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1

Anion polarizability functions in alkali halide crystals  

Science.gov (United States)

Anion polarizabilities in alkali halide crystals are analysed as a function of interionic separation R . The anion polarizability is treated as a function of the anion and cation radii, with its partial derivatives approximated by those with respect to R for fixed cation and anion, respectively. With pressure derivatives of the ionic radii deduced from the crystal compressibility, assuming transferability among crystals, the polarizability derivatives with respect to ionic radius yield pressure derivatives of the polarizability that agree with experiment to within a factor of two. These results offer a useful means of predicting the pressure dependence of dielectric data.

Batana, A.; Bruno, J.; Munn, R. W.

2

Radiation damage in the alkali halide crystals  

International Nuclear Information System (INIS)

A general review is given of the experimental data on radiation damage in the alkali halide crystals. A report is presented of an experimental investigation of irradiation produced interstitial dislocation loops in NaCl. These loops are found to exhibit the usual growth and coarsening behaviour during thermal annealing which operates by a glide and self-climb mechanism. It is shown that the recombination of defects in these crystals is a two stage process, and that the loss of interstitials stabilized at the loops is caused by extrinsic vacancies. The theoretical techniques used in simulating point defects in ionic crystals are described. Shell model potentials are derived for all the alkali halide crystals by fitting to bulk crystal data. The fitting is supplemented by calculations of the repulsive second neighbour interactions using methods based on the simple electron gas model. The properties of intrinsic and substitutional impurity defects are calculated. The HADES computer program is used in all the defect calculations. Finally the report returns to the problems of irradiation produced interstitial defects. The properties of H centres are discussed; their structure, formation energies, trapping at impurities and dimerization. The structure, formation energies and mobility of the intermediate and final molecular defects are then discussed. The thermodynamics of interstitial loop formation is considered for all the alklai halide crystals. The nucleation of interstitial loops in NaCl and NaBr is discussed, and the recombination of interstitial and vacancy defects. The models are found to account for all the main features of the experimental data. (author)

3

Ion clusters sputtered from alkali halide crystals  

International Nuclear Information System (INIS)

Sputtered ion clusters of alkali halides possess magic numbers of N = 13,22, etc, which can be well explained by classical electrostatic interactions and quantum 'short-range' interactions. When lithium fluoride crystals of high purity were bombarede by 8 keV argon ions, two groups of cluster ions were observed. Both were positively charged, but one of them, [Li(LiF)N]+, with microcrystal structure, and the other, (LiF)N+, complex ions. And, as the natural lithium has two isotopes, both groups contain great amount of hetero-isotopic clusters. The isotopic effect suggests another important property, in addition to the magic numbers, of mass spectra of the sputtered ion cluster

4

Dielectric and anharmonic behaviour of alkali halide crystals  

International Nuclear Information System (INIS)

The dielectric and anharmonic behaviour of alkali halide crystals is studied by determining the volume derivatives of low frequency dielectric constant and polarizability. An interionic force model which takes into account the contributions arising from the short range overlap repulsion and the van der Waals interactions is used in calculations. The implicit and explicit temperature derivatives of low frequency and high frequency dielectric constants are obtained separately for all the alkali halide crystals with NaCl and CsCl structures. The anharmonic contribution to the dielectric constant is calculated using theoretical models due to Szigeti and Havinga. The recent analysis of pressure dependence of effective charge parameter and dielectric constant of ionic crystals performed by Varotsos is shown to be invalid. (author)

5

Radiation damage in alkali halide crystals  

International Nuclear Information System (INIS)

The correspondence between the depth of F-centers produced by energetic protons bombarding a KCl single crystal and the range of the protons in the crystal is investigated. A photomicrographic technique was developed to obtain the depth of the color centers. The range of the protons in KCl was interpolated from the results of prior investigators who reported the range of protons in argon. A correspondence between the depth of the F centers and the range of the protons was established. The radiation damage produced during a channeled backscattering experiment is investigated. The formation of radiation damage was monitored by measuring the change in the dechanneling length of the incident 15-MeV 16O3+ which were aligned along the (100) plane of a KI(Tl) scintillation crystal. The formation of this damage was compared to the formation of F centers in a KI(Tl) crystal with 0.95-MeV H, which have the same energy to mass ratio as the 15-MeV 16O. It was found that although the oxygen ions lose forty times more energy per unit distance than the protons, the damage was formed at the same rate. This lack of particle identity in the formation of radiation damage is due to the saturation of F centers within particle tracks during irradiation. (Diss. Abstr. Int., B)

6

THEORY OF PLASTICO ML IN ?–IRRADIATED ALKALI HALIDE CRYSTALS  

Directory of Open Access Journals (Sweden)

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

NAMITA RAJPUT

2011-06-01

7

Volume dependence of ion polarizabilities in alkali-halide crystals  

Energy Technology Data Exchange (ETDEWEB)

The volume dependence of the static, linear polarizabilities of alkali-halide crystals is computed in a local-density-approximation (LDA) scheme. The calculated polarizabilities are inserted into the Clausius-Mossotti relation in order to obtain the high-frequency dielectric constant and its volume dependence. The theoretical values agree well with direct experimental values, as well as those inferred from photoelastic coefficients. A perfect linear relationship between the change in the refraction index and the volume strain is obtained all the way to the phase transition in RbCl in agreement with experiment. These results lend support to the LDA and the use of the spherical-averaging approximation for these crystals.

Pettersson, S. (Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN (USA) Department of Physics and Astronomy, University of Tennessee, Knoxville, TN (USA)); Subbaswamy, K.R. (Department of Physics and Astronomy, University of Kentucky, Lexington, KY (USA))

1990-09-15

8

Transmission electron microscopy of weakly deformed alkali halide crystals  

International Nuclear Information System (INIS)

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

9

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

International Nuclear Information System (INIS)

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

10

Statistics and correlation of phase equilibria. Correlation estimation of distribution coefficients of crystal-melt in alkali halide binary systems  

International Nuclear Information System (INIS)

Experimental material on distribution coefficients of the equilibrium crystal-melt K in the angles of binary systems, formed by alkali metal halides, is systematized. The experimental material is presente.d in the form of curves of lg K dependence on internuclear distance in crystal lattice. Correlation evaluations for unstudied systems are made, including the systems with francium halides and alkali metal astatides

11

An optical criterion to obtain miscible mixed crystals in alkali halides  

Directory of Open Access Journals (Sweden)

Full Text Available This work gives a novel criterion to predict the formation of alkali halide solid solutions and discusses some results obtained in the development of ternary and quaternary miscible crystalline dielectric mixtures of alkali halides. These mixtures are miscible in any concentration of their components. The miscibility of these mixed crystals is quite related to the F center through the behavior observed in the spectral position of the optical absorption F band as a function of the lattice constant of the alkali halide where the F center was formed. By inspection of an energy graph of the F band energy versus lattice constant (Mollwo-Ivey law, a set of points is observed corresponding to several pure alkali halides (such as KCl, KBr, RbCl, which gives a notion of possible mixed materials that would correspond to adjacent points and a solid solution could be obtained, meaning a single phase crystal, which result in ternary and quaternary mixed crystals. Thus, the optical absorption F band allows have a numerical criterion, based on the percentage respective of the F band energy, in order to predict possible solid solutions. We obtained experimental information using diffractograms of the mixed crystals, from which the lattice constant was obtained and compared with a theoretical calculus using a generalization of Vegard's law, finally it is discussed the case of a crystal growing, starting from five components, picking up five consecutive dots from the graph of Mollwo-Ivey's law.

R. Rodr\\u00EDguez-Mij\\u00E1ngos

2008-01-01

12

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

International Nuclear Information System (INIS)

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

13

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

Energy Technology Data Exchange (ETDEWEB)

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)

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

14

Radiophotoluminescence of alkali-halide crystals stimulated by Bessel laser beam  

International Nuclear Information System (INIS)

A new approach to realization of optimal high-resolution reading of deep X-ray images in X-ray-sensitive materials on the base of alkali-halide crystals modified with admixtures has been suggested and investigated experimentally. A possibility to use diffraction axicons with ring aperture for forming micron bright light beams (spatially truncated Bessel beams) which can efficiently de-excite radiophotoluminescence centers lying at large depth in crystals is also presented

15

Heterogeneous reactions in the system alkali-halide crystal/air at X-ray activation  

International Nuclear Information System (INIS)

The method of electron microscopy is used to study heterogeneous synthesis of alkali metal nitrates in the system crystal (KCl, KBr, KI, NaCl, RbBr)/air at X-ray activation. Nitrate accumulation kinetics at different doses and rates (830 and 3 R s-- cm-2) of X-radiation is investigated. Peculiarities of kinetic regularities of radiation nitration of alkali-halide microcrystals are considered, and basic stages of heterogeneous process of nitrates solid-phase synthesis in the system

16

Helium irradiation of alkali halides  

International Nuclear Information System (INIS)

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

17

Temperature dependence of fourth-order elastic constants of alkali halide crystals  

International Nuclear Information System (INIS)

A method for evaluating the temperature dependence of fourth-order elastic constants (FOEC) of NaCl as well as CsCl-structure alkali halides is develoed on the basis of the phonon-pressure theory. Eleven distinct values of FOEC for each alkali halide crystal are calculated at 0 K and at room temperature (300 K). The pressure derivatives of second and thrid-order elastic constants are calculated at both the temperatures. The method is based on the phonon-pressure theory incorporating Lundqvist's three-body potential. The second-order temperature derivatives of second-order elastic constants are also evaluated. The results obtained are discussed and compared with other investigations. The importance and significance of temperature contributions to various order elastic constants are discussed. (author)

18

Role of vacancy clusters in thermostimulated luminescence of alkali halide single crystals  

International Nuclear Information System (INIS)

It is shown that low-temperature deformation peaks of thermostimulated luminescence (TSL) are related to the presence of vacancy clusters in the crystal. The simultaneous realization of a series of cluster forms determines the complex character of the high-temperature peak, and the fluctuational rearrangements of the cluster structure can account for the anomalies of the luminescence process. The proposed cluster model of the anomalies of high-temperature TSL peaks is also applicable to the case of high-dose irradiation of alkali halide crystals, which involves the formation of traps that also determine the formation of analogous high-temperature TSL peaks

19

Anisotropy of paramagnetic cadmium centers in alkali-halide crystals  

International Nuclear Information System (INIS)

Anisotropic and paramagnetic centers of Cdsub(F)sup(+), which are Cd+ cation ions located beside anion vacancies, have been found and studied by the EPR method in LiCl, NaCl, KCl crystals with cadmium impurity, the crystals being irradiated by X-rays at a room temperature. The unpairing electron wave function is delocalized approximately 30% from a Cdsub(F)sup(+) cation ion to an anion vacancy along C4 axis. The parameters of the spin-hamiltonian of Cdsub(F)sup(+) centers in LiCl, NaCl, KCl crystals are determined. Cd+ cation ions located beside a cation vacancy are also studied. Several types of such centers differing in mutual arrangement of a Cd+ ion and a vacancy have been revealed

20

Light scattering in additively colored alkali-halide crystals  

International Nuclear Information System (INIS)

Studied is extinction in ultra-violet, visible and infrared spectrum ranges, caused by light scattering in additively colored KCl and KBr crystals. The crystals were prepared of the powder. The specimens were annealed in saturated potassium vapours: KBr - at 600-630 deg C, KCl - at 700 deg C. While investigating the spectra it is observed that the optical density of the specimens processed in such a regime is more than 2 in the ultraviolet and visible spectrum ranges at the 0.1-0.05 cm thickness of the specimens. In the infrared spectra the growth of the extinction coefficient with the wave length decrease is observed. The spectrum character shows IR radiation scattering by the defects in the crystal lattice. The attempt of determination of the scattering centres nature is taken. It is shown that the possible centres causing the light scattering observed can be colloid and quasicolloid centres in the additively colored materials

 
 
 
 
21

Ion bombardment of alkali halides  

International Nuclear Information System (INIS)

Color-center effects unique to crystals irradiated to high fluence (1016 particles/cm2) are reported for KCl and other alkali halides. These include (1) a minimum in F-center concentration at the end of the proton range and (2) an F-center distribution profile which changes with time in the dark at room temperature after irradiation. The first effect is due to annihilation of F centers by hydrogen atom capture (U-center formation) and the second is due to F-center diffusion and aggregation in a heavily damaged region of the crystal. (author)

22

An optical criterion to obtain miscible mixed crystals in alkali halides  

Scientific Electronic Library Online (English)

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

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

2008-11-01

23

Study of dislocation loops in alkali halide crystals by diffuse X-ray scattering  

International Nuclear Information System (INIS)

It has been known for some time that characteristic intensity oscillations occur in diffuse scattering patterns due to the displacement field of strong defects like clusters and dislocation loops. Besides the scattering of the displacement field the core structure of extended defects may cause an extra line close to the Bragg-peak. Only recently it has been found theoretically that for dislocation loops there is a correlation between oscillations and the extra line. The position of the extra line relative to a nearby reciprocal lattice point depends on the orientation of the Burgers vector and the reciprocal lattice vector as well. X-ray diffuse scattering results on irradiated alkali halide crystals containing large defect clusters are presented. Results are discussed in terms of loops with dose-dependent size

24

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

International Nuclear Information System (INIS)

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

25

A mass-spectrometric determination of the work function of alkali metal halide crystals  

Science.gov (United States)

Thermochemical cycles including experimentally measured enthalpies of sublimation of alkali metal halides in the form of M2X+ and MX{2/?} ionic clusters and MX molecules were used to calculate work functions for NaCl, NaBr, NaI, KCl, KBr, KI, RbCl, and RbI.

Kudin, L. S.; Dunaev, A. M.; Butman, M. F.; Kryuchkov, A. S.

2011-02-01

26

Muonium centers in the alkali halides  

International Nuclear Information System (INIS)

Muonium centers (Mu) in single crystals and powdered alkali halides have been studied using the high-timing-resolution transverse field ?SR technique. Mu has been observed and its hyperfine parameter (HF) determined in every alkali halide. For the rocksalt alkali halides, the HF parameter A? shows a systematic dependence on the host lattice constant. A comparison of the Mu HF parameter with hydrogen ESR data suggests that the Mu center is the muonic analogue of the interstitial hydrogen Hi0-center. The rate of Mu diffusion can be deduced from the motional narrowing of the nuclear hyperfine interaction. KBr shows two different Mu states, a low-temperature MuI-state and a high-temperature MuII-state. (orig.)

27

CO2 laser absorption and saturation studies of molecular impurities in alkali halide crystals  

International Nuclear Information System (INIS)

The objective of this research program has been to explore the equilibrium and non-equilibrium dynamical properties of ReO4- molecules embedded in alkali halide lattices using electromagnetic radiation. Both incoherent sources and CO2 laser radiation have been used to explore the full dynamic range of the molecular vibrational modes. To achieve this objective stable molecular dopant - alkali halide combinations have been fabricated which have vibrational modes near the CO2 laser frequencies. In order to uncouple the molecular modes from the lattice modes, to simplify the analysis as much as possible, low temperature spectroscopic measurements were required. In general, it was found that the molecular vibrational modes in the low temperature quiescent lattice had extremely narrow linewidths (less than 0.1 cm-1) so that most of the coincidences with the CO2 laser lines were eliminated

28

Elastic constants of alkali halides: Multipole expansion  

Science.gov (United States)

The elastic constants at zero temperature are calculated for the alkali-halide crystals. Two new terms are included: the induced quadrupole and induced octupole polarizabilities of the ions. These terms are significant, and affect the final result by 5-50%. The elastic constants are a good quantity for testing theories of ionic bonding.

Mahan, G. D.

1984-05-01

29

Quantum-chemical simulation of halogen aggregation in irradiated alkali halide crystals  

International Nuclear Information System (INIS)

It is known, that in irradiated alkali halide crystals (AHC) in a wide temperature band stable radiating defects are X3- and the F-centers. For studying mechanisms of formation and destruction of X3- centers in irradiated AHC by semiempirical quantum-chemical method MNDO us models process of disintegration of X3- centers in crystals KCl and KI. We simulate process of dissociation of X3- centers in crystals KCl and KI from the basic singlet, excited triplet and excited singlet states. At modeling process of dissociation of X3- centers from the basic singlet state all atoms of structure, except for external, were optimized. Calculations have shown, that X3- center from the basic singlet state dissociates on Cl20 and Cl- fragments with dissociation energy 1.15 eV, and I3- center dissociates on I20 and I- fragments with dissociation energy 1.48 eV. For localization of excitation in the X3- center processes of dissociation from triplet and excited singlet states are modeled at the fixed atoms of a crystal environment. We consider process of dissociation of X3- center of singlet-excited state. Cl3-, center from singlet excited state breaks up on Cl20 and Cl- fr>20 and Cl- fragments with dissociation energy 1.2 eV. And I3- center in crystal KI breaks up on I20 and I0 fragments with dissociation energy 1.3 eV. Process of dissociation of X3- center of the excited triplet state is modeled. Cl3- center from the excited triplet state breaks up on Cl2- and Cl0 fragments with dissociation energy 1.5 eV. And I3- center in crystal KI breaks up on I2- and I0 fragments with dissociation energy 0.4 eV. Thus, X3- centers in irradiated AHC at modeling in view of an environment dissociate from a singlet state on fragments X20 and X- on reaction: X3-?X20+X- and from a triplet state on fragments X2- and X0 on reaction: X3-?X2+X0. Reactions of disintegrations and values of bond energy of X3- molecules correspond to experimental data

30

Effect of the surface of alkali metal halide crystal on electronic structure of the defects and their interaction with each other and with water  

International Nuclear Information System (INIS)

Process of oxidation product formation on the surface of alkali metal halide crystals under the action of ionizing radiation is considered. A mechanism of catalytic oxidation of the KCl crystal surface is proposed, suggesting water molecule sorption on surface Vsub(h) centers with their further decomposition to H- and OH-radicals

31

Alkali Halide Nanotubes: Structure and Stability  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Accurate density functional theory (DFT) and coupled-cluster (CCSD) calculations on a series of (LiF)n=2,36 neutral clusters suggest that nanotube structures with hexagonal and octagonal transversal cross sections show stability equal to or greater than that of the typical cubic form of large LiF crystals. The nanotube stability was further corroborated by quantum dynamic calculations at room temperature. The fact that stable nanotube structures were also found for other alkali halides (e.g.,...

Fernandez-lima, Francisco A.; Henkes, Aline Vero?nica; Da Silveira, Enio F.; Nascimento, Marco Antonio Chaer

2012-01-01

32

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

International Nuclear Information System (INIS)

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

33

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

Science.gov (United States)

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

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

1975-01-01

34

Specific features of the temperature quenching of luminescence of self-trapped excitons in alkali halide crystals under low-temperature deformation  

Science.gov (United States)

The activation energy of temperature quenching of luminescence of self-trapped excitons in alkali halide crystals subjected to low-temperature uniaxial deformation is evaluated experimentally. It is found that an increase in the activation energy is observed in the following series of crystals: KBr ? NaCl ? KI ? NaBr ? CsBr ? RbI. The effect of enhancement of intrinsic luminescence of alkali halide crystals due to the lowering of the symmetry of the crystal lattice under low-temperature uniaxial deformation is interpreted by analyzing the observed increase in the activation energy that characterizes the height of the potential barrier separating channels of radiative and nonradiative decay (with the formation of radiation defects) of self-trapped excitons.

Shunkeev, K.; Sarmukhanov, E.; Barmina, A.; Myasnikova, L.; Sagimbaeva, Sh.; Shunkeev, S.

2008-10-01

35

Structure of molten alkali halides  

International Nuclear Information System (INIS)

The results of X-ray and neutron diffraction experiments on molten alkali halides in which some data of our experiments by X-ray diffraction such as those of molten LiCl, NaCl, KCl, LiBr and KBr are included were summarized. The first peak positions in the radial distribution function in molten alkali halides by X-ray or neutron diffraction experiments are always longer than those by computer simulations and the differences of 0.1 -- 0.3 A exceed the experimental error. It seems to be due to the deformation of the electron shell. In the computer simulation, the shell model which has the spherical deformation was expected to have more closer value of the first peak position to the experimental one than the rigid ion model by taking the polarization of ions. However, no change in the first peak position was found. Therefore, the non-spherical deformation of electron shell at the point where ions are in contact with each other has to be taken into account. The neutron diffraction method with isotopic substitution has a merit of getting the partial correlation functions which are difficult to be obtained by the ordinary X-ray diffraction method and can compare directly with the results by the computer simulation. However, results of some molten salts such as KCl and CsCl by the neutron diffraction method with isotopic substitution have significant errors and there are something left to be improved for accuracy in measurements or correction of data in this method. (author)orrection of data in this method. (author)

36

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

Science.gov (United States)

Suitable conditions for growth of high quality single crystals of ternary alkali lead halides prepared by a Bridgman method were explored using direct observation of a crystal/melt interface when pulling an ampoule out of a furnace, deliberated striations' induction and measurement of a temperature field in the filled ampoule in the vertical Bridgman arrangement, as model compounds lead chloride and ternary rubidium lead bromide were used. By direct observation only position of the crystal/melt interface was markedly determined, while by induced striations both the position and the shape of the interface were visualized but their contrast had to be intensified by adding admixtures. Performed temperature measurements in the filled ampoule brought both a view of temperature field in the 3D radial symmetry and basic data for comparison of a real temperature field with those obtained by projected modeling.

Král, Robert

2012-12-01

37

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

Science.gov (United States)

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%.

Schlosser, Herbert

1992-01-01

38

Thermal diffusivity of alkali and silver halide crystals as a function of temperature  

Science.gov (United States)

The phonon component of thermal diffusivity (D) for ten synthetic single-crystals (LiF, NaCl, NaI, NaI:Tl, KCl, KBr, CsI, CsI:Tl, AgCl, and AgBr) with the B1 and B2 structures was measured from ambient temperature (T) up to ˜1093 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. We investigated optical flats from different manufacturers as well as pellets made from compressed powders of most of the above chemical compositions plus LiI, NaBr, KI, RbCl, RbBr, RbI, CsCl, CsBr, and AgI. Impurities were characterized using various spectroscopic methods. With increasing T ,D decreases such that near melting the derivatives ?D/?T are low, -0.0006±0.0004 mm2 s-1 K-1. Our results are ˜16% lower than D298 previously obtained with contact methods, which are elevated by ballistic radiative transfer for these infrared (IR) windows, and are well described by either D-1 following a low order polynomial in T, or by D-1?T+n, where n ranges from 1.0294 to 1.9429. Inverse correlations were found between D298 and both density and thermal expansivity (?). Primitive lattice constant times compressional velocity correlates directly with D but changes much more slowly with temperature. Instead, D(T ) is proportional to (T?L)-1 from ˜0 K up to the limit of measurements, in accord with these physical properties being anharmonic. On average, the damped harmonic oscillator-phonon gas model reproduces D298 based on two physical properties: compressional velocity and the damping coefficient (? ) from analysis of IR reflectivity data. Given large uncertainties in ?(T ), D-1(T) is reproduced for LiF, NaCl, MgO, and the silver halides, for which IR reflectivity data are available. Our correlations show that optical phonons largely govern heat transport of insulators, and permit prediction of D and thus thermal conductivity for simple, diatomic solids.

Yu, Xueyang; Hofmeister, Anne M.

2011-02-01

39

Dissociation of alkali halides under electron bombardment  

International Nuclear Information System (INIS)

The low-energy electron bombardment of alkali halides results in their dissociation and emission of halogen. The alkali metal excess on the irradiated surface is found by the electron Auger-spectroscopy, neutron-activated analysis, electron microscopy, conductivity and secondary electron emission coefficient measurements

40

Relaxation processes of the triplet state of self-trapped excitons in alkali-halide crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The spin lattice relaxation, radiative and microwave excitation processes of the triplet self-trapped exciton have been studied in alkali chlorides and bromides by measuring the transient response of the X-ray excited luminescence to resonant pulse microwave. The model is applied to magnetic circular polarization data. The symmetry of dominant exciton-phonon coupling are discussed.

Mori, Y.; Jaccard, C.; Von Weid, J.; Aegerter, M.

1980-01-01

 
 
 
 
41

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Optical surface breakdown of alkali halide crystals by microsecond pulses from a wide-aperture CO2 laser  

Science.gov (United States)

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

Kazantsev, S. G.

1998-04-01

42

Ground state properties of heavy alkali halides  

CERN Document Server

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

Doll, K; Doll, Klaus; Stoll, Hermann

1998-01-01

43

Defect formation and desorption of metal atoms from alkali halide crystals under low energy electron bombardment studied by optical absorption and mass spectroscopy  

International Nuclear Information System (INIS)

This work presents an extensive investigation of electronically induced desorption of ground-state alkali atoms from alkali halides and for the first time correlates directly the desorption with the stability and spatial distribution of the defects formed during bombardment. The electron impact results in the formation of stable F-centers and F-center clusters in the bulk of the crystals. In striking contrast a significant metallization of the surface is observed. Even at temperatures as low as 90 deg C the metallization is achieved within the time resolution of our detection system, which can only be explained by the rapid diffusion of hot holes. Superimposed to the fast and short diffusion of hot holes is the slow F-center diffusion. Measuring the distribution of defects with low energy ion sputtering techniques indicates that at least in the case of LiF the observed diffusion constant of F-centers agrees with values derived by using methods different from that applied here. At low temperatures the formation of F-center clusters and metal on the surface dominates. Colloid formation clearly requires higher temperatures (typically around 200 deg C). This is a strong evidence that efficient F-center diffusion is necessary for the formation of metallic particles (colloids) in the bulk of the crystals. Desorption of alkali atoms from alkali halides at temperatures around room temperature is due to weakly bound alkali atoms. For elevated temperatures the stability of the levated temperatures the stability of the metallic clusters in the bulk of the crystals (i.e. colloids) are the rate limiting process. (author)

44

Dechanneling of electrons by thermally produced lattice vacancies in the crystals of alkali halides  

International Nuclear Information System (INIS)

Single crystals of NaCl, KCl and KI were treated at various elevated temperatures. Lattice vacancies generated in the crystals are found to dechannel the incident energetic electrons. A factor for the increase of the energy loss of electrons due to dechanneling is determined, which is observed to be an increasing function of the concentration of lattice vacancies. (author)

45

The influence of dislocation charge on the cleavage surface charge of alkali halide crystals  

International Nuclear Information System (INIS)

In order to study the role of charged dislocations in the formation of charge of the fresh surface of ionic crystals the investigated samples were cleaved from single crystals of NaCl, KCl, and LiF with various impurity (Ca) contents or from ?-irradiated single crystals. The dislocation charge per unit length was measured with the aid of indentation of the crystal surface, that was neutralized before testing. The indentor penetration depth was maintained approximately constant by load variation from 10 to 40 N from different crystals. To estimate the dynamic surface charge during fast specimen cleavage under the action of impact load both the electric field intensity around the specimen and the crack length were simultaneously measured. The residual surface charge was measured 1 min after the sample cleavage by the aid of an electrometer

46

Polarizabilities of the alkali halide dimers. II  

International Nuclear Information System (INIS)

We have measured the average electric dipole polarizabilities of twenty alkali halide dimers, using a molecular beam electric deflection method. This is a continuation of the earlier measurements of five alkali halide dimers [R. Kremens et al., J. Chem. Phys. 81, 1676 (1984)]. We compare our measurements with a simple combination of bond (via a ''spring'' model) and effective ionic polarizabilities, using literature values for the required molecular constants. Agreement between our measured and calculated values is reasonable, in most cases, considering the relative crudeness of the model

47

Analysis of the structural phase transition in mixed alkali halide crystals  

International Nuclear Information System (INIS)

An analysis of structural transition in CsCl-KCl and CsCl-TbCl mixed crystals is presented by studying the lattice stability in terms of interionic potentials. The potential parameters are determined by fitting the experimental values of lattice energies in standard observed structure viz. CsCl structure for CsCl and CsBr crystals, and NaCl structure for RbCl and KCl crystals. It is found that CsCl-KCl mixed crystals remain stable in CsCl structure only for KCl less than 25%, and are transformed to NaCl structure when the proportion of KCl becomes equal to or more than 25%. For CsCl-RbCl mixed crystals, the transition from CsCl to NaCl structure is predicted when the RbCl component becomes equal to or more than 50%. These predictions are found to be in good agreement with experimental results. The lattice theory of structural stability is also applied to predict the transition temperatures for the mixed crystals viz. CsCl-KCl, CsCl-RbCl and CsCl-CsBr at which they transform from CsCl to NaCl structure. (author)

48

Point defect production by ultrafast laser irradiation of alkali-containing silica glasses and alkali halide single crystals  

International Nuclear Information System (INIS)

The high instantaneous powers associated with femtosecond lasers can color many nominally transparent materials. Although the excitations responsible for this defect formation occur at subpicosecond time scales, subsequent interactions between the resulting electronic and lattice defects complicate the evolution of color center formation and decay. These interactions must be understood in order to account for the long-term behavior of coloration. In this work, we probe the evolution of color centers produced by femtosecond laser radiation in soda lime glass and single-crystal sodium chloride at time scales from microseconds to hundreds of seconds. By using an appropriately chosen probe laser focused through the femtosecond laser spot, we can follow the changes in coloration due to individual or multiple femtosecond pulses, and follow the evolution of that coloration for long times after the femtosecond laser radiation is terminated. For the soda lime glass, the decay of color centers is well described in terms of bimolecular annihilation reactions between electron and hole centers. Similar processes are also occurring in single-crystal sodium chloride. Finally, we report fabrication of permanent periodic patterns in soda lime glass by two time coincident femtosecond laser pulses

49

Pressure and temperature dependence of the mechanoluminescence of ?-irradiated alkali halide crystals  

International Nuclear Information System (INIS)

The intensity of mechanoluminescence (ML) produced during application and release of uniaxial pressure, in ?-irradiated KBr, KCl, KI, LiF, and NaCl crystals decreases with the number of applications and releases of the pressure. The ML intensity of ?-irradiated KBr, KCl, LiF, and NaCl crystals increases with the temperature, however, the ML intensity of ?-irradiated KI crystals decreases with the temperature. The ratio of the ML intensity during the release of the pressure to the ML intensity during the corresponding number of applications of the pressure, decreases with the temperature of the crystals. Assuming that the movement of dislocations is responsible for the ML excitation, the pressure and temperature dependence of the ML is discussed. The activation energy related to the increase in the number of dislocations with the temperature is estimated from the ML measurement and it is found to be 0.24, 0.25, 0.24, and 0.32 eV for ?-irradiated KBr, KCl, LiF, and NaCl crystals respectively. (author)

50

Effect of impurities on the hardness of alkali halide single crystals  

Science.gov (United States)

Micro hardness number of KCl, KBr and KCl-Br grown by Czocharlski technique, in the presence of homovalent and aliovalent ions of different ionic radii were measured in the indentation load range from 5 to 80*10-3 N. The measured data showed that there is an indentation size effect and classical Meyer's law was used for the characterization of crystal hardness of these crystals. The Meyer's index was also found to be smaller than 2 indicating brittle material characteristic. The P.R.S. model was used for the determination of the load independent micro hardness value. Result can be explained on the basis of interaction between created dislocation and point defect. It was found that hardness of these crystals is depending on the type of impurity.

Verma, Ashok K.; Ojha, Chaturbhuj; Shrivastava, A. K.

2014-04-01

51

Evaluation of electronic dielectric constant and fractional ionic character of mixed alkali halide crystals  

International Nuclear Information System (INIS)

The electronic dielectric constant and fractional ionic character of the chemical bond are calculated for the mixed crystals NaCl-NaBr, KCl-KBr, KBr-KI, CsCl-CsBr, CsCl-RbCl, and CsCl-KCl for the entire range of composition. The first four solid solutions are with common cations whereas the last two are formed of substances with common anions. For the electronic dielectric constant a comparison is given of the values calculated from the Clausius-Mossotti relation and the Pantelides formulation. For evaluating the fractional ionic character application is made of Phillips' and Pauling's theories. The calculated values are found to depend sensitively on the composition parameter of mixed crystals. (author)

52

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

International Nuclear Information System (INIS)

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)

53

Temperature dependent dynamic ESD processes in alkali halides  

International Nuclear Information System (INIS)

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

54

Refractive indices, electronic polarizabilities and dielectric constants of alkali halides  

Science.gov (United States)

New relations are proposed for the evaluation of refractive indices, electronic polarizabilities and optical dielectric constants of alkali halides. Refractive indices and optical dielectronic constants for alkali halides have been estimated based on the following relations: E ge 1.4n = 63.8 + 0.03? eE ge 1.4n = 68.5 + 3.9? ex e and ? = {E 2g}/{83.1}-0.5E g + 5.9 where Eg, n, ? e, ? exe and ? are the energy gap (in eV), refractive index, equilibrium vibrational frequency (in cm -1), vibrational anharmonicity constant term (in cm -1) and optical dielectric constant, respectively. Strain derivative values of the electronic dielectric constant in ionic crystals are also evaluated using the energy gap. In all cases the calculated and the literature values are in good agreement with each other.

Reddy, R. R.; Anjaneyulu, S.; Rao, T. V. R.

1992-09-01

55

Solvation at nanoscale: Alkali-halides in water clusters  

International Nuclear Information System (INIS)

The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.

56

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

International Nuclear Information System (INIS)

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

57

Magnetic susceptibility of liquid alkali metal-alkali halide solutions  

International Nuclear Information System (INIS)

The static magnetic susceptibility chi of five liquid alkali metal-alkali halide mixtures (Na-NaBr, Na-NaCl, K-KCl, Cs-CsCl, Cs-CsJ) has been measured over the whole concentration range up to a maximum temperature of 11500C. In all systems a small paramagnetic deviation from ideal (additive) behaviour is observed. In the metallic regime no significant spin enhancement of chi occurs contrary to the behaviour found in the liquid alkali metals. Thus electronic correlation effects probably are not dominant for the metal-nonmetal transition in these solutions. In the salt rich solutions a Curie type paramagnetism consistent with F-center like states is found. For more concentrated solutions a strong concentration dependence of chi is established. Approaching the metal-nonmetal transition region spin pairing processes become important possibly leading to the formation of small metal clusters. (orig.)

58

Electronic excitation in bulk and nanocrystalline alkali halides  

Science.gov (United States)

The lowest energy excitations in bulk alkali halides are investigated by considering five different excited state descriptions. It is concluded that excitation transfers one outermost halide electron in the fully ionic ground state to the lowest energy vacant s orbital of one closest cation neighbour to produce the excited state termed dipolar. The excitation energies of seven salts were computed using shell model description of the lattice polarization produced by the effective dipole moment of the excited state neutral halogen-neutral metal pair. Ab initio uncorrelated short-range inter-ionic interactions computed from anion wavefunctions adapted to the in-crystal environment were augmented by short-range electron correlation contributions derived from uniform electron-gas density functional theory. Dispersive attractions including wavefunction overlap damping were introduced using reliable semi-empirical dispersion coefficients. The good agreement between the predicted excitation energies and experiment provides strong evidence that the excited state is dipolar. In alkali halide nanocrystals in which each ionic plane contains only four ions, the Madelung energies are significantly reduced compared with the bulk. This predicts that the corresponding intra-crystal excitation energies in the nanocrystals, where there are two excited states depending on whether the halide electron is transferred to a cation in the same or in the neighbouring plane, will be reduced by almost 2 eV. For such an encapsulated KI crystal, it has been shown that the greater polarization in the excited state of the bulk crystal causes these reductions to be lowered to a 1.1 eV-1.5 eV range for the case of charge transfer to a neighbouring plane. For intra-plane charge transfer the magnitude of the polarization energy is further reduced thus causing the excitation in these encapsulated materials to be only 0.2 eV less than in the bulk crystal.

Bichoutskaia, Elena; Pyper, Nicholas C.

2012-11-01

59

Low energy electron scattering by alkali halides  

International Nuclear Information System (INIS)

The energy distribution curves (EDC's) of the electrons scattered by the evaporated films of twenty kinds of alkali halides are obtained by impact with low energy electrons of 10-30 eV. Stationary bands observed in the EDC's are interpreted as the reflection of the high density of state levels in the conduction band. Energy loss structures due to the valence electron excitation are also observed in the EDC's. Furthermore the structures observed in the yield spectra are found to relate with exciton formation, band-to-band transition, plasmon and double excitation of valence electrons. (auth.)

60

Cohesive properties of alkali halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We calculate cohesive properties of LiF, NaF, KF, LiCl, NaCl, and KCl with ab-initio quantum chemical methods. The coupled-cluster approach is used to correct the Hartree-Fock crystal results for correlations and to systematically improve cohesive energies, lattice constants and bulk moduli. After inclusion of correlations, we recover 95-98 % of the total cohesive energies. The lattice constants deviate from experiment by at most 1.1 %, bulk moduli by at most 8 %. We also fi...

Doll, Klaus; Stoll, Hermann

1997-01-01

 
 
 
 
61

Crystal field constants calculation in the spin-Hamiltonian for Eu2+ in alkali-halide crystals  

International Nuclear Information System (INIS)

The spin-Hamiltonian constants b02 and b22 for the center Eu2+-vacancy in NaCl, KCl and KBr crystals are calculated. Agreement with experimental data for b02 is obtained by taking into account the second and the fourth orders of perturbations in H = Hsub(L-S) + Vsub(C) + Hsub(S-S). Different values of b02 in the succession NaCl, KCl, KBr are explained under the assumption that Cl- ions, which are located in XY plane in the first sphere of Eu2+ surrounding, are shifted. (Auth.)

