WorldWideScience
1

THEORY OF PLASTICO ML IN ?–IRRADIATED ALKALI HALIDE CRYSTALS  

OpenAIRE

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...

NAMITA RAJPUT

2011-01-01

2

Radiation damage products in ionic crystals impurity doped alkali halides  

International Nuclear Information System (INIS)

Various radiation damage products in impurity doped alkali halide crystals and the experimental tools used to unravel the physical properties and models of such products are reviewed. Depending on the nature of material and the intended extent of damage, irradiation has been performed with UV radiation (approximately 5.0 eV), X radiation (approximately 50 keV), gamma radiation (approximately 1 MeV), neutrons (approximately 2 MeV) or electrons (1 to 30 MeV). The role of impurities is discussed and the various solids have been categorized into different types considering the similarity of the end products an the materials themselves

3

Synthetic Alkali Halides  

Science.gov (United States)

This complex experimental investigation uses alkali halides (NaCl, KCl, and mixtures of both) to simulate the melting of alkali feldspars which melt at too high of temperatures to work with in lab. Three hypotheses are tested: It is possible to crystallize alkali-chloride salts from a magma with any composition between NaCl and KCl. Because K+ and Na+ do not have the same ionic size, the atomic spacing in alkali chlorides will vary systematically with composition. Alkali chlorides are equally stable at high (just below liquidus) and low (subsolidus)temperatures. This project takes more than one class period, depending on how many students are in the class, because there will be lines at the scales, oven, and XRD. It is advisable to introduce the lab in class and have students complete various parts on their own time. There are three main parts. Part one: Synthesize all alkali halide compositions at high temperature (hopefully above the solvus. Part two: Put grown crystals back in an oven at lower temperature to see if they will unmix. Part three: Write a report evaluating and interpreting all results, relevant graphs, and the above three hypothesis.

Dexter Perkins

4

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

Scientific Electronic Library Online (English)

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

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

2006-04-01

5

Theoretical and experimental investigation of force imaging at the atomic scale on alkali halide crystals  

Science.gov (United States)

Assuming a model tip (Si4O10H10) as a reasonable representation of the surface of a Si3N4 cantilever stylus having a hydrogen-terminated asperity and a broader load-bearing base, we investigate the interaction of an atomic force microscope (AFM) with an alkali halide crystal by quantum chemical methods. Structural relaxation of the sample during engagement is allowed, and defect formation is investigated. Force curves above cation and anion positions are calculated, determining maximum sustainable loads and indicating a basis for atomic contrast. Experiments using a Si3N4 cantilever for AFM imaging of 12 alkali halide and alkaline earth fluoride crystals in air and desiccated helium are reported, in the widest AFM survey of such materials to date. Adsorbed water is shown to significantly enhance the observation of atomic periodicity on ionic halide samples, and rapid surface diffusion on alkali halide crystals is illustrated as it affects prospects for defect investigations. Observations of step edges and point-defect candidates at atomic scale are reported. The theoretical and experimental results are discussed together in the effort to provide a quantum-mechanical model for observations of alkali halide samples at atomic resolution, and to examine a possible basis for atomic resolution in the presence of long-range attractive forces.

Shluger, A. L.; Wilson, R. Mark; Williams, R. T.

1994-02-01

6

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

7

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)

8

Mechanoluminescence response to the plastic flow of coloured alkali halide crystals  

Energy Technology Data Exchange (ETDEWEB)

The present paper reports the luminescence induced by plastic deformation of coloured alkali halide crystals using pressure steps. When pressure is applied onto a gamma-irradiated alkali halide crystal, then initially the mechanoluminescence (ML) intensity increases with time, attains a peak value and later on it decreases with time. The ML of diminished intensity also appears during the release of applied pressure. The intensity I{sub m} corresponding to the peak of ML intensity versus time curve and the total ML intensity I{sub T} increase with increase in value of the applied pressure. The time t{sub m} corresponding to the ML peak slightly decreases with the applied pressure. After t{sub m}, initially the ML intensity decreases at a fast rate and later on it decreases at a slow rate. The decay time of the fast decrease in the ML intensity is equal to the pinning time of dislocations and the decay time for the slow decrease of ML intensity is equal to the diffusion time of holes towards the F-centres. The ML intensity increases with the density of F-centres and it is optimum for a particular temperature of the crystals. The ML spectra of coloured alkali halide crystals are similar to the thermoluminescence and afterglow spectra. The peak ML intensity and the total ML intensity increase drastically with the applied pressure following power law, whereby the pressure dependence of the ML intensity is related to the work-hardening exponent of the crystals. The ML also appears during the release of the applied pressure because of the movement of dislocation segments and movements of dislocation lines blocked under pressed condition. On the basis of the model based on the mechanical interaction between dislocation and F-centres, expressions are derived for the ML intensity, which are able to explain different characteristics of the ML. From the measurements of the plastico ML induced by the application of loads on gamma-irradiated alkali halide crystals, the pinning time of dislocations, diffusion time of holes towards F-centres, the energy gap E{sub a} between the bottom of acceptor dislocation band and the energy level of interacting F-centres, and work-hardening exponent of the crystals can be determined. As in the elastic region the strain increases linearly with stress, the ML intensity also increases linearly with stress, however, as in the plastic region, the strain increases drastically with stress and follows power law, the ML intensity also increases drastically with stress and follows power law. Thus, the ML is intimately related to the plastic flow of alkali halide crystals.

Chandra, B.P., E-mail: bpchandra4@yahoo.co.i [Shri Shankaracharya College of Engineering and Technology, Junwani, Bhilai (C.G.) 490020 (India); Bagri, A.K. [Department of Postgraduate Studies and Research in Physics, Rani Durgawati University, Jabalpur 482001 (India); Chandra, V.K. [Department of Electrical and Electronics Engineering, Chhatrapati Shivaji Institute of Technology, Shivaji Nagar, Kolihapuri, Durg (C.G.) 491001 (India)

2010-02-15

9

SURFACE AND SPACE CHARGESElectrostatic charge effects on surface defects in alkali halide crystals  

OpenAIRE

The presence of a surface charge and a compensating Debye-Hückel layer of charged point defects in ionic crystals was suggested by Lehovec [1]. The surface charge was later associated [2, 3] with charged surface entities. Indirect evidence from sublimation measurements supported such a view, but direct evidence was lacking. In the present work, the direct effect of an externally applied electrostatic field on the topography of monomolecular ledges was determined for sublimated alkali halide ...

Yacama?n, M.; Hirth, J.

1980-01-01

10

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

11

Characteristics of F centers of alkali-halide crystals in ground and excited states  

International Nuclear Information System (INIS)

The molecular-statics method is used to calculate the displacements of the lattice ions nearest to the F center in alkali halide crystals with NaCl and CsCl structures (altogether twenty crystals). The calculations are made for the 1s and 2p states of the F-center electron with allowance for the angular dependence of the Coulomb potential created by the electron in the 2p state. The absorption and emission energies of the F center are calculated. The calculated energies agree qualitatively with experiment and reproduce the experimentally found tendencies of changes in these energies when passing from one crystal to another

12

Electrical conduction of alkali-halide crystals after ion-heat modification  

International Nuclear Information System (INIS)

The influence of ion-heat modification modes on the change of electrical conduction ? of alkali-halide crystals is explored. The most essential changes of ? are result in ionic intermixing and subsequent heat treatment at 550-750 K. The conduction elevation is stipulated by defect formation accompanying radiolysis product appearance on the surface and forming the metal formation in modified layer and on the surface. Evaporation of crystals and change of their morphology and annealing of defects at temperature above optimum (individual for each compounds) lead to decrease of electrical conduction also

13

Defects in alkali halide crystals irradiated under applied stress  

International Nuclear Information System (INIS)

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

14

Coupling between molecular and charge transfer excitations in mixed alkali halide-cyanide crystals  

International Nuclear Information System (INIS)

The optical absorption spectra of mixed alkali halide cyanide crystals (M(CN) sub(x) Y sub(1-x) where M = Na, K, Rb and Y = F, Cl, Br, I) were measured at temperatures ranging from 300K down to 4.2K and CN- concentrations from 10-2% up to pure cyanide crystals. The absorption cross sections of the parity forbidden X sup(1)?+ ? a'3?+ vibronic transition of the CN- molecular ions were found to present a strong, non linear dependence on the x-composition of the mixed crystal as well as on the halide ion. This behaviour is explained by the coupling of the triplet molecular excitations to singlet charge transfer excitations in their neighbourhood. The experimental data were fit with a coupling energy of a few meV, depending mainly on the type of excitations involved (localized or collective) and not on the particular halide ion. The coupling mechanism is discussed and it is found to be due to the overlap between the wavefunctions of the two excitations. (Author)

15

FA(Li) centers in mixed crystals of alkali halides  

Science.gov (United States)

The emission and absorption of FA(Li) centers in mixed crystals of KCl and KBr have been studied from 1.6 to 100 K at atmospheric and high pressures. While only one pair, FA1 and FA2, of absorption bands is observed, two types of emission bands, type I and type II, are obtained. The relative intensities of the type-I and type-II emissions depend both on the composition of the solid solution and on temperature. A possible formation mechanism of two relaxed excited states in a complete solid solution is discussed. The energy separation and intensity of the FA absorption band (FA1 and FA2) in the KCl1-xBrx:Li system are observed under various pressures. Information about the off-center behavior in the mixed crystals is obtained from the pressure dependence of the separation between FA1 and FA2 absorption. The pressure variation of intensity in type-I and type-II emissions is also measured. These results show a different pressure effect on the relaxation processes of the two types of emission: the type-II emission is scarcely affected by the applied pressure contrary to a considerable pressure-induced nonradiative transition in the type-I emission. This situation leads us to investigate the relaxation process of the type-II emission under hydrostatic pressure.

Asami, Kumiko; Ishiguro, Masakazu

1986-09-01

16

BRIEF COMMUNICATIONS: Self-locking of neodymium laser modes by alkali halide crystals with Z color centers  

Science.gov (United States)

Ultrashort YAG:Nd laser pulses were generated using alkali halide crystals containing Z-type color centers as saturable absorbers. It was found experimentally that the most promising absorber was rubidium bromide doped with divalent alkali or rare-earth ions. This absorber was used in generation of pulses of ~40 psec duration with the probability of complete self-locking close to 100%.

Sobolev, L. M.; Varnavski?, O. P.; Penzina, É. É.; Leontovich, Aleksandr M.; Parfianovich, I. A.; Bryukvin, V. V.

1984-02-01

17

An optical criterion to obtain miscible mixed crystals in alkali halides  

Scientific Electronic Library Online (English)

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

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

2008-11-01

18

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

CERN Document Server

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

Mao, Albert H; 10.1063/1.4742068

2012-01-01

19

New AIG Method of Growing Alkali Halide Crystals and Potential Application to CZT  

Science.gov (United States)

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

Gleyzer, A.; Rhodes, E.

2002-10-01

20

The Additive Coloration of Alkali Halides  

Science.gov (United States)

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

Jirgal, G. H.; and others

1969-01-01

21

The experimental estimation of screen barrier of self trapped excitons' relaxation in alkali halide crystals  

International Nuclear Information System (INIS)

Full text: Earlier the effect of intrinsic luminescence ignition of alkali halide crystals (AHC) at lattice symmetry lowering was found. This is probably connected with the efficiency decrease of nonradiative channel of exciton decay into initial radiation defects. It is well known that at self trapped exciton (STE) luminescence quenching the radiation defects creation efficiency increases. Experimental method for the estimation of nonradiative STE transfer activation energy in AHC at low temperature uniaxial stress is proposed. On the basis of values of STE luminescence quenching activation energy for the range of AHC obtained by temperature dependence of X-ray luminescence for both in absentia and at low temperature uniaxial stress, we can mark out the main rule: the activation energy increase at elastic uniaxial stress is observed in the range KBr?NaCl ?KI?Rbl?CsBr and explained by the increase of potential barrier of STE nonradiative decay into radiation defects. It is represented the values of STE luminescence quenching activation energy for the range of AHC for both in absentia and at low temperature uniaxial stress. Thus, it becomes obvious that radiation defects' creation decrease in KI and Rbl crystals depends on elastic stress degree because of the increase of potential barrier sharing radiative and nonradiative STE decay channels

22

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)

23

Evaluation of the first- and higher-order volume and pressure derivatives of dielectric constants of alkali halide crystals  

International Nuclear Information System (INIS)

An analysis of first and higher order volume and pressure derivatives of low frequency or static dielectric constant is presented for sixteen alkali halide crystals with NaCl structure using seven different potential forms for the short range overlap repulsive energy. The potential parameters are calculated using recent values of van der Waals potentials and taking proper account of the thermal contribution derived from consistent experimental ultrasonic data. Calculated values of volume derivatives of dielectric constant and optic mode Grueneisen parameters are compared with available experimental data. The results obtained from some potential forms present distinctly better agreement with experiment in comparison of others. The usefulness of such potential forms is demonstrated in predicting the higher order pressure derivatives of dielectric constants of ionic crystals. (author)

24

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

25

Ultraviolet optical absorption of alkali cyanides and alkali halide cyanides  

International Nuclear Information System (INIS)

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

26

Thermodynamic properties of Alkali Halides  

International Nuclear Information System (INIS)

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

27

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

28

Defects induced melting in alkali halides  

International Nuclear Information System (INIS)

In the present paper we study the pressure dependence of melting of NaCl and CsCl crystals. A formulation has been presented for the pressure dependence of melting temperature on the basis of the vacancy model using the expression for the pressure dependence of the volume of Schottky defects from the Roy-Roy equation of state. Values of pressure derivatives of melting temperature have been calculated at elevated pressures to determine the rate of change of melting temperature with increase in pressures using the data of vacancy formation energy and effective volume of Schottky defects. The vacancy model revised in the present study takes into account the variation of bulk modulus with pressure, whereas in the Ksiazek and Gorecki model, it was treated constant. Results for pressure derivative of melting temperature are calculated for the solids under study. The melting curves have also been obtained and found to compare well with results based on molecular dynamics simulation and experimental data reported in recent literature. -- Research Highlights: ? We have studied the pressure dependence of melting in alkali halides on the basis of the vacancy model. ? We have taken into account the pressure dependence of volume of Schottky defects. ? The pressure derivatives of melting temperature are calculated for the alkali halide solids. ? The results have been found to compare well with the corresponding experimental data. ? This work will be useful in the analysisk will be useful in the analysis of thermal equation of state for solids.

29

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

30

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)

31

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

International Nuclear Information System (INIS)

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

32

Recombination of radiation defects in alkali halide crystals at low temperature  

International Nuclear Information System (INIS)

The complex investigation of the ionic-electronic processes of the charge transport and thermally stimulated luminescence of colour centres (I, ?, F, F', Vsub(K) and H) in X-irradiated KBr, NaCl, NaI and KCl crystals at 4.2 K has been carried out. The experiment has been performed on X-irradiated KBr at 4.2 K by a complex of thermally stimulated methods. A number of substages of temperature annealing of different defects was studied. The effect of electron tunneling ''recharge'' in the excited defect pair (F-H) during photostimulation in the F-band of KBr is observed which results in the charged Frenkel defect pair formation (?-I). The conclusion is drawn that the tunneling ''recharge'' of the non-excited F-H pair is unlikely. It was observed that the Frenkel defect (I, ?, ''H-Vsub(K)'', F, H') accumulation efficiencies increases by 10% or more if the X-irradiation at 4.6 K is carried out under an applied DC field of 3 kV/cm. Two competitive mechanism of the primary generation of the anion Frenkel defects are discussed. The formation of the self-trapped excitons and their luminescence as a result of the H and F centers direct recombination could be noneffective. It is found that anion exciton dissociation into the electron- hole pair is a process competitive to the exciton decay into the Frenkel defect pair

33

Ground state properties of heavy alkali halides  

OpenAIRE

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 ...

Doll, Klaus; Stoll, Hermann

1998-01-01

34

Hot working alkali halides for laser window applications  

International Nuclear Information System (INIS)

The techniques used to hot work alkali halide crystals into laser window blanks are reviewed. From the point of view of high power laser window applications one of the materials with a high figure of merit is KCl. Thus the materials examined are KCl and alloys of KCl-KBr containing 5 mole percent KBr. The fabrication techniques include conventional and constrained press forging, isostatic press forging and hot rolling. Optical properties are paramount to the ultimate usefulness of these materials. Results on the optical properties of the hot worked material are included together with mechanical properties and microstructural data

35

Optical and Spectral Studies on ? Alanine Metal Halide Hybrid Crystals  

Science.gov (United States)

We have synthesized and grown ? alanine metal halide hybrid crystals viz. ? alanine cadmium chloride (BACC), an amino acid transition metal halide complex crystal and ? alanine potassium chloride (BAPC), an amino acid alkali metal halide complex crystal by slow evaporation method. The grown crystals were found to be transparent and have well defined morphology. The optical characteristics of the grown crystals were carried out with the help of UV-Vis Spectroscopy. The optical transmittances of the spectrums show that BAPC is more transparent than BACC. The Photoluminescence of the materials were determined by the Photoluminescent Spectroscopy

Sweetlin, M. Daniel; Selvarajan, P.; Perumal, S.; Ramalingom, S.

2011-10-01

36

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

Czech Academy of Sciences Publication Activity Database

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

Král, Robert

2012-01-01

37

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

Science.gov (United States)

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

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

2014-12-01

38

A new polarizable force field for alkali and halide ions  

Energy Technology Data Exchange (ETDEWEB)

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

Kiss, Péter T.; Baranyai, András [Institute of Chemistry, Eötvös University, 1518 Budapest 112, PO BOX 32 (Hungary)

2014-09-21

39

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

40

Thermoluminescence, optical absorption and ESR studies in (KCl)1-x(KBr)x mixed alkali halide crystals doped with gold  

International Nuclear Information System (INIS)

Mixed crystals of KCl-KBr of different compositions were grown with Czochralski technique. Crystals were doped with gold. Both the undoped and gold doped crystals were ?-irradiated using 60Co source. All the irradiated samples were subjected to thermoluminescence, optical absorption and ESR studies. The present study shows the composition dependence of the parameters and enhancement in the luminescence intensity as well as the absorption coefficient with gold doping. Non-linear variation of color center peak position and half band width of F-center with composition has been observed. The results of the above studies are presented in this paper

41

Measurement of surface phonon dispersion curves of alkali halide single crystals by time of flight spectroscopy of He atom beams  

International Nuclear Information System (INIS)

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

42

Lattice defect formation via exciton dissociation in ammonium halide crystals  

International Nuclear Information System (INIS)

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

43

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.)

44

Optical and magnetic resonance studies of transition metal ions and complexes in alkali halides  

International Nuclear Information System (INIS)

Literature on optical absorption, ESR and ENDOR investigations of Ti, V, Cr, Mn, Fe, Co, Ni and Cu ions in alkali halides since 1966 is thoroughly scanned. A general survey is followed by a survey of individual elements including Sc. All charge states reported in as-grown crystals as well as in crystals subjected to radiation damage are considered. Results of optical ESR and ENDOR measurements on the same element in different alkali halides are grouped together and models proposed to explain these results are discussed. In addition to ionic centers, the molecular complexes, if any, of that element are also reviewed. In the last section an overview of the subject is given

45

Hot-carrier transport processes in stimulated desorption of alkali halides  

Science.gov (United States)

Electron- and photon-stimulated desorption of epitaxial thin films and bulk single crystals of alkali halides has been investigated. It has been found that the widely accepted model based on self-trapped exiton decay and thermally activated defect diffusion cannot account for a number of experimental observations. In particular, it cannot explain the stability of the very thin alkali-halide films against the electron beam, and it fails to interpret correctly the yield dependence of the halogen atoms emitted with nonthermal energies on the film thickness and sample temperature. It is shown that for satisfactory interpretation of those data one has to take into account early stages of crystal excitation, i.e., hot carrier formation and transport processes occurring prior to self-trapped exciton phase. Consequently, a comprehensive description of the observed desorption features is presented.

Kolodziej, J. J.; Szymonski, M.

1998-11-01

46

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

47

Volcanic Origin of Alkali Halides on Io  

Science.gov (United States)

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

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

2003-01-01

48

EPR isotropic hyperfine triplets in alkali halides of the molecular point defects containing 14N  

International Nuclear Information System (INIS)

The EPR spectra of molecular point defects in alkali halides have been studied. Diamagnetic ions NO2- and NO3- from various nitrites and nitrates have been introduced into KCl, KBr, KI, NaCl, NaBr and isomorphic KCl-KBr crystals. The crystals containing these ions have been X-rayed to obtain the paramagnetic molecular point defects. In KCl at room temperature 5 isotropic hyperfine triplets were found with the intensity ratio 1:1:1 in each of the triplets. (author)

49

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

50

Apparent electron radius in homogeneous molten alkali metal-alkali halide mixtures  

International Nuclear Information System (INIS)

Effective electron radii in liquid homogeneous mixtures of alkali metals and their halides are evaluated within the framework of rigid-sphere approximation, halide melt complex structure model and respective state theory. It is shown that application of the respective state theory based on the search and introduction of dimensionless parameters (criteria) of similaring for the description of liquids with different character of interparticle x linkings and taking account of their complex structure, can be useful when evaluating the density of particle packing and other properties of ion-electron metls, linked with the molar volume

51

Vibrational relaxation in seeded supersonic alkali halide beams  

International Nuclear Information System (INIS)

A seeded supersonic beam source for alkali halides is described which can provide high intensity, a narrow velocity distribution, enhanced or reduced translational energy (by choice of diluent mass), low rotational temperature, and partially relaxed vibrational populations. Alkali halide vapor at approx.1200--1400 0K and approx.0.1 Torr is mixed with a diluent gas at approx.30--100 Torr and expanded through a pinhole nozzle 0.1 mm in diameter. Velocity analysis of a seeded CsF beam with Ar as the diluent indicates the beam properties conform approximately to the theory of isentropic expansions, with deviations attributable to the relatively low source pressure used. The vibrational populations of the v=0, 1, 2, 3 states in seeded beams of LiF with Ar, NH3, ND3, and SF6 as diluents were determined by electric resonance spectroscopy. For Ar as diluent, the LiF vibrational energy has a Boltzmann distribution with a temperature only approx.10% lower than the beam source. For the polyatomic diluents, the LiF vibrational distribution is markedly non-Boltzmann. The nominal vibrational temperature T/sub v/, defined by comparing the population of state v to that of the ground state, drops substantially for the higher v states. The vibrational relaxation becomes more pronounced as the source pressure of alkali halide or diluent gas is increased. For the experimental conditions used here, T/sub v/ for the v=3 state drops to approx.2/3 v/ for the v=3 state drops to approx.2/3 of the source temperature; much stronger relaxation can be expected at higher source pressures

52

Scintillation properties of pure alkali halides at low temperatures  

International Nuclear Information System (INIS)

Fragmentary studies in various laboratories on the scintillation behaviour of several of the alkali halides, both with and without impurity activators, indicate that in general the activated alkali halides scintillate best at room-temperature with pulse-height decreasing at lower temperatures, while the unactivated materials scintillate best at low temperatures and decrease in efficiency as the temperature increases. In our laboratory, a systematic research study on the scintillation properties of the alkali halides is underway and to date we have examined twelve pure (unactivated) alkali halides with both ?-particle and ?-ray excitation over the temperature range of 4oK to 300oK. Lil, KI, and Csl exhibit a constant scintillation pulse-height and decay-time at temperatures below 80oK. Nal exhibits a maximum in pulse-height at 60oK similar to that reported previously by VAN SCIVER et al. A second CsI sample shows both a low-temperature scintillation-component and a room-temperature component similar to that induced by overheating as in the experiments of KNOEPFEL et al. Rbl shows two regions of linearly decreasing pulse-height as temperature increases. The scintillation pulse-heights of the iodides are comparable to that observed from thallium-activated sodium iodide and the decay times are about 0.1 to 2 ?s. CsBr, KBr, and NaCl scintillate at low temperatures, but with a much lower intensity than the iodides. LiF, NaF, KCntensity than the iodides. LiF, NaF, KCl, and RbBr exhibit no detectable scintillation over the entire temperature range studied. The temperature dependence of pulse-heights and decay-constants is the same for both ? and ?-excited emission. Analysis of the scintillation pulse-shape and the temperature-dependence gives an indication of the number of luminescence components and the mode of decay of the excited luminescence centres. (author)

53

Thermal conductivity of molten alkali halides and their mixtures  

International Nuclear Information System (INIS)

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

54

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

55

Absorption lineshape of FA centers in alkali halides  

International Nuclear Information System (INIS)

The line shape of the absorption bands of FA centers in alkali halides have been studied for the first time. The new method used for this investigation is based on the determination of the overlap between the FA1 and FA2 bands from luminescence measurements. The experimental results have been compared with calculated values deduced from the theoretical FA bands of different shapes. For both FA(I) centers in KCl:Na+ and FA(II) centers in KCl:Li+ and RbCl:Li+ the absorption lineshape at low temperature is much closer to a sum of two Lorentzian curves than that of two Gaussian or Poissonian bands. This results shows an unexpected difference with the F centers, whose absorption lineshape is known to be Poissonian at the same temperatures

56

Thermoluminescence studies in ternary halide mixed crystals doped with LiCl  

International Nuclear Information System (INIS)

The mixed and impurity added doped crystals of alkali halides are found to be harder than the end members and so they are more useful. In view of this, it becomes necessary and useful to prepare binary and ternary-mixed crystals regardless of miscibility problem and characterize them by measuring their physical properties. In the present work we have grown (KCl)0.9?x(KBr)x(KI)0.1 ternary alkali halide crystals with and without LiCl dopant for various values of x by the melt method and physically characterized. Crystals were ?-irradiated. For the irradiated crystals, Thermoluminescence studies have been made. Thermoluminescence glow curves were analyzed as function of composition x and irradiation strength. A thermoluminescence enhancement, relative to the pure end components is found and mixed crystal presents a significant increase in thermoluminescence efficiency.

57

Formation of structured nanophases in halide crystals.  

Czech Academy of Sciences Publication Activity Database

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

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

2013-01-01

58

Thermoluminescence, optical absorption and ESR studies in (KCl){sub 1-x}(KBr){sub x} mixed alkali halide crystals doped with gold  

Energy Technology Data Exchange (ETDEWEB)

Mixed crystals of KCl-KBr of different compositions were grown with Czochralski technique. Crystals were doped with gold. Both the undoped and gold doped crystals were {gamma}-irradiated using {sup 60}Co source. All the irradiated samples were subjected to thermoluminescence, optical absorption and ESR studies. The present study shows the composition dependence of the parameters and enhancement in the luminescence intensity as well as the absorption coefficient with gold doping. Non-linear variation of color center peak position and half band width of F-center with composition has been observed. The results of the above studies are presented in this paper.

