory of mantle-derived magmas. Crystal fractionation exerts a control on major element compositions although variations in incompatible element and isotopic ratios among the more evolved volcanic rocks require open system behavior. The basement at Jebel and Marra is compositionally unlike the basalts, with much higher 87Sr/86Sr, δ18O and Rb/Nb, together with highly variable Pb isotopic compositions and low 143Nd/144Nd. The strong compositional contrast between crust and magma allows the influence of crustal interaction on magma compositions to be assessed. Simple two-component bulk mixing trends are not observed, but models of simultaneous assimilation and fractional crystallization (AFC) reproduce many of the data trends. It is suggested that contamination takes place at more than one stage, with a change in the composition of the assimilant at different levels, coupled with a change in the rate ratio of assimilation to crystal fractionation. (orig.)

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

    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. The Antimicrobial Action of Silver Halides in Calcium Phosphate

    Kalniņa, D; Gross, K; Onufrijevs, P.; Daukšta, E; Nikolajeva, V; Stankeviciute, Z; Kareiva, A.

    2015-01-01

    Silver halides represent a yet unexplored avenue for imparting antimicrobial activity to calcium phosphates. Negtively charged silver halide colloids (AgI, AgBr and AgCl) were added to synthesized amorphous calcium phosphate. Concurrent melting of silver halides and crystallization to carbonated apatite at 700 oC increased the silver halide surface area available to bacteria and formed a lower solubility apatite. The effect of the matrix solubility on antimicrobial response could ...

  19. Electrodepositions on Tantalum in alkali halide melts

    Barner, Jens H. Von; Jensen, Annemette Hindhede; Christensen, Erik

    2012-01-01

    Surface layers of tantalum metal were electrodeposited on steel from K 2TaF7-LiF-NaF-KF melts. With careful control of the oxide contents dense and adherent deposits could be obtained by pulse plating. In NaCl-KCl-NaF-Na2CO3 and NaCl-KCl-Na2CO 3 melts carbonate ions seems to be reduced to carbon in...... a single 4 electron step. By electrolyses at a constant potential of - 1.4 V vs. Pt in a NaCl-KCl-NaF-Na2CO3 melt at 800 °C coherent carbon containing surface layers could be obtained on tantalum substrates, when a CO2 atmosphere was applied. Copyright © 2012 by The Electrochemical Society....

  20. Electrodepositions on Tantalum in Alkali Halide Melts

    Barner, Jens H. Von; Jensen, Annemette Hindhede; Christensen, Erik

    2013-01-01

    Surface layers of tantalum metal were electrodeposited on steel from K2TaF7-LiF-NaF-KF melts. With careful control of the oxide contents dense and adherent deposits could be obtained by pulse plating. In NaCl-KCl-NaF-Na2CO3 and NaCl-KCl-Na2CO3 melts carbonate ions seems to be reduced to carbon in...

  1. Impurity segregation in zone-refined precursors for crystalline halide scintillators

    Swider, S., E-mail: swider@capesym.com [CapSym, Inc., Natick, MA (United States); Lam, S.; Motakef, S. [CapSym, Inc., Natick, MA (United States); Donohoe, E.; Coers, L.; Taylor, S.; Spencer, S. [SAFC-Hitech, Urbana, IL (United States)

    2015-06-01

    Successful growth of halide scintillator crystals depends on a supply of ultra-high purity (UHP) precursor materials. Metallic interstitials and substitutions may provide traps that quench luminescence. Oxygen impurities can create competing compounds within a matrix, such as oxyhalides, that disrupt crystallinity and nucleate cracks. Using mass spectroscopy and oxygen combustion analysis, we analyzed impurities in SrI{sub 2}, EuI{sub 2}, and YCl{sub 3} precursors before and after zone refining. The data show most alkali and alkali earth impurities segregated easily. However, with the exception of iron, many transition metals were incorporated into the solid. Reliable oxygen measurements proved difficult to achieve. Additional oxygen was measured in nitrates and sulfates, via ion chromatography. Zone refining reduced the overall impurity content, but levels remained above a 10 ppm target.

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

    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 π–anion interaction between a triazolium carbon and iodide displayed by the layers. For salts without the para-substitution on the aryl ring, the π–π interactions are between the triazolium and aryl rings. The melting points of these salts agree with the predicted substituent inductive effects.

  3. High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites and Pressure Effects on their Electronic and Optical Properties

    2016-01-01

    We report the first high-pressure single-crystal structures of hybrid perovskites. The crystalline semiconductors (MA)PbX3 (MA = CH3NH3+, X = Br– or I–) afford us the rare opportunity of understanding how compression modulates their structures and thereby their optoelectronic properties. Using atomic coordinates obtained from high-pressure single-crystal X-ray diffraction we track the perovskites’ precise structural evolution upon compression. These structural changes correlate well with pressure-dependent single-crystal photoluminescence (PL) spectra and high-pressure bandgaps derived from density functional theory. We further observe dramatic piezochromism where the solids become lighter in color and then transition to opaque black with compression. Indeed, electronic conductivity measurements of (MA)PbI3 obtained within a diamond-anvil cell show that the material’s resistivity decreases by 3 orders of magnitude between 0 and 51 GPa. The activation energy for conduction at 51 GPa is only 13.2(3) meV, suggesting that the perovskite is approaching a metallic state. Furthermore, the pressure response of mixed-halide perovskites shows new luminescent states that emerge at elevated pressures. We recently reported that the perovskites (MA)Pb(BrxI1–x)3 (0.2 compression can mitigate this PL redshift and may afford higher steady-state voltages from these absorbers. These studies show that pressure can significantly alter the transport and thermodynamic properties of these technologically important semiconductors. PMID:27163050

  4. Dislocations in SmS single crystals

    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)

  5. Ultraviolet laser ablation of halides and oxides

    We compare and contrast recent measurements of the behavior of ions and excited ions desorbed from samples of alkali halides and oxide ferroelectrics by an excimer laser at 308 nm wavelength. At the intensities used in these experiments, the density of local electronic excitation is low in the halides and high in the ferroelectrics, corresponding to two- and one-photon band-to-band transitions, respectively. The observed desorption yields and changes in the sample surfaces are discussed in terms of the density of electronic excitation, the relative strengths of electron-lattice coupling, and the role of thermal relaxation processes in the two materials. (orig.)

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

    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, β-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

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

    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. High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites and Pressure Effects on their Electronic and Optical Properties.

    Jaffe, Adam; Lin, Yu; Beavers, Christine M; Voss, Johannes; Mao, Wendy L; Karunadasa, Hemamala I

    2016-04-27

    We report the first high-pressure single-crystal structures of hybrid perovskites. The crystalline semiconductors (MA)PbX3 (MA = CH3NH3 (+), X = Br(-) or I(-)) afford us the rare opportunity of understanding how compression modulates their structures and thereby their optoelectronic properties. Using atomic coordinates obtained from high-pressure single-crystal X-ray diffraction we track the perovskites' precise structural evolution upon compression. These structural changes correlate well with pressure-dependent single-crystal photoluminescence (PL) spectra and high-pressure bandgaps derived from density functional theory. We further observe dramatic piezochromism where the solids become lighter in color and then transition to opaque black with compression. Indeed, electronic conductivity measurements of (MA)PbI3 obtained within a diamond-anvil cell show that the material's resistivity decreases by 3 orders of magnitude between 0 and 51 GPa. The activation energy for conduction at 51 GPa is only 13.2(3) meV, suggesting that the perovskite is approaching a metallic state. Furthermore, the pressure response of mixed-halide perovskites shows new luminescent states that emerge at elevated pressures. We recently reported that the perovskites (MA)Pb(Br x I1-x )3 (0.2 < x < 1) reversibly form light-induced trap states, which pin their PL to a low energy. This may explain the low voltages obtained from solar cells employing these absorbers. Our high-pressure PL data indicate that compression can mitigate this PL redshift and may afford higher steady-state voltages from these absorbers. These studies show that pressure can significantly alter the transport and thermodynamic properties of these technologically important semiconductors. PMID:27163050

  9. P- T conditions of crystallization and origin of plagioclase-mantled alkali feldspar megacrysts in the Mesozoic granitoids in the Qinling orogen (China)

    Wang, Xiaoxia; Wang, Tao; Haapala, Ilmari; Mao, Jingwen

    2008-07-01

    The Qinling orogen between the North China and South China cratons was intruded at 211-217 Ma by calc-alkaline quartz monzonitic to monzogranitic plutons characterized by I- to A-type geochemistry and in many places contain plagioclase-mantled alkali feldspar megacrysts (rapakivi texture sensu lato). The felsic rocks contain mafic to intermediate magmatic enclaves suggestive of mingling and mixing of mafic and felsic magmas. The P- T conditions of crystallization have been determined for early mineral assemblages (inner parts of alkali feldspar megacrysts and their plagioclase, quartz, amphibole and biotite inclusions) and late assemblages (matrix minerals) of the rapakivi-textured granitoids. Al contents in amphibole from the early and late mineral assemblages yield pressures of 1.2-3.0 and 0.7-3.0 kbar, respectively, and indicate only minor pressure change between the crystallization of the early and late assemblages. Amphibole-plagioclase thermometry gives temperatures mainly of the order of 900 to 1000 °C for both the early and late assemblages indicating nearly isothermal conditions. Feldspar thermometers yield lower temperatures. Relative abundances of minerals and their chemical compositions indicate that the late mineral assemblages tend to be richer in MgO, Na 2O and CaO than the early assemblages. Rapakivi texture is interpreted in this case mainly as a result of compositional changes related to the hybridization between granitic and more mafic magmas. Small release of pressure during crystallization of the magmas may have contributed to the origin of the mantled alkali feldspar megacrysts.