62

Interaction of wide band gap single crystals with 248 nm excimer laser radiation. XII. The emission of negative atomic ions from alkali halides  

International Nuclear Information System (INIS)

Many wide band gap materials yield charged and neutral emissions when exposed to sub-band-gap laser radiation at power densities below the threshold for optical breakdown and plume formation. In this work, we report the observation of negative alkali ions from several alkali halides under comparable conditions. We observe no evidence for negative halogen ions, in spite of the high electron affinities of the halogens. Significantly, the positive and negative alkali ions show a high degree of spatial and temporal overlap. A detailed study of all the relevant particle emissions from potassium chloride (KCl) suggests that K- is formed by the sequential attachment of two electrons to K+

63

Thermoluminescence of alkali halides and its implications  

International Nuclear Information System (INIS)

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

64

Thermoluminescence of alkali halides and its implications  

Energy Technology Data Exchange (ETDEWEB)

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.

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

2012-03-01

65

Cluster ion formation of alkali halides by electrospray droplet impact  

Science.gov (United States)

Positive and negative cluster ions formed by electrospray droplet impact on the alkali halides (MX) were measured for all alkali halides. Small amounts of powder samples deposited and crushed into thin films on the metal substrate were served for the measurement. The size distribution of cluster ions is very limited for LiF, CsF, and LiI. Little or no fluoride cluster ions F-(MF)n were detected. In general, distribution of n for negative cluster ions X-(MX)n is narrower than that for positive cluster ions M+(MX)n, probably due to the instability caused by the mutual Coulomb repulsion between the larger-size halide ions than alkali ions. While the cubic-like structures are preferred for alkali halides with smaller ionic radii, the stacked hexagonal structures with n = 3, 6, and 9 are preferred for those with larger ionic radii.

Mori, Kunihiko; Hiraoka, Kenzo

2008-01-01

66

Structured alkali halides for medical applications  

Science.gov (United States)

Image plates based on storage phosphors are a major application of radiation defects in insulators. Storage phosphors absorb X-ray quanta creating trapped electron-hole pairs in the material. Optical stimulation of the electron causes recombination leading to light emission. Application of image plates requires an optimal compromise between resolution (represented by the modulation transfer function (MTF)) and sensitivity. In our paper we present a new solution of the problem of combining a high MTF with a high sensitivity by structuring the image plates in form of thin needles acting as light guides. This suppresses the lateral spread of light which is detrimental to resolution. As doped CsBr, e.g. CsBr:Ga [Physica Medica XV (1999) 301], can pose a good storage phosphor evaporated layers are of interest in computed radiography. Needle structured CsI:Tl is used as scintillator in direct radiography [IEEE Trans. Nucl. Sci. 45 (3) (1998)]. CsBr layers have been produced by evaporation in vacuum and in inert gas atmosphere varying pressure and temperature. The resulting structures are of fibrous or columnar nature being in good agreement with the zone model of Thornton [Ann. Rev. Mater. Sci. 7 (1977) 239]. A zone model for CsBr has been developed. Measurements on doped alkali halide image plates having needle structure show good MTF at high sensitivity making a significant progress in image plate technology.

Schmitt, B.; Fuchs, M.; Hell, E.; Knüpfer, W.; Hackenschmied, P.; Winnacker, A.

2002-05-01

67

Structured alkali halides for medical applications  

International Nuclear Information System (INIS)

Image plates based on storage phosphors are a major application of radiation defects in insulators. Storage phosphors absorb X-ray quanta creating trapped electron-hole pairs in the material. Optical stimulation of the electron causes recombination leading to light emission. Application of image plates requires an optimal compromise between resolution (represented by the modulation transfer function (MTF)) and sensitivity. In our paper we present a new solution of the problem of combining a high MTF with a high sensitivity by structuring the image plates in form of thin needles acting as light guides. This suppresses the lateral spread of light which is detrimental to resolution. As doped CsBr, e.g. CsBr:Ga [Physica Medica XV (1999) 301], can pose a good storage phosphor evaporated layers are of interest in computed radiography. Needle structured CsI:Tl is used as scintillator in direct radiography [IEEE Trans. Nucl. Sci. 45 (3) (1998)]. CsBr layers have been produced by evaporation in vacuum and in inert gas atmosphere varying pressure and temperature. The resulting structures are of fibrous or columnar nature being in good agreement with the zone model of Thornton [Ann. Rev. Mater. Sci. 7 (1977) 239]. A zone model for CsBr has been developed. Measurements on doped alkali halide image plates having needle structure show good MTF at high sensitivity making a significant progress in image plate technology

68

Investigation of the structure of impurity defects in alkali halide crystals by the method of fluorescence EXAFS  

International Nuclear Information System (INIS)

It has been shown by experiment that the structure of impurity centers in NaCl-Sr crystals depends on impurity concentration and storage time of crystals. At low concentration and in quenched crystals the impurity is in site of the lattice. At concentrations higher than 0.15 wt% Sr, the impurity forms SrCl2 phase. For the crystals containing Cu+ impurity, it has been shown that an increase in the impurity concentration leads to the formation of clusters with CuCl structure. At the same time the existence of isolated copper ions shifted from the sites of the lattice is obvious. This leads to asymmetry of the environment of copper, which is manifested both in the absorption spectra in the ultraviolet region and in the EXAFS spectra. Heating of the crystals leads to destruction of complex clusters and formation exclusively of centers containing isolated copper ions

69

Sulfate ion impurity as a sensor for point defects and dislocations in alkali halide crystals. Anion vacancy  

International Nuclear Information System (INIS)

A study of the vibrational spectrum of the molecular impurity ions in ionic crystals is proposed as a selective method for the direct investigations of point defects and dislocations in wide temperature range up to the melting point and even higher. The method is based on the sensitivity of intramolecular vibrations (IMV) of a molecular impurity to the presence of lattice defects in the nearest heigbourhood of the molecular ion. The method is restricted by the possibility to detect directly only defects interacting with the molecular impurity used as a detector. The migration of anion vacancies in KBr crystals in the temperature range from the room temperature to the melting point is studied in detail with sulphate ion. The IMV of the sulphate ions are determined from IR absorption spectra. By assuming the leading role of only one microprocess in any observed macroprocess in a certain temperature region, the following energies have been determined: the migration activation energy of a single anion vacancy in unperturbated lattice-0.9 eV; the upper limit of the anion vacancy migration activation energy in the quenched crystal-1.4 eV; the lower limit of the thermal generation of anion vacancy in the annealed crystal-2.0 eV; the dissociation energy of the sulphate ion- anion vacancy complexes-2.3 eV; the disarrangement activation energy of the preliminary aligned sulphate ion-anion vacancy complexes-2.3 eV

70

On the mechanism of lyoluminescence in alkali halides  

International Nuclear Information System (INIS)

Lyoluminescence or irradiated alkali halides is explained as a process of recombination of electrons from F-centres with trapped holes on the surface of dissolving lattice. Explanations are also offered for the mechanisms of lyoluminescence in presence of luminol, T1+ ions and fluorescent dyes

71

Development of alkali halide-optics for high power-IR laser  

International Nuclear Information System (INIS)

In this work 'Development of Alkali Halide-Optics for High Power-IR Laser' we investigated the purification of sodiumchloride-, potassiumchloride- and potassiumbromide-raw materials. We succeeded to reduce the content of impurities like Cu, Pb, V, Cr, Mn, Fe, Co and Ni in these raw materials to the lower of ppb's by a Complex-Adsorption-Method (CAM). Crystals were grown from purified substances by 'Kyropoulos' method'. Windows were cur thereof, polished and measured by FTIR-spectroscopy. Analytical data showed, that the resulting crystals were of lower quality than the raw materials. Because of this fact crystal-growing-conditions have to undergo a special improvement. Alkali halide windows from other sources on the market had been tested. (orig.)

72

An overlap model for exchange-induction: application to alkali halides  

Science.gov (United States)

An existing method for estimating intermolecular exchange energies in weak Van der Waals interactions, based on the overlap between their ground-state charge densities, is extended to ionic interactions using the overlap between the polarised charge density of a negative ion and the ground-state charge density of surrounding positive ions. This enables the exchange-induction energy to be included in the model. One adjustable parameter for each ion pair is fitted to the dimer interaction energy. The prediction of in-crystal anion polarizabilities is excellent for the five alkali halides tested, and polarizabilities of anions in ionic dimers and trimers are reasonably well reproduced for lithium halides.

Wheatley, Richard J.

1998-09-01

73

Relaxation of the rocksalt (001) surface: Alkali halides, MgO, and PbS  

Science.gov (United States)

We evaluate the static relaxation of the (001) face of rocksalt-structured ionic crystals, using shell models. The results for moderately polarizable compounds, namely, the alkali halides and MgO, are in qualitative agreement with those of earlier calculations but overall somewhat smaller. PbS is treated as an example of highly polarizable substances close to an instability. The results for PbS show a larger and deeper penetrating relaxation than in the case of the alkali halides. Preliminary results for PbTe, which has a large (T-dependent) anion polarizability, show a precursor of a total crystal reconstruction. It is conjectured that in such cases the lowered symmetry at the surface can act as a trigger for a structural phase transition.

de Wette, F. W.; Kress, W.; Schröder, U.

1985-09-01

74

Oxoacidity scales of ionic solvents based on alkali metal halides  

International Nuclear Information System (INIS)

The relative acidity scales of the ionic melts on the basis of the halides of the alkali metals MIX (MI = Li-Cs; X = Cl-I) and alkaline earth metals MIIX2 (MII = Ca-Ba; X = Cl) are plotted with application of the method of the oxides solubility in the halides melts at the temperature of 600, 700 and 800 deg C. The regularities of the effect of the solvent composition on its acidic-basic properties and also on the acidic-basic reactions on its background are identified

75

A new fundamental hydrogen defect in alkali halides  

International Nuclear Information System (INIS)

Atom hydrogen in neutral (H0) and negative (H-) form on substitutional and interstitial lattice sites gives rise to well characterized model defects in alkali-halides (U,U1,U2,U3 centers), which have been extensively investigated in the past. When studying the photo-decomposition of OH- defects, a new configuration of atomic charged hidrogen was discovered, which can be produced in large quantities in the crystal and is apparently not connected to any other impurity. This new hidrogen defect does not show any pronounced electronic absorption, but displays a single sharp local mode band (at 1114cm-1 in KCl) with a perfect isotope shift. The defect can be produced by various UV or X-ray techniques in crystais doped with OH-, Sh- or H- defects. A detailed study of its formation kinetics at low temperature shows that it is primarily formed by the reaction of a mobile CI2- crowdion (H-center) with hidrogen defects

76

Interfacial tension in immiscible mixtures of alkali halides.  

Science.gov (United States)

The interfacial tension of the liquid-phase interface in seven immiscible reciprocal ternary mixtures of lithium fluoride with the following alkali halides: CsCl, KBr, RbBr, CsBr, KI, RbI, and CsI was measured using the cylinder weighing method over a wide temperature range. It was shown that for all mixtures the interfacial tension gradually decreases with growing temperature. The interfacial tension of the reciprocal ternary mixtures at a given temperature increases both with the alkali cation radius (K(+) < Rb(+) < Cs(+)) and with the radius of the halogen anion (Cl(-) < Br(-) < I(-)). PMID:20094678

Lockett, Vera; Rukavishnikova, Irina V; Stepanov, Victor P; Tkachev, Nikolai K

2010-02-01

77

Anharmonicity of the Debye-Waller factor in alkali halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using high intensity (${\\sim}70$ Ci) $\\sp{183}$Ta Mossbauer sources, we have measured the elastic scattering fraction values, $\\cal F$, and the relative integrated scattering intensities for several (nnn) and (h00) Bragg reflections of three alkali halides: sodium chloride, potassium chloride, and potassium bromide. The experiments were done as a function of temperature from 85 K to 900 K. The $\\cal F$ values were found by Mossbauer line-shape studies (1) and were used to correct the measured...

Shepard, Carmen Kay

1996-01-01

78

Electronic structure, lattice energies and Born exponents for alkali halides from first principles  

Directory of Open Access Journals (Sweden)

Full Text Available First principles calculations based on DFT have been performed on crystals of halides (X = F, Cl, Br and I of alkali metals (M = Li, Na, K, Rb and Cs. The calculated lattice energies (U0 are in good agreement with the experimental lattice enthalpies. A new exact formalism is proposed to determine the Born exponent (n for ionic solids. The values of the Born exponent calculated through this ab-initio technique is in good agreement with previous empirically derived results. Band Structure calculations reveal that these compounds are wide-gap insulators that explains their optical transparency. Projected density of states (PDOS calculations reveal that alkali halides with small cations and large anions, have small band gaps due to charge transfer from X ? M. This explains the onset of covalency in ionic solids, which is popularly known as the Fajans Rule.

C. R. Gopikrishnan

2012-03-01

79

High Pressure phase transition in some alkali halides using interatomic potential model  

International Nuclear Information System (INIS)

We have predicted the phase transition pressure in some alkali halides using an interatomic potential approach based on rigid ion model.The phase transition pressures(28.69 and 2.4 GPa) obtained by us for two alkali halides (NaCl and KCl ) are in closer agreement with their corresponding experimental data(29.0 and 2.0 GPa).This potential is promising with respect to prediction of the phase transition pressure of other alkali halides as well

80

Ionic sizes and strain derivative of electronic susceptibility in alkali halides  

Science.gov (United States)

An analysis of the electronic susceptibility of alkali halides related to ionic sizes is performed. The model based on the decomposition of the optical susceptibility into contributions of valence and core electrons is applied to obtain ionic radii, photoelastic constants p11 + 2 p12, the strain derivative of electronic dieletric constants, and changes in the refractive index with density and strain polarizability constants. An attempt is made to predict p11 and p12 in some alkali halides. The relationship between the ratio of electronic polarizabilities of alkali and halide ions and the ratio of cation to anion radii {r c}/{r a} is observed. The photoelastic and strain polarizability constants are found to be nearly linearly dependent on {r c}/{r a}. Correlations between crystal ionicity and effective ionic charge and their dependences on {r c}/{r a} are discussed. The approach relates photoelastic constants to the volume dependence of the effective ionic charge. The contribution of second- neighbour interactions is considered and the failure of the Cauchy relationis correlated with {r c}/{r a}.

Kucharczyk, W.

1991-07-01

 
 
 
 
81

Color-center and radiation-damage effects in alkali halides irradiated to high particle fluence  

International Nuclear Information System (INIS)

Alkali metal halide crystals were examined photographically after bombardment to a high dose (greater than 1016/cm2) of high-energy (typically 1.5-MeV) protons. The crystals showed a minimum in the F- and M-center profile at the end of the proton range immediately after irradiation. During storage in the dark at room temperature, this minimum became deeper and a peak of absorption appeared within the minimum. These effects were explained using reasonable physical processes involving color-center diffusion and aggregation and energy-loss-radiation-damage correlations. (Diss. Abstr. Int., B)

82

Surface topography dependent desorption of alkali halides  

Science.gov (United States)

Electron-stimulated desorption of the (100)KBr surface has been investigated in vacuum with noncontact atomic force microscopy and mass spectroscopy. It has been found that both desorption components (K and Br) show oscillatory dependence on the electron dose with the oscillation amplitude decaying gradually. These results correspond with periodically varying, as a result of a layer-by-layer desorption, surface topography. It is proposed that the surface terrace edges act as traps for excited F centers diffusing in the crystal. The oscillating density of terrace edges varies surface recombination/reflection rates for the F centers and modulates the balance between surface and bulk deexcitation of the crystal. PMID:10978122

Such; Kolodziej; Czuba; Piatkowski; Struski; Krok; Szymonski

2000-09-18

83

Debye-Waller factors of alkali halides  

International Nuclear Information System (INIS)

Using very-high-intensity (?70 Ci) 183Ta Moessbauer sources, we have measured the Debye-Waller factors (DWF close-quote s) of sodium chloride, potassium chloride, and potassium bromide single crystals for several of the (h00) and (nnn) Bragg reflections. We have used an approach which properly accounts for thermal expansion over the temperature range of our experiment, from 90 K to 900 K, about 100 K below the melting point of our crystals. We have found that a procedure used to analyze data by earlier workers leads to incorrect parameters in the Debye-Waller factor exponent, and our procedure does not require empirical parameters to account for the effects of thermal expansion. Additionally, we find three items of significance. Contrary to earlier results, we observe that the cations and the anions have identical DWF close-quote s in NaCl and also in KBr. We observe terms in the expansion of the DWF exponential which are quartic in the scattering wave vector rvec Q in NaCl and KCl, with some evidence for a Q4 term in KBr. The size of the Q4 contribution is reported and varies with the direction of momentum transfer. We also observe that the Debye temperature and the coefficient of the anharmonic Q2 term also vary with the direction of momentum transfer. We believe our data are the definitive evidence for a nonspherical thermal cloud in a cubic crystal; the ions have a larger amplitude of oscillation in the [h00] directionde of oscillation in the [h00] direction than in the [nnn] direction, contrary to the commonly held view of crystallographers that the most general form of the mean-square thermal motion is of an ellipsoid shape. copyright 1998 The American Physical Society

84

Photoelectron spectroscopy of alkali halide clusters with excess electrons  

International Nuclear Information System (INIS)

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

85

Structure and Bonding in Small Neutral Alkali-Halide Clusters  

CERN Document Server

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...

Aguado, A; López, J M; Alonso, J A

1997-01-01

86

Alkali halide clusters produced by fast ion impact  

International Nuclear Information System (INIS)

The most abundant geometries and relative stabilities of alkali halide clusters with a (XY)n0 configuration (e.g., LiF, NaCl, KBr) are described. Five main series were obtained: linear, cyclic, cubic, arc strips and nanotubes. The stability analysis shows that higher members are likely to be formed from the lower member of the same series and/or from two building blocks (n = 1, 2). The energy analysis (D-plot) indicates that the most compact ones (e.g., cubic and nanotubes) present higher stability when compared to the linear, cyclic and arc strip structures; moreover, relative stability between the cubic and nanotube series varies with the cluster size.

87

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

Energy Technology Data Exchange (ETDEWEB)

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)

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

88

Microscopic model for the two-phonon Raman spectra of alkali halides  

Science.gov (United States)

The second-order Raman-scattering (SORS) cross section of alkali halides has been evaluated by using the Buckingham expansion for the induced polarizability. This ab initio approach leads to a microscopic expression of the SORS cross section without free parameters. The first two nonzero contributions of the expansion, namely, the dipole-induced dipole (DID) coming from the first-order dressed polarizability and the BTQ (second-dipole hyperpolarizability × dipole propagator × effective charge) coming from the second-dipole-quadrupole polarizability, have been considered. The short-range contribution to the induced polarizability coming from the electronic overlap has not been included in the present work. The SORS spectra are expressed in terms of the dynamical quantities of the crystal (eigenvectors and eigenfrequencies) and in terms of some bare ionic susceptibilities, namely, the ions' bare polarizabilities ?+ and ?- and the second-dipole-quadrupole bare polarizabilities B+ and B-. As an example the results are shown in the case of KBr. Considerations on the long-range nature of the DID spectrum and on the short-range nature of the BTQ spectrum are made. The relative weights of the two contributions to the SORS in the whole class of alkali halides are also discussed.

Gallo, P.; Mazzacurati, V.; Ruocco, G.; Signorelli, G.

1993-05-01

89

Desorption and surface topography changes induced by He+ ion bombardment of alkali halides  

International Nuclear Information System (INIS)

Desorption fluxes from alkali halide (RbI, KBr) crystals under 5 keV He+ bombardment and the corresponding surface topography evolution were investigated by means of quadruple mass spectroscopy (QMS) and dynamic force microscopy (DFM) in UHV. Although, for the energy range of He+ ions used, desorption of alkali halides occurs predominantly via electronic processes, there are significant differences between the ion-stimulated desorption (ISD) and the electron-stimulated desorption (ESD). The latter proceeds in a layer-by-layer mode and, as a result, oscillating desorption fluxes are observed. For ISD the DFM images show that the surface erosion does not follow the layer-by-layer scheme and no oscillation in desorption fluxes are found but they exhibit monotonic decrease to some saturation level. We suggest that these differences between electron- and ion-stimulated desorption are caused by ballistic processes disturbing the perfect lattice and introducing defects in the bulk and at the surface. Such lattice defects can act as recombination centres for diffusing Frenkel defects and inhibit the desorption process. Additionally, projectiles colliding violently with top-layer ions introduce additional nucleation centres for vacancies on the surface which lead to the surface erosion in the multi-layer mode

90

Analysis of the repulsive hardness parameters in alkali hydrides, silver halides, and alkaline-earth fluorides  

International Nuclear Information System (INIS)

The validity of an additivity rule is demonstrated for the repulsive hardness parameters in three crystal families viz. alkali hydrides, silver halides, and alkaline earth fluorides. The additivity rule provides a direct method of determining the repulsive hardness parameters for individual ions and thereby reduces the number of parameters considerably. Using the repulsive hardness parameters for individual ions derived from the overlap integrals an investigation is made on the crystal binding of LiH, NaH, KH, RbH, CsH, AgCl, AgBr, CaF2, SrF2, and BaF2. The interionic force model used here takes into account the long-range electrostatic interactions, three-body forces, short-range repulsive, and van der Waals interactions. The cohesive energy and the pressure derivative of bulk modulus are calculated. The results are found to compare well with experimental data. (author)

91

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

International Nuclear Information System (INIS)

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

92

Photostimulated luminescence and its fading characteristics in alkali halide phosphors  

Energy Technology Data Exchange (ETDEWEB)

Photostimulated luminescence (PSL) phenomenon is based on the presence of electron and/or hole traps and luminescence centers in storage phosphor materials. Recently, a new system of computerized digital radiography utilizing this phenomenon has been developed. This system consists of a superior imaging plate (IP) with a photostimulable Eu-doped BAFBr (BaFBr:Eu) phosphor-powder-screened IP or Tl-doped RbBr (RbBr:Tl) film-type IP and a computer. There is an urgent need for the development of new materials with good fading characteristics, because commercially-available IP using BaFBr:Eu or RbBr:Tl phosphor has relatively poor fading characteristics of the x-ray image. It was found that the x-ray-irradiated KBr:Eu phosphor exhibits an intense PSL, a good linearity between the PSL intensity and x-ray irradiation dose and excellent fading characteristics of the PSL. This result strongly suggests that the KBr:Eu phosphor is useful as a novel candidate as a storage phosphor material for the medical imaging utilizing the PSL phenomenon. It was also found that the PSL characteristics, especially the fading characteristics, in KCl{sub x}Br{sub 1-x}:Eu alkali halide phosphors is affected by crystallinity of the phosphor, Eu concentrations and ambient temperature and humidity. (S.Y.)

Douguchi, Yoshiteru; Sato, Tomoyuki; Miyazaki, Makoto; Imai, Atsushi; Kusano, Eiji; Kinabara, Akira; Nanto, Hidehito [Industrial Research Inst. of Ishikawa, Kanazawa (Japan)

1998-08-01

93

Ion Segregation and Deliquescence of Alkali Halide Nanocrystals on SiO2  

Energy Technology Data Exchange (ETDEWEB)

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.

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

2009-08-11

94

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

International Nuclear Information System (INIS)

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 alternatively from different accelerators into a common scattering chamber. Details are given of the beam transport and scattering chamber, the latter being designed to make in-beam studies of different modes of radiation damage in the target material. An on-line experimental control and data acquisition system with an IBM 1800 computer is used. Experimental studies are described of simultaneous detection of backscattered helium ions, X-rays and optical absorption in single-crystal alkali halide samples, performed during continuous irradiation by a 1 MeV helium beam, as well as of backscattered 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

95

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

CERN Document Server

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

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

2006-01-01

96

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

CERN Document Server

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

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

2005-01-01

97

Deformation-induced phonon scattering by debris defects in alkali halides  

Energy Technology Data Exchange (ETDEWEB)

A number of investigations have shown that the thermal conductivity of alkali halide crystals is markedly affected by crystalline defects, chiefly in the low temperature region, say below around 10 K. The effects are very prominent after plastic deformation, where the conductivity is reduced by more than a factor of 10 after deformation by several percent already. Albeit a considerable amount of data and respective models have been elaborated, the correspondence between models and the body of experimental results still needs improvement, especially in the temperature range between around 1 and 5 K. As will be shown for the case of NaCl, where most of the experimental results exist, a satisfactory description of the thermal conductivity properties can be obtained when relying on, instead of dislocations and/or vacancy defects, a debris defect as suggested by transmission electron microscopy.

Strunk, H P; Wasserbaech, W, E-mail: strunk@mf.mpg.d [Institute of Metal Science, University of Stuttgart, Heisenbergstr. 3, 70569 Stuttgart (Germany)

2010-11-01

98

Deformation-induced phonon scattering by debris defects in alkali halides  

International Nuclear Information System (INIS)

A number of investigations have shown that the thermal conductivity of alkali halide crystals is markedly affected by crystalline defects, chiefly in the low temperature region, say below around 10 K. The effects are very prominent after plastic deformation, where the conductivity is reduced by more than a factor of 10 after deformation by several percent already. Albeit a considerable amount of data and respective models have been elaborated, the correspondence between models and the body of experimental results still needs improvement, especially in the temperature range between around 1 and 5 K. As will be shown for the case of NaCl, where most of the experimental results exist, a satisfactory description of the thermal conductivity properties can be obtained when relying on, instead of dislocations and/or vacancy defects, a debris defect as suggested by transmission electron microscopy.

99

On the origin of atomistic mechanism of rapid diffusion in alkali halide nanoclusters  

Science.gov (United States)

To elucidate the atomistic diffusion mechanism responsible for the rapid diffusion in alkali halide nano particles, called Spontaneous Mixing, we execute molecular dynamics simulations with empirical models for KCl-KBr, NaCl-NaBr, RbCl-RbBr and KBr-KI. We successfully reproduce essential features of the rapid diffusion phenomenon. It is numerically confirmed that the rate of the diffusion clearly depends on the size and temperature of the clusters, which is consistent with experiments. A quite conspicuous feature is that the surface melting and collective motions of ions are inhibited in alkali halide clusters. This result indicates that the Surface Peeling Mechanism, which is responsible for the spontaneous alloying of binary metals, does not play a dominant role for the spontaneous mixing in alkali halide nanoclusters. Detailed analysis of atomic motion inside the clusters reveals that the Vacancy Mechanism is the most important mechanism for the rapid diffusion in alkali halide clusters. This is also confirmed by evaluation of the vacancy formation energy: the formation energy notably decreases with the cluster size, which makes vacancy formation easier and diffusion more rapid in small alkali halide clusters.

Niiyama, Tomoaki; Sawada, Shin-ichi Sawada; Ikeda, Kensuke S.; Shimizu, Yasushi

2014-04-01

100

Molecular beam scattering from clean surfaces of alkali halides  

International Nuclear Information System (INIS)

Molecular beam scattering of light gases from in situ cleaved alkali halide surfaces has been studied as a means of developing molecular beam scattering as a surface characterization tool and as a means of obtaining information about the gas atom-solid surface potential interaction. For 4He scattering from LiF carried out under improved resolution the main results are: (1) there are four bound states in the surface potential well, as energies of -5.8, -2.2, -0.6 and -0.1 MeV. (2) Most of the structure designated as ''fine structure'' is due either to transitions to these four levels via various small reciprocal lattice vectors or to the opening of diffraction channels. (3) The transitions involving the (01) and (0 anti 1) reciprocal lattice vectors (i.e., the ones nearly perpendicular to the incident wavevector) are strong; as much as 85 percent of the specular intensity may be removed. Transitions via the other small reciprocal lattice vectors are much weaker. (4) The widths of the lines are consistent with the velocity distribution, which has a half-width of about 2 percent. (5) The observed energies agree fairly well with those calculated for a zeta-function potential, but are not consistent with a Morse potential. The preliminary results for 4He/NaF scattering are that there are three bound-states in the surface potential well and are quite similar to the LiF results. These energies are -5.0, -1.9, and -0.5 MeV. 4He/NaF selective ad -0.5 MeV. 4He/NaF selective adsorption also shows ''fine structure'' and a more detailed analysis is called for here

 
 
 
 
101

Evidence for the direct ejection of clusters from alkali-halides during laser vaporization  

International Nuclear Information System (INIS)

We have studied the formation of clusters of alkali halides during laser vaporization. Measurements of the abundances of cluster ions produced by several different source configurations indicate that clusters are ejected directly from the source sample and do not necessarily grow from an atomic or molecular vapor. Using samples consisting of mixed alkali halide powders, we have found that unalloyed clusters are easily produced in a source that prevents growth from occurring after the cluster leave the sample surface. Melting the sample or encouraging growth after vaporization lead to the production of alloyed cluster species. We also obtain information about the relative binding energies for substituted halogen ions bound to alkali halide clusters. (orig.)

102

Interaction of soft x-ray photons with free alkali-halide molecular clusters  

International Nuclear Information System (INIS)

Alkali-halide molecular clusters were formed from the vaporized molecules in collisions with an intense beam of argon clusters. Photoionization of the alkali-halide clusters as the result of interaction with x-ray radiation has been utilized in a photoelectron spectroscopy study of cluster bonding mechanisms. The changes in the energy structure due to the transformation from molecules to the solid salt were observed both in the inner and outer shells of constituent elements (metal and halogen) and were used to deduce the geometric structure of the clusters in question.

103

Interaction of soft x-ray photons with free alkali-halide molecular clusters  

Science.gov (United States)

Alkali-halide molecular clusters were formed from the vaporized molecules in collisions with an intense beam of argon clusters. Photoionization of the alkali-halide clusters as the result of interaction with x-ray radiation has been utilized in a photoelectron spectroscopy study of cluster bonding mechanisms. The changes in the energy structure due to the transformation from molecules to the solid salt were observed both in the inner and outer shells of constituent elements (metal and halogen) and were used to deduce the geometric structure of the clusters in question.

Zhang, Chaofan; Andersson, Tomas; Huttula, Marko; Mikkelä, Mikko-Heikki; Anin, Dmitri; Tchaplyguine, Maxim; Öhrwall, Gunnar; Svensson, Svante; Björneholm, Olle

2012-11-01

104

Experimental and theoretical studies of the structure of alkali halide clusters  

International Nuclear Information System (INIS)

We have investigated the structures and properties of alkali halide cluster ions produced by laser vaporization of solid samples. In many alkali halide cluster ions, we observe the appearances of bulk-like characteristics even at sub-nanometer sizes: fcc crystalline structures (including surface terraces), ionic binding, and a susceptibility to common bulk defects such as F and H color-centers. To understand the origins of cluster structures, we have made calculations of ground state energetics, high-temperature molecular dynamics, and the electronic structure of clusters having excess electrons. (orig.)

105

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

International Nuclear Information System (INIS)

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

106

Relationship between electric conductivity, self-diffusion coefficients and the ionic composition of molten alkali metal halides  

International Nuclear Information System (INIS)

Relationships connecting electroconductivity and self-diffusion coefficients of elementary components of molten (1000-1100 deg C) alkali metal halides (specifically Cs halides) with their ionic composition are proposed. Self-diffusion coefficients and elementary component transfer numbers calculated on the basis of autocomplex composition model of molten alkali metal halides from their electrocunductivity test values are shown to be in better agreement with the experimentally determined ones than those found in the assumption of the elementary composition of these melts

107

Energy distributions of atoms sputtered from alkali halides by 540 eV electrons, Ch.1  

International Nuclear Information System (INIS)

The emission of halogen and alkali atoms, occurring under bombardment of alkali halides with electrons has been investigated. The electron energy was 540 eV and the temperature of the target was varied between room temperature and 4000C. The energy distribution of the emitted neutral particles was measured with a time of flight method. It was found that either diffusing interstitial halogen atoms or moving holes dominate the sputtering process above 2000C. Below 1500C alkali halides with lattice parameters s/d >= 0.33 show emission of non-thermal halogen atoms. s is the interionic space between two halogen ions in a direction and d is the diameter of a halogen atom. In general the energy distribution of the alkali and halogen atoms is thermal above 2000C, but not Maxwellian. (Auth.)

108

Electron density in the alkali halide crystals  

International Nuclear Information System (INIS)

Structure factors at room temperature are computed for LiF, NaF, NaCl and KCl by means of theoretical ionic form factors and theoretical Debye-Waller factors. The values obtained are compared with the best available experimental data. For LiF, KCl and NaF - for which good experimental data are available - there is generally very good agreement, with only a few sizeable discrepancies for NaF that can be attributed to deficiencies of the experimental data. It is concluded that there is no apparent need to question the validity of the Debye-Waller theory as recently proposed in the literature. (orig.)

109

Electron localization and the nonmetal-metal transition in alkali-alkali halide solutions  

International Nuclear Information System (INIS)

We evaluate and extend an earlier proposal for a microscopic theory of the nonmetal-to-metal (NM-M) transition which occurs on dissolving an alkali metal in its molten halide. The transition is viewed as involving a balance between the free energy gain from the binding of valence electrons into localization centres and the excess free energy of the ionic assembly screened by the electrons. Using parameters estimated for solutions of potassium in potassium chloride and assuming that the elementary process of electronic trapping is the formation of F-centre-like clusters, Thomas-Fermi screening by metallic electrons is shown to lead to a very sharp NM-M transition at a concentration in the range of 25-30% added metal. Thermally activated hopping of the localized electrons and the evolution of the localization centres with composition are next crudely taken into account by allowing for an additional contribution to the inverse screening length, which is estimated from the electronic localization length. This is shown to lead to a progressive break-up of the localization clusters, accelerating into a NM-M transition in the same concentration range. This simplified theoretical scenario is consistent with the available experimental evidence. (author). 18 refs, 5 figs

110

Lattice parameters of alkali halides by the Simons-Parr-Finlan technique  

International Nuclear Information System (INIS)

The lattice parameters of the twenty alkali halides are evaluated by using the Rittner potential through the Simons-Parr-Finlan technique. It is found that the values obtained are better than those obtained by earlier methods and further dispense the dependence of the potential on arbitrary and sensitive exponents encountered in the Woodcock potential. (author)

111

Use of alkali halide clusters in a gas-jet recoil-transport system  

International Nuclear Information System (INIS)

Transport yields for nuclear reaction products in a gas-jet recoil-transport system using nitrogen loaded with alkali halide clusters as transport medium have been measured. Yields of 60 to 70% were achieved even over extended operation periods. (author)

112

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

International Nuclear Information System (INIS)

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

113

On the change of polarization of positive muons in alkali halides  

International Nuclear Information System (INIS)

Positive muons implanted in nonconducting solids form with high probability hydrogenlike muonium atoms (?+e-) with properties similar to those of U2-centers. The influence of superhyperfine interactions with neighbor nuclei on the evolution of the polarization of the muon is investigated theoretically. The resulting muon polarization in longitudinal magnetic fields is calculated for muonic U2-centers in some alkali halides. (orig.)

114

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

Energy Technology Data Exchange (ETDEWEB)

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.

Klick, David Ira

1977-01-01

115

The role of halide ions on the electrochemical behaviour of iron in alkali solutions  

Science.gov (United States)

Active dissolution and passivation of transition metals in alkali solutions is of technological importance in batteries. The performance of alkaline batteries is decided by the presence of halides as they influence passivation. Cyclic voltammetric studies were carried out on iron in different sodium hydroxide solutions in presence of halides. In alkali solutions iron formed hydroxo complexes and their polymers in the interfacial diffusion layer. With progress of time they formed a cation selective layer. The diffusion layer turned into bipolar ion selective layer consisted of halides, a selective inner sublayer to the metal side and cation selective outer layer to the solution side. At very high anodic potentials, dehydration and deprotonation led to the conversion of salt layer into an oxide.

Begum, S. Nathira; Muralidharan, V. S.; Basha, C. Ahmed

2008-02-01

116

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  

CERN Document Server

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.

Georgiev, Mladen

2008-01-01

117

Reactions between cold methyl halide molecules and alkali-metal atoms  

International Nuclear Information System (INIS)

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

118

The ultrasonic speed as a guide of the concentration of alkali-halides ions in water  

International Nuclear Information System (INIS)

The speed of an ultrasonic wave has been examined in many alkali-halides water solutions at 35 deg. C and different concentrations. The speed seems to be subject to substantial changes with changing the mass of the negative ions rather than the positive ions. The results indicate that the negative ion masses affect the water bulk modulus in a nonlinear way and each mass has its own characteristic effects. (author). 7 refs, 4 figs, 1 tab

119

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

International Nuclear Information System (INIS)

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

120

A new contribution to the synthesis and characterization of binary/ternary alkali- and alkaline earth halides as well as individual hydrates  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work presents the synthesis and characterization of binary and ternary alkali and alkali earth metal halides in the framework of the so-called "rational synthesis planning" in the solid state chemistry. Furthermore, double salts of selected alkali-metal halides and magnesium halides on the basis of the carnallite structure are examined. In the first part of the work, a newly developed ?Low-Temperature Deposition? technique, which consists on the deposition of gaseous phase compon...

Liebold Ribeiro, Yvonne

2008-01-01

 
 
 
 
121

Thermodynamic reactivity, growth and characterization of mercurous halide crystals  

Science.gov (United States)

Thermodynamic calculations were carried out for the Hg-X-O system (X = Cl, Br, I) to identify the potential sources of contamination and relative stability of oxides and oxy-halide phases. The effect of excess mercury vapor pressure on the optical quality of mercurous halide crystal was studied by growing several mercurous chloride crystals from mercury-rich composition. The optical quality of crystals was examined by birefringence interferometry and laser scattering studies. Crystals grown in slightly mercury-rich composition showed improved optical quality relative to stoichiometric crystals.

Singh, N. B.; Gottlieb, M.; Henningsen, T.; Hopkins, R. H.; Mazelsky, R.; Singh, M.; Glicksman, M. E.; Paradies, C.