Ananda Kumari, R. [Sree Siddaganga Women' s College, Tumkur, Karnataka (India)], E-mail: ranandakumari61@yahoo.com; Chandramani, R. [Bangalore University, Bangalore, Karnataka (India)

2008-02-15

59

First-principal calculations of physical properties of F-centers in alkali-halide crystals with CsCl structure  

International Nuclear Information System (INIS)

The results of theoretical simulation of F-centers in CsCl, CsBr and CsI crystals which has been carried out from first principles in CRYSTAL06 program system in representation of linear combination of atomic orbitals are given. The CRYSTAL program allows to simulate electronic structure both within the framework of the Hartree-Fock approximation and on the base of density functional theory. Microscopic spatial defect structure is obtained in periodic model for 250-atomic supercell with complete account of relaxation. Energies of optical transition are calculated after Franck-Condon principle with respect to difference of complete energies of corresponding states. Obtained theoretical data agree well with known experimental ones

60

Fractal characteristics of metal clusters self-assembled in alkali halide matrices  

Energy Technology Data Exchange (ETDEWEB)

Metal nanoclusters of Ag and Au were obtained in alkali halide crystals (NaCl, KBr and KCl). The fractal character of the structures is proved by the fractal dimensions calculated using a home made computer program. The self aggregation of the metallic structures is governed in both cases (Ag and Au) by the DLA mechanism. This is proved by the values of the fractal dimension calculated using two methods, sandbox and box-counting, which are between 1.7 and 1.8 for Ag and for Au between 1.7 and 1.9. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Enculescu, M.; Enculescu, I. [National Institute for Materials Physics, P.O. Box MG-7, Magurele-Bucharest 077125 (Romania)

2007-03-15

61

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

62

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

63

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

64

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

International Nuclear Information System (INIS)

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

65

Alkali halide phosphors as a storage material for two-dimensional X-ray imaging sensor utilizing photostimulated luminescence phenomenon  

International Nuclear Information System (INIS)

The PSL phenomenon in alkali halides such as NaCl : Cu and KCl : Eu induced by excitation with X-rays were studied. The efficient PSL with a peak at about 353 [nm] and two less intense PSL peaks at about 420 [nm] and 680 [nm] were observed in X-ray irradiated NaCl : Cu phosphor crystal. The intense PSL with a peak at about 420 [nm] was also observed in X-ray irradiated KCl : Eu phosphor crystal. The emission mechanism of the PSL in both phosphor crystals, based on the recombination of electrons optically stimulated from the radiation-induced F centers with the luminescence centers such as Cu2+ ions in NaCl and Eu3+ ions in KCl, was proposed. It was found that the 353 [nm] PSL intensity in NaCl : Cu and the 420 [nm] PSL intensity in KCl : Eu linearly increased with increasing the intensity of the F-band which was created by X-ray irradiation. The alkali halide phosphor materials such as NaCl : Cu and KCl : Eu, especially KCl : Eu, thus, are the most attractive candidate as a material for two-dimensional X-ray imaging sensor utilizing PSL phenomenon, because the NaCl : Cu and the KCl : Eu phosphor crystals exhibited an efficient PSL, especially the KCl : Eu phosphor crystal also exhibited thermally stable PSL characteristics. (J.P.N)

66

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

67

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)

68

The electronic structure of F-centers in allkali halide crystals  

International Nuclear Information System (INIS)

A method is presented for estimating the number of bound states of different orbital angular momentum quantum number for an F-centre residing in an alkali halide crystal through the introduction of a spherically symmetric potential well of finite depth. The method is illustrated through its application to the F-centre in sodium chloride, and the results for F-centres in various alkali halide lattices are tabulated. The results provide a good account of the experimental features of the F-centre including the K-band which we suggest is due to transitions from the 2p to excited levels. Values for the effective range of penetration of the defect electron with the neighbouring cation in different crystals are determined by requiring that the well depth be independent of orbital angular momentum quantum number. The technique is applied to estimate the Madelung constant and Madelung potential for the host crystal. (Author)

69

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

70

Molecular heat transfer in molten alkali metal halides and their binary mixtures  

International Nuclear Information System (INIS)

The nature of heat transfer in ion melts, mainly determined by energy exchange between charged particles as a result of their vibrations, is considered. The equation connecting thermal conductivity with density, viscosity and adiabatic compressibility of salt melts is derived. The experimental and calculated values of thermal conductivity of molten halides of alkali metals and their binary mixtures are in a satisfactory agreement

71

Processes that Intervene in the Generation of the Photoacoustic Effect in Alkali Halides with F-Centers  

Science.gov (United States)

The photoacoustic effect, produced by the F-center in alkali halide crystals, is analyzed using the configuration coordinate model. By using the configuration coordinate model it is possible to explain the temperature increase of the sample when the sample is illuminated and the F-centers absorb light. Also this model explains the piston effect upon the atmosphere that surrounds the sample when the sample is illuminated. The temperature increase and the piston effect, produced during the development of the photoacoustic effect, cause the sound wave generation in the atmosphere that surrounds the sample when the F-centers absorb light. Using this model, the temperature increase value for a KCl sample and the displacement of the faces of the crystal during the process for the following crystals: KCl, KBr, KI and NaCl, have been determined.

Da Silva, Luis F.

2004-01-01

72

a Behavior-Type Raman Study of Orientationally Degenerate Defects in Doped Alkali Halides.  

Science.gov (United States)

Localized defects with unusual rotational or translational motion in alkali halides are investigated by polarized Raman scattering. Molecular impurities reorient between several equivalent equilibrium orientations. The KI:Ag ^{+} system occupies a regular lattice site at 2K and goes off-center, when the temperature is raised to 25K. The free electron in the heavy-metal dimer centers is moving between two equivalent configurations. These motions influence the composition of the Raman spectra, their temperature dependence, and their polarization properties. Raman data represented for several diatomic (CN^{-}, SH^{-}, O_sp {2}{-}, and OD^ {-}) and triatomic (NCO^ {-}) linear molecules, and for the bent triatomic NO_sp{2}{-} molecular ion in KCl, KBr, KI, and NaBr. Preliminary results for KI_{1-x}(NH _4)I are also reported. The symmetry assignment by polarized Raman scattering is in agreement with previous results for the diatomic systems. The C _{3v} symmetry of the static NCO^{-} in KBr is established for the first time. Surprising and new results are obtained for the symmetries of NO_sp{2} {-} and NH_sp{4} {+}. The influence of rotational motion and polarizability of the surrounding ions on the polarized Raman data is discussed. New and different polarized Raman behavior is established for mixed molecular crystals of higher concentrations, reflecting electric/elastic dipole interactions. The on- to off-center transition of the KI:Ag^+ system is tracked by the temperature dependence of the Raman scattering data in the range between 2 and 25K. Calculations for the on-center configuration indicate that the temperature behavior is in contrast with that of 'soft-mode' systems. A possible mechanism, involving localized anharmonic modes trapped at the impurity site, is discussed and correlated with the unusual polarization properties of the Raman scattering. Thermally activated reorientation and superionic motion are compared. The resonant Raman data for Tl^+Tl ^0(1)-like dimer centers in Ga^+ - and In^+-doped alkali halides are presented. The Ga^+Ga ^0(1) (In^+In ^0(1)) defects in KCl and RbCl are identified. The correspondence with previously suggested models is discussed. The Raman response of the dimer centers is determined by the non-adiabatic motion of the unpaired electron. The non -atomic behavior of the third excited state of Tl ^0(1)-like defects is shown to be reflected in the Raman data.

Fleurent, Hilde Berthe

73

Theoretical calculation of the electron-phonon coupling parameters of the F-centre in alkali halides  

International Nuclear Information System (INIS)

The coupling parameters of the F-centre to lattice modes of cubic, tetragonal, and trigonal symmetry are calculated using the pseudopotential theory of Bartram, Stoneham, and Gash, for all 20 alkali-halides. Different analytical forms for the trial pseudo wave function are used. The results are compared with uniaxial stress and hydrostatic pressure experiments. General trends for the whole series of alkali-halides agree with experiments. (author)

74

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

75

Formation of structured nanophases in halide crystals  

Science.gov (United States)

When halide crystals KCl and NaCl are slightly doped by PbCl_2, (in orders of 10^{-4} mol/mol) the structurally stable nanophases ("quantum dots") are formed via nucleation within the bulks of their matrices. Using lattice modeling we have found in KCl-Pb system natural nucleation pathway from single impurity-vacancy complex to Suzuki phase, not demonstrated in previous analyses; further transition to PbCl_2 is difficult due to high stability of this phase. In the case of NaCl-Pb, no stable "end point" of aggregation was observed and our calculations suggest nucleation may readily proceed to large PbCl_2 clusters when initially formed platelike cluster reaches a certain critical thickness. These results coincide with our experimental data.

Kulveit, J.; Demo, P.; Polák, K.; Sveshnikov, A. M.; Kožíšek, Z.

2011-04-01

76

Theory of metal atom-water interactions and alkali halide dimers  

Science.gov (United States)

Theoretical studies of the interactions of metal atoms with water and some of its isoelectronic analogs, and of the properties of alkali halides and their aggregates are discussed. Results are presented of ab initio calculations of the heats of reaction of the metal-water adducts and hydroxyhydrides of Li, Be, B, Na, Mg, and Al, and of the bond lengths and angles an; the heats of reaction for the insertion of Al into HF, H2O, NH3, H2S and CH3OH, and Be and Mg into H2O. Calculations of the electron affinities and dipole moments and polarizabilities of selected gas phase alkali halide monomers and dimers are discussed, with particular attention given to results of calculations of the polarizability of LiF taking into account electron correlation effects, and the polarizability of the dimer (LiF)2.

Jordan, K. D.; Kurtz, H. A.

1982-01-01

77

Reactions between cold methyl halide molecules and alkali-metal atoms  

CERN Document Server

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

Lutz, Jesse J

2013-01-01

78

Reactions between cold methyl halide molecules and alkali-metal atoms  

Energy Technology Data Exchange (ETDEWEB)

We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH{sub 3}X (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, CH{sub 3}X + A ? CH{sub 3} + AX. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

Lutz, Jesse J.; Hutson, Jeremy M. [Joint Quantum Centre (JQC) Durham-Newcastle, Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom)

2014-01-07

79

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

Energy Technology Data Exchange (ETDEWEB)

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

Aqra, Fathi, E-mail: fathiaqra2009@hotmail.com

2014-05-15

80

Determination of Alkali and Halide Monovalent Ion Parameters for Use in Explicitly Solvated Biomolecular Simulations  

OpenAIRE

Alkali (Li+, Na+, K+, Rb+, and Cs+) and halide (F?, Cl?, Br?, and I?) ions play an important role in many biological phenomena, roles that range from stabilization of biomolecular structure, to influence on biomolecular dynamics, to key physiological influence on homeostasis and signaling. To properly model ionic interaction and stability in atomistic simulations of biomolecular structure, dynamics, folding, catalysis, and function, an accurate model or representation of the monovalen...

Joung, In Suk; Cheatham,, Thomas E.

2008-01-01

81

Development of processes for the production of solar grade silicon from halides and alkali metals  

Science.gov (United States)

High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost were studied. Experiments were performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process.

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

1980-01-01

82

Measurement of velocity of Ultrasonic sound in alkali halide R R solutions with different Normality  

OpenAIRE

Velocity of sound in solutions is very large as compared to that in air, and this velocity is density dependent. In this experiment the alkali halide solutions of different normality was prepared and the velocity of sound was observed using Ultrasonic Interferometer at 2 M Hz of frequency. The velocity of sound was observed to be increasing with increasing Normality of solutions except for the potassium iodide solution, where this change is marginal. As an extension to this experiment sodium ...

Nyayate, M. N.; Atul Jadhav; Pendharkar, J. K.; Saxena, S. K.; Yogesh Ghalsasi

2012-01-01

83

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

84

The sputtering processes of alkali halides during 6 keV Xe+ ion bombardment, Ch.4  

International Nuclear Information System (INIS)

RbCl, RbBr, RbI and NaI targets have been bombarded with 6 keV Xe+ ions. The energy distributions of the sputtered alkali and halogen atoms were examined with a time of flight method. It was observed that random collision cascades, thermal spikes and evaporation of decomposed surface material contribute to the sputtering. The binding energies were found to be 3 to 8 times lower than the heat of atomization. The spike temperatures were of the order of 1500K and a satisfactory agreement with theoretical expectations could be obtained. It is argued that the decomposition of surface material and the subsequent evaporation of alkali and halogen atoms is caused by the same inelastic processes that occur during the sputtering of alkali halides with electrons. (Auth.)

85

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

86

Making Solid Solutions with Alkali Halides (and Breaking Them)  

Science.gov (United States)

In this exercise, the class will grow a variety of crystals of the same mineral, but with different chemical compositions. These crystals will be made from mixtures of halite (NaCl)and sylvite (KCl) that are melted and cooled. Because K+1 is significantly larger than Na+1,the unit cell is larger in sylvite than in halite. Intermediate compositions have intermediate unit cell sizes. Thus, a measurement of the lattice spacing of the crystalline products of your experiments can be used to determine their chemical composition. The principle goal of these experiments is to demonstrate that solid solutions do occur and that their physical properties vary with their chemical composition. Additional goals include studying the effect of composition on melting, exploring the process of exsolution as a function of temperature, and seeing the effect of fluids and deformation on crystallization kinetics.

John Brady

87

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

88

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

89

Transport of alkali halides through a liquid organic membrane containing a ditopic salt-binding receptor.  

Science.gov (United States)

A ditopic receptor is shown to have an impressive ability to recognize and extract the ion pairs of various alkali halides into organic solution. X-ray diffraction analysis indicates that the salts are bound in the solid state as contact ion pairs. Transport experiments, using a supported liquid membrane and high salt concentration in the source phase, show that the ditopic receptor can transport alkali halide salts up to 10-fold faster than a monotopic cation or anion receptor and 2-fold faster than a binary mixture of cation and anion receptors. All transport systems exhibit the same qualitative order of ion selectivity; that is, for a constant anion, the cation selectivity order is K+ > Na+ > Li+, and for a constant cation, the anion transport selectivity order is I- > Br- > Cl-. The data suggest that with a ditopic receptor, the polarity of the receptor-salt complex can be lowered if the salt is bound as an associated ion pair, which leads to a faster diffusion through the membrane and a higher maximal flux. PMID:15360239

Mahoney, Joseph M; Nawaratna, Gayathri U; Beatty, Alicia M; Duggan, Peter J; Smith, Bradley D

2004-09-20

90

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

Science.gov (United States)

Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I-. 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.; Vrabec, J.; Hasse, H.

2014-01-01

91

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

92

Alkali Halide Interfacial Behavior in a Sequence of Charged Slit Pores  

Energy Technology Data Exchange (ETDEWEB)

In this paper, a variety of alkali halide, aqueous electrolyte solutions in contact with charged, planar-graphite slit-pores are simulated using classical molecular dynamics. Size trends in structure and transport properties are examined by varying the choice of ions among the alkali metal and halide series. As with the uncharged pores, system dynamics are driven by changes in water hydration behavior and specifically by variations in the number of hydrogen bonds per water molecule. Overall, the larger ions diffuse more rapidly under high surface charge conditions than the smaller ions. In particular, for the 1 nmslit, ion diffusivity increased by a factor of 4 compared to the uncharged case. Finally, a quantitative fit to the interfacial charge structure is presented, which confirms the presence of two distinct types of layers in an aqueous interface. This model indicates that the chemistry of the interface is able to create a small interfacial potential, and it shows how water molecules can rotate to increase charge separation in response to a surface potential.

Wander, Matthew C [ORNL; Shuford, Kevin L [ORNL

2011-01-01

93

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)

94

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

International Nuclear Information System (INIS)

Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li+, Na+, K+, Rb+, Cs+, F?, Cl?, Br?, and I?. 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

95

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

96

Repulsive energy and the Grueneisen parameter of alkali halides calculated on the basis of a quantum-statistical ab initio theory  

International Nuclear Information System (INIS)

The Grueneisen parameter of alkali halides is calculated by an ab initio quantum-statistical method and then compared with the experimental data. The crystal model applied assumes the crystal ions to be compressible but impenetrable spheres. The ions are described with the aid of a modified Thomas-Fermi theory with exchange. At the next step it is possible to calculate the energy needed to transform the system of the non-interacting ions into the ionic system represented by the crystal lattice. This calculation allows for an ab initio estimate of the parameters entering the Born, or the Born-Mayer, repulsive part of the crystal energy. The parameters are then used in the calculation of the Grueneisen parameter and its dependence on the crystal compression. (author)

97

F2+ center stabilization and tuneable laser operation in OH- doped alkali halides  

International Nuclear Information System (INIS)

Doping of alkali halides with large amounts (10-3 to 10-2) of OH- defects can be used to drastically increase the production and stabilization of F2+ centers. Under electron irradiation, the coloration efficiency and F2:F ratio is increased, and the OH- defect is decomposed into various substitutional and interstitial hydrogen and oxygen defects, part of which work as electron traps. As a consequence, optical ionization of F2 centers leads to stable F2+ center production, as tested in LiF, NaF, NaCl, KCl, and KBr hosts. Tuneable laser operation is achieved for the first time for F2+ centers in NaCl and KCl using this technique. A systematic study into the decomposition kinetics of OH- defects is started, which reveals the existence of a new hydrogen defect, identified by its ir local mode absorption, which may play the crucial role in the F2+ stabilization. (author)

98

Dynamics of the defect-mediated desorption of alkali halide surfaces  

International Nuclear Information System (INIS)

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: thermal (which can be fitted with Maxwellian distribution) and 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 halides.

99

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

100

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

101

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

OpenAIRE

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 i...

Kancharla Rajendar Reddy; Sariah Sana; Kusampally Uppalaiah; Kamatala Chinna Rajanna; Puppala Veerasomaiah

2012-01-01

102

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

103

Dynamics of nuclear wave packets at the F center in alkali halides  

Energy Technology Data Exchange (ETDEWEB)

The F center in alkali halides is a well-known prototype of a strongly coupled localized electron-phonon system. This colour center is one of the long studied targets in the field of photophysics because it is simple but rich in variety. Steady-state spectroscopy, such as modulation spectroscopy and Raman scattering spectroscopy, has elucidated the strength of the electron-phonon coupling in the (meta-)stable state, i.e. the ground state and the relaxed excited state. Picosecond spectroscopy has improved understanding of the state mixing in the transient state. Owing to recent developments of ultrafast lasers with pulse widths shorter than oscillation periods of phonons, it has been possible to perform real-time observation of lattice vibration, and the understanding of the transient state has been remarkably expanded. In this paper, we review early and present studies on dynamics of electron-phonon coupling at the F center, especially recent real-time observations on the dynamics of nuclear wave packets in the excited state of the F center in KI, KBr, KCl and RbCl. These real-time observations reveal (i) spatial extension of the electronic wave function of a trapped electron, (ii) the difference between the coupled phonons in the ground state and the excited state, (iii) diabatic transition between the adiabatic potential energy surfaces and (iv) anharmonicity of the potential energy surface.

Koyama, Takeshi; Suemoto, Tohru, E-mail: koyama@nuap.nagoya-u.ac.jp [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8581 (Japan)

2011-07-15

104

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)

105

Halide electrodeposition on single-crystal electrodes  

Science.gov (United States)

In this dissertation, we investigate in depth by computational and theoretical methods the processes and behavior of submonolayer electrochemical deposition of Br onto single-crystal Ag(100) electrodes. Although this system has little direct industrial application, it provides a test bed for developing theoretical and computational techniques which can be used to study systems of more applied interest. Br electrodeposited onto a Ag(100) substrate at room temperature displays a disordered phase at low electrochemical potentials. At higher electrochemical potentials, the adlayer undergoes a disorder-order phase transition to a c(2 x 2) ordered phase. The phase transition, the equilibrium properties of the adlayer, and the dynamics of the ordering and disordering processes are studied by a variety computational techniques, including static and dynamic lattice-gas models, an off-lattice equilibrium model, and Langevin simulations. Using a two-dimensional lattice-gas approximation for the adlayer, Monte Carlo simulations are used to explore the equilibrium properties of the Br adlayer under different values of the electrochemical potential. The model predicts the existence of low-temperature phases which are not stable at room temperature. The effects of these low-temperature phases on the room-temperature properties of the adlayer are discussed. Starting from the lattice-gas model developed for equilibrium simulations, a dynamic Monte Carlo simulation program is constructed, and the phase-ordering, disordering, and hysteresis behaviors are studied. The phase-ordering process is in the dynamic universality class known as Model A (Lifshitz-Allen-Cahn dynamics), but the disordering behavior is not as easily classified. Dynamic simulations of cyclic-voltammetry experiments show hysteresis due to kinetic limitations associated with the ordering and disordering processes. To further investigate the properties of the adlayer, the lattice-gas approximation was relaxed and replaced by a corrugation-potential approximation. Within this two-dimensional off-lattice model, the equilibrium properties were found to be similar to those of the lattice-gas model. However, the off-lattice model obviously allows calculations of additional quantities, such as the average lateral displacement from the adsorption site. Langevin dynamic simulations of the off-lattice model were also performed to test the validity of the assumptions used in the dynamic Monte Carlo simulations. However, these dynamic simulations were far too computationally intensive to allow off-lattice simulations of the ordering, disordering, and hysteresis behaviors. As a first step towards developing accelerated simulation methods for off-lattice simulations, we construct an advanced dynamic algorithm for continuum spin systems.

Mitchell, Steven James

2001-07-01

106

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

International Nuclear Information System (INIS)

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

107

Range of protons and helium ions in alkali halide crystals  

International Nuclear Information System (INIS)

The coloration depth in NaF, NaCl, KCl, KBr, and KJ induced by implantation of H+- or He+-ions (energy 0.3-1.7 MeV) has been measured microscopically. The results have been compared with ion-ranges calculated by means of a computer program developed for monoatomic targets using average atomic numbers and mass values. (author)

108

Photography: enhancing sensitivity by silver-halide crystal doping  

Energy Technology Data Exchange (ETDEWEB)

The physical chemistry of the silver photography processes, exposure, development and fixing, is briefly summarized. The mechanism of the autocatalytic development by the developer of the clusters produced in silver bromide crystals during the exposure which is controlled by the critical nuclearity of these clusters was understood from pulse radiolysis studies. The effective quantum yield PHI{sub eff} of photoinduced silver cluster formation in silver halide microcrystals is usually much lower than the photoionization theoretical limit PHI{sub theor}=1 electron-hole pair per photon absorbed, owing to a subsequent very fast intra-crystal recombination of a part of the electron-hole pairs. In order to inhibit this recombination and favor the silver reduction by photo-electrons, the AgX crystals were doped with the formate HCO{sub 2}{sup -} as a specific hole scavenger. First, the dopant scavenges the photoinduced hole, thus enhancing the electron escape from the pair recombination. Second, the CO{sub 2}{sup {center_dot}}{sup -} radical so formed transfers an electron to another silver cation, so that the PHI{sub eff} limit may be of 2Ag{sup 0} per photon. This Photoinduced Bielectronic Transfer mechanism is strictly proportional to the light quanta absorbed and induces an exceptional efficiency for enhancing the radio- or photographic sensitivity insofar as it totally suppresses the electron-hole recombination.

Belloni, Jacqueline

2003-06-01

109

Spectroscopic techniques to investigate aggregation and precipitation of cation impurities in alkali halides: application to impurity hardening and irradiation sensitivity  

International Nuclear Information System (INIS)

The clustering and precipitation of cation impurities in alkali halides is discussed and techniques for their investigation are reviewed. Non-spectroscopic techniques such as dielectric relaxation, X-ray diffraction, optical and electron microscopy, are summarized, together with the results obtained using them. The main body of the review is given over, however, to a more detailed consideration of optical absorption, luminescence, Raman and paramagnetic resonance spectroscopy. New results obtained by means of these techniques on monovalent and divalent cation doped systems are presented. The usefulness of the techniques is illustrated by specific attention to the correlation between impurity aggregation/precipitation and two phenomena, mechanical hardening and F-centre production under irradiation. (UK)

110

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

111

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

112

A self-consistent model for the electronic structure of the u-center in alkali-halides  

International Nuclear Information System (INIS)

A simple one-orbital per site model Hamiltonian for the U center in alkali-halides with rock-salt structure where correlation effects are introduced via an Anderson type Hamiltonian is presented. The Cluster-Bethe lattice method is used to determine the local density of states, yielding both localized and extended states. A one-electron approximation is assumed and the problem is solved self consistently in the Hartree-Fock scheme. The optical excitation energy is in fair agreement with experiment. The present approach is compared with other models previously used to describe this center and the results indicate that is adequately incorporates the relevant features of the system indicating the possibility of its application to other physical situations

113

A Review of Luminescent Anionic Nano System: d10 Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts  

Directory of Open Access Journals (Sweden)

Full Text Available Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration.

Howard H. Patterson

2013-06-01

114

On the interpretation of luminescence of lead halide crystals.  

Czech Academy of Sciences Publication Activity Database

Ro?. 229, ?. 3 (2002), s. 1295-1304. ISSN 0370-1972 Institutional research plan: CEZ:AV0Z1010914 Keywords : luminescence * lead halide * exciton Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.930, year: 2002

Babin, V.; Krasnikov, A.; Nikl, Martin; Stolovits, A.; Zazubovich, S.

2002-01-01

115

Bivalent rare earth elements spectra in ammonium halide crystals  

International Nuclear Information System (INIS)

It is shown by optical methods that absorption band in ammonium halides with bivalent rare earth mixtures are conditioned transition from the main 4fn-a conditions in mixture 4fn-15d-a level. The methods to indignations theories are calculated split-pouring 5d-a level rare earth ions in crystalline field of ammonium halides. Electronic-background interaction and non-radioactive transitions are experimentally explored. (author)

116

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

117

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)

118

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

119

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

Science.gov (United States)

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

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

2012-01-01

120

THE LATTICE-RELAXATION ENERGY ASSOCIATED WITH SELF-TRAPPING OF A POSITIVE HOLE AND AN EXCITON IN ALKALI-HALIDES  

OpenAIRE

The authors have evaluated the upper and lower bounds to the lattice relaxation energy gained on the self-trapping of excitons, using experimental values of transition energies for free and self-trapped excitons and theoretical values for lattice relaxation energies and optical transition energies. The lattice relaxation energy upon self-trapping of an exciton in alkali halides proves to be appreciably larger than that of a self-trapped hole. They discuss the implications for a number of soli...

Itoh, N.; Tanimura, K.; Stoneham, A. M.; Harker, A. H.

1989-01-01

121

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

Czech Academy of Sciences Publication Activity Database

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

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

2008-01-01

122

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

123

A theoretical study of desorption induced by electronic transitions in alkali halides  

OpenAIRE

We have studied desorption following the excitation of core- or valence-electrons using quantum chemical calculations of the potential energy surfaces. For core excitation, we simulate the state of two holes localised on a halogen ion using an extended semi-empirical molecular method (CNDO) to calculate the energy change associated with the displacement of the halogen ion or a neighbouring alkali ion. No instability was found for a bulk halogen ion with two localised holes, in agreement with ...

Itoh, N.; Stoneham, A. M.; Harker, A. H.

1989-01-01

124

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

125

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

126

Characterization of alkali halides doped 1-(2-methoxy benzyloxy)-8- hydroxy-9,10-anthraquinone films for photovoltaic applications  

Science.gov (United States)

Thin films of 1-(2-methoxy benzyloxy)-8-hydroxy-9, 10-anthraquinone (AQ) have been prepared by hot wall technique onto glass substrates kept at 348 K in a vacuum of 10-5 Torr. Chemical modifications of films have been performed by their treatment with different alkali halides. The films so obtained are systematically studied for their electrical and optical properties. The electrical conductivities of the resulting films exhibited semiconductor-like temperature dependence in the experimental range studied. LiCl and LiBr doped films exhibit almost three orders of magnitude higher conductivity, than untreated films, whereas NaCl, NaBr and KBr do not show any remarkable change in the conductivity. Analysis of optical absorption measurements indicate that the interband transition energies of films lie in the range of 2.57-2.66 eV. Keeping in view the electrical and optical properties of films, ITO/AQ/Al solar cells have been fabricated and characterized. The J-V characteristics of these devices are found to be in good agreement with standard diode equation. Power conversion efficiency of Li doped AQ based devices are found to increase by an order of two as compared to undoped AQ based devices.