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

    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 β-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, β = 131.2°, and diffract to better than 2.2 Å resolution

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

    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

  12. The Silver Halides

    Sahyun, M. R. V.

    1977-01-01

    Illustrates the type of fractional bonding for solid silver halides. Treats the silver halides as electron excess compounds, and develops a model of a localized bonding unit that may be iterated in three dimensions to describe the bulk phase. (MLH)

  13. Application of radioisotopes to studies of crystal imperfections

    Radioisotopes have been used in two important ways in studying imperfections in alkali halide crystals. The zone refining of the compounds has been monitored by addition of tracers, and segregation coefficients have been determined from such measurements. The other application has been to insert small concentrations of impurity ions into alkali halides in order to study the phonon scattering by such impurities or by the vacancies they introduce; these measurements are carried out at very low temperatures where the phonon mean free path is limited by lattice imperfections. The most commonly used radioisotope in this work has been Ca45. This work is reviewed and some current and possible future applications of radioisotopes in this field are mentioned. (author)

  14. Local fields in ionic crystals

    Local fields arising from the electronic distortion in perfect ionic crystals are described in terms of multipolar excitations. Field factors for the alkali halides and chalcogenide ions are found to differ significantly from the Lorentz value of 4π/3, the correction size following an exponential dependence on the difference in ionic radii. Local fields are only slightly modified by these corrections however, and together with the Clausius-Mossotti relation may be regarded as accurate to within 2% if the Lorentz value is adopted. (author)

  15. Effect of an electric field on nucleation and growth of crystals

    Yurov, V. M.; Guchenko, S. A.; Gyngazova, M. S.

    2016-02-01

    The effect of the electric field strength on nucleation and growth of the crystals of ammonium halides and alkali metal sulfates has been studied. The optimal electric field strength for NH4Cl and NH4Br crystals was found to be 15 kV/cm, and for NH4I, it equaled 10 kV/cm. No effect of the electric field strength on the crystal growth was found for alkali metal sulfates. This difference is analyzed in terms of the crystal growth thermodynamics. In case, when the electric field is small and the Gibbs energy is of a significant value, the influence of the electric field at the crystal growth is negligible. A method to estimate the critical radius of homogeneous nucleation of the crystal is suggested.

  16. Framework solids based on copper(II) halides (Cl/Br) and methylene-bridged bis(1-hydroxybenzotriazole): synthesis, crystal structures, magneto-structural correlation, and density functional theory (DFT) studies.

    Sasmal, Ashok; Shit, Shyamapada; Rizzoli, Corrado; Wang, Hongfeng; Desplanches, Cédric; Mitra, Samiran

    2012-10-01

    A methylene-bridged 1-hydroxybenzotriazole derived ligand L [L = 1, 3-bis(benzotriazol-1-yl)-1,3-dioxapropane] has been synthesized and characterized by spectroscopic and structural methods. Reaction of L with two different copper(II) halides [CuX(2); X = Br, Cl] in an identical condition yields two different compounds of similar compositions, {[Cu(μ-Br)(Br)(μ-L)](2)}(n)·2nH(2)O (1) and {[Cu(μ-Cl)(Cl)(μ-L)](2)}(n)·2nH(2)O (2), both being characterized by various physicochemical techniques. Single crystal X-ray studies reveal that they appear as 2D coordination polymers with similar bridging fashion of L. Low temperature magnetic susceptibility measurements reveal antiferromagnetic and ferromagnetic behaviors for 1 and 2 with magnetic coupling constants J = -15.2 and +1.7 cm(-1), which are in a reasonable agreement with their calculated values (J = -9.79 and +0.68 cm(-1) respectively, for 1 and 2). The role of bridging halides in the structure and magnetic properties of the complexes are investigated, and a possible magneto-structural correlation has been established. Influence of spin density of bridging halides on the magnitude of coupling constants has been discussed with the help of density functional theory (DFT) calculations. PMID:22974283

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

    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...

  18. Polynuclear technetium halide clusters

    Development of chemistry of polynuclear technetium halide clusters in works devoted to synthesis, structure and investigation of their chemical and physical properties is considered. The role of academician V.I. Spitsyn as an initiator of investigation of polynuclear technetium halide clusters in the Institute of Physical Chemistry of Academy of Science of USSR is noted. Reactions and stability of cluster halides, their molecular and electronic structures are analyzed. Prospects of development of polynuclear technetium halide clusters chemistry as a direction being on the junction of cluster chemistry and theory of metal-metal multiple bonds are appreciated

  19. Crystal growth and evaluation of scintillation properties of Eu and alkali-metal co-doped LiSrAlF{sub 6} single crystals for thermal neutron detector

    Wakahara, Shingo; Yokota, Yuui; Yamaji, Akihiro; Fujimoto, Yutaka; Sugiyama, Makoto; Kurosawa, Shunsuke [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Yanagida, Takayuki [New Industry Creation Hatchery Center (NICHe), 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan); Pejchal, Jan [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Institute of Physics AS CR, Cukrovarnicka 10, Prague 16253 (Czech Republic); Kawaguchi, Noriaki [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Tokuyama, Co. Ltd., Shibuya 3-chome, Shibuya-ku, Tokyo 150-8383 (Japan); Fukuda, Kentaro [Tokuyama, Co. Ltd., Shibuya 3-chome, Shibuya-ku, Tokyo 150-8383 (Japan); Yoshikawa, Akira [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); New Industry Creation Hatchery Center (NICHe), 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan)

    2012-12-15

    In recent work, Na co-doping have found to improve the light output of Eu doped LiCaAlF{sub 6} (Eu:LiCAF) for thermal neutron scintillator. We grew Eu 2% and alkali metal 1% co-doped LiSAF crystals by Micro-Pulling down method to understand the effect of alkali metal co-doping on scintillation properties and mechanism compared with LiCAF. In photo- and {alpha}-ray induced radio-luminescence spectra of the all grown crystals, the emissions from d-f transition of Eu{sup 2+} were observed. Without relation to excitation source, decay times of co-doped LiSAF were longer than Eu only doped one. The light yield of Na, K and Cs co-doped LiSAF under {sup 252}Cf neutron excitation were improved. Especially, K co-doped Eu:LiSAF reached 33200 ph/n, which outperformed Eu only doped one by approximately 20% (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

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

    2013-01-01

    Roč. 54, č. 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

  1. Space-dependent self-diffusion processes in molten copper halides: a molecular dynamics study

    Alcaraz Sendra, Olga; Trullàs Simó, Joaquim

    2001-01-01

    This work is concerned with single ion dynamics in molten copper halides (CuI and CuCl) which exhibit fast ionic conduction before melting. The self-dynamic structure factor of the two ionic species in each melt have been calculated by molecular dynamics simulations and the corresponding effective wavelength-dependent self-diffusion coefficients have been studied. The results have been compared with those obtained for molten alkali halides (KCl and RbCl).

  2. Atomistic simulation of ion solvation in water explains surface preference of halides

    Caleman, C.; Hub, J. S.; van Maaren, P.; van der Spoel, D

    2011-01-01

    Water is a demanding partner. It strongly attracts ions, yet some halide anions—chloride, bromide, and iodide—are expelled to the air/water interface. This has important implications for chemistry in the atmosphere, including the ozone cycle. We present a quantitative analysis of the energetics of ion solvation based on molecular simulations of all stable alkali and halide ions in water droplets. The potentials of mean force for Cl-, Br-, and I- have shallow minima near the surface. We demons...

  3. Oxidation of hydrogen halides to elemental halogens with catalytic molten salt mixtures

    Rohrmann, Charles A.

    1978-01-01

    A process for oxidizing hydrogen halides by means of a catalytically active molten salt is disclosed. The subject hydrogen halide is contacted with a molten salt containing an oxygen compound of vanadium and alkali metal sulfates and pyrosulfates to produce an effluent gas stream rich in the elemental halogen. The reduced vanadium which remains after this contacting is regenerated to the active higher valence state by contacting the spent molten salt with a stream of oxygen-bearing gas.

  4. 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

    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.

