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1

Radiation damage in the alkali halide crystals  

International Nuclear Information System (INIS)

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

2

Theory of interionic forces in alkali halide crystals  

International Nuclear Information System (INIS)

The widely used Born-Mayer potential in the classical theory of ionic crystals is replaced by a quantum mechanical analytical potential form following the recent tight binding theory developed by Harrison. It is found that the crystalline data on interionic distance, separation energies, isothermal bulk modulus, and its pressure derivative for all the alkali halides can be fitted to a very good extent by taking the Madelung energy and Harrison's overlap potential form. It is emphasised that Harrison's overlap potential can be a useful tool for studying the properties of ionic crystals within the framework of conventional approach based on Madelung's energies. (author)

3

Self-trapped holes in alkali silver halide crystals  

International Nuclear Information System (INIS)

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

4

Problems of colloidal centres creation in irradiated alkali halide crystals  

International Nuclear Information System (INIS)

Theory of growth and destruction of colloidal centres in irradiated alkali halide crystals is analysed as dose-rate, dose- and-irradiation-temperature dependent. Comparison between theory and experiment is carried out which shows that the theory of colloidal centre growth is applicable (without any changes) only for relatively small doses and at root temperature. In the heavy dose range at high irradiation temperatures the account of spatial distribution and concentration of F- and H- centres, as well as of size distribution of colloidal centre amounts, is necessary

5

THEORY OF PLASTICO ML IN ?–IRRADIATED ALKALI HALIDE CRYSTALS  

Directory of Open Access Journals (Sweden)

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

NAMITA RAJPUT

2011-06-01

6

Colloidal centres formation in alkali halide crystals under irradiation  

International Nuclear Information System (INIS)

Kinetics of the electron radiolysis products accumulations in alkali halide crystals after electron irradiation (3.5 MeV, 0.45 Mradxsec-1) in the absorbed dose interval from 102 up to 5x104 Mrad at high temperatures (400 up to 1000 K) has been studied. The investigation methods comprise optical spectroscopy, electron microscopy, chemical analysis of crystal dissolution products electron microdiffraction, measurement of stored energy. It shown that colloid particles distribution with respect to particle size i s widened with absorbed dose increasing and its maximum is shifted to larger particles. But at higher temperature of irradiation (870 K) the distributions cease to depend on irradiation dose absorbed and are fully determined by the irradiation temperature. The analysis of the temperature dependence of the colloid formation process in NaCl crystal allows one to outline three stages of the process: the first stage up to 520 K is characterized by intensive coagulation (the increase of colloidal particles number and size); thermal distruction of alkaline metal colloidal particles and chemical transformations of them into alkaline metal oxide colloidal particles are characteristic of the second stage (520 up to 670 K); at the third stage the next increase of colloidal particles concentration due to oxidation process is observed. It is shown also that the dose rate increase in several times leads to a considerable increase in colloidal metal yield

7

Polaron theory for description of electron excitations auto-localization peculiarity in alkali-halide crystals  

International Nuclear Information System (INIS)

In continual model for autolocalized excitons in low symmetry conditions the potential barrier height for excitons autolocalization of KI, CsI and KBr has been determined. Analytical expression for exciton full energy functional minimized by asymmetric oscillator wave function related to elastic uniaxial stress case of alkali halide crystal is received. In the work values of polaron effective mass for alkali halide crystal obtained with help continual integration are presented

8

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish 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.

9

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

10

Two-electron defect systems in ionic crystals: application to F' centres in alkali halides  

International Nuclear Information System (INIS)

The extended-ion method for the study of excited states in ionic crystals is modified for such two-electron defect systems as the F' centre and positronium in alkali halides. Exclusive use of 1s floating Gaussian functions as the basis is the main feature of the method. Some degree of electron correlation is built-in in this method. Applied to F' centres, it is found that in Nal the spin-singlet ground state is deeply bound, and there is also a bound triplet state. Comparison with experimental data regarding the optical and thermal dissociation energies in several alkali halides gives reasonable agreement. (author)

11

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-08-15

12

Colour centre phenomena in alkali halide crystals X-ray-irradiated under high electric fields  

International Nuclear Information System (INIS)

Some colour centre phenomena, such as the F-band absorption, thermoluminescence (TL) etc., in alkali halide crystals (NaCl and KCl particularly) subjected to high AC or DC electric fields and later irradiated with X-rays, have been studied. Similar investigations have also been carried out when these crystals are X-ray irradiated under high AC or DC fields. Interesting results are obtained in the work. An attempt is made to understand the results. (author)

13

Amplitude dependence of the internal friction of alkali-halide crystals in an electric field  

Science.gov (United States)

The influence of an electrical field on the internal friction of an alkali-halide crystal (AHC) was investigated for relative deformation amplitudes corresponding to separation of dislocations from fastening centers, and for higher amplitudes when plastic deformation of the specimen occurs in an ultrasonic wave field. The influence of the electrical field in the deformation domain under consideration reduces to direct action on charged dislocations, re-orientation of dipole fastening centers, and activation of sources in block boundaries.

Belozerova, É. P.