Mahajan, Aman; Singh, Mandeep; Gupta, Himani; Bedi, R. K.; Kumar, S.; Aswal, D. K.

2012-06-01

127

Growth and Studies of Halides doped Zinc Tris-Thiourea Sulphate(HZTS) Crystals  

Science.gov (United States)

Single crystals of Sodium chloride and Potassium iodide (Halides) doped Zinc tris-thiourea sulphate (ZTS) were grown from low temperature solution growth technique by slow evaporation method using water as solvent. The powder X-Ray diffraction pattern were recorded and indexed. The UV transmittance spectrum has been recorded. The optical band gap was estimated using Taucís plot. The TGA/DTA studies show the thermal properties of the crystals.

Suveetha, P.; Sathya, T.; Sudha, S.; Raj, M. B. Jessie

2012-10-01

128

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

129

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)

130

Electronic and cascade processes in ion-induced sputtering of alkali halides  

International Nuclear Information System (INIS)

Ion interaction with solid surfaces results in the emission of various secondary particles as ions, electrons, atoms, and molecules. A dominant fraction of this emission is in the form of neutral sputtered atoms. Mass spectra and kinetic energy distributions of sputtered particles are measured by means of both mass selected time-of-flight spectroscopy and laser-induced fluorescence spectroscopy. In particular the balance between electronic and cascade sputtering processes in NaCl, KBr, and CsI single crystals is studied. The influence of the projectile stopping power and the target temperature on the sputtering mechanisms are investigated as well, and compared with predictions of recent theoretical models. (author)

131

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

132

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

133

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

134

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

135

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

Directory of Open Access Journals (Sweden)

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

Laurent Nony

2012-03-01

136

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

Scientific Electronic Library Online (English)

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

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

2011-04-01

137

Transport and deposition of halide in alkali metal-stainless steel systems, (3)  

International Nuclear Information System (INIS)

Solubility of sodium iodide in liquid sodium was determined over a temperature range of 350?650degC by using capsules of two different kinds. Stainless steel capsule of short type loaded with 2?3.5 g sodium and fragments of sodium iodide crystal was put in a pair of holders and heated under an uniform temperature distribution in a vertical electric furnace. Stainless steel capsule of long type loaded with 20 g sodium and powders of the iodide was heated at its upper part in the furnace and cooled at its bottom to establish a large temperature gradient along the capsule tube. After a given term of heating, the iodide was fixed in solidified sodium by quick quenching of these capsules. The iodide solubility data measured by using the capsules are in good agreement with the data reported by Miyahara, Power Reactor and Nuclear Fuel Development Corp. (PNC). It is not observed in the measurement that the iodide is enriched at free surface of the liquid sodium and forms particles in the solution; these were thought of as reasons why PNC expressions of the solubility are about 10 times as large as Allan's expression. (author)

138

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

139

Mollwo-Ivey relations for optical absorption bands of the atomic and F' centres in alkali halides  

Energy Technology Data Exchange (ETDEWEB)

Evidence indicates that two classes of the transient IR-absorption bands: (a) with maxima at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl and due to shallow electron traps or bound polarons according to Jacobs (Phys. Stat. Sol. B 129 (1985) 755) and Korovkin and Lebedkina (Fiz. Tverd. Tela (Russian) 35 (1993) 642), and (b) with maxima at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, RbCl:I and RbBr:I, due to on-centre STE localised at iodine-dimer according to Hirota et al. (J. Phys. Soc. Japan 63 (1994) 2774, Phys. Rev. B 52 (1995) 7779) and Edamatsu and Hirai (Mater. Sci. Forum 239-241 (1997) 525), are caused by the same defect. We propose that the defect is an atomic alkali impurity centre [M{sup +}]{sub c}{sup 0}e{sup -}, i.e. an electron e{sup -} trapped by a smaller size substitutional alkali cation impurity [M{sup +}]{sub c}{sup 0}. The Mollwo-Ivey plots for the transient IR-absorption bands of the zero-phonon line energy E{sub 0} for NaCl, KCl, KBr, RbCl and NaBr, KCl:I and/or the low-energy edge values E{sub 0} for NaI, RbCl:I and RbBr:I versus anion-cation distance, d, are obtained for the first time. These data suggest that two types of the [M{sup +}]{sub c}{sup 0}e{sup -} centres are predominant: (i) [Na{sup +}]{sub c}{sup 0}e{sup -} in KX and RbX host crystals with the relation E{sub 0}{approx}6.15/d{sup 2.74} and (ii) [Li{sup +}]{sub c}{sup 0}e{sup -} in NaX host crystals with E{sub 0}{approx}29.4/d{sup 4.72}. The Mollwo-Ivey relation E{sub 0}{approx}18.36/d{sup 2.70} is fulfilled as well for the F' band in NaCl, KCl, KBr, KI, RbCl, RbI if we use the F' centre optical binding energy values for E{sub 0}.

Ziraps, V. E-mail: ziraps.v@cfi.lu.lv

2001-10-01

140

Mollwo-Ivey relations for optical absorption bands of the atomic and F' centres in alkali halides  

International Nuclear Information System (INIS)

Evidence indicates that two classes of the transient IR-absorption bands: (a) with maxima at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl and due to shallow electron traps or bound polarons according to Jacobs (Phys. Stat. Sol. B 129 (1985) 755) and Korovkin and Lebedkina (Fiz. Tverd. Tela (Russian) 35 (1993) 642), and (b) with maxima at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, RbCl:I and RbBr:I, due to on-centre STE localised at iodine-dimer according to Hirota et al. (J. Phys. Soc. Japan 63 (1994) 2774, Phys. Rev. B 52 (1995) 7779) and Edamatsu and Hirai (Mater. Sci. Forum 239-241 (1997) 525), are caused by the same defect. We propose that the defect is an atomic alkali impurity centre [M+]c0e-, i.e. an electron e- trapped by a smaller size substitutional alkali cation impurity [M+]c0. The Mollwo-Ivey plots for the transient IR-absorption bands of the zero-phonon line energy E0 for NaCl, KCl, KBr, RbCl and NaBr, KCl:I and/or the low-energy edge values E0 for NaI, RbCl:I and RbBr:I versus anion-cation distance, d, are obtained for the first time. These data suggest that two types of the [M+]c0e- centres are predominant: (i) [Na+]c0e- in KX and RbX host crystals with the relation E0?6.15/d2.74 and (ii) [Li+]c0e-]c0e- in NaX host crystals with E0?29.4/d4.72. The Mollwo-Ivey relation E0?18.36/d2.70 is fulfilled as well for the F' band in NaCl, KCl, KBr, KI, RbCl, RbI if we use the F' centre optical binding energy values for E0

141

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

142

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)

143

Photofragmentation of metal halides  

International Nuclear Information System (INIS)

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

144

Growth and characterisation of YBa sub 2 Cu sub 3 O sub 7-. delta. single crystals  

Energy Technology Data Exchange (ETDEWEB)

Single crystals of YBCO have been grown by two different flux techniques, one based on excess CuO the other on mixed alkali halides. In the as-grown state, the crystallinity and the superconducting properties of the CuO flux crystals are superior but post growth oxygen anneals are found to greatly improve the characteristics of the alkali halide flux crystals. (orig.).

Abell, J.S.; Darlington, C.N.W.; Drake, A.; Hollin, C.A.; Forgan, E.M.; O' Connor, D.A.; Sutton, S.D. (Superconductivity Research Group, Univ. of Birmingham (UK))

1989-12-01

145

The crystallography of metal halides formed within single walled carbon nanotubes  

OpenAIRE

The crystal growth behaviour and crystallography of a variety of metal halides incorporated within single walled carbon nanotubes (SWNTs) as determined by high resolution electron microscopy (HRTEM) is described. Simple packed structures, such as the alkali halides, form related structures within SWNTs that are found to be integral atomic layers in terms of their thickness as a function of the encapsulating SWNT diameter. An enhanced HRTEM image restoration technique reveals precise data conc...

Sloan, J.; Brown, G.; Bailey, Sr; Coleman, Ks; Flahaut, E.; Friedrichs, S.; Xu, C.; Green, Mlh; Dunin-borkowski, Re; Hutchison, Jl; Kirkland, Ai; Meyer, Rr

2001-01-01

146

Synthesis and crystal structure of new alkali metal hydrogen tellurates  

International Nuclear Information System (INIS)

New alkali metal hydrogen tellurates have been synthesized, and their structures have been determined by X-ray crystallography. Hydrogen tellurates in question contain centrosymmetric binuclear anions [Te2O10H4+x](4-x)-, where x = 0, 1, 2. In addition to the binuclear anion, some of the hydrogen tellurates contain mononuclear species [TeO6H4]2- and Te(OH)6, respectively. The coordination numbers of alkali metals vary from 8 to 12. In all structures, the hydrogen atoms (of both the hydroxy groups and water molecules) are involved in hydrogen bonding

147

Changes to alkali ion content adjacent to crystal-glass interfaces  

International Nuclear Information System (INIS)

Atomic scale molecular dynamics simulations have been used to predict the location of glass modifying Na, Li and Mg species in a borosilicate Magnox type waste glass adjacent to interfaces with the (100) and (110) surfaces of MgO, CaO and SrO crystals. These simulations show a considerable increase in alkali and alkali earth concentration adjacent to specific interfaces. In particular, there are significant, systematic changes in Na, Li and Mg position and concentration as a function of both the crystals terminating surface and composition. (authors)

148

Comparison of the spectroscopic behaviour of single crystals of lanthanide halides (X = Cl, Br)  

International Nuclear Information System (INIS)

Halides belong to large band gap matrices that have the perspective of wide applications when doped by optical active ions. This paper presents the results of spectroscopic studies of single crystals of halides (Cl, Br) of Ce, Pr and Nd. Their spectroscopic behaviour: electron-phonon coupling, ion pair interactions and the effect of covalency, is compared. Absorption, emission and emission excitation spectra of single crystals of LnCl3·yH2O (Ln = Nd, Pr, Ce; y=6, 7) were recorded at room temperatures and low temperatures down to 4.2 K. The intensities of the electronic lines and the Judd-Ofelt parameters were calculated (Nd, Pr) and compared to those of LnBr3·yH2O presented earlier by us. The relationship between the hypersensitivity and covalency was discussed. With increasing soft character of the halides (Br- > Cl-), the covalent character of Ln-ligand bond increases and the hypersensitive bands become more intense. The Judd-Ofelt intensity analysis resulted in a set of ?? parameters evaluated with quite low standard deviations. The temperature dependences of the intensities have been found and the vibronic coupling in the f-f transitions were analysed. At the low temperature (4.2 K), strong vibronic components occur in the electronic lines of the Nd(III) and Pr(III) ions, mainly with the Ln-X vibrations. The modes, which are in resonance with the splitting of the ground state multiplesplitting of the ground state multiplet, mediate in the cooperative transitions. Vibrational studies of the compounds under test were performed at the ambient temperature using IR and Raman spectroscopy. The assignment of the bands was done on the basis of the factor group analysis. The spectral features below 300 cm-1 point at the differences between the spectra of the bromides and chlorides of Nd and Pr. Although the spectral features within the FIR region are complex, the bands of the praseodymium monocrystals originated by halogen bridges are clearly visible

149

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)

150

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.)

151

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

152

Rare-earth tri-halides methanol-adduct single-crystal scintillators for gamma ray and neutron detection  

Science.gov (United States)

Cerium activated rare-earth tri- halides represent a well-known family of high performance inorganic rare-earth scintillators - including the high-light-yield, high-energy-resolution scintillator, cerium-doped lanthanum tribromide. These hygroscopic inorganic rare-earth halides are currently grown as single crystals from the melt - either by the Bridgman or Czochralski techniques - slow and expensive processes that are frequently characterized by severe cracking of the material due to anisotropic thermal stresses and cleavage effects. We have recently discovered a new family of cerium-activated rare-earth metal organic scintillators consisting of tri-halide methanol adducts of cerium and lanthanum - namely CeCl3(CH3OH)4 and LaBr3(CH3OH)4:Ce. These methanol-adduct scintillator materials can be grown near room temperature from a methanol solution, and their high solubility is consistent with the application of the rapid solution growth methods that are currently used to grow very large single crystals of potassium dihydrogen phosphate. The structures of these new rare-earth metal-organic scintillating compounds were determined by single crystal x-ray refinements, and their scintillation response to both gamma rays and neutrons, as presented here, was characterized using different excitation sources. Tri-halide methanol-adduct crystals activated with trivalent cerium apparently represent the initial example of a solution-grown rare-earth metal-organic molecular scintillator that is applicable to gamma ray, x-ray, and fast neutron detection.

Boatner, L. A.; Wisniewski, D. J.; Neal, J. S.; Bell, Z. W.; Ramey, J. O.; Kolopus, J. A.; Chakoumakos, B. C.; Custelcean, R.; Wisniewska, M.; Pena, K. E.

2009-08-01

153

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

154

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

International Nuclear Information System (INIS)

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

155

Creation of molecular defects in alkali iodide crystals by irradiation with fast heavy ions  

International Nuclear Information System (INIS)

We show for the first time that irradiation at room temperature of alkali iodide crystals by fast heavy ions (40Ar14+ ions of 5.53 MeV/A at a fluence of 1013 ions/cm2) leads to the formation of V-type defects. By means of UV visible optical absorption and resonant Raman scattering measurements, we have identified I3-, I5- and (I2)n in Kl and only I3- and I5- in RbI irradiated under similar conditions. These preliminary results are consistent with previous investigations obtained in iodide crystals after exposure to X or ? rays at room temperature. (orig.)

156

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

157

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.

158

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

159

DFT-D study of 14N nuclear quadrupolar interactions in tetra-n-alkyl ammonium halide crystals.  

Science.gov (United States)

The density functional theory-based method with periodic boundary conditions and addition of a pair-wised empirical correction for the London dispersion energy (DFT-D) was used to study the NMR quadrupolar interaction (coupling constant CQ and asymmetry parameter ?Q) of (14)N nuclei in a homologous series of tetra-n-alkylammonium halides (C(x)H(2x+1))4N(+)X(-) (x = 1-4), (X = Br, I). These (14)N quadrupolar properties are particularly challenging for the DFT-D computations because of their very high sensitivity to tiny geometrical changes, being negligible for other spectral property calculations as, for example, NMR (14)N chemical shift. In addition, the polarization effect of the halide anions in the considered crystal mesophases combines with interactions of van der Waals type between cations and anions. Comparing experimental and theoretical results, the performance of PBE-D functional is preferred over that of B3LYP-D. The results demonstrated a good transferability of the empirical parameters in the London dispersion formula for crystals with two or more carbons per alkyl group in the cations, whereas the empirical corrections in the tetramethylammonium halides appeared to be inappropriate for the quadrupolar interaction calculation. This is attributed to the enhanced cation-anion attraction, which causes a strong polarization at the nitrogen site. Our results demonstrated that the (14)N CQ and ?Q are predominantly affected by the molecular structures of the cations, adapted to the symmetry of the anion arrangements. The long-range polarization effect of the surrounding anions at the target nitrogen site becomes more important for cells with lower spatial symmetry. PMID:24758512

Dib, Eddy; Alonso, Bruno; Mineva, Tzonka

2014-05-15

160

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

161

Alkali metal tetrahydroindates  

International Nuclear Information System (INIS)

Synthesis conditions of alkali metal tetrahydroindates of the composition MInH4 (M = Na-Cs) in the medium of tetrahydrofuran (THF) using indium alumohydride as basic reagent were studied. The latter was prepared by means of interaction between sodium alumohydride and indium chloride for 2 h in THF at a temperature of minus 40 deg C. For prepared of tetrahydroindates of heavy alkali metals the method of alkali metal alumohydride synthesis by interaction between sodium alumohydride and the relevant halide in THF was used. By the methods of IR and 115In NMR spectroscopy the presence of In-H chemical bond in all prepared tetrahydroindates of alkali metals was ascertained

162

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

163

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

164

Structure of luminescence spectra of UO2+2 impurity ions in halide salt solid solutions  

International Nuclear Information System (INIS)

Luminescence spectra of impurity polyatomic ions of UO22+ in water and aqueous solutions of alkali-halide salts are studied in the 1.62-77 K temperature range. The emission spectra of these solutions at 77 K are characterized by a pronounced vibrational structure specified by the interaction of an electron transition with an impurity ion intramolecular vibration #betta#1. At 1.62-4.2 K individual vibrational bands are splitted to phononless lines and structural phonon wings (FW). The PW structure is defined by an excitation of crystalline vibrations of a solution solid matrix. For the H2O-UO22+ solution the PW maximum frequences are shown to be comparable with the main critical points of the vibration spectrum of an orientation-disorded ice crystal. In case of aqueous solutions of alkali-halide salts with UO22+ impurity ions the PW luminescence spectra are compared with the density functions of undistorted vibrations of alkali-halide salt crystals and ice

165

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

166

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

167

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.)

168

Basic properties of the F-type centers in halides, oxides and perovskites  

Energy Technology Data Exchange (ETDEWEB)

We present a short survey of the optical properties of primary radiation-induced point defects in alkali halides, simple oxides and some ABO{sub 3} perovskites. We discuss in details the optical properties of single electron F and F{sup +} centers in rock-salt (f.c.c.) alkali halides and oxides and show that the Mollwo-Ivey law well-known for the F-type centers in alkali halides may be extended for other rock-salt structure insulators. We also discuss the major differences in point defect production mechanisms in halides and oxides. We show that the Rabin-Klick diagram may be generalized for a whole family of alkali halides. The F-type center migration and aggregation into metal colloids in alkali halides and oxides is also discussed.

Popov, A.I., E-mail: popov@ill.f [Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569 Stuttgart (Germany); Institute for Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV-1063 (Latvia); Institute Laue Langevin, 6 rue Jule Horovitz, 38042 Grenoble (France); Kotomin, E.A. [Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569 Stuttgart (Germany); Institute for Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV-1063 (Latvia); Maier, J. [Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569 Stuttgart (Germany)

2010-10-01

169

Basic properties of the F-type centers in halides, oxides and perovskites  

International Nuclear Information System (INIS)

We present a short survey of the optical properties of primary radiation-induced point defects in alkali halides, simple oxides and some ABO3 perovskites. We discuss in details the optical properties of single electron F and F+ centers in rock-salt (f.c.c.) alkali halides and oxides and show that the Mollwo-Ivey law well-known for the F-type centers in alkali halides may be extended for other rock-salt structure insulators. We also discuss the major differences in point defect production mechanisms in halides and oxides. We show that the Rabin-Klick diagram may be generalized for a whole family of alkali halides. The F-type center migration and aggregation into metal colloids in alkali halides and oxides is also discussed.

170

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

OpenAIRE

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

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

2014-01-01

171

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

International Nuclear Information System (INIS)

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

172

Some uranium halide complexes  

International Nuclear Information System (INIS)

Uranium halide complex salts [MeEtim]X (where[MeEtim] 1-methyl-3-ethyl-imidazolium; X-Cl, Br, I) have been used for synthesis of room temperature ionic liquids AlX3 [Me Etim]X. The crystal structure of [MeEtim]I revealed significant H bonding between cation and anion. This interaction, detected here for the first time, is important for the structure of these ionic liquids which are efficient solvents for studying electrochemical and spectroscopic properties of novel uranium halide complex salts. The cyclic voltammogram of [UO2X4]2- salts showed irreversible and reversible reduction processes. X-ray structural analysis of this salt showed tetragonal symmetry and no evidence of H bonds between anions and cations. The X-ray structure of a pseudo-halide compound [U(NCS)]4- showed significant cation-anion bonding. (U.K.)

173

Lattice relaxation of luminescence centres of the X-line emission of ns2 impurity ions in alkali halides; anomalous geometry of the impurity centre in the excited nsnp state  

International Nuclear Information System (INIS)

Clear evidence was found that in the active centre from which the X-line emission of ns2 impurities in alkali halides originates the excited impurity ion is statically displaced over an anomalously large distance in a direction which depends on the lattice structure. For fcc this is one of the (111) directions and the centre has trigonal symmetry, and for the bcc lattice it is one of the (001) directions and the symmetry is tetragonal. The displacement only occurs in the excited state and probably is a result of covalency effects. The study was performed using a readily available code for lattice relaxation around impurity ions. For the fcc lattice we have studied the relaxation of Ga+, In+ and Tl+ in KCl and of In+ in KBr. For the bcc case we considered In+ in high-pressure KCl. A comparison with well known experimental data for the three impurity ions and the good agreement found for both the T- and X-line emission wavelengths supports our theoretical results. (author)

174

Room-temperature and low-ordered, amphotropic-lyotropic ionic liquid crystal phases induced by alcohols in phosphonium halides.  

Science.gov (United States)

Tri- n-decylmethylphosphonium chloride and bromide ( 1P10X) salts are not liquid crystalline. However, mesophases are induced by adding very small amounts of an alcohol or water. The temperature ranges of the induced smectic A 2 (SmA 2) liquid-crystalline phases can be very broad and the onset temperatures can be below room temperature depending upon the concentration of the alcohol or water and the structure of the alcohol. At least one molar equivalent of hydroxyl groups is necessary to convert the 1P10X completely into a liquid crystal. Strong association between the hydroxyl groups of an alcohol or water and the head groups of the 1P10X is indicated by spectroscopic, diffraction, and thermochemical data. Unlike many other smectic phases, those of the 1P10X/alcohol complexes are easily aligned in strong magnetic fields and the order parameters of selectively deuterated alcohols as measured by (2)H NMR spectroscopy, approximately 10 (-2), are much lower than the values found when the host is a commonly employed thermotropic liquid crystal. The dependence of the specific values of the order parameters on temperature, the nature of the halide anion, and the structure and concentration of the alcohol are reported. In sum, a detailed picture is presented to explain how and why an alcohol or water induces liquid crystallinity in the 1P10X salts. The data also provide a blueprint for designing media with even lower order parameters that can be hosts to determine the conformations and shapes of guest molecules. PMID:18686978

Ma, Kefeng; Shahkhatuni, Astghik A; Somashekhar, B S; Gowda, G A Nagana; Tong, Yuye; Khetrapal, C L; Weiss, Richard G

2008-09-01

175

Zirconium tungstate hydroxide hydrate revisited: Crystallization dependence on halide and hydronium ions  

International Nuclear Information System (INIS)

The formation of zirconium tungstate hydroxide hydrate, a precursor to the negative thermal expansion material cubic zirconium tungstate, shows a strong dependence on hydrothermal reaction conditions. It was found that not only the acid concentration, but also the acid counterion plays a significant role in the crystallization of ZrW2O7(OH)2.2H2O. High temperatures, high acid concentrations, and the presence of chloride or bromide ions promote the formation of well-crystallized ZrW2O7(OH)2.2H2O. For low acid concentrations, a new zirconium tungstate hydrate polymorph is observed, which transforms to tetragonal ZrW2O7(OH)2.2H2O at longer reaction times. A study of crystallization kinetics in hydrochloric acid is presented. - Graphical abstract: The formation of ZrW2O7(OH)2.2H2O shows a strong dependence on reaction conditions. Both acid concentration and acid counterion play a significant role in the crystallization. High temperatures, high acid concentrations, and the presence of chloride or bromide ions promote the formation of well-crystallized ZrW2O7(OH)2.2H2O. For low acid concentrations, a new zirconium tungstate hydrate polymorph is observed

176

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

177

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

Science.gov (United States)

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.

De Bastiani, Michele; D'Innocenzo, Valerio; Stranks, Samuel D.; Snaith, Henry J.; Petrozza, Annamaria

2014-08-01

178

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

179

Color center studies in KBr–NaI mixed crystals doped with gold  

International Nuclear Information System (INIS)

Mixed Alkali halide crystals containing KBr and NaI in different compositions were grown by slow evaporation technique. Obtained transparent crystals were doped with gold to study the role of dopant on the mixed crystals. Crystals were subjected to 60Co ?-radiation. The irradiated samples were subjected to Thermoluminescence, Optical Absorption and Electron Spin Resonance studies. Effect of Au+ doping on TL intensity and absorption coefficient is discussed in the present paper.

180

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

International Nuclear Information System (INIS)

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

181

Structure of luminescence spectra of UO/sup 2 +//sub 2/ impurity ions in halide salt solid solutions  

Energy Technology Data Exchange (ETDEWEB)

Luminescence spectra of impurity polyatomic ions of UO/sub 2//sup 2 +/ in water and aqueous solutions of alkali-halide salts are studied in the 1.62-77 K temperature range. The emission spectra of these solutions at 77 K are characterized by a pronounced vibrational structure specified by the interaction of an electron transition with an impurity ion intramolecular vibration ..nu../sub 1/. At 1.62-4.2 K individual vibrational bands are split to phononless lines and structural phonon wings (PW). The PW structure is defined by an excitation of crystalline vibrations of a solution solid matrix. For the H/sub 2/O-UO/sub 2//sup 2 +/ solution the PW maximum frequences are shown to be comparable with the main critical points of the vibration spectrum of an orientation-disorded ice crystal. In case of aqueous solutions of alkali-halide salts with UO/sub 2//sup 2 +/ impurity ions the PW luminescence spectra are compared with the density functions of undistorted vibrations of alkali-halide salt crystals and ice.

Kushnirenko, I.Ya.; Sheremet, V.I.

1982-10-01

182

Glycosyl Halides  

Science.gov (United States)

This chapter describes the preparations and chemical glycosylation reactions of glycosyl halides as glycosyl donors including glycosyl bromides, chlorides, iodides, and fluorides. For a survey on the general current methodological advances, glycosyl halide donors are classified into four groups based on the type of anomeric functional group and their activating methods. Among them, glycosyl fluorides, which are frequently and widely used in current glycosylation reactions, are particularly emphasized and discussed in this chapter.

Toshima, Kazunobu

183

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

Science.gov (United States)

Here, the crystallization and initial phasing of the C-terminal domain of human KIN17, a 45 kDa protein mainly expressed in response to ionizing radiation and overexpressed in certain tumour cell lines, are reported. Crystals diffracting to 1.4 A resolution were obtained from 10% ethylene glycol, 27% PEG 6000, 500 mM LiCl and 100 mM sodium acetate pH 6.3 in space group P2(1)2(1)2(1), with unit-cell parameters a = 45.75, b = 46.31, c = 60.80 A and one molecule in the asymmetric unit. Since this domain has a basic pI, heavy-atom derivatives were obtained by soaking the crystals with negatively charged ions such as tungstate and iodine. The replacement of LiCl by KI in the cryosolution allowed the determination of phases from iodide ions to give an interpretable electron-density map. PMID:16511313

le Maire, Albane; Schiltz, Marc; Braud, Sandrine; Gondry, Muriel; Charbonnier, Jean-Baptiste; Zinn-Justin, Sophie; Stura, Enrico

2006-03-01

184

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

185

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

186

Molecular compressibility of some halides in alcohols  

Science.gov (United States)

After measuring ultrasonic velocity and density, the molecular compressibility values from Wada's formula were calculated, for alkali metal halide solutions in methyl, ethyl, butyl, and glycol alcohol. The temperature and concentration dependence were studied, finding deviations due to the hydrogen bonds of the solvent.

Serban, C.; Auslaender, D.