  5. Excitonic ionizations of the electron centres in caesium iodide crystal and exoemission of electrons

    In the wide-band-gap alkali halide crystals recombination of defects may result in formation of the excitons, which can ionize an electron F-centre; thus the phenomenon of exoelectron emission takes place. According to this excitonic model, the energy spectrum and mean energy of CsI exoelectrons were attained. The results of theoretical evaluation are compared with experimental and the reasons suggested for the explanation of the observed difference are discussed. The conclusion based on the peculiarities of exoemission from CsI and CsBr crystals, was done

  6. Excitonic ionizations of the electron centres in caesium iodide crystal and exoemission of electrons

    Galiy, P.V. [Faculty of Electronics, Lviv National University 50 Dragomanov Str., Lviv 79005 (Ukraine); Mel' nyk, O.Ya. [Faculty of Electronics, Lviv National University 50 Dragomanov Str., Lviv 79005 (Ukraine)]. E-mail: moyafis@yahoo.com; Tsvetkova, O.V. [Faculty of Electronics, Lviv National University 50 Dragomanov Str., Lviv 79005 (Ukraine)

    2005-04-15

    In the wide-band-gap alkali halide crystals recombination of defects may result in formation of the excitons, which can ionize an electron F-centre; thus the phenomenon of exoelectron emission takes place. According to this excitonic model, the energy spectrum and mean energy of CsI exoelectrons were attained. The results of theoretical evaluation are compared with experimental and the reasons suggested for the explanation of the observed difference are discussed. The conclusion based on the peculiarities of exoemission from CsI and CsBr crystals, was done.

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

    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

  8. Optical break-down in alkali-haloed single crystals by laser focused radiation: the stage of local thermal explosion

    Based on the results of experimental studying the pore formation kinetics and morphology in KCl single crystals under conditions of optical break-down by laser focused radiation were studied. It was shown that with observed parameters of the seats of energetic bursts and the dynamics of their formation, the optical break-down is similar to a powerful point explosion. In the heated area, a shock wave is generated. Having the velocity more than by an order exceeding the acoustic speed, the shock wave comes to the single crystal boundary earlier than other lattice disturbances and initiates formation of crowdions and their movement along atomic close-packed rows parallel to <110> type directions in both sublattices. From the condition of self-consistency between the flows of generated crowdions initiated by the supersonic shock wave and ones passing into unstressed crystal, it follows that the crowdion velocity would be also supersonic that was earlier predicted (A.M. Kosevich and L.S. Kovalyov). An assumption on possible participation of cumulative effect in the process has been made

  9. Lead (II) selenite halides Pb3(SeO3)2X2 (X = Br, I): Synthesis and crystal structure

    Two lead selenite halides, Pb3(SeO3)2Br2 and Pb3(SeO3)2I2, have been prepared by solid-phase synthesis and structurally characterized. These compounds are isotypic and can be considered 3D with a microporous framework composed of lead polyhedra (distorted Archimedean antiprisms formed by oxygen and halogen atoms). The framework contains channels oriented in the [010] direction. These channels contain selenium atoms, which are bound with framework oxygen atoms belonging to different lead polyhedra.

  10. Vitrification of IFR and MSBR halide salt reprocessing wastes

    Both of the genuinely sustainable (breeder) nuclear fuel cycles (IFR - Integral Fast Reactor - and MSBR - Molten Salt Breeder Reactor -) studied by the USA's national laboratories would generate high level reprocessing waste (HLRW) streams consisting of a relatively small amount ( about 4 mole %) of fission product halide (chloride or fluoride) salts in a matrix comprised primarily (about 95 mole %) of non radioactive alkali metal halide salts. Because leach resistant glasses cannot accommodate much of any of the halides, most of the treatment scenarios previously envisioned for such HLRW have assumed a monolithic waste form comprised of a synthetic analog of an insoluble crystalline halide mineral. In practice, this translates to making a 'substituted' sodalite ('Ceramic Waste Form') of the IFR's chloride salt-based wastes and fluoroapatite of the MSBR's fluoride salt-based wastes. This paper discusses my experimental studies of an alternative waste management scenario for both fuel cycles that would separate/recycle the waste's halide and immobilize everything else in iron phosphate (Fe-P) glass. It will describe both how the work was done and what its results indicate about how a treatment process for both of those wastes should be implemented (fluoride and chloride behave differently). In either case, this scenario's primary advantages include much higher waste loadings, much lower overall cost, and the generation of a product (glass) that is more consistent with current waste management practices. (author)

  11. Process for oxidation of hydrogen halides to elemental halogens

    Lyke, Stephen E.

    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.

  12. Transport and deposition of halide in alkali metal-stainless steel systems, (IV). Measurement of sodium iodide solubility in sodium with major constituents of stainless steel and oxide in sodium

    Solubility of sodium iodide in sodium is measured separately (a) with concentrations of major constituents leached from stainless steel in sodium and (b) with controlled concentration of oxide in sodium by the use of stainless steel capsule. The capsules loaded with 20 g sodium and 0.1-0.3 g powder of additives are heated at their upper part in a furnace and cooled at their bottom on brass plates. (a) After a given period of run for sodium iodide equilibration, the distribution of the iodide and constituents is fixed in solidified sodium by quenching the capsules. Sodium samples taken from the sectioned capsule tube are submitted to sodium dissolution by steam for determining the iodide and to vacuum distillation for determining the constituents. The iodide solubility appears to be in a reverse correlation with concentrations of iron and nickel and to be insensitive to change in those of chromium, manganese and silicon. (b) After a given period of run for sodium oxide equilibration, the sodium is solidified by quenching the capsule. Deposits on the capsule bottom is removed by sectioning the capsule tube and crystals of sodium iodide are introduced to the sectioned capsule on which an end plug is seal-welded. The capsule is again set under the large temperature gradient for a period of run for iodide equilibration. After fixing the iodide distribution in solidified sodium by the quenching, sodium samples are taken from the sectioned capsule tube and submitted to the sodium dissolution by steam for determining iodide in sodium. The iodide solubility data obtained from the present measurement are observed to be scarcely affected by the oxide concentration. (author)

  13. Intra-zoned luminescence in alkali earth metal carbonates

    Full text: The fundamental plasma luminescence of wide band alkali halide crystals has been found out by Vaisburd et al. This broadband luminescence with very short duration of attenuation (∼10-12 s) arises at an irradiations of crystals with electronic beam powerful pulses of nanosecond duration. It is related to radiating 'hot' electrons and holes in a conductivity zone and in a valent zone, accordingly and in later time began to refer to as an intra-zoned luminescence. The data set on revealing features of display of an intra-zoned luminescence in different classes of crystals now proceeds. We investigated a fast luminescence at excitation with pulse electrons (3 nanoseconds) in crystals CaCO3, SrCO3, BaCO3 and MgCO3. In spectra all investigated carbonates it is possible to allocate two areas: area concerning high intensity of a fast luminescence (from 2 eV down 3 eV) and area of low intensity (is higher 4 eV) with slow recession at increase in photon energy. Thus it is typical, that in area concerning high intensity at rise in temperature from 80 up to 300 K a sample intensity of luminescence falls down, whereas in area is higher 5 eV with rise in temperature of a sample increase of intensity is observed. This broadband fast (is shorter than the time sanction of the equipment) should be connected a luminescence poorly dependent on temperature and a modular status of a sample with intra zoned transitions This luminescence reaches from 2 eV down to 7 eV but as for carbonates while is absent the reliable data on structure of a valent zone, division of an intra-zoned luminescence into electronic and hole components is not obviously possible on the basis of spectra of a fast luminescence. The nature of other luminescence processes arising at excitation with pulse electrons is discussed

  14. Synthesis and crystal structure of alkali metal uranium sulfides, Li2US3 and Na2US3

    New mixed uranium sulfides, A2US3 (A=Li,Na), in which uranium is in a tetravalent state, have been synthesized. In the disordered state, the compounds are written as A(A1/3,U2/3)S2 which have a hexagonal (R anti 3m) structure the same as the lanthanide homologue, ALnS2 (Ln=trivalent lanthanides). In the ordered state, the compounds take on a monoclinic (C2/m) structure in which the atom arrangement is very close to the above hexagonal structure. The partial ordering is realized by the coexistence of the two phases. The lattice parameters of hexagonal Li2US3 are a=3.898 and c=18.391 A, while those of monoclinic Li2US3 are a=6.747, b=11.679, c=6.537 A and β=110.2 . The lattice parameters of hexagonal Na2US3 are a=4.036 and c=19.780 A. Those of monoclinic Na2US3 are a=6.990, b=12.105, c=6.992 A and β=109.5 . The molar ratios of the hexagonal and monoclinic phases are 52.2:47.8 for Li2US3 and 68.0:32.0 for Na2US3, respectively. The atom parameters of uranium and sulfur were obtained by Rietveld calculation of the observed X-ray peaks. The atom separations are discussed in relation to the crystal radii of the component ions. (orig.)