1989-08-01

14

Helium irradiation of alkali halides  

International Nuclear Information System (INIS)

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

15

Analogy between temperature dependent radiation effects in alkali halide crystals and crystalline ammonia  

International Nuclear Information System (INIS)

Pikaev, Ershov, and Makarov recently reported the characteristic shape of Arrhenius-type dependence for F-centers slow part (millisecond) decay in alkali halide crystals irradiated at different temperatures. The decay rate is constant when the temperature is below the limiting value (T/sub lim/) and exhibits constant activation energy (E/sub A/) at temperatures above T/sub lim/ up to the melting point. A similar dependence has been observed for crystalline ammonia radiolysis yields (H2 and N2) in the temperature range from 77 to 1950K (ammonia melting point) with a limiting value of 1050K for N2 and 1190K for H2. The coincidence between the alkali halide and ammonia data does not seem to be formal and there are indications showing a closer analogy between these two cases

16

Thermoluminescence of coloured alkali halide crystals after plastic deformation  

International Nuclear Information System (INIS)

Changes in the thermoluminescence (TL) intensity and the glow profile are found due to the plastic deformation caused by the application of the periodic uniaxial pressure in X-irradiated KBr, KCl, KI, LiF-TLD-100 and NaCl crystals. Trap destruction and trap competition models are discussed for the decrease in the TL intensity of the crystals. The increase in the TL intensity of some of the glow peaks is possible by the creation of new defects which act as traps, which are intrinsic in the crystal. If during the plastic deformation some of the interstitial atoms are released from one trap and are trapped again in some other trap, then the TL intensity corresponding to the first trap may decrease and the TL intensity corresponding to the other trap may increase. If the deformation of a crystal creates some traps which are different in energy from the intrinsic traps, then a new glow peak may appear. (author)

17

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

18

An optical criterion to obtain miscible mixed crystals in alkali halides  

Scientific Electronic Library Online (English)

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

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

2008-11-01

19

An optical criterion to obtain miscible mixed crystals in alkali halides  

Scientific Electronic Library Online (English)

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

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

20

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

 
 
 
 
21

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

International Nuclear Information System (INIS)

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

22

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

23

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

CERN Document Server

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

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

2000-01-01

24

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

International Nuclear Information System (INIS)

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

25

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

26

Effect of strong electric fields on the damage and coagulation radiation processes of electron cemters in whisker alkali-halide crystals  

International Nuclear Information System (INIS)

Effect of electric field on electric processes in whisker alkali-halide crystals is shown to boil down to spatial division of charged particles, that is, to reduction of probability of their recombination. Growth of the rate of radiation destruction of F2-centers and reduction of the efficiency of their coagulation with increase of constant electric field stress are determined experimentally

27

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)

28

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

Science.gov (United States)

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

Yu, Xueyang; Hofmeister, Anne M.

2011-02-01

29

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

International Nuclear Information System (INIS)

The spin lattice relaxation processes of the triplet state of the self trapped exciton have been studied in Alkali Chlorides and Bromides by measuring the transient response of the X ray excited luminescence under resonant pulse microwave. The symmetry properties and phonon coupling are discussed. Application of the model to magnetic circular polarization data also shows good agreement. (Author)

30

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

International Nuclear Information System (INIS)

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

31

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

International Nuclear Information System (INIS)

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

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

Optical radiation from electron sputtering of alkali halides  

International Nuclear Information System (INIS)

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

34

Solvation at nanoscale: Alkali-halides in water clusters  

Energy Technology Data Exchange (ETDEWEB)

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

Partanen, Leena [Department of Physics, Tampere University of Technology, Box 692, 33101 Tampere (Finland); Mikkelae, Mikko-Heikki; Huttula, Marko [Department of Physics, University of Oulu, Box 3000, 90014 University of Oulu (Finland); Tchaplyguine, Maxim [MAX-lab, Lund University, Box 118, 22100 Lund (Sweden); Zhang Chaofan; Andersson, Tomas; Bjoerneholm, Olle [Department of Physics and Astronomy, University of Uppsala, Box 516, 75120 Uppsala (Sweden)

2013-01-28

35

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

International Nuclear Information System (INIS)

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

36

Cohesive properties of alkali halides  

CERN Document Server

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

Doll, K; Doll, Klaus; Stoll, Hermann

1997-01-01

37

Excitons and point defect creation in alkali halides  

International Nuclear Information System (INIS)

in the report, on an example of face- and body-centered alkali halide crystals (kcl and csbr) the following problems are biefly considered: 1. particularities of electronic excitations conditioned by the coexistence of free excitons and self-trapped excitons. 2. decay of excitons with the creation of neutral defects. 3. decay of excitons with the creation of the frenkel defects. 4. recombination of defects with the creation of luminescent self-trapped excitons. 5. creation of defects due to the recombination of electrons with self-trapped holes. 6. creation of cation defects

38

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

International Nuclear Information System (INIS)

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

39

Dipole-dipole van der Waals interaction in alkali halides  

International Nuclear Information System (INIS)

Values of van der Waals dipole-dipole constants and interaction energetics of alkali halides are reported using the recent data. The values obtained are somewhat larger than those of earlier workers. (orig.)

40

A new polarizable force field for alkali and halide ions  

Science.gov (United States)

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

Kiss, Péter T.; Baranyai, András

2014-09-01

 
 
 
 
41

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

42

Does the TL supralinearity occur during irradiation in alkali halides?  

Energy Technology Data Exchange (ETDEWEB)

In the last ten to fifteen years, there has been a predominant belief that the linear-supralinear-sublinear behaviour of the TL response of alkali halides to the radiation dose necessarily occurs in the heating stage for TL reading. It is based on the assumption that coloration in these crystals grows linear-sublinearly with the dose during irradiation. Since both colour centre and TL centre are based on the same point defects the TL response should also grow linear-sublinearly with dose. In 1950, half a dozen authors showed that the coloration of F-centres in KCl takes place in two stages, the second one being responsible for non-linear behaviour. In this paper, we show that indeed in NaCl both F-centre and TL grow linear-supralinear-sublinearly with the dose during irradiation.