1974-01-01

187

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

International Nuclear Information System (INIS)

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

188

Electronic and optical properties of alkali metal selenides in anti-CaF2 crystal structure from first-principles  

International Nuclear Information System (INIS)

We have performed FP-LAPW calculations in the framework of density functional theory (DFT) to compute ground-state electronic and optical properties of alkali metal selenides M2Se [M: Li, Na, K, Rb] in anti-CaF2 crystal structure. The generalized gradient approximation (GGA) parameterization schemes proposed by Wu and Cohen (WC) and Engel and Vosko (EV) have been utilized for these calculations and some trends in the electronic properties of alkali metal selenides have been analyzed in the light of available theoretical and experimental data of other group IA-VI crystals. Electronic density of states for these compounds has been obtained to elucidate contribution from different anion and cation states to the electronic structure. Optical properties such as complex dielectric function ?(?), absorption coefficient I(?), refractive index n(?), extinction coefficient k(?) and reflectivity R(?) for incident photon energy up to 35 eV and energy-loss functions have been predicted for M2Se compounds. Various interband transitions and the possible contributions of the cation and anion states to these transitions have been presented.

189

Crystal Dynamics from Neutron Spectrometry  

International Nuclear Information System (INIS)

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

190

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

International Nuclear Information System (INIS)

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

191

The fast light of CsI(Na) crystals  

CERN Document Server

The responds of different common alkali halide crystals to alpha-rays and gamma-rays are tested in our research. It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others have not this phenomena. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals.

Sun, Xilei; Hu, Tao; Zhou, Li; Cao, Jun; Wang, Yifang; Zhan, Liang; Yu, Boxiang; Cai, Xiao; Fang, Jian; Xie, Yuguang; An, Zhenghua; Wang, Zhigang; Xue, Zhen; Zhang, Aiwu; Lu, Qiwen; Ning, Feipeng; Ge, Yongshuai; Liu, Yingbiao

2011-01-01

192

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

193

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

Energy Technology Data Exchange (ETDEWEB)

The suite of alkali basalts and differentiates (hawaiites, mugearites and trachytes) erupted at Jebel Marra volcano, Sudan, provides an excellent opportunity to examine the differentiation theory of mantle-derived magmas. Crystal fractionation exerts a control on major element compositions although variations in incompatible element and isotopic ratios among the more evolved volcanic rocks require open system behavior. The basement at Jebel and Marra is compositionally unlike the basalts, with much higher {sup 87}Sr/{sup 86}Sr, {delta}{sup 18}O and Rb/Nb, together with highly variable Pb isotopic compositions and low {sup 143}Nd/{sup 144}Nd. The strong compositional contrast between crust and magma allows the influence of crustal interaction on magma compositions to be assessed. Simple two-component bulk mixing trends are not observed, but models of simultaneous assimilation and fractional crystallization (AFC) reproduce many of the data trends. It is suggested that contamination takes place at more than one stage, with a change in the composition of the assimilant at different levels, coupled with a change in the rate ratio of assimilation to crystal fractionation. (orig.).

Davidson, J.P.; Wilson, I.R. (Leeds Univ. (UK). Dept. of Earth Sciences)

1989-10-01

194

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

International Nuclear Information System (INIS)

The suite of alkali basalts and differentiates (hawaiites, mugearites and trachytes) erupted at Jebel Marra volcano, Sudan, provides an excellent opportunity to examine the differentiation theory of mantle-derived magmas. Crystal fractionation exerts a control on major element compositions although variations in incompatible element and isotopic ratios among the more evolved volcanic rocks require open system behavior. The basement at Jebel and Marra is compositionally unlike the basalts, with much higher 87Sr/86Sr, ?18O and Rb/Nb, together with highly variable Pb isotopic compositions and low 143Nd/144Nd. The strong compositional contrast between crust and magma allows the influence of crustal interaction on magma compositions to be assessed. Simple two-component bulk mixing trends are not observed, but models of simultaneous assimilation and fractional crystallization (AFC) reproduce many of the data trends. It is suggested that contamination takes place at more than one stage, with a change in the composition of the assimilant at different levels, coupled with a change in the rate ratio of assimilation to crystal fractionation. (orig.)

195

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

196

Electrodepositions on Tantalum in Alkali Halide Melts  

DEFF Research Database (Denmark)

Surface layers of tantalum metal were electrodeposited on steel from K2TaF7-LiF-NaF-KF melts. With careful control of the oxide contents dense and adherent deposits could be obtained by pulse plating. In NaCl-KCl-NaF-Na2CO3 and NaCl-KCl-Na2CO3 melts carbonate ions seems to be reduced to carbon in 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 oC coherent carbon containing surface layers could be obtained on tantalum substrates, when a CO2 atmosphere was applied

Barner, Jens H. Von; Jensen, Annemette Hindhede

2013-01-01

197

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

198

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

199

The Silver Halides  

Science.gov (United States)

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

Sahyun, M. R. V.

1977-01-01

200

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

201

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

202

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

Energy Technology Data Exchange (ETDEWEB)

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.

1992-01-01

203

Application of radioisotopes to studies of crystal imperfections  

International Nuclear Information System (INIS)

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

204

Density and molar volume of molten mixtures of potassium rubidium and cesium with their halides  

International Nuclear Information System (INIS)

Density of KI-K, RbCl-Rb and CsCl-Cs melts countaining from 5 to 95 at% of alkali metal is measured by means of hydrostatic weighting. The molar volumes of metal-salt melts are calculated. The results obtained are compared to data for other alkali metal solutions in their molten halides

205

Crystal growth and characterization of mixed lead halides PbCl2xBr2(1-x)  

OpenAIRE

Single crystals of PbCl2-type solid solutions PbCl2xBr2(1?x) have been grown using the Bridgeman technique. XRD measurements reveal preferential site occupancy for Cl and Br, while the anion array of PbClBr is completely ordered. The temperature and composition dependence of the ionic conductivity of the solid solution crystals have been studied. While cation conducting Schottky- or Frenkel-type solid solutions obtained by homovalent anion doping reveal substantial conductivity enhancements...

Lumbreras, M.; Protas, J.; Jebbari, S.; Dirksen, G. J.; Schoonman, J.

1985-01-01

206

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)

207

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.)

208

Growth and characterization of YBa2Cu3O7 - ? single crystals  

International Nuclear Information System (INIS)

Measurement of the anisotropy of the physical properties of YBCO requires good quality single crystals. Small crystals have been widely grown from a CuO-BaCuO2 flux, but are usually in the form of thin platelets making many measurements difficult. More recently, an alternative additive flux route based on a mixed alkali halide eutectic has produced crystals with a three-dimensional morphology. In this paper the authors compare the morphology, crystallinity and physical properties of crystals grown by the two routes

209

Vibrational spectroscopy and theory of alkali metal adsorption and co-adsorption on single-crystal surfaces  

Science.gov (United States)

Alkali-metal (AM) atoms adsorbed on single-crystal surfaces are a model system for understanding the properties of adsorption. AM adsorption, besides introducing new overlayer vibrational states, induces significant modifications in the surface vibrational structure of the metal substrate. Several studies of the vibrational properties of AM on metal surfaces have been carried out in last decades. Most of these investigations have been performed for low coverages of AM in order to make the lateral interaction among co-adsorbates negligible. The adsorbed phase is characterized by a stretch (S) vibrational mode, with a polarization normal to the surface, and by other two modes polarized in the surface plane, known as frustrated translation (T) modes. The frequencies and intensities of these modes depend on the coverage, thus providing a spectroscopic signature for the characterization of the adsorbed phases. The vibrational spectroscopy joined to an ab-initio theoretical analysis can provide useful information about surface charge re-distribution and the nature of the adatom-surface bond, establishing, e.g., its partial ionicity and polarization. Gaining this information implies a significant advancement in our knowledge on surface chemical bonds and on catalytic reactions occurring in AM co-adsorption with other chemical species. Hence, systematic studies of co-adsorption systems are essential for a more complete understanding of heterogeneous catalysis. The two principal experimental techniques for studying the vibrations of AM adsorbed phases are high-resolution electron energy loss spectroscopy (HREELS) and inelastic helium atom scattering (HAS), the former being better suited to the analysis of the higher part of the vibrational spectrum, while the latter exploits its better resolution in the study of slower dynamics, e.g., T modes, surface acoustic phonons and diffusive phenomena. Concerning AM co-adsorption systems, reflection-absorption infrared spectroscopy (RAIRS) has been also used (as well as HREELS) for obtaining information on the influence of AM adsorption on the vibrational properties of co-adsorbates. In this review an extended survey is presented over: the existing HREELS and HAS vibrational spectroscopic studies for AM adsorbed on single-crystal metal surfaces; the theoretical studies based on semi-empirical and ab-initio methods of vibrational structure of AM atoms on metal surfaces; the vibrational (HREELS, RAIRS, TRSHG) characterization of the co-adsorption on metal surfaces of AM atoms with reactive species.

Politano, A.; Chiarello, G.; Benedek, G.; Chulkov, E. V.; Echenique, P. M.

2013-11-01

210

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

Science.gov (United States)

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

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

1986-01-01

211

????????????????? ???????? 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

212

Halogens and Halides (GCMP)  

Science.gov (United States)

Halogens and Halides: this is a resource in the collection "General Chemistry Multimedia Problems". In this problem we will study the oxidation-reduction reactions between the halogens and the halide ions. The halogens and halides will be dissolved in water and hexane. General Chemistry Multimedia Problems ask students questions about experiments they see presented using videos and images. The questions asked apply concepts from different parts of an introductory course, encouraging students to decompartmentalize the material.

213

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

CERN Document Server

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

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

2002-01-01

214

Alkaline halides crystal growth; Effect of ion beam from accelerator on these crystals measuring penetration depth and range of proton beams on these materials  

International Nuclear Information System (INIS)

This project was began by modification of the Czochralski/Kyropoulos crystal growth system, present in the Solid State Division of the Laser Research Center of Atomic Energy Organization of Iran, in order to be suitable of growing different K Br single crystals. The crystals were then cleaved in the direction of their (100) planes and irradiated by protons with various fluences and energies using van de Graaff accelerator. Many photomicrographs with the different modification were obtained for each samples by a microscope equipped with a camera. The obtained micrographs were then densitometerized by a laser densitometer linked with 386 IBM pc computer using an available software program (Zeineh Programs). The drawn optical density graphs, which indicate the color layers relative to the depth of damages, were used to calculate the range and damage profiles for each samples

215

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth. Progress report, May 1, 1991--April 30, 1992  

Energy Technology Data Exchange (ETDEWEB)

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.

1992-05-01

216

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

217

Recombination luminescence and energy transfer in ionic crystals at XUV excitation by synchrotron radiation  

Energy Technology Data Exchange (ETDEWEB)

The relative quantum yield spectra of recombination luminescence for MgO, ..cap alpha..-Al/sub 2/O/sub 3/, SiO/sub 2/, and several alkali halide crystals are measured by synchrotron radiation in the photon energy interval 50 to 250 eV. The main feature of the spectra of oxides is a suppression of the volume luminescence due to surface losses of electrons and holes. For alkali halides surface as well as volume recombination luminescence take place. The more intensive the surface luminescence is the larger the absorption coefficient for exciting photons. The quantum yield spectra may be interpreted quantitatively on the basis of the hot carrier diffusion theory, the diffusion lengths being 2200 A for MgO, 1500 A for ..cap alpha..-Al/sub 2/O/sub 3/, and 300 A for SiO/sub 2/.

Elango, M.; Pruulmann, J.; Zhurakovskii, A.P. (AN Ehstonskoj SSR, Tartu. Inst. Fiziki)

1983-02-01

218

SURFACE STRUCTURES OF OXIDES AND HALIDES AND THEIR RELATIONSHIPS TO CATALYTIC PROPERTIES  

OpenAIRE

In this review, the relationships between structure, morphology, and surface reactivity of microcrystals of oxides and halides are assessed. The investigated systems we discuss include alkali halides, alkaline earth oxides, NiO, CoO, NiO–MgO, CoO–MgO solid solutions, ZnO, spinels, cuprous oxide, chromia, ferric oxide, alumina, lanthana, perovskites, anatase, rutile, and chromia/silica. A combination of high-resolution transmission electron microscopy with vibrational spectroscopy of...

Zecchina, Adriano; Bordiga, Silvia; Scarano, Domenica; Spoto, Giuseppe; Lamberti, Carlo

2001-01-01

219

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

220

Spectra of impurity ions in the bismuth and antimony oxo-halides  

International Nuclear Information System (INIS)

The ion spectra in oxo-halides crystals of bismuth and antimony have been investigated. The opportunity of practical use of investigated crystals in the capacity of radio-luminophores is shown. (author)

221

Tertiary phosphine derivatives of the f-block metals. Preparation of X4M(Me2PCH2C2Me2)2, where X is halide, methyl, or phenoxo and M is thorium or uranium. Crystal structure of tetra(phenoxo)bis[bis(1,2-dimethylphosphino)ethane]-uranium(IV)  

International Nuclear Information System (INIS)

Through a number of tertiary phosphine complexes or uranium halides have been claimed, most of the claims have been shown to be false. In this communication we describe the synthesis of some authentic bis(1,2-dimethylphosphino)ethane (dmpe) complexes of uranium(IV) and thorium(IV) halides of the type X4M(dmpe)2 and their conversion to the tetramethyl and tetraphenoxo derivatives. The crystal structure of the phenoxo derivative, (PhO)4U(dmpe)2, is described

222

Crown ether uranyl halide complexes  

International Nuclear Information System (INIS)

Uranium oxide is recovered from an aqueous solution of uranyl halides by extracting uranyl halide from the aqueous solution with an organic liquid, forming a crown ether uranyl halide complex in the organic liquid, and then contacting the uranyl halide crown ether complex with water, carboxylate ion, and light under suitable conditions. Also disclosed are certain novel crown ether uranyl halide complexes and their preparation. Also disclosed is the use of 18-crown-6 to selectively recover uranyl halide from a solution thereof containing other metal salts

223

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

224

Fast light of CsI(Na) crystals  

International Nuclear Information System (INIS)

The responses of different common alkali halide crystals to alpha-rays and gamma-rays are tested in this research, It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others do not exhibit this phenomena. The rise time of the fast light is about 5 ns and the decay time is 17±12 ns. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals. (authors)

225

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

226

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

227

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

228

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

229

Exciton-relaxation dynamics in lead halides  

OpenAIRE

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

Iwanaga, Masanobu; Hayashi, Tetsusuke

2002-01-01

230

Excitons in Alkali Halides: Analysis of Type I STE Spectrafootnote[1] Supported in part by the State of Vermont and the National Science Foundation under EPSCoR/grant RII-8610679.  

Science.gov (United States)

We have analyzed the newly observedfootnote[2] K. Edamatsu and M Hirai, Mat. Sci. Forum (in press). transient IR absorption spectra of ``Type I'' self-trapped excitons in NaBr and NaI for the exciton's spatial extent and the exciton Rydberg. A Vinti sum-rule analysis shows that the electron orbits extend well into the bulk crystal with radii 2.6 to 4 times the interatomic spacing. This corresponds to an electron distribution covering 100 or more lattice sites. The transient absorption line shape can be fit extremely well with a phonon-broadened hydrogenic spectrum. Gaussian broadening yields significantly better fits than Lorentzians. Rydberg values are 0.27 eV for NaBr and 0.19 eV for NaI. The large radii, small Rydberg and approximate Wannier-exciton-like properties of the absorption strongly suggest the originalfootnote[3]M. N. Kabler, Phys. Rev. 136, A1296 (1964); R. B. Murray and F. J. Keller, Phys. Rev. 137, A942 (1965). ``on-center'' model for STEs applies to these materials.

Malghani, M. S.; Smith, D. Y.

1997-03-01

231

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

International Nuclear Information System (INIS)

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

232

Luminescent defects created in alkali iodides by plastic deformation at 4.2 K  

Energy Technology Data Exchange (ETDEWEB)

Several new types of luminescent defects have been found to appear in KI, RbI and CsI crystals deformed plastically at 4.2 K. The spectral characteristics of their luminescence have been studied at 4.2 K and compared with those reported earlier for the self-trapped excitons as well as for the localized excitons created in alkali halide crystals by plastic deformation at 295 K. The amount and the origin of the defects have been found to depend on the stress magnitude, deformation temperature and crystal plasticity. The emission bands observed have been ascribed to the excitons localized near various crystal structure defects and divided into three groups according to the crystal lattice relaxation. An analysis method has been proposed for the determination of the defect structure on the basis of the characteristics of the corresponding exciton luminescence, and the origin and the structure of the defects produced by the deformation at 4.2 K have been discussed. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

Babin, V.; Elango, A.; Kalder, K.; Maaroos, A.; Vasil' chenko, E.; Zazubovich, S. [Institute of Physics, University of Tartu, Riia 142, EE2400 Tartu (Estonia); Shunkeev, K. [Aktybinsk University, Aktybinsk (Kazakhstan)

1999-01-04

233

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

234

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

Science.gov (United States)

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

2014-08-01

235

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

236

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

Energy Technology Data Exchange (ETDEWEB)

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

237

Neutron scattering experiments of the ionic crystal deformed plastically with uniaxial compression under high temperature  

International Nuclear Information System (INIS)

As an aim of huge growth of alkali halide (AH) single crystal, a mosaic structure of small size AH single crystal deformed plastically with uniaxial compression under high temperature was evaluated due to its neutron irradiation experiment. Using TAS-2 installed at JRR-3M guide hole of Japan Atomic Energy Research Institute, locking curve at a representative face factor of the specimen was measured to observe the mosaic structure accompanied with expansion of the crystal due to compression. As a result, though the specimen before compression could be supposed to be divided to some parts already, the locking curve under 10 sec. of compression time showed already some fracture to divisions to suppose finer degradation of the crystal, and division of the locking curve at 600 sec. of compression time could be observed onto its 220 face. And, every compressed specimens showed some changes of crystallization method from standard sample. (G.K.)

238

Linkage Isomerism of CO Adsorbed on Alkali Halides.  

Science.gov (United States)

Variable-temperature FTIR spectra of CO adsorbed on NaCl and KBr films are shown to reveal linkage isomerism, that is, formation of C- and O-bonded adsorption complexes with the same cationic sites. Not all of the sites can be involved in that, only the three- or four-coordinated cations located on kinks, edges, or steps of microcrystals. For NaCl, these adsorption complexes account for the high-frequency (HF) C-O stretching bands at 2175 and 2160 cm(-1). Coresponding LF bands of O-bonded CO were found at 2115 and 2124 cm(-1). In the spectrum of KBr, the HF band is poorly resolved, and only one LF band can be clearly seen, near 2124 cm(-1). The value of the isomerization enthalpy for complexes that account for the bands at 2160 and 2124 cm(-1) of CO adsorbed on NaCl, estimated from the experiment, is 4.0 ± 0.2 kJ/mol. Quantum mechanical calculations by DFT methods applied to NaCl model clusters interacting with the CO molecule confirm the existence of two potential wells with adsorption and isomerization energies close to the experimentally measured values, and enable us to estimate the height of the potential barrier between the two adsorption states. PMID:25222795

Belykh, Roman; Maevskaya, Maria; Krauklis, Irina; Tsyganenko, Alexey

2015-03-19

239

Cold ablation driven by localized forces in alkali halides  

Science.gov (United States)

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

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

2014-05-01

240

Electrical measurements on multiphased (NaCl)x(KCl)y-x(KBr)1-y single crystals  

International Nuclear Information System (INIS)

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

241

Ultraviolet absorption spectra of mercuric halides.  

Science.gov (United States)

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

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

1972-01-01

242

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

243

Chemical ionization of pentacarbonylrhenium halides in vapors of water, methanol and ethanol  

International Nuclear Information System (INIS)

The behaviour of pentacarbonylrhenium (PCR) halides at the chemical ionization in vapors of water, methanol and ethanol is studied by the method of mass-spectrometry. Energy of ionizing electron beam is 90 eV, temperature of ionizing chamber is 170-200 deg C. It is found out that ?-linked with metal halide atom is the most active group in Re(Co)5X complexes, with tendency to detachment and displacement in ionizing water vapors as well as in vapors of some simplest alkalies

244

40 CFR 721.4095 - Quaternary ammonium alkyltherpropyl trialkylamine halides.  

Science.gov (United States)

...ammonium alkyltherpropyl trialkylamine halides. 721.4095 Section 721.4095 ...ammonium alkyltherpropyl trialkylamine halides. (a) Chemical substance and significant...ammonium alkyltherpropyl trialkylamine halides (PMNs...

2010-07-01

245

Effect of uniaxial stress on luminescence of X- and VUV- irradiated NaCl and NaBr crystals  

Energy Technology Data Exchange (ETDEWEB)

The effect of uniaxial stress applied at 80 K along the <1 1 0> crystal axis on the self-trapped exciton (STE) and impurity-induced luminescence has been studied for NaCl and NaBr crystals under X-ray and VUV-light excitation. It has been shown that the intensities of both the {pi} and the {sigma} STE luminescence bands increased in X-rayed NaCl more than 10 times under the applied uniaxial stress, whereas only a small stress-induced increase of the intrinsic luminescence has been observed in NaBr crystal. TSL measurements have shown that the creation of fundamental radiation defects (F-H pairs) is strongly suppressed in stressed NaCl. It is concluded that the influence of the uniaxial stress is less pronounced in alkali halides with the on-centre final configuration of the STE (NaBr) whereas the stress-induced effects may be very large in alkali halides in which the relaxation of the electronic excitations occurs by means of the off-centre relaxation (NaCl, KI and RbI). In the latter case, a strong stress-induced effect is mainly connected with an increase in the energy barrier between the minima of two different STE configurations, a radiative off-centre one and the one forming the radiation defects (F-H pairs)

Elango, A. E-mail: svet@fi.tartu.ee; Sagimbaeva, Sh.; Sarmukhanov, E.; Savikhina, T.; Shunkeev, K

2001-10-01

246

A simple theory of thermal effects in ionic crystals  

International Nuclear Information System (INIS)

An equation of state is obtained for ionic crystals based on the Born theory by assuming that the thermal motions of ions are uncorrelated and that the mean vibration energy of each ion is kT. The important feature of the theory is that the ''thermal pressure'' term is written entirely in terms of the interaction potentials. This is an advance over current Born theory equations of state which require a knowledge of the experimental coefficient of thermal expansion. The calculated volume thermal expansivities of the alkali halides at room temperature and atmospheric pressure are in good agreement with experiment (r.m.s. error 12.5%). For many purposes, the present theory appears to be an adequate approximation for ionic crystals at finite temperatures. (author)

247

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

OpenAIRE

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...

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

2014-01-01

248

Research update : physical and electrical characteristics of lead halide perovskites for solar cell applications  

OpenAIRE

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...

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

2014-01-01

249

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

250

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

251

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

Science.gov (United States)

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.

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

2014-04-01

252

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

253

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

254

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

255

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.)

256

Exchange experiments of C60 and halides on a Au(1 1 1) surface  

Science.gov (United States)

The influence of halides (I-, Br-, Cl-) on the stability of C60 adlayers on Au(1 1 1) was studied by scanning tunneling microscopy (STM) in air at room temperature. The C60 layers on gold were immersed into alkali halides solutions of several concentrations for different time intervals. The results show that C60 can be removed from the gold surface by iodide when the halide concentration is high and time of immersion is long. A rotated hexagonal structure of iodide is formed on some surface areas although with distortion. Bromide and chloride do not remove C60 completely from the gold surface. Nevertheless, they are able to penetrate the C60 layer. The result is that bromide and chloride adsorb on top of the gold and C60 sits on the halide adlayer. This condition enables the growth of well organized domains of C60. It is possible to identify the formation of multilayers of the fullerene on some areas. Intramolecular resolution for C60 was attained in the STM images when the halides were present on the surface.

Pinheiro, Lucidalva dos Santos; Filho, Josué Mendes

2013-09-01

257

Radiochemical synthesis of pure anhydrous metal halides  

Science.gov (United States)

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

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

1973-01-01

258

Forecasting of zinc and cadmium extraction by tributylphosphate in chloride and bromide systems with alkali metal cations  

International Nuclear Information System (INIS)

Regularities of the cation effect on Zn(2) and Cd(2) extraction from chloride (bromide) solutions by tributylphosphate and their complex formation with halide-ions were used to predict the extraction distribution of those metals in the systems with alkali metal cations. 7 refs., 3 tabs

259

Anharmonic properties of rubidium halides  

International Nuclear Information System (INIS)

The anharmonic properties of rubidium halides are investigated using a three-body interaction (TBI) potential. This includes the prediction of second-, third- and fourth-order elastic constants, the pressure dependence of second- and third-order elastic constants. The agreement between experimental and theoretical results is, generally, good. The inclusion of anharmonic terms in the potential might lead to further improvements. (author)

260

Generalized estimation method of interactions in melts of double halide systems. 4. Systems with similar and different-type halides on the base of mono- and trivalent metals  

International Nuclear Information System (INIS)

The interactions in melts of the systems of similar halides on the base of alkali and transition (3+) metals and different-type halides on the base of alkaline metals and lanthanum are investigated. The values of the coefficient of interaction predominance Ki.p. in melts of one group over the other are determined. By Ki.p. values all double systems by compositions can be divided into six specific fields, five of which include the compositions where the components interaction in melt occurs with energy release and one field of compositions were the interaction occurs with energy absorption. For each of the fields on the base of specific systems possible forms of interactions are discussed and the estimation of the value of formation enthalpy of the solution is made

261

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

262

Separation of alkali metals  

International Nuclear Information System (INIS)

A new environmentally friendly method of separation and purification of alkali metals, according to which gallium intermetallic compound (IC) with alkali metal is used instead of amalgam, while separation of alkali metal pairs occurs as a result of exchange between IC and aqueous solution of the metal hydroxide, has been developed. Influence of temperature and concentration of the exchanging phases on separation factor in the system LiGa - NaOH and LiGa - KOH is considered. Kinetic parameters of lithium, sodium and potassium exchange are ascertained. Comparison is made of characteristics of gallium IC base and amalgam-exchange systems studied

263

Development of Halide and Oxy-Halides for Isotopic Separations  

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-10-01

264

Raman spectroscopic study of high temperature rare earth metal - rare earth halide solutions: Ln-LnX3- and LnX2-LnX3-(LiX-KX)eu systems (Ln: Nd, Ce; X: Cl, I) [online].  

OpenAIRE

In this work new Raman spectroscopic experiments on rare earth metal-rare earth trihalide melts (Ln-LnX3 and LnX2-LnX3: Ln=Ce, Nd; X=Cl, I) and their mixtures in alkali halide eutectic solvents ((LiX-KX)eu; X=Cl, I) are presented. The main results can be summarized as follows: - The Raman spectra of following trihalide systems have been measured for the first time: CeCl3, CeI3, NdI3 and their mixtures in the respective alkali halide eutectic solvent. The structure of the LnX3 in the s...

Rodriguez Betancourtt, V. M.

2003-01-01

265

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

International Nuclear Information System (INIS)

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

266

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

Energy Technology Data Exchange (ETDEWEB)

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.

Ding Yuan, Paul Guss, and Sanjoy Mukhopadhyay

2009-04-01

267

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

Science.gov (United States)

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

268

Synthesis and physicochemical investigation of double alkali metal hexafluorotitanates  

International Nuclear Information System (INIS)

Titanium hexafluorocomplexes with alkali metals of NaMTiF6 composition crystallizing in rhombic crystal system are synthetized and studied for the first time. Periods of their unit cells are determined. IR absorption spectra of fluorocomplexes within 4000-200 cm-1 range are measured and cheracterized

269

Energy transfer in crystalline alkali nitrates  

Energy Technology Data Exchange (ETDEWEB)

The radiation annealing of peroxynitrite ions in pre-photolyzed (253.7nm) alkali nitrate crystals has been studied. This process is stated to be due to interaction with high-energy excited states of the nitrate ion symmetry E' than to low-energy excited states symmetry A{sub 1}{sup '}'. The distance of energy transfer has been found to be {approx}10nm.