  15. Preparation and characterization of cadmium(II) halide complexes with N-substituted glycines, and the crystal structures of dichloro(N-methylglycine)cadmium(II) and diaquadichloro(N,N-dimethylglycine)cadmium(II)

    Yamada, Junichi; Hashimoto, Haruki; Inomata, Yoshie; Takeuchi, Toshio [Jochi Univ., Tokyo (Japan). Faculty of Science and Technology

    1994-12-01

    Eight cadmium(II) halide complexes with N-methylglycine (sarcosine, Hsar), N,N-dimethylglycine (Hdmgly), and N,N,N-trimethylglycine (betaine, Hbet) have been prepared and characterized by using their infrared absorption spectra and thermal analyses. In addition, the crystal and molecular structures of [CdCl{sub 2}(Hsar)] (1) and [CdCl{sub 2}(Hdmgly)(H{sub 2}O){sub 2}] (2) were determined by a single-crystal X-ray diffraction method. The crystal data for these two complexes are as follows: Complex (1): monoclinic, space group P2{sub 1}/n, a=7.960(2), b=13.844(1), c=6.917(1) A, {beta}=92.42(2)deg, Z=4. Complex (2): monoclinic, space group P2{sub 1}/a, a=7.696(2), b=21.854(4), c=6.253(2) A, {beta}=103.69(2)deg, Z=4. These structures were solved by the heavy-atom method and refined by full-matrix least-square methods to final R values of 0.043 for 2533 reflections about 1 and 0.068 for 3615 reflections about 2, respectively. For 1 the structure consists of a one-dimensional polymer bridged by two chlorine atoms. The cadmium atom is hexa-coordinated, being ligated with two oxygen atoms of a carboxyl group and four chlorine atoms. For 2 the cadmium atom is in a distorted octahedral geometry, ligated by a carboxylato oxygen atom, two water molecules, and three chlorine atoms, in which one is terminal and the other two are bridging cadmium atoms to make a polymer. (author).

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

    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 field 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.

  17. Synthesis of chalcogenide and pnictide crystals in salt melts using a steady-state temperature gradient

    Chareev, D. A.; Volkova, O. S.; Geringer, N. V.; Koshelev, A. V.; Nekrasov, A. N.; Osadchii, V. O.; Osadchii, E. G.; Filimonova, O. N.

    2016-07-01

    Some examples of growing crystals of metals, alloys, chalcogenides, and pnictides in melts of halides of alkali metals and aluminum at a steady-state temperature gradient are described. Transport media are chosen to be salt melts of eutectic composition with the participation of LiCl, NaCl, KCl, RbCl, CsCl, AlCl3, AlBr3, KBr, and KI in a temperature range of 850-150°C. Some crystals have been synthesized only using a conducting contour. This technique of crystal growth is similar to the electrochemical method. In some cases, to exclude mutual influence, some elements have been isolated and forced to migrate to the crystal growth region through independent channels. As a result, crystals of desired quality have been obtained using no special equipment and with sizes sufficient for study under laboratory conditions.

  18. 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

    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)

  19. Stability analysis for complexes in calcium-alkali bromide solutions

    We discuss the dependence of the stability of tetrahedral complexes in molten halide mixtures on the halogen species. This is done by calculating the equilibrium concentration of (CaBr4)2- complexes in calcium-alkali bromide solutions as a function of composition, in comparison with earlier calculations on the calcium-alkali chloride systems. The comparison supports a possible trend of increasing stability from chlorides to bromides, provided that halogen polarizability or chemical bonding contribute appreciably to the binding of a complex. Supporting evidence is noted and further experiments are suggested. (author). 10 refs, 2 figs

  20. High Biomass Specific Methyl Halide Production Rates of Selected Coastal Marsh Plants and its Relationship to Halide Content

    Manley, S. L.; Wang, N.; Cicerone, R. J.

    2002-12-01

    Salt tolerant coastal marsh plants (halophytes) have previously been shown to be globally significant producers of methyl chloride (MeCl) and methyl bromide (MeBr). While halophytes are known for their high salt content, there are few reports of their halide content. Our studies have attempted to quantify biomass specific methyl halide (MeX) production from these plants and relate it to tissue halide levels. MeCl, MeBr and MeI production rates and tissue chloride, bromide and iodide concentrations from selected coastal marsh plants were measured for nearly a year. Certain halophyte species (i.e. Batis and Frankenia) have very high summer biomass specific production rates for MeX (e.g. Frankenia: 1 ug MeCl /gfwt/hr; 80 ng MeBr/gfwt/hr; 8 ng MeI/gfwt/hr). These rates of MeCl and MeBr production are much higher than those from other coastal marsh plants or seaweeds. Plant halide levels remain high throughout the year, while MeX production peaks at a high level in mid summer falling to low winter rates. This implies a linkage to plant growth. Higher levels of chloride and bromide were seen in the fleshy marsh plants such as Batis (saltwort, approximately 20 percent dry wt chloride, 0.4 percent dry wt bromide) and Salicornia (pickleweed) than in the others such as Frankenia (alkali heath) approx 7 percent dry wt chloride, 0.1 percent dry wt bromide) or Spartina (cordgrass). No such trend was seen for iodide, which ranged from 4 - 10 ppm. Calculations show the daily halide losses from MeX production are far less than the variability in tissue halide content. MeX production removes a small fraction of the total tissue halide from these plants suggesting that MeX production is not a mechanism used by these species to control internal halide levels. Saltwort cell-free extracts incubated with bromide or iodide in the presence of S-adenosyl-L-methionine (SAM) produced the corresponding MeX. MeBr production was inhibited by caffeic acid the substrate of lignin-specific O

  1. Studies on multiphased mixed crystals grown from NaBr and KCl

    Padma, C.M. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamilnadu (India); Mahadevan, C.K. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamilnadu (India)], E-mail: mahadevan58@yahoo.co.in

    2008-05-01

    We have grown multiphased binary and ternary mixed crystals by the melt method using the miscible alkali halides, viz. NaBr and KCl and physically characterized. Thermal parameters like Debye-Waller factor, Debye temperature, Debye frequency and mean square amplitude of vibration were determined using the X-ray powder diffraction intensity data. DC and AC electrical measurements were carried out by using the parallel plate capacitor method at various temperatures. Activation energies (DC and AC), mean jump frequency, compressibility and mean sound velocity were also determined. The results obtained are reported here.

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

    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).

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

    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

  4. Thermoluminescence studies in lead doped KCl and KBr crystals

    Lead is known to enter substitutionally in divalent state when doped in alkali halides. When irradiated at room temperature these lead centers (Pb++) act as traps for electrons knocked off from the halogen ions and become Pb+ and Pb0 (for large doses of irradiation). These changes could be followed in the optical absorption studies. These lead-doped crystals after X-ray irradiation yield a thermoluminescence output smaller than that observed in 'pure' crystals. However, two new glow peaks are observed in additions to those due to F-centers. In KCl : Pb and Kbr : Pb crystals part of the F-center glow preceds the new glow peaks. The new peaks are attributed to the Pb+ and Pb0 centers. The glow peak temperatures and trap depths for these peaks an obtained by total-curve fitting method are reported. (author)

  5. Methods for synthesizing alane without the formation of adducts and free of halides

    Zidan, Ragaiy; Knight, Douglas A; Dinh, Long V

    2013-02-19

    A process is provided to synthesize an alane without the formation of alane adducts as a precursor. The resulting product is a crystallized .alpha.-alane and is a highly stable product and is free of halides.

  6. Milk-alkali syndrome

    ... this page: //medlineplus.gov/ency/article/000332.htm Milk-alkali syndrome To use the sharing features on this page, please enable JavaScript. Milk-alkali syndrome is a condition in which there ...

  7. The low temperature electrochemical growth of iron, nickel and other metallic single crystals from halide eutectic fluxes in a temperature gradient

    Chareev, Dmitriy A.

    2015-11-01

    Single crystals of metallic Fe, Ni, Co, Cr, Al, Cu, Ag, Au, Pd, Pt and a few alloys were grown using the AlCl3/KCl and CsCl/NaCl/KCl fluxes for Men+ transport and an inert metallic wire for electron transport in a permanent temperature gradient from 350-600 °C that produced single crystalline samples with dimensions of approximately 2×2×2 mm3. Energy dispersive X-ray spectroscopy established crystal formation of pure metals.

  8. A new route to the syntheses of alkali metal bis(fluorosulfuryl)imides: Crystal structure of LiN(SO2F)2

    Beran, Martin; Příhoda, J.; Žák, Z.; Černík, M.

    2006-01-01

    Roč. 25, č. 6 (2006), s. 1292-1298. ISSN 0277-5387 Institutional research plan: CEZ:AV0Z40310501 Keywords : imido-bis( sulfuric acid ) difluoride * lithium bis(fluorosulfuryl)imide * alkali metal bis(fluorosulfuryl)imides Subject RIV: CA - Inorganic Chemistry Impact factor: 1.843, year: 2006

  9. PREPARATION OF HALIDES OF PLUTONIUM

    Garner, C.S.; Johns, I.B.

    1958-09-01

    A dry chemical method is described for preparing plutonium halides, which consists in contacting plutonyl nitrate with dry gaseous HCl or HF at an elevated temperature. The addition to the reaction gas of a small quantity of an oxidizing gas or a reducing gas will cause formation of the tetra- or tri-halide of plutonium as desired.

  10. Making and Breaking of Lead Halide Perovskites

    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

  11. Making and Breaking of Lead Halide Perovskites.

    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

  12. Ultraviolet absorption spectra of mercuric halides.

    Templet, P.; Mcdonald, J. R.; Mcglynn, S. P.; Kendrow, C. H.; Roebber, J. L.; Weiss, K.

    1972-01-01

    The gas phase transitions of the mercuric halides were observed in the UV region by operating at temperatures above 400 K and at vapor pressures on the order of 0.5 mm. Spectral features exhibited by the chloride, bromide, and iodide of mercury correlate energetically with bands previously designated as intermolecular charge transfer transitions. The solution spectra of mercuric iodide and deep color of the crystals (if not due to some solid state interactions) indicate that this molecule may also have longer wavelength transitions.