Watanabe, S; Ayta, W E F; Paiao, J R B; Ferraz, G M; Farias, T M B; Cano, N F [Institute of Physics, University of Sao Paulo, CP 66318, CEP 05315-970, Sao Paulo - SP (Brazil)], E-mail: watanabe@if.usp.br

2008-05-21

43

Theoretical study of Tl0 and Pb+ centers in alkali halide and alkaline earth fluoride type crystals  

International Nuclear Information System (INIS)

A theoretical study has been carried out on the hfi of Pb+ defects in KCl, CaF2 and BaF2 using an earlier developed crystal field model. Experimental results can be explained in the same way as was done for Tl0 in KCl. However some parameters seem to have a less physical meaning than in the case of Tl0. A new method is in progress using the ASW band structure procedure in order to estimate genuine solid state effects. Preliminary results are encouraging. (orig.)

44

Luminescence excitation by VUV photons in alkali and silver halides  

International Nuclear Information System (INIS)

Excitation spectra of luminescence quantum yield in alkali and silver halides are measured at low temperatures using synchrotron radiation for the energy range up to 30eV. The yields at the valence exciton excitation are low (0.1 at most) in alkali halides (KCl, KBr and NaBr), but high (0.4) in AgCl. Enhancement of the yield indicative of multiple exciton production is observed at higher energies, and the yields in NaBr and AgCl exceed unity in the energy range studied. Discussion is given for the competition between radiative and non-radiative decay channels during relaxation of excited states. (author)

45

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.)

46

Interfacial tension in immiscible mixtures of alkali halides.  

Science.gov (United States)

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

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

2010-02-01

47

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, 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)

48

F-center optical absorption in alkali halides  

International Nuclear Information System (INIS)

The transition energies of F-centers for six alkali halides are calculated with the point-ion approximation and the ion-size correction. We show the correct expression of the energy functional for the Gourary and Adrian wave function of type II. We compare our results with other works and find that they do not differ by more than 13% from the experimental results, except for LiI, with ? = 0.53 (Author)

49

Positive-ion production by electron bombardment of alkali halides  

International Nuclear Information System (INIS)

We present an experimental investigation of positive-ion production by electron bombardment of alkali halides. Measurements of the mass distributions and yields of both positive ions and neutral species indicate that the positive ions are formed by gas-phase ionization of ground-state neutral atoms and molecules. The gas-phase mechanism is shown to account for the ion mass distributions, the magnitude of the ion yields, and the dependence of ion yield on incident electron current

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

Molten Alkali Halides: Straightforward Prediction of Surface Tension  

Science.gov (United States)

This article provides a new model for predicting the surface tension of molten alkali halides, because the subject is worthy of investigation. A relationship exists between the surface tension ( ?) at the melting point ( T m ), molar volume ( V), internuclear distance ( D), and radius ratio The basic idea results from the assumption that all of the parameters are constants. The relation depends on the reliability and accuracy of all the constants on which it is based. The formula was examined and showed remarkable agreement between the calculated surface tension and experimental data within a difference of less than 10 pct for most of the salts studied.

Aqra, Fathi

2014-05-01

52

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)

53

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

International Nuclear Information System (INIS)

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

54

Theory of freezing of alkali halides and binary alloys  

International Nuclear Information System (INIS)

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

55

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

Science.gov (United States)

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

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

2012-12-01

56

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

International Nuclear Information System (INIS)

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

57

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

58

Correlation between standard enthalpy of formation, structural parameters and ionicity for alkali halides  

Directory of Open Access Journals (Sweden)

Full Text Available The standard enthalpy of formation (?Ho has been considered to be an interesting and useful parameter for the correlation of various properties of alkali halides. The interrelation between ?Ho and structural parameters for the halides of Li, Na, K and Rb has been thoroughly analyzed. When cationic component element is kept constant in a homologous series of alkali halides, the negative value of ?Ho has been observed to decrease linearly with increase of interionic distance (d and accordingly following empirical equation ?Ho = ? + ?d (where ? and ? are empirical constants has been established. However, for common anionic series of alkali halides an opposite nonlinear trend has been observed with the exception of common fluorides. The correlation study on the standard enthalpy of formation has been extended in term of radius ratio and also discussed in the light of ionization energy of the metal, electron affinity of the halogen, size of the ions, ionic character of bond and lattice energy of the compound.

Nasar Abu

2013-01-01

59

Investigation of condensation and evaporation of alkali halide crystals by molecular beam methods. VIII. Molecular beam pulse experiments with lithium flouride  

Science.gov (United States)

Experiments with molecular beam pulses allow the determination of the relaxation times of monomeric, dimeric, and trimeric molecules of lithium fluoride on (100) surfaces of LiF as functions of the crystal temperature T and of the molecular flux jon impinging onto the surface. At high T and low jon the relaxation times increase exponentially with 1/ T. The corresponding activation energies are 0.79, 0.77, and 1.14 eV for the monomers, dimers, and trimers. At lower T and higher jon they become independent of T but increase with decreasing jon. The experiments were performed with different lithium isotopes: 6Li for the impinging molecular beam and 7Li for the crystal. Measurements with dimers and trimers of differing isotopic composition show that the measured relaxation times are independent of the isotope exchange on the surface. Therefore, the Li exchange times are immeasurably small ( < 10 ?s).

Dabringhaus, H.; Meyer, H. J.