Anan' ev, Vladimir [Department of Analytical Chemistry, Kemerovo State University, Krasnaya Str., 6, Kemerovo 650043 (Russian Federation)]. E-mail: eprlab@kemsu.ru

2007-08-15

270

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

International Nuclear Information System (INIS)

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

271

Solvation of hydrogen halides on the surface of ice  

OpenAIRE

Heterogeneous processes on the surface of ice crystals in polar stratospheric clouds are thought to play a crucial role in the catalysis of reactions such as HCl + ClONO 2. An important consideration is the mechanism of solvation of the HCl molecules on the ice surface. A molecular dynamics simulation of the solvation of HCl, HF and HBr by an ice surface at 190 K is reported. The model allows for the solvation of the hydrogen halide by water molecules on the ice sur...

Robertson, Sh; Clary, Dc

1995-01-01

272

Alkali metal ion battery with bimetallic electrode  

Energy Technology Data Exchange (ETDEWEB)

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

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

2015-04-07

273

ALKALI FUSION OF ROSETTA ZIRCON  

International Nuclear Information System (INIS)

The decomposition of Rosetta zircon by fusion with different types of alkalis has been investigated. These alkalis include sodium hydroxide, potassium hydroxide and eutectic mixture of both. The influences of the reaction temperature, zircon to alkalis ratio, fusion time and the stirring of the reactant on the fusion reaction have been evaluated. The obtained results favour the decomposition of zircon with the eutectic alkalis mixture by a decomposition efficiency of 96% obtained at 500 0C after one hour

274

Spectra of the f-d transitions of solutions of uranium(III) halides in organic solvents  

Energy Technology Data Exchange (ETDEWEB)

The absorption spectra of the f-d transitions of uranium(III) halides in tetrahydrofuran (THF), hexamethylphosphoric triamide (HMPA), acetonitrile, and water have been studied, and some energy characteristics of the uranium(III) ion in these solvents have been obtained on their basis. It has been shown that the crystal-field splitting parameter for uranium(III) in aqueous solutions is not dependent on the halide ion and that in HMFA and acetonitrile its value decreases along the series Cl/sup -/ > Br/sup -/ > I/sup -/, while in THF the reverse order for the influence of the halide ions is observed, i.e., the series Cl/sup -/ < Br/sup -/ < I/sup -/ is found. It has been established that decreases in the dielectric constant of the solvent and its solvating ability result in enhancement of the interaction of the U/sup 3 +/ ion with the halide ion.

Kamenskaya, A.N.; Kulyukhin, S.A.; Mikheev, N.B.

1987-07-01

275

Spectra of the f-d transitions of solutions of uranium(III) halides in organic solvents  

International Nuclear Information System (INIS)

The absorption spectra of the f-d transitions of uranium(III) halides in tetrahydrofuran (THF), hexamethylphosphoric triamide (HMPA), acetonitrile, and water have been studied, and some energy characteristics of the uranium(III) ion in these solvents have been obtained on their basis. It has been shown that the crystal-field splitting parameter for uranium(III) in aqueous solutions is not dependent on the halide ion and that in HMFA and acetonitrile its value decreases along the series Cl- > Br- > I-, while in THF the reverse order for the influence of the halide ions is observed, i.e., the series Cl- - - is found. It has been established that decreases in the dielectric constant of the solvent and its solvating ability result in enhancement of the interaction of the U3+ ion with the halide ion

276

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.)

277

Equilibrium coverage of halides on metal electrodes  

Science.gov (United States)

The adsorption of halides on Cu(111) and Pt(111) has been studied using periodic density functional theory calculations. The equilibrium coverage of the halides as a function of the electrode potential was determined using a thermodynamic approach in which the electrochemical environment is not explicitly taken into account. For all considered systems, halide coverages between 1/3 and 3/8 should be stable over a wide potential range. Although some quantitative discrepancies with experiment are obtained, the qualitative trends derived from the calculations are consistent with experimental observations. The reasons for the remaining discrepancies with the experiment are discussed.

Gossenberger, Florian; Roman, Tanglaw; Groß, Axel

2015-01-01

278

Reactive scattering of electronically excited alkali atoms with molecules  

International Nuclear Information System (INIS)

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

279

Crystals  

Science.gov (United States)

In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

Lawrence Hall of Science

2009-01-01

280

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

International Nuclear Information System (INIS)

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

281

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

282

Optical absorption of triplet molecular excitons in alkali cyanides  

International Nuclear Information System (INIS)

The optical absorption spectra of alkali cyanides in the UV region present a set of weak absorption bands which are identified as triplet a'3?+ molecular excitons. The nature of the molecular exciton transitions in the ionic-molecular crystals is discussed and the existence of an admisture between molecular exciton and charge transfer exciton states is suggested. (Author)

283

On the order-disorder phase transition of anilinium halides. 127I-NQR investigation of the anilinium iodides C6H5NH3+Idirectdifference, C6H5ND3+Idirectdifference; C6D5ND3+Idirectdifference. Dilatometric studies on anilinium bromide and anilinium iodide single crystals  

International Nuclear Information System (INIS)

127I-NQR measurements in the range 77?T/K 6H5NH3+Idirectdifference, C6H5ND3+Idirectdifference, C6D5NH3+Idirectdifference, and C6D5ND3+Idirectdifference. The compound undergoes a ferroelastic phase transition at 240.3 K (C6H5NH3+Idirectdifference). The transition temperature changes to 233.6 K (C6H5ND3+Idirectdifference) and to 233.4 K (C6D5ND3+Idirectdifference) by deuteration. The NQR parameters are thereby influenced too. At 293 K the -NH3+ group deuteration influences e2?zzQh-1 and ? much stronger than the ring deuteration, whereas at 77 K these effects are of comparable magnitude. - The thermal expansion coefficients were measured for C6H5NH3+Xdirectdifference, X=Br, I, from 120 K to 300 K by dilatometry and by X-ray diffraction. In C6H5NH3+Idirectdifference ?[010] increases and both, ?[100] and ?]001], decrease with increasing temperature. On hand of the known crystal structures the ferroelastic phase transition in the anilinium halides is discussed. The basic mechanism of the transition is the same for C6H5NH3+Idirectdifference and C6H5NH3+Brdirectdifference. Freezing in of the -NH3+ group hindered rotation is the main process governing the phase transition, but motions of the phenyl ring are of influence, too. (orig.)

284

Oxofluorovanadates (4) of alkali metals and ammonia  

International Nuclear Information System (INIS)

Interaction of VOF2 with fluorides of alkalimetals and ammonium over a wide range of molal ratios of the components was studied and the resulting complex fluorides of V(4) characterized. All the synthesized oxofluorovanadates were crystalline substances tinged with various shades of light blue and poorly soluble in water. The composition of the complexes obtained was established and they were studied roentgenographically. The crystalline structure and crystal lattice parameters were determined. The infrared spectra of compounds of the type of M2VOF4xH2O (M= an alkali metal and ammonium) were studied

285

Halide Ion Enhancement of Nitrate Ion Photolysis  

Science.gov (United States)

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

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

2009-12-01

286

Mass spectroscopic and matrix isolation studies on the ternary metal halides CsMCl3 (M = Pb, Cd, Co)  

International Nuclear Information System (INIS)

Mass spectrometric and matrix isolation infrared studies have been carried out on the vapor species present in the high temperature ternary halide systems Cs/Pb/Cl, Cs/Cd/cl, and Cs/Co/Cl, and for all three systems, both binary and ternary halide molecules are identified. In particular, the ternary species present in the Cs/Pb/Cl system is identified as molecular CsPbCl3, and on the basis of IR band intensities nd isotopic data, a C3v structure is proposed for this species. The high temperature vapors above the Cs/Cd/Cl and Cs/Co/Cl systems also contain ternary CsMCl3 species, but for these molecules, the vibrational data indicate planar C2v geometries involving bidentate coordination at the alkali metal

287

Secondary emission of negative ions and electrons resulting from electronic sputtering of cesium salts. Differences between halides and oxygenated salts  

Energy Technology Data Exchange (ETDEWEB)

Secondary ion emission of negative ions and electrons from alkali salts bombarded with high energy (9 MeV) Ar{sup +++} is discussed. Quite different features are observed according to the nature of the salt investigated (halide or oxygenated). In the case of cesium, the electron emission from halides is characterized by intense electron showers (several hundred electrons) with narrow distributions in intensity and orientation. Conversely, for oxygenated salts, these distributions are broader, much less intense (one order of magnitude), and the ion emission exhibits an dissymmetry, which has never been observed for inorganics. This last result is interpreted in terms of radiolysis of the oxygenated salt, a process well documented for gamma-ray irradiation, but not yet reported in secondary ion emission. (author) 17 refs.; 10 figs.

Allali, H.; Nsouli, B.; Thomas, J.P.

1993-04-01

288

Halide based MBE of crystalline metals and oxides  

Energy Technology Data Exchange (ETDEWEB)

A halide based growth chemistry has been demonstrated which can deliver a range of transition metals using low to moderate effusion cell temperatures (30-700 C) even for high melting point metals. Previously, growth with transition metal species required difficult to control electron beam or impurity inducing metal organic sources. Both crystalline oxide and metal films exhibiting excellent crystal quality are grown using this halide-based growth chemistry. Films are grown using a plasma assisted Molecular Beam Epitaxy (MBE) system with metal-chloride precursors. Crystalline niobium, cobalt, iron, and nickel were grown using this chemistry but the technology can be generalized to almost any metal for which a chloride precursor is available. Additionally, the oxides LiNbO{sub 3} and LiNbO{sub 2} were grown with films exhibiting X-ray diffraction (XRD) rocking curve full-widths at half maximum of 150 and 190 arcseconds respectively. LiNbO{sub 2} films demonstrate a memristive response due to the rapid movement of lithium in the layered crystal structure. The rapid movement of lithium ions in LiNbO{sub 2} memristors is characterized using impedance spectroscopy measurements. The impedance spectroscopy measurements suggest an ionic current of.1 mA for a small drive voltage of 5 mV AC or equivalently an ionic current density of {proportional_to}87 A/cm{sup 2}. This high ionic current density coupled with low charge transfer resistance of {proportional_to}16.5 {omega} and a high relaxation frequency (6.6 MHz) makes this single crystal material appealing for battery applications in addition to memristors. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Greenlee, Jordan D.; Calley, W. Laws; Henderson, Walter; Doolittle, W. Alan [Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, Georgia (United States)

2012-02-15

289

Modelling current transfer to cathodes in metal halide plasmas  

International Nuclear Information System (INIS)

This work is concerned with investigation of the main features of current transfer to cathodes under conditions characteristic of metal halide (MH) lamps. It is found that the presence of MHs in the gas phase results in a small decrease of the cathode surface temperature and of the near-cathode voltage drop in the diffuse mode of current transfer; the range of stability of the diffuse mode expands. Effects caused by a variation of the work function of the cathode surface owing to formation of a monolayer of alkali metal atoms on the surface are studied for particular cases where the monolayer is composed of sodium or caesium. It is found that the formation of the sodium monolayer affects the diffuse mode of current transfer only moderately and in the same direction that the presence of metal atoms in the gas phase affects it. Formation of the caesium monolayer produces a dramatic effect: the cathode surface temperature decreases very strongly, the diffuse-mode current-voltage characteristic becomes N-S-shaped

290

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

291

Aspects of crystal growth within carbon nanotubes  

OpenAIRE

The comparative crystallisation and HRTEM imaging properties of simple binary halides formed by the alkali iodides MI (M = Li, K, Na, Rb and Cs) within single walled carbon nanotubes (SWNTs) are described. The most common structure type observed within SWNTs is the rocksalt archetype, although CsI was observed to form both bcc and rocksalt structure types. In SWNTs forming in the 1.2-1.6 nm diameter range, all of the incorporated halides showed preferred orientation, with the (100) growth dir...

Sloan, J.; Kirkland, Ai; Hutchison, Jl; Green, Mlh

2003-01-01

292

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

Science.gov (United States)

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

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

1974-01-01

293

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

294

Dialkylzinc-mediated cross-coupling reactions of perfluoroalkyl and perfluoroaryl halides with aryl halides.  

Science.gov (United States)

A highly chemoselective perfluoroalkylation reaction of aromatic halides is reported. Thermally stable perfluoroalkylzinc reagents, generated by a rapid halogen-zinc exchange reaction between diorganozinc and perfluoroalkyl halide species, couple with a wide range of aryl halides in the presence of a copper catalyst, in moderate to high yields. Good stability of the perfluoroalkylzinc species was indicated by DFT calculation and the reagents were storable for at least three months under argon without loss of activity. This method is applicable to gram-scale synthesis, and its functional group tolerance compares favorably with reported protocols. PMID:25630706

Kato, Hisano; Hirano, Keiichi; Kurauchi, Daisuke; Toriumi, Naoyuki; Uchiyama, Masanobu

2015-03-01

295

Stability of V-type defects in Ca2+ and Tl+ potassium iodide crystals  

International Nuclear Information System (INIS)

In alkali halides, interstitial halide atoms are created under ionizing radiations at room temperature and their stabilization is known to play an important role in the coloration process. In alkali iodides such as KI, the coloration efficiency is known to be drastically increased by the addition of divalent cations. By means of Raman experiments, we describe the different stages of formation of V-type defects in the case of Ca+2 doped KI. By using traps like Tl+ cations, we show that the interstitial stabilization is different and does not lead to the formation of polyiodides as observed in KI:Ca+2. (author)

296

Crystal Growth Technology  

Science.gov (United States)

This volume deals with the technologies of crystal fabrication, of crystal machining, and of epilayer production and is the first book on industrial and scientific aspects of crystal and layer production. The major industrial crystals are treated: Si, GaAs, GaP, InP, CdTe, sapphire, oxide and halide scintillator crystals, crystals for optical, piezoelectric and microwave applications and more. Contains 29 contributions from leading crystal technologists covering the following topics: General aspects of crystal growth technology Silicon Compound semiconductors Oxides and halides Crystal machining Epitaxy and layer deposition Scientific and technological problems of production and machining of industrial crystals are discussed by top experts, most of them from the major growth industries and crystal growth centers. In addition, it will be useful for the users of crystals, for teachers and graduate students in materials sciences, in electronic and other functional materials, chemical and metallurgical engineering, micro-and optoelectronics including nanotechnology, mechanical engineering and precision-machining, microtechnology, and in solid-state sciences.

Scheel, Hans J.; Fukuda, Tsuguo

2004-06-01

297

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.)

298

Molten state and supercooling of lead halides.  

Czech Academy of Sciences Publication Activity Database

Ro?. 264, - (2004), s. 492-498. ISSN 0022-0248 R&D Projects: GA ?R GA203/00/1423; GA ?R GA202/03/0428 Institutional research plan: CEZ:AV0Z1010914 Keywords : melt supercooling * thermal history of the melt * halides Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.707, year: 2004

Nitsch, Karel; Cihlá?, Antonín; Rodová, Miroslava

2004-01-01

299

Breakdown processes in metal halide lamps  

Science.gov (United States)

Metal halide lamps typically have cold fills of tens to a few hundred Torr of a rare gas and the vapour from the dosing of a metal halide solid and mercury. Breakdown and starting of the lamp occurs following application of multi-kV pulses across electrodes separated by a few centimetres. Restarting of warm lamps is often problematic as the available voltage is insufficient to break down the higher pressure (>many atm) of metal halide vapour. In this paper, fundamental processes during breakdown in cold and warm, idealized metal halide lamps in mixtures of Ar and Hg are investigated using a two-dimensional fluid model for plasma transport. We find that the capacitances of the walls of the discharge tube and adjacent ground planes are important in determining the breakdown voltage and avalanche characteristics. The prompt capacitance represented by, for example, external trigger wires provides a larger E/N to sustain ionization early in the avalanche. This effect is lost as the walls charge and shield the plasma from the ground planes. More rapid breakdown occurs in slightly warm lamps having small vapour pressures of Hg due to the resulting Penning mixture. Warmer lamps, having larger mole fractions of Hg, have less efficient breakdown as the increase in momentum transfer of the electrons is not offset by the additional ionization sources of the Penning mixture.

Lay, Brian; Moss, Richard S.; Rauf, Shahid; Kushner, Mark J.

2003-02-01

300

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)

301

Superconductivity of alkali metal intercalated ZrSe/sub 2/  

Energy Technology Data Exchange (ETDEWEB)

Alkali metal intercalated ZrSe/sub 2/ (Asub(x)ZrSe/sub 2/) has been synthesized by the reaction of ZrSe/sub 2/ single crystals with n-butyllithium in hexane solution, or alkali metal (Na, K, Rb, Cs) in hexamethylphosphoric triamide solution. Semiconductive ZrSe/sub 2/ has been converted into a metallic substance by the alkali metal intercalation. Superconductivity has been found for Lisub(x)-, Nasub(x)-, Ksub(x)-, Rbsub(x)- and Cssub(x)ZrSe/sub 2/ (0 < x <= 1) below 1.7, 2.0, 2.1, 1.7, and 1.4 K, respectively. The angular dependence of the upper critical fields Hsub(c2) for Asub(x)ZrSe/sub 2/ is interpreted by the effective mass model. The Ginzburg-Landau coherence lengths perpendicular to the layer planes of the crystals at zero temperature are ten to twenty times larger than the layer repeat distances, showing a three dimensional character. Anisotropic superconductivity is discussed on the basis of the Fermi surface of Asub(x)ZrSe/sub 2/ whose electron number is determined by the charge transfer from alkali metal atoms to ZrSe/sub 2/.

Onuki, Y. (Saitama Institute of Technology, Fusaiji, Okabe, Saitama-ken (Japan)); Yamanaka, S. (Hiroshima Univ. (Japan). Faculty of Engineering); Inada, R.; Kido, M.; Tanuma, S. (Tokyo Univ. (Japan). Inst. for Solid State Physics)

1983-02-15

302

Superconductivity of alkali metal intercalated ZrSe2  

International Nuclear Information System (INIS)

Alkali metal intercalated ZrSe2 (Asub(x)ZrSe2) has been synthesized by the reaction of ZrSe2 single crystals with n-butyllithium in hexane solution, or alkali metal (Na, K, Rb, Cs) in hexamethylphosphoric triamide solution. Semiconductive ZrSe2 has been converted into a metallic substance by the alkali metal intercalation. Superconductivity has been found for Lisub(x)-, Nasub(x)-, Ksub(x)-, Rbsub(x)- and Cssub(x)ZrSe2 (0 2 is interpreted by the effective mass model. The Ginzburg-Landau coherence lengths perpendicular to the layer planes of the crystals at zero temperature are ten to twenty times larger than the layer repeat distances, showing a three dimensional character. Anisotropic superconductivity is discussed on the basis of the Fermi surface of Asub(x)ZrSe2 whose electron number is determined by the charge transfer from alkali metal atoms to ZrSe2. (Auth.)

303

Strengthening CsI crystals for optical applications  

International Nuclear Information System (INIS)

Cesium iodide (CsI) is a very useful optical material combining a low refractive index with broad spectral transparency. Unfortunately, the mechanical weakness of CsI crystals severely limits practical applicability of the material. Nearly all uses require mechanical strengthening. The strengthening treatment cannot, of course, degrade desirable single crystal optical properties. Previous work at Honeywell has involved strengthening of alkali halides having the rocksalt structure (KCl, NaCl, etc.). Processed materials have been strengthened by as much as an order of magnitude without measurable optical degradation. Direct application of these processing methods to the dissimilar structure of CsI is impossible due to the limited number of slip systems active in the material. This investigation was, therefore, concerned with development of CsI processing methods that would effectively strengthen the material without introducing cracks or other optically degrading defects. This paper describes successful uniaxial and plane strain processing methods. Detailed process parameters and strengthened CsI material properties are included

304

Upgrading platform using alkali metals  

Science.gov (United States)

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

305

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.)

306

Comparative first-principles study of structural and optical properties of alkali metal azides.  

Science.gov (United States)

A comparative first-principles study of the structural and optical properties of the alkali metal azides has been performed with density functional theory within the generalized gradient approximation. The crystal structures of the alkali azides compare well with experimental data. Their ionic character is manifested by the closeness of their internitrogen distances to the calculated N-N bond length for the free azide ion. An analysis of electronic structure, charge transfer, and bond order shows that the alkali azides are all wide-gap insulators and ionic compounds. The energy band and density of states for lithium azide and alpha-sodium azide are very similar, while these for potassium azide, alpha-rubidium azide, and alpha-cesium azide are alike, but some modifications are observed with the increment of alkali metals' electropositivity. These changes are closely related to the differences of the crystal structures. The general shapes of the real and imaginary parts of the dielectric function, adsorption coefficient, and electron energy-loss spectra are quite similar. The peaks originate from the electron transitions from the alkali metal s and p states to the conduction band. Our calculated optical properties for the alkali azides are found to be in good agreement with available experimental data. The absorption spectra of the alkali azides show a number of absorption peaks, which are believed to be associated with different exciton states, in the fundamental absorption region. In general, the electron energy-loss spectra have two plasma frequencies. PMID:16706439

Zhu, Weihua; Xiao, Jijun; Xiao, Heming

2006-05-25

307

Theoretical characterization of dihydrogen adducts with halide anions  

International Nuclear Information System (INIS)

The interaction between a hydrogen molecule and the halide anions F-, Cl-, Br-, and I- has been studied at different levels of theory and with different basis sets. The most stable configurations of the complexes have a linear geometry, while the t-shaped complexes are saddle points on the potential energy surface, opposite to what is observed for alkali cations. An electrostatic analysis conducted on the resulting adducts has highlighted the predominance of the electrostatic term in the complexation energy and, in particular, of the quadrupole- and dipole-polarizability dependent contributions. Another striking difference with respect to the positive ions, is the fact that although the binding energies have similar values (ranging between 25 and 3 kJ/mol for F- and I-, respectively), the vibrational shift of the ?-tildeH-H and in general the perturbation of the hydrogen molecule in complexes are much greater in the complexes with anions (??-tildeH-H ranges between -720 and -65 cm-1). Another difference with respect to the interaction with cations is a larger charge transfer from the anion to the hydrogen molecule. The ??-tilde is the result of the cooperative role of the electrostatics and of the charge transfer in the interaction. The correlation between binding energies and vibrational shift is far from linear, contrary to what is observed for cation complexes, it is observed for cation complexes, in accordance with the higher polarizability and dynamic polarizability of the molecule along the molecular axis. The observed correlation may be valuable in the interpretation of spectra and thermodynamic properties of adsorbed H2 in storage materials

308

Equilibrium and nonequilibrium molecular dynamics simulations of the thermal conductivity of molten alkali halides  

Science.gov (United States)

The thermal conductivity of molten NaCl and KCl was calculated through the Evans-Gillan nonequilibrium molecular dynamics (NEMD) algorithm and Green-Kubo equilibrium molecular dynamics (EMD) simulations. The EMD simulations were performed for a "binary" ionic mixture and the NEMD simulations assumed a pure system for reasons discussed in this work. The cross thermoelectric coefficient obtained from Green-Kubo EMD simulations is discussed in terms of the homogeneous thermoelectric power or Seebeck coefficient of these materials. The thermal conductivity obtained from NEMD simulations is found to be in very good agreement with that obtained through Green-Kubo EMD simulations for a binary ionic mixture. This result points to a possible cancellation between the neglected "partial enthalpy" contribution to the heat flux associated with the interdiffusion of one species through the other and that part of the thermal conductivity related to the coupled fluxes of charge and heat in "binary" ionic mixtures.

Galamba, N.; Nieto de Castro, C. A.; Ely, James F.

2007-05-01

309

X-ray induced precipitation of Eu2+ in the alkali halides  

International Nuclear Information System (INIS)

The stability of the europium second phase precipitates in NaCl, NaBr, KCl, and KBr under room temperature X-irradiation has been analyzed using the photoluminescence technique. The irradiation tends to destroy the pre-existing metastable precipitates creating complexes of a much simpler nature. In parallel with this destruction an enhanced europium precipitation into the stable dihalide phase EuX2 (X = Cl, Br) was found to occur. (author)

310

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.)

311

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

OpenAIRE

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 counte...

Druchok, M.; C?, Podlipnik; Vlachy, V.

2013-01-01

312

Scattering of electrons by alkali-halide molecules: LiBr and CsCl  

Energy Technology Data Exchange (ETDEWEB)

We have investigated small-angle electron scattering by highly polarmolecules. Recoil experiments are performed at 5 and 20 eV for electronsscattered by LiBr and CsCl, within the shadow of the unscattered molecularbeam. Low-angular-range scattering described by the Born approximation forrotating dipoles, combined with different theories for intermediate- andhigh-angle scattering, are compared with our results. Evaluated totalscattering cross sections as well as momentum-transfer and viscosity crosssections are given. A general two-dimensional analysis of the recoil experimentis presented.

Vuat/rsat; wkovic, L.; Zuo, M.; Shen, G. F.; Stumpf, B.; Bederson, B.

1989-07-01

313

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

314

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)

315

Ordering of alkali halide salts dissolved in bacteriophage Pf1 solutions: A nuclear magnetic resonance study  

Science.gov (United States)

The nuclear magnetic resonance (NMR) spectra of the I=3/2 monovalent ions 23Na, 35Cl, 39K, and 79Br for NaCl and KBr dissolved into filamentous bacteriophage Pf1 solutions display line splittings and shifts consistent with an interaction between the nuclear spin and the electric field gradient produced by the Pf1 particles. The average electric field gradient and thus the spectral splitting for ions in the void space between magnetically aligned Pf1 particles is modeled using a numerical solution to the Poisson-Boltzmann equation. An NMR titration experiment in a 57 mg/mL Pf1 solution is used to determine the background Na+ ion concentration in solution as 32 mM which compares well with the 31.1 mM negative surface charge on Pf1.

Vyas, S.; Hernandez, C. J.; Augustine, M. P.

2002-04-01

316

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

International Nuclear Information System (INIS)

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

317

IR and visible wavelength obscuration by pyrotechnically generated alkali-halide smokes  

Science.gov (United States)

In pursuit of an effective IR wavelength screen and an increased understanding of the particle formation mechanisms and resultant size distribution, this year's efforts focused on two primary objectives: (1) Through a series of chamber tests, assess the visible and IR wavelength extinction characteristics of four recently developed NWC pyrotechnics: LiC1 1, LM9, LM11 and LM12 and (2) Through a series of chamber tests conducted by Calspan with participants from NRL and NWC, investigate the smoke particle size distribution as functions of pyrotechnic and associated burn parameters.

Hanley, J. T.; Kile, J. N.; Wattle, B. J.; Mack, E. J.

1983-01-01

318

Thermodynamics of ion conductivity of alkali halides across a polystyrene-based titanium arsenate membrane  

International Nuclear Information System (INIS)

The electric conductance of ion across titanium arsenate membrane has been recorded. Aqueous solutions of KCl, NaCl and LiCl were used. The conductance values of titanium arsenate membrane have been found to increase with increase in concentrations as well as temperature (10-50 oC) in these cases. The conductance values of electrolytes follow the sequence for the cations: K+ > Na+ > Li+. Negative ?S values are considered to indicate formation of bond between the permeating species and the membrane material. The physico-chemical characterization of the hybrid material was established by XRD, TGA and simultaneous SEM studies.

319

Effects of alkali cations and halide anions on the DOPC lipid membrane.  