  13. Deciphering Halogen Competition in Organometallic Halide Perovskite Growth.

    Yang, Bin; Keum, Jong; Ovchinnikova, Olga S; Belianinov, Alex; Chen, Shiyou; Du, Mao-Hua; Ivanov, Ilia N; Rouleau, Christopher M; Geohegan, David B; Xiao, Kai

    2016-04-20

    Organometallic halide perovskites (OHPs) hold great promise for next-generation, low-cost optoelectronic devices. During the chemical synthesis and crystallization of OHP thin films, a major unresolved question is the competition between multiple halide species (e.g., I(-), Cl(-), Br(-)) in the formation of the mixed-halide perovskite crystals. Whether Cl(-) ions are successfully incorporated into the perovskite crystal structure or, alternatively, where they are located is not yet fully understood. Here, in situ X-ray diffraction measurements of crystallization dynamics are combined with ex situ TOF-SIMS chemical analysis to reveal that Br(-) or Cl(-) ions can promote crystal growth, yet reactive I(-) ions prevent them from incorporating into the lattice of the final perovskite crystal structure. The Cl(-) ions are located in the grain boundaries of the perovskite films. These findings significantly advance our understanding of the role of halogens during synthesis of hybrid perovskites and provide an insightful guidance to the engineering of high-quality perovskite films, essential for exploring superior-performing and cost-effective optoelectronic devices. PMID:26931634

  14. On the reaction of tellurium with tungsten halides: synthesis and crystal structure of Te7WOCl5, a compound with a polymer tellurium cation

    The reaction of tellurium with WOCl4 in the presence of a large excess of WCl6 in a sealed evacuated glass ampoule at 150degC yields beside the main product Te8(WCl6)2 a small amount of Te7WOCl5. The crystal structure determination (orthorhombic space group Pcca, lattice parameters at 173 K: a = 2596.5(9) pm, b = 810.0(3) pm, c = 775.7(2) pm) shows that Te7WOCl5 is built of one-dimensional band shaped polymeric tellurium cations, one-dimensional associated pyramidal WOCl4anions and of isolated Cl- anions. Te7WOCl5 can thus be formulated as [Te72+]n [WOCl4-]n (Cl-). The structure is closely related but not isotypic to the bromine containing analogue Te7WOBr5. The difference between the two structures lies in different directions of the polar [WOX4-]n chains (X = Cl, Br). The strongly elongated thermal ellipsoid of one tellurium atom is shown to be caused by thermal vibration by determining the crystal structure of Te7WOCl5 at three different temperatures (223, 173 and 123 K). All displacement parameters of all atoms can be extrapolated to zero for 0 K. (orig.)

  15. Finding New Perovskite Halides via Machine learning

    Pilania, Ghanshyam; Balachandran, Prasanna V.; Kim, Chiho; Lookman, Turab

    2016-04-01

    Advanced materials with improved properties have the potential to fuel future technological advancements. However, identification and discovery of these optimal materials for a specific application is a non-trivial task, because of the vastness of the chemical search space with enormous compositional and configurational degrees of freedom. Materials informatics provides an efficient approach towards rational design of new materials, via learning from known data to make decisions on new and previously unexplored compounds in an accelerated manner. Here, we demonstrate the power and utility of such statistical learning (or machine learning) via building a support vector machine (SVM) based classifier that uses elemental features (or descriptors) to predict the formability of a given ABX3 halide composition (where A and B represent monovalent and divalent cations, respectively, and X is F, Cl, Br or I anion) in the perovskite crystal structure. The classification model is built by learning from a dataset of 181 experimentally known ABX3 compounds. After exploring a wide range of features, we identify ionic radii, tolerance factor and octahedral factor to be the most important factors for the classification, suggesting that steric and geometric packing effects govern the stability of these halides. The trained and validated models then predict, with a high degree of confidence, several novel ABX3 compositions with perovskite crystal structure.

  16. Finding New Perovskite Halides via Machine learning

    Ghanshyam ePilania

    2016-04-01

    Full Text Available Advanced materials with improved properties have the potential to fuel future technological advancements. However, identification and discovery of these optimal materials for a specific application is a non-trivial task, because of the vastness of the chemical search space with enormous compositional and configurational degrees of freedom. Materials informatics provides an efficient approach towards rational design of new materials, via learning from known data to make decisions on new and previously unexplored compounds in an accelerated manner. Here, we demonstrate the power and utility of such statistical learning (or machine learning via building a support vector machine (SVM based classifier that uses elemental features (or descriptors to predict the formability of a given ABX3 halide composition (where A and B represent monovalent and divalent cations, respectively, and X is F, Cl, Br or I anion in the perovskite crystal structure. The classification model is built by learning from a dataset of 181 experimentally known ABX3 compounds. After exploring a wide range of features, we identify ionic radii, tolerance factor and octahedral factor to be the most important factors for the classification, suggesting that steric and geometric packing effects govern the stability of these halides. The trained and validated models then predict, with a high degree of confidence, several novel ABX3 compositions with perovskite crystal structure.

  17. Hall Determination of Atomic Radii of Alkali Metals

    Houari, Ahmed

    2008-01-01

    I will propose here an alternative method for determining atomic radii of alkali metals based on the Hall measurements of their free electron densities and the knowledge of their crystal structure. (Contains 2 figures.)

  18. Coprecipitation of alkali metal ions with calcium carbonate

    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)

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

    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.

  20. Electrical measurements on multiphased (NaCl){sub x}(KCl){sub y-x}(KBr){sub 1-y} single crystals

    Mahadevan, C.K. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamil Nadu (India)], E-mail: mahad@sancharnet.in; Jayakumari, K. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamil Nadu (India)

    2008-11-30

    Alkali halide mixed crystals were melt grown from NaCl, KCl and KBr starting materials. DC and AC electrical measurements were carried out on the resulting ternary compositions at temperatures ranging from 308 to 423 K. Activation energies and mean jump frequencies were also estimated. The present study indicates an increase of DC and AC electrical conductivities and dielectric constant with the increase of temperature. Also, it indicates a nonlinear variation of all the electrical parameters (both DC and AC) with the bulk composition, which is explained to be due to the enhanced diffusion of charge carriers along dislocations and grain boundaries.

  1. METHOD OF PREPARING METAL HALIDES

    Hendrickson, A.V.

    1958-11-18

    The conversion of plutonium halides from plutonium peroxide can be done by washing the peroxide with hydrogen peroxide, drying the peroxide, passing a dry gaseous hydrohalide over the surface of the peroxide at a temperature of about lOO icient laborato C until the reaction rate has stabillzed, and then ralsing the reaction temperature to between 400 and 600 icient laborato C until the conversion to plutonium halide is substantially complete.

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

    It is well known that ammonium halide (NH4X) crystals, on γ-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

  3. Approaching Bulk Carrier Dynamics in Organo-Halide Perovskite Nanocrystalline Films by Surface Passivation.

    Stewart, Robert J; Grieco, Christopher; Larsen, Alec V; Maier, Joshua J; Asbury, John B

    2016-04-01

    The electronic properties of organo-halide perovskite absorbers described in the literature have been closely associated with their morphologies and processing conditions. However, the underlying origins of this dependence remain unclear. A combination of inorganic synthesis, surface chemistry, and time-resolved photoluminescence spectroscopy was used to show that charge recombination centers in organo-halide perovskites are almost exclusively localized on the surfaces of the crystals rather than in the bulk. Passivation of these surface defects causes average charge carrier lifetimes in nanocrystalline thin films to approach the bulk limit reported for single-crystal organo-halide perovskites. These findings indicate that the charge carrier lifetimes of perovskites are correlated with their thin-film processing conditions and morphologies through the influence these have on the surface chemistry of the nanocrystals. Therefore, surface passivation may provide a means to decouple the electronic properties of organo-halide perovskites from their thin-film processing conditions and corresponding morphologies. PMID:26966792

  4. Transformation of the luminescent centres in KCl-In crystals under synchrotron radiation

    Gyunsburg, K E; Kochubey, D I; Sedova, Y G

    2000-01-01

    In view of the opportunity to use alkali-halide crystals with indium impurity for the registration of ionising radiation we have studied the influence of a method of impurity doping and mechanical treatment of a crystal on its sensitivity to X-ray. It is shown that the doping of a crystal with In sup 3 sup + reduces the sensitivity of medium. Optical and X-ray spectral experiments have allowed us to conclude that this phenomenon is caused by a change in the impurity centre structure. It is proved experimentally that mechanical crushing results in the transformation of the luminescent centres. This does not allow the effective conversion of the centres under synchrotron radiation.