1983-02-01

60

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

 
 
 
 
61

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

62

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

DEFF Research Database (Denmark)

The electrochemical behaviour of polypyrrole films doped with dodecyl benzene sulfonate (PPy/DBS) in LiCl aqueous electrolytes has been investigated in order to find the electrolyte concentration suitable for the operation of PPy/DBS-based soft actuators. For this investigation, PPy/DBS films deposited on gold-coated quartz crystals by electropolymerization and simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance techniques were used. During the first redox cycle, while large water movement is observed along with the counter ions in dilute electrolytes, such water transport in concentrated electrolytes is found to be very low. In dilute electrolytes, water molecules accompany counter ions as solvated molecules and due to osmotic effect. In concentrated electrolytes, water movement is less due to limited availability of free water as well as a smaller osmotic pressure difference. In highly concentrated aqueous electrolytes, the mass of the PPy/DBS film at the end of each redox cycle is found to drift, which can be controlled by changing the concentration of the electrolyte. The PPy/DBS films were also cycled at different scan rates in various alkali halide aqueous electrolytes of concentrations 0.1 and 1 M to determine the effective diffusion coefficients of alkali ions in the films. The effective diffusion coefficients were found to increase with the concentration of the electrolytes and decrease with the increase in size of cations.

Skaarup, Steen

2014-01-01

63

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)

64

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

65

Band-bending in organic semiconductors: the role of alkali-halide interlayers.  

Science.gov (United States)

Band-bending in organic semiconductors, occurring at metal/alkali-halide cathodes in organic-electronic devices, is experimentally revealed and electrostatically modeled. Metal-to-organic charge transfer through the insulator, rather than doping of the organic by alkali-metal ions, is identified as the origin of the observed band-bending, which is in contrast to the localized interface dipole occurring without the insulating buffer layer. PMID:24338797

Wang, Haibo; Amsalem, Patrick; Heimel, Georg; Salzmann, Ingo; Koch, Norbert; Oehzelt, Martin

2014-02-12

66

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

International Nuclear Information System (INIS)

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

67

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

68

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

Energy Technology Data Exchange (ETDEWEB)

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

Klick, David Ira

1977-01-01

69

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 halide solutions were tested, and again the change in Sodium iodide was observed to be much less. This showed that the velocity of sound in alkali halide solutions was observed to be frequency dependent also that is at certain frequency for a solution velocity remains almost constant with change in normality.

M. N. Nyayate

2012-06-01

70

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

71

Reactions between cold methyl halide molecules and alkali-metal atoms  

International Nuclear Information System (INIS)

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

72

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

73

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

Science.gov (United States)

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 (Es). The basic idea results from the assumption that all the parameters are constants that are usually easy to acquire. Moreover, two previous models (Furth and Schytil equations) were also checked and applied for calculating surface tension of molten salts. The three formulas have been examined for 20 salts and showed remarkable agreement between calculated and experimental data with a difference of less than 10% for most of the salts studied. The heats of sublimation of alkali halides were, theoretically, calculated and compared to literature values.

Aqra, Fathi

2014-05-01

74

Formation of structured nanophases in halide crystals  

Science.gov (United States)

When halide crystals KCl and NaCl are slightly doped by PbCl2, (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 PbCl2 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 PbCl2 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

75

A Kirkwood-Buff Derived Force Field for Aqueous Alkali Halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A classical nonpolarizable force field is presented for the simulation of aqueous alkali halide solutions (MX), where M = Li+, Na+, K+, Rb+, Cs+ and X = F?, Cl?, Br?, I?, and their interactions with biomolecules. The models are specifically designed to reproduce the experimental Kirkwood-Buff integrals, and thereby the solution salt activities, as a function of salt concentration. Additionally, we demonstrate that these models reasonably reproduce other experimental properties includi...

Gee, Moon Bae; Cox, Nicholas R.; Jiao, Yuanfang; Bentenitis, Nikolaos; Weeerasinghe, Samantha; Smith, Paul E.

2011-01-01

76

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

77

Chemical effects induced by gamma-irradiated alkali halides in organic emulsions  

International Nuclear Information System (INIS)

Dissolution of ?-irradiated alkali halides in the emulsions of aromatic hydrocarbon and water results in the formation of halogen charge transfer complexes and hydrogen. These were identified by spectrophotometry. Further, their formation was verified by studying the absorption of a chemical model involving hydrogen incorporated in halogen complex. These products are correlated to the F and hole centers of the irradiated salts. 13 refs.; 4 figs

78

Simultaneous fluorimetric determination of aluminium, indium and magnesium in high-pure alkali metal halides  

International Nuclear Information System (INIS)

Methods for increasing the accuracy of impurity determination in high-pure alkali metal halides are considered taking simultaneous fluorimetric determination of aluminium, indium and magnesium in potassium chloride as an example. It is shown that optimization of analysis by a set of initial spectroscopic data depending on several parameters, leads to the maximum increase of the analysis accuracy. The developed methods of simultaneous determination of metal ions in the form of their complexes with 8-oxyquinoline were preliminary tested using artificial mixtures

79

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

80

Crystal structure and density data. 2. Titanium halides and chalcogenides  

Energy Technology Data Exchange (ETDEWEB)

The following data are tabulated for titanium binary and complex halides and chalcogenides: compound, structural type, crystal system and space group, unit cell dimensions, number of formula units in the unit cell and density.