1992-01-01

122

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

International Nuclear Information System (INIS)

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

123

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

International Nuclear Information System (INIS)

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

124

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

International Nuclear Information System (INIS)

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

125

Features of radiation processes in ammonium halide crystals with rare-earth impurity  

International Nuclear Information System (INIS)

Full text: The ammonium halide crystals (NH4X, X-halogen) are a touchstone for various theories of phase transition of type the order-disorder. Being analogues alkali halide crystals, they sharply differ from them processes radiation-induced defects because of presence complex cation NH4+. In the present work the review of our researches on radiation processes in NH4X with an impurity bivalent rare-earth ions (TR2+) is resulted- Yb2+, Eu2+, Pr2+, Nd2+, Dy2+. At an irradiation in X-ray quanta NH4X-TR2+ in spectra of absorption there is a induced band-doped the band connected to radiation defects. As well as in alkali halide crystals, there are HZ-centers representing impurity-vacancy a dipole, stabilizing interstitial, and also - VKZ -centers. As against alkali halide crystals the F-centers in ammonium halide crystals are not found out neither in optical spectra, nor in spectra electron paramagnetic resonance. Because of reaction NH4++ e?NH40?NH30+H0, in ammonium halide crystals there are centers of type TR2+NH30. In X-ray luminescence spectra the luminescence band connected to transition radiation in molecules TR2+NH30. In absorption and photoconductivity spectra the paintnd photoconductivity spectra the painting centers of type TR+, luminescence Yb+Vc- are shown and the isolated centers Yb+ is not observed even at the lowest temperatures. At transition phase the order -disorder spectra of TR2+-ions in ammonium halide crystals and the radiation defects connected to them in steps change. These changes are connected to change of static interaction of an impurity with a field of ligands, parameters of electron-phonon interactions, probabilities radiationless transitions.On phase transition in spectra of thermoluminescence is revealed and the radiation-induced luminescence possessing unusual properties - is investigated by independence of his occurrence of an electronic structure of an impurity: having the recombination nature with identical energy of activation for all TR2+. The spectral structure of peak of thermoluminescence on phase transition contains two radiation bands - short-wave and long-wave. Short-wave bands are caused by transitions from the mixed 4fn-15d configuration in the basic condition 4fn. Long-wave bands are connected to radiating transitions TR2+NH30. At research of dependence of the reserved energy from a dose of an irradiation on the transition phase two stages of accumulation of defects -fast and slow -are found out. Presence slow components is connected to action of the channel of repeated capture of carriers of a charge. In work all features of radiating processes in ammonium halide crystals with an impurity bivalent rare-earth are discussed

126

Sublattice identification in scanning force microscopy on alkali halide surfaces  

International Nuclear Information System (INIS)

We propose and apply to the KBr(001) surface a new procedure for species recognition in scanning force microscopy (SFM) of ionic crystal surfaces which show a high symmetry of the charge arrangement. The method is based on a comparison between atomistic simulations and site-specific frequency versus distance measurements. First, by taking the difference of force-distance curves extracted at a few judiciously chosen surface sites we eliminate site-independent long-range forces. The obtained short-range force differences are then compared with calculated ones assuming plausible tip apex models. This procedure allows for the first time identification of the tip apex polarity and of the positive and negative sublattices in SFM images of the (001) cleavage surface of an ionic crystal with the rock salt structure

127

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

International Nuclear Information System (INIS)

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

128

Branching Transport Model of Alkali-Halide Scintillators  

CERN Document Server

We measure the time dependence of the scintillator light-emission pulses in NaI(Tl) crystals at different temperatures, after activation by gamma rays. We confirm that there are two main nonexponential components to the time decay and find that their amplitude ratio shows Arrhenius temperature dependence. We explain these nonexponential components as arising from two competing mechanisms of carrier transport to the Tl activation levels. The total light output of the NaI(Tl) detectors shows a linear temperature dependence explained by our model.

Alexandrov, B S; Littlewood, P B

2007-01-01

129

Thermoluminescence in alkali halides irradiated at 80K  

International Nuclear Information System (INIS)

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

130

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-01-28

131

Nanometer-scale patterning of alkali halide surfaces by ion bombardment  

International Nuclear Information System (INIS)

Structural properties of alkali halide surfaces (KBr, KI, and RbI) have been modified by low energy Ar+ ion beam bombardment. The morphology developed on the irradiated surfaces was investigated by the atomic-force microscopy (contact mode) under UHV conditions. The results indicate that for the incidence angles between 30o and 40o a periodic ripple morphology is developed with the ripple vector parallel to the beam direction, whereas for the angles larger than 60o the vector is perpendicular to the beam. The average surface roughness and the wavelength of the ion-induced periodic structures were measured as a function of the ion fluence (1013-1018 ions/cm2), the beam energy (1-5 keV), and the sample temperature (from 300 K to 600 K). The results are explained in terms of a new atomic-scale model taking into account the fact that ion sputtering of alkali halides in the investigated energy range is dominated by electronic processes rather than ballistic collisions.

132

Nanometer-scale patterning of alkali halide surfaces by ion bombardment  

Science.gov (United States)

Structural properties of alkali halide surfaces (KBr, KI, and RbI) have been modified by low energy Ar + ion beam bombardment. The morphology developed on the irradiated surfaces was investigated by the atomic-force microscopy (contact mode) under UHV conditions. The results indicate that for the incidence angles between 30° and 40° a periodic ripple morphology is developed with the ripple vector parallel to the beam direction, whereas for the angles larger than 60° the vector is perpendicular to the beam. The average surface roughness and the wavelength of the ion-induced periodic structures were measured as a function of the ion fluence (10 13-10 18 ions/cm 2), the beam energy (1-5 keV), and the sample temperature (from 300 K to 600 K). The results are explained in terms of a new atomic-scale model taking into account the fact that ion sputtering of alkali halides in the investigated energy range is dominated by electronic processes rather than ballistic collisions.

Saeed, S. R.; Sinha, O. P.; Krok, F.; Szymonski, M.

2008-12-01

133

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

CERN Document Server

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

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

2012-01-01

134

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

International Nuclear Information System (INIS)

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

135

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Gobetto, Roberto; Chierotti, Michele Remo

2010-01-01

136

Chemical effects induced by dissolving. gamma. -irradiated alkali halides in aqueous nitrate, permanganate and chromate solutions  

Energy Technology Data Exchange (ETDEWEB)

Dissolution of ..gamma..-irradiated alkali halides in aqueous solutions of sodium nitrate, potassium permanganate and potassium chromate at neutral pH induces chemical changes leading to the formation of NO/sub 2//sup -/ in nitrate, Mn(IV) and Cr(III) species in permanganate and chromate solutions, respectively. Further, the studies on nitrate and permanganate systems show that the amount of NO/sub 2//sup -/ and Mn(IV) formed grows by increasing the dose of ..gamma..-irradiation of the salt and the amount of irradiated salt. Moreover, the extent of chemical changes effected by irradiated chlorides has been found to be more than that of bromides. The mesh size of the irradiated salt and the presence of scavengers like I/sup -/ and methanol in the system, affects the yield of NO/sub 2//sup -/.

Phansalkar, V.K.; Bapat, L.; Ravishankar, D. (Poona Univ. (India). Dept. of Chemistry)

1982-02-25

137

Investigation into oxidizing products of radiolysis of alkali metal halide melts  

International Nuclear Information System (INIS)

The investigation results of properties of GITA2- oxidizing products by the method of pulse radiolysis are given. The installation of pulse radiolysis with linear electron accelerator U-12 (electron energy 5 MeV, pulse current up to 0.2 A, pulse duration 2.3 mks) is investigated. Optical spectra of radiolysis oxidizing componenets of alkali metals halide melts - molecular anion-radicals GITA2- - are similar to the spectra of the corresponding particles in aqueous solutions. The rate constants of the GITA2- disappearance, which takes place mainly in the reaction of GITA2- with reduced form of cation are measured. Contribution of relative slow reaction of the GITA2- disproportionation increases in the presence of cations of alkaline-earth metals at the expense of rapid disproportionation of their reduced form, that results in the observed decrease of the GITA2- disappearance rate and increase of molecular halogen yield

138

Ground-state properties and optical excitations of a solvated electron in molten alkali halides  

International Nuclear Information System (INIS)

Properties of solvated electrons at high dilution in four molten alkali halides are investigated theoretically. A self-consistent evaluation of the bound ground state of the electron and of the surrounding liquid structure, already developed in a previous paper, is compared with the results of NMR hyperfine shifts and magnetic susceptibility measurements. The absorption bands associated with Franck-Condon 1s?2p and 1s?3p transitions are calculated and compared with the available data of optical absorption, with special emphasis on the detailed analysis by Yuh and Nachtrieb for molten CsCl. An instability of the excited states against ionic relaxation and the origin of a finite lifetime for the ground state are also discussed. Finally, the perturbation induced by the solvated electron in the fundamental absorption of the molten salt is estimated. (author)

139

Measurements of the electric dipole polarizabilities of the alkali halide dimers  

International Nuclear Information System (INIS)

We report the first measurements of the average electric dipole polarizabilities of five alkali halide dimers. A combined monomer--dimer molecular beam deflection pattern in an inhomogeneous electric field is subject to an appropriate computational analysis to extract the polarizabilities. A simple combination of bond and effective ionic models to estimate the polarizabilities gives reasonably good agreement with the measured values. The values are, in units of 10-24 cm2, (DF(2: 25.3 +- 3.2; (KDl)2: 28.6 +- 3.0; (RbCl)2:43.4 +- 4.2; (CsCl)2:36.6 +- 5.0; (CsF)2:21.2 +- 2.6

140

Determination Factor of Lattice Structure in Hexadecafluorovanadylphthalocyanine Epitaxially Grown on Alkali-Halide Substrates  

Science.gov (United States)

The epitaxial growth of fluorine-substituted vanadylphtalocyanine (FxVOPc; x = 15.4) on KBr, KI, and RbI was studied. The lattice structure of F15.4VOPc changes from (\\sqrt{10} × \\sqrt{10})R ± 27° to (\\sqrt{8} × \\sqrt{8})R0° as the lattice constants of the substrates increase. This sequence is different from that of other shuttlecock-shaped phthalocyanines(Pcs) such as VOPc, TiOPc and AlPcCl, in which the structure changes from (\\sqrt{10} × \\sqrt{10})R ± 27° to (3 × 3)R45°. The difference suggests that the orientation of molecules on the substrates plays an important role in the determination of the lattice structure of F15.4VOPc on alkali-halide substrates.

Uno, So-ichiro; Hoshi, Hajime; Takezoe, Hideo; Ishikawa, Ken

2005-03-01

 
 
 
 
141

Studies of Non-Proportionality in Alkali Halide and Strontium Iodide Scintillators Using SLYNCI  

Energy Technology Data Exchange (ETDEWEB)

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators [1-3]. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, L; Bizarri, G; Boatner, L; Cherepy, N J; Choong, W; Moses, W W; Payne, S A; Shah, K; Sheets, S; Sturm, B W

2009-05-05

142

Studies of non-proportionality in alkali halide and strontium iodide scintillators using SLYNCI  

Energy Technology Data Exchange (ETDEWEB)

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, Larry; Bizarri, Gregory; Boatner, Lynn; Cherepy, Nerine J.; Choong, Woon-Seng; Moses, William W.; Payne, Stephen A.; Shah, Kanai; Sheets, Steven; Sturm, Benjamin, W.

2010-10-14

143

Silicon Halide-alkali Metal Flames as a Source of Solar Grade Silicon  

Science.gov (United States)

A program is presented which was aimed at determining the feasibility of using high temperature reactions of alkali metals and silicon halides to produce low cost solar-grade silicon. Experiments are being conducted to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, and determine the effects of the reactants and/or products on materials of reactor construction. During the current reporting period, the results of heat release experiments were used to design and construct a new type of thick-wall graphite reactor to produce larger quantities of silicon. A reactor test facility was constructed. Material compatibility tests were performed for Na in contact with graphite and several coated graphites. All samples were rapidly degraded at T = 1200K, while samples retained structural strength at 1700K. Pyrolytic graphite coatings cracked and separated from substances in all cases.

Olson, D. B.; Gould, R. K.

1979-01-01

144

Dynamics of the defect-mediated desorption of alkali halide surfaces  

Science.gov (United States)

Dynamic processes leading to desorption of Rb and I atoms from the RbI (100) surface co-irradiated with 1 keV electrons and visible light (with a wavelength corresponding to the F-center absorption band) have been studied by means of mass-selected time-of-flight (TOF) spectroscopy. Depending on the sample temperature, substantial enhancement of the desorption yield as well as pronounced changes in the TOF spectra of the emitted atoms have been found. The TOF spectra of halogen atoms consist of two components: the thermal (which can be fitted with Maxwellian distribution) and the non-thermal one. The non-thermal peak is temperature-independent. There is no non-thermal component for alkali atoms. The comparison of TOF spectra for I atoms emitted from electron bombarded sample with and without simultaneous light irradiation indicates that the yield increase is caused by thermally desorbed atoms, while the non-thermal peak remains unchanged. Presented results confirm well the predictions of the theoretical model of desorption proposed earlier, known as the defect-mediated (F and H center) desorption of alkali halide.

Szymonski, M.; Droba, A.; Struski, P.; Krok, F.

2012-08-01

145

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

Science.gov (United States)

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

Lee, Min-Hong

146

Environmentally Benign Electrophilic Halogenation of Naphthalenes by H2O2Alkali Metal Halides in An Aqueous Cationic Micellar Media  

Directory of Open Access Journals (Sweden)

Full Text Available An efficient and greener protocol for the synthesis of 1-halo-naphthols by the action of hydrogen peroxide and alkali metal halides in aqueous micellar media is been described in the present work. This is an environmentally clean and safe procedure, which involved insitu generation of the active halogen in presence of alkali halides. Cationic surfactants such as cetyltrimethylammoniumbromide (CTAB and cetyltrimethylammoniumchloride (CTAC were found to facilitate efficiency of halogenation in aqueous media.

Kancharla Rajendar Reddy

2012-09-01

147

Calculation of electronic, structural, and vibrational properties in alkali halides using a density-functional method with localized densities  

Science.gov (United States)

A recently developed density-functional method based on localized densities is applied to calculate electronic, structural, and vibrational properties of 20 alkali halides with elements lithium through cesium and fluorine through iodine. Properties calculated include dissociation energy, lattice parameter, dielectric constant, elastic moduli, and phonon frequencies for the high-symmetry points of the Brillouin zone. Results are discussed and compared with experiment and other calculations.

Mei, W. N.; Boyer, L. L.; Mehl, M. J.; Ossowski, M. M.; Stokes, H. T.

2000-05-01

148

Three empirical correlations connecting gaseous cluster energies and solvation energies of alkali metal and halide ions.  

Science.gov (United States)

This paper gives two empirical correlations of formation Gibbs energies of gaseous clusters DeltaG(f)n as function of number of solvent molecules attached to the ion, n, and one correlation connecting the DeltaG(f)n for each individual cluster with the total DeltaG(o)hydr value. The experimental ratios of DeltaG(f)2/DeltaG(f)1 and DeltaG(f)3/DeltaG(f)1 for both alkali metal and halide ions are on average equal to 0.75 and 0.5, respectively. DeltaG(f)n values for n > or = 4 are correlated with n as DeltaG(f)n = [a/(n - 1)] DeltaG(f)1 + b DeltaG(f)1. For all available data on cluster energies and each individual cluster, the DeltaG(f)n's are straight-line functions of DeltaG(o)hydr. This well corresponds to another empirical rule stating that the Gibbs energies of transfer of ions between two solvents are often as well straight-line functions of DeltaG(o)(hydr) [J. Rais and T. Okada, J. Phys. Chem. A, 2000, 104, 7314]. Tentative models of the found behavior are proposed. A full data set of the gaseous cluster energies of formation based on inclusion of new, usually not used entries from the literature is provided. PMID:16760593

Rais, Jirí; Rais, Ji í; Okada, Tatsuhiro

2006-04-01

149

UV laser-induced desorption mechanism analyzed through two-layer alkali halide samples.  

Science.gov (United States)

Time of flight-mass spectrometry (TOF-MS) is used to analyze positive and negative desorbed ions generated by UV laser ablation of several alkali (X) halide (Y) salts. Most of the observed desorbed cluster ions have the structure (XY)(n)X(+) or (XY)(n)Y(-). Their desorption yields decrease as exp(-kn), where k approximately 2 for both series, suggesting that the neutral component (XY)(n) plays the dominant role in the desorption process. Mass spectrum measurements were performed for compound samples in which two salts (out of CsI, RbI, KBr, KCl and KI) are homogeneously mixed or disposed in two superposed layers. The detection of small new ion species and large cluster ions of the original salts supports the scenario that the uppermost layers are completely atomized while deep layers are emitted colder and fragmented: It is proposed that ns-pulsed laser induced desorption of ionic salts occurs via two sequential mechanisms: (1) ejection of cations and anions in the hot plume, followed by recombination into new cluster ions and (2) ejection of relatively cold preformed species originated from deep layers or from periphery of the irradiated region. PMID:18095386

Fernández-Lima, F A; Ponciano, C R; da Silveira, E F

2008-05-01

150

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

CERN Document Server

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

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

2005-01-01

151

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

International Nuclear Information System (INIS)

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

152

Anomalous behavior of the F19 motional relaxation in PbF2 doped with alkali halides  

International Nuclear Information System (INIS)

The F19 motional relaxation in PbF2 doped with alkali halides is studied as a function of temperature and frequency using nuclear magnetic resonance. The results of spin lattice relaxation rate measurements in the rotating frame and in the laboratory frame are reported and some striking anomalies are pointed out. It is proposed that these anomalies, not accountable by a straightforward application of the predictions of the Bloembergen-Purcell-Pound theory, arise from a non-uniform mobility of fluorine atoms around the impurities. A model that attempts to explain some of these discrepancies is discussed. (Auth.)

153

Aqueous alkali halide solutions: can osmotic coefficients be explained on the basis of the ionic sizes alone?  

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We use the AMSA, associative mean spherical theory of associative fluids, to study ion–ion interactions in explicit water. We model water molecules as hard spheres with four off-center square-well sites and ions as charged hard spheres with sticky sites that bind to water molecules or other ions. We consider alkali halide salts. The choice of model parameters is based on two premises: (i) The strength of the interaction between a monovalent ion and a water molecule is inversely proportional...

Kalyuzhnyi, Yu V.; Vlachy, Vojko; Dill, Ken A.

2010-01-01

154

The enhancement effect of the lattice barrier of nonradiative decay of excitons at non-axial stress of alkali halides  

International Nuclear Information System (INIS)

Full text: According to the modern notions the formation processes of radiation defects and the luminescence of alkali halides (AH) are explained by the non-radiative and radiative relaxations of electronic excitons through various excitonic slates. In AH the luminescence of self-trapped excitons (STE) at 80 K has a small quantum efficiency, but its intensity sharply increases at elastic deformation when in contrast to STE luminescence the formation process of radiation defects decreases. This effect was interpreted by the increasing of exciton self-trapping probability in the regular lattice sites wi:b radiative annihilation. The enhancement of the STE luminescence intensity due to possible decreasing of the non-radiative decay efficiency of excitons with creation of radiation detects can be estimated by registration of the temperature dependence of luminescence of deformed AH at 80 K. The basic regularity of the intrinsic luminescence of AH are studied in less detail than the impurity luminescence. For the first time we studied the influence of the elastic deformation on the temperature quenching of the STE emission. The STE luminescence can be considered as a local interaction of excitons with lattice vibrations in analogy with the impurity luminescence according to the Mott model. At such an approach by determining the dependence of X-luminescence on temperature can be judged on the probability of the non-radiative annihilation of excitons and from the slope of station of excitons and from the slope of straightforward lg(1/?-1)-(1/T) can be determined the activation energy required for the creation of primary radiation defects before (Q) and at (Q') elastic lattice deformation. Experimental results show that for crystals in which the luminescence efficiency close to unity (? ?1, CsI) or zero (??0.1, KCl) before and at the elastic deformation, the activation energies for non-radiative transitions of STE are not essentially different (Q?Q'). For other crystals (KI, RbI, KBr. NaCl) at their elastic deformation the activation energies for non-radiative annihilation of excitons are sharply increased (Q'>Q). The enhancement of the STE luminescence intensity in the presence of the elastic lattice deformation, caused by the decreasing of the non radiative decay efficiency of excitons or by the reduction of a barrier for exciton self-trapping or by the increasing of the probability of tunneling luminescence between the radiation defects are discussed

155

Universal scaling of potential energy functions describing intermolecular interactions. II. The halide-water and alkali metal-water interactions  

Science.gov (United States)

The scaled versions of the newly introduced [S. S. Xantheas and J. C. Werhahn, J. Chem. Phys. 141, 064117 (2014)] generalized forms of some popular potential energy functions (PEFs) describing intermolecular interactions - Mie, Lennard-Jones, Morse, and Buckingham exponential-6 - have been used to fit the ab initio relaxed approach paths and fixed approach paths for the halide-water, X-(H2O), X = F, Cl, Br, I, and alkali metal-water, M+(H2O), M = Li, Na, K, Rb, Cs, interactions. The generalized forms of those PEFs have an additional parameter with respect to the original forms and produce fits to the ab initio data that are between one and two orders of magnitude better in the ?2 than the original PEFs. They were found to describe both the long-range, minimum and repulsive wall of the respective potential energy surfaces quite accurately. Overall the 4-parameter extended Morse (eM) and generalized Buckingham exponential-6 (gBe-6) potentials were found to best fit the ab initio data for these two classes of ion-water interactions. The fitted values of the parameter of the (eM) and (gBe-6) PEFs that control the repulsive wall of the potential correlate remarkably well with the ionic radii of the halide and alkali metal ions.

Werhahn, Jasper C.; Akase, Dai; Xantheas, Sotiris S.

2014-08-01

156

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

CERN Document Server

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.

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

2014-01-01

157

Conditions leading to the epitaxial growth of vacuum evaporated Ag thin films onto doped alkali halide substrate  

International Nuclear Information System (INIS)

Thin Ag films up to 1800 A in thickness were vacuum evaporated onto freshly air cleaved doped NaCl substrates at constant temperature and deposition rate (T = 150 +- 20 deg C and R = 11 +- 0.5 Assup(-1)). The structural features of these films (growth stage, grain size and morphology, epitaxial orientation degree, densities of pinholes, dislocations, microtwins and stacking-faults etc.) induced by some deposition conditions (preheating treatment of air cleaved substrates and postdeposition vacuum annealing and by the nature and amount of NaCl substrate impurities Ag, Cu, Pb, Ca) are determined by means of electron-microscopy and electron diffraction. A parallel survey concerning the conditions leading to the epitaxial growth of continuous Ag and Au thin films onto deoped alkali halide substrates is also made. (author)

158

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

International Nuclear Information System (INIS)

Electrolytic conductivities of some alkali metal halides, MX (M+ = Li+, Na+, and K+; X- = Cl-, Br-, and I-), NaBPh4 and Bu4NBr have been investigated in (20, 40, and 60) mass% {dimethyl sulfoxide (DMSO) in DMSO + acetonitrile} at T = 298.15 K. The conductance results have been analyzed by the Fuoss-conductance-concentration equation in terms of the limiting molar conductance ?o the association constant KA and the association diameter R. The ionic contributions to the limiting molar conductance have been estimated using Bu4NBPh4 as the 'reference electrolyte'. The association constant KA tends to increase in the order mass percent 20 o and Walden product ?o?. The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvents.

159

Development of processes for the production of solar grade silicon from halides and alkali metals, phase 1 and phase 2  

Science.gov (United States)

High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon are described. Product separation and collection processes were evaluated, measure heat release parameters for scaling purposes and effects of reactants and/or products on materials of reactor construction were determined, and preliminary engineering and economic analysis of a scaled up process were made. The feasibility of the basic process to make and collect silicon was demonstrated. The jet impaction/separation process was demonstrated to be a purification process. The rate at which gas phase species from silicon particle precursors, the time required for silane decomposition to produce particles, and the competing rate of growth of silicon seed particles injected into a decomposing silane environment were determined. The extent of silane decomposition as a function of residence time, temperature, and pressure was measured by infrared absorption spectroscopy. A simplistic model is presented to explain the growth of silicon in a decomposing silane enviroment.

Dickson, C. R.; Gould, R. K.; Felder, W.

1981-01-01

160

Size distributions and geometries of alkali halide nanoclusters probed using ESI FT-ICR mass spectrometry and quantum chemistry  

Science.gov (United States)

The structures and energetic properties of ionic alkali metal halide clusters play a significant role in our understanding of aqueous geochemical processes such as salt dissolution, precipitation and neutralization reactions. Mass spectrometric and quantum chemical studies of such systems offer new opportunities to study the size-dependent evolution of cluster structures, the occurrence of magic number species as well as their fundamental properties. The work here presents new results for the stability, abundance and structure of pure [Na(NaClm)]+ , [K(KCl)m]+ and mixed [Na(NaCl)p(KCl)q]+ metal halide clusters with mcluster experiments were conducted on a modified 7T Bruker FT-ICR/MS equipped with electrospray ionization (ESI) sources and a custom-designed solvent gas inlet interface. In ESI FT-ICR/MS experiments performed with solutions containing NaCl and KCl salts (1mM; 80/20 CH3CN/H2O), singly and doubly charged salt clusters were generated up to a cluster size of [Na(NaCl)22]+, [K(KCl)17]+ and [K2(KCl)21,23]2+, respectively, including “magic number” clusters that correspond to the completed cluster cuboids with the dimensions 3x3x1 (m=4), 3x3x2+3 (m=10) 3x3x3 (m=13) and 3x3x5 (m=22) (see Figure). On the other hand, no pure clusters except [K(KCl)1-3]+ were generated when alkali halides were electrosprayed from 1mM NaCl/KCl solutions. Instead, mixed [Na(NaCl)p(KCl)q]+ clusters are generated up to p+q=14, which are the largest mixed alkali halide clusters yet generated in mass spectrometric experiments, including a suite of ionic species that are generated via CH3CN fragmentation and charge transfer in [Na(CH3CN)n]+ to yield the clusters [Na(NaCN)(CH3CN)n-1]+. We describe our ESI FT-ICR/MS experiments and discuss ion cluster abundances and extent of clustering in terms of variation of the solvent, desolvation temperature, ESI capillary and cone voltage as well as solution concentration. We also report and compare local minima geometries and relative energies for a number of representative [Na(NaCl)m]+ and [K(KCl)m]+ clusters using the composite CBS-QB3 and G4 methods and comment on the onset of the doubly charged cluster series. FT-ICR mass spectra for [Na(NaCl)n]+ clusters generated from 1mM NaCl in 20%H2O 80% acetonitrile in positive ion mode.

Lemke, K.; Sadjadi, S.; Seward, T.

2010-12-01

 
 
 
 
161

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

Directory of Open Access Journals (Sweden)

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

A. P\\u00E9rez-Rodr\\u00EDguez

2006-01-01

162

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2011-02-01

163

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

International Nuclear Information System (INIS)

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

164

First stage coloration of alkali halides doped with M2+ impurities that change their valence state by irradiation as a function of x-irradiation dose rate  

International Nuclear Information System (INIS)

The amount of room temperature first stage coloration of ten alkali halide systems, i.e., NaCl:Pb, NaCl:Co, NaCl:Mg, NaCl:Sn, NaCl:Fe, KCl:Eu, KBr:Eu, Kl:Eu, RbCl:Eu and RbBr:Eu has been analyzed as a function of X-irradiation dose rate. In all systems the amount of first stage coloration was found to be proportional to the square root of irradiation dose rate. These results are in very good agreement with the prediction of the theoretical model recently developed by our group to account for the F-center production in alkali halides doped with doubly valent impurity ions that change their valence state by irradiation and give evidence of its validity. (author)

165

Lattice model calculation of elastic and thermodynamic properties at high pressure and temperature. [for alkali halides in NaCl lattice  

Science.gov (United States)

The elastic constants and the entire frequency spectrum were calculated up to high pressure for the alkali halides in the NaCl lattice, based on an assumed functional form of the inter-atomic potential. The quasiharmonic approximation is used to calculate the vibrational contribution to the pressure and the elastic constants at arbitrary temperature. By explicitly accounting for the effect of thermal and zero point motion, the adjustable parameters in the potential are determined to a high degree of accuracy from the elastic constants and their pressure derivatives measured at zero pressure. The calculated Gruneisen parameter, the elastic constants and their pressure derivatives are in good agreement with experimental results up to about 600 K. The model predicts that for some alkali halides the Grunesen parameter may decrease monotonically with pressure, while for others it may increase with pressure, after an initial decrease.

Demarest, H. H., Jr.

1972-01-01

166

Universal scaling of potential energy functions describing intermolecular interactions. II. The halide-water and alkali metal-water interactions  

Energy Technology Data Exchange (ETDEWEB)

The scaled forms of the newly introduced generalized potential energy functions (PEFs) describing intermolecular interactions [J. Chem. Phys. xx, yyyyy (2011)] have been used to fit the ab-initio minimum energy paths (MEPs) for the halide- and alkali metal-water systems X-(H2O), X=F, Cl, Br, I, and M+(H2O), M=Li, Na, K, Rb, Cs. These generalized forms produce fits to the ab-initio data that are between one and two orders of magnitude better in the ?2 than the original forms of the PEFs. They were found to describe both the long-range, minimum and repulsive wall of the potential energy surface quite well. Overall the 4-parameter extended Morse (eM) and generalized Buckingham exponential-6 (gB-e6) potentials were found to best fit the ab-initio data. Furthermore, a single set of parameters of the reduced form was found to describe all candidates within each class of interactions. The fact that in reduced coordinates a whole class of interactions can be represented by a single PEF, yields the simple relationship between the molecular parameters associated with energy (well depth, ?), structure (equilibrium distance, rm) and spectroscopy (anharmonic frequency, ?):€? = A? (? /?)1/ 2 /rm + B?? /rm 3 , where A and B are constants depending on the underlying PEF. This more general case of Badger’s rule has been validated using the experimentally measured frequencies of the hydrogen bonded OH stretching vibrations in the halide-water series.

Werhahn, Jasper C.; Akase, Dai; Xantheas, Sotiris S.

2014-08-14

167

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

Directory of Open Access Journals (Sweden)

Full Text Available The chain polymer [{Cd(?-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.

Ulli Englert

2011-07-01

168

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

Science.gov (United States)

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

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

2015-01-22

169

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-11-15

170

Photostimulated luminescence in alkali halides induced by excitation with ionizing radiation  

International Nuclear Information System (INIS)

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.))

171

Theory of negative-ion conversion of neutral atoms in grazing scattering from alkali halide surfaces  

Science.gov (United States)

The theoretical approach proposed by Borisov et al. [Phys. Rev. Lett. 77, 1893 (1996)] to treat negative-ion conversion of neutral atoms at ionic crystal surfaces is described in detail. Due to the localization of the valence-band electrons at the anionic sites of the crystal, the conversion process is viewed as a result of successive binary collisions between the projectile and the negatively charged sites at the surface. Parameter-free calculations of F- formation in grazing scattering from LiF(100) and KI(100) are performed using a model in which all sites of the crystal lattice but one, the active site, are represented by eventually polarizable point charges. Parallel velocity thresholds for negative-ion formation, relative efficiency of the negative-ion formation for LiF and KI crystals, and dependences of this efficiency on the scattering angle correspond well to the experimental results.

Borisov, A. G.; Sidis, V.

1997-10-01

172

Photochemistry and reactions of OH- defects and F centers in alkali halides  

International Nuclear Information System (INIS)

Aditively colored KCl:OH- crystals showed under a combined UV and VIS irradiation, a nearly complete and irreversible destruction of all F centers and visible absorption in the crystal. Only upon heating the crystal above 6500C the F center coloration becomes partially restored. The photodissociation of the OH-(under UV light) together with the photoionization of the F center (under VIS light) produces a not effects where all the F centers are converted into U centers. These photoreactions produces high contrast visible images that are completely stable under light at RT. Besides the optical information storage aspect of this effect these photoreaction s can also be used for controlled production of Usub(A) centers if the crystal also contains a foreign metallic impurity such a Na+ ion

173

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

Science.gov (United States)

The effect of halide ions on density, electrical, magnetic and crystallization kinetics for (20X-50P 2O 5-30V 2O 5) mole% has been investigated, where X=CaO, CaF 2, CaCl 2 and CaBr 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.

Assem, E. E.

2011-02-01

174

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

International Nuclear Information System (INIS)

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

175

Electron paramagnetic resonance, optical transmission spectra and DC conductivity studies of vanadyl-doped alkali halide borate glasses  

International Nuclear Information System (INIS)

Electron paramagnetic resonance, optical transmission spectra and DC conductivity of the glasses 2xMX·(0.30-x)M2O·0.70B2O3 (M=Na or K; X=Cl or Br) (0.01?x?0.10) containing 2.0 mol% of V2O5 have been studied. The spin-Hamiltonian parameters (SHP) of the VO2+ ions, the dipolar hyperfine parameter, P, the Fermi contact interaction parameter, K, and the molecular orbital coefficients (?2 and ?2) have been calculated. It is observed that in KX·K2O·B2O3 (X=Cl or Br) glasses, the tetragonal nature of V4+O6 complex decreases with KBr for x?0.05. An increase in the 2KX:K2O ratio (x?0.05) also results in the contraction of 3dxy orbit of the unpaired electron in the vanadyl ion, whereas in case of NaX·Na2O·B2O3 (X=Cl or Br) glasses, the SHP are independent of change in 2NaX:M2O ratio. It is observed that the SHP in these alkali halide borate glasses are independent of the theoretical optical basicity, ?th. It is also observed that the DC conductivity increases with increase in temperature. The order of conductivity is 10-6 ?-1 m-1 at low temperatures and 10-4 ?-1 m-1 at high temperatures. In MCl·M2O·B2O3 (M=Na or K) glasses, the conductivity increases and tivity increases and the activation energy decreases with an increase in mol% of the NaCl or KCl content whereas, in MBr·M2O·B2O3 (M=Na or K) glasses, the conductivity first increases and then decreases with mol% of the MBr content

176

Crystallization of iron phosphate glass containing mixed alkali oxides  

International Nuclear Information System (INIS)

Iron phosphate glass (IPG) is a versatile alternate glass matrix for immobilization of high level nuclear waste. In the present work, 20 wt % mixed alkali oxides (added in the form of eutectic chlorides, LiCl-55 wt % KCl) were immobilized in IPG and the glass waste form was characterized by X-ray diffraction (XRD) technique. Crystallization behavior was studied by using Differential Scanning Calorimetry (DSC). Good glass forming characteristics, high % of waste loading and good chemical durability are the superior salient features of a versatile iron phosphate glass (IPG) as a host for nuclear waste immobilization. In the present work, the possibility of vitrification of 20 wt % of LiCl-KCl eutectic in IPG was explored along with its crystallization studies in order to study the feasibility of immobilizing pyrometallurgical chloride waste

177

Molecular Cluster-Indo calculations of substitutional defects in Alkali-Halides  

International Nuclear Information System (INIS)

The one electron level structure of LiF, NaF, LiCl and NaCl crystals containing F and U centers and of NaCl crystal containing U3 centers are calculated using the INDO method and the molecular cluster (MC) approximation, with special enphasis in parameterization; spin polarization is considered in the Unrestricted Hartree Fock formulation of the method. The F and U band transition energies are estimated through a limited configuration interaction (CI) calculation, being the electronic mechanism involved in the U3 absorption band also examined. It is made a rough estimation of the spin density at the substitutional H atom nucleus in NaCl. (Author)

178

MC-UHF INDO CI calculation of F centers in alkali halides  

International Nuclear Information System (INIS)

The one-electron level structure of NaCl, NaF, LiF and LiCl crystals containing F centers is calculated using the INDO method in the molecular cluster (MC) approximation. Spin-polarization is considered in the Unrestricted Hartree-Fock (UHF) formulation of the method and F-band transition energies are estimated through limited configuration interaction (CI). (Author)

179

Low temperature deposition and characterization of alkali and alkaline earth metal halides and indium chlorides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work deals with the synthesis of material systems, according to the concept of rational synthesis planning. Main goal is the experimental verification of theoretically predicted structural candidates. This includes the investigation of nucleation, crystallization and phase transformations of the produced compounds. The materials were deposited as thin films by vapour deposition on heavily cooled substrates. The experimental apparatus has been enhanced in order to improve the potential of...

Bach, Andreas Harald

2012-01-01

180

Branching transport model of NaI(Tl) alkali-halide scintillator  

Science.gov (United States)

We measure the time dependence of the scintillator light-emission pulses in NaI(Tl) crystals at different temperatures, after activation by gamma rays. We confirm that there are two main nonexponential components to the time decay and find that their amplitude ratio shows Arrhenius temperature dependence. We explain these nonexponential components as arising from two competing mechanisms of carrier transport to the Tl activation levels. The total light output of the NaI(Tl) detectors shows a linear temperature dependence explained by our model.

Alexandrov, B. S.; Ianakiev, K. D.; Littlewood, P. B.