  5. Thermoluminescence studies in cerium doped NaCl crystals

    Cerium is known to enter substitutionally in trivalent state when doped in alkali halides. Cerium doped NaCl crystals exhibit greatly enhanced thermoluminescence output upon X-irradiation at RT, the intensity of emission being about 10 times that in undoped crystals for similar dosage of irradiation. The cerium doped crystals give upon X-irradiation a very intense glow peak at 145degC with shoulders at 120degC and 210degC. Upon partially bleaching the crystal with F-light, the peak at 120degC becomes prominent probably due to faster bleaching of the glow at 145degC. From further optical bleaching studies, it is concluded that the glow peak at around 120degC is due to cerium centres in the irradiated crystal and the 145degC peak due to F centres. This F centre emission occurs at lower temperature, compared to that in the undoped crystals where it occurs at around 180degC. The spectral emission in the Ce doped crystals is in the blue-green region as compared to the emission in the blue region in undoped crystals. The trap depth and other parameters of the 120degC glow peak are estimated by the total curve fitting method. (author)

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

    Bretschneider, Simon A.; Jonas Weickert; James A. Dorman; Lukas Schmidt-Mende

    2014-01-01

    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...

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

    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.

  8. Radiochemical synthesis of pure anhydrous metal halides

    Philipp, W. H.; Marsik, S. J.; May, C. E.

    1973-01-01

    Method uses radiation chemistry as practical tool for inorganic preparations and in particular deposition of metals by irradiation of their aqueous metal salt solutions with high energy electrons. Higher valence metal halide is dissolved in organic liquid and exposed to high energy electrons. This causes metal halide to be reduced to a lower valence metal halide.

  9. Electronic conduction in molten halides

    Heus, R.J.; Egan, J.J.

    1976-01-01

    Methods of measuring electronic conductivity in molten halides are reviewed. These include increase of total conductivity with addition of metal, polarization techniques, chronopotentiometry, and motion of colored subhalides in a potential gradient. The applicability of the Nernst-Einstein equation and the role of convection are considered. Results are presented for several halide melts. Applications of these results are elucidated, including self-discharge rate of molten salt batteries, measurement of alloy thermodynamics using molten salt electrolytes, and kinetics of tarnishing reactions with formation of liquid films.

  10. Alkali metal ionization detector

    Bauerle, James E.; Reed, William H.; Berkey, Edgar

    1978-01-01

    Variations in the conventional filament and collector electrodes of an alkali metal ionization detector, including the substitution of helical electrode configurations for either the conventional wire filament or flat plate collector; or, the substitution of a plurality of discrete filament electrodes providing an in situ capability for transferring from an operationally defective filament electrode to a previously unused filament electrode without removing the alkali metal ionization detector from the monitored environment. In particular, the helical collector arrangement which is coaxially disposed about the filament electrode, i.e. the thermal ionizer, provides an improved collection of positive ions developed by the filament electrode. The helical filament design, on the other hand, provides the advantage of an increased surface area for ionization of alkali metal-bearing species in a monitored gas environment as well as providing a relatively strong electric field for collecting the ions at the collector electrode about which the helical filament electrode is coaxially positioned. Alternatively, both the filament and collector electrodes can be helical. Furthermore, the operation of the conventional alkali metal ionization detector as a leak detector can be simplified as to cost and complexity, by operating the detector at a reduced collector potential while maintaining the sensitivity of the alkali metal ionization detector adequate for the relatively low concentration of alkali vapor and aerosol typically encountered in leak detection applications.

  11. The first pseudo-ternary thiocyanate containing two alkali metals. Synthesis and single-crystal structure of LiK{sub 2}[SCN]{sub 3}

    Reckeweg, Olaf; DiSalvo, Francis J. [Cornell Univ., Ithaca, NY (United States). Baker Lab.

    2016-04-01

    A procedure was empirically developed to prepare the compound LiK{sub 2}[SCN]{sub 3}, which forms colorless, transparent, very fragile, and extremely hygroscopic thin rectangular plates. Its unique crystal structure was determined by single-crystal X-ray diffraction. LiK{sub 2}[SCN]{sub 3} adopts the orthorhombic space group Pna2{sub 1} (no. 33, Z = 4) with the cell parameters a = 1209.32(9), b = 950.85(9), and c = 849.95(6) pm.

  12. Investigation of change regularity of energy states of Mn2+ in halides

    Data on 4E, 4A1 (4G) and 4T1 (4G) energy states of Mn2+ ion in some halides have been obtained and analyzed. With use of the dielectric theory of the chemical bond for complex crystals, several chemical bond parameters were calculated. The change regularity of the energy states of Mn2+ in halides has been studied. The results show that the covalence, the coordination number and the radius of the central ion are the main factors influencing the energy states of Mn2+ ion in halides. The relationships between these factors and the energy state 4T1 (4G), the energy difference ΔE (ΔE=4E, 4A1 (4G)→4T1 (4G)) of Mn2+ ion in halides were established: E=2.0898+0.8618 exp (−F/0.2431); ΔE=0.3201+0.9713⁎F. These relationships allow us to predict the position of energy state 4T1 (4G) and the energy difference ΔE of Mn2+ in halides. This work can be significant for further understanding the luminescent properties of Mn2+ and can be used to develop new Mn2+-doped phosphors. - Highlights: ► Relationship between F and energy state 4T1(4G) of Mn2+ in halides was set up. ► Relationship between F and energy difference ΔE of Mn2+ in halides was set up. ► Site occupation of Mn2+-doped halides with two or more cations can be made clear. ► Energy state 4T1(4G) and emission band of Mn2+ in halides can be predicted.

  13. Fluorescence Properties of Colour Centres Produced by Ultrashort Laser Irradiation in LiF Crystals

    Samad, R. E.; Courrol, L. C.; Gomes, L.; Ranieri, I. M.; Baldochi, S. L.; de Freitas, A. Z.; Vieira, N. D., Jr.

    2010-11-01

    LiF is a nonhygroscopic alkali halide crystal which possesses good optical and physical properties, and can host different species of colour centres at room temperature. Colour centres in LiF present broad absorption and emission bands in the near UV, visible and near IR regions of the spectrum. In this paper we study spectroscopic properties of colour centres produced in LiF by ultrashort laser pulses. The absorption and emission properties of these materials were measured showing that during the irradiation F, F2, F2+, F3+ and F2- colour centres were created in the crystals. A colour centres formation dose-like curve as a function of the ultrashort pulse energy was determined using fluorescence spectroscopy.

  14. Alkali and Halogen Chemistry in Volcanic Gases on Io

    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...

  15. Correlations between entropy and volume of melting in halide salts

    Melting parameters and transport coefficients in the melt are collated for halides of monovalent, divalent and trivalent metals. A number of systems show a deficit of entropy of melting relative to the linear relationships between entropy change and relative volume change on melting that are found to be approximately obeyed by a majority of halides. These behaviours are discussed on the basis of structural and transport data. The deviating systems are classified into three main classes, namely (i) fast-ion conductors in the high-temperature crystal phase such as AgI, (ii) strongly structured network-like systems such as ZnCl2, and (iii) molecular systems melting into associated molecular liquids such as SbCl3. (author). 35 refs, 1 fig., 3 tabs

  16. Melting and liquid structure of polyvalent metal halides

    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

  17. Alkalis and Skin.

    Greenwood, John E; Tan, Jin Lin; Ming, Justin Choong Tzen; Abell, Andrew D

    2016-01-01

    The aim of this editorial is to provide an overview of the chemical interactions occurring in the skin of our patients on contact with alkaline agents. Strongly basic alkali is highly aggressive and will readily hydrolyze (or cleave) key biological molecules such as lipids and proteins. This phenomenon is known as saponification in the case of lipids and liquefactive denaturation for peptides and proteins. A short section on current first-aid concepts is included. A better understanding of the basic science behind alkali burns will make us better teachers and provide an insight into the urgency needed in treating these common and dangerous chemical injuries. PMID:26182072

  18. Tris(bipyridineMetal(II-Templated Assemblies of 3D Alkali-Ruthenium Oxalate Coordination Frameworks: Crystal Structures, Characterization and Photocatalytic Activity in Water Reduction

    Alla Dikhtiarenko

    2016-02-01

    Full Text Available A series of 3D oxalate-bridged ruthenium-based coordination polymers with the formula of {[ZII(bpy3][MIRu(C2O43]}n (ZII = Zn2+ (1, Cu2+ (3, 4, Ru2+ (5, 6, Os2+ (7, 8; MI = Li+, Na+; bpy = 2,2’-bipyridine and {[ZnII(bpy3](H2O[LiRu(C2O43]}n (2 has been synthesized at room temperature through a self-assembly reaction in aqueous media and characterized by single-crystal and powder X-ray diffraction, elemental analysis, infrared and diffuse reflectance UV–Vis spectroscopy and thermogravimetric analysis. The crystal structures of all compounds comprise chiral 3D honeycomb-like polymeric nets of the srs-type, which possess triangular anionic cages where [ZII(bpy3]2+ cationic templates are selectively embedded. Structural analysis reveals that the electronic configuration of the cationic guests is affected by electrostatic interaction with the anionic framework. Moreover, the MLCT bands gaps values for 1–8 can be tuned in a rational way by judicious choice of [ZII(bpy3]2+ guests. The 3D host-guest polymeric architectures can be used as self-supported heterogeneous photocatalysts for the reductive splitting of water, exhibiting photocatalytic activity for the evolution of H2 under UV light irradiation.