Czech Academy of Sciences Publication Activity Database

Ro?. 113, ?. 26 (2009), s. 7235-7243. ISSN 1089-5639 R&D Projects: GA MŠk LC512; GA ?R GA203/08/0114; GA ?R(CZ) GD203/05/H001 Grant ostatní: NSF(US) MCB-0615469 Institutional research plan: CEZ:AV0Z40550506; CEZ:AV0Z40400503 Keywords : DOPC membrane * ions * molecular dynamics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.899, year: 2009

Vácha, Robert; Siu, S. W. I.; Petrov, Michal; Böckmann, R. A.; Barucha-Kraszewska, Justyna; Jurkiewicz, Piotr; Hof, Martin; Berkowitz, M. L.; Jungwirth, Pavel

2009-01-01

320

75 FR 5544 - Energy Conservation Program: Energy Conservation Standards for Metal Halide Lamp Fixtures: Public...  

Science.gov (United States)

...Energy Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and Availability...conservation standards for certain metal halide lamp fixtures. This document announces...energy conservation standards for metal halide lamp fixtures and provide docket...

2010-02-03

321

76 FR 18127 - Energy Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and Availability of...  

Science.gov (United States)

...Energy Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and Availability...energy conservation standards for metal halide lamp fixtures (MHLFs); the analytical...appliance_standards/commercial/metal_halide_lamp_fixtures.html. DATES:...

2011-04-01

322

EVALUATION OF METHODS FOR THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER AND WASTE  

Science.gov (United States)

Various methods for the determination of total organic halides (TOX) in groundwater and in waste oil samples have been evaluated. Of three inorganic halide species generation approaches and three inorganic halide determinative techniques evaluated for groundwater analyses, one co...

323

10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.  

Science.gov (United States)

...false Definitions concerning metal halide lamp ballasts and fixtures. 431...COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide lamp ballasts and fixtures....

2010-01-01

324

40 CFR 721.10181 - Halide salt of an alkylamine (generic).  

Science.gov (United States)

...2010-07-01 2010-07-01 false Halide salt of an alkylamine (generic). ...Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). ...chemical substance identified generically as halide salt of an alkylamine (PMN...

2010-07-01

325

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-08-15

326

Lanthanide-halide based humidity indicators  

Science.gov (United States)

The present invention discloses a lanthanide-halide based humidity indicator and method of producing such indicator. The color of the present invention indicates the humidity of an atmosphere to which it is exposed. For example, impregnating an adsorbent support such as silica gel with an aqueous solution of the europium-containing reagent solution described herein, and dehydrating the support to dryness forms a substance with a yellow color. When this substance is exposed to a humid atmosphere the water vapor from the air is adsorbed into the coating on the pore surface of the silica gel. As the water content of the coating increases, the visual color of the coated silica gel changes from yellow to white. The color change is due to the water combining with the lanthanide-halide complex on the pores of the gel.

Beitz, James V. (Hinsdale, IL); Williams, Clayton W. (Chicago, IL)

2008-01-01

327

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

328

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

329

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

330

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

331

Cerium doped lanthanum halides: fast scintillators for medical imaging  

International Nuclear Information System (INIS)

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

332

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

333

Epitaxial growth of perfluoropentacene films with predefined molecular orientation: A route for single-crystal optical studies  

Science.gov (United States)

Using atomic-force microscopy and x-ray diffraction we show that perfluoropentacene (C22F14, PFP) forms long-range ordered, epitaxial films on KCl(100) and NaF(100) cleavage planes. On both substrates the films adopt the same crystalline bulk phase, but surprisingly exhibit quite different molecular orientations, being upright oriented on NaF and recumbent oriented on KCl. Accompanied thermal desorption spectroscopy measurements indicate the absence of a stabilized seed layer, like on metals, hence suggesting that in both cases the PFP films are stabilized by an electrostatic point-in-line relationship between the outermost fluorine atoms and the alkali cations of the alkali halide surfaces. Furthermore, the transparency of both substrates was utilized to perform detailed transmission UV/Vis spectroscopy and polarized optical microscopy measurements along well-defined crystallographic directions. From these data the orientation of transition dipole moments of the various optical excitations were experimentally determined and a directional anisotropic exciton coupling was observed, which is attributed to the asymmetric molecular packing motif within the (100) plane of the PFP crystal lattice.

Breuer, Tobias; Witte, Gregor

2011-04-01

334

Corrosion by the Alkali Metals  

International Nuclear Information System (INIS)

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

335

The association of ammonia with halide ions in the gas phase  

International Nuclear Information System (INIS)

The enthalpy changes, ?H0, and entropy changes, ?S0, for the gas-phase association of ammonia to Cl-, Br-, and I- have been measured using high pressure mass spectrometry. The -?H0 were determined to be 8.2, 7.7, and 7.4 kcal/mole (0.36, 0.33, and 0.32 eV) and the -?S0 were 15.4, 19.1, and 20.9 cal/K-mole, respectively, for 35Cl-, 81Br-, and I-. The -?H0 values are considerably smaller than those for the association of ammonia to alkali ions and also of water and sulfur dioxide to both halide and alkali ions. One explanation can be based on electrostatic considerations. The quadrupole moment of ammonia leads to a repulsive interaction (considerably greater than that of water) when the ion-dipole orientation is most favorable for a negative ion. Similarly, these opposing interactions may be responsible for the relatively little variation in the enthalpy change for ammonia association between Cl- and I-

336

Molybdocalixarene structure control via rim deprotonation. synthesis, characterization, and crystal structures of calix[4]arene Mo(VI) monooxo complexes and calix[4]arene alkali metal/Mo(VI) dioxo complexes.  

Science.gov (United States)

We report a series of calix[4]arene Mo(VI) dioxo complexes M2RC4MoO2 (M = alkali metal, R = H or Bu(t)) that were fully characterized by NMR, X-ray, IR, UV/vis, and elemental analysis. Molybdocalix[4]arene structures can be controlled via lower rim deprotonation, groups at para positions of calix[4]arene, and alkali metal counterions. Mono deprotonation at the lower rim leads to calix[4]arene Mo(VI) monooxo complexes RC4MoO (R = H, Bu(t), or allyl), and full deprotonation gives rise to calix[4]arene Mo(VI) dioxo complexes. Structural studies indicate that HC4 Mo(VI) dioxo complexes easily form polymeric structures via cation-pi interaction and coordination between different calixarene units. However, Bu(t)C4 Mo(VI) dioxo complexes tend to form dimers or tetramers due to steric hindrance of the tert-butyl groups at para positions in calixarene. The structures of the reduced side products A and C were determined by X-ray diffraction studies. The mechanism of RC4MoO formation from the reaction of calixarene monoanions with MoO2Cl2 appears to include the addition of a calixarene -OH group across a Mo=O bond. PMID:16676988

Liu, Lihua; Zakharov, Lev N; Golen, James A; Rheingold, Arnold L; Watson, William H; Hanna, Tracy A

2006-05-15

337

Synthesis and physicochemical study of tin hexafluorocomplexes with mixed alkali metal cations  

International Nuclear Information System (INIS)

From aqueous solutions tin hexafluorocomplexes with mixed cations of alkali metals of the composition NaMSnF6 (M = K, Rb, Cs), which are crystallized in rhombic crystal system, have been synthesized for the first time. Unit cell parameters of the substances are determined. The compounds synthesized are biaxial optically positive crystals. Their optical and refractometric constants are presented. In IR spectra of all fluorocomplexes synthesized splitting of valence vibration frequency (?3) for octahedral anion SnF62- is observed

338

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

Science.gov (United States)

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

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

2008-06-03

339

Induced amphotropic and thermotropic ionic liquid crystallinity in phosphonium halides: "lubrication" by hydroxyl groups.  

Science.gov (United States)

The influence of covalently attaching hydroxymethylene to the methyl groups of methyl-tri-n-alkylphosphonium halides (where the alkyl chains are decyl, tetradecyl, or octadecyl and the halide is chloride or bromide) or adding methanol as a solute to the salts on their solid, liquid-crystalline (smectic A2), and isotropic phases has been investigated using a variety of experimental techniques. These structural and compositional changes are found to induce liquid crystallinity in some cases and to enhance the temperature range and lower the onset temperature of the liquid-crystalline phases in some others. The results are interpreted in terms of the lengths of the three n-alkyl chains attached to the phosphorus cation, the nature of the halide anion, the influence of H-bonding interactions at the head group regions of the layered phases, and other solvent-solute interactions. The fact that at least 1 molar equiv of methanol must be added to effect complete (isothermal) conversion of a solid methyl-tri-n-alkylphosphonium salt to a liquid crystal demonstrates a direct and strong association between individual methanol molecules and the phosphonium salts. Possible applications of such systems are suggested. PMID:18278957

Ma, Kefeng; Somashekhar, B S; Gowda, G A Nagana; Khetrapal, C L; Weiss, Richard G

2008-03-18

340

A negative ion source for alkali ions  

OpenAIRE

An ion source is described which delivers negative alkali ions. With this source, which consists of a duoplasmatron and a charge exchange canal with alkali vapour, negative Li, Na and K ions are produced. The oven in which alkali metals are evaporated can reach temperatures up to 575°C.

Vermeer, A.; Zwol, N. A.

1980-01-01

341

Evaluation of Ce3+ and alkali metal ions Co-doped LiSrAlF6 crystalline scintillators  

International Nuclear Information System (INIS)

High scintillation efficiency of Eu-doped LiSrAlF6 (LiSAF) and LiCaAlF6 (LiCAF) codoped with alkali metal ions has been reported in our recent studies. Thus in this paper, we demonstrated the scintillation properties of 1% Ce-doped LiSAF crystals with 1% alkali metal ions co-doping to increase the light yield and understand the scintillation mechanism. The crystals showed intense emission band corresponding to the 5d-4f transition of Ce3+, and their light yields under thermal neutron excitation were higher than that of the Ce only doped crystal. Especially, the light yield of Ce–Na co-doped crystal exceeded about two times that of Ce only doped one. -- Highlights: ? Ce-doped and alkali metal co-doped LiSAF crystals were grown by ?-PD method. ? Alkali metal co-doped crystals showed higher light yield than Ce only doped crystal. ? Decay time of alkali metal co-doped LiSAF were longer than that of Ce only doped one

342

ACCUMULATION OF ALKALIS IN THE RECYCLING FILTRATE OF THE PHOSPHOGYPSUM PULPS  

Directory of Open Access Journals (Sweden)

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

ANTANAS KAZILIUNAS

2011-12-01

343

Growth and characterization of polycrystalline lanthanide halide scintillators  

International Nuclear Information System (INIS)

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

344

Alkali metal and rare earth element evolution of rock-forming minerals from the Gatumba area pegmatites (Rwanda): Quantitative assessment of crystal-melt fractionation in the regional zonation of pegmatite groups  

Science.gov (United States)

This study presents a general model for the evaluation of Rayleigh fractional crystallisation as the principal differentiation mechanism in the formation of regionally zoned common and rare-element pegmatites. The magmatic evolution of these systems from a granitic source is reconstructed by means of alkali element and rare earth element (REE) analyses of rock-forming minerals (feldspars, micas and tourmaline), which represent a whole sequence of regional pegmatite zonation. The Gatumba pegmatite field (Rwanda, Central Africa) is chosen as case study area because of its well-developed regional zonation sequence. The pegmatites are spatially and temporally related to peraluminous G4-granites (986 ± 10 Ma). The regional zonation is developed around a G4-granite and the proximal pegmatites grade outwardly into biotite, two-mica and muscovite pegmatites. Rare-element (Nb-Ta-Sn) pegmatites occur most distal from the granite.

Hulsbosch, Niels; Hertogen, Jan; Dewaele, Stijn; André, Luc; Muchez, Philippe

2014-05-01

345

SYNTHESIS AND COORDINATION CHEMISTRY OF NEW SCHIFF-BASE BIS(CROWN ETHER) LIGANDS CONTAINING RECOGNITION SITES FOR ALKALI-METAL AND TRANSITION-METAL GUEST CATIONS - CRYSTAL-STRUCTURE OF A COPPER(I)-POTASSIUM COMPLEX  

OpenAIRE

New Schiff-base bis(crown ether) ligands L1-L5 containing recognition sites for alkali- and transition-metal guest cations have been prepared by the condensation of two equivalents of 15-formyl-2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecine with diamines H2NXNH2 (X = [CH2]2S[CH2]2, [CH2]2S[CH2]2S[CH2] 2, [CH2]2S[CH2]3S[CH2] 2, [CH2]3S[CH2]2S[CH2] 3 or [CH2]2NH[CH2]2). The sodium cation forms 2:1 Na+:L complexes, whereas the larger potassium cation produces 1: 1 intramol...

Beer, P.; Crane, C.; Drew, M.

1991-01-01

346

Halide ordering in reduced mixed halides, chlorides/iodides, of zirconium: syntheses and structures of Cs2[(Zr6B)(Cl,I)15] cluster compounds.  

Science.gov (United States)

A series of high-temperature solid state chemical reactions was carried out in the quasi-quarternary mixed-halide Cs-Zr-B-(Cl,I) system with stoichiometries aiming for zirconium cluster phases of the Cs(2)[(Zr(6)B)X(15)] type (X = mixture of Cl + I). In the phase range from ~ Cs(2)[(Zr(6)B)Cl(13)I(2)] to Cs(2)[(Zr(6)B)Cl(3)I(12)] the structures of the obtained cluster phases are derived from the orthorhombic CsK[(Zr(6)B)Cl(15)]. At a composition of Cs(2)[(Zr(6)B)Cl(~10) I(~4)] a lower symmetry, monoclinic derivative has been found. X-ray diffraction data of single crystals of three compounds of this phase system were collected, orthorhombic Cs(2)[(Zr(6)B)Cl(12.99(3))I(2.01)] (1), (Pmma, Z = 4, a = 19.304(4), b = 14.617(3), c = 9.921(2) Å, R1/wR2 = 0.0444/0.0886), monoclinic Cs(2)[(Zr(6)B)Cl(10.63(3))I(4.37)] (2), (P2/c, Z = 4, a = 14.9502(3), b = 10.0098(2), c = 19.8798(4) Å, ? = 90.977(1) R1/wR2 = 0.0460/0.1182), and orthorhombic Cs(2)[(Zr(6)B)Cl(8.79(4))I(6.21)] (3) (Pmma, Z = 4, a = 20.0534(4), b = 15.1488(3), c = 10.1739(2) Å, R1/wR2 = 0.0494/0.1123). These compounds are obtained as single phase products. As in other known mixed-halide systems halide ordering is observed, such that the different halide sites have different amounts of Cl and I. With increasing amount of iodide, relative to Cl, the cluster-interconnecting halide sites are more and more occupied by I. For the first time it is observed for 3 that a halide site, which forms a linear bridge between two neighboring Zr(6)B cluster units (so far known examples are solely occupied by Cl), is statistically mixed occupied by Cl and I. Nevertheless, both halide types achieve acceptable bonding situations (bond lengths) because the I atoms are moved out of the linearly bridging position, thereby achieving longer Zr-X distances than the Cl atom, which remains linearly bridging. The generally interesting aspect of this paper is that in the very complex systems the atoms of the mixed occupied sites as well as those of the cation sites arrange with respect to the atomic environment, such that all of them have optimized bonding situations. PMID:22998521

Pigorsch, Arne; Köckerling, Martin

2012-10-15

347

Water Content of Lunar Alkali Fedlspar  

Science.gov (United States)

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

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

2016-01-01

348

Water Content of Lunar Alkali Fedlspar  

Science.gov (United States)

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

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

2016-01-01

349

Structural Characterization of Methanol Substituted Lanthanum Halides  

OpenAIRE

The first study into the alcohol solvation of lanthanum halide [LaX3] derivatives as a means to lower the processing temperature for the production of the LaBr3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(µ-Br)(H2O)7](Br)2}2 (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H2O)7(MeOH)2](Br)3 (2) compound was isolated where the La metal center retains its original 9-coordination throug...

Boyle, Timothy J.; Ottley, Leigh Anna M.; Alam, Todd M.; Rodriguez, Mark A.; Yang, Pin; Mcintyre, Sarah K.

2010-01-01

350

Transient photocurrent measurements in alkali chalcogenide ternary compound semiconductors  

Science.gov (United States)

The charge transport properties of two alkali metal chalcogenide, semiconductor ternary compounds Cs2Cd3Te4 and Cs2Hg6S7, having potential as efficient high-energy radiation detectors, were investigated. A key property that determines the detector performance is the minority carrier lifetime, which was determined by measurement of photocurrent transients using pulsed laser excitation. The alkali metal chalcogenide semiconductor crystals were grown by a modified Bridgman method. The Cs2Cd3Te4 compound has a minority lifetime of 2.45 µs at 295 K, which is comparable to that of cadmium zinc telluride (CZT). The Cs2Hg6S7 showed charge trapping with decay times of 120 µs. The excellent charge transport properties of Cs2Cd3Te4 indicate that this ternary compound semiconductor should be well suited for gamma radiation detector devices that operate at room temperature.

Liu, Z.; Peters, J. A.; Li, H.; Kanatzidis, M. G.; Wessels, B. W.

2013-01-01

351

Effect of uniaxial stress on luminescence of undoped and thallium-doped KI and RbI crystals  

Energy Technology Data Exchange (ETDEWEB)

The effect of uniaxial stress applied at various temperatures along the (100) crystal axis on the self-trapped exciton (STE) and impurity-induced luminescence has been studied for pure and Tl{sup +}, Na{sup +}-containing KI and RbI crystals under excitation in the exciton and band-to-band absorption region as well as under x-ray excitation. An increase of the intrinsic/extrinsic emission intensity ratios has been observed and explained by the stress-induced (i) enhancement of the self-trapping efficiency of electronic excitations and the decrease of their migration length and (ii) suppression of the nonradiative decay of excitons into stable radiation defects. A strong influence of the uniaxial stress on the structure of the STE adiabatic potential energy surface has been detected in RbI which is evident in the stress-induced increase of the E{sub x}/{pi} and, particularly, of the {sigma}/E{sub x} emission intensity ratios. This effect has been connected with the increase in the energy barriers between various STE configurations in the compressed crystal lattice. The dependence of the on-centre STE emission intensity in alkali halides on the distance between the nearest lattice anions and on their size has been discussed. (author)

Babin, V. [Institute of Physics, University of Tartu, Riia Street 142, 51014 Tartu (Estonia); Tartu University, Taehe Street 4, EE2400 Tartu (Estonia); Bekeshev, A.; Shunkeev, K. [Aktybinsk University, Aktybinsk (Kazakhstan); Elango, A.; Kalder, K.; Maaroos, A.; Vasil' chenko, E.; Zazubovich, S. [Institute of Physics, University of Tartu, Riia Street 142, 51014 Tartu (Estonia)

1999-03-15

352

Performance of Alkali Activated Slag with Various Alkali Activators  

OpenAIRE

The need to meet a sustainable development is now an important challenge to the cement industry. The production of OPC is responsible for about 7% of the world?s CO2 emission, a major contributor to the green house effect which is implicated in global warming and climatic changes, lead to the search for more environmentally viable alternative to cement. One of those alternative material is alkali activated slag (AAS) where ground granulated blast furnace slag is used not as partial replacem...

Rajesh, D. V. S. P.; Narender Reddy, A.; Venkata Tilak, U.; Raghavendra, M.

2013-01-01

353

Two dimensional condensation of argon adsorbed on lamellar halides  

International Nuclear Information System (INIS)

Lamellar halides such as NiCl2, FeCl2, NiBr2, MnBr2, MgBr2, CdBr2, CoI2, FeI2, MnI2, CaI2 and PbI2 were sublimed in a rapid stream of dry nitrogen. The adsorption of argon on such materials shows stepped isotherms which reveal two dimensional condensations. From sets of isotherms the Helmholtz free energy, the internal energy and the entropy of the successive layers are determined. From the entropy of the first layer the role of the potential relief of the adsorbent surface on the structure of the adsorbed layer may be determined while the Helmholtz free energy reveals how the ionic character of the adsorbent governs the attractive force of adsorption. The study of the second third and fourth layers shows that their growth follows quite a different behaviour depending on whether the Van der Waals diameter of argon is greater or smaller than the distance between adjacent anions on the crystal surface. A proposition is made to account for the difference in the critical temperatures of the first and second dense layers in terms of the vibrationnal state of their respective substrate. The occurence for the maximum critical temperature observed of corresponding to a triangular layer 3% more expanded than the (111) plane of solid argon is discussed

354

Moessbauer spectroscopy study of 57Fe implanted in simple ionic crystals  

International Nuclear Information System (INIS)

Conversion electron Moessbauer spectroscopy is used to study the hyperfine interactions of 57Fe nuclei implanted in a series of alkali halides crystals: LiF, LiI, NaF, NaCl, KF, KCl, KBr, KI and RbCl. Iron ions Fe+ were implanted at an energy of 70 keV and a dose of 1016/cm2. Implantations and measurements of Moessbauer spectra were performed at room temperature. The Moessbauer spectra obtained present either well-resolved symmetric quadrupole doublets in LiI, NaCl, KBr, KI and RbCl or unresolved broad structures in NaF and KF. In all implanted crystals iron was found mostly in Fe3+ state, with the exception of LiF and KCl in which a significant fraction of Fe2+ was also detected. In order to explain the electric field gradients at iron nuclei it was assumed that Fe3+ ions are located at cationic sites and are associated with two vacancies (linear and planar V--Fe3+-V- complexes). Extensive calculations of the electric field gradients were carried out including dipolar polarizability of anions. A fairly good agreement between experimental and theoretical quadrupole splittings has been achieved. (orig.)

355

Aqueous microsolvation of mercury halide species.  

Science.gov (United States)

The effects of aqueous solvation on the thermochemistry of reactions between mercury and small halogen molecules has been investigated by the microsolvation approach using ab initio and density functional theory (DFT) calculations. The structures, vibrational frequencies, and binding energies of 1, 2, and 3 water molecules with mercury-halide (HgBr2, HgBrCl, HgCl2, HgBr, and HgCl) and related mercury and halogen species (Br2, BrCl, Cl2, Cl, Hg, and Br) have been computed with second order Møller-Plesset perturbation theory (MP2) and the B3LYP density functional method. Accurate incremental water binding energies have been obtained at the complete basis set (CBS) limit using sequences of correlation consistent basis sets, including higher order correlation effects estimated from coupled cluster calculations. The resulting energetics were used to calculate the influence of water molecules on the thermochemistry of a number of reactions between mercury and small halogen-containing molecules. In general, the presence of water favors the formation of oxidized mercury halide species. PMID:17595065

Shepler, Benjamin C; Wright, Ashby D; Balabanov, Nikolai B; Peterson, Kirk A

2007-11-01

356

Electronic and structural ground state of heavy alkali metals at high pressure  

Science.gov (United States)

Alkali metals display unexpected properties at high pressure, including emergence of low-symmetry crystal structures, which appear to occur due to enhanced electronic correlations among the otherwise nearly free conduction electrons. We investigate the high-pressure electronic and structural ground state of K, Rb, and Cs using x-ray absorption spectroscopy and x-ray diffraction measurements together with a b i n i t i o theoretical calculations. The sequence of phase transitions under pressure observed at low temperature is similar in all three heavy alkalis except for the absence of the o C 84 phase in Cs. Both the experimental and theoretical results point to pressure-enhanced localization of the valence electrons characterized by pseudogap formation near the Fermi level and strong s p d hybridization. Although the crystal structures predicted to host magnetic order in K are not observed, the localization process appears to drive these alkalis closer to a strongly correlated electron state.

Fabbris, G.; Lim, J.; Veiga, L. S. I.; Haskel, D.; Schilling, J. S.

2015-02-01

357

On-line alkali monitoring - Part 1  

International Nuclear Information System (INIS)

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

358

Barium halide nanocrystals in fluorozirconate based glass ceramics for scintillation application  

Energy Technology Data Exchange (ETDEWEB)

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

Selling, J.

2007-07-01

359

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 an iridium catalyst.

Andrew Tigchelaar

2012-10-01

360

Performance of Alkali Activated Slag with Various Alkali Activators  

Directory of Open Access Journals (Sweden)

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

D.V.S.P.RAJESH

2013-02-01

361

Investigation regarding the role of chloride in organic-inorganic halide perovskites obtained from chloride containing precursors.  

Science.gov (United States)

As the photovoltaic performance of a device is strongly influenced by the morphology of perovskite, achieving precise control over the crystal formation of organic-inorganic halide perovskites synthesized in the ambience of chloride ions has garnered much attention. Although the resulting morphology dictates the performance of the device considerably, the understanding of the role of chloride ions has been scant. To unravel this mystery, we investigated three different organic-inorganic halide perovskite materials grown from the chloride-containing precursors under different but optimized conditions. Despite the presence of chloride ions in the reaction mixture, scanning transmission electron microscopy- energy dispersive spectroscopy (STEM-EDS) reveals that the CH3NH3PbI3 perovskites formed are chloride-free. Moreover bright field transmission electron microscopy indicates that chloride ions effect the growth of the CH3NH3PbI3. PMID:25392941

Dar, M Ibrahim; Arora, Neha; Gao, Peng; Ahmad, Shahzada; Grätzel, Michael; Nazeeruddin, Mohammad Khaja

2014-12-10

362

Novel niobium and tantalum fluoro complexes with mixed alkali metal cations: synthesis and characterization  

International Nuclear Information System (INIS)

Fluorocomplexes of niobium and tantalum with mixed alkali metal cations of the compositions NaMNb(Ta)F7 and NaMNbOF5 (M K, Rb, Cs), crystallizing in rhombic crystal system have been synthesized for the first time. During NaRbNbF7 recrystallization from water a new compound of the composition NaRbNbF7, crystallizing in monoclinic crystal system has been prepared. Unit cell parameters of the compounds have been defined. IR absorption spectra of the synthesized fluorocomplexes in the range of 4000-80 cm-1 have been measured and characterized

363

Novel Silver Cobaltacarborane Complexes with a Linearly Bridging Halide  

International Nuclear Information System (INIS)

The structural versatility of halides mainly originates from their coordinating abilities of adopting a bridging bond between two or more metal atoms, as well as a terminal bond. Moreover, a halide bridging bond angle is so flexible that thermodynamic stability can be endowed with proper geometry, which conceptually varies from acute to right, obtuse, and linear. In spite of innumerable reports on molecular metal halides, examples of the linearly bridging fashion are very scarce. The reason for the rarity of the linear M. X. M arrangement can be easily explained by the VSEPR (Valence Shell Electron Pair Repulsion) concept. The linear M. X. M formation has only been achieved by adopting a macrocyclic chelate ligand, which is structurally demanding, so that the VSEPR repulsions among lone-pair electrons on the halide atom could be overcome

364

Novel Silver Cobaltacarborane Complexes with a Linearly Bridging Halide  

Energy Technology Data Exchange (ETDEWEB)

The structural versatility of halides mainly originates from their coordinating abilities of adopting a bridging bond between two or more metal atoms, as well as a terminal bond. Moreover, a halide bridging bond angle is so flexible that thermodynamic stability can be endowed with proper geometry, which conceptually varies from acute to right, obtuse, and linear. In spite of innumerable reports on molecular metal halides, examples of the linearly bridging fashion are very scarce. The reason for the rarity of the linear M. X. M arrangement can be easily explained by the VSEPR (Valence Shell Electron Pair Repulsion) concept. The linear M. X. M formation has only been achieved by adopting a macrocyclic chelate ligand, which is structurally demanding, so that the VSEPR repulsions among lone-pair electrons on the halide atom could be overcome.