2008-03-01

 
 
 
 
181

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

International Nuclear Information System (INIS)

Highlights: •The 10 KM–64.7 B2O3–25 Na2O–0.3 Cr2O3 (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 B2O3–25 Na2O–0.3 Cr2O3 (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 N4 ratio increases by replacing the KCl by KBr or KI, and it was found that the tetrahedral coordination of Cr+ ions becomes preferential in the host glasses with increasing the optical basicity

182

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2013-10-15

183

Branching transport model of NaI(Tl) alkali-halide scintillator  

International Nuclear Information System (INIS)

We measure the time dependence of the scintillator light-emission pulses in NaI(Tl) crystals at different temperatures, after activation by gamma rays. We confirm that there are two main nonexponential components to the time decay and find that their amplitude ratio shows Arrhenius temperature dependence. We explain these nonexponential components as arising from two competing mechanisms of carrier transport to the Tl activation levels. The total light output of the NaI(Tl) detectors shows a linear temperature dependence explained by our model

184

Remarkable properties of alkali halides and new techniques for determining Debye-Waller factors  

International Nuclear Information System (INIS)

We have used 70 Ci 183Ta Moessbauer sources to measure the Debye-Waller factors of NaCl, KCl, and KBr single crystals for several of the (h00) and (nnn) Bragg reflections. We have found that the procedure used to analyze data by earlier workers leads to incorrect parameters in the Debye-Waller factor exponent, and we use a procedure that eliminates the need to introduce an empirical parameter to account for thermal expansion effects. We observe that both the cations and anions in NaCl and KBr have identical Debye-Waller factors in the [nnn] direction. We observe Q4 terms in NaCl and KCl, with some evidence for a Q4 term in KBr. The size of this contribution varies with the direction of momentum transfer and will be reported. We observe that the Debye temperature and the coefficient of the anharmonic Q2 term also vary with direction of momentum transfer. We believe this to be the first definitive evidence for a non-spherical thermal cloud in a cubic crystal; the ions have a larger amplitude of oscillation in the [h00] direction than in the [nnn] direction. This effect is temperature dependent and greater at lower temperatures

185

Influence of a vc-vacancy on luminescence of Pb+ centres in alkali halides  

International Nuclear Information System (INIS)

Luminescence of Pb+ centres in X-irradiated Pb2+ doped KCl, KBr, and KI crystals is first observed at 1.29, 1.21, and 1.14 eV, respectively. It is excited in the bands of KCl:Pb2+ at 4.93, 4.45, 3.70, 2.03 eV, of KBr:Pb2+ at 5.20, 4.55, 4.20, 3.20, and at 5.10, 4.30, 3.91, 3.52, 3.02 eV for KI:Pb2+. The effect is studied of the presence of the cation vacancy on both, the excitation and emission spectra of the Pb+ centre. Temperature, kinetic, and polarization characteristics of Pb+ and Pb+vc--centres in KCl:Pb2+ are investigated. (author)

186

Temperature Dependence of Auger-Free Luminescence in Alkali and Alkaline-Earth Halides  

Science.gov (United States)

Auger-free luminescence (AFL) resulting from a radiative transition between theoutermost-core bands and the valence bands in BaF2, RbF, CsF, CsCl and CsBrhas been studied in a wide range of temperatures from 10 to 300 K. The AFLspectra are separated from those originating from the valence-band excitationwith use of time-resolved luminescence spectroscopy. It is found that the decayprofile of AFL in each crystal is essentially the same throughout the spectrum. The remarkable thermal broadening of the linewidth is verified for all systems. This strongly suggests that the core hole generated on a positive ion inducesconsiderable displacement of the surrounding ions within its lifetime. Based onthe present results, the spectral shape of AFL is discussed in terms of acluster model and a two-band model, requiring further development of theinvestigations in theory and experiment.

Itoh, Minoru; Kamada, Masao; Ohno, Nobuhito

1997-08-01

187

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

International Nuclear Information System (INIS)

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

188

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

Energy Technology Data Exchange (ETDEWEB)

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.

Jimenez de Castro, M.

1978-07-01

189

Creation and destruction of X-3 centres in alkali halides by X-radiation  

International Nuclear Information System (INIS)

The production (etasub(X3-)) and destruction efficiencies of X3-centres in NaCl, KCl, KBr, and KI by X-radiation versus the irradiation temperature (in the range of 80 to 320 K) are investigated by optical absorption and thermoluminescence methods. Both, the increase (80 to 150 K) and decrease (200 to 250 K) of etasub(X3-) in KBr and KI at the adsorbed dose of 1019 to 1021 eV cm-3 are shown to be in correlation with the F-centre creation efficiency (etasub(F)). In chlorides etasub(F) does not decrease with etasub(X3-) and these crystals are characterized by a high defect creation efficiency at approximately room temperatures. It is supposed that the creation of large halogen aggregates is much more efficient in chlorides than in bromides and iodides. (author)

190

Ab initio adiabatic dynamics involving excited states combined with Wigner distribution approach to ultrafast spectroscopy illustrated on alkali halide clusters  

Science.gov (United States)

We investigate the ultrafast multistate nuclear dynamics involving adiabatic electronic excited states of nonstoichiometric halide deficient clusters (NanFn-1) characterized by strong ionic bonding and one excess electron, which is localized either in the halide vacancy or on the alkali atom attached to the ionic subunit depending on the cluster size. For this purpose we developed an ab initio adiabatic nuclear dynamics approach in electronic excited and ground states "on the fly" at low computational demand by introducing the "frozen ionic bonds" approximation, which yields an accurate description of excited states considering the excitation of the one excess electron in the effective field of the other n-1 valence electrons involved in the ionic bonding. We combined this multistate dynamics approach with the Wigner-Moyal representation of the vibronic density matrix forming the ab initio Wigner distribution approach to adiabatic dynamics. This method allows the simulation of femtosecond NeExPo-pump-probe and NeExNe-pump-dump signals based on an analytic formulation which utilizes temperature-dependent ground-state initial conditions (Ne), an ensemble of trajectories carried out on the electronic excited state (Ex) for the investigation of the dynamics of the system, and either the cationic (Po) or the ground state (Ne) for the probing step. The choice of the systems has been made in order to determine the time scales of processes involving (i) metallic bond breaking such as during the dynamics in the first excited state of Na2F, and (ii) fast geometric relaxation leaving the bonding frame intact as during the dynamics in the first excited state of Na4F3. The bond-breaking process via a conical intersection involving nonadiabatic dynamics will be presented in the accompanying paper [Hartmann et al., J. Chem. Phys. 114, 2123 (2001)]. The dynamics in the first excited state of Na2F from triangular-to linear-to triangular structure gives rise to fast geometric relaxation due to Na-Na bond breaking at the time scale of ˜90 fs but no signature of internal vibrational energy redistribution (IVR) is present in NeExNe-pump-dump signals since the broken metallic bond prevents the coupling between stretching and bending modes. Instead, anharmonicities of the bending periodic motion have been identified. In contrast, in the case of Na4F3, which is the smallest finite system for a surface F-center prototype of bulk color centers, after the geometric relaxation in the excited state of ˜100 fs leading to the deformed cuboidal type of structure without breaking of bonds, different types of IVR have been identified in NeExNe signals by tuning the dump laser: one-mode selective energy leaving IVR, resonant, and restricted energy arriving IVR corresponding to the selection of different parts of the phase space. Dissipative IVR could not be identified in NeExNe signals of Na4F3 at low initial temperature on the time scale up to 2 ps in spite of 15 degrees of freedom. Due to similar structural and electronic properties such as F centers in bulk, these findings can serve as guidance for establishing the time scales for geometric relaxation and IVR in excited states of larger systems.

Hartmann, Michael; Pittner, Ji?í; Bona?i?-Koutecký, Vlasta

2001-02-01

191

Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy.  

Science.gov (United States)

In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces. We have found that, together with molecular islands of upright standing pentacene, a new phase of tilted molecules appears near step edges on KBr. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density functional theory calculations. Our images reveal that differently oriented molecules display different LCPD and that their value is independent of the number of molecular layers. These results point to the formation of an interface dipole, which may be explained by a partial charge transfer from the pentacene to the surface. Moreover, the monitoring of the evolution of the pentacene islands shows that they are strongly affected by dewetting: Multilayers build up at the expense of monolayers, and in the Kelvin images, previously unknown line defects appear, which reveal the epitaxial growth of pentacene crystals. PMID:24601525

Neff, Julia L; Milde, Peter; León, Carmen Pérez; Kundrat, Matthew D; Eng, Lukas M; Jacob, Christoph R; Hoffmann-Vogel, Regina

2014-04-22

192

Monte Carlo simulation of the structural properties of concentrated aqueous alkali halide solutions at 25 °C using a simple civilized model  

Science.gov (United States)

In this paper we present the results of a Monte Carlo (MC) simulation study of the structural properties of concentrated aqueous solutions of various alkali halides at 25 °C using a simple civilized model (SCM). A simplified version of the rigid nonpolarizable SPC model of liquid water, in which the Lennard-Jones interaction between intermolecular oxygen sites is changed into a hard-core repulsion, is combined in our SCM with a treatment of the ions as charged hard spheres. Changes in the structure of the solvent, and the behavior of ionic solvation and ion pairing upon varying the concentration and size of the ions, are determined by computing the corresponding ten radial distribution functions from sufficiently long MC simulation runs for various aqueous alkali halide solutions at concentrations above 1 M. Hydration numbers are reported for the first time for NaBr and KBr, and the first simulation-based estimates for LiBr, NaI, and KI are also obtained. Whenever possible, results for the hydration numbers are compared with available experimental data and also with other simulation studies. The excellent predictive capability and simplicity of the SCM proposed here, should lead to the development of tractable theoretical approaches to aqueous 1:1 electrolyte solutions in the near future.

Llano-Restrepo, Mario; Chapman, Walter G.

1994-06-01

193

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-01-01

194

Crystal Structures of Three Framework Alkali Metal Uranyl Phosphate Hydrates  

Science.gov (United States)

Three homeotypic hydrated alkali metal uranyl phosphates, A2(UO 2)[(UO 2)(PO 4)] 4(H 2O) 2, A=Cs ( CsUP), Rb ( RbUP), K ( KUP), were synthesized by hydrothermal methods. Intensity data were collected at room temperature using Mo K? radiation and a CCD-based area detector. Their crystal structures were solved by Patterson ( CsUP) and direct ( RbUP, KUP) methods and refined by full-matrix least-squares techniques to agreement indices ( CsUP, RbUP, KUP) w R2=0.048, 0.230, 0.072 for all data, and R1=0.023, 0.078, 0.038 calculated for 5338, 4738, 4514 unique observed reflections (? Fo??4 ?F), respectively. The compound CsUP is orthorhombic, space group Cmc2 1, Z=4, a=14.854(1), b=13.879(1), c=12.987(1) Å, V=2677.5(3) Å 3. Both RbUP and KUP are monoclinic, space group Cm, but are presented in the unconventional pseudo-orthorhombic space group Fm11 to facilitate comparison with CsUP and to allow a model for RbUP that includes the effects of pseudo-merohedral twinning. RbUP is monoclinic, space group Fm11, Z=4, a=15.72(2), b=13.84(1), c=13.05(1) Å, ?=90.39°(2), V=2839(5) Å 3; KUP is monoclinic, space group Fm11, Z=4, a=15.257(1), b=13.831(1), c=13.007(1) Å, ?=91.760°(1), V=2743.4(3) Å 3. The structures consist of sheets of phosphate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO 2)(PO 4)] -, that are topologically identical to the uranyl silicate sheets in uranophane-beta. These sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with two phosphate tetrahedra on each of two adjacent sheets and whose fifth equatorial vertex is an H 2O group, resulting in an open framework with alkali metal cations in the larger cavities of the structures. Where CsUP and RbUP have two alkali metal positions and a H 2O group in these cavities, KUP has four K atoms and two H 2O groups, all of which are partially occupied, in the interstitial sites.

Locock, Andrew J.; Burns, Peter C.

2002-08-01

195

Decay of 5pCs-core excitations in halide crystals with core valence luminescence  

International Nuclear Information System (INIS)

The decay of 5pCs-core excitons and holes is studied in halide crystals with intrinsic and impurity core valence luminescence (CVL). Under excitation in the range of 5pCs(j=((3)/(2))) core exciton creation, the CVL does not appear in CsCl and CsBr crystals. However impurity CVL is observed for RbCl-CsCl and RbBr-CsBr mixed crystals under the excitation in the above mentioned region. This peculiarity is interpreted to be a result of thermal decay of core excitations and subsequent interaction of released core holes with valence electrons. The change in the intrinsic CVL decay time in CsCl-Tl crystals is ascribed to the interaction of core holes with impurity Tl ions

196

Advances in the growth of alkaline-Earth halide single crystals for scintillator detectors  

Science.gov (United States)

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

Boatner, L. A.; Ramey, J. O.; Kolopus, J. A.; Neal, J. S.; Cherepy, N. J.; Beck, P. R.; Payne, S. A.; Burger, A.; Rowe, E.; Bhattacharya, P.

2014-09-01

197

New halides of neodymium and their crystal structures  

International Nuclear Information System (INIS)

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

198

Potential Advantage of Multiple Alkali Metal Doped KNbO3 Single Crystals  

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

Hideo Kimura

2014-06-01

199

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

Science.gov (United States)

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.

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

2014-06-01

200

SANS, infrared, and 7Li and 23Na NMR studies on phase separation of alkali halide-acetonitrile-water mixtures by cooling.  

Science.gov (United States)

Phase separation of alkali halide (MX) (M = Li+, Na+, and K+ and X = Cl– and Br–)–acetonitrile (AN)–water mixtures by cooling has been investigated at the molecular level. The phase diagram obtained for the MX–AN–H2O ternary systems showed that the temperatures of phase separation for the mixtures with MCl are higher than those with MBr. The phase-separation temperatures of the mixtures with MCl and MBr are higher in the sequence of NaX > KX > LiX, although the magnitude of the hydration enthalpies for the alkali metal ions is larger in the sequence of Li+ > Na+ > K+. To elucidate the reasons for the sequence of phase separation on the meso- and microscopic scales, small-angle neutron scattering (SANS), infrared (IR), and 7Li and 23Na NMR measurements have been conducted on MX–AN–water mixtures with lowering temperature. The results of SANS and IR experiments showed that the mechanism of phase separation of the mixtures by cooling is the same among all of the mixtures but did not clearly reveal the reasons for the phase separation sequence. In contrast, the spin–lattice relaxation rates and the chemical shifts of 7Li and 23Na NMR for the mixtures suggested the different solvation structure of Li+ and Na+ in the mixtures. In conclusion, the solvation of acetonitrile molecules for Li+ and the formation of Li+–X– contact ion pairs in the mixtures cause the weakest effect of LiX on phase separation of the mixtures by cooling among the alkali metal ions. PMID:23360538

Haramaki, Hiroki; Shimomura, Takuya; Umecky, Tatsuya; Takamuku, Toshiyuki

2013-02-28

 
 
 
 
201

The initial production of defects in alkali halides: F and H centre production by non-radiative decay of the self-trapped exciton  

International Nuclear Information System (INIS)

Radiation damage in KCl can be produced by the decay of a self-trapped exciton into an F centre and an H centre. Calculations are presented of the energies of the states involved for various stages in the evolution of the damage. These lead to important conclusions about the very rapid damage process, and support strongly Itoh and Saidoh's suggestion (J.Physique;34:C19:101(1973)) that damage proceeds through an excited hole state. The results also help in understanding the prompt decay of F and H pairs at low temperatures, the thermal annihilation of F and H centres, the effects of optical excitation of the self-trapped exciton, and some of the trends within the alkali halides. The calculations use a self-consistent semi-empirical molecular-orbital method, here the CNDO method as implemented in the MOSES code. A large cluster of ions is used (either 42 or 57 ions) plus long-range Madelung terms. The ion positions were obtained from separate lattice-relaxation calculations with the HADES code. The choice of CNDO parameters and the adequacy of the method were checked by a number of separate predictions. These include the energy ? luminescence, where the 2.33 eV predicted is very close to the 2.31 eV observed. (author)

202

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

International Nuclear Information System (INIS)

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

203

Molecular model parameters for the saddle-point configuration of F, Fsub(A), Fsub(B), and Fsub(H) centres in the alkali halides  

International Nuclear Information System (INIS)

A molecular model for the saddle-point configuration of F-type centres, which previously led to the correct prediction of type II emission for Fsub(A) centres in RbF:Li and RbF:Na, based on an empirical parameter Z, is extended to other impurity F centres in the alkali halides. CsF:Li and CsF:Na are predicted to have type II Fsub(A) centres, and a number of triangular Fsub(B) centres in the NaCl structure are also predicted to be type II, particularly in materials with small host anions combined with Li+ or Na+ impurities. Materials having small Z values, presumed to favour type II behaviour, are also identified, for Fsub(H) centres with large host anions and H- or F- impurities, and for Fsub(A) and triangular Fsub(B) centres in the CsCl structure containing Li+ or Na+ impurities, where the Fsub(B) centre which has impurities on adjacent corners of a unit-cube face is strongly favoured. (author)

204

Experimental determination of the thermal diffusivity of molten alkali halides by the forced Rayleigh scattering method. I. Molten LiCl, NaCl, KCl, RbCl, and CsCl  

Energy Technology Data Exchange (ETDEWEB)

As a series of experimental determinations of the thermal diffusivity of molten alkali halides, this paper describes measurements on five molten alkali metal chlorides (LiCl, NaCl, KCl, RbCl, and CsCl) in the temperature range up to 1440 K by the forced Rayleigh scattering method. K[sub 2]Cr[sub 2]O[sub 7] is employed as a dye substance to color the transparent molten salts. In comparison with the present results converted into thermal conductivity, most of the previous experimental data obtained by steady-state methods show larger values, up to about five times, which may be due to the systematic error caused by the presence of convection and radiation. It is found that the thermal conductivity of these series of molten alkali metal chlorides decreases with increasing molecular weight, and their temperature coefficients are weakly negative. 24 refs., 9 figs., 6 tabs.

Nagasaka, Y.; Nakazawa, N.; Nagashima, A. (Keio Univ., Yioshi, Yokohama (Japan))

1992-07-01

205

Crystallization of methyl ammonium lead halide perovskites: implications for photovoltaic applications.  

Science.gov (United States)

Hybrid organic/lead halide perovskites are promising materials for solar cell fabrication, resulting in efficiencies up to 18%. The most commonly studied perovskites are CH3NH3PbI3 and CH3NH3PbI3-xClx where x is small. Importantly, in the latter system, the presence of chloride ion source in the starting solutions used for the perovskite deposition results in a strong increase in the overall charge diffusion length. In this work we investigate the crystallization parameters relevant to fabrication of perovskite materials based on CH3NH3PbI3 and CH3NH3PbBr3. We find that the addition of PbCl2 to the solutions used in the perovskite synthesis has a remarkable effect on the end product, because PbCl2 nanocrystals are present during the fabrication process, acting as heterogeneous nucleation sites for the formation of perovskite crystals in solution. We base this conclusion on SEM studies, synthesis of perovskite single crystals, and on cryo-TEM imaging of the frozen mother liquid. Our studies also included the effect of different substrates and substrate temperatures on the perovskite nucleation efficiency. In view of our findings, we optimized the procedures for solar cells based on lead bromide perovskite, resulting in 5.4% efficiency and Voc of 1.24 V, improving the performance in this class of devices. Insights gained from understanding the hybrid perovskite crystallization process can aid in rational design of the polycrystalline absorber films, leading to their enhanced performance. PMID:25171634

Tidhar, Yaron; Edri, Eran; Weissman, Haim; Zohar, Dorin; Hodes, Gary; Cahen, David; Rybtchinski, Boris; Kirmayer, Saar

2014-09-24

206

First-principles study of the local structure and crystal field of Yb2+ in sodium and potassium halides  

International Nuclear Information System (INIS)

The local coordination structures around the doping Yb2+ ions in sodium and potassium halides were calculated by using the first-principles supercell model. Both the cases with and without the charge compensation vacancy in the local environment of the doping Yb2+ were calculated to study the effect of the doping on the local coordination structures of Yb2+. Using the calculated local structures, we obtained the crystal-field parameters for the Yb2+ ions doped in sodium and potassium halides by a method based on the combination of the quantum-chemical calculations and the effective Hamiltonian method. The calculated crystal-field parameters were analyzed and compared with the fitted results. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

207

Surface Structure and Lattice Dynamics of Alkali Halide Crystals Studied by High-Resolution Ion Scattering  

Science.gov (United States)

The rumpled surface structure and thermal lattice vibrations of KI(001) and RbI(001) were measured directly by high-resolution medium energy ion scattering (MEIS). The relaxation of interlayer distance between the top and second layer and the rumpling of the top and second layers were determined using the ion shadowing effect with an accuracy of 0.01 Å. From the displaced lattice positions determined above, we derived the dipole moments of the top- and second-layer ions self-consistently employing the polarizabilities estimated from the optical refractive index combined with the Clausius Mossotti relation. The balance between a short-range force and a long-range Coulombic one made it possible to judge the applicability of the short-range pair potentials proposed so far. We also determined the root-mean-square (rms) thermal vibration amplitudes of the bulk and the top-layer ions together with the correlations of the ions in the [001] and [101] strings by taking various kinds of scattering geometries. The results obtained were compared with those calculated from the molecular dynamics (MD) simulations based on a classical model using the dipole moments determined above and the Born Mayer type pair potential. The present MEIS results are in overall agreement with the MD simulations.

Kido, Yoshiaki; Okazawa, Tetsuaki

208

Atomic forces between noble gas atoms, alkali ions, and halogen ions for surface interactions  

Science.gov (United States)

The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base developed from analysis of the two-body potential data, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas surfaces and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

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

1988-01-01

209

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

Science.gov (United States)

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. PMID:24915287

Brander, Søren; Mikkelsen, Jørn D; Kepp, Kasper P

2014-01-01

210

Some autoradiographic observations on alkali chloride crystals containing sup(35)S  

International Nuclear Information System (INIS)

The distribution of sup(35)S is investigated by autoradiography in neutron irradiated sodium and potassium chloride crystals cleaved from Kyropoulos grown single crystals of high purity. The observations suggest that the sup(35)S enters the alkali chloride crystal by two mechanisms during vapour doping. One is a slow diffusive process giving continuously distributed sup(35)S. The other involves localized movement of the sup(35)S along dislocations and cracks. The relative importance of the two mechanisms depends on the temperature and time of doping and the vapour pressure of sulfur. At low pressure the dislocation process dominates the entry of the sup(35)S. (author)

211

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

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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 beh...

Medrano, C.; Georgiev, M.

2007-01-01

212

CN B?X emission in electron-stimulated desorption from alkali halides: Population analysis via nonlinear models  

International Nuclear Information System (INIS)

Excitation of crystalline KBr, KCl, and LiF with electrons of energy 60--1000 eV produces weak emission in the 360--420 nm region, identified as the B? X electronic transition in the CN radical. The emission is attributed to CN molecules that leave the surface of the crystal in their electronically excited B 2?+ state. The resulting spectra, which are rotationally unresolved, are analyzed by novel nonlinear fitting procedures to yield information about the vibrational and rotational population distributions. For CN(B) produced via electron-stimulated desorption from LiF, the vibrational populations approximate a temperature of 1500 K, while the rotational abundances can be represented as a sum of two Boltzmann distributions having temperatures of 660 K (81%) and 90 K (19%). For ESD from KBr, the rotational distribution is adequately represented as a single Boltzmann at ? 590 K

213

Computation of methodology-independent single-ion solvation properties from molecular simulations. IV. Optimized Lennard-Jones interaction parameter sets for the alkali and halide ions in water  

Science.gov (United States)

The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions and treatment of electrostatic interactions used during these simulations. However, as shown recently [M. A. Kastenholz and P. H. Hünenberger, J. Chem. Phys. 124, 224501 (2006), 10.1529/biophysj.106.083667; M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144103 (2010)], the application of appropriate correction terms permits to obtain methodology-independent results. The corrected values are then exclusively characteristic of the underlying molecular model including in particular the ion-solvent van der Waals interaction parameters, determining the effective ion size and the magnitude of its dispersion interactions. In the present study, the comparison of calculated (corrected) hydration free energies with experimental data (along with the consideration of ionic polarizabilities) is used to calibrate new sets of ion-solvent van der Waals (Lennard-Jones) interaction parameters for the alkali (Li+, Na+, K+, Rb+, Cs+) and halide (F-, Cl-, Br-, I-) ions along with either the SPC or the SPC/E water models. The experimental dataset is defined by conventional single-ion hydration free energies [Tissandier et al., J. Phys. Chem. A 102, 7787 (1998), 10.1021/jp982638r; Fawcett, J. Phys. Chem. B 103, 11181] along with three plausible choices for the (experimentally elusive) value of the absolute (intrinsic) hydration free energy of the proton, namely, ? G_hyd^{ominus }[H+] = -1100, -1075 or -1050 kJ mol-1, resulting in three sets L, M, and H for the SPC water model and three sets LE, ME, and HE for the SPC/E water model (alternative sets can easily be interpolated to intermediate ? G_hyd^{ominus }[H+] values). The residual sensitivity of the calculated (corrected) hydration free energies on the volume-pressure boundary conditions and on the effective ionic radius entering into the calculation of the correction terms is also evaluated and found to be very limited. Ultimately, it is expected that comparison with other experimental ionic properties (e.g., derivative single-ion solvation properties, as well as data concerning ionic crystals, melts, solutions at finite concentrations, or nonaqueous solutions) will permit to validate one specific set and thus, the associated ? G_hyd^{ominus }[H+] value (atomistic consistency assumption). Preliminary results (first-peak positions in the ion-water radial distribution functions, partial molar volumes of ionic salts in water, and structural properties of ionic crystals) support a value of ? G_hyd^{ominus }[H+] close to -1100 kJ.mol-1.

Reif, Maria M.; Hünenberger, Philippe H.

2011-04-01

214

Computation of methodology-independent single-ion solvation properties from molecular simulations. IV. Optimized Lennard-Jones interaction parameter sets for the alkali and halide ions in water  

International Nuclear Information System (INIS)

The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions and treatment of electrostatic interactions used during these simulations. However, as shown recently [M. A. Kastenholz and P. H. Huenenberger, J. Chem. Phys. 124, 224501 (2006); M. M. Reif and P. H. Huenenberger, J. Chem. Phys. 134, 144103 (2010)], the application of appropriate correction terms permits to obtain methodology-independent results. The corrected values are then exclusively characteristic of the underlying molecular model including in particular the ion-solvent van der Waals interaction parameters, determining the effective ion size and the magnitude of its dispersion interactions. In the present study, the comparison of calculated (corrected) hydration free energies with experimental data (along with the consideration of ionic polarizabilities) is used to calibrate new sets of ion-solvent van der Waals (Lennard-Jones) interaction parameters for the alkali (Li+, Na+, K+, Rb+, Cs+) and halide (F-, Cl-, Br-, I-) ions along with either the SPC or the SPC/E water models. The experimental dataset is defined by conventional single-ion hydration free energies [Tissandier et al., J. Phys. Chem. A 102, 7787 (1998); Fawcett, J. Phys. Chem. B 103, 11181] along with three plausible choices for the (experimentally elusive) choices for the (experimentally elusive) value of the absolute (intrinsic) hydration free energy of the proton, namely, ?Ghyd O-minus [H+]=-1100, -1075 or -1050 kJ mol-1, resulting in three sets L, M, and H for the SPC water model and three sets LE, ME, and HE for the SPC/E water model (alternative sets can easily be interpolated to intermediate ?Ghyd O-minus [H+] values). The residual sensitivity of the calculated (corrected) hydration free energies on the volume-pressure boundary conditions and on the effective ionic radius entering into the calculation of the correction terms is also evaluated and found to be very limited. Ultimately, it is expected that comparison with other experimental ionic properties (e.g., derivative single-ion solvation properties, as well as data concerning ionic crystals, melts, solutions at finite concentrations, or nonaqueous solutions) will permit to validate one specific set and thus, the associated ?Ghyd O-minus [H+] value (atomistic consistency assumption). Preliminary results (first-peak positions in the ion-water radial distribution functions, partial molar volumes of ionic salts in water, and structural properties of ionic crystals) support a value of ?Ghyd O-minus [H+] close to -1100 kJ·mol-1.

215

The structure of alkali halide dimers: A critical test of ionic models and new ab initio results  

Science.gov (United States)

In semiempirical ionic models a number of adjustable parameters have to be fitted to experimental data of either monomer molecules or crystals. This leads to strong correlations between these constants and prevents a unique test and a clear physical interpretation of the fit parameters. Moreover, it is not clear whether these constants remain unchanged when the model is applied to dimers or larger clusters. It is shown that these correlations can be substantially reduced when reliable information about dimers is available from experiments or ab initio calculations. Starting with Dunham coefficients of the monomer potential determined from microwave measurements, we have calculated the monomer to dimer bond expansion and the bond angle without any additional adjustable parameter. Assuming that the overlap repulsion between nearest neighbors remains unchanged, the bond expansion is mainly determined by the simple Coulomb repulsion between equally charged ions and depends only very little on the effective ion polarizabilities. Deviation of the bond angle from 90° sensitively tests the difference of effective polarizabilities of the two ions. A comparison with previously available data and new ab initio MP2 results presented here for the heavy-atom containing dimers shows that bond angles can be modeled reasonably well with Seitz-Ruffa corrected Pauling polarizabilities while calculated bond expansions are much too long. This shows that changes of the overlap repulsion term must be considered for reliable predictions of the structure of dimers and larger clusters.

Törring, T.; Biermann, S.; Hoeft, J.; Mawhorter, R.; Cave, R. J.; Szemenyei, C.

1996-05-01

216

Synthesis and single-crystal structure determination of the zinc nitride halides Zn2NX (X=Cl, Br, I)  

International Nuclear Information System (INIS)

A series of zinc nitride halides, Zn2NX (X=Cl, Br, I), has been synthesized from solid–liquid reactions of zinc nitride with the respective zinc halides under vacuum, and their crystal structures were determined using single-crystal and powder X-ray diffraction. While Zn2NCl and Zn2NBr crystallize in the acentric orthorhombic space group Pna21, Zn2NI adopts the centrosymmetric space group Pnma; Zn2NCl and Zn2NBr can be considered to belong to the anti-?-NaFeO2 type, and Zn2NI is closely related. Each N3? is tetrahedrally coordinated by zinc atoms, and the X? anions are located in the vacancies of the framework formed by corner-sharing [NZn4] tetrahedra. According to TGA/DTA analyses, the Zn2NX compounds exhibit good thermal stability. The electronic structure has been analyzed by employing density-functional theory and the HSE06 hybrid functional. - Graphical abstract: Zn2NCl, Zn2NBr, and Zn2NI have been synthesized, and their crystal structures (Cl and Br phases: Pna21; I phase: Pnma) have been determined from XRD; the direct band gap of Zn2NCl is theoretically (HSE06 hybrid functional) predicted as 3.7 eV. - Highlights: • Zn2NCl, Zn2NBr, and Zn2NI have been synthesized from solid–liquid reactions. • The crystal structures of Zn2NCl, Zn2NBr, and Zn2NI have been determined from single-crystal X-ray diffraction. • Zn2NCl and Zn2NBr crystallize in the acentric space group Pna21 whereas Zn2NI adopts the centrosymmetric space group Pnma. • Zn2NCl and Zn2NBr are stable up to 750 °C whereas Zn2NI decays at 600 °C already. • The direct band gap of Zn2NCl is theoretically predicted as 3.7 eV using the HSE06 hybrid functional

217

A combined metal-halide/metal flux synthetic route towards type-I clathrates: crystal structures and thermoelectric properties of A8Al8Si38 (A = K, Rb, and Cs).  

Science.gov (United States)

Single-phase samples of the compounds K8Al8Si38 (1), Rb8Al8Si38 (2), and Cs7.9Al7.9Si38.1 (3) were obtained with high crystallinity and in good quantities by using a novel flux method with two different flux materials, such as Al and the respective alkali-metal halide salt (KBr, RbCl, and CsCl). This approach facilitates the removal of the product mixture from the container and also allows convenient extraction of the flux media due to the good solubility of the halide salts in water. The products were analyzed by means of single-crystal X-ray structure determination, powder X-ray and neutron diffraction experiments, (27)Al-MAS NMR spectroscopy measurements, quantum chemical calculations, as well as magnetic and transport measurements (thermal conductivity, electrical resistivity, and Seebeck coefficient). Due to the excellent quality of the neutron diffraction data, the difference between the nuclear scattering factors of silicon and aluminum atoms was sufficient to refine their mixed occupancy at specific sites. The role of variable-range hopping for the interpretation of the resistivity and the Seebeck coefficient is discussed. PMID:25267571

Baran, Volodymyr; Senyshyn, Anatoliy; Karttunen, Antti J; Fischer, Andreas; Scherer, Wolfgang; Raudaschl-Sieber, Gabriele; Fässler, Thomas F

2014-11-10

218

Crystal structure search and electronic properties of alkali-doped phenanthrene and picene  

Science.gov (United States)

Alkali-doped aromatic compounds have shown evidence of metallic and superconducting phases whose precise nature is still mysterious. In potassium and rubidium-doped phenanthrene, superconducting temperatures around 5 K have been detected, but such basic elements as the stoichiometry, crystal structure, and electronic bands are still speculative. We seek to predict the crystal structure of M3-phenanthrene (M = K, Rb) using ab initio evolutionary simulation in conjunction with density functional theory (DFT), and find metal but also insulator phases with distinct structures. The original P21 herringbone structure of the pristine molecular crystal is generally abandoned in favor of different packing and chemical motifs. The metallic phases are frankly ionic with three electrons acquired by each molecule. In the nonmagnetic insulating phases the alkalis coalesce reducing the donated charge from three to two per phenanthrene molecule. A similar search for K3-picene yields an old and a new structure, with unlike potassium positions and different electronic bands, but both metallic retaining the face-to-edge herringbone structure and the P21 symmetry of pristine picene. Both the new K3-picene and the best metallic M3-phenanthrene are further found to undergo a spontaneous transition from metal to antiferromagnetic insulator when spin polarization is allowed, a transition which is not necessarily real, but which underlines the necessity to include correlations beyond DFT. Features of the metallic phases that may be relevant to phonon-driven superconductivity are underlined.

Naghavi, S. Shahab; Tosatti, Erio

2014-08-01

219

Preparation of cerium halide solvate complexes  

Science.gov (United States)

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.

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

2013-08-06

220

Multipole interaction effects on cohesive and anharmonic properties of alkali cyanide crystals  

International Nuclear Information System (INIS)

The cohesive and anharmonic properties of alkali cyanide crystals are investigated using a three-body potential consisting of long-range Coulomb and three-body interactions, and the short-range van der Waals attraction and overlap repulsion operative up to the second neighbour ions. The results on cohesive energy, compressibility, molecular force constant, and infrared absorption frequencies are in better agreement with their experimental data than those obtained earlier from a logarithmic potential. An overall systematic trend, followed by the values of third-and fourth-order elastic constants and the pressure and temperature derivatives of the second-order elastic constants, is discussed. (author)

 
 
 
 
221

Growth habit control of ZnO single crystals in molten hydrous alkali solutions  

Science.gov (United States)

Hexagonal prism-like and plate-like wurtzite zinc oxide (ZnO) single crystals have been grown in a molten hydrous alkali solution using the spontaneous nucleation method. It has been found that the growth habit of the crystals depends strongly on the basicity of the solution. In molten hydrous KOH solution, the highest growth rate of the crystal is along the + c-axis and slender hexagonal prisms were obtained. In molten hydrous KOH+LiOH or NaOH+LiOH solutions, the growth rate of the + c face slows down as more LiOH is introduced to the solution, resulting in the formation of thin hexagonal plates. This was confirmed by XRD analysis of the single crystals. We conclude that the growth habit of ZnO crystals can be successfully controlled by adjusting the basicity of the solution. It is proposed that there are two individual growth units, [Zn(OH) 3(H 2O)] - and [Zn(OH) 4] 2-, in the solution. The growth habit can be explained by the polar structure of the ZnO single crystal and the character of the growth units.

Zhang, Sufang; Yao, Shuhua; Li, Jing; Zhao, Lanling; Wang, Jiyang; Boughton, Robert I.

2011-12-01

222

Luminescent quantum efficiency of Eu2+ ions in mixed KCl1-xBrx crystals  

International Nuclear Information System (INIS)

In this work, the luminescent quantum efficiency of Eu2+ ions in mixed KCl1-xBrx crystals is determined by using simultaneous and multiwavelength measurement of photoacoustic and luminescent signals after pulsed laser excitation. This method, which was first demonstrated in Eu2+ doped alkali halides (NaCl, KCl, KBr and KI) is now extended to mixed crystals. It is found that the quantum efficiency is reduced for mixed KCl1-xBrx crystals from ??100%, in pure alkali halides (KCl and KBr), to a value ??60% for x?0.6. (author)

223

Comparative analysis of spectral characteristics of triplet autolocalized excitons and F2 centers in alkaline-halide crystal  

International Nuclear Information System (INIS)

The comparative analysis of the spectral characteristics of the autolocalized excitons (AE) and F2-centers in the states with the similar spin multiplicity is carried out. The criterion of separating the triplet-triplet (T-T) absorption transitions in the AE electron and hole components in any alkaline-halide crystal is proposed on the basis of the above analysis. The conclusion is made, that the spectral position of the T-T transitions in the AE electron and hole components is influenced not by the AE hole component spatial position but by the presence, in particular, of the nonuniformity in the form of the homologous cation and anion admixture in the AE near coordination spheres

224

Radiation processes in crystal solid solutions  

CERN Document Server

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.

Gladyshev, Gennadi

2012-01-01

225

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

Energy Technology Data Exchange (ETDEWEB)

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.)

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

2013-11-01

226

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

International Nuclear Information System (INIS)

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.)