  19. Mineralogy of silicate inclusions of the Colomera IIE iron and crystallization of Cr-diopside and alkali feldspar from a partial melt

    Takeda, Hiroshi; Hsu, Weibiao; Huss, Gary R.

    2003-06-01

    We studied the mineralogy, mineral chemistry, and compositions of 48 interior silicate inclusions and a large K-rich surface inclusion from the Colomera IIE iron meteorite. Common minerals in the interior silicate inclusions are Cr diopside and Na plagioclase (albite). They are often enclosed by or coexist with albitic glasses with excess silica and minor Fe-Mg components. This mineral assemblage is similar to the "andesitic" material found in the Caddo County IAB iron meteorite for which a partial melt origin has been proposed. The fairly uniform compositions of Cr diopside (Ca 44Mg 46Fe 10) and Na plagioclase (Or 2.5Ab 90.0An 7.5 to Or 3.5Ab 96.1An 0.4) in Colomera interior inclusions and the angular boundaries between minerals and metal suggest that diopside and plagioclase partially crystallized under near-equilibrium conditions from a common melt before emplacement into molten metal. The melt-crystal assemblage has been called "crystal mush." The bulk compositions of the individual composite inclusions form an array between the most diopside-rich inclusion and plagioclase. This is consistent only with a simple mechanical mixing relationship, not a magmatic evolution series. We propose a model in which partly molten metal and crystal mush were mixed together by impact on the IIE parent body. Other models involving impact melting of the chondritic source material followed by growth of diopside and plagioclase do not easily explain near equilibrium growth of diopside and Na plagioclase, followed by rapid cooling. In the K-rich surface inclusion, K feldspar, orthopyroxene, and olivine were found together with diopside for the first time. K feldspar (sanidine, Or 92.7Ab 7.2An 0.1 to Or 87.3Ab 11.0An 1.7) occurs in an irregular veinlike region in contact with large orthopyroxene crystals of nearly uniform composition (Ca 1.3Mg 80.5Fe 17.8 to Ca 3.1Mg 78.1Fe 18.9) and intruding into a relict olivine with deformed-oval shape. Silica and subrounded Cr diopside are

  20. Fine structures in the optical absorption spectra of photochemical silver in silver halides? A call for further research

    Georgiev, Mladen

    2007-01-01

    A survey is presented of the work done so far to check earlier claims that a fine structure may be observed to occur under certain circumstances in the impurity spectral range of the optical absorption spectra of silver halides following photostimulation in the intrinsic range. This structure, associated with the photochemical formation of silver specks, has been questioned over the years. We now weigh carefully the experimental evidence on the silver halides against a background of similar data on the alkali halides, where competing processes run slower. We come to the conclusion that present day advances in experimental techniques may be quite adequate for providing a solid experimental basis to solve the problem unambiguously.

  1. Saucy-Marbet Rearrangements of Alkynyl Halides in the Synthesis of Highly Enantiomerically Enriched Allenyl Halides

    Tang, Yu; Shen, Lichun; Dellaria, Becky J.; Richard P. Hsung

    2008-01-01

    A stereospecific Saucy-Marbet rearrangement of alkynyl halides is described here. These rearrangements provide an entry to highly enantiomerically enriched allenyl bromides and chlorides through excellent chirality transfer and the reservation of optical integrity of alkynyl halides.

  2. Methods of recovering alkali metals

    Krumhansl, James L; Rigali, Mark J

    2014-03-04

    Approaches for alkali metal extraction, sequestration and recovery are described. For example, a method of recovering alkali metals includes providing a CST or CST-like (e.g., small pore zeolite) material. The alkali metal species is scavenged from the liquid mixture by the CST or CST-like material. The alkali metal species is extracted from the CST or CST-like material.

  3. Self-Correction of Lanthanum-Cerium Halide Gamma Spectra (pre-print)

    Ding Yuan, Paul Guss, and Sanjoy Mukhopadhyay

    2009-04-01

    Lanthanum-cerium halide detectors generally exhibit superior energy resolutions for gamma radiation detection compared with conventional sodium iodide detectors. However, they are also subject to self-activities due to lanthanum-138 decay and contamination due to beta decay in the low-energy region and alpha decay in the high-energy region. The detector’s self-activity and crystal contamination jointly contribute a significant amount of uncertainties to the gamma spectral measurement and affect the precision of the nuclide identification process. This paper demonstrates a self-correction procedure for self-activity and contamination reduction from spectra collected by lanthanum-cerium halide detectors. It can be implemented as an automatic self-correction module for the future gamma radiation detector made of lanthanum-cerium halide crystals.

  4. Self-Correction of Lanthanum-Cerium Halide Gamma Spectra (pre-print)

    Lanthanum-cerium halide detectors generally exhibit superior energy resolutions for gamma radiation detection compared with conventional sodium iodide detectors. However, they are also subject to self-activities due to lanthanum-138 decay and contamination due to beta decay in the low-energy region and alpha decay in the high-energy region. The detector's self-activity and crystal contamination jointly contribute a significant amount of uncertainties to the gamma spectral measurement and affect the precision of the nuclide identification process. This paper demonstrates a self-correction procedure for self-activity and contamination reduction from spectra collected by lanthanum-cerium halide detectors. It can be implemented as an automatic self-correction module for the future gamma radiation detector made of lanthanum-cerium halide crystals.

  5. TRANSURANIC METAL HALIDES AND A PROCESS FOR THE PRODUCTION THEREOF

    Fried, S.

    1951-03-20

    Halides of transuranic elements are prepared by contacting with aluminum and a halogen, or with an aluminum halide, a transuranic metal oxide, oxyhalide, halide, or mixture thereof at an elevated temperature.

  6. 40 CFR 721.4095 - Quaternary ammonium alkyltherpropyl trialkylamine halides.

    2010-07-01

    ... trialkylamine halides. 721.4095 Section 721.4095 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.4095 Quaternary ammonium alkyltherpropyl trialkylamine halides. (a... generically as quaternary ammonium alkyltherpropyl trialkylamine halides (PMNs...

  7. Spectra of alkali atoms

    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.)

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

    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.

  9. Halogen versus halide electronic structure

    Willem-Jan; van; Zeist; F.Matthias; Bickelhaupt

    2010-01-01

    Halide anions X-are known to show a decreasing proton affinity(PA),as X descends in the periodic table along series F,Cl,Br and I.But it is also well-known that,along this series,the halogen atom X becomes less electronegative(or more electropositive).This corresponds to an increasing energy of the valence np atomic orbital(AO) which,somewhat contradictorily,suggests that the electron donor capability and thus the PA of the halides should increase along the series F,Cl,Br,I.To reconcile these contradictory observations,we have carried out a detailed theoretical analysis of the electronic structure and bonding capability of the halide anions X-as well as the halogen radicals X-,using the molecular orbital(MO) models contained in Kohn-Sham density functional theory(DFT,at SAOP/TZ2P as well as OLYP/TZ2P levels) and ab initio theory(at the HF/TZ2P level).We also resolve an apparent intrinsic contradiction in Hartree-Fock theory between orbital-energy and PA trends.The results of our analyses are of direct relevance for understanding elementary organic reactions such as nucleophilic substitution(SN2) and base-induced elimination(E2) reactions.

  10. Hydrothermal alkali metal recovery process

    Wolfs, Denise Y.; Clavenna, Le Roy R.; Eakman, James M.; Kalina, Theodore

    1980-01-01

    In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by treating them with a calcium or magnesium-containing compound in the presence of water at a temperature between about 250.degree. F. and about 700.degree. F. and in the presence of an added base to establish a pH during the treatment step that is higher than would otherwise be possible without the addition of the base. During the treating process the relatively high pH facilitates the conversion of water-insoluble alkali metal compounds in the alkali metal residues into water-soluble alkali metal constituents. The resultant aqueous solution containing water-soluble alkali metal constituents is then separated from the residue solids, which consist of the treated particles and any insoluble materials formed during the treatment step, and recycled to the gasification process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preferably, the base that is added during the treatment step is an alkali metal hydroxide obtained by water washing the residue solids produced during the treatment step.

  11. Coordination chemistry of halides and oxohalides of tungsten (6)

    Literature data on the structure of molecular complexes of halides, exo- and dioxohalides of tungsten (6), as well as results of the study of WX6, WOX4 and WO2X2 structures in gaseous phase, crystal state and in solutions of organic solvents, were generalized. The greatest volume of structural studies involved complexes W6 with oxygen-containing ligands. The presence of cis- and trans- effects of aliquotly bound oxygen atoms in complexes of exo- and dioxohalides of tungsten is pointed out

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

    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.