Franzen, H.F. (Iowa State Univ., of Science and Technology, Ames (USA). Dept. of Chemistry; Ames Lab., IA (USA))

1983-01-01

 
 
 
 
81

On the formation of Z centres in irradiated alkali halides  

International Nuclear Information System (INIS)

The effect of mechanical bleaching on the formation of Z centres in ?-irradiated KCl:Ca has been investigated by examining glow curves from single crystals as-irradiated and from crushed powders from the same sample. (U.K.)

82

Single crystals of alkali aromatic ion pairs  

Energy Technology Data Exchange (ETDEWEB)

The information obtained about ionic structures in solution is necessarily indirect. It has been inferred from shifts in absorption bands and changes in chemical shifts, hyperfine splitting constants, changes in conductance with concentration or from a detailed analysis of measured linewidths. To obtain direct information about their structures, the authors set about to prepare single crystals of alkali aromatic ion pairs. Others have succeeded in preparing single crystals of the paramagnetic alkali biphenyl (Bp) ion pairs. Their crystal structures were successfully elucidated by X-ray diffraction. It appeared that they could be characterized as loose or solvent separated ion pairs. Later on, the authors succeeded in preparing single crystals of potassium cyclooctatetraene (COT) and rubidium cyclooctatetraene. Solving their crystal structures, they could be classified as tight or contact ion pairs. In this paper, they review the crystal structures of the alkali biphenyl ion pairs viz. that of NaBp.2Tg (Tg = triglyme = CH/sub 3/O(CH/sub 2/CH/sub 2/O)/sub 3/CH/sub 3/), of KBp2Ttg (Ttg = tetraglyme = CH/sub 3/O(CH/sub 2/CH/sub 2/O)/sub 2/CH/sub 3/) and Rb/sub 2/COT . Dg. In addition, they describe the crystal structure of Na/sub 2/Tp . 6THF, where TP = terphenyl and THF = tetrahydrofuran. The structures of the ion pairs in the crystal confirm the predictions made for them in solution.

De Boer, E.; Gribnau, M.C.M.

1986-09-01

83

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.

Brady, John

84

Investigation of relations between absorption band positions and crystalline environment in Pb2+-doped alkali halides.  

Science.gov (United States)

The relationships between sp energy levels (A, B and C bands) as well as the charge transfer band (D band) of Pb(2+)-doped alkali halides and the crystalline environment were thoroughly investigated by means of dielectric theory of chemical bonds for complex crystals. It is found that the coordination number of the central ion, the bond volume polarizability, and the fractional covalence of the chemical bond between the central ion and the nearest anion are the major factors influencing the positions of A, B, C and D bands of Pb(2+). Our model has successfully built links between the E(A), E(B), E(C) and E(D) of Pb(2+) and the environmental factor h. Results indicated that the energies of sp levels and the charge transfer band of Pb(2+) all decrease with increase of h. The h has a linear relationship with the sp energy levels, and an exponential relationship with the charge transfer band. The model calculation results are in good agreement with experimental data. The current model can serve as a prediction tool and can be applied to assign and reassign the A, B, C and D band positions of Pb(2+). The model predicts the positions of B, C and D bands of NaF:Pb(2+) at 7.516, 8.688 and 12.796 eV, respectively; the D band of CsCl:Pb(2+), CsBr:Pb(2+) and CsI:Pb(2+) at 6.633, 6.389 and 5.275 eV, respectively. We reassign the C band of Pb(2+) in NaBr as 5.276 eV but not the reported 5.636 eV, which is more reasonable to be ascribed to the charge transfer band. PMID:20379510

Sun, Qiang; Qu, Baohan; Shi, Jinsheng

2010-04-28

85

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

International Nuclear Information System (INIS)

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

86

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

87

Phonon force models and surfaces of near degeneracy in the isobaric alkali halides  

International Nuclear Information System (INIS)

A number of near degeneracies occur in the measured phonon spectra of the isobaric alkali halides NaF, KCl, RbBr, and CsI, in which the alkali- and halogen-ion masses are nearly equal. The lattice dynamics of KCl and RbBr are reexamined in terms of several different shell models. It is shown that the observed eigenfrequencies in these materials can be fitted essentially as well by an artificial model in which the two ions are treated as identical except for their charge as by a general 11-parameter model. The calculations indicate the existence of surfaces of near degeneracy in the Brillouin zone, as predicted by Segall and Foldy. Neutron-structure-factor measurements may be required to distinguish among realistic competing force models

88

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

89

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

90

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

91

- and Photon-Stimulated Desorption of Excited Hydrogen Atoms from Alkali Halide Surfaces  

Science.gov (United States)

This dissertation presents the first extensive investigation of electronically-stimulated desorption of excited hydrogen atoms from alkali halide surfaces. Such desorption is observed in fluorescence spectra from alkali halide compounds which are irradiated by electrons or photons in the presence of H_{rm 2} . The fundamental adsorbate-surface interactions which lead to the emission of excited hydrogen atoms has long been an open question. This treatise addresses the nature of this surface bond, its bonding site, and the bond-breaking processes involved in the desorption of excited hydrogen atoms from these surfaces. To this end, the desorption yields of excited hydrogen atoms from the surfaces of KCl, KBr, NaCl, NaF and LiF have been measured as a function of incident photon and electron energy and flux, time of irradiation, dosing pressure of H_{rm 2} and sample temperature. Under electron or photon bombardment, halogen atoms are preferentially desorbed leaving a metal -rich surface. The results of this study indicate that the desorption yields of H^{* } follow the time evolution of this excess metal and its subsequent evaporation as the substrate is heated. Energy dependent yields of H^{ *} exhibit a prominent resonance at threshold when irradiated by photons. This is the first observation of a selective bond-breaking process leading to desorption of neutral hydrogen atoms from a surface. Resonant yields stimulated from compounds which contain the same alkali metal occur energetically at the same incident photon energies. The energy thresholds of electron bombardment studies are also correlated to the alkali component of the substrate. These observations suggest that H_ {rm 2} is dissociatively chemisorbed at surface sites possessing surplus alkali metal. The desorption of excited hydrogen atoms with several electron volts of kinetic energy follows a Franck-Condon excitation analogous to gas-phase dissociative excitation of diatomic molecules. In this study the electron- or photon-induced valence excitation is to a neutral, antibonding state of the surface alkali hydride molecule.