227

Stability diagrams for complexes in molten mixtures of halide salts  

International Nuclear Information System (INIS)

The stability of local fourfold coordination for divalent and trivalent metal ions in liquid mixtures of polyvalent metal halides and alkali halides is classified by means of structural coordinates obtained from properties of the elements. In parallel with earlier classifications of compound crystal structures and molecular shapes, the elemental properties are taken from first-principles calculations of valence electron orbitals in atoms, in the form of (i) the nodal radii of Andreoni, Baldereschi and Guizzetti or (ii) the 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

228

Radiolysis, radiation-induced diffusion and condensation of phosphorus-oxygen ions in alkali-halogenide single crystals  

International Nuclear Information System (INIS)

Single-crystal specimens of alkali halogenides containing phosphorus-oxygen molecular centres were grown and exposed to 60Co gamma-radiation. Radiolysis effects were studied by IR spectroscopy and by the radiochemical analysis of 32P labelled compounds. The destruction of molecular centres in alkali halogenides containing phosphite or trimetaphosphate type impurities is substantially different: the destruction of phosphite type molecular centres is due to the low-energy electron excitation of the lattice matrix, while that of the trimetaphosphate type centres is caused by the direct effect of the high energy ionizing radiation. During radiolysis, radiation-induced diffusion could be observed. (V.N.)

229

Heat capacity of molten halides.  

Science.gov (United States)

The heat capacities of molten salts are very important for their practical use. Experimental investigation of this property is challenging because of the high temperatures involved and the corrosive nature of these materials. It is preferable to combine experimental investigations with empirical relationships, which allows for the evaluation of the heat capacity of molten salt mixtures. The isobaric molar heat capacities of all molten alkali and alkaline-earth halides were found to be constant for each group of salts. The value depends on the number of atoms in the salt, and the molar heat capacity per atom is constant for all molten halide salts with the exception of the lithium halides. The molar heat capacities of molten halides do not change when the anions are changed. PMID:25530462

Redkin, Alexander A; Zaikov, Yurii P; Korzun, Iraida V; Reznitskikh, Olga G; Yaroslavtseva, Tatiana V; Kumkov, Sergey I

2015-01-15

230

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

Science.gov (United States)

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.

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

2013-01-01

231

Synthesis, crystal structure, magnetism, and absorption spectra of A2UX5 type halides (A = K, Rb; X = Cl, Br, I)  

International Nuclear Information System (INIS)

The ternary uranium(III) halides A2UX5 (A = K, Rb; X = Cl, Br, I) have been prepared from the binary components AX and UX3 in sealed tantalum containers. According to their Guinier X-ray powder patterns, they all crystallize with the K2PrCl5/Y2HfS5 type of structure. Lattice constants for ambient temperature are reported. Single-crystal structure refinements were undertaken for K2UI5 and Rb2UCl5. Magnetic susceptibility data were recorded with a SQUID magnetometer from liquid helium to room temperature. One-dimensional (intrachain) and three-dimensional antiferromagnetic ordering occur at low temperatures dependent upon the U3+-U3+ distance. Absorption spectra were recorded between 4000 and 28000 cm-1. They show f-f transition typical for U3+ and, depending on the halide, very strong f-d transitions above 14000 to 15000 cm-1, respectively. (orig.)

232

Associated equilibria with participatian of single and mixed silver, lead and cadmium halide complexes in mixtures of molten alkali and alkaline earth metal nitrates  

International Nuclear Information System (INIS)

Associated equilibria in the systems, which contain single and mixed silver, cadmium and lead halide complexes in the KNO3-Ba(N03)2 (87.6:12.4 and 89:11 mol.%) and NaNO3-Ba(NO3)2 (94.2-5.8 mol%) melts in the temperature range from 568.2 up to 698.2 K are investigated. Applicability of equations derivated on the base of quasi-lattice model to description of temperature coefficients of association constants is analized

233

Tabular silver halide crystals prepared by controlled Ostwald growth in the presence of dimethyl sulphoxide  

Energy Technology Data Exchange (ETDEWEB)

The results of research in the size and shape of silver bromide crystals precipitated by the Ostwald controlled growth method at the presence of dimethyl sulphoxide were presented in the paper. The silver bromide crystals were produced in the form of microcrystal suspension stabilised by gelatine. In the course of the synthesis of crystals, the constant concentration of dimethyl sulphoxide, concentration of excessive bromide ions and the constant ionic strength were achieved. The tabular crystals of silver bromide with their average size of 50 {mu}m and their aspect ratio equal to 100 were obtained by means of this method. The suspensions of flat silver bromide crystals produced in this manner can be used in the production of high-sensitivity materials. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Dyonizy, A.; Nowak, P.; Mora, C.; Krol-Gracz, A.; Michalak, E. [Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze St. Wyspianskiego 27, 50-370 Wroclaw (Poland)

2010-03-15

234

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Michel, K. H.; Nikolaev, A. V.

2000-01-01

235

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

Directory of Open Access Journals (Sweden)

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.

Michele De Bastiani

2014-08-01

236

White X-ray pulse emission of alkali halide aqueous solutions irradiated by focused femtosecond laser pulses: a spectroscopic study on electron temperatures as functions of laser intensity, solute concentration, and solute atomic number  

Science.gov (United States)

Aqueous solutions of alkali halides were irradiated with focused femtosecond laser pulses (130 fs, 780 nm, 1 kHz) in air, and X-ray emission spectra were measured. The laser power density at the focus was estimated to be 2 PW/cm 2 when the laser intensity was 0.65 mJ/pulse. Broad X-ray emission spectra having tails to the higher energy were commonly observed, often accompanied by characteristic K and L lines of solutes. Electron temperatures ( Te) were obtained from the slopes of the broad X-ray spectra on the basis of the assumption of Maxwell-Boltzmann distribution of electron energy. The value of Te was 1.90 keV in the case of distilled water irradiated with laser pulses of 0.53 mJ/pulse laser pulses, while two components of Te (2.67 and 9.83 keV) were observed in the case of saturated cesium chloride aqueous solution (6.5 mol/dm 3). These two components may be related to different electron acceleration processes such as inverse-bremsstrahlung and resonance absorption.

Hatanaka, Koji; Miura, Toshifumi; Fukumura, Hiroshi

2004-04-01

237

White X-ray pulse emission of alkali halide aqueous solutions irradiated by focused femtosecond laser pulses: a spectroscopic study on electron temperatures as functions of laser intensity, solute concentration, and solute atomic number  

International Nuclear Information System (INIS)

Aqueous solutions of alkali halides were irradiated with focused femtosecond laser pulses (130 fs, 780 nm, 1 kHz) in air, and X-ray emission spectra were measured. The laser power density at the focus was estimated to be 2 PW/cm2 when the laser intensity was 0.65 mJ/pulse. Broad X-ray emission spectra having tails to the higher energy were commonly observed, often accompanied by characteristic K and L lines of solutes. Electron temperatures (Te) were obtained from the slopes of the broad X-ray spectra on the basis of the assumption of Maxwell-Boltzmann distribution of electron energy. The value of Te was 1.90 keV in the case of distilled water irradiated with laser pulses of 0.53 mJ/pulse laser pulses, while two components of Te (2.67 and 9.83 keV) were observed in the case of saturated cesium chloride aqueous solution (6.5 mol/dm3). These two components may be related to different electron acceleration processes such as inverse-bremsstrahlung and resonance absorption

238

Oxidation of hydrogen halides to elemental halogens  

Science.gov (United States)

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.

Rohrmann, Charles A. (Kennewick, WA); Fullam, Harold T. (Richland, WA)

1985-01-01

239

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2013-11-15

240

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

Science.gov (United States)

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.

Fukazawa, Y.; Kihara, K.; Iwamoto, K.; Susuki, Y.

2013-11-01

 
 
 
 
241

Effective acoustooptical Q-switching of a CO sub 2 laser using thallium halide crystals  

Energy Technology Data Exchange (ETDEWEB)

Experimental results are presented concerning the possible use of KRS5 and KRS6 crystals for acoustooptical Q-swithcing of a medium-power CO{sub 2} laser. It is suggested that KRS5 and KRS6 may be used as an acoustic line of an intracavity acoustooptic refractive-type modulator for implementing the LF modulation of the output radiation of a waveguide CO{sub 2} laser. 15 refs.

Kozlov, K.V.; Pashkevich, G.A.; Chizhevskii, V.N.; Churakov, V.V. (Institut Fiziki, Minsk (Belorussian SSR))

1989-04-01

242

Structure of polyvalent metal halide melts  

International Nuclear Information System (INIS)

A short review is given of recent progress in determining and understanding the structure of molten halide salts involving polyvalent metal ions. It covers the following three main topics: (i) melting mechanisms and types of liquid structure for pure polyvalent-metal chlorides; (ii) geometry and stability of local coordination for polyvalent metal ions in molten mixtures of their halides with alkali halides; and (iii) structure breaking and electron localization on addition of metal to the melt. (author). 28 refs, 3 figs, 1 tab

243

Metal halide reduction with molten sodium/potassium alloy  

International Nuclear Information System (INIS)

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

244

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

DEFF Research Database (Denmark)

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

Brander, SØren; Mikkelsen, JØrn Dalgaard

2014-01-01

245

Isotopic Ligand Exchange of Some Hexa-Coordinated Inorganic Complexes with Halide Ions in Solution and in Crystals  

International Nuclear Information System (INIS)

The kinetics of isotopic exchange reactions give information about the lability of complexes in solution and about the mechanisms of substitution. The exchange of 82Br-labelled [Rh(NH3)5Br]2+ and [Ii(NH3)5Br]2+ complexes with Br- ions, of trans-[Rh(en)2Cl2]+ and trans- [Co(en)2 Cl2]+]+ with Cl- ions, of trans- [Co(en)2Br2]+ with Br- and of [OSCl6]2- and [OsI6]2- with Cl- and I- ions, respectively, was investigated in acid solutions. The iridium pentamminebromo complex exchanges about 60 times slower than the corresponding rhodium pentamminebromo complex. The rate constant for the Rh- complex was found to be k = (1.03 ± 0,02) x 10-2 min-1 at 100°C, for the Ir-complex k100°C = 1.7 x 10-4 min-1. For both complexes the exchange rate R is first-order in the complex concentration; in acid solution R is nearly independent of the bromide and hydrogen concentration as well as of the ionic strength. This indicates that the exchange takes place by a dissociation mechanism. Activation energies of 24 and 23 kcal/ mole forthe Rh- and Ir-complex, respectively, were calculated. Rate constants of the 36Cl isotopic exchange between 60 and 100°C wetopic exchange between 60 and 100°C were measured for the trans- [Rh(en)2 Cl2]+ complex and an Arrhenius activation energy of 25 kcal/mole was determined. Here again the increase of the rate R is of first order in the complex concentration; but it is only slightly dependent on the hydrogen and chloride concentration. The exchange seems to occur by aquation. In methanolic HCl solution the exchange rate of this complex is immeasurably slow at 60°C. The halide exchanges of trans-[Co(en)2 Cl2]+ and trans [Co(en)2 Br2]+ were measured in methanolic solutions between 30 and 60°C. Further , the halide exchange of [OsCl6]2- and [Osl6]2- was investigated in hydrochloric acid and hydroiodic acid, respectively, in methanolic acid and in ethanolic acid solution. The rates measured are compared with earlier results of the isotopic exchange of the corresponding hexabromo complex. Beside these investigations of the dissolved complexes, displacement reactions of labelled cis- and trans-[Co(en)2Cl*2] Cl and trans- [Rh(en)2Cl*2] Cl in the lattice were studied. The half-time of the exchange for both solid isomeric Co complexes is about 4 h at 150°C. For the Rh complex a half-time of about 26 h was found at 225°C. Activation energies of 30-35 kcal/mole were calculated. X-ray irradiation leads to an exchange increasing with the dose. In addition, the thermal exchange of irradiated crystals is accelerated. In contrast to the ethylenediamine complexes, the solid Rh and Ir pentamminebromo bromides or chlorides exchange only very slowly by raising the temperature even to 210°C. But in these solid complexes ''activated'' exchange reactions take place if the complex receives excitation energy from a nuclear process such as the 80mBr -> 80Br isomeric transition. This phenomenon was investigated in some detail. (author)

246

Metal--metal bonding in reduced scandium halides. Synthesis and crystal structure of scandium monochloride  

International Nuclear Information System (INIS)

The synthesis of a number of reduced scandium chlorides is achieved by reaction of excess metal with ScCl3 in sealed Ta tubing above 8770C for periods of weeks to months. Extreme conditions are necessary because of both the kinetic problems of forming extended metal--metal bonded structures and the fact that ScCl1.5 effectively blocks further reaction on metal surfaces below this temperature. Single-crystal x-ray diffraction data showed that a gray-black laminar phase was ScCl with a sheet structure consisting of close-packed homoatomic layers sequenced Cl--Sc--Sc--Cl along [001] (R3m, trigonal cell; a = 3.473 (2) A, c = 26.71 (4) A, Z = 6; R = 0.088, R/sub w/ = 0.101 for 79 independent reflections taken with Mo K? radiation). The phase is thus polytopic (ignoring the difference in metal atom) with ZrCl and isostructural with ZrBr even though there are only two-thirds as many electrons for bonding the double-metal sheets of scandium. The general occurrence of metal-metal bonding in clusters, ribbons, and sheets in transition metal groups 3--5 is considered

247

Ionic crystals  

Energy Technology Data Exchange (ETDEWEB)

The theme of the second Petra School of Physics was the optical properties of solids. The author's lectures will discuss the theory of ionic crystals such as the alkali halides. The general topics will include a discussion of: the local electric fields, multipole polarizability, core level spectra, and electron energy levels. The subject of alkali halides is today regarded as unfashionable. They were quite popular years ago, but fashions and fancies in science have moved elsewhere. One should not think they are well understood. The author's impression of this field is that activity stopped, not because the problems were solved, but rather because the workers got tired of not being able to solve them. For example, we still do not have a good theory of crystal structure, since microscopic forces are not well characterized. One concludes that other quantities which depend upon forces, such as the elastic constants, are also not well understood, although theories of them are published all of the time. As another example, we still do not have a good theory of bonding. Here there are two camps: one which regards the bonding as ionic, while the other advocates significant amounts of covalency. Recently we have shown that both the elastic constants, and the amount of covalent bonding, depend significantly upon the higher multipole polarizabilities. In summary, the subject of ionic crystals is a field where there are still many unresolved issues awaiting good research. 21 refs., 5 figs., 4 tabs.

Mahan, G.D.

1985-03-01

248

Evaluation of third-order and fourth-order elastic constants of cesium halides and thallium halides  

International Nuclear Information System (INIS)

The third-order and fourth-order elastic constants for CsCl, CsBr, CsI, TlCl, and TlBr crystals are calculated taking into account the effect of Lundqvist's three body potential. The nearest neighbour and next-nearest neighbour repulsive interactions and the Van der Waals interactions are also included according to a recent scheme developed for NaCl-structure alkali halides. The three body charge transfer parameter and its derivatives are evaluated using an exponential form suggested by Cochran. The pressure derivatives of second-order and third-order elastic constants are also calculated for the crystals under study. The results obtained are found to be in reasonable agreement with available experimental data. (author)

249

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

International Nuclear Information System (INIS)

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

250

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

Energy Technology Data Exchange (ETDEWEB)

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.

Delgado Martinez, L.

1977-07-01

251

Dissolving alkali metals in zeolites: Genesis of the perfect cluster crystal  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The interaction of alkali metals with dehydrated zeolites Y and A leads, in a process which bears many similarities to the dissolution of those metals in non-aqueous liquid solvemts, to the formation of inclusion compounds which may be regarded as ordered arrays of closely spaced clusters, and whose properties are dependent on interactions between the clusters. A combined analysis of electron spin resonance, magnetic susceptibility and powder neutron diffraction results enabled us to follow i...

Woodall, Lj; Anderson, Pa; Armstrong, Ar; Edwards, Pp

1996-01-01

252

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

International Nuclear Information System (INIS)

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

253

Electrodepositions on Tantalum in alkali halide melts  

DEFF Research Database (Denmark)

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.

Barner, Jens H. Von; Jensen, Annemette Hindhede

2012-01-01

254

Sputtering of alkali halides under ion bombardment  

International Nuclear Information System (INIS)

New measurements prove the point that under any circumstances the halogen is primarily sputtered, and this at a very high rate. This high yield was found to be proportional to the electronic stopping power and to be far in excess of what can be explained by 'normal' collision cascades or replacement collision sequences (following a Pooley process). These 'giant' sputtering yields can only be explained by contributions from deeper layers of the bulk (a few thousand aengstroems, depending on temperature). The only theoretical model consistent with the above observations, and the fact that the sputtered atoms are found in a cosine angular distribution and in a Maxwell energy distribution, proves to be the following: H centers as defects of lowest energy and longest lifetime migrate in a random walk until eventually getting trapped at the surface, where they provide the neutral halogen atom which can be removed thermally. This mechanism will be explained in some detail. (orig.)

255

Ionic crystals  

Science.gov (United States)

The theory of ionic crystals such as the alkali halides is discussed. The general topics include a discussion of: the local electric fields, multipole polarizability, core level spectra, and electron energy levels. A good theory of crystal structure, since microscopic forces are not well characterized, is still not available. One concludes that other quantities which depend upon forces, such as the elastic constants, are also not well understood, although theories of them are published all of the time. A good theory of bonding is also not available. Here there are two camps: one which regards the bonding as ionic, while the other advocates significant amounts of covalency. Recently it was shown that both the elastic constants, and the amount of covalent bonding, depend significantly upon the higher multipole polarizabilities.

Mahan, G. D.

1985-03-01

256

Formation of tungsten monocarbide from a molten tungstate-halide phase by gas sparging  

International Nuclear Information System (INIS)

Tungsten monocarbide is prepared by sparging a molten composition comprising an alkali metal halide and an oxygen compound of tungsten with a gas comprising a gaseous hydrocarbon, particularly methane

257

Synthesis, Crystal Structure, and Second-Order Optical Nonlinearity of Bis(2-chlorobenzaldehyde thiosemicarbazone)cadmium Halides (CdL(2)X(2); X = Br, I).  

Science.gov (United States)

The new Schiff base ligand 2-chlorobenzaldehyde thiosemicarbazone (L, 1) has been synthesized and characterized by spectral techniques and single-crystal X-ray analysis. Crystals of 1 are monoclinic, space group P2(1)/n with a = 12.964(4) Å, b = 5.131(5) Å, c = 4.970(1) Å, beta = 94.32(2) degrees, and Z = 4. The thiosemicarbazone moiety adopts a configuration with N(1) cis to N(3) and places the E configuration about both the bonds C(1)-N(2) and C(2)-N(3). The monodentate behavior of the neutral ligand (L) has been investigated in two cadmium halides CdL(2) Br(2) (2) and CdL(2)I(2) (3). Compound 2 crystallizes in space group Cc witha = 8.175(1) Å, b = 14.176(1) Å, c = 21.073(1) Å, beta = 94.02(1) degrees, and Z = 4. Compound 3 crystallizes in space group P&onemacr; with a = 10.9577(1) Å, b = 16.174(1) Å, c = 7.878(1) Å, alpha = 100.50(1) degrees, beta = 109.39(1) degrees, gamma = 83.67(1) degrees, and Z = 2. The coordination geometry about the cadmium(II) atom in compound 2 conforms to a tetrahedral configuration with two sulfur atoms from two unequivalent neutral ligands and two bromide atoms. Whereas the coordination geometry about the cadmium(II) atom in compound 3 is (4 + 1) distorted trigonal bipyramidal with two iodide atoms and one sulfur atom in the equatorial plane, the other thiosemicarbazone sulfur and the iodide atom I(1a) of an adjacent moiety occupy the axial positions. Compound 2 exhibits powder SHG efficiencies ca. 20 times that of urea, whereas compound 3 does not exhibit any SHG efficiency. Theory and experiment suggested that intermolecular contact is the main factor controlling the SHG efficiencies of compounds. PMID:11669693

Tian Yp, Yu-peng; Duan Cy, Chun-ying; Zhao Cy, Cun-yuan; You Xz, Xiao-zeng; Mak, Thomas C. W.; Zhang Zy, Ze-ying

1997-03-12

258

Dipole and Deformation Dipole Polarization of Ions in Rock-Salt Structure Crystals  

Science.gov (United States)

The comparative study is done on the dipole and deformation dipole polarization. With the local density approximation, the values of the dipole polarizability and the deformation dipole tensor of the ions in the rock-salt structure alkali iodide crystals are calculated. The Szigeti effective charge is obtained from the deformation dipole tensor. The crystalline potential is treated by the spherical solid model. The response to the perturbation is calculated by the self-consistent field potential. The calculated results are compared with those in other alkali halide crystals. The ease of the ionic migration is discussed by using the deformation dipole tensor.

Michihiro, Yoshitaka; Rahman, Md. Mahbubar; Nakamura, Koichi; Kanashiro, Tatsuo

2005-02-01

259

Shallow halogen vacancies in halide optoelectronic materials  

Science.gov (United States)

Halogen vacancies (VH ) are usually deep color centers (F centers) in halides and can act as major electron traps or recombination centers. The deep VH contributes to the typically poor carrier transport properties in halides. However, several halides have recently emerged as excellent optoelectronic materials, e.g., C H3N H3Pb I3 and TlBr. Both C H3N H3Pb I3 and TlBr have been found to have shallow VH , in contrast to commonly seen deep VH in halides. In this paper, several halide optoelectronic materials, i.e., C H3N H3Pb I3 , C H3N H3Sn I3 (photovoltaic materials), TlBr, and CsPbB r3 (gamma-ray detection materials) are studied to understand the material chemistry and structure that determine whether VH is a shallow or deep defect in a halide material. It is found that crystal structure and chemistry of n s2 ions both play important roles in creating shallow VH in halides such as C H3N H3Pb I3 , C H3N H3Sn I3 , and TlBr. The key to identifying halides with shallow VH is to find the right crystal structures and compounds that suppress cation orbital hybridization at VH , such as those with large cation-cation distances and low anion coordination numbers and those with crystal symmetry that prevents strong hybridization of cation dangling bond orbitals at VH . The results of this paper provide insight and guidance to identifying halides with shallow VH as good electronic and optoelectronic materials.

Shi, Hongliang; Du, Mao-Hua

2014-11-01

260

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

International Nuclear Information System (INIS)

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

 
 
 
 
261

Subvalent bismuth monocation Bi+ photoluminescence in ternary halide crystals KAlCl4 and KMgCl3  

International Nuclear Information System (INIS)

Monocation Bi+ isomorphically substitutes potassium in KAlCl4 and KMgCl3 chlorides. Having the unique 6p2 open-shell electronic configuration, Bi+ possesses a number of low-lying excited states, and displays broadband long-lived NIR photoluminescence in ternary chloride crystals. - Highlights: ? Monocation Bi+ can isomorphically substitute K+ in ternary chloride crystals. ? Bi+ doped ternary chlorides can be crystallized from Lewis acidic melts. ? Bi+ doped ternary chlorides possess broadband NIR luminescence.

262

Synthesis, growth conditions, and crystal structures of alkali metal hypophosphites MH2PO2  

International Nuclear Information System (INIS)

Metal hypophosphites are widely used in various fields. However, their structures have not been adequately studied. The synthesis conditions (the temperature and precursors) were found and crystals of anhydrous Li, K, Rb, Cs, and NH4 hypophosphites were grown. The structures of these compounds were established by X-ray diffraction analysis. These crystal structures can be described as packings of layers consisting of hypophosphite anions coordinated to metal cations. In all these salts, the hypophosphite anions serve as bridges between four cations belonging to the same layer. Each oxygen atom is bound to two cations

263

Radiation Damage in Scintillating Crystals  

CERN Document Server

Crystal Calorimetry in future high energy physics experiments faces a new challenge to maintain its precision in a hostile radiation environment. This paper discusses the effects of radiation damage in scintillating crystals, and concludes that the predominant radiation damage effect in crystal scintillators is the radiation induced absorption, or color center formation, not the loss of the scintillation light yield. The importance of maintaining crystal's light response uniformity and the feasibility to build a precision crystal calorimeter under radiation are elaborated. The mechanism of the radiation damage in scintillating crystals is also discussed. While the damage in alkali halides is found to be caused by the oxygen or hydroxyl contamination, it is the structure defects, such as oxygen vacancies, cause damage in oxides. Material analysis methods used to reach these conclusions are presented in details.

Zhu Ren Yuan

1998-01-01

264

Temperature and pressure dependences of the NQR frequency in alkali metal halogenates crystals  

International Nuclear Information System (INIS)

Values of coefficients of compressibility and thermal expansion have been calculated on the basis of measured baric and temperature dependences of nuclear quadrupole resonance frequencies in crystals of potassium chlorate, lithium and cesium iodates according to the technique suggested. The data obtained are compared with data measured directly in experiments on measuring compressibility and thermal expansion. Taking account of obtained values of thermodynamic coefficients, radiospectroscopic data are compared with data on infrared and quadrupole resonance spectra

265

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

International Nuclear Information System (INIS)

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

266

Thermoluminescence studies of gamma irradiated mixed crystals  

International Nuclear Information System (INIS)

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

267

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

International Nuclear Information System (INIS)

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

268

Tunable lasers utilizing color centers in ionic crystals (review)  

Energy Technology Data Exchange (ETDEWEB)

A review is given of investigations of tunable lasers utilizing color centers in ionic crystals. An analysis is made of the microstructure, spectral, luminescence, and kinetic properties of various complex electron color centers in alkali-halide crystals and alkaline-earth fluoride crystals used or capable of being used as active media in near infrared tunable lasers. Possible causes of optical and thermal instability are discussed for centers having different structures and methods of improving the stability are considered. The parameters of existing color center lasers are presented and the prospects for their development and application are discussed.

Arkhangel' skaya, V.A.; Feofilov, P.P.

1980-06-01

269

Structural criteria for the design of anion receptors: The interaction of halides with electron-deficient arenes  

Energy Technology Data Exchange (ETDEWEB)

This paper refines the nature of the interactions between electron-deficient arenes and halide anions. Conclusions are based on (i) new crystal structures containing alkali halide salts with 1,2,4,5-tetracyanobenzene (TCB) and 18-crown-6, (ii) evaluation of crystal structures found in the Cambridge Structural Database, and (iii) MP2/aug-cc-pVDZ calculations of F-, Cl-, and Br- complexes with TCB, 1,3,5-tricyanobenzene, triazine, and hexafluorobenzene. When the halide lies above the plane of the pi system, the results establish that three distinctly different types of complexes are possible: strongly covalent sigma complexes, weakly covalent donor-pi-acceptor complexes, and noncovalent anion-pi complexes. When aryl C-H groups are present, a fourth type of interaction leads to C-H center dot center dot center dot X- hydrogen bonding. Characterization of the different geometries encountered with the four possible binding motifs provides criteria needed to design host architectures containing electron-deficient arenes.

Berryman, Mr. Orion B. [University of Oregon; Bryantsev, Vyacheslav S. [California Institute of Technology, Pasadena; Stay, Mr. David P. [University of Oregon; Johnson, Prof. Darren W. [University of Oregon; Hay, Benjamin [ORNL

2007-01-01

270

Structural Criteria for the Design of Anion Receptors: The Interaction of Halides with Electron-Deficient Arenes  

Energy Technology Data Exchange (ETDEWEB)

This paper refines the nature of the interactions between electron-deficient arenes and halide anions. Conclusions are based on (1) new crystal structures containing alkali halide salts with 1,2,4,5-tetracyanobenzene (TCB) and 18-crown-6, (2) evaluation of crystal structures found in the Cambridge Structural Database, and (3) MP2/aug-cc-pVDZ calculations of F?, Cl?, and Br? complexes with TCB, 1,3,5-tricyanobenzene, triazine, and hexafluorobenzene. When the halide lies above the plane of the ? system, the results establish that three distinctly different types of complexes are possible: strongly covalent ? complexes, weakly covalent donor ?-acceptor complexes, and electrostatic anion-? complexes. When aryl C?H groups are present, a fourth type of interaction leads to C?H???X? hydrogen bonding. Characterization of the different geometries encountered with the four possible binding motifs provides criteria needed to design host architectures containing electron-deficient arenes. This research was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences laboratory, a national scientific user facility sponsored by the U.S. Department of Energy?s Office of Biological and Environmental Research located at the Pacific Northwest National Laboratory. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Berryman, Orion B.; Bryantsev, Vyacheslav; Stay, David P.; Johnson, Darren W.; Hay, Benjamin P.

2007-01-10

271

Local fields in ionic crystals  

International Nuclear Information System (INIS)

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 4?/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)

272

Study of absorption spectra for alkali and alkaline earth metal salts in flameless atomic absorption spectrometry using a carbon tube atomizer  

International Nuclear Information System (INIS)

Absorption spectra of various salts such as alkali metal salts, alkaline earth dichlorides, and ammonium halides were investigated and absorptions of some molecular species produced in the carbon tube were identified. The aqueous solution (20 ?l) containing 1.0 mg/ml of each salt was placed in the carbon tube atomizer and heated in a similar manner to usual flameless atomic absorption method. D2-lamp was used as a continuous light source and argon gas was employed as an inert sheath gas. The spectra were obtained over the range of wavelength 200 to 350 nm. When alkali halides were feeded, the absorption spectra agreed with those of alkali halide vapors. Therefore, in such cases vapors of the alkali halides were probably produced by the sublimation or vaporization in the atomizer. The spectra of alkali perchlorates were considered to be those of alkali chlorides produced by the pyrolysis of the perchlorates in the atomizer. The absorptions of alkaline earth chlorides below 250 nm were probably due to their gaseous states. Sulfur dioxide was found to be produced by the pyrolysis of alkali sulfates, bisulfates and sulfites in the atomizer, Alkali phosphates and pyrophosphates gave almost identical spectra below 300 nm. Gamma band spectrum of nitrogen monoxide was observed from 200 to 240 nm during ashing at bout 3300C for alkali nitrates and nitrites. Ammonia vapor was produced from ammonium halides during drying at about 1700C. Althoughrying at about 1700C. Although the absorptions of alkali carbonates and hydroxides were almost undetectable, the same spectra as those of alkali halides were observed by the addition of ammonium halides to the solutions of alkali compounds. This shows that alkali halides are produced in the atomizer by the addition of halide ions. (auth.)

273

Luminescent quantum efficiency of Eu{sup 2+} ions in mixed KCl{sub 1-x}Br{sub x} crystals  

Energy Technology Data Exchange (ETDEWEB)

In this work, the luminescent quantum efficiency of Eu{sup 2+} ions in mixed KCl{sub 1-x}Br{sub x} crystals is determined by using simultaneous and multiwavelength measurement of photoacoustic and luminescent signals after pulsed laser excitation. This method, which was first demonstrated in Eu{sup 2+} doped alkali halides (NaCl, KCl, KBr and KI) is now extended to mixed crystals. It is found that the quantum efficiency is reduced for mixed KCl{sub 1-x}Br{sub x} crystals from {phi}{approx}100%, in pure alkali halides (KCl and KBr), to a value {phi}{approx}60% for x{approx}0.6. (author)

Munoz, J.A.; Paolo, R. di; Tocho, J.O.; Cusso, F. [Departamento Fisica de Materiales, C-IV, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Castaneda, B. [Departamento de Investigacion en Fisica, Universidad de Sonora, PO Box 1626, Hermosillo, Sonora 83000 (Mexico); Perez-Salas, R.; Aceves, R.; Barboza-Flores, M. [Centro de Investigacion en Fisica, Universidad de Sonora, PO Box 5-088, Hermosillo, Sonora 83190 (Mexico)

1998-05-11

274

????????????????? ???????? Effect of the Ratio of SiO2 and Al2O3 on the Viscosity and Crystallization of Non-Alkali Aluminoborosilicate Glasses at High Temperature  

Directory of Open Access Journals (Sweden)

Full Text Available ????????????????????????????????????????????????????????????????????????????????????????????????Effect of the ratio of SiO2 and Al2O3 on the viscosity and crystallization of non-alkali aluminoborosilicate glasses at high temperature was investigated. The results showed that the viscosity, the fiber-drawing temperature and the activation energy for vicious flow were increased, the liquidus temperature was decreased and the difference between the fiber-drawing temperature & the liquidus temperature was increased with the ratio of SiO2 and Al2O3 increased.

???

2013-05-01

275

Polynuclear technetium halide clusters  

International Nuclear Information System (INIS)

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

276

STUDIES OF DEFECT PROPERTIESAn X-ray Study of Defective Ionic Single Crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The line profiles of the (200) and (220) reflections of large (2 x 2 x 1 cm3) pure and doped i.e. deformed alkali-halide single crystals were investigated with CuK? radiation. The defective state of the crystals presents itself in the formation of a diffuse background and the shift of the Bragg angle. A negative correlation was found between the lattice parameter and residual stress values. Heavily doped crystals develop complex line profiles which can be deconvoluted in the vicinity of the ...

Morlin, Z.; Pe?ter, A?; Fo?ldva?ri, I.; Mecseki, A.

1980-01-01

277

Hygroscopicity Evaluation of Halide Scintillators  

Energy Technology Data Exchange (ETDEWEB)

A collaborative study of relative hygroscopicity of anhydrous halide scintillators grown at various laboratories is presented. We have developed a technique to evaluate moisture sensitivity of both raw materials and grown crystals, in which the moisture absorption rate is measured using a gravimetric analysis. Degradation of the scintillation performance was investigated by recording gamma-ray spectra and monitoring the photopeak position, count rate and energy resolution. The accompanying physical degradation of the samples exposed to ambient atmosphere was photographically recorded as well. The results were compared with ben

Zhuravleva, M [The University of Tennessee; Stand, L [The University of Tennessee; Wei, H [The University of Tennessee; Hobbs, C. L. [University of Tennessee, Knoxville (UTK); Boatner, Lynn A [ORNL; Ramey, Joanne Oxendine [ORNL; Burger, Arnold [Fisk University, Nashville; Rowe, E [Fisk University, Nashville; Bhattacharya, P. [Fisk University, Nashville; Tupitsyn, E [Fisk University, Nashville; Melcher, Charles L [University of Tennessee, Knoxville (UTK)

2014-01-01

278

Effect of alkali metal Oxides on viscosity and crystallization of the MgO–Al2O3–SiO2 glasses  

International Nuclear Information System (INIS)

MgO–Al2O3–SiO2 glasses were prepared by using TiO2 and ZrO2 as nucleation agents, and 2% (wt%, the same as below) content of alkali metal oxide was added. The viscosity of MAS glass melt was investigated by the rotating crucible viscometer, and the melting temperature and activation energy for viscous flow of the melt were derived by the Arrhenius equation. After melting and casting, the glass samples were crystallized in the temperature range from 880 to 1145 °C. The prepared glass-ceramics presented transparent to opaque with the increasing of crystallization temperature, which had been investigated by X-ray diffraction and field emission–environment scanning electron microscope. The results showed that the melting temperature of glass containing 2% Na2O was about 1585 °C. The MgAl2O4, ZrTiO4 and the sapphirine crystalline phases precipitated from matrix glass successively as the crystallization temperature raising. When 1% Na2O was replaced by Li2O, the melting temperature of the glasses decreased to 1508 °C, meanwhile, the main crystal phase changed from MgAl2O4 to high-/low—quartz solid solution, therefore, the crystallization behavior was uncontrollable and the transparent glass ceramic cannot be obtained. As 1% K2O substituted for Na2O, the melting temperature decreased to 1573 °C. The adding of K2O could broaden the crystallization temperature range of preparing transparent glass-ceramics. After crystallized at the range from 900 °C to 1000 °C, the fine spinel (MgAl2O4) crystals which had average size about 25 nm precipitated from matrix glasses, and the specimens kept transparent

279

Effect of alkali metal Oxides on viscosity and crystallization of the MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glasses  

Energy Technology Data Exchange (ETDEWEB)

MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glasses were prepared by using TiO{sub 2} and ZrO{sub 2} as nucleation agents, and 2% (wt%, the same as below) content of alkali metal oxide was added. The viscosity of MAS glass melt was investigated by the rotating crucible viscometer, and the melting temperature and activation energy for viscous flow of the melt were derived by the Arrhenius equation. After melting and casting, the glass samples were crystallized in the temperature range from 880 to 1145 °C. The prepared glass-ceramics presented transparent to opaque with the increasing of crystallization temperature, which had been investigated by X-ray diffraction and field emission–environment scanning electron microscope. The results showed that the melting temperature of glass containing 2% Na{sub 2}O was about 1585 °C. The MgAl{sub 2}O{sub 4}, ZrTiO{sub 4} and the sapphirine crystalline phases precipitated from matrix glass successively as the crystallization temperature raising. When 1% Na{sub 2}O was replaced by Li{sub 2}O, the melting temperature of the glasses decreased to 1508 °C, meanwhile, the main crystal phase changed from MgAl{sub 2}O{sub 4} to high-/low—quartz solid solution, therefore, the crystallization behavior was uncontrollable and the transparent glass ceramic cannot be obtained. As 1% K{sub 2}O substituted for Na{sub 2}O, the melting temperature decreased to 1573 °C. The adding of K{sub 2}O could broaden the crystallization temperature range of preparing transparent glass-ceramics. After crystallized at the range from 900 °C to 1000 °C, the fine spinel (MgAl{sub 2}O{sub 4}) crystals which had average size about 25 nm precipitated from matrix glasses, and the specimens kept transparent.

Wang, Jing, E-mail: wangjing7683@sina.com [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Cheng, Jin-shu; Deng, Zhen-lu [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China)

2013-04-15

280

Activation of glycosyl halides by halogen bonding.  

Science.gov (United States)

Halogen bonding is the formation of a non-covalent interaction between an electrophilic halogen substituent and a Lewis base, for instance, a halide. These kinds of relatively weak interactions have found applications in crystal engineering and initial applications in solution-phase chemistry are starting to appear. We report on the exploration of bis(iodoimidazolium) compounds as halogen-based Lewis acids in the activation of glycosyl halides. We show that these dicationic halogen-bond donors can be used to activate glycosyl halides if the carbohydrate core is sufficiently reactive enough. Furthermore, we provide comparison experiments which indicate that the mode of activation is indeed based on halogen bonding. This represents the first glycosylation reaction mediated by a (carbon-backbone-based) halogen-bond donor. PMID:24962953

Castelli, Riccardo; Schindler, Severin; Walter, Sebastian M; Kniep, Florian; Overkleeft, Herman S; Van der Marel, Gijsbert A; Huber, Stefan M; Codée, Jeroen D C

2014-08-01

 
 
 
 
281

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 de...