Park, Hyun Seo; Bae, Hye Jin; Do, Youngkyu [KAIST, Daejeon (Korea, Republic of); Park, Youngwhan [LG Chem/Research Park, Daejeon (Korea, Republic of); Go, Min Jeong; Lee, Junseong [Chonnam National Univ., Gwangju (Korea, Republic of)

2013-10-15

365

Palladium-catalyzed carboxylative coupling of allylstannanes and allyl halides  

Energy Technology Data Exchange (ETDEWEB)

A three-component carboxylative coupling between allyl halides, allylstannanes, and CO{sub 2} to produce allyl esters is catalyzed by Pd and Pt phosphine complexes. Tentative mechanistic pathways for the catalytic reaction are proposed.

Franks, R.J.; Nicholas, K.M.

2000-04-17

366

Shape-controlled synthesis of organolead halide perovskite nanocrystals and their tunable optical absorption  

Science.gov (United States)

Hybrid organolead halide perovskites (CH3NH3PbI3) with polymorphic structures have been successfully synthesized by controlling their solubility in solvents with different polarities. Crystal formation stages of the perovskites have been demonstrated for the first time. Shape changes of such perovskites are accompanied by transition in their crystal structures and variation of optical properties. Herein, a new trigonal phase for CH3NH3PbI3 has been observed with a rod-like morphology. Photoemission study indicates a significant red shift in the perovskite nanoparticles, compared to that of the rod-like nanocrystals. This solvent-controlled formation of polymorphic phases provide an additional approach for controlling the optical properties of CH3NH3PbI3 for various optoelectronic applications.

Chen, Zhenhua; Li, Hui; Tang, Yongbing; Huang, Xing; Ho, Derek; Lee, Chun-Sing

2014-03-01

367

Recent advances in new holographic silver halide materials  

OpenAIRE

Photographic emulsions are still one of the most widely used recording materials, due to the high energetic and spectral sensitivity and ease of processing. In order to obtain holograms of high quality on photographic emulsions, the different chemical procedures applied to the emulsions must be optimized. In this work we study two particular procedures, silver halide sensitized gelatin and fixation-free rehalogenating bleaching applied to two new commercial silver halide emulsions: the BB-64...

Neipp Lo?pez, Cristian; Pascual Villalobos, Inmaculada; Bele?ndez Va?zquez, Augusto

2000-01-01

368

BEAM EXPOSURE DEPENDENCE AND MECHANISMS OF PHOTON-STIMULATED DESORPTION FROM ALKALI FLUORIDES  

Energy Technology Data Exchange (ETDEWEB)

Photon-stimulated desorption experiments were performed on the (001) face of LiF for photon energies near the F(2s) and Li(ls) edges (from 37 to 72 eV). There are structures in the F{sup +} yield above the F(2s) edge which are absent in the Li{sup +} spectrum, differences in detail in the Li{sup +} and F{sup +} yields near the Li(1s) edge, and considerable broadening of the desorption yields as compared to the bulk photoabsorption spectrum. The first observation of a strong x-ray, and visible, beam exposure dependence of ion yields from LiF and NaF is also presented. These results are discussed in terms of electronic and defect properties of alkali halides.

Parks, C.C.; Shirley, D.A.; Loubriel, G.

1983-11-01

369

Alkali burns from wet cement.  

OpenAIRE

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

Peters, W. J.

1984-01-01

370

Genetic control of methyl halide production in Arabidopsis.  

Science.gov (United States)

Methyl chloride (CH(3)Cl) and methyl bromide (CH(3)Br) are the primary carriers of natural chlorine and bromine, respectively, to the stratosphere, where they catalyze the destruction of ozone, whereas methyl iodide (CH(3)I) influences aerosol formation and ozone loss in the boundary layer. CH(3)Br is also an agricultural pesticide whose use is regulated by international agreement. Despite the economic and environmental importance of these methyl halides, their natural sources and biological production mechanisms are poorly understood. Besides CH(3)Br fumigation, important sources include oceans, biomass burning, tropical plants, salt marshes, and certain crops and fungi. Here, we demonstrate that the model plant Arabidopsis thaliana produces and emits methyl halides and that the enzyme primarily responsible for the production is encoded by the HARMLESS TO OZONE LAYER (HOL) gene. The encoded protein belongs to a group of methyltransferases capable of catalyzing the S-adenosyl-L-methionine (SAM)-dependent methylation of chloride (Cl(-)), bromide (Br(-)), and iodide (I(-)) to produce methyl halides. In mutant plants with the HOL gene disrupted, methyl halide production is largely eliminated. A phylogenetic analysis with the HOL gene suggests that the ability to produce methyl halides is widespread among vascular plants. This approach provides a genetic basis for understanding and predicting patterns of methyl halide production by plants. PMID:14561407

Rhew, Robert C; Østergaard, Lars; Saltzman, Eric S; Yanofsky, Martin F

2003-10-14

371

10 CFR 431.324 - Uniform test method for the measurement of energy efficiency of metal halide ballasts.  

Science.gov (United States)

...measurement of energy efficiency of metal halide ballasts. 431.324 Section 431...COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures Test Procedures...measurement of energy efficiency of metal halide ballasts. (a) Scope. This...

2010-01-01

372

Method for preparation of alkali metal fluorotantalates  

International Nuclear Information System (INIS)

A method permitting to simplify preparation of alkali metal fluorotantalates is suggested. Mixture comprising tantalum (5) oxide, ammonium hydrogendifluoride and alkali metal fluoride at the ratio of 1:10:X respectively (X=2, 4, 6) is used in this case. The process takes place in the air at 400-800 deg C up to he evolution of ammonium fluoride vapour is completed

373

Process for the disposal of alkali metals  

International Nuclear Information System (INIS)

Large quantities of alkali metals may be safely reacted for ultimate disposal by contact with a hot concentrated caustic solution. The alkali metals react with water in the caustic solution in a controlled reaction while steam dilutes the hydrogen formed by the reaction to a safe level. 6 claims

374

Isothermal equation of state of a lithium fluoride single crystal  

Energy Technology Data Exchange (ETDEWEB)

An isothermal equation of state of a LiF single crystal was determined from length change measurements of the specimen as a function of hydrostatic pressure up to approximately 7 kbars at 28 to 41/sup 0/C. The length change was measured with an accuracy of approximately 500 A by using a Fabry Perot type He--Ne laser interferometer for a 1-m long specimen at temperatures constant to less than 0.002/sup 0/C. Several two- and three-parameter equations of state were used in analyzing the measured pressure-volume data. The computer fit for each equation of state determines not only the value of its parameters but also the standard deviations associated with them and one dependent variable, either pressure or volume. With the parameters determined, the equations of state are extrapolated to approximately 5 megabars in order to see discrepancies. Using the Born model of ionic solids, two equations of state were derived both from a power law potential and from an exponential form for the repulsive energy of alkali metal halides and used to fit the pressure-volume data of a LiF single crystal. They are also extrapolated to approximately 5 megabars. The Birch's two-parameter equation and the Grover, Getting, and Kennedy equation are indistinguishable from the two equations of state derived from the Born model for pressures approximately equal to or less than 800 kbars within +-20 kbars. The above four equations of state also fit closely the Pagannone and Drickamer static compression data, the Christian shock wave data, and the Kormer et al. shock wave data. The isothermal bulk modulus and its first pressure derivative at atmospheric pressure and 28.83/sup 0/C are 664.5 +- 0.5 kbars and 5.40 +- 0.18, respectively, in close agreement with those values ultrasonically measured by R. A. Miller and C. S. Smith. (auth)

Kim, K.Y.

1975-01-01

375

Carbon and proton shielding tensors in methyl halides.  

Science.gov (United States)

The series of methyl halides, CH(3)X (X = F, Cl, Br, and I), is prototypic for demonstrating the s.c. normal halogen dependence of light-atom nuclear magnetic resonance shielding constants in the presence of halogen atoms of varying electronegativity. We report a systematic experimental and first-principles theoretical study of the (13)C and (1)H shielding tensors in this series. The experimental shielding constants were obtained from gas-phase NMR experiments and the anisotropies were determined using liquid crystal NMR spectroscopy. After taking into account rovibrational effects and solute-solvent interactions, this provided the currently best experimental estimates for the full shielding tensors. Quantum chemical calculations were carried out at ab initio and density functional theory levels, involving relativistic corrections taken into account at the leading-order Breit-Pauli perturbation level. Anharmonic and harmonic vibrational corrections were performed. The main trends of the shielding constants and anisotropies of the nearby light (13)C and (1)H nuclei as functions of the halogen mass, were confirmed to be mainly due to relativistic spin-orbit effects. For carbon, also the scalar relativistic effects are important for quantitative results. Thermal averaging at 300 K decreases the magnitude of all the parameters but exhibits partial cancellation between the nonrelativistic and smaller relativistic rovibrational averages. For the shielding anisotropy, the relativistic terms add to the negative rovibrational effect. Overall, the current experimental and theoretical results are in excellent agreement for all the shielding parameters, setting a standard for further investigations of normal halogen dependence. PMID:20200746

Kantola, Anu M; Lantto, Perttu; Vaara, Juha; Jokisaari, Jukka

2010-03-20

376

Elaboration of phosphate ceramics as a safe form for halide salt waste immobilization of `dry` fuel reprocessing  

Energy Technology Data Exchange (ETDEWEB)

The conception of high level radwaste immobilization from M{sup 1}-containing molten salts and their solid forms into NZP-like structure phosphate ceramics are considered. The crystal-chemical principle on radionuclide incorporation into this structure is described. The prepared NZP ceramics was tested and it was shown that they had stability to action of such factors as temperature (up to 1200-1600degC), pressure (up to 500 MPa), radiation ({gamma}, up to 5{center_dot}10{sup 8} Gy), water solutions (up to 400degC, 60 MPa). Their structure is able to contain alkali elements up to 30-40%. Such monophase phosphate compositions may be formed at process of alkali chloride wastes solidification. The reactions of alkali chlorides, radionuclides, with phosphates are taken up here. (author)

Orlova, A.I.; Petkov, V.I.; Egorkova, O.V.; Kurazhkovskaya, V.S.; Kemenov, D.V. [Nizhny Novgorod State Univ. Chemical Dept., Nizhny Novgorod (Russian Federation); Skiba, O.V.

1997-12-31

377

Elaboration of phosphate ceramics as a safe form for halide salt waste immobilization of 'dry' fuel reprocessing  

International Nuclear Information System (INIS)

The conception of high level radwaste immobilization from M1-containing molten salts and their solid forms into NZP-like structure phosphate ceramics are considered. The crystal-chemical principle on radionuclide incorporation into this structure is described. The prepared NZP ceramics was tested and it was shown that they had stability to action of such factors as temperature (up to 1200-1600degC), pressure (up to 500 MPa), radiation (?, up to 5·108 Gy), water solutions (up to 400degC, 60 MPa). Their structure is able to contain alkali elements up to 30-40%. Such monophase phosphate compositions may be formed at process of alkali chloride wastes solidification. The reactions of alkali chlorides, radionuclides, with phosphates are taken up here. (author)

378

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

International Nuclear Information System (INIS)

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

379

Evidence of Production of Neutral Cl35 Atoms by the Cl35 (n, p)S35 Process in Alkali Metal Chlorides  

International Nuclear Information System (INIS)

A number of investigations reported in the literature have shown that S35 produced by the Cl35 (n, p)S35 process in neutron-irradiated alkali metal halides may be separated as S= , SO=3 and SO=4 after the irradiated crystals are dissolved in aqueous solutions of the appropriate carriers. The relative amounts of the three chemical forms depend on the purity of the sample and the conditions of irradiation and analysis. Attempts to identify neutral S35 atoms among the products of the neutron irradiation have been limited by the fact that elemental sulphur is too insoluble to use as a carrier in aqueous solution and by the exchange and adsorption processes which interfere when heterogeneous extraction processes are used. However, we have observed chemical evidence for an S35 species with properties which might be expected for neutral monatomic sulphur. When vacuum-sublimed, neutron-irradiated KCl is dissolved in degassed 0.3N aqueous NaOH containing S=, SO=3 and SO=4 , analysis for the three species typically shows 90% of the S35 activity as S=, 7% as SO=3 and 3% as SO=4 . When an identical experiment is done in which the carriers are added to the 0.3N NaOH solution after adding the KCl the typical S35 yields are 30% S=, 30% SO3 and 40% SO=4. Thus some 60% of the S35 species found in the S=3 fraction when the KCl is dissolved in the presence of carriers is found as SO=4 and SO=3 when the carriers are added after dissolution of the KCl. Since monatomic sulphur is thermodynamically unstable in H2O with respect to oxidation (?F = -5900 kcal/mole for S + 4H2O ? 3H2O ? 3H2 + H2SO4), and since it would also be expected to exchange readily with S= carrier these results suggest that some 60% of the S35 may be present in the irradiated KCl crystals as neutral monatomic S. Similar evidence for neutral S35 atoms has been obtained from neutron-irradiated crystals of NaCl, RbCl and CsCl. The effects of S= carrier concentration at the time of dissolution and of gamma irradiation administered before, after and during neutron irradiation have been investigated. (author)

380

Water Content of Lunar Alkali Fedlspar  

Science.gov (United States)

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

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

2016-01-01

381

Water Content of Lunar Alkali Fedlspar  

Science.gov (United States)

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

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

2016-01-01

382

Effect of alkali addition on DC conductivity and thermal properties of vanadium-bismo-borate glasses  

Energy Technology Data Exchange (ETDEWEB)

The DC Conductivity and Differential Thermal Analysis of glasses with composition (30?x)Li{sub 2}O?xV{sub 2}O{sub 5}?20Bi{sub 2}O{sub 3}?50B{sub 2}O{sub 3}(x=15, 10, 5) has been carried out in order to study the effect of replacing the Transition Metal Oxide (TMO) with alkali oxide. A significant increase in the DC conductivity has been observed with increase in alkali content. Again the thermal measurements have shown the decrease in both glass transition temperature (T{sub g}) and crystallization temperature (T{sub x}). The Glass Stability (GS) and Glass Forming Ability (GFA) have also been calculated and these also were found to decrease with increase in alkali oxide content at the cost of TMO.

Khasa, S., E-mail: skhasa@rediff.com; Dahiya, M. S., E-mail: skhasa@rediff.com [Physics Department, Deenbandhu Chhotu Ram University of Science and Technology, Murthal-131039 (India); Agarwal, A. [Physics Department, Guru Jambheshwara University of Science and Technology, Hisar-125001 (India)

2014-04-24

383

Optical properties of halide and oxide compounds including the excitonic effects  

Science.gov (United States)

We have studied the optical properties of alkali halide and alkaline-earth oxide compounds including the excitonic effects by using the newly developed bootstrap kernel approximation for the exchange-correlation kernel of the Time-Dependent Density Functional Theory (TD-DFT) implemented in Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method in the elk code. The bootstrap calculations are computationally less expensive and give results the same quality as the Bethe-Salpeter equation. We found improved results when compared to normal Density Functional Theory calculations, and observed results are comparable with the experiments. The lower energy peak of imaginary part of dielectric spectra shifts to lower energy regions as we move from MgO to BaO indicating the decrease in the band gap of these compounds from MgO to BaO. In all the studied compounds, the lower energy peak of the imaginary part of dielectric function is due to the transition from halogen p or oxide p states to metal derived s/d states.

Shwetha, G.; Kanchana, V.

2014-04-01

384

Crystal structure of a new adduct between telluric acid and alkali cyclo-triphophates: Te(OH)6.Na3P3O9.K3P3O9  

International Nuclear Information System (INIS)

Mr=889.74, monoclinic, C2/c, a=18.42(1), b=10.644(5), c=12.348(8) A, ?=119.76(5)0, V=2102(2) A3, Z=4, Dx=2.811 Mg m-3, ?(Ag K?)=0.5608 A, ?=1.38 mm-1, F(000)=1720, T=298 K, R=0.017 for 2553 independent reflexions. The crystal structure is built up of planes (z?0.0 and 0.5) of a hexagonal network of P3O9 groups centred by Te(OH)6 groups, alternating with planes (z?0.25 and 0.75) of the associated cations. (orig.)

385

An above-room-temperature ferroelectric organo-metal halide perovskite: (3-pyrrolinium)(CdCl?).  

Science.gov (United States)

Hybrid organo-metal halide perovskite materials, such as CH3NH3PbI3, have been shown to be some of the most competitive candidates for absorber materials in photovoltaic (PV) applications. However, their potential has not been completely developed, because a photovoltaic effect with an anomalously large voltage can be achieved only in a ferroelectric phase, while these materials are probably ferroelectric only at temperatures below 180?K. A new hexagonal stacking perovskite-type complex (3-pyrrolinium)(CdCl3) exhibits above-room-temperature ferroelectricity with a Curie temperature T(c)=316?K and a spontaneous polarization P(s)=5.1??C?cm(-2). The material also exhibits antiparallel 180°?domains which are related to the anomalous photovoltaic effect. The open-circuit photovoltage for a 1?mm-thick bulky crystal reaches 32?V. This finding could provide a new approach to develop solar cells based on organo-metal halide perovskites in photovoltaic research. PMID:25196506

Ye, Heng-Yun; Zhang, Yi; Fu, Da-Wei; Xiong, Ren-Gen

2014-10-13

386

TG-FTIR, DSC and quantum chemical studies of the thermal decomposition of quaternary methylammonium halides  

International Nuclear Information System (INIS)

The thermal decomposition of quaternary methylammonium halides was studied using thermogravimetry coupled to FTIR (TG-FTIR) and differential scanning calorimetry (DSC) as well as the DFT, MP2 and G2 quantum chemical methods. There is almost perfect agreement between the experimental IR spectra and those predicted at the B3LYP/6-311G(d,p) level: this has demonstrated for the first time that an equimolar mixture of trimethylamine and a methyl halide is produced as a result of decomposition. The experimental enthalpies of dissociation are 153.4, 171.2, and 186.7 kJ/mol for chloride, bromide and iodide, respectively, values that correlate well with the calculated enthalpies of dissociation based on crystal lattice energies and quantum chemical thermodynamic barriers. The experimental activation barriers estimated from the least-squares fit of the F1 kinetic model (first-order process) to thermogravimetric traces - 283, 244 and 204 kJ/mol for chloride, bromide and iodide, respectively - agree very well with theoretically calculated values. The theoretical approach assumed in this work has been shown capable of predicting the relevant characteristics of the thermal decomposition of solids with experimental accuracy

387

Hydrogen adsorption on alkali modified aluminum  

Science.gov (United States)

Coadsorption experiments of alkali metals and hydrogen on Al(100) are reported. The probability for H-H (D-D) dissociation and subsequent atomic adsorption is less than 1:10 4 at all alkali coverages. As a consequence, each overlayer had to be prepared by exposing the sodium or potassium modified surface to a beam of hydrogen (deuterium) atoms. We observed an attractive alkali-hydrogen interaction at all coverages. This interaction is best described as the formation of an alkali hydride in the presence of excess alkali atoms. The formation of the hydride shifts the recombination and desorption temperature of hydrogen adatoms on Al(100) from around 350 to around 500 K. While no isotope effect was detected on the clean aluminum surface (diffusion limited recombination), a significant 10-15 K shift was observed for both alkali hydrides (bond breaking). Furthermore, both alkali hydrides observed intense vibrational losses, thus revealing the ionic character of the metal-hydrogen bond. Electron energy loss spectra of an annealed monolayer of sodium hydride (deuteride) showed metal-hydrogen stretching bands at 1850 (1350) cm -1 and 1715 (1250) cm -1, a deformation band at 800 (600) cm -1, and a metal-metal band at 200 (200) cm -1. Corresponding peak positions for potassium hydride (deutride) were 1650 (1200) cm -1, 1500 (1100) cm -1, and 775 (585) cm -1. The metal-metal vibration could not be separated from the elastic peak because of the larger mass of potassium compared to sodium.

Paul, J.; Hoffmann, F. M.

388

Thermodynamic quantities of surface formation of aqueous electrolyte solutions VII. Aqueous solution of alkali metal nitrates LiNO3, NaNO3, and KNO3.  

Science.gov (United States)

To compare the effect of nitrate anions on the surface tension increments of aqueous solutions with that of halide anions, the surface tension of aqueous solutions of lithium nitrate, sodium nitrate, and potassium nitrate was measured as a function of temperature and concentration. It is shown that the surface tension of aqueous alkali metal nitrate solutions is determined primarily by the kinds of anions, since the surface tension increments of these nitrates were of the same magnitude. The importance of the electrical double layer at the surface is discussed in relation to these surface tension increments. PMID:17707855

Matubayasi, Norihiro; Yoshikawa, Ryuji

2007-11-15

389

Diode pumped alkali vapor fiber laser  

Science.gov (United States)

A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

Payne, Stephen A. (Castro Valley, CA); Beach, Raymond J. (Livermore, CA); Dawson, Jay W. (Livermore, CA); Krupke, William F. (Pleasanton, CA)

2007-10-23

390

Application of lanthanum halide scintillators and low-resolution dense plastics for modern MC and A needs  

International Nuclear Information System (INIS)

Recent developments in lanthanum halide scintillators and low-resolution dense plastics give breadth to gamma-ray methods of nuclear material detection suitable for modern MC and A needs. Demanding goals for modernization of MC and A cover both portable and continuous on-line measurement applications that are quantitative for inventory/verification, and that serve those quantitative measurement needs plant-wide. Improved performance (sensitivity and reoslution) is important for portable applications in which a single detector must measure many types of materials. Budget is a major issue for continuous inventory measurements with hundreds or even thousands of detectors placed throughout a facility. Experimentally proven resolution of under 4% for 662 keV 137Cs gamma rays measured with large cerium-doped LaCl3 (lanthanum chloride) crystals set a new performance standard for versatile, efficient portable applications comparable in price to NaI(Tl), which has been dominant for decades. While the relatively high cost of crystals remains an obstacle for the application of very large numbers of lanthanum halide scintillators as distributed networked detectors, scintillators made from high-density plastic offer a different type of solution for these gamma-ray measurements. Compared to lanthanum halide crystals they are inexpensive and can be larger in size. Despite lower resolution than NaI(Tl), a quantitative interpretation of the photopeak response of terpretation of the photopeak response of the low-cost dense plastic detectors can be tailored to the unique mechanical and spectral properties of different materials at each of hundreds of fixed on-line locations in a plant. This paper describes the properties and presents experimental results for the two new spectrometer types that, together, bracket NaI(Tl) detectors in both performance and cost, fulfilling modern demands for portable and continuous on-line accountability of uranium and plutonium.

391

Solvated Positron Chemistry. Competitive Positron Reactions with Halide Ions in Water  

DEFF Research Database (Denmark)

It is shown by means of the angular correlation technique that the binding of positrons to halides is strongly influenced by solvation effects. For aqueous solutions we find increasing values for the binding energies between the halide and the positron with increasing mass of the halide. This is contrary to the calculations of Cade and Farazdel for the vacuum case

Christensen, Palle; Pedersen, Niels JØrgen

1979-01-01

392

Phonon Dispersion Relations in Alkali Metals  

International Nuclear Information System (INIS)

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

393

Atomic Force Microscopy Studies of Radiation Damage on Ionic Crystal Surfaces.  

Science.gov (United States)

The goal adopted at the start of work leading to this thesis was to image products of radiation damage on ionic surfaces with as high a resolution as possible. With this goal in mind, we explored the use of atomic force microscopy (AFM) as a novel tool for studying surface defects on insulators at mesoscopic scales (>10 nm), in anticipation of extending these measurements to the atomic scale. We studied the progressive desorption and defect evolution of KI using the tuning range of 4th harmonic Ti:sapphire laser light to excite the strongly absorbing exciton bands of the alkali iodides. We also studied CaF_2 metallization using low energy electrons. The first part of the thesis discusses the extent to which AFM may image non-periodic local atomic structures, and the significance of forces and surface adsorbates on the scanning process. Since our instrument was restricted to ambient atmosphere, we studied how sensitive the surface was to humidity using NaCl imaged at atomic resolution in a helium desiccated chamber. The intrusive nature of the tip makes defect observation difficult and transient, since the interaction may be unavoidably strong. But a thin water layer produces the best imaging conditions with humidities near ~25% to help buffer the loading force of the tip by supporting the main part of the mesoscopic (van der Waals) force, lubricating the surface and damping vibrations. We studied 12 alkali halide and alkaline earth fluoride crystals at atomic scale, the widest AFM survey of such materials to date, using an objective figure of merit to investigate correlations of different images with lattice constant, solubility, ratio of ionic radii, and polarizability, for example. As a class, ionic crystals are often unstable in electronic excited states, making it possible for electron or photon irradiation to produce vacancy-interstitial defect pairs from the relaxation of electron-hole pairs into self -trapped excitons. We performed in situ measurements of KI using uv laser irradiation to monitor the surface erosion and metallization in real time. This thesis addresses the important question of how reliably the AFM can image a surface at scales >10 nm while a laser producing near surface excitation densities ~10 ^{22} cm^{ -3} per second is focused on the sample around the cantilever. As in the case of alkali halides, when CaF _2 crystals are irradiated by electrons in vacuum at elevated temperature, F centers diffuse to the surface and nucleate forming calcium metal. Upon ceasing the irradiation and cooling the sample, the surface topography on the 10 nm and larger scale remains mostly stable upon exposure to air and consequent oxidation, so that AFM observations in air can detail the evidence of formation and migration of beam induced metallization achieved in vacuum. (Abstract shortened by UMI.).