Hudson, Lawrence Thomas

92

Quantitative determination of elements and identification of compounds of alkali halides by depth-sensitive secondary neutral mass spectrometry  

International Nuclear Information System (INIS)

In the development of a depth-sensitive analysis of saline microparticles, alkali halide salts were studied by plasma-based SNMS in an effort to check on the quantitative determination of elements and the detection of compounds for the example of salts. (orig./BBR)

93

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

Science.gov (United States)

Pressing solid barbituric acid with KBr to prepare samples for IR spectroscopy leads to the formation of an ionic co-crystal, in which the co-former is a classical ionic salt; co-crystal formation is also obtained with the other alkali bromides (LiBr, NaBr, RbBr and CsBr) and with caesium iodide. The simultaneous presence of alkali and halide ions affects the dissolution properties of barbituric acid in water. PMID:20852785

Braga, Dario; Grepioni, Fabrizia; Maini, Lucia; Prosperi, Susanna; Gobetto, Roberto; Chierotti, Michele R

2010-11-01

94

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Gobetto, Roberto; Chierotti, Michele Remo

2010-01-01

95

A Kirkwood-Buff Derived Force Field for Aqueous Alkali Halides.  

Science.gov (United States)

A classical nonpolarizable force field is presented for the simulation of aqueous alkali halide solutions (MX), where M = Li(+), Na(+), K(+), Rb(+), Cs(+) and X = F(-), Cl(-), Br(-), I(-), and their interactions with biomolecules. The models are specifically designed to reproduce the experimental Kirkwood-Buff integrals, and thereby the solution salt activities, as a function of salt concentration. Additionally, we demonstrate that these models reasonably reproduce other experimental properties including ion diffusion constants, dielectric decrements, and the excess heats of mixing. The parameters are developed by considering the properties of aqueous NaX and MCl solutions using a previously established model for NaCl. Transferability of the parameters to other salts is then established by the successful simulation of additional aqueous salt solutions, KI and CsBr, not originally included in the parameterization procedure. PMID:21789033

Gee, Moon Bae; Cox, Nicholas R; Jiao, Yuanfang; Bentenitis, Nikolaos; Weeerasinghe, Samantha; Smith, Paul E

2011-04-26

96

Electron resonance-fluctuation transport and hole thermally activated migration mechanism in alkali halides  

International Nuclear Information System (INIS)

Experiments on the hole capture by the activator in thallium activated alkali halides were interpreted in terms of the model of thermally activated hole migration taking into account tunnel recombination of the electron having virtually changed its energy (the latter being caused by local fluctuations in a lattice point with a virtually excited hole in the Vk-centre potential well). It has been shown that there manifests itself a new mechanism of non-coherent small polaron motion - resonance transitions from the Vk-centre vibrationally excited level to virtual fluctuation levels in the lattice - which is proved by the two-times degradation of the effective activation energy at the hole capture by the activator. This mechanism is preconditioned by the interaction of virtual fluctuations as well as their life-time dependence on energy

97

Identification of a Tl dimer centre in alkali halides by ODMR  

International Nuclear Information System (INIS)

In Tl+-doped alkali halides laser-active centres can be produced by ionising irradiation. This treatment inevitably produces other Tl-associated centres, which might degrade the laser performance. One of these centres that absorbs in the wavelength region where the laser centre is pumped was identified in the hosts KCl, RbCl and KBr by measuring its magnetic circular dichroism (MCD) tagged by electron spin resonance (ESR). The positions of the lowest-energy absorption and emission bands as well as sign and magnitude of the MCD resemble closely those of the laser centre. From the analysis of the optically detected ESR the structure of this new centre was determined. It consists of two neighbouring Tl+ cations adjacent to an anion vacancy, which share an electron. The ESR spectrum is explained be a fast hopping of the unpaired electron between the two Tl+ positions. (author)

98

Impact-induced cleaving and melting of alkali-halide nanocrystals.  

Science.gov (United States)

Impact of nanocrystalline alkali-halide clusters against solid surfaces causes them to fission exclusively into low surface-energy fragments. In time-of-flight scattering experiments, this process appears at an impact energy so low that it must result from a single-step cleavage of the nanocrystal along low surface-energy cleavage planes. At higher energies (more than 1 electron volt per atom), a crossover occurs to an entirely different behavior-evaporative cascades that proceed irrespective of the structureenergetic properties of the fragments. These cascades, and the approximately linear scaling of the crossover energy with cluster size, are characteristic of impact-induced transformation of the cluster to a molten state. Collision with the high-rigidity surface of silicon gives a substantially greater cleavage probability than the soft basal-plane surface of graphite. PMID:17751822

Beck, R D; John, P S; Homer, M L; Whetten, R L

1991-08-23

99

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

International Nuclear Information System (INIS)

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

100

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-10-14

 
 
 
 
101

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-05-05

102

Mechanoluminescence in ?- irradiated potassium halide crystals induced by pressure pulse  

International Nuclear Information System (INIS)

During the application of pressure pulse in ?-irradiated potassium halide crystals, two peaks are observed in the ML intensity versus time curves. The ML intensity corresponding to the first peak is always greater than that of the second peak. The ML intensity after first peak and second peak decays exponentially with time. ML is a volumetric phenomenon, and its intensity increases with increasing size of the crystals. (author)

103

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

104

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Georgiev, Mladen

2007-01-01

105

X- (X = O, S) ions in alkali halide lattices through density functional calculations. 1. Substitutional defect models.  