Caleman, C.; Desy, Forschung Mit Photonen; Hub, J. S.; Maaren, P.; Spoel, D.

2011-01-01

282

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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).

Alcaraz Sendra, Olga; Trull??s Sim??, Joaquim

2001-01-01

283

Thermally stimulated luminescence and lattice defects in crystals of alkali metal borate LiB{sub 3}O{sub 5} (LBO)  

Energy Technology Data Exchange (ETDEWEB)

The recombination processes and lattice defects in crystals of alkali metal borate LiB{sub 3}O{sub 5} (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{sup -} center in three different planes were measured in the temperature range from 80 to 400 K. The luminescence bands were assigned to the electron (E{sub m}=4.0 eV) and hole (E{sub m}=4.2 eV) recombination processes. The model of the trapped hole center O{sup -} 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.

Ogorodnikov, I.N. E-mail: ogo@dpt.ustu.ru; Isaenko, L.I.; Kruzhalov, A.V.; Porotnikov, A.V

2001-10-01

284

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

Energy Technology Data Exchange (ETDEWEB)

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.)

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

285

Binary technetium halides  

Science.gov (United States)

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

Johnstone, Erik Vaughan

286

Synthesis and Crystal Structures of 1,1?-Methylene-bis(imidazolidine-2,4-dione) and Alkali Metal Salts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Single-crystal structures of 1,1?-methylenebis(imidazolidine-2,4-dione) and its sodium and dipotassium salts were determined. Powder X-ray diffraction was also employed to characterize the bulk materials and those phases which did not yield single-crystals. These compounds are of interest for intumescent coatings.

Robert Salchner; Volker Kahlenberg; Roman Lackner; Klaus Wurst; Doris Braun; Gerhard Laus; Herwig Schottenberger

2014-01-01

287

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

Science.gov (United States)

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.

Berdonosov, P. S.; Olenev, A. V.; Dolgikh, V. A.

2012-03-01

288

Single crystal X-ray structure of Lawsone anion: Evidence for coordination of alkali metal ions and formation of naphthosemiquinone radical in basic media  

Science.gov (United States)

2-hydroxy-1,4-naphthoquinone; Lawsone (Lw) is a natural compound found in henna leaves. The reaction of lawsone with 'Na' metal (Lw-1), CH3COONa (Lw-2), NaOH (Lw-3), KOH (Lw-4), K2CO3 (Lw-5) and Tris(hydroxymethyl)aminomethane (Lw-6) were studied. Red orange solids obtained for Lw-1 to Lw-6 are characterized by Elemental Analysis, FTIR, 1HNMR and EPR studies. The results reveal the coordination of alkali metals 'Na' and 'K' to lawsone anion. The single crystal X-ray structure of Lw-6 was solved and it crystallizes in triclinic space group P-1 with extensive hydrogen bonding network of Csbnd H⋯O, Nsbnd H⋯O and Osbnd H⋯O between cations and anions. Polycrystalline powder X-band EPR spectra of Lw-1 to Lw-5 shows signals ˜2.004 at 133 K, while Lw-6 is EPR silent. The naphthosemiquinone (NSQ-rad ) radical formed in Lw-2 to Lw-5, is due to disproportion reaction of catechol and naphthoquinone.

Salunke-Gawali, Sunita; Kathawate, Laxmi; Shinde, Yogesh; Puranik, Vedavati G.; Weyhermüller, Thomas

2012-02-01

289

Recent advances in technetium halide chemistry.  

Science.gov (United States)

Transition metal binary halides are fundamental compounds, and the study of their structure, bonding, and other properties gives chemists a better understanding of physicochemical trends across the periodic table. One transition metal whose halide chemistry is underdeveloped is technetium, the lightest radioelement. For half a century, the halide chemistry of technetium has been defined by three compounds: TcF6, TcF5, and TcCl4. The absence of Tc binary bromides and iodides in the literature was surprising considering the existence of such compounds for all of the elements surrounding technetium. The common synthetic routes that scientists use to obtain binary halides of the neighboring elements, such as sealed tube reactions between elements and flowing gas reactions between a molecular complex and HX gas (X = Cl, Br, or I), had not been reported for technetium. In this Account, we discuss how we used these routes to revisit the halide chemistry of technetium. We report seven new phases: TcBr4, TcBr3, ?/?-TcCl3, ?/?-TcCl2, and TcI3. Technetium tetrachloride and tetrabromide are isostructural to PtX4 (X = Cl or Br) and consist of infinite chains of edge-sharing TcX6 octahedra. Trivalent technetium halides are isostructural to ruthenium and molybdenum (?-TcCl3, TcBr3, and TcI3) and to rhenium (?-TcCl3). Technetium tribromide and triiodide exhibit the TiI3 structure-type and consist of infinite chains of face-sharing TcX6 (X = Br or I) octahedra. Concerning the trichlorides, ?-TcCl3 crystallizes with the AlCl3 structure-type and consists of infinite layers of edge-sharing TcCl6 octahedra, while ?-TcCl3 consists of infinite layers of Tc3Cl9 units. Both phases of technetium dichloride exhibit new structure-types that consist of infinite chains of [Tc2Cl8] units. For the technetium binary halides, we studied the metal-metal interaction by theoretical methods and magnetic measurements. The change of the electronic configuration of the metal atom from d(3) (Tc(IV)) to d(5) (Tc(II)) is accompanied by the formation of metal-metal bonds in the coordination polyhedra. There is no metal-metal interaction in TcX4, a Tc?Tc double bond is present in ?/?-TcCl3, and a Tc?Tc triple bond is present in ?/?-TcCl2. We investigated the thermal behavior of these binary halides in sealed tubes under vacuum at elevated temperature. Technetium tetrachloride decomposes stepwise to ?-TcCl3 and ?-TcCl2 at 450 °C, while ?-TcCl3 converts to ?-TcCl3 at 280 °C. The technetium dichlorides disproportionate to Tc metal and TcCl4 above ?600 °C. At 450 °C in a sealed Pyrex tube, TcBr3 decomposes to Na{[Tc6Br12]2Br}, while TcI3 decomposes to Tc metal. We have used technetium tribromide in the preparation of new divalent complexes; we expect that the other halides will also serve as starting materials for the synthesis of new compounds (e.g., complexes with a Tc3(9+) core, divalent iodide complexes, binary carbides, nitrides, and phosphides, etc.). Technetium halides may also find applications in the nuclear fuel cycle; their thermal properties could be utilized in separation processes using halide volatility. In summary, we hope that these new insights on technetium binary halides will contribute to a better understanding of the chemistry of this fascinating element. PMID:24393028

Poineau, Frederic; Johnstone, Erik V; Czerwinski, Kenneth R; Sattelberger, Alfred P

2014-02-18

290

Vitrification of IFR and MSBR halide salt reprocessing wastes  

International Nuclear Information System (INIS)

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)

291

Process for oxidation of hydrogen halides to elemental halogens  

Science.gov (United States)

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.

Lyke, Stephen E. (Middleton, WI)

1992-01-01

292

Vitrification of IFR and MSBR halide salt reprocessing wastes  

Energy Technology Data Exchange (ETDEWEB)

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)

Siemer, D.D. [Idaho National Laboratory, 12N 3167E, Idaho Falls, ID 83402 (United States)

2013-07-01

293

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

International Nuclear Information System (INIS)

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

294

Phase separation of crystal surfaces a lattice gas approach  

CERN Document Server

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

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

1994-01-01

295

Structural phase transitions in tetra(isopropylammonium) decachlorotricadmate(II), [(CH3)2CHNH3]4Cd3Cl10, crystal with a two-dimensional cadmium(II) halide network.  

Science.gov (United States)

Single crystals of tetra(isopropylammonium) decachlorotricadmate(II) as a rare example of a two-dimensional cadmium(II) halide network of [Cd(3)Cl(10)](n)(4-) have been synthesized and characterized by means of calorimetry and X-ray diffraction. The crystals exhibit polymorphism in a relatively narrow temperature range (three phase transitions at 353, 294 and 259 K). Our main focus was to establish the mechanism of these successive transformations. The crystal structure was solved and refined in the space group Cmce at 375 K (Phase I), Pbca at 320 K (Phase II) and P2(1)2(1)2(1) (Phase III) at 275 K in the same unit-cell metric. The structure is composed of face-sharing polyanionic [Cd(3)Cl(10)](4-) units which are interconnected at the bridging Cl atom into four-membered rings forming a unique two-dimensional network of [Cd(3)Cl(10)](n)(4-). The interstitial voids within the network are large enough to accommodate isopropylammonium cations and permit thermally activated rotations. While in Phase I isopropylammonium tetrahedra rotate almost freely about the C-N bond, the low-temperature phases are the playground of competition between the thermally activated disorder of isopropylammonium cations and stabilizing N-H···Cl hydrogen-bond interactions. The transition from Phase I to II is dominated by a displacive mechanism that leads to significant rearrangement of the polyanionic units. Cation order-disorder phenomena become prominent at lower temperatures. PMID:21422611

Gagor, Anna; Wa?kowska, Alicja; Czapla, Zbigniew; Dacko, Slawomir

2011-04-01

296

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

Science.gov (United States)

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-methyl transferase. MeX production may be a result of non-specific methylation of halides by SAM utilizing methyl transferases used in other biosynthetic pathways.

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

2002-12-01

297

Superionicity Study from Electronic State Calculation of Metal Halide Cluster  

Science.gov (United States)

The electronic states of silver halides and sodium halides are calculated by the DV-X? cluster method to get more microscopic evidence for the p-d hybridization in noble metal halides. The calculations are carried out for the (A13B14)- (A=Ag+ and Na+, B = halogen ion) clusters. It is found that both components of anti-bonding and bonding exist in the diagram of overlap population (DOP) for AgX (X=halogen) and these two components are made up of the 4\\textit{d} band of Ag+ and the \\textit{p} band of halogen ion, which form the \\textit{p}--\\textit{d} hybridization. On the other hand, the DOP of alkali halides is occupied by almost only bonding component. It is inferred that the origin of AgI type superionic conductor is in the weakness of \\textit{p}--\\textit{d} hybridization. The hypothetical rock-salt AgI is also discussed to investigate the unstableness of rock-salt AgI.

Ono, Shinji; Kobayashi, Michisuke

2005-02-01

298

Subvalent bismuth monocation Bi{sup +} photoluminescence in ternary halide crystals KAlCl{sub 4} and KMgCl{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

Monocation Bi{sup +} isomorphically substitutes potassium in KAlCl{sub 4} and KMgCl{sub 3} chlorides. Having the unique 6p{sup 2} open-shell electronic configuration, Bi{sup +} possesses a number of low-lying excited states, and displays broadband long-lived NIR photoluminescence in ternary chloride crystals. - Highlights: Black-Right-Pointing-Pointer Monocation Bi{sup +} can isomorphically substitute K{sup +} in ternary chloride crystals. Black-Right-Pointing-Pointer Bi{sup +} doped ternary chlorides can be crystallized from Lewis acidic melts. Black-Right-Pointing-Pointer Bi{sup +} doped ternary chlorides possess broadband NIR luminescence.

Romanov, Alexey N., E-mail: alexey.romanov@list.ru [Research Computer Center of M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 4, 119991 Moscow (Russian Federation); Dimonta Ltd., 15 Nagornaya Str., Build. 8, 117186 Moscow (Russian Federation); Veber, Alexander A. [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow (Russian Federation); Fattakhova, Zukhra T. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygina Str., 119991 Moscow (Russian Federation); Usovich, Olga V. [Department of Chemistry, M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 3, 119991 Moscow (Russian Federation); Haula, Elena V. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygina Str., 119991 Moscow (Russian Federation); Trusov, Lev. A.; Kazin, Pavel E. [Department of Chemistry, M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 3, 119991 Moscow (Russian Federation); Korchak, Vladimir N. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygina Str., 119991 Moscow (Russian Federation); Tsvetkov, Vladimir B. [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow (Russian Federation); Sulimov, Vladimir B. [Research Computer Center of M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 4, 119991 Moscow (Russian Federation); Dimonta Ltd., 15 Nagornaya Str., Build. 8, 117186 Moscow (Russian Federation)

2013-02-15

299

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

Energy Technology Data Exchange (ETDEWEB)

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.

Moore, David T.; Sai, Hiroaki; Wee Tan, Kwan; Estroff, Lara A.; Wiesner, Ulrich, E-mail: ubw1@cornell.edu [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853 (United States)

2014-08-01

300

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

International Nuclear Information System (INIS)

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

 
 
 
 
301

Dislocation spectroscopy of crystals  

International Nuclear Information System (INIS)

The new method for studying the dislocations energy characteristics, based on investigation of interaction of moving dislocations with directly introduced electron and hole centers is proposed. The studies on alkali-halide crystals KCl, NaCl, RBr, LiF and KI, containing electron F- and hole VK- and Me++(Cu++, Ag++, Tl++, In++)-centers, are carried out. The study on temperature dependence of interaction of the dislocations with the F-centers made it possible to determine the position of the electron dislocation zone (EDZ) in the crystal zone scheme. The EDZ in KCl is remote from the zone bottom by ? 2.2 eV. It is shown, that the dislocations transfer holes from the centers, located below the hole dislocation zone (HDZ) (X+, In++, Tl++, VK), on to the centers located above the HDZ, the (Cu+, Ag+)-centers. Such a process does not depend on temperature. The HDZ position in the crystal zone scheme is determined. In the KCl crystal it is remote from the vertex of the valent zone by ? 1.6 eV. The effective radii of the dislocations interaction with the electron F- and hole X+, VK, Tl++-centers are determined

302

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

Science.gov (United States)

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.

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

2013-02-19

303

Decay of the F- centre in some alkali halides  

International Nuclear Information System (INIS)

The production and subsequent decay of the F- centre in NaF, NaCl, KBr and KI has been studied by pulse radiolysis. The centre decays by a mixture of thermal and photolytic processes, with temperature-independent photolysis dominant at low temperature. The thermal decay exhibited first order kinetic behaviour in all cases, with a rate constant which was independent of both the dose per pulse and the previous radiation history of the sample: this is used as evidence that decay is via thermal ionisation rather than the vacancy capture process postulated previously. The temperature dependence of the rate constant leads to the following values for the Arrhenius activation energy: NaF: 1.5 +- 0.15, NaCl: 1.10 +- 0.04, KBr: 0.43 +- 0.03, KI: 0.47 +- 0.02 eV. (author)

304

Temperature jump induction of isomerization dynamics of alkali halide clusters  

International Nuclear Information System (INIS)

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

305

Studies on multiphased mixed crystals grown from NaBr and KCl  

International Nuclear Information System (INIS)

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

306

Studies on multiphased mixed crystals grown from NaBr and KCl  

Energy Technology Data Exchange (ETDEWEB)

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.

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

307

New hypodiphosphates of the alkali metals: Synthesis, crystal structure and vibrational spectra of the hypodiphosphates(IV) M2[(H2P2O6)(H4P2O6)] (M=Rb and Cs)  

International Nuclear Information System (INIS)

The new hypodiphosphates(IV) Rb2[(H2P2O6)(H4P2O6)] (1) and Cs2[(H2P2O6)(H4P2O6)] (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 (H2P2O6)2? and (H4P2O6) units in staggered conformation for the P2O6 skeleton and the corresponding alkali-metal cations. In the (H2P2O6)2? ion the hydrogen atoms are in a “trans–trans” conformation. O·H–O hydrogen bonds between the (H2P2O6)2? and (H4P2O6) groups consolidate the structures into a three-dimensional network. The FT-Raman and 31P and 1H and MAS NMR spectra of the title compounds have been recorded and interpreted, especially with respect to their assignment to the (H2P2O6)2? and (H4P2O6) groups. Thermogravimetric data of 2 havgravimetric data of 2 have been interpreted in terms of a thermal decomposition model. - Graphical Abstract: The layered compounds Rb2[(H2P2O6)(H4P2O6)] and Cs2[(H2P2O6)(H4P2O6)] have been synthesized and investigated. Both crystallize isotypic. The structures are built up by discrete (H2P2O6)2? and (H4P2O6) units and the corresponding alkali-metal cations. Highlights: ? Synthesis and single-crystal structure of new alkali hypodiphosphates. ? Structures are characterized by [(H2P2O6)(H4P2O6)]2? units and M+ cations. ? (H2P2O6)2? and (H4P2O6) units are linked by short hydrogen bonds. ? Both compounds are characterized by 31P MAS-NMR spectra.

308

Single crystal growth by self-flux method of the mixed valence gold halides Cs2[AuIX2][AuIIIX4] (X=Br,I)  

Science.gov (United States)

High quality single crystals of Cs2Au2X6 (X=Br,I) were grown using a ternary self-flux method. Structural refinements based on single crystal X-ray diffraction measurements show that both materials have a distorted perovskite structure belonging to the I4/mmm space group with full site occupancy. Transport measurements reveal a large bandgap of 550±100 meV for Cs2Au2I6 and 520±80 meV for Cs2Au2Br6. Initial attempts at chemical substitution are described.

Riggs, Scott C.; Shapiro, M. C.; Corredor, F.; Geballe, T. H.; Fisher, I. R.; McCandless, Gregory T.; Chan, Julia Y.

2012-09-01

309

Solution enthalpies of trivalent defects in alkali chlorides  

International Nuclear Information System (INIS)

Calculations of the heat of formation of dilute solid solutions of AlCl3, ScCl3, GaCl3, YCl3, and InCl3 in each of the three alkali chlorides NaCl, KCl, and RbCl are reported. The Born-Mayer repulsive parameters (B-M RPs) for nearest-neighbour interaction and the solution enthalpies of trivalent defects in alkali halides have been derived from the correlation between B-M RPs and the charge density overlap parameters of the interacting ions

310

Exciton-relaxation dynamics in lead halides  

CERN Document Server

We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of self-trapped states, we discuss the origin of luminescence components which are mainly induced under one-photon excitation into the exciton band in lead fluoride, lead chloride, and lead bromide.

Iwanaga, M; Iwanaga, Masanobu; Hayashi, Tetsusuke

2003-01-01

311

Exciton-relaxation dynamics in lead halides  

International Nuclear Information System (INIS)

We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of self-trapped states, we discuss the origin of luminescence components which are mainly induced under one-photon excitation into the exciton band in lead fluoride, lead chloride, and lead bromide

312

Halide laser glasses  

International Nuclear Information System (INIS)

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

313

Halide laser glasses  

Energy Technology Data Exchange (ETDEWEB)

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

Weber, M.J.

1982-01-14

314

Nanosized alkali-metal-doped ethoxotitanate clusters.  

Science.gov (United States)

The synthesis and crystallographic characterization of alkali-metal-doped ethoxotitanate clusters with 28 and 29 Ti atoms as well as a new dopant-free Ti28 cluster are presented. The light-metal-doped polyoxotitanate clusters in which the alkali-metal atom is the critical structure-determining component are the largest synthesized so far. Calculations show that doping with light alkali atoms narrows the band gap compared with the nondoped crystals but does not introduce additional energy levels within the band gap. PMID:23587091

Chen, Yang; Trzop, Elzbieta; Makal, Anna; Sokolow, Jesse D; Coppens, Philip

2013-05-01

315

Alkali metal intercalates of molybdenum disulfide.  

Science.gov (United States)

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

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

1973-01-01

316

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

International Nuclear Information System (INIS)

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

317

Formation of tungsten monocarbide from a molten tungstate-halide phase by gas sparging  

International Nuclear Information System (INIS)

A process for preparation of tungsten monocarbide is described comprising: (a) providing a molten composition comprising an alkali metal halide and an oxygen compound of tungsten; (b) sparging the composition with a gas comprising a gaseous hydrocarbon which is selected from the group consisting of natural gas, methane, ethane, acetylene, propane, butane, mixtures thereof, and admixtures of these gases with H2 or CO, at a temperature of about 9000 to 11000C for a sufficient time for the tungsten compound to be substantially converted to tungsten carbide; and (c) decanting the molten halide from the tungsten carbide product

318

Solution enthalpy of alkali halogenides in D2O  

International Nuclear Information System (INIS)

The enthalpy of solution of NaF, HCl, KI, RbBr, and CsCl in heavy water and the enthalpy of dilution of KCl and KI solutions in D2O were measured calorimetrically. The enthalpies of solution of 20 alkali halides in D2O in the low-concentration range up to infinite dilution were found by the method of differences in transfer enthalpies

319

Search for improved-performance scintillator candidates among the electronic structures of mixed halides  

Science.gov (United States)

The application of advanced theory and modeling techniques has become an essential component to understand material properties and hasten the design and discovery of new ones. This is true for diverse applications. Therefore, current efforts aimed towards finding new scintillator materials are also aligned with this general predictive approach. The need for large scale deployment of efficient radiation detectors requires discovery and development of high-performance, yet low-cost, scintillators. While Tl-doped NaI and CsI are still some of the widely used scintillators, there are promising new developments, for example, Eu-doped SrI2 and Ce-doped LaBr3. The newer candidates have excellent light yield and good energy resolution, but challenges persist in the growth of large single crystals. We will discuss a theoretical basis for anticipating improved proportionality as well as light yield in solid solutions of certain systems, particularly alkali iodides, based on considerations of hot-electron group velocity and thermalization. Solid solutions based on NaI and similar alkali halides are attractive to consider in more detail because the end point compositions are inexpensive and easy to grow. If some of this quality can be preserved while reaping improved light yield and possibly improved proportionality of the mixture, the goal of better performance at the low price of NaI:Tl might be attainable by such a route. Within this context, we will discuss a density functional theory (DFT) based study of two prototype systems: mixed anion NaIxBr1-x and mixed cation NaxK1-xI. Results obtained from these two prototype candidates will lead to further targeted theoretical and experimental search and discovery of new scintillator hosts.

Li, Qi; Williams, Richard T.; Burger, Arnold; Adhikari, Rajendra; Biswas, Koushik

2014-09-01

320

Synthesis, characterization, crystal structure determination and computational study of the two new bidentate O, N Schiff bases derived from bromosalicylaldehyde and amines containing alkyl halide pendant groups  

Science.gov (United States)

Two new Schiff base compounds 2-{(E)-[2-(bromoethyl)imino]methyl}-4-bromophenol (1) and 2-{(E)-[2-(chloroethyl)imino]methyl}-4-bromophenol (2) have been synthesized and characterized by FT-IR and 1H NMR spectroscopy, elemental analysis, thermal studies and single-crystal X-ray diffraction. They crystallize in the triclinic system, space group P-1. Both Schiff base compounds 1 and 2 display a trans configuration with respect to the CN double bond. Quantum theory of atoms in molecules (QTAIM) has been also used to find intramolecular interactions and investigate their chemical nature. The results show that in both of the compounds 1 and 2, there is a hydrogen bonding between nitrogen of imine and oxygen of phenol which is considerably stronger than normal hydrogen bonds. In addition, it has been shown that these hydrogen bonds are partially covalent and partially electrostatic in nature, in contrast to normal hydrogen bonds, which are usually considered as electrostatic interactions.

Grivani, Gholamhossein; Tahmasebi, Vida; Eskandari, Keiamars; Khalaji, Aliakbar Dehno; Bruno, Giuseppe; Rudbari, Hadi Amiri

2013-12-01

 
 
 
 
321

Freezing in Halide Salts  

Science.gov (United States)

The static criterion that the amplitude of the principal peak of the liquid structure factor has a constant value along the freezing line and the onset of freezing are studied from the structure factors and the static dielectric functions of halide salts interacting via the effective pair potentials through the hypernetted-chain approximation. It is observed that the criterion above is restricted to the effective charge difference. The critical value of plasma parameter at freezing is affected by the mobility and number concentration of anions and cations. The distribution of the value of the static dielectric function closest to the wave number axis in the negative region is also determined by the charge difference and the ordering of ions and related to the onset of freezing.

Akdere, ?.; Y?lmaz, M.; Kavanoz, H. B.; Ta?seven, Ç.

2008-06-01

322

Raman spectra of ionic liquids: A simulation study of LaCl3 and its mixtures with alkali chlorides  

Science.gov (United States)

Theoretical Raman spectra of the elpasolite-structured crystal Cs2NaLaCl6 and of molten mixtures of LaCl6 with NaCl and CsCl have been obtained from computer simulations in order to examine how the Raman spectra reflect the coordination structure around the La3+ ions. This system is a model for many other trivalent metal halides and for examining how the network structure of the pure melts is broken down by the addition of alkali halides with different structure-breaking powers. The results suggest a way of reconciling the conclusions of Raman studies about the structures of the melts with those of neutron and x-ray-diffraction studies, which have already been examined with the same simulation methods. The Raman spectra, both polarized and depolarized, are calculated from a model for the dependence of the polarizability of the system on the ionic coordinates which was inspired by electronic structure calculations of the polarizabilities of ions in a condensed phase environment. Some results on the lifetimes of the coordination complexes responsible for the appearance of the discrete Raman bands are discussed.

Glover, William J.; Madden, Paul A.

2004-10-01

323

Synthesis, crystal structure, and characterization of thiophene-3-carboxaldoxime complexes with cobalt(II), nickel(II) and copper(II) halides  

Science.gov (United States)

The reaction of cobalt(II), nickel(II), copper(II) chlorides and bromides with thiophene-3-carboxaldoxime (3TCOH) leads to a series of new complexes: [CoCl2(3TCOH)4], [CoBr2(3TCOH)4], [NiCl2(3TCOH)4], [NiBr2(3TCOH)4], [CuCl2(3TCOH)4], [CuBr2(3TCOH)2] respectively. The crystal structures of [CoBr2(3TCOH)4], [NiBr2(3TCOH)4] have been determined by X-ray diffraction methods showing octahedral complex species. In all complexes, the oxime functional group remains protonated and the coordination occurs through the nitrogen atom of the oxime moiety.

Alomar, Kusaï; Hélesbeux, Jean-Jacques; Allain, Magali; Bouet, Gilles

2012-07-01

324

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

International Nuclear Information System (INIS)

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

325

Melt synthesis of inorganic nitrides and halides  

Science.gov (United States)

Novel halide chlorides Sr7Cl2H12, Sr 7Br2H12, and Ba2ClH3 were formed from sodium chloride and strontium metal in sodium metal melts at 900°C. Sr7Br2H12 crystallizes in the anti-Fe 12Zr2P7 structure type, and Sr7Cl 2H12 crystallizes in a slightly distorted variant of this structure. Ba2ClH3 crystallizes in a structure containing infinite two-dimensional sheets of edge-sharing Ba6Cl chlorine-centered octahedra. Single crystals of gallium nitride can be obtained by reaction of gallium metal and dinitrogen gas at 750°C. Small amounts of alkaline earth metals added to the reaction mixture promote the formation of large crystals. Polycrystalline GaN nucleates rapidly under these conditions on the surface of a stainless steel autoclave; nucleation is far less pronounced on tungsten surfaces. Trace concentrations of hydrogen greatly enhance GaN nucleation. Melts of magnesium metal with cerium, gadolinium, and lanthanum were exposed to ammonia and nitrogen gas at temperatures from 700°C to 900°C. Binary rare earth and magnesium nitrides and hydrides are formed, but no ternary compounds are seen. The absence of ternary compounds is discussed in the light of a thermodynamic model predicting ternary formation in these systems.

Molstad, Jay Clark

326

Methyl Halide Production by Fungi  

Science.gov (United States)

Methyl chloride (CH3Cl), methyl bromide (CH3Br) and methyl iodide (CH3I) are methyl halide gases that contribute significant amounts of halogen radicals to the atmosphere. In an effort to better understand the global budget of methyl halides and their impact on the atmosphere, we need to identify the natural sources in addition to the known anthropogenic sources of these compounds. We are investigating the role of fungi in the production of methyl halides in the soils and wetlands in southern New Hampshire, USA. Previous research has shown that wood decay fungi and ectomycorrhizal fungi, which are within a group of fungi called basidiomycetes, emit methyl halides. In our study, measurements of headspace gas extracted from flasks containing fungi grown in culture demonstrate that a variety of fungi, including basidiomycetes and non-basidiomycetes, emit methyl halides. Our research sites include four ecosystems: an agricultural field, a temperate forest, a fresh water wetland, and coastal salt marshes. We have collected and isolated fungi at each site by culturing tissue samples of fruiting bodies and plant material, by using wood baits, and from the direct culture of soil. We compared the rates of methyl halide emissions from the fungi in the four ecosystems. In addition, we measured emissions from previously assayed fungal isolates after reintroducing them to sterilized soils that were collected from their original environments. Fungal biomass was determined by substrate-induced respiration (SIR). The emission rate by the fungus was determined by a linear regression of the concentration of methyl halide in the sample headspace over time divided by the fungal biomass.

Dailey, G. D.; Varner, R. K.; Blanchard, R. O.; Sive, B. C.; Crill, P. M.

2005-12-01

327

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  

Energy Technology Data Exchange (ETDEWEB)

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{sup +} = Li{sup +}, Rb{sup +}, Cs{sup +}) and alkaline-earth (R{sup 2+} = Sr{sup 2+}, Ba{sup 2+}) 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{sup +} and R{sup 2+} cations on both glass structure and melt crystallization tendency during cooling, two glass series were prepared by replacing either Na{sup +} or Ca{sup 2+} cations in the simplified glass by respectively (Li{sup +}, K{sup +}, Rb{sup +}, Cs{sup +}) or (Mg{sup 2+}, Sr{sup 2+}, Ba{sup 2+}) cations. From these substitutions, it was established that alkali ions are preferentially involved in the charge compensation of (AlO{sub 4}){sup -} 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)

Quintas, A.; Caurant, D.; Majerus, O. [Laboratoire de Chimie de la Matiere Condensee de Paris (UMR 7574), Ecole Nationale Superieure de Chimie de Paris - ENSCP, ParisTech, Paris, 75005 (France); Charpentier, T. [CEA Saclay, Laboratoire de Structure et Dynamique par Resonance Magnetique, DSM/DRECAM/SCM - CEA CNRS URA 331, Gif-sur-Yvette, 91191 (France); Dussossoy, J.L. [Laboratoire d' Etude de Base sur les Verres, CEA Valrho, DEN/DTCD/SCDV/LEBV, Bagnols-sur-Ceze, 30207 (France)

2008-07-01

328

Development and spectral characteristics of new scintillation materials based on oxide crystals  

Science.gov (United States)

Scintillation crystals as components of scintillation detectors are widely used in modern science and technique, especially, in medicine and high energy physics. High density of scintillation material is one of the basic requirements for creating of effective detecting devices. This advantage is incident to oxide crystals, that possess low radiation length and high atomic weight. Therefore such substances as bismuth germanate, yttrium silicate, bivalent metals tungstates, and others became an object of intensive investigations, especially seeing the elaboration of large calorimetric devices for elementary particles accelerators. The analysis of scintillation properties of various scintillator types showed that oxide materials, being at disadvantage in relation to traditional alkali-halide crystal systems in some scintillation parameters, excel them in rapidity, radiation hardness, chemical and thermal stability and operate successfully under conditions of strong irradiation, high temperatures, chemically active environment, mechanical stress, etc.

Bilyi, Mykola U.; Nedel'ko, S. G.; Hizhnyi, Yu. A.

1998-08-01

329

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

International Nuclear Information System (INIS)

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 In3+ 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

330

Coprecipitation of alkali metal ions with calcium carbonate  

International Nuclear Information System (INIS)

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

331

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

Energy Technology Data Exchange (ETDEWEB)

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW{sub 12}O{sub 40}]{sub 2}[Cu{sub 2}(Phen){sub 4}Cl](H{sub 2}4, 4 Prime -bpy){sub 4}{center_dot}H{sub 3}O{center_dot}5H{sub 2}O (1) and [HPW{sub 12}O{sub 40}][Cd{sub 2}(Phen){sub 4}Cl{sub 2}](4, 4 Prime -bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW{sub 12}O{sub 40}]{sup 5-}, metal halide clusters [Cu{sub 2}(Phen){sub 4}Cl]{sup +}and 4, 4 Prime -bpy ligands, while compound 2 is constructed from [PW{sub 12}O{sub 40}]{sup 3-}, metal halide cluster [Cd{sub 2}(Phen){sub 4}Cl{sub 2}]{sup 2+} and 4, 4 Prime -bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. - Graphical Abstract: Two new compounds have been synthesized and characterized. Structure analyses revealed that the two compounds are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Highlights: Black-Right-Pointing-Pointer First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Two different kinds of metal halide clusters. Black-Right-Pointing-Pointer Supramolecular structures based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Hybridization of three different of building blocks.

Wang Lamei; Fan Yong; Wang Yan; Xiao Lina; Hu Yangyang; Peng Yu; Wang Tiegang; Gao Zhongmin; Zheng Dafang [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Cui Xiaobing, E-mail: cuixb@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Xu Jiqing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China)

2012-07-15

332

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

International Nuclear Information System (INIS)

Two new organic–inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW12O40]2[Cu2(Phen)4Cl](H24, 4?-bpy)4·H3O·5H2O (1) and [HPW12O40][Cd2(Phen)4Cl2](4, 4?-bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV–vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW12O40]5?, metal halide clusters [Cu2(Phen)4Cl]+and 4, 4?-bpy ligands, while compound 2 is constructed from [PW12O40]3?, metal halide cluster [Cd2(Phen)4Cl2]2+ and 4, 4?-bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. - Graphical Abstract: Two new compounds have been synthesized and characterized. Structure analyses revealed that the two compounds are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Highlights: ? First examples of hybrids based oles of hybrids based on polyoxometalates, metal halide clusters and organic ligands. ? Two different kinds of metal halide clusters. ? Supramolecular structures based on polyoxometalates, metal halide clusters and organic ligands. ? Hybridization of three different of building blocks.

333

Hall Determination of Atomic Radii of Alkali Metals  

Science.gov (United States)

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.)

Houari, Ahmed

2008-01-01

334

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

Directory of Open Access Journals (Sweden)

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.

Simon A. Bretschneider

2014-04-01

335

Polar binary Zn/Cd-rich intermetallics: Synthesis, crystal and electronic structure of A(Zn/Cd){sub 13} (A = alkali/alkaline earth) and Cs{sub 1.34}Zn{sub 16}  

Energy Technology Data Exchange (ETDEWEB)

The binary alkali/alkaline earth (A) zinc and cadmium (M) compounds that form the NaZn{sub 13} structure type (cubic, space group Fm3-bar c), which were known only from indexed X-ray powder diagrams, have been synthesized from stoichiometric mixtures of the elements and have been structurally characterized using a combination of single crystal data and the Rietveld method. The alkali zinc phases A{sup I}Zn{sub 13} are only formed with the lighter alkali elements sodium to rubidium (A{sup I}=Na: a -bar =-bar 1227.3(2)-bar pm, R1=0.0205;A{sup I}=K: a -bar =-bar 1237.9(3)-bar pm, R1=0.0154;A{sup I}=Rb: a -bar =-bar 1245.19(1)-bar pm, R{sub p}=0.0250), whereas the cadmium compounds A{sup I} Cd{sub 13} are stable only for the heavier alkali metals potassium to cesium (A{sup I}=K: a -bar =-bar 1379.2(4)-bar pm, R1=0.0118;A{sup I}=Rb: a -bar =-bar 1384.5(2)-bar pm, R1=0.0139;A{sup I}=Cs: a -bar =-bar 1392.0(3)-bar pm, R1=0.0381). In the crystal structures M-centered M(2)M(1){sub 12} icosahedra are connected via strong exobonds (forming tetrahedral stars, stella quadrangula) to form a 3D net, in the interstices of which the alkali metals are located in a snub cube 24 coordination. In contrast, the alkaline earth (A{sup II}) zinc compounds with calcium, strontium and barium (A{sup II}=Ca: a -bar =-bar 1215.4(1)-bar pm, R1=0.0274;A{sup II}=Sr: a -bar =-bar 1222.2(2)-bar pm, R1=0.0154;A{sup II}=Ba: a -bar =-bar 1235.8(2)-bar pm, R1=0.0227) show statistical defects at the Zn(2) position centering the Zn(1) icosahedra. Both the geometric and the electronic stability of the NaZn{sub 13} structure type, which can be assessed from the pseudo-bandgap calculated using FP-LAPW-DFT methods, are discussed. In contrast to the aforementioned systems, the NaZn{sub 13} type ceases to exist in the binary system Cs-Zn. In this case a phase Cs{sub 1.36}Zn{sub 16} with a new structure type but very similar stoichiometry emerges. This compound is the first and only known phase in the system Cs-Zn and crystallizes with a new incommensurably modulated structure: its average structure (orthorhombic, space group Imma, a=264.2(5) -bar pm,b=720.8(14) -bar pm,c=1760(5) -bar pm, R1=0.0198) already indicates the representative structural features: in a 3D net of Zn atoms tubular channels filled by the Cs atoms are formed. This Cs filling is, due to geometric requirements, not commensurate with the Zn host structure resulting in a modulated structure with satellite reflections that can be indexed with a q-> vector of (0,-bar 0,-bar 0.2755). The final refinement in the superspace group (Pcn2(00g)sso,a=1760(5) -bar pm,b=720.8(14) -bar pm,c=264.2(5) -bar pm, wR{sub main}=0.0550,wR{sub satellites}=0.140) shows a strong occupational and a weak positional modulation of Cs in the channels formed by the Zn partial structure.