  13. Reactive scattering of electronically excited alkali atoms with molecules

    Representative families of excited alkali atom reactions have been studied using a crossed beam apparatus. For those alkali-molecule systems in which reactions are also known for ground state alkali and involve an early electron transfer step, no large differences are observed in the reactivity as Na is excited. More interesting are the reactions with hydrogen halides (HCl): it was found that adding electronic energy into Na changes the reaction mechanism. Early electron transfer is responsible of Na(5S, 4D) reactions, but not of Na(3P) reactions. Moreover, the NaCl product scattering is dominated by the HCl- repulsion in Na(5S, 4D) reactions, and by the NaCl-H repulsion in the case of Na(3P). The reaction of Na with O2 is of particular interest since it was found to be state specific. Only Na(4D) reacts, and the reaction requires restrictive constraints on the impact parameter and the reactants' relative orientation. The reaction with NO2 is even more complex since Na(4D) leads to the formation of NaO by two different pathways. It must be mentioned however, that the identification of NaO as product in these reactions has yet to be confirmed

  14. Alkali Aggregate Reaction in Alkali Slag Cement Mortars

    2002-01-01

    By means of "Mortar Bar Method",the ratio of cement to aggregate was kept as a constant 1∶2.25,the water-cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing proportions with dimensions of 10×10×60mm3 at 38±2℃ and RH≥95%, the influences of content and particle size of active aggregate, sort and content of alkali component and type of slag on the expansion ratios of alkali-activated slag cement(ASC) mortars due to alkali aggregate reaction(AAR) were studied. According to atomic absorption spectrometry,the amount of free alkali was measured in ASC mortars at 90d.The results show above factors affect AAR remarkably,but no dangerous AAR will occur in ASC system when the amount of active aggregate is below 15% and the mass fraction of alkali is not more than 5% (Na2O).Alkali participated in reaction as an independent component, and some hydrates containing alkali cations were produced, free alkalis in ASC system can be reduced enormously.Moreover,slag is an effective inhibitor, the possibility of generating dangerous AAR in ASC system is much lower at same conditions than that in ordinary Portland cement system.

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

    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

  16. Natural Alkali Shifts to the Methanol Business

    2007-01-01

    @@ Inner Mongolia Yuanxing Natural Alkali Co., Ltd. (Natural Alkali SZ: 000683) established in 1997 is a large chemical enterprise with new energy as its leading business and natural gas chemicals and natural alkali chemicals as the supplement business.

  17. Computational screening of mixed metal halide ammines

    Jensen, Peter Bjerre; Lysgaard, Steen; Quaade, Ulrich;

    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......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...

  18. Fullerenes doped with metal halides

    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. Toxicity of organometal halide perovskite solar cells

    Babayigit, Aslihan; Ethirajan, Anitha; Muller, Marc; Conings, Bert

    2016-03-01

    In the last few years, the advent of metal halide perovskite solar cells has revolutionized the prospects of next-generation photovoltaics. As this technology is maturing at an exceptional rate, research on its environmental impact is becoming increasingly relevant.

  20. PREPARATION OF ALKYL HALIDES VIA ORGANOTELLURIUMS

    チカマツ, キヨフミ; オオツボ, テツオ; オグラ, フミオ; ヤマグチ, ハチロウ; Kiyofumi, CHIKAMATSU; Tetsuo, OTSUBO; Fumio, OGURA; Hachiro, YAMAGUCHI

    1982-01-01

    The conversion of phenyltelluroalkanes to haloalkanes was studied in connection with the homologation of alkyl halides. Similar reactions of 1,1-bis(phenyltelluro)alkanes provided a new synthetic method of aldehydes.

  1. Copper Catalyzed Oceanic Methyl Halide Production

    Robin Kim, Jae Yun; Rhew, Robert

    2014-01-01

    Methyl halides are found in all of Earth’s biomes, produced naturally or through manmade means. Their presence in the atmosphere is problematic, as they catalyze depletion of stratospheric ozone. To understand the full environmental impact of these compounds, it is important to identify their chemical cycling processes. Iron increases methyl halide production in soils and oceans, yet copper’s influence remains unknown despite its similar chemical oxidation properties to iron. I experimentally...

  2. Superconductivity in alkali metal intercalated iron selenides.

    Krzton-Maziopa, A; Svitlyk, V; Pomjakushina, E; Puzniak, R; Conder, K

    2016-07-27

    Alkali metal intercalated iron selenide superconductors A x Fe2-y Se2 (where A  =  K, Rb, Cs, Tl/K, and Tl/Rb) are characterized by several unique properties, which were not revealed in other superconducting materials. The compounds crystallize in overall simple layered structure with FeSe layers intercalated with alkali metal. The structure turned out to be pretty complex as the existing Fe-vacancies order below ~550 K, which further leads to an antiferromagnetic ordering with Néel temperature fairly above room temperature. At even lower temperatures a phase separation is observed. While one of these phases stays magnetic down to the lowest temperatures the second is becoming superconducting below ~30 K. All these effects give rise to complex relationships between the structure, magnetism and superconductivity. In particular the iron vacancy ordering, linked with a long-range magnetic order and a mesoscopic phase separation, is assumed to be an intrinsic property of the system. Since the discovery of superconductivity in those compounds in 2010 they were investigated very extensively. Results of the studies conducted using a variety of experimental techniques and performed during the last five years were published in hundreds of reports. The present paper reviews scientific work concerning methods of synthesis and crystal growth, structural and superconducting properties as well as pressure investigations. PMID:27248118

  3. Superconductivity in alkali metal intercalated iron selenides

    Krzton-Maziopa, A.; Svitlyk, V.; Pomjakushina, E.; Puzniak, R.; Conder, K.

    2016-07-01

    Alkali metal intercalated iron selenide superconductors A x Fe2‑y Se2 (where A  =  K, Rb, Cs, Tl/K, and Tl/Rb) are characterized by several unique properties, which were not revealed in other superconducting materials. The compounds crystallize in overall simple layered structure with FeSe layers intercalated with alkali metal. The structure turned out to be pretty complex as the existing Fe-vacancies order below ~550 K, which further leads to an antiferromagnetic ordering with Néel temperature fairly above room temperature. At even lower temperatures a phase separation is observed. While one of these phases stays magnetic down to the lowest temperatures the second is becoming superconducting below ~30 K. All these effects give rise to complex relationships between the structure, magnetism and superconductivity. In particular the iron vacancy ordering, linked with a long-range magnetic order and a mesoscopic phase separation, is assumed to be an intrinsic property of the system. Since the discovery of superconductivity in those compounds in 2010 they were investigated very extensively. Results of the studies conducted using a variety of experimental techniques and performed during the last five years were published in hundreds of reports. The present paper reviews scientific work concerning methods of synthesis and crystal growth, structural and superconducting properties as well as pressure investigations.

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

    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

  5. Crystal Electrostatic Energy

    Ivanchin, Alexander

    2010-01-01

    It has been shown that to calculate the parameters of the electrostatic field of the ion crystal lattice it sufficient to take into account ions located at a distance of 1-2 lattice spacings. More distant ions make insignificant contribution. As a result, the electrostatic energy of the ion lattice in the alkaline halide crystal produced by both positive and negative ions is in good agreement with experiment when the melting temperature and the shear modulus are calculated. For fcc and bcc metals the ion lattice electrostatic energy is not sufficient to obtain the observed values of these parameters. It is possible to resolve the contradiction if one assumes that the electron density is strongly localized and has a crystal structure described by the lattice delta - function. As a result, positive charges alternate with negative ones as in the alkaline halide crystal. Such delta-like localization of the electron density is known as a model of nearly free electrons.

  6. Upgrading platform using alkali metals

    Gordon, John Howard

    2014-09-09

    A process for removing sulfur, nitrogen or metals from an oil feedstock (such as heavy oil, bitumen, shale oil, etc.) The method involves reacting the oil feedstock with an alkali metal and a radical capping substance. The alkali metal reacts with the metal, sulfur or nitrogen content to form one or more inorganic products and the radical capping substance reacts with the carbon and hydrogen content to form a hydrocarbon phase. The inorganic products may then be separated out from the hydrocarbon phase.

  7. Characterization of alkali-metal and alkaline-earth nitrates by vibrational spectroscopy

    Martínez, S.; Acción, F.; Puertas, F.

    1992-01-01

    Infrared spectra of sodium and potassium alkaline-metal nitrates and magnesium and calcium alkali-earth nitrates in solid phase had been recorded in order to assign the fundamental bands. The influence of the dispersal médium (alkaline halide), employed in the solid sample preparation have been discussed. The quantitative measurements of the band in ten sities at 1387 cm-1 (present in the I.R. spectra of the four nitrates in KBr médium) allowed us to determine the Lambe...

  8. The Remarkable Reactivity of Aryl Halides with Nucleophiles

    Bunnett, Joseph F.

    1974-01-01

    Discusses the reactivity of aryl halides with nucleophilic or basic reagents, including nucleophilic attacks on carbon, hydrogen, halogen, and arynes. Suggestions are made concerning revisions of the sections on aryl halide chemistry courses and the corresponding chapters in textbooks. (CC)

  9. Circular Photogalvanic Effect in Organometal Halide Perovskite CH$_3$NH$_3$PbI$_3$

    Li, Junwen; Haney, Paul M.

    2016-01-01

    We study the circular photogalvanic effect in the organometal halide perovskite solar cell absorber CH$_3$NH$_3$PbI$_3$. For crystal structures which lack inversion symmetry, the calculated photocurrent density is about $10^{-9}$ A/W, comparable to the previously studied quantum well and bulk Rashba systems. Because of the dependence of the circular photogalvanic effect on inversion symmetry breaking, the degree of inversion asymmetry at different depths from the surface can be probed by tuni...

  10. 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)

    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