Science.gov (United States)

Monoatomic X- (X = O, S) chalcogen centers in MZ (M = Na, K, Rb and Z = Cl, Br, I) alkali halide lattices are investigated within the framework of density functional theory with the principal aim to establish defect models. In electron paramagnetic resonance (EPR) experiments, X- defects with tetragonal, orthorhombic, and monoclinic g-tensor symmetry have been observed. In this paper, models in which X- replaces a single halide ion, with a next nearest neighbor and a nearest neighbor halide vacancy, are validated for the X- centers with tetragonal and orthorhombic symmetry, respectively. As such defect models are extended, the ability to reproduce experimental data is a stringent test for various computational approaches. Cluster in vacuo and embedded cluster schemes are used to calculate energy and EPR parameters for the two vacancy configurations. The final assignment of a defect structure is based on the qualitative and quantitative reproduction of experimental g and (super)hyperfine tensors. PMID:16623497

Stevens, F; Vrielinck, H; Van Speybroeck, V; Pauwels, E; Callens, F; Waroquier, M

2006-04-27

106

Anomalous high-field electron injection and photoconduction in thin-film alkali halides  

Energy Technology Data Exchange (ETDEWEB)

Transient ion currents in thin-film alkali halides at ca. <2 V, which may exceed 10/sup -4/ A cm/sup -2/ at 1 ms, decay rapidly according to Iproportionalt/sup -m/ with 0

Pisanias, M.N.; Hamill, W.H.

1980-03-01

107

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)

108

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)

109

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

International Nuclear Information System (INIS)

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

110

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

International Nuclear Information System (INIS)

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

111

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-01-01

112

On the interpretation of luminescence of lead halide crystals  

Energy Technology Data Exchange (ETDEWEB)

Emission and excitation spectra, and the luminescence decay kinetics have been studied for PbCl{sub 2} crystals at the temperatures 0.45-100 K. It has been found that even at the lowest temperatures, where the non-radiative decay of exciton states in PbCl{sub 2} does not take place, the decay times of both the ultraviolet (UV) and the blue (B) exciton emission are by a few orders of magnitude shorter than the decay times of the emission arising from the triplet relaxed excited state of Pb{sup 2+} centres in lead-doped ionic crystals. A conclusion has been drawn that the luminescence of lead halides cannot be connected with single Pb{sup 2+} ions. It is proposed that the radiative decay of the self-trapped excitons of the type of {l_brace}(Pb{sub 2}){sup 3+} + hole{r_brace} is responsible for the UV and the B emission of PbCl{sub 2} crystals, while the lowest-energy (BG) emission arises from the tunnelling recombinations between the (Pb{sub 2}){sup 3+}-type self-trapped electrons and V{sub K}-type self-trapped holes. (orig.)

Babin, V.; Krasnikov, A.; Stolovits, A.; Zazubovich, S. [Tartu Univ. (Estonia). Inst. of Physics; Nikl, M. [ASCR, Prague (Czech Republic). Inst. of Physics

2002-02-01

113

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)

114

Studies of Non-Proportionality in Alkali Halide and Strontium Iodide Scintillators Using SLYNCI 6-16-2009  

International Nuclear Information System (INIS)

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

115

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

116

Integrating 2-D position sensitive X-ray detectors with low-density alkali halide storage targets  

International Nuclear Information System (INIS)

For the use in scattering experiments with synchrotron radiation, integrating position sensitive X-ray detectors are discussed. These detectors store the photon number equivalent charge (PNEC) in low-density alkali halide targets. Performance tests are given for a detector which uses a Gd2O2S fluorescence screen for X-ray detection and the low-density KCl storage target of a television SEC vidicon tube for photon integration. Rather than directly by X-rays, this target is charged by 6 keV electrons from the image intensifier section of the vidicon. Its excellent storage capability allows measurements of extremely high-contrast, high-flux X-ray patterns with the same accuracy as achieved with any single photon detection system if the discussed readout techniques are applied. (orig.)

117

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

118

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

119

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

International Nuclear Information System (INIS)

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

120

Assembly of 2D ionic layers by reaction of alkali halides with the organic electrophile 7,7,8,8-tetracyano-p-quinodimethane (TCNQ).  