Wendorff, Marco [Institut fuer Anorganische und Analytische Chemie, Universitaet Freiburg/Brsg. (Germany); Roehr, Caroline [Institut fuer Anorganische und Analytische Chemie, Universitaet Freiburg/Brsg. (Germany)]. E-mail: caroline@ruby.chemie.uni-freiburg.de

2006-09-14

336

Polar binary Zn/Cd-rich intermetallics: Synthesis, crystal and electronic structure of A(Zn/Cd)13 (A = alkali/alkaline earth) and Cs1.34Zn16  

International Nuclear Information System (INIS)

The binary alkali/alkaline earth (A) zinc and cadmium (M) compounds that form the NaZn13 structure type (cubic, space group Fm3-bar c), which were known only from indexed X-ray powder diagrams, have been synthesized from stoichiometric mixtures of the elements and have been structurally characterized using a combination of single crystal data and the Rietveld method. The alkali zinc phases AIZn13 are only formed with the lighter alkali elements sodium to rubidium (AI=Na: a -bar =-bar 1227.3(2)-bar pm, R1=0.0205;AI=K: a -bar =-bar 1237.9(3)-bar pm, R1=0.0154;AI=Rb: a -bar =-bar 1245.19(1)-bar pm, Rp=0.0250), whereas the cadmium compounds AI Cd13 are stable only for the heavier alkali metals potassium to cesium (AI=K: a -bar =-bar 1379.2(4)-bar pm, R1=0.0118;AI=Rb: a -bar =-bar 1384.5(2)-bar pm, R1=0.0139;AI=Cs: a -bar =-bar 1392.0(3)-bar pm, R1=0.0381). In the crystal structures M-centered M(2)M(1)12 icosahedra are connected via strong exobonds (forming tetrahedral stars, stella quadrangula) to form a 3D net, in the interstices of which the alkali metals are located in a snub cube 24 coordination. In contrast, the alkaline earth (AII) zinc compounds with calcium, strontium and barium (AII=Ca: a -bar =-bar 1215.4(1)-bar pm, R1=0.0274;AII=Sr: a -bar =-bar 1222.2(2)-bar pm, R1=0.0154;AII=222.2(2)-bar pm, R1=0.0154;AII=Ba: a -bar =-bar 1235.8(2)-bar pm, R1=0.0227) show statistical defects at the Zn(2) position centering the Zn(1) icosahedra. Both the geometric and the electronic stability of the NaZn13 structure type, which can be assessed from the pseudo-bandgap calculated using FP-LAPW-DFT methods, are discussed. In contrast to the aforementioned systems, the NaZn13 type ceases to exist in the binary system Cs-Zn. In this case a phase Cs1.36Zn16 with a new structure type but very similar stoichiometry emerges. This compound is the first and only known phase in the system Cs-Zn and crystallizes with a new incommensurably modulated structure: its average structure (orthorhombic, space group Imma, a=264.2(5) -bar pm,b=720.8(14) -bar pm,c=1760(5) -bar pm, R1=0.0198) already indicates the representative structural features: in a 3D net of Zn atoms tubular channels filled by the Cs atoms are formed. This Cs filling is, due to geometric requirements, not commensurate with the Zn host structure resulting in a modulated structure with satellite reflections that can be indexed with a q-> vector of (0,-bar 0,-bar 0.2755). The final refinement in the superspace group (Pcn2(00g)sso,a=1760(5) -bar pm,b=720.8(14) -bar pm,c=264.2(5) -bar pm, wRmain=0.0550,wRsatellites=0.140) shows a strong occupational and a weak positional modulation of Cs in the channels formed by the Zn partial structure

337

Competitive hydrated positron reactions with halides  

International Nuclear Information System (INIS)

The hydrated positron, esub(aq)sup(+), reactions with halides and pseudohalides were studied by angular correlation technique. At halide concentrations below 0.02 M, the reaction of esub(aq)sup(+) with halides, x-, to form bound states [x-,e+] is diffusion controlled. On adding two halides to water containing a Ps inhibitor, the first positron transfer rate constants could be determined. For example, the reaction [Br-,e+] + I- ? Br- + [I-,e+] was studied. (Auth.)

338

Growth, Morphology and Solid State Miscibility of Alkali Nitrates  

Digital Repository Infrastructure Vision for European Research (DRIVER)

[eng] This PhD thesis is focused in structural aspects of alkali nitrates. In the first chapter, we recollected the most important advancement in this field in alkali nitrates compounds published since 1970. Along this lines, crystal structure, polymorphism and phase transition is discussed first; second, crystal growth, and third, the morphology. And, finally a section concerning solid state miscibility and binary phase diagrams between these compounds is presented. The following chapters pr...

Benages Vilau, Rau?l

2013-01-01

339

Alkali metal hydride formation  

International Nuclear Information System (INIS)

The present invention relates to a method of producing alkali metal hydrides by absorbing hydrogen gas under pressure into a mixture of lower alkyl mono amines and alkali metal alkyl amides selected from sodium and potassium amides formed from said amines. The present invention also includes purification of a mixture of the amines and amides which contain impurities, such as is used as a catalytic exchange liquid in the enrichment of deuterium, involving the formation of the alkali metal hydride

340

Intra-zoned luminescence in alkali earth metal carbonates  

International Nuclear Information System (INIS)

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 luminescen 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

 
 
 
 
341

Rare earth ions doped chalco-halide glasses and glass ceramics for luminescence in the visible range  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The present work deals with the study of new chalco halide glass-ceramics doped with rare earth ions for visible luminescence. The effect of the addition of different alkali-halide into glasses belonging to the Ga2S3-GeS2 system has been studied with the aim to extend their transparency into the ultraviolet region. Glasses transparent over the visible range (400-750 nm) up to the mid infrared (11,5 ?m) have been obtained in the Ga2S3-GeS2-CsCl system. Transparent and homogeneous glass-cerami...

Ledemi, Yannick

2008-01-01

342

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

International Nuclear Information System (INIS)

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 ?E (?E=4E, 4A1 (4G)?4T1 (4G)) of Mn2+ ion in halides were established: E=2.0898+0.8618 exp (?F/0.2431); ?E=0.3201+0.9713?F. These relationships allow us to predict the position of energy state 4T1 (4G) and the energy difference ?E 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 ?E of Mn2+rence ?E 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.

343

Creation of CsAu nanoclusters by UV-light irradiation on CsBr:Au- crystals  

Science.gov (United States)

We have investigated the optical absorption spectra of the CsBr:Au- crystals irradiated with an ultraviolet (UV) light. Before the UV-light irradiation, the absorption bands associated with the isolated Au- ion (monomer) are observed in the energy region of UV. After a slight UV-light irradiation, the absorption intensities of the monomer bands decrease and the absorption bands due to paired Au- ions appear around the monomer bands. Furthermore, UV-light irradiation on the CsBr:Au- crystals brings about the appearance of several new absorption bands in the visible region. From the analogy with the aggregation of the F centers in alkali halide crystals, the new absorption bands are attributed to the aggregate centers of the Au- ions. They can also be regarded as the CsAu nanocluster constructed from the Cs+ cations and the Au- anions.

Kawai, Taketoshi; Yamano, Asuka

2006-02-01

344

Crystal growth, transport phenomena and two gap superconductivity in the mixed alkali metal $(K_{1-z}Na_z)_{x}Fe_{2-y}Se_2$ iron selenide  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using the self-flux technique we grew superconducting $(K_{1-z}Na_z)_{x}Fe_{2-y}Se_2$ (z = 0.3) single crystals. The EDX mapping revealed the uniform elements distribution on the crystal surface while the XRD measurements indicate that the crystals are compositionally inhomogenous on nanoscale. The physical properties of the as-prepared sample are characterized by electrical resistivity, magnetization and specific heat measurements. Resistivity measurements show the onset of...

Roslova, Maria; Kuzmichev, Svetoslav; Kuzmicheva, Tatiana; Ovchenkov, Yevgeny; Liu, Min; Morozov, Igor; Boltalin, Aleksandr; Shevelkov, Andrey; Chareev, Dmitry; Vasiliev, Alexander

2013-01-01

345

Charged-soft-sphere potentials for trivalent metal halides  

International Nuclear Information System (INIS)

Octahedral-type coordination by halogens in the liquid state has been reported for a number of trivalent metal ions from diffraction and Raman scattering experiments on their molten trihalides and from Raman scattering spectroscopy of liquid mixtures of trihalides with alkali halides. We analyze the available data on bond lengths and Raman frequencies by treating an isolated (MX6)3- species within a model which adopts charged-soft-sphere interionic potentials supplemented by an account of ionic polarization. The trivalent metal ions that we consider are M = La, Ce, Pr, Nd, Sm, Gd, Dy and Y for X = Cl and M = Al for X = F. The main result of the analysis is the prediction of trends in the soft-sphere repulsive parameters for the trivalent metal ions, leading to estimates of all the vibrational frequencies and the binding energy of such octahedral species. (author). 26 refs, 1 fig., 4 tabs

346

Correlations between entropy and volume of melting in halide salts  

International Nuclear Information System (INIS)

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

347

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

International Nuclear Information System (INIS)

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.

348

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

Energy Technology Data Exchange (ETDEWEB)

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, F{sub 2}, F{sub 2}{sup +}, F{sub 3}{sup +} and F{sub 2}{sup -} 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.

Samad, R E; Courrol, L C; Gomes, L; Ranieri, I M; Baldochi, S L; De Freitas, A Z; Vieira, N D Jr, E-mail: resamad@gmail.co

2010-11-01

349

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

CERN Document Server

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 the flow stress at the range of athermic anomalies is modeled by changing the mechanism of the dislocation motion from the thermally activated hopping over the barriers to the quantum tunnelling through them. Some results of previous calculations are represented in a more explicit convenient for applications form. The pronounced effect of the switching between the normal and the superconducting states on the flow stress of metals is explained on the basis of the change in the dissipative properties of the electron subsyste...

Petukhov, B V

2007-01-01

350

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

CERN Document Server

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.

Georgiev, Mladen

2007-01-01

351

Crystal structures of hydrates of simple inorganic salts. III. Water-rich aluminium halide hydrates: AlCl3 · 15H2O, AlBr3 · 15H2O, AlI3 · 15H2O, AlI3 · 17H2O and AlBr3 · 9H2O.  

Science.gov (United States)

Water-rich aluminium halide hydrate structures are not known in the literature. The highest known water content per Al atom is nine for the perchlorate and fluoride. The nonahydrate of aluminium bromide, stable pentadecahydrates of aluminium chloride, bromide and iodide, and a metastable heptadecahydrate of the iodide have now been crystallized from low-temperature solutions. The structures of these hydrates were determined and are discussed in terms of the development of cation hydration spheres. The pentadecahydrate of the chloride and bromide are isostructural. In AlI(3) · 15H2O, half of the Al(3+) cations are surrounded by two complete hydration spheres, with six H2O in the primary and 12 in the secondary. For the heptadecahydrate of aluminium iodide, this hydration was found for every Al(3+). PMID:25186362

Schmidt, Horst; Hennings, Erik; Voigt, Wolfgang

2014-09-15

352

Nonlinear refractive index of optical crystals  

International Nuclear Information System (INIS)

The nonlinear refractive indices (n2) of a large number of optical crystals have been measured at a wavelength near one micrometer with use of nearly degenerate three-wave mixing. The measurements are compared with the predictions of an empirical formula derived by Boling, Glass, and Owyoung. This formula, which relates n2 to the linear refractive index and its dispersion, is shown to be accurate to within about 30% for materials with nonlinear indices ranging over 3 orders of magnitude. Measurements for a number of binary oxide and fluoride crystals have been analyzed under the assumption that the hyperpolarizability of the anion is much larger than that of the cation. It is found that the hyperpolarizability of oxygen varies by a factor of 10, and that of fluorine varies by a factor of 7, depending on the size of the coordinating cation. This behavior is similar to that of the linear polarizability, although the hyperpolarizability is much more sensitive than the linear polarizability to the identity of the cation. The measured halide ion hyperpolarizabilities for several alkali-halide crystals are in reasonable agreement with recent self-consistent calculations. A semiempirical model was proposed by Wilson and Curtis to account for the dependence of the linear anionic polarizability on the radius of the cation. This model also accounts quite well for the variation of the hyperpolarizability of both fluorine and oxygen, except for cation partneorine and oxygen, except for cation partners that have filled or unfilled d-electron shells. The nonlinear indices of a number of complex oxides (i.e., those with more than one cation) have been calculated from the partial hyperpolarizabilities deduced from the data for the binary oxides. The calculated and measured values of n2 agree to within an average error of 13%

353

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

International Nuclear Information System (INIS)

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.

354

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

Science.gov (United States)

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW12O40]2[Cu2(Phen)4Cl](H24, 4'-bpy)4·H3O·5H2O (1) and [HPW12O40][Cd2(Phen)4Cl2](4, 4'-bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW12O40]5-, metal halide clusters [Cu2(Phen)4Cl]+and 4, 4'-bpy ligands, while compound 2 is constructed from [PW12O40]3-, metal halide cluster [Cd2(Phen)4Cl2]2+ and 4, 4'-bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands.

Wang, La-Mei; Fan, Yong; Wang, Yan; Xiao, Li-Na; Hu, Yang-Yang; Peng, Yu; Wang, Tie-Gang; Gao, Zhong-Min; Zheng, Da-Fang; Cui, Xiao-Bing; Xu, Ji-Qing

2012-07-01

355

Bis(dicyanomethylene)squarate squaraines in their 1,2- and 1,3-forms: Synthesis, crystal structure and spectroscopic study of compounds containing alkali metals and tetrabutylammonium ions  

Science.gov (United States)

In this paper, we describe a new synthetic methodology and the spectroscopic characterization of two squaraines 1,2- and 1,3-substituted, named sodium 1,2-bis(dicyanomethylene)squarate and sodium 1,3-bis(dicyanomethylene)squarate. The squaraine species are derived from 1,2-dihydroxycyclobuten-3,4-dione, also known as squaric acid. A modification in the synthetic route has been developed in order to improve the yield in the synthesis of the 1,3-derivative: the in situ use of the 1,3-dianilinesquarate intermediate. In both cases, an excess basic medium was added to the solution containing all the reactants. These squaraines consist of a cyanine-type chromophore with high thermal stability and several different spectroscopic properties. In addition, it was made a comparative analysis based on the spectroscopic study of the 1,3- and 1,2-compounds, as well as their derivatives with several metal alkalis (K +, Rb +, Mg 2+, Ca 2+, Sr 2+ and Ba 2+), besides tetrabutylammonium ion (TBA). The vibrational spectroscopic data demonstrate the centrosymmetric structure in solid state phase of the 1,3-compound due to non-coincidence between the infrared and Raman bands in the vibrational spectra. The crystal structures were also obtained for Ca 2+ and Ba 2+ ions with the 1,3-isomer. These salts crystallize in different space groups, also showing very distinct coordination properties and intermolecular interactions. This study provides a sound basis for the future expansion of structural and spectroscopic investigations of this interesting group of metal-ligand compounds as building blocks systems in supramolecular chemistry.

de Oliveira, Vanessa E.; de Carvalho, Gustavo S.; Yoshida, Maria I.; Donnici, Claudio L.; Speziali, Nivaldo L.; Diniz, Renata; de Oliveira, Luiz Fernando C.

2009-11-01

356

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

International Nuclear Information System (INIS)

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

357

Methods of recovering alkali metals  

Science.gov (United States)

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.

Krumhansl, James L; Rigali, Mark J

2014-03-04

358

Spectra of alkali atoms  

International Nuclear Information System (INIS)

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

359

Chlor-Alkali Technology.  

Science.gov (United States)

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

Venkatesh, S.; Tilak, B. V.

1983-01-01

360

Physicochemical and spectroscopic investigations of crystals of alkali-rare earth fluorides K/sub 2/LnF/sub 5/  

Energy Technology Data Exchange (ETDEWEB)

The compounds K/sub 2/LnF/sub 5/ (Ln = Nd, ..., Lu, Y) and K/sub 2/LnF/sub 5/ (Ln = Gd, Lu, Y), activated by Nd/sup 3 +/ ions, are synthesized by the hydrothermal method. A spectroscopic investigation of this series of compounds is made. It is shown that the compounds K/sub 2/LnF/sub 5/-Nd/sup 3 +/ are convenient media for exciting the generation of stimulated emission in the near IR. By spectroscopic methods the coefficient of distribution of Nd/sup 3 +/ ions is estimated for hydrothermal synthesis of the crystals of K/sub 2/GdF/sub 5/-Nd/sup 3 +/.

Kaminskii, A.A.; Sarkisov, S.E.; Kurbanov, K.A.; Dem' yanets, L.N.; Khaidukov, N.M.

1988-05-01

 
 
 
 
361

Positron annihilation on the F'-centers in ionic crystals  

International Nuclear Information System (INIS)

The Pekar-Tomasevich and Simpson-Wills approximations were used to calculate the lifetime ?2? with respect to self-annihilation of a positron bound to the F'-center (the so-called F double-prime +-center, that is, the polyelectron Wheeler system e-2e+ in an anion vacancy) in a defect ionic crystal. It turned out that positron lifetimes for various ionic crystals most likely fall into the nanosecond range in the time-resolved annihilation spectra. The obtained values of ?2? enable the overall lifetimes ?s,tFdouble-prime+ of the F double-prime +-centers with account for annihilation in crystals, the so-called open-quotes pick-offclose quotes -annihilation, to be more accurately calculated. Formulas were derived for calculating the angular correlation of annihilation radiation (ACAR) and the halfwidths ? of ACAR curves for the case of F double-prime +-center self-annihilation. The obtained estimates led to the conclusion that positron annihilation from the F double-prime +-centers [for example, in alkali halide crystals (AHC) most likely contributes to the intensities of the ?2 ?6x10-10 s and ?3?10-9 s components in the experimental time-resolved annihilation spectra

362

Temperature dependence of volume thermal expansion for NaCl and KCl crystals  

International Nuclear Information System (INIS)

A new relation for predicting volume thermal expansion of alkali halides at high temperatures is derived based on the assumption that the two different diffusional driving force models presented, respectively, by Sharma and Sharma (Indian J. Pure Appl. Phys. 29 (1991) 637) and Singh (J. Phys. Chem. Solids 63 (2002) 1935) are equivalent. The input parameters needed for the calculation are the volume thermal expansion coefficient and the isothermal Anderson-Gruneisen parameter, both at room temperature and zero pressure, which are available from the literature. The tests on NaCl and KCl crystals demonstrate that the agreement between the calculated results obtained by this relation and the corresponding experimental data is very good. The applicability of the relation as well as some thermodynamic relationships included in its derivation is discussed

363

Thermoelastic behaviour and higher-order elastic constants of ionic crystals  

International Nuclear Information System (INIS)

The relationships are given between thermoelastic properties and higher-order (third and fourth order) elastic constants for twenty alkali halides with NaCl and CsCl structures, and for four alkaline earth oxides viz. MgO, CaO, SrO, and BaO crystals. Expressions for thermoelastic quantities such as the Grueneisen parameter and its volume derivative, Anderson parameters, and thermal expansion coefficient, are obtained in terms of higher-order elastic constants. These expressions provide a new method for estimating thermoelastic quantities from higher-order elastic constants. Calculations are performed using an interionic potential model which takes account of three body interactions, van der Waals interactions, and overlap repulsive interactions upto second neighbours. The results are discussed and compared with experimental data. (author)

364

Structural change in polar nanoregion in alkali niobate added Pb(Zn1/3Nb2/3)0.95Ti0.05O3 single crystal and its effect on ferroelectric properties  

Science.gov (United States)

Pb(Zn1/3Nb2/3)0.95Ti0.05O3 (PZNT) single crystals with 5 mol. % alkali niobate such as LiNbO3 (LN), NaNbO3 (NN), and KNbO3 (KN) were fabricated by using a flux method to investigate the effect of A-site cation radius on the structure and ferroelectric properties of PZNT under electric field (E-field). Their structure and properties showed different electric field dependence. Polarization versus electric field and strain versus electric field curves of PZNT-0.05LN showed E-field induced phase transition from a relaxor state to a normal ferroelectric state. However, only relaxor behavior was observed in PZNT-0.05NN and PZNT-0.05KN. The effect of A-site ion doping is attributed to the change in local lattice distortion and polar nano-region. When smaller cation such as Li ion substitutes Pb ion, the off-center displacement of Nb ion stabilizes rhombohedral lattice distortion. They, in turn, facilitate the development of macro-domains under electric field (E-field) in PZNT-0.05LN. In contrast, the substitution of Pb with larger cations such as Ni and K decreases the rhombohedral distortion of PZNT, which leads to the disappearance of unique E-field induced phase transition from rhombohedral to tetragonal phase in PZNT. Therefore, non-linear electrostrictive behavior of relaxor ferroelectrics is found in PZNT-0.05NN and PZNT-0.05KN.

Park, Jong-Sung; Jung, Youngsoo; Lee, Jung-Kun

2012-10-01

365

Transfer of Aryl Halide to Alkyl Halide: Reductive Elimination of Alkylhalide from Alkylpalladium Halides Containing syn-?-Hydrogen Atoms.  

Science.gov (United States)

?-Hydride abstraction is a well-accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn-?-hydrogen atoms will undergo ?-hydride abstraction to afford the Heck-type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn-?-hydrogen atoms may surpass the ?-hydride abstraction or even become exclusive in certain cases. PMID:25367776

Hao, Wei; Wei, Junnian; Geng, Weizhi; Zhang, Wen-Xiong; Xi, Zhenfeng

2014-12-22

366

Inhibition of palmito polyphenoloxidase by halide salts.  

Science.gov (United States)

The inhibitory properties of halide salts on palmito polyphenoloxidase (PPO) are described. Halide salts have the same inhibitory effect on the two forms of palmito PPO separated by hydrophobic chromatography. Fluoride and chloride ions showed a non-competitive, mixed type inhibition while bromide and iodide ions were found to be non-competitive inhibitors. A study of the Ki for the different halide salts showed that the smaller F- ion is a stronger inhibitor than I- and Br- and that Cl- has the highest Ki value. This suggests that the active site of the palmito PPO is not easily accessible. The inhibition by chloride and fluoride ion was found to be pH-dependent. The inhibitory effects of these ions increased with a decrease in pH. It is suggested that halide ions (X) could bind to either the protonated enzyme (EH) or the protonated substrate-enzyme complex (EHS) to yield inactive forms EHX and EHSX, respectively. PMID:9795866

Robert, C; Rouch, C; Cadet, F

1998-07-01

367

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

International Nuclear Information System (INIS)

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

368

Heidelberg polarized alkali source  

International Nuclear Information System (INIS)

A new atomic beam type polarized alkali ion source has been installed at Heidelberg. In order to improve the beam polarization considerably optical pumping is applied in combination with an adiabatic medium field transition which results in beams in single hyperfine sublevels. The m state population is determined by laser-induced fluorescence spectroscopy. Highly polarized beams (P/sub s/ > 0.9, s = z, zz) with intensities of 30 to 130 ?A can be extracted for Li+ and Na+, respectively

369

A method for the selective hydrogenation of alkenyl halides to alkyl halides.  

Science.gov (United States)

A general method for the selective hydrogenation of alkenyl halides to alkyl halides is described. Fluoro, chloro, bromo, iodo, and gem-dihaloalkenes are viable substrates for the transformation. The selectivity of the hydrogenation is consistent with reduction by a hydrogen atom transfer pathway. PMID:24824195

King, Sandra M; Ma, Xiaoshen; Herzon, Seth B

2014-05-14

370

Calcium phosphate cements with strontium halides as radiopacifiers.  

Science.gov (United States)

High radiopacity is required to monitor the delivery and positioning of injectable implants. Inorganic nonsoluble radiopacifiers are typically used in nondegradable bone cements; however, their usefulness in resorbable cements is limited due to their low solubility. Strontium halides, except strontium fluoride, are ionic water-soluble compounds that possess potential as radiopacifiers. In this study, we compare the radiopacity, mechanical properties, composition, and cytotoxicity of radiopaque brushite cements prepared with strontium fluoride (SrF2 ), strontium chloride (SrCl2 ·6H2 O), strontium bromide (SrBr2 ), or strontium iodide (SrI2 ). Brushite cements containing 10 wt % SrCl2 ·6H2 O, SrBr2 , or SrI2 exhibited equal to or higher radiopacity than commercial radiopaque cements. Furthermore, the brushite crystal lattice in cements that contained the ionic radiopacifiers was larger than in unmodified cements and in cements that contained SrF2 , indicating strontium substitution. Despite the fact that the strontium halides increased the solubility of the cements and affected their mechanical properties, calcium phosphate cements containing SrCl2 ·6H2 O, SrBr2 , and SrI2 showed no significant differences in Saos-2 cell viability and proliferation with respect to the control. Strontium halides: SrCl2 ·6H2 O, SrBr2 , and SrI2 may be potential candidates as radiopacifiers in resorbable biomaterials although their in vivo biocompatibility, when incorporated into injectable implants, is yet to be assessed. PMID:23997030

López, Alejandro; Montazerolghaem, Maryam; Engqvist, Håkan; Ott, Marjam Karlsson; Persson, Cecilia

2014-02-01

371

Specific heat and thermal diffusivity of aqueous solutions of alkali metal salts in a wide pressure range  

International Nuclear Information System (INIS)

The values of the isobaric heat capacity and temperature conductivity of the alkali metal halides (LiCl, NaCl, KCl and KBr) are measured with application of the heat-conducting calorimeter within the concentration range from 298 up to 348 K and pressures from 0.098 up to 147 MPa. The generalized dependences for determining the heat capacity and thermal conductivity with the calculation error less than 3% are proposed

372

New halide clusters of technetium  

International Nuclear Information System (INIS)

The present work is devoted to the synthesis, identification, and investigation of the physicochemical properties of new halide clusters of technetium(II) which are forms in which the disproportionation products of Tc2X83- (X = Cl, Br, I) are stabilized. Comparing the results obtained in the present work with earlier data it is concluded that the cluster compounds of technetium are very inclined to undergo easy redox conversion, staggered-eclipsed conformational changes, oxidative addition of oxygen, formation of multinuclear compounds, ligand-substitution reactions, hydrolysis reactions, and hydrolysis and disproportionation with cleavage of the Tc-Tc bond. Small changes in the external synthesis conditions (an increase in temperature, the presence or absence of atmospheric oxygen, the use of organic solvents or different hydrohalic acids) can result in the stabilization of technetium clusters differing in composition and structure. It is also noted that, in contrast to the cases of rhenium and molybdenum, in the case of technetium, binuclear clusters with an order of the M-M bond equal to 3.5 or 3.0 (or even multinuclear clusters) may be more stable than the analogous compounds with a quadruple bond, depending on the conditions

373

Dimming of metal halide lamps  

Science.gov (United States)

We ran some tests on the effect of dimming of metal halide (MH) lamps upon the stability and the spectral quality of the light output. Lamps used were a new Philips lamp HPI-T 250W, a similar Philips lamp with a few thousand burning hours and a new Osram lamp HQI-T 250W/D. The ballast was a BBC type DJ 250/2KS, the starter a BAS TORGI type MZN 250 SE and the dimmer an Elstrom Control System type ERHQ-T 250. Power was derived from a Philips stabilizer, type PE 1602. Lamp output was monitored with a PAR meter. Spectra were taken at 100% and at 50% output as measured with the PAR meter. Lamps were allowed to stabilize at any setting for 30 minutes before measurements were made. Lamp manufacturers advise against dimming for fear of poor stability and intolerable changes of the spectrum. However, none of the lamps showed a decrease in stability, no flicker or wandering of the discharge, and the changes of the spectrum were not negligible, but certainly not dramatic. Lamps of either manufacture retain their white color, relative peak heights of spectral lines did shift, but no gaps in the spectrum occurred. Spectra taken at 50% with 30 minutes intervals coincided. Differences between the new and the older Philips lamp were noticeable, but not really significant.

Schurer, Kees

1994-01-01

374

Single crystal growth by self-flux method of the mixed valence gold halides Cs$_2$[Au$^{I}$X$_2$][Au$^{III}$X$_4$] (X=Br,I)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

High quality single crystals of Cs$_2$Au$_2$X$_6$ (X=Br,I) were grown using a ternary self-flux method. Structural refinements based on single crystal X-ray diffraction measurements show that both materials have a distorted perovskite structure belonging to the I4/mmm space group with full site occupancy. Transport measurements reveal a large bandgap of 550 $\\pm$ 100 meV for Cs$_2$Au$_2$I$_6$ and 520 $\\pm$ 80 meV for Cs$_2$Au$_2$Br$_6$. Initial attempts at chemical substitut...

Riggs, Scott C.; Shapiro, M. C.; Corredor, F.; Geballe, T. H.; Fisher, I. R.; Mccandless, Gregory T.; Chan, Julia Y.

2011-01-01

375

Chlor-alkali electrolysis  

International Nuclear Information System (INIS)

The chlor-alkali industry produces simultaneously chlorine (Cl2) and caustic soda (NaOH) by decomposition of a salt solution in water. Additionally to the chlorine and caustic soda, hydrogen (H2) is produced. The global production capacity of chlorine in 1995 was approximately 44 million tons. The development of the chlorine production capacity in Western Europe since 1960 is presented. The most important chlorine producer in Western Europe is Germany with 38 % of the annual chlorine capacity of Western Europe. The chlorine capacity in 1997 in different Western European countries and their share an the total capacity in Western Europe is also presented. World-wide several processes are available for the production of chlorine and caustic soda. The most important routes are the following: ion exchange membrane process; mercury cell process; diaphragm process. Several other processes are available but do not have a significant contribution to the total production. The geographical distribution of the processes differs widely. In Japan the membrane process is predominate with 73 %, in the United States the diaphragm process with 75 %, whereas in Western Europe the mercury cell process is the most important one (64 %) [EIPPCB, 2000]. Approximately 65 % of the global chlorine capacity is located in these three regions. A comparison of the relative contribution of different production technologies to the chlor-alkali capacity in these three regions andalkali capacity in these three regions and in the world in 1994 is given. The distribution of processes and capacities of chlor-alkali plants in some European countries is presented (October 1999). Note that any one plant can have more than one cell technology installed. (author)

376

The Remarkable Reactivity of Aryl Halides with Nucleophiles  

Science.gov (United States)

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)

Bunnett, Joseph F.

1974-01-01

377

Solvation energy and gas-phase stability influences on alkali metal cluster ion formation in electrospray ionization mass spectrometry.  

Science.gov (United States)

The ability to observe abundant gas-phase metal cluster ions in electrospray ionization mass spectrometry (ESI-MS) is highly dependent on experimental conditions. Alkali halides (MX) and other alkali metal salts were used to investigate the formation of cluster ions in ESI-MS. All compounds were found to give cluster ions of the form (M(n)(+1)X(n))(+) and (M(n)X(n+1))(-), with only two alkali salts yielding doubly charged cluster ions. In homologous alkali halide series, the relative abundances of cluster ions increased with increasing size of either the cation (positive ion mode) or the anion (negative ion mode). Calculations using an electrostatic model show that the gas-phase stability of cluster ions is greater for smaller cations or anions when a fixed counterion is employed. This stability calculation goes in a direction just opposite to the trend in cluster ion abundances observed in ESI-MS. Studies of equimolar mixtures consisting of two alkali halides reveal two distinct trends. When the equimolar mixture was composed of differing ions that participate in the droplet charge excess with the same counterion, the less solvated ions were found to form more abundant cluster ions. When the ions participating in the charge excess were fixed, the preferred counterion in observed clusters was the one that is more solvated in solution and forms more stable clusters in the gas phase. These observations can be rationalized by an extended form of the charged residue model where the weakly solvated ions that are part of the charge excess are preferentially enriched in offspring droplets during uneven fission. By contrast, transfer of a particular counterion located in the bulk of the droplets to the offspring droplets is not disfavored when this counterion is strongly solvated. PMID:21644619

Wang, G; Cole, R B

1998-03-01

378

Synthesis of methyl halides from biomass using engineered microbes.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Methyl halides are used as agricultural fumigants and are precursor molecules that can be catalytically converted to chemicals and fuels. Plants and microorganisms naturally produce methyl halides, but these organisms produce very low yields or are not amenable to industrial production. A single methyl halide transferase (MHT) enzyme transfers the methyl group from the ubiquitous metabolite S-adenoyl methionine (SAM) to a halide ion. Using a synthetic metagenomic approach, we chemically synth...

Bayer, Ts; Widmaier, Dm; Temme, K.; Mirsky, Ea; Santi, Dv; Voigt, Ca

2009-01-01

379

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

Science.gov (United States)

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

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

2014-05-28

380

Interaction of halides in ternary mutual systems in melt  

International Nuclear Information System (INIS)

The character of halides interaction in ternary mutual systems of diagonal type is analyzed. It is shown that the direction of exchange reaction and equilibrium state in the melt are determined by a halide solubility ratio. The interaction parameter (mixing heat) of the halides is calculated. Difficulty soluble salts in the melt are noted to behave as weak electrolytes

 
 
 
 
381

Multiline operation of mercury halide lasers  

Energy Technology Data Exchange (ETDEWEB)

Emission spectrum of the (B-X) band system of HgX radicals (X=chlorine, bromine, iodine) was observed by passing electrical discharge through flowing vapors of mercury halides. The emission intensity of the most intense band of the (B-X) system of these radicals was observed to decrease in the presence of other mercury halide vapors at temperatures higher than 130C. Laser action was observed from the (B-X) transition of mercurous chloride, mercurous bromide, and mercurous iodide radicals by electrical discharge pumping of mercuric chloride, mercuric bromide and mercuric iodide vapors individually.

Kushawaha, M.; Mahmood, M.

1988-01-01

382

EPR of substituted Ru(3) and Os(3) halide complexes  

International Nuclear Information System (INIS)

Interaction of chlorine and bromine (X=Cl, Br) complexes of ruthenium (3) and osmium (3) with a series of reagents (L=DMSO, acetonitrile, pyridine, triphenyl phosphine) in aqueous solutions of HX is studied by EPR method. Formation of new complexes identified as [MLX5]n- (n=3, 2), trans-[ML2X4]n- (n=2, 1) and rib isomers [ML3X3] (M=Ru, Os) is determined. Comparative analysis of EPR parameters and ligand field of sixty compounds of ruthenium and osmium of similar structure is conducted. Solvation effects in solutions and crystal lattice on symbasic change of splitting energy of levels of d?-electrons and factor of orbital contraction are estimated. As a result of superfine interaction analysis it is established that in ruthenium halide complexes with significant axial distortion unpaired electron is localized on dxy-orbital of metal practically completely

383

Coordination polymers of copper(I) halides.  

Science.gov (United States)

A total of 21 complexes of CuX (X = Cl, Br, I) with bridging ligand (B = 4,4'-dipyridyl (Bpy), pyrazine (Pyz), quinoxaline (Quin), phenazine (Phz), 1,4-diazabicyclo[2.2.2]octane (DABCO), and hexamethylenetetramine (HMTA)) have been synthesized. The products show two stoichiometries: [CuXB] (type 1) and [(CuX)2B] (type 2). Both types can be obtained for B = Bpy, depending on the conditions of preparation. In these cases, the type 2 stoichiometry is the kinetic product. Type 2 complexes only are found for B = Pyz (X = I), Quin, Phz, DABCO, and HMTA. Type 1 complexes form for Pyz (X = Cl, Br). Thermogravimetic analyses of the complexes reveal the general decomposition trend: 1 --> 2 --> [(CuX)2B(1/2)] --> CuX. The X-ray crystal structure of [CuBr(Pyz)] (type 1) features copper atoms bridged by Br and Pyz, forming 2D sheets of fused rectangular Cu4Br2(Pyz)2 units. The X-ray structure of [(CuI)2(Quin)] (type 2) shows 2D layers composed of [Cu2I2]infinity "stair step" chains which are cross-linked by Quin ligands. A total of 16 complexes of CuXL (L = P(OPh)3) with bridging ligand (B = those above and 1,4-dimethylpiperazine (DMP)) have also been prepared. All of these products, except those of HMTA, are of type 3 formulation, [(CuXL)2B]. The HMTA products have the formula [CuX(HMTA)], type 4. Thermal decomposition of the type 3 and 4 complexes occurs with initial loss of B, L, or both. The X-ray structures of [(CuBrL)2(Bpy)] and [(CuBrL)2(Pyz)] (type 3) reveal 1D chains formed from rhomboidal (LCu)2Br2 units linked by the B ligand. The type 4 structure of [CuBrL(HMTA)] is shown by X-ray to be a simple halide-bridged dimer. PMID:11233211

Graham, P M; Pike, R D; Sabat, M; Bailey, R D; Pennington, W T

2000-10-30

384

Crystal Electrostatic Energy  

CERN Document Server

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.

Ivanchin, Alexander

2010-01-01

385

Synthesis, characterization and thermal properties of small R2R?2N+X--type quaternary ammonium halides  

Science.gov (United States)

Twenty-one R2R'2N +X- -type ( R=methyl or ethyl, R'=alkyl, X=Br or I) quaternary ammonium (QA) halides have been prepared by using a novel one-pot synthetic route in which a formamide (dimethyl-, diethylformamide, etc.) is treated with alkyl halide in the presence of sodium or potassium carbonate. The formation of QA halides was verified with 1H-NMR, 13C-NMR, MS and elemental analysis. The crystal structures of four QA halides (two bromide and two iodide) were determined using X-ray single crystal diffraction, and the powder diffraction method was used to study the structural similarities between the single crystal and microcrystalline bulk material. The thermal properties of all compounds were studied using TG/DTA and DSC methods. The smallest compounds decomposed during or before melting. The decreasing trend of melting points was observed when the alkyl chain length was increased. The liquid ranges of 120-180 °C were observed for compounds with 5-6 carbon atoms in the alkyl chain. The low melting points and wide liquid ranges suggest potential applicability of these compounds for example as ionic liquids precursors.