Wilson, Robert Mark

1995-01-01

394

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

International Nuclear Information System (INIS)

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

395

Study of conduction current of NaCl and KCl crystals during x-ray radiation  

International Nuclear Information System (INIS)

The variation of conduction current with time under high constant D.C. field for NaCl and KCl crystals, has been studied. The direction of high constant D.C. field is kept parallel to the direction of x-ray by holding the crystal between two aluminium electrodes before x-ray beam. The change in conduction current due to change in direction of the D.C. field, has also been studied by changing the polarity of the field. The alkali halide crystals thus irradiated by x-ray in the presence of D.C. field, show colour centres. The concentration of colour centre due to presence of D.C. field is found to decrease than the concentration of colour centres produced by x-ray irradiation only. The prominent F and M band peak position are found to be shifted in the longer wave length side due to D.C. field during x-ray irradiation. On applying D.C. field in a direction parallel to x-ray, the conduction current is found to increase rapidly with time. It attains a peak value and then decays slowly. It reaches to a steady state after about one hour. When the D.C. field is reversed i.e. applied in a direction opposite to x-ray beam, then conduction current decreases slowly for a short time, and reaches to a minimum value. Then the conduction current increases rapidly up to a peak value, after which it decreases slowly and becomes steady in about one hour. (author)

396

Calcium silicate hydrate: Crystallisation and alkali sorption  

International Nuclear Information System (INIS)

Homogeneous single C-S-H gels has been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, Rd, was introduced to express the partition of alkali between solid and aqueous phases at 25 deg. C. Rd is independent of alkali hydroxide concentration and depends only on Ca:Si ratio over wide ranges of alkali concentration. The trend of numerical values of Rd indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant Rd value of the material. Al has been introduced to form C-A-S-H gels and their alkali sorption properties also determined. Al substituted into C-S-H markedly increases Rd, indicating enhancement of alkali binding. However, the dependence of Rd on alkali concentration is non-ideal with composition. A two-site model for bonding is presented. Crystallisation both under saturated steam and 1 bar vapour pressure has been investigated. It has been shown that heat treatment by saturated steam causes crystallisation of gels. The principal minerals obtained were (i) C-S-H gel and Ca(OH)2 at -55 deg. C, (ii) 1.1 nm tobermorite, jennite and afwillite at 85 -130 deg. C, and (iii) xonotlite, foshagite and hillebrandite at 150-180 deg. C. Properties of crystalline C-S-H were also reported for reversible phase transformation, pH conditioning ability, seednsformation, pH conditioning ability, seeding effect and solubility. At 1 bar pressure, crystallisation is slower than in saturated steam due to lower water activity. Tobermorite-like nanodomains develop during reaction at low Ca/Si ratios. In some Ca-rich compositions, Ca(OH)2 is exsolved and occurs as nano-sized crystallites. (author)

397

Full-potential study of the electronic structure of silver halides  

Energy Technology Data Exchange (ETDEWEB)

We present first-principles structural and electronic structure calculations of the silver halides AgF, AgCl, AgBr and AgI in their rocksalt NaCl-structure. The full-potential linearized augmented plane-wave (FP-LAPW) method is used, and for the exchange and correlation, the local density approximation (LDA) and generalized gradient approximations (GGA) are employed. The effect of spin-orbit coupling has also been incorporated. The results obtained using generalized gradient approximations are in better agreement with experimental data than those obtained using local density approximations. The inclusion of spin-orbit coupling leads to slight changes in the results. The location of the valence band maximum, the conduction band minimum as well as the peaks in the density of states (DOS) are correctly predicted for all the crystals. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

Okoye, C.M.I. [Department of Physics and Astronomy, University of Nigeria, Nsukka (Nigeria)

2002-11-08

398

Raman and mid-infrared spectroscopic study of geometrically frustrated hydroxyl cobalt halides at room temperature  

International Nuclear Information System (INIS)

Mid-infrared absorption and Raman spectra of the geometrically frustrated material series, hydroxyl cobalt halides ß-Co2(OH)3Cl and ß-Co2(OH)3Br, are first, to the best of our knowledge, measured at room temperature, to study the corresponding relationship between their vibrational spectral properties and crystal microstructures. Through the comparative analysis of the four spectra we have categorically assigned the OH-related vibration modes of hydroxyl groups in the trimeric hydrogen bond environment (Co3 ?OH)3 ... Cl/Br, and tentatively suggested vibration modes of O-Co-O, Co-O and Cl/Br-Co-Cl/Br units. These results can also become the basis for analysing their low-temperature spectral properties, which can help to understand the underlying physics of their exotic geometric frustration phenomena around phase transition temperatures. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

399

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

Science.gov (United States)

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

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

2014-04-01

400

Measurements of the electric dipole tensor polarizabilities of the alkali dimers: Na2, Cs2  

International Nuclear Information System (INIS)

Molecular beam inhomogeneous electric field spatial deflection measurements of the static effective average electric dipole polarizability ? = 1/3(2?xx + ?zz) and polarizability anisotropy ? = (?xx - ?zz) (where ?xx and ?zz are the two independent tensor polarizability components which define the polarizability tensor of the alkali dimer molecule), are reported for the homonuclear alkali dimers Na2 and Cs2. A general three dimensional (in space) molecular beam deflection calculation has been developed in which all experimental parameters are taken into account, using a model in which the axially symmetric dimers are treated as linear rigid rotator molecules interacting with an applied external E field. The data analysis consists of a two independent parameter (?xx, ?zz) least square best fit computed to experimentally measured spatial beam intensity deflection curves. The results are normalized to the standard known scalar polarizabilities of the atomic monomers Na, Cs. The measured average polarizabilities, and polarizability anisotropies in units of (angstrom 3) are: Na2 (T = 660K): ? = 31.0±1.7, ? = 0±2, Cs2(T = 500K): ? = 82.4±6.2, ? = 0±6. All monomer and dimer analysis sets clearly indicate that the beams indeed possess Maxwell-Boltzmann velocity distributions. In addition remeasurements of the average erements of the average electric dipole polarizabilities of atomic strontium, using the above full curve fit analysis yields Sr(T = 500K): ? = 24.7±1.5 angstrom 3, and for the alkali halide dimers in units of angstrom 3: (CsF)2(T = 835K): ? = 27.6±3.1, (CsCl)2(T = 844K): ? = 52.1±5.9, using the linear peak deflection analysis method

401

Efficient Use Of Silver Halide In X-Ray Film  

Science.gov (United States)

Silver halide is a unique imaging receptor because the absorption of only a few light photons can produce up to 109 silver atoms. Recently, the cost of silver has increased dramatically although there is no shortage of the metal. These price increases have focused attention on making more efficient use of this precious metal in silver halide films and on its recovery after use. Photographic manufacturers have developed technology necessary to make X-ray films using less silver without affecting photographic performance. Other non-silver imaging systems have been developed for use when high photographic speed is not required.

Wayrynen, R. E.

1981-07-01

402

Ternary aqueous systems of praseodymium and alkali metal sulfate salts at 25 deg C  

International Nuclear Information System (INIS)

Solubility in ternary systems of praseodymium and alkali metal sulfate salt in aqueous solutions at 25 deg C has been studied by the isothermal method. Over the wide range of salt concentrations, the processes of crystallization of binary hydrated salts Me2SO4xPr2(SO4)3x2H2O, where Me - Na, K, Rb, Cs, is revealed. The aqueous system of lithium and praseodymium sulfate salts is of an eutonic type

403

Alkali metal and alkali metal hydroxide intercalates of the layered transition metal disulfides  

Science.gov (United States)

The intercalation reaction of some layered transition metal disulfides with alkali metals, alkali metal hydroxides, and tetraalkylammonium hydroxides were investigated. The alkali metal intercalates were prepared in the respective metal-hexamethylphosphoric triamide solutions in vacuo, and the hydroxide intercalates in aqueous hydroxide solutions. According to the intercalation reaction, the c-lattice parameter was increased, and the increase indicated the expansion of the interlayer distance. In the case of alkali metal intercalates, the expansion of the interlayer distance increased continuously, corresponding to the atomic radius of the alkali metal. On the other hand, the hydroxide intercalates showed discrete expansion corresponding to the effective ionic radius of the intercalated cation. All intercalates of TaS 2 and NbS 2 were superconductors. The expansion of the interlayer distance tended to increase the superconducting transition temperature in the intercalates of TaS 2 and vice versa in those of NbS 2.

Kanzaki, Y.; Konuma, M.; Matsumoto, O.

1981-05-01

404

Alkali metal and alkali metal hydroxide intercalates of the layered transition metal disulfides  

International Nuclear Information System (INIS)

The intercalation reaction of some layered transition metal disulfides with alkali metals, alkali metal hydroxides, and tetraalkylammonium hydroxides were investigated. The alkali metal intercalates were prepared in the respective metal-hexamethylphosphoric triamide solutions in vaccuo, and the hydroxide intercalates in aqueous hydroxide solutions. According to the intercalation reaction, the c-lattice parameter was increased, and the increase indicated the expansion of the interlayer distance. In the case of alkali metal intercalates, the expansion of the interlayer distance increased continuously, corresponding to the atomic radius of the alkali metal. On the other hand, the hydroxide intercalates showed discrete expansion corresponding to the effective ionic radius of the intercalated cation. All intercalates of TaS2 amd NbS2 were superconductors. The expansion of the interlayer distance tended to increase the superconducting transition temperature in the intercalates of TaS2 and vice versa in those of NbS2. (orig.)

405

Kinetic Studies of the Solvolysis of Two Organic Halides  

Science.gov (United States)

Describes an undergraduate organic chemistry laboratory experiment which utilizes the solvolysis of organic halides to demonstrate first and second order reaction kinetics. The experiment also investigates the effect of a change of solvent polarity on reaction rate, common-ion and noncommon-ion salt effects, and the activation parameters of a…

Duncan, J. A.; Pasto, D. J.

1975-01-01

406

Semiempirical and DFT Investigations of the Dissociation of Alkyl Halides  

Science.gov (United States)

Enthalpy changes corresponding to the gas phase heats of dissociation of 12 organic halides were calculated using two semiempirical methods, the Hartree-Fock method, and two DFT methods. These calculated values were compared to experimental values where possible. All five methods agreed generally with the expected empirically known trends in the…

Waas, Jack R.

2006-01-01

407

Copper catalysed amidation of aryl halides through chelation assistance.  

Science.gov (United States)

A copper mediated C-N bond formation for the amidation of aryl halides using 8-aminoquinoline has been developed. This strategy provides efficient access to amides bearing two contiguous heterocyclic moieties and does not require the presence of additional ligands. PMID:25695680

Kathiravan, Subban; Ghosh, Shishir; Hogarth, Graeme; Nicholls, Ian A

2015-03-01

408

On the Boiling Points of the Alkyl Halides.  

Science.gov (United States)

Discusses the variety of explanations in organic chemistry textbooks of a physical property of organic compounds. Focuses on those concepts explaining attractive forces between molecules. Concludes that induction interactions play a major role in alkyl halides and other polar organic molecules and should be given wider exposure in chemistry texts.…

Correia, John

1988-01-01

409

Students' understanding of alkyl halide reactions in undergraduate organic chemistry  

Science.gov (United States)

Organic chemistry is an essential subject for many undergraduate students completing degrees in science, engineering, and pre-professional programs. However, students often struggle with the concepts and skills required to successfully solve organic chemistry exercises. Since alkyl halides are traditionally the first functional group that is studied in undergraduate organic chemistry courses, establishing a robust understanding of the concepts and reactions related to them can be beneficial in assuring students' success in organic chemistry courses. Therefore, the purpose of this study was to elucidate and describe students' understanding of alkyl halide reactions in an undergraduate organic chemistry course. Participants were interviewed using a think-aloud protocol in which they were given a set of exercises dealing with reactions and mechanisms of alkyl halide molecules in order to shed light on the students' understanding of these reactions and elucidate any gaps in understanding and incorrect warrants that may be present. These interviews were transcribed and analyzed using qualitative inquiry approaches. In general, the findings from this study show that the students exhibited gaps in understanding and incorrect warrants dealing with: (1) classifying substances as bases and/or nucleophiles, (2) assessing the basic or nucleophilic strength of substances, (3) accurately describing the electron movement of the steps that take place during alkyl halide reaction mechanisms, and (4) assessing the viability of their proposed reactive intermediates and breakage of covalent bonds. In addition, implications for teaching and future research are proposed.

Cruz-Ramirez de Arellano, Daniel

410

Photoluminescence of Au- formed in 12CaO . 7Al2O3 single crystal by Au+-implantation  

International Nuclear Information System (INIS)

Au+ ion implantation with fluences from 1 x 1014 to 3 x 1016 cm-2 into 12CaO . 7Al2O3 (C12A7) single crystals was carried out at a sample temperature of 600 deg. C. The implanted sample with the fluence of 1 x 1015 cm-2 exhibited photoluminescence (PL) bands peaking at ?3.1 and ?2.3 eV at ?150 K when excited by He-Cd laser (325 nm). This was the first observation of PL from C12A7. These two PL bands are possibly due to intra-ionic transitions of an Au- ion having the electronic configuration of 6s 2, judged from their similarities to those reported on Au- ions in alkali halides. However, when the concentration of the implanted Au ions exceeded the theoretical maximum value of anions encaged in C12A7 (?2.3 x 1021 cm-3), surface plasmon absorption appeared in the optical absorption spectrum, suggesting Au colloids were formed at such high fluences. These observations indicate that negative gold ions are formed in the cages of C12A7 by the Au+ implantation if an appropriate fluence is chosen

411

Photoluminescence of Au - formed in 12CaO · 7Al 2O 3 single crystal by Au +-implantation  

Science.gov (United States)

Au + ion implantation with fluences from 1 × 10 14 to 3 × 10 16 cm -2 into 12CaO · 7Al 2O 3 (C12A7) single crystals was carried out at a sample temperature of 600 °C. The implanted sample with the fluence of 1 × 10 15 cm -2 exhibited photoluminescence (PL) bands peaking at ˜3.1 and ˜2.3 eV at ?150 K when excited by He-Cd laser (325 nm). This was the first observation of PL from C12A7. These two PL bands are possibly due to intra-ionic transitions of an Au - ion having the electronic configuration of 6 s2, judged from their similarities to those reported on Au - ions in alkali halides. However, when the concentration of the implanted Au ions exceeded the theoretical maximum value of anions encaged in C12A7 (˜2.3 × 10 21 cm -3), surface plasmon absorption appeared in the optical absorption spectrum, suggesting Au colloids were formed at such high fluences. These observations indicate that negative gold ions are formed in the cages of C12A7 by the Au + implantation if an appropriate fluence is chosen.

Miyakawa, M.; Kamioka, H.; Hirano, M.; Kamiya, T.; Hosono, H.

2006-09-01

412

Band structure and chemical bond in alkali metal carbonates  

Science.gov (United States)

The band structure, state density, optical functions, and distribution of valence and difference density in alkali-metal carbonates are calculated within the local electron-density functional theory using the method of pseudopotential in the basis of numerical pseudoorbitals. When passing from a lithium cation to a potassium one, the character of hybridization between the crystal sublattices changes to result in an increase in the valence-band width, a decrease in the forbidden-band width, a complication of the structure of state-density spectrum, and a shift of the maxima of optical functions to the low-energy range. It is found that the electron overflow between the ?-and ?-orbitals of crystallographically nonequivalent oxygen atoms can occur in different ways, hence their interaction force with the surrounding atoms is different. The role of cations in stabilization of anion chains resulting from the electron-cloud overlapping in lithium and sodium carbonates is shown.

Fedorov, I. A.; Zhuravlev, Yu. N.; Korabel'Nikov, D. V.

2006-10-01

413

The Alkali Metals Induced Reconstructions of the GOLD(110) Surface  

Science.gov (United States)

The atomically clean Au(110) surface is reconstructed and shows a (1 x 2) low energy electron diffraction pattern. The structure corresponds to a missing row reconstruction. We found that the adsorption of alkali metals induce further reconstructions of the Au(110) surface. Low coverages of Cs (0.05 ML) on this surface induce a (1 x 3) surface structure. This behavior is not restricted to Cs exclusively. Our study have also shown that K induces a (1 x 3) structure. We believe then that the tendency to induce these reconstructions is common to all alkali metals. At high coverages we have studied the c(2 x 2) K induced reconstruction of the Au(110) surface. Using medium energy ion scattering (MEIS) with channeling and blocking we have determined the structural models for both reconstructions. With the help of Monte Carlo simulations we have determined the interlayer distances and other surface distortions. The structural model for the (1 x 3) reconstruction is of the missing row type with narrow (111) microfacets and large surface relaxations. This model agrees with theoretical calculations showing that facetted structures are energetically favored in the (110) surface of fcc crystals and in particular in Au. In the high coverage regime (~ 0.50 ML) we found that K mixes strongly with the substrate. The c(2 x 2) structure correspond to a model where the top layer of the crystal is formed by a two dimensional alloy. In this case the force behind the reconstruction is the formation of a surface compound.

Haberle, Patricio

414

Freezing of liquid alkali metals as screened ionic plasmas  

International Nuclear Information System (INIS)

The relationship between Wigner crystallization of the classical ionic plasma and the liquid-solid transition of alkali metals is examined within the density wave theory of freezing. Freezing of the classical plasma on a rigid neutralizing background into the bcc structure is first re-evaluated, in view of recent progress in the determination of its thermodynamic functions by simulation and of the known difficulties of the theory relating to the order parameter at the (200) star of reciprocal lattice vectors. Freezing into the fcc structure is also considered in this context and found to be unfavoured. On allowing for long-wavelength deformability of the background, the ensuing appearance of a volume change on freezing into the bcc structure is accompanied by reduced stability of the fluid phase and by an increase in the entropy of melting. Freezing of alkali metals into the bcc structure is next evaluated, taking their ionic pair structure as that of an ionic plasma reference fluid screened by conduction electrons and asking that the correct ionic coupling strength at liquid-solid coexistence should be approximately reproduced. The ensuring values of the volume and entropy changes across the phase transition, as estimated from the theory by two alternative routes, are in reasonable agreement with experiment. The order parameters of the phase transition, excepting the (200) one, conform rather closely to a Gaussian behaviour and yield a Lindemann ratio in reasonable agreement with the empirical value for melting of bcc crystals. It is suggested that ionic ordering at the (200) star in the metal may be (i) assisted by medium range ordering in the conduction electrons, as indicated by differences in X-ray and neutron diffraction intensities from the liquid, and/or (ii) quite small in the hot bcc solid. Such a possible premelting behaviour of bcc metals should be worth testing experimentally by diffraction. (author). 48 refs, 1 fig., 1 tab

415

Mechanism of low-temperature radiation hardening in alkali halides. III. The elastic interaction of single halogen interstitials with dislocations  

International Nuclear Information System (INIS)

The interaction of single halogen interstitials and dislocations has been studied in terms of their elastic interaction. The linear-elastic calculation is made to show that the maximum force in the I-center--dislocation interaction is greater than that in the case of the H center. This result is shown to be relevant for the elastic interaction of the H/sub A/ and I/sub A/ centers with dislocations. We reveal the relation between the maximum interaction force and the magnitude of strain around a defect, and conclude that the greater hardening effect of the interstitial ion than the atom originates from the stronger elastic-interaction force caused by the larger strain around the ion. The hardening effect of the interstitial ion is compared with that of the V/sub K/ center

416

Molecular Simulation of Aqueous Electrolyte Solubility. 3. Alkali-halide Salts and Their Mixtures in Water and in Hydrochloric Acid.  

Czech Academy of Sciences Publication Activity Database

Ro?. 116, ?. 18 (2012), s. 5468-5478. ISSN 1520-6106 R&D Projects: GA ?R GA203/08/0094; GA MŠk LH12020 Grant ostatní: NSERC(CA) OGP1041; EC(XE) COST TD0802 Institutional research plan: CEZ:AV0Z40720504 Keywords : molecular simulations * electrolyte hydrates * oemc simulations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.607, year: 2012

Mou?ka, F.; Lísal, Martin; Smith, W. R.

2012-01-01

417

Study of the point defect creation and of the excitonic luminescence in alkali halides irradiated by swift heavy ions  

International Nuclear Information System (INIS)

The aim of this experimental thesis is to study the excitonic mechanisms and of the defect creation, in NaCl and KBr, under dense electronic excitations induced by swift heavy ion irradiations. In the first part, we present the main features of the interaction of swift heavy ions with solid targets, and after we review the well known radiolytic processes of the defect creation during X-ray irradiation. In the second chapter, we describe our experimental set-up. In the chapter III, we present our results of the in-situ optical absorption measurements. This results show that defect creation is less sensitive to the temperature than during a classical irradiation. Besides, we observe new mechanisms concerning the defect aggregation. In the chapter IV, we present the results of excitonic luminescence induced by swift by swift heavy ions. We observe that the luminescence yields only change with the highest electronic stopping power. In the chapter V, we perform thermal spike and luminescence yields calculations and we compare the numerical results to the experiments presented in the chapter IV. (author). 121 refs., 65 figs., 30 tabs

418

Thermoelastic behaviour of mixed ammonium halides  

Science.gov (United States)

A theory for the temperature derivatives of second order elastic constants of ammonium chloride and ammonium bromide, crystalizing in ceasium chloride structure has been developed incorporating contributions due to the thermal phonons and three body interactions in the lattice energy in the framework of Hildebrand approximation. The expressions for the temperature derivatives have been derived by differentiating the expressions of the second order elastic constants. The repulsive potential which is taken to be of the Born-Mayer type is assumed significant up to the first neighbours only. Computations have been made for pure and mixed crystals NH4Cl1-xBrx for x=0, 0.13, 0.23 and 1.00. The results have been found in agreement with the experimental data wherever these are available.

Bedi, S. S.; Singh, Jaspal

1992-04-01

419

Core repulsion effects in alkali trimers  

CERN Document Server

The present paper is related to a talk presented during the Symposium on Coherent Control and Ultracold Chemistry held during the Sixth Congress of the International Society for Theoretical Chemical Physics (ISTCP-VI, July 2008). The talk was entitled "Electronic structure properties of alkali dimers and trimers. Prospects for alignment of ultracold molecules". Here we report on the electrostatic repulsion forces of the ionic cores at short separation, involved when the potential energy surfaces of alkali trimers are calculated with a quantum chemistry approach based on effective large-core potentials for ionic core description. We demonstrate that such forces in the triatomic molecule can be obtained as the sum of three pairwise terms. We illustrate our results on the lowest electronic states of Cs$_3$, which are computed for the first time within a full configuration interaction based on a large Gaussian basis set. As a preliminary section, we also propose a brief introduction about the importance of alkali...

Guérout, Romain; Aymar, Mireille; Deiglmayr, Johannes; Dulieu, Olivier

2009-01-01

420

Alkali ion exchange in ?-irradiated glasses  

International Nuclear Information System (INIS)

The alkali ion exchange of ?-irradiated glasses was investigated using the structural energy barrier model for ion exchange of glasses. It is shown that rates of alkali ion exchange have a non-Arrhenius behaviour depending both on irradiation dose and dose rate. For this reason some effects cannot be simulated by external irradiation and require in situ measurements. Higher doses and dose rates of ?-radiation lead to increased ion exchange rates. Significant changes occur in the activation energies demonstrating a many times decrease depending on glass composition. Radiation-induced changes are higher at relatively low temperatures being diminished by increased glass temperature. Numerical estimations show that changes in alkali ion exchange kinetics occur below the glass network damaging doses

421

Alkali ion exchange in ?-irradiated glasses  

Science.gov (United States)

The alkali ion exchange of ?-irradiated glasses was investigated using the structural energy barrier model for ion exchange of glasses. It is shown that rates of alkali ion exchange have a non-Arrhenius behaviour depending both on irradiation dose and dose rate. For this reason some effects cannot be simulated by external irradiation and require in situ measurements. Higher doses and dose rates of ?-radiation lead to increased ion exchange rates. Significant changes occur in the activation energies demonstrating a many times decrease depending on glass composition. Radiation-induced changes are higher at relatively low temperatures being diminished by increased glass temperature. Numerical estimations show that changes in alkali ion exchange kinetics occur below the glass network damaging doses.

Ojovan, Michael I.; Lee, William E.

2004-12-01

422

Lighter Alkali hydride and deuteride 1: Electronic properties of pure solids  

International Nuclear Information System (INIS)

The properties of lighter alkali hydrides of metals which crystallize in the rock-salt structure are discussed. First, the properties of pure crystals which are dominated by the electrons, in particular the energy levels and the eigenstates of the electrons in the absence of lattice defects are considered. After that, the optical properties of the solids excited at photon energies larger than those appropriate to lattice vibration and dominated by the transition of electron from the occupied core and valence levels to the normally empty conduction states, are discussed. 127 refs, 29 figs, 17 tabs

423

Synthesis and physicochemical properties of new niobium fluoro complexes with mixed alkali-metal cations  

International Nuclear Information System (INIS)

Niobium fluorocomplexes with mixed cations of alkali metals of NaMNbF7 and NaMNbOF5 (M=K, Rb, Cs) composition, crystallized into orthorhombic syngony are prepares and investigated for the first time. During recrystallization of NaRbNbF7 from water a new compound Na2RbNbO3F21·H2O crystallizing into monoclinic syngony is obtained. Lattice parameters of the compounds are determined. IR absorption spectra of the synthesized fluoro complexes in 4000-80 cm-1 is measured and characterized

424

Selection of non-adsorbing alkali components  

Energy Technology Data Exchange (ETDEWEB)

This project consists of three phases of laboratory experimental study. In phase I (screening), eight candidate materials, 304SS (serves as a base material for comparison), Hastelloy C-276, Hastelloy X, Haynes No. 188, Allonized 304SS, Pt-coated 304SS, and ceramic-coated 304SS, will be subjected to atmospheric TGA study under the simulated PFBC (oxidizing) environment with and without alkali vapor doping. Each candidate material will be evaluated for its resistance toward alkali-vapor capture. In addition, a post-test metallographic characterization of the sample will be performed to obtain a better understanding of the alkali capture mechanism and material behavior. The material(s) with little or no alkali-vapor adsorption will be selected as the promising material(s) for the Phase II study. In Phase II, the promising material(s) will be further tested in the TGA under elevated pressure to simulate the PFBC environment (in terms of temperature, pressure, and gas composition). The effect of pressure on the extent of alkali-vapor adsorption will be evaluated, and the test samples will be metallographically characterized. The most promising candidate material(s) will be identified and recommended for further tesfing in the actual PFBC environment. In Phase III, four materials will be selected from the eight candidate materials screened in the PFBC environment and will be evaluated for their alkali-vapor capture by atmospheric TGA under the coal gasification fuel gas (reducing) environment. The tested samples will also be metallographically characterized. The most promising material(s) will be identified and recommended for further testing in the actual coal gasification environment.

Lee, S.H.D.; Natesan, K.; Swift, W.M.

1992-11-01

425

Alkali ion conductivity in rapidly quenched glasses  

International Nuclear Information System (INIS)

A number of new glasses have been prepared without any network formers, by rapid quenching from the melt. These include alkali niobates, tantalates, tungstates, molybdates, aluminates, gallates, bismuthates, zincates and a variety of sulfates. Many of these do not devitrify below 4000C. The glasses exhibit considerably greater ionic conductivity than crystalline solids of the same composition. Room temperatures conductivities close to 10-5 (ohm cm)-1 have been achieved. We report a systematic study of the effect of ionic radius and alkali ion content on the conductivity in an effort to optimize the structure and composition for application as solid electrolytes

426

A procedure for preparing alkali metal hydrides  

International Nuclear Information System (INIS)

A plain low cost, procedure for the continuous, low temperature preparation of sodium or potassium hydrides using cheap reagents is presented. Said invention is especially concerned with a process of purifying of a catalytic exchange liquid used for deuterium enrichment, in which an alkali metal hydride is produced as intermediate product. The procedure for producing the sodium and potassium hydrides consists in causing high pressure hydrogen to be absorbed by a mixture of at least a lower monoalkylamine and an alkylamide of an alkali metal from at least one of said amines

427

Matrix isolation infrared spectra of hydrogen halide and halogen complexes with nitrosyl halides  

Science.gov (United States)

Matrix isolation infrared spectra of nitrosyl halide (XNO) complexes with HX and X2 (X = Cl, Br) are presented. The relative frequency shifts of the HX mode are modest (ClNO H-Cl, delta-nu/nu = -0.045; BrNO H-Br, delta-nu/nu = -0.026), indicating weak hydrogen bonds 1-3 kcal/mol. These shifts are accompanied by significant shifts to higher frequencies in the XN-O stretching mode (CIN-O HCl, delta-nu/nu = +0.016; BrN-O HBr, delta-nu/nu = +0.011). Similar shifts were observed for the XN-O X2 complexes (ClN-O Cl2, delta-nu/nu = +0.009; BrN-O-Br2, delta-nu/nu = +0.013). In all four complexes, the X-NO stretching mode relative shift is opposite in sign and about 1.6 times that of the NO stretching mode. These four complexes are considered to be similar in structure and charge distribution. The XN-O frequency shift suggests that complex formation is accompanied by charge withdrawal from the NO bond ranging from about .04 to .07 electron charges. The HX and X2 molecules act as electron acceptors, drawing electrons out of the antibonding orbital of NO and strengthening the XN-O bond. The implications of the pattern of vibrational shifts concerning the structure of the complexes are discussed.

Allamandola, Louis J.; Lucas, Donald; Pimentel, George C.

1982-01-01

428