Busi, Sara; Lahtinen, Manu; Mansikkamäki, Heidi; Valkonen, Jussi; Rissanen, Kari

2005-06-01

386

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

International Nuclear Information System (INIS)

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

387

Barium halide nanocrystals in fluorozirconate based glass ceramics for scintillation application  

International Nuclear Information System (INIS)

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

388

Effect of nuclear radiation on alkali-silica reaction of concrete  

International Nuclear Information System (INIS)

The effect of electron beam-irradiation on the reactivity of plagioclase, one of the major minerals composing volcanic rocks, to alkali has been examined to clarify whether nuclear radiations accelerate the alkali-silica reaction of concrete containing volcanic rocks as aggregates. Irradiation of plagioclase with a 30 keV electron beam at a dose of more than 0.9 x 108 Gy converts a crystalline plagioclase to an amorphous one that is 35 times more reactive to alkali than the crystal. The high reactivity of the irradiated plagioclase indicates that the deterioration of concrete by alkali-silica reaction is possible to be induced by nuclear radiations even when the aggregates are inert to alkali before the irradiation. (author)

389

First Tin Pnictide Halides Sn(24)P(19.3)I(8) and Sn(24)As(19.3)I(8): Synthesis and the Clathrate-I Type of the Crystal Structure.  

Science.gov (United States)

Sn(24)P(19.3)I(8) (I) and Sn(24)As(19.3)I(8) (II) have been prepared by a standard ampule synthesis. I crystallizes in a cubic space group Pm&thremacr;n, a = 10.9540(10) Å, z = 1. The crystal structure of I is built of the 3D net composed of tin and phosphorus atoms, while iodine atoms occupy large polyhedral holes of two different types, pentagonal dodecahedral and tetrakaidodecahedral. An arrangement of such polyhedra follows that of the clathrate-I type. The 3D net has vacancies at one of the phosphorus atoms positions. The vacancies cause the split of the tin atomic position into two, having different coordination, which is reflected in the (119)Sn Mössbauer spectrum. The vacancy concentration correlates well with the occupancy factors of the split tin atomic positions, and in accordance with the Zintl-Klemm formalism for valence compounds, I is a narrow-gap semiconductor. Powder diffraction data shows that II belongs to the same clathrate family, but has an 8 times larger face-centered cubic unit cell. PMID:11671088

Shatruk, Mikhail M.; Kovnir, Kirill A.; Shevelkov, Andrei V.; Presniakov, Igor A.; Popovkin, Boris A.

1999-07-26

390

Asymmetric intermolecular Heck reaction of aryl halides.  

Science.gov (United States)

The asymmetric intermolecular Heck reaction has been limited to aryl and vinyl triflates. Herein, we extend the reaction to aryl and vinyl bromides. Various cyclic olefins coupled with high enantioselectivity. Only bisphosphine oxides on a spiro backbone formed highly stereoselective Pd catalysts. The use of alcoholic solvents and alkylammonium salts were essential to promote halide dissociation from neutral arylpalladium complexes. PMID:24383764

Wu, Chunlin; Zhou, Jianrong Steve

2014-01-15

391

Reactivity of halide and pseudohalide ligands  

International Nuclear Information System (INIS)

Reactivity of halide and pseudohalide (cyanide, azide, thiocyanate, cyanate) ligands tending to form bridge bonds in transition metal (Re, Mo, W) complexes is considered. Complexes where transition metal salts are ligands of other, complex-forming ion, are described. Transformation of innerspheric pseudohalide ligands is an important way of directed synthesis of these metal coordination compounds

392

Configuration and migration of point defects in alkali metals  

International Nuclear Information System (INIS)

A computer calculation of vacancy and interstitial migration using a pair interaction potential deduced from the theory of pseudo-potentials is described. The parameters involved in the expression of the potential are adjusted so as to reproduce the elastic constants and the phonon spectrum of the perfect crystal. One obtains the relaxation energies at equilibrium configuration and at the saddle point and the migration energy of a vacancy and an interstitial in the alkali metals. For Na, K and Rb, the vacancy mechanism is the most probable whereas in Li, there is a possibility of an interstitial mechanism, which would explain the experimental results. The diffusion of alkali solutes in alkali metals is analysed by means of a pair interaction potential deduced from the physical properties of the pure solvent and solute crystals. For solute atoms bigger than the solvent, the substitutional mechanism explains the experimental results whereas an interstitial mechanism is more probable for small impurities. This phenomenon may explain the experimental results observed for the diffusion of Na in K and K in Na. The ?Q values are given for several combinations of the four alkali metals Li, Na, K and Rb. (authors)

393

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

International Nuclear Information System (INIS)

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

394

Upgrading platform using alkali metals  

Energy Technology Data Exchange (ETDEWEB)

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.

Gordon, John Howard

2014-09-09

395

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

International Nuclear Information System (INIS)

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

396

Double molybdates and tungstates of alkali metal compounds and rare earths synthesized at high pressure  

International Nuclear Information System (INIS)

By using X-ray phase analysis methods, double molybdates and tungstates of alkali and rare earths elements of composition MLn(EO4)2 have been produced, synthesized under a high pressure (about 25 to 80 kbars) and at temperatures of 800 to 1000 deg C. It has been shown that characteristic of those compounds with light alkali metals (Li) is the structural type of tungstate, and that compounds with heavy alkali metals (K-C) are crystallized under a high pressure in a structure which is similar to P-KV(WO4)2

397

Elastic properties of alkali-feldspars  

Science.gov (United States)

New measurements of single crystal elastic moduli for a suite of the alkali feldspars are reported. In order to interpret Earth's seismic structure, knowledge of the elastic properties of constituent minerals is essential. The elasticity of feldspar minerals, despite being the most abundant phase in Earth's crust (estimated to be more than 60%), were previously poorly characterized. All prior seismic and petrologic studies have utilized 50-year-old results, of questionable quality, based on 1-bar measurements on pseudo-single crystals. Alkali-feldspars present a large experimental challenge associated with their structural complexity. In the K-end member (KAlSi3O8) the symmetry is governed by Al/Si ordering, in the Na-end member (NaAlSi3O8) the symmetry is governed by whether or not there is a displacive collapse of the framework independent of the Al/Si ordering. K-feldspars exhibit monoclinic (C2/m) symmetry (necessitating determination of 13 elastic moduli) if disordered and triclinic (C-1) symmetry (21 elastic moduli) if ordered. Exsolution of Na-rich and K-rich phases is ubiquitous in natural samples, making it difficult to find suitable single phase and untwinned samples for study. The small single domain samples selected for this study were previously characterized by x-ray diffraction and microprobe analysis to ensure adequate sample quality. Surface wave velocities were measured on oriented surfaces of natural and synthetic single crystals using impulsively stimulated light scattering. A surface corrugation with a spacing of about 2 microns was impulsively created by the overlap of 100 ps infrared light pulses. The time evolution of the stimulated standing elastic waves was detected by measuring the intensity of diffraction from the surface corrugation of a variably delayed probe pulse. This method allows accurate (better than 0.2%) determination of velocities on samples smaller than 100 microns. The combination of measured surface wave velocities and separately determined compressibilities, based on high-pressure x-ray studies, allowed determination of the full elastic tensor for alkali-feldspars as a function of composition and structure.

Waeselmann, N.; Brown, J.; Angel, R. J.; Ross, N.; Kaminsky, W.

2013-12-01

398

The electronic structure of alkali aurides. A four-component Dirac-Kohn-Sham study.  

Science.gov (United States)

Spectroscopic constants, including dissociation energies, harmonic and anharmonic vibrational frequencies, and dipole moments, are calculated for the complete alkali auride series (LiAu, NaAu, KAu, RbAu, CsAu). The four-component formulation of relativistic density functional theory has been employed in this study, using the G-spinor basis sets implemented recently in the program BERTHA. The performance of four standard nonrelativistic density functionals employed is investigated by comparing the results with the best available theoretical and experimental data. The present work provides the first theoretical predictions on the molecular properties of RbAu. The intermetallic bond that occurs in the alkali auride series is highly polar and is characterized by a large charge transfer from the alkali metals to gold. The extent of this electron transfer has been investigated using several different charge analysis methods, enabling us to reach some general conclusions on their relative performance. We further report a detailed analysis of the topological properties of relativistic electron density in the bonding region, discussing the features of this approach which characterize the nature of the chemical bond. We have also computed the fully relativistic density for the alkali halides MBr and MI (M = Li, Na, K, Rb, and Cs). The comparative study shows that, on the basis of several topological properties and the variation in bond lengths, the gold atom behaves similarly to a halogen intermediate between Br and I. PMID:16571062

Belpassi, Leonardo; Tarantelli, Francesco; Sgamellotti, Antonio; Quiney, Harry M

2006-04-01

399

A Novel Synthetic Route For The Preparation Of Ammonium And Alkali-Metal Tetrafluoroborates And Alkyl Substituted Ammonium Tetrafluoroborates Using Pyridinium Tetrafluoroborate As The Precursor  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ammonium and alkali metal tetrafluoroborates have been prepared by the cation exchange reaction of pyridinium tetrafluoroborate with the corresponding hydroxides/halides. The reaction of pyridinium tetrafluoroborate with primary, secondary and tertiary alkyl amines at room temperature gives rise to mono-, di- and tri-alkylammonium tetrafluoroborates, respectively. The yields are good and the samples are of high purity. The products have been characterised by elemental analysis, IR and PMR ...

Mohamed, Syed K.; Padma, Dk

1988-01-01

400

Halide and nitrite recognizing hexanuclear metallacycle copper(II) pyrazolates.  

Science.gov (United States)

Halide-centered hexanuclear, anionic copper(II) pyrazolate complexes [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)X](-), X = Cl, Br, I are isolated in a good yield from the redox reaction of the trinuclear copper(I) pyrazolate complex [?-Cu(3)((3,5-CF(3))(2)pz)(3)] with a halide source such as PPh(3)AuCl or [Bu(4)N]X, X = Cl, Br, or I, in air. X-ray structures of the anion-centered hexanuclear complexes show that the six copper atoms are bridged by bis(3,5-trifluoromethyl)pyrazolate and hydroxyl ligands above and below the six copper atom plane. The anions are located at the center of the cavity and weakly bound to the six copper atoms in a ?(6)-arrangement, Cu-X = ~3.1 Å. A nitrite-centered hexanuclear copper(II) pyrazolate complex [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))](-) was obtained when a solution of [PPN]NO(2) in CH(3)CN was added dropwise to the trinuclear copper(I) pyrazolate complex [?-Cu(3)((3,5-CF(3))(2)pz)(3)] dissolved in CH(3)CN, in air. Blue crystals are produced by slow evaporation of the acetonitrile solvent. The X-ray structure of [PPN][trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))] complex shows the nitrite anion sits in the hexanuclear cavity and is perpendicular to the copper plane with a O-N-O angle of 118.3(7)°. The (19)F and (1)H NMR of the pyrazolate ring atoms are sensitive to the anion present in the ring. Anion exchange of the NO(2)(-) by Cl(-) can be observed easily by (1)H NMR. PMID:21190383

Mohamed, Ahmed A; Ricci, Simone; Burini, Alfredo; Galassi, Rossana; Santini, Carlo; Chiarella, Gina M; Melgarejo, Doris Y; Fackler, John P

2011-02-01

 
 
 
 
401

Thermal conductivity of molten alkali halides from equilibrium molecular dynamics simulations.  

Science.gov (United States)

The thermal conductivity of molten sodium chloride and potassium chloride has been computed through equilibrium molecular dynamics Green-Kubo simulations in the microcanonical ensemble (N,V,E). In order to access the temperature dependence of the thermal conductivity coefficient of these materials, the simulations were performed at five different state points. The form of the microscopic energy flux for ionic systems whose Coulombic interactions are calculated through the Ewald method is discussed in detail and an efficient formula is used by analogy with the methods used to evaluate the stress tensor in Coulombic systems. The results show that the Born-Mayer-Huggins-Tosi-Fumi potential predicts a weak negative temperature dependence for the thermal conductivity of NaCl and KCl. The simulation results are in agreement with part of the experimental data available in the literature with simulation values generally overpredicting the thermal conductivity by 10%-20%. PMID:15267797

Galamba, N; Nieto de Castro, C A; Ely, J F

2004-05-01

402

Holding onto electrons in alkali metal halide clusters: decreasing polarizability with increasing coordination.  

Science.gov (United States)

The connection between the electronic polarizability and the decrease of the system size from macroscopic solid to nanoscale clusters has been addressed in a combined experimental and model-calculation study. A beam of free neutral potassium chloride clusters has been probed using synchrotron-radiation-based photoelectron spectroscopy. The introduction of "effective" polarizability for chlorine, lower than that in molecules and dimers and decreasing with increasing coordination, has allowed us to significantly improve the agreement between the experimental electron binding energies and the electrostatic model predictions. Using the calculated site-specific binding energies, we have been able to assign the spectral details of the cluster response to the ionizing X-ray radiation, and to explain its change with cluster size. From our assignments we find that the higher-coordination face-atom responses in the K 3p spectra increase significantly with increasing cluster size relative to that of the edge atoms. The reasons behind the decrease of polarizability predicted earlier by ab initio calculations are discussed in terms of the limited mobility of the electron clouds caused by the interaction with the neighboring ions. PMID:23157589

Zhang, Chaofan; Andersson, Tomas; Svensson, Svante; Björneholm, Olle; Huttula, Marko; Mikkelä, Mikko-Heikki; Anin, Dmitri; Tchaplyguine, Maxim; Öhrwall, Gunnar

2012-12-13

403

A Cluster-Bethe lattice treatment for the U2-center in alkali-halides  

International Nuclear Information System (INIS)

A Cluster-Bethe lattice calculation for the electronic density of states of a U2 center in the rock-salt structure is presented for a simple one-orbital Hamiltonian. The parameters involved in the Hamiltonian are given values based on qualitative arguments for Na, K, Rb chlorides and bromides and the proton contact term is calculated for these sets of parameters, in fair agreement with experimental data

404

Is surface layering of aqueous alkali halides determined by ion pairing in the bulk solution?  

Science.gov (United States)

This contribution aims to elucidate the connection between ion-ion-solvent interactions in the bulk of aqueous electrolyte solutions and the properties of their liquid-air interface. In particular, we were interested in the conditions under which ion pairs form at the surface and whether this is linked to ion pairing in the bulk. For this reason different combinations of hard (Cl-, Li+) and soft ions (I-, Cs+) were investigated. Ion hydration and possible ion association in the bulk was probed with dielectric relaxation spectroscopy. This technique monitors the cooperative reorientation of the dipolar solvent molecules and detects all ion-pair species possibly present in the solution. At the interface, the formation of contact ion pairs was investigated by infrared-visible-sum frequency spectroscopy (SFG). This nonlinear optical technique possesses an inherent surface specificity and can be used for the characterization of interfacial water. The intensity of the SFG-active vibrational stretching modes depends on the number of oriented water molecules. The electric field at the surface of a charged aqueous interface aligns the water dipoles, which in turn increases the SFG response. Hence, the enhancement of the oscillator strengths of the water vibrational modes can be used to draw some conclusions on the strengths and geometrical extension of the electric field. The formation of ion pairs at the interface reduces the intensity of the band associated with hydrogen-bonded water. The underlying theory is presented. The combined data show that there are no contact ion pairs in the bulk of the fluid and—at best—only small amounts of solvent shared ion pairs. On the other hand, the combination of hard/hard or soft/soft ions leads to the formation of ion pairs at the liquid-air interface.

Brandes, Eva; Stage, Christiane; Motschmann, Hubert; Rieder, Julian; Buchner, Richard

2014-11-01

405

Electron emission from surfaces of alkali halides under the impact of metastable helium and neon atoms  

International Nuclear Information System (INIS)

Energy distributions of the electrons ejected from the evaporated film surfaces of LiF, LiCl, LiBr, NaF and NaCl by the impact of metastable He and Ne atoms have been measured. The observed distribution curves have two distinct structures: one peak is dentified as the valence band structure caused by Penning ionization, while the other peak is ascribed to scattered electrons. The positions of the valence band peaks are shifted to lower ionization energy from the corresponding photoelectron peaks (by 0.1-1.5 eV depending on the substance). In contrast to the photoelectron spectra, the structure attributable to conduction bands appears only very weakly. The relative intensity of the peak caused by scattered electrons is either strong or weak depending on the combination of the metastable atom and the sample. The interpretation of this observation is that the scattered electron peak is enhanced when the energy of the metastable atom exceeds twice the band gap energy, i.e. when the electron-electron scattering of Penning electrons in the solid is feasible. (orig.)

406

Behaviour of defects introduced by a nanosecond intense electron pulse at high temperatures in alkali halides  

International Nuclear Information System (INIS)

Measurements have been made on decay curves of the F centers (vacancies) created with a nanosecond electron pulse in non-treated and plastically deformed KBr or NaCl in a temperature range between 400 and 700 K. It is found that decay curves are decomposed into four decay stages: three bimolecular stages (referred to as stages I, II and III in order of increasing decay time) and a monomolecular stage (referred to as stage IV), which occurs at the last. The reaction rate constants for stages I and II are found to be not influenced by plastic deformation but those for the stages III and IV are strongly influenced. The pre-exponential factors of the reaction rate constants for the stages I and II in KBr and for the stage I in NaCl are explained in terms of the recombination of the pairs of the isolated di-H centers (di-interstitials) and the F centers but those for the stage III in KBr and the stages II and III in NaCl are of the pairs of the trapped-interstitials and the F centers. The stage IV is ascribed to the recombination of the F centers with the mobile interstitials released from the interstitial clusters, or the recombination of the mobile F centers with the interstitial clusters. The effect of the Na-impurity on the decay curves for KBr is also studied. (author)

407

The Brout sum rule, Debye-Waller factors and melting criteria for alkali halides  

International Nuclear Information System (INIS)

This paper presents the theoretical calculations of compressibilities using Brout's sum rule and the temperature dependence of mean square displacements (MSD) for ten compounds (LiF, NaCl, NaBr, NaI, KCl, KBr, KI, RbCl, RbBr and RbI) of our interest having NaCl structure. The eigenfrequencies and eigenvectors utilized for this purpose were determined by using a 7-parameter bond-bending force model (BBFM) recently proposed for phonons in NaCl structure. The theoretical values of the MSD were also used to check the validity of Lindemann's melting criteria. It is observed that the Brout sum rule fits well and Lindemann's parameter (ratio of root-mean-square displacements (RMSD) to the nearest-neighbour distance (NND)) is almost constant for all these compounds. The present results have been discussed in the light of available experimental and latest theoretical results. (author)

408

Optical properties of cubic and tetragonal Cu- centers in alkali halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the excitation spectrum of KC1 : Cu- the A band due to 1A1g(4s2) ? 3T1u(4s 4p) is detected. Its flat-topped shape reveals equal coupling to eg and t2g modes, whereas the near-gaussian shape of the C band signifies preponderant coupling of the 1T1u state to the t2g mode. Negligible quadratic coupling is deduced from a moment analysis of several C bands. A newly detected absorption band in the D band region and the splitting of the D1 band of tetragonal Cu-A centers seem to confirm Tsuboi'...

Kleemann, W.; Grawe, E.; Becker, L.

1980-01-01

409

Is surface layering of aqueous alkali halides determined by ion pairing in the bulk solution?  

Science.gov (United States)

This contribution aims to elucidate the connection between ion-ion-solvent interactions in the bulk of aqueous electrolyte solutions and the properties of their liquid-air interface. In particular, we were interested in the conditions under which ion pairs form at the surface and whether this is linked to ion pairing in the bulk. For this reason different combinations of hard (Cl(-), Li(+)) and soft ions (I(-), Cs(+)) were investigated. Ion hydration and possible ion association in the bulk was probed with dielectric relaxation spectroscopy. This technique monitors the cooperative reorientation of the dipolar solvent molecules and detects all ion-pair species possibly present in the solution. At the interface, the formation of contact ion pairs was investigated by infrared-visible-sum frequency spectroscopy (SFG). This nonlinear optical technique possesses an inherent surface specificity and can be used for the characterization of interfacial water. The intensity of the SFG-active vibrational stretching modes depends on the number of oriented water molecules. The electric field at the surface of a charged aqueous interface aligns the water dipoles, which in turn increases the SFG response. Hence, the enhancement of the oscillator strengths of the water vibrational modes can be used to draw some conclusions on the strengths and geometrical extension of the electric field. The formation of ion pairs at the interface reduces the intensity of the band associated with hydrogen-bonded water. The underlying theory is presented. The combined data show that there are no contact ion pairs in the bulk of the fluid and--at best--only small amounts of solvent shared ion pairs. On the other hand, the combination of hard/hard or soft/soft ions leads to the formation of ion pairs at the liquid-air interface. PMID:25399174

Brandes, Eva; Stage, Christiane; Motschmann, Hubert; Rieder, Julian; Buchner, Richard

2014-11-14

410

MAGNETIC PROPERTIES OF PRECIPITATED PHASES IN Mn2+ DOPED ALKALI HALIDES  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The susceptibility and specific heat data on NaCl : Mn2+ in the 0.07-4.2 K range reflect the existence of an antiferromagnetic phase transition at TN = 0.2 K. Below TN, the susceptibility reveals the presence of loose spins associated to Mn2+ in (or near) the surface of the Suzuki phase precipitates. The E.P.R., susceptibility and optical, measurements performed on RbCl : Mn2+ indicate that the nature of the precipitates is not MnCl2, RbMnCl3, Rb2MnCl4 or Rb2MnCl7, but the distorted Mn Cl4-6 ...

Moreno, M.; Rodriguez, F.; Gomez Sal, J.

1988-01-01

411

Two-electron F' centers in alkali halides: A negative-U analysis  

CERN Document Server

The existence of bound excited states of two-electron centers loosely trapped in an anion vacancy, the F' centers, is a long-standing problem of color center physics. Optical absorption bands attributed to F' centers in NaI and NaBr as observed by Baldacchini et al. seem to confirm the existence of F' bound snglet states. Nevertheless, a paper by Zhang et al. published not long ago reports extended ion calculations predicting bound excited states for F' centers in NaI alone while the evidence for NaBr is only marginal. For the first time we apply the negative-U mechanism in order to see whether bound excited F' states do not arise by virtue of the lattice polarization produced by the two trapped charge carriers. The result is positive for NaI and less so for NaBr, in agreement with Zhang et al. Other hosts, such as CsI and RbI also show a tendency towards sustaining F' bound excited states. However, the lack of entry data for LiI makes it presently too hard to obtain a complete negative-U picture for the iodi...

Georgiev, M

2005-01-01

412

Luminescence and formation of alkali halide ionic excimers in solid Ne and Ar  

International Nuclear Information System (INIS)

Transitions from ionic states A2+X- of alkalihalides CsF, CsCl and RbF isolated in solid Ne and Ar films recorded under pulsed e-beam excitation are studied. The B(2SIGMA1/2)-X(2SIGMA1/2) and C(2PI3/2)-A(2PI3/2) luminescence bands of Cs '2 '+F- (196.5 nm, 227 nm), Cs2+Cl- (220.1 nm, 249.2 nm) and Rb2+F- (136 nm) in Ne, and a weaker B-X emission of Cs2+F- (211.2 nm) in Ar are identified. For CsF the depopulation of the A2+X - state is dominated by the radiative decay. A ratio of the recorded exciplex emission intensities of I(CsF)/I(CsCl)/I(RbF) = 20/5/1 reflects the luminescence efficiency and for RbF and CsCl a competitive emission channel due to predissociation in the A2+X-(B2SIGMA1/2) state is observed. For these molecules an efficient formation of the state X*2 is confirmed through recording the molecular D'(3PI2g)-A'(3PI2u) transition. A strong dependence of the luminescence intensities on the alkalihalide content reveals quenching at concentrations higher than 0.7%

413

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

Directory of Open Access Journals (Sweden)

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

M. Druchok

2013-01-01

414

Role of cation impurities as electron and hole traps in alkali halides  

International Nuclear Information System (INIS)

A very simple Born-Haber type calculation is used to locate cation impurity levels in the gap of NaCl and KCl. Results are used to interpret valence changes induced by electron and hole trapping during irradiation. (author)

415

Annealing of chemical radiation damage in alkali metal nitrates  

International Nuclear Information System (INIS)

Annealing of chemical radiation damage in ?-irradiated alkali metal nitrates is presented. The order of annealing, LiNO3 > RbNO3 > CsNO3, is in the reverse order of free space in these crystals. Sodium and potassium nitrates are less susceptible to thermal annealing. The annealing data have been analysed on the models of simple interstitial vacancy recombination and also on the basis of conventional chemical kinetics. (author)

416

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

International Nuclear Information System (INIS)

Highlights: ? We provide the first standardized chemical durability test on tellurite glasses. ? The glasses we studied showed a wide variety of chemical durability. ? The best-performing glass showed good halide retention following melting and durability testing. ? These glasses have very high densities resulting in high volumetric waste loading ability. - Abstract: Tellurite glasses have historically been shown to host large concentrations of halides. They are here considered for the first time as a waste form for immobilizing chloride wastes, such as may be generated in the proposed molten alkali salt electrochemical separations step in nuclear fuel reprocessing. Key properties of several tellurite glasses are determined to assess acceptability as a chloride waste form. TeO2 glasses with other oxides (PbO, Al2O3 + B2O3, WO3, P2O5, or ZnO) were fabricated with and without 10 mass% of a simulated (non-radioactive) mixed alkali, alkaline-earth, and rare earth chloride waste. Measured chemical durability is compared for the glasses, as determined by the product consistency test (PCT), a common standardized chemical durability test often used to validate borosilicate glass waste forms. The glass with the most promise as a waste form is the TeO2–PbO system, as it offers good halide retention, a low sodium release (by PCT) comparable with high-level waste silicate with high-level waste silicate glass waste forms, and a high storage density.

417

Point defect stabilization in ionic crystals at high defect concentrations  

International Nuclear Information System (INIS)

Stabilization of point defects in ionic crystals differs from that in metals or other monatomic solids in that there is the need to maintain both stoichiometry (or accommodate non-stoichiometry) and order. Primary point defects in these solids, whether produced thermally, chemically, or by irradiation, seldom are present or aggregate in exactly stoichiometric proportions, and in consequence at high defect concentrations extended secondary defect structures arise which can be quite distinct from those formed in monatomic solids. Non-stoichiometry can be accommodated in several ways. In oxygen-deficient transition metal oxides, oxygen vacancies can be effectively eliminated by alteration of the mode of linking metal-oxygen octahedra together, giving rise to so-called crystallographic shear planes. This process effectively delocalizes a change in cation valency. In cation deficient/anion excess systems (e.g. Fesub(1-x)O, UOsub(2+x), CaF2:YF3), accommodation occurs by a localized change in cation valency (and often position) and formation of point defect cluster complexes (cation vacancies, anion interstitials) which when stacked together can form embryonic nuclei for a new phase of altered stoichiometry. Where valency changes are not possible, for example in alkali halides or undoped alkaline earth halides and oxides, stoichiometric extended defects (such as dislocation loops) are generated, but these must be accompanied by other more stable forms oe accompanied by other more stable forms of point defect species. Aggregation of point defects at high density can additionally result in precipitation of separate elemental phases, and thus decomposition of the solid

418

Computational Screening of Mixed Metal Halide Ammines  

DEFF Research Database (Denmark)

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

Jensen, Peter Bjerre; Lysgaard, Steen

419

Flame inhibition by hydrogen halides - Some spectroscopic measurements  

Science.gov (United States)

The far-ultraviolet absorption spectrum of an air-propane diffusion flame inhibited with hydrogen halides has been studied. Plots of the absorption of light by hydrogen halides as a function of position in the flame and also as a function of the amount of hydrogen halide added to the flame have been obtained. The hydrogen halides are shown to be more stable on the fuel side of the reaction zone than they are on the air side. Thermal diffusion is seen to be important in determining the concentration distribution of the heavier hydrogen halides in diffusion flames. The relationship between the concentration distribution of the hydrogen halides in the flame and the flame inhibition mechanism is discussed.

Lerner, N. R.; Cagliostro, D. E.

1973-01-01

420

Reduction of Saturated Alkyl Halides to Alkanes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This chapter describes the hydrogenolysis of a saturated halide (I, Br, Cl, and F) to an alkane. A number of methods have been developed for these reductions, and the ones that are thought to be the most useful are described here. The methods are assessed by the type of reagent that is being used to carry out the transformation, with the emphasis being placed on reliable methods that are chemoselective and generally applicable. References to reviews are provided to facilitate an indepth view ...

Ziffle, Ve; Fletcher, Sp

2014-01-01

 
 
 
 
421

Comparison of the morphology of alkali–silica gel formed in limestones in concrete affected by the so-called alkali–carbonate reaction (ACR) and alkali–silica reaction (ASR)  

International Nuclear Information System (INIS)

The morphology of alkali–silica gel formed in dolomitic limestone affected by the so-called alkali–carbonate reaction (ACR) is compared to that formed in a siliceous limestone affected by alkali–silica reaction (ASR). The particle of dolomitic limestone was extracted from the experimental sidewalk in Kingston, Ontario, Canada that was badly cracked due to ACR. The siliceous limestone particle was extracted from a core taken from a highway structure in Quebec, affected by ASR. Both cores exhibited marked reaction rims around limestone particles. The aggregate particles were polished and given a light gold coating in preparation for examination in a scanning electron microscope. The gel in the ACR aggregate formed stringers between the calcite crystals in the matrix of the rock, whereas gel in ASR concrete formed a thick layer on top of the calcite crystals, that are of the same size as in the ACR aggregate

422

Comparison of the morphology of alkali–silica gel formed in limestones in concrete affected by the so-called alkali–carbonate reaction (ACR) and alkali–silica reaction (ASR)  

Energy Technology Data Exchange (ETDEWEB)

The morphology of alkali–silica gel formed in dolomitic limestone affected by the so-called alkali–carbonate reaction (ACR) is compared to that formed in a siliceous limestone affected by alkali–silica reaction (ASR). The particle of dolomitic limestone was extracted from the experimental sidewalk in Kingston, Ontario, Canada that was badly cracked due to ACR. The siliceous limestone particle was extracted from a core taken from a highway structure in Quebec, affected by ASR. Both cores exhibited marked reaction rims around limestone particles. The aggregate particles were polished and given a light gold coating in preparation for examination in a scanning electron microscope. The gel in the ACR aggregate formed stringers between the calcite crystals in the matrix of the rock, whereas gel in ASR concrete formed a thick layer on top of the calcite crystals, that are of the same size as in the ACR aggregate.

Grattan-Bellew, P.E., E-mail: p.grattan-bellew@sympatico.ca [Materials and Petrographic Research G-B Inc., 472 Edison Avenue, Ottawa, ON, Canada K2A 1T9 (Canada); Chan, Gordon [NRC Construction, Bldg., M20, 1200 Montreal Road, Ottawa, ON, Canada K1A 0R6 (Canada)

2013-05-15

423

Process and composition for drying of gaseous hydrogen halides  

Science.gov (United States)

A process for drying a gaseous hydrogen halide of the formula HX, wherein X is selected from the group consisting of bromine, chlorine, fluorine, and iodine, to remove water impurity therefrom, comprising: contacting the water impurity-containing gaseous hydrogen halide with a scavenger including a support having associated therewith one or more members of the group consisting of: (a) an active scavenging moiety selected from one or more members of the group consisting of: (i) metal halide compounds dispersed in the support, of the formula MX.sub.y ; and (ii) metal halide pendant functional groups of the formula -MX.sub.y-1 covalently bonded to the support, wherein M is a y-valent metal, and y is an integer whose value is from 1 to 3; (b) corresponding partially or fully alkylated compounds and/or pendant functional groups, of the metal halide compounds and/or pendant functional groups of (a); wherein the alkylated compounds and/or pendant functional groups, when present, are reactive with the gaseous hydrogen halide to form the corresponding halide compounds and/or pendant functional groups of (a); and M being selected such that the heat of formation, .DELTA.H.sub.f of its hydrated halide, MX.sub.y.(H.sub.2 O).sub.n, is governed by the relationship: .DELTA.H.sub.f .gtoreq.n.times.10.1 kilocalories/mole of such hydrated halide compound wherein n is the number of water molecules bound to the metal halide in the metal halide hydrate. Also disclosed is an appertaining scavenger composition and a contacting apparatus wherein the scavenger is deployed in a bed for contacting with the water impurity-containing gaseous hydrogen halide.

Tom, Glenn M. (New Milford, CT); Brown, Duncan W. (Wilton, CT)

1989-08-01

424

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)]2 as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon–halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75–94%). These results are the first examples of cycloadditions of alkynyl halides using a...

Andrew Tigchelaar; William Tam

2012-01-01

425

Coordination Networks of Mercury(II) Halides and Polyether Ligand  

Digital Repository Infrastructure Vision for European Research (DRIVER)

New crystalline mercury halide adducts with polyetheras ligands were isolated, characterized, and identified as trans-[HgIICl?(diox)?]n (1) and trans-[HgIII?(diox)]n (2). The compounds were obtained from the metal halide salts in solution of 1,4-dioxane and can be considered as “cutting-out” products from the metal halide as they show similarity in the arrangement with starting compounds.

Crochet, Aure?lien; Fromm, Katharina M.

2012-01-01

426

Computational screening of mixed metal halide ammines  

DEFF Research Database (Denmark)

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

Jensen, Peter Bjerre; Lysgaard, Steen

427

Alkali metal and ammonium fluoro(trifluoroacetato)metallates M?[M??3(?3-F)(CF3COO)6(CF3COOH)3], where M? = Li, Na, K, NH4, Rb, or Cs and M?? = Ni or Co. Synthesis and crystal structures  

International Nuclear Information System (INIS)

A series of fluoro(trifluoroacetato)metallates were synthesized by crystallization from solutions in trifluoroacetic acid containing nickel(II) or cobalt(II) nitrate hydrates and alkali metal or ammonium fluorides: Li[Ni3(?3-F)(CF3COO)6(CF3COOH)3](CF3COOH)3 (I), M?[Ni3(?3-F)(CF3COO)6(CF3COOH)3] (M? = Na (II), NH4 (IV), Rb (V), and Cs (VI)), NH4[Co3(?3-F) (CF3COO)6(CF3COOH)3] (III), and Cs[Ni3(?3-F)(CF3COO)6(CF3COOH)3](CF3COOH)0.5 (VII). The crystal structures of these compounds were determined by single-crystal X-ray diffraction. All structures contain triangular trinuclear complex anions [M3?(?3-F)(CF3COO)6(CF3COOH)3]? (M? = Ni, Co) structurally similar to trinuclear 3d metal oxo carboxylate complexes. The three-coordinated F atom is located at the center of the triangle formed by Ni(II) or Co(II) atoms. The metal atoms are linked in pairs by six bridging trifluoroacetate groups located above and below the plane of the [M?3 F] triangle. The oxygen atoms of the axial CF3COOH molecules complete the coordination environment of M? tion environment of M? atoms to an octahedron.

428

Characterization of a novel alkali metal and transition metal plasma source  

International Nuclear Information System (INIS)

Results of characterization studies of a metal vapor plasma, and potentially an ion source, are presented. The source is well suited to solids having dielectric and thermal properties which permit rapid heating of the solid by a high-frequency (2-3 GHz) signal. By proper placement in a resonant cavity, the conductively and dielectrically heated solid surface emits a vapor stream which is then ionized in the near-surface region, yielding a metal ion rich plasma. The work presented here concerns plasmas produced from two alkali metal halides, NaCl and KBr, as well as from graphite, titanium dioxide, and iron oxide. The power densities involved are characteristic of high-frequency plasmas and range from 1 to 30 W/cm3. The factor of two or three difference between the ionization potentials of the metals and of the halides or oxygen results in an enrichment of the metal ion content of the plasma and in the presence of the halides or oxygen as atoms rather than ions. In addition to the description of the novel source, its operation, and that of the plasmas produced in it, results of preliminary attempts at extraction and characterization of a beam are presented

429

The mechanism of interaction of dislocations with point defects in ionic crystals  

International Nuclear Information System (INIS)

A mechanism of interaction of dislocations with point defects is suggested on the basis of a study of deformation-stimulated luminescence (DL) from irradiated KCl. DL is considered to be a result of destruction of hole colour centres by dislocations. The centres destroyed by dislocations are responsible for irradiation-induced strengthening of alkali halides. (author)

430

Mechanism and selectivity in nickel-catalyzed cross-electrophile coupling of aryl halides with alkyl halides.  

Science.gov (United States)

The direct cross-coupling of two different electrophiles, such as an aryl halide with an alkyl halide, offers many advantages over conventional cross-coupling methods that require a carbon nucleophile. Despite its promise as a versatile synthetic strategy, a limited understanding of the mechanism and origin of cross selectivity has hindered progress in reaction development and design. Herein, we shed light on the mechanism for the nickel-catalyzed cross-electrophile coupling of aryl halides with alkyl halides and demonstrate that the selectivity arises from an unusual catalytic cycle that combines both polar and radical steps to form the new C-C bond. PMID:23952217

Biswas, Soumik; Weix, Daniel J

2013-10-30

431

Alkali Metal Cluster Theory.  

Science.gov (United States)

Available from UMI in association with The British Library. Requires signed TDF. In this thesis, we apply the tight-binding Hubbard model to alkali metal clusters with Hartree-Fock self-consistent methods and perturbation methods for the numerical calculations. We have studied the relation between the equilibrium structures and the range of the hopping matrix elements in the Hubbard Hamiltonian. The results show that the structures are not sensitive to the interaction range but are determined by the number of valence electrons each atom has. Inertia tensors are used to analyse the symmetries of the clusters. The principal axes of the clusters are determined and they are the axes of rotational symmetries of clusters if