Science.gov (United States)

Sublimation of alkali halides (NaCl and LiCl) onto a pre-assembled hydrogen-bonded layer of TCNQ on Au(111) resulted in the formation of 2D ionic layers via a direct charge-transfer reaction without involvement of the substrate. The presented approach allows for the fabrication of different ionic layers, decoupled from the substrate and offering new, potentially interesting properties. PMID:21750826

Wäckerlin, Christian; Iacovita, Cristian; Chylarecka, Dorota; Fesser, Petra; Jung, Thomas A; Ballav, Nirmalya

2011-08-28

 
 
 
 
121

Temperature dependence of the rate of reactions of the solvated electron in irradiated melts of alkali metal halides  

International Nuclear Information System (INIS)

The temperature dependence of the rate of disappearance of e-/sub s/ in molten alkali metal halides in the presence of various electron acceptors, was investigated so that data on the mechanism of the reactions of solvated electrons (es) in melts could be investigated. The investigation was conducted by the method of microsecond pulsed radiolysis with optical recording. A U-12 linear electron accelerator was used as the radiation source (energy of electrons 5 NeV, duration of pulse 2.3 ?sec). The parameters of the rapid-action spectro-photometric setup, techniques of preparation of the samples and irradiation correspond to those described in previous reports. To conduct the experiments in a wide range of temperatures, melts of NaC1-CsC1 (34/66 mole %) and LiBr-KBr (60/40 mole %) mixtures, the melting points of which are 493 and 3480C, respectively, were selected as the main systems. The disappearance e-/sub s/ in the investigated melts proceeds very rapidly even in the absence of an electron acceptor (in less than 3 ?sec after passage of the pulse). A quatitative measurement of the reactivity of e-/sub s/, was conducted on the basis of the dependence of its limiting concentration during the pulse on the concentration of the introduced acceptor

122

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

123

Temperature dependence of rate of solvated electron reactions in alkali metal halide irradiated melts  

International Nuclear Information System (INIS)

Temperature dependence of the reaction rate of solvated electron (esub(S)sup(-)) disappearance in molten mixture NaCl-CsCl (34/66 mol. %) and LiBr-KBr (60/40 mol. %) in the presence of different electron acceptors is studied. The investigation is made using the method of microsecond pulse radiolysis with optical recording. A linear electron accelerator electron energy 5 MeV and pulse duration 2.3 ?s is used as a radiation source. Quantitative measurement of reactivity esub(S)sup(-) is conducted on the basis of dependence of its limiting concentration during the pulse on the concentration of the acceptor introduced. It is established that the observed disappearance rate constant esub(S)sup(-) in pure matrix, i. e. according to reaction with alkali metal cation, with the temperature increase up to 600-700 deg C increases, it is explained by the activation nature of the process. However, with further temperature increase the decrease of Ksub(observed) takes place, which is conditioned by reversibility of esub(S)sup(-) reaction with Msup(n+) cation. The decrease of Ksub(observed) is still more effective for reactions with higher rate constants (for Cd2+, for instance)

124

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

International Nuclear Information System (INIS)

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

125

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)

126

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

127

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

128

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

International Nuclear Information System (INIS)

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

129

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

International Nuclear Information System (INIS)

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

130

Ion-selective electrodes with liquid membranes based on solvates of alkali metal salts of metal halide anions in voltammetry in solvating solvents  

International Nuclear Information System (INIS)

Alkali metal salts of metal halide anions, dissolved in oxygen-bearing solvents and solvated by them via the hydrate-solvate mechanism, may be considered as a new class of electrode-active substances and used as ion exchangers of liquid membranes for ion-selective electrodes. The membranes exhibit both the anionic and cathionic functions, the first being stronger. Such membranes are more selective in some cases towards certain complex anions and tend to carry higher charged anions compared with a membrane based on tetradecyl ammonium bromide. Some solvate liquid membranes are characterized by satisfactory analytical functions. 16 refs., 4 figs., 3 tabs

131

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

132

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

International Nuclear Information System (INIS)

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

133

Spatial correlation of latent image centers active in photostimulable luminescence of irradiated doped alkali halides  

Science.gov (United States)

Changes in the photostimulated luminescence (PSL) spectrum of an electron irradiated KBr:Tl single crystal in relation to the A-luminescence spectrum upon direct activator ion excitation in the A-absorption band (AL) are found. Based on the view about the spatial correlation between F and activator hole centers, it is suggested that anion vacancy is an additional perturbing factor fot he activator (Tl+) excited (p-electron) state which is already subject to the dynamical Jahn-Teller effect. Dependences of the PSL efficiency on activator (In+) concentration in KBr:In samples irradiated by UV-light (6.30-6.45 eV), X-rays (30 keV or electrons (5.6 keV), are compared. The possible role of 6.45 eV photons is discussed in context with the hypothesis of efficient exciton energy transfer at room temperature (RT).

Tale, Aija; Plavina, Irena

2001-03-01

134

Heteroepitaxial strain in alkali halide thin films: KCl on NaCl  

DEFF Research Database (Denmark)

We have pet-formed Monte Carlo simulations of the properties of a NaCl (001) surface covered by full or partial layers of KCl, for coverages up to 5 monolayers (ML). A wide variety of structures of the film is found. For integer ML coverages we find the continuous, so-called floating mode rumple structure, as was previously found in the KBr/NaCl system. However, for a coverage of similar to 2.1 ML, we find a discrete structure of periodicity 3:4 of small regularly spaced KCl pyramids. It has the same scattering characteristics as the structure observed by Henzler et al. [Phys. Rev. B 52, 17 060 (1995)], but it is two-dimensional modulated, rather than the rowlike stacking fault structure proposed by Henzler et al. Also, at a coverage of similar to 0.8 ML there is a stable 3:4 structure. Other structures are found at intermediate coverages, corresponding to regular arrays of dislocation lines with periodicity 9:10. A further growth from such structures would give rise to growth of a similar to 5 degrees miscutKCl crystal relative to the NaCl lattice. The reciprocal space patterns corresponding to the continuous and the discrete film deformations are also calculated.

Lindgård, Per-Anker

1999-01-01

135

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

136

Construction of a double-layered tetrahedral network within a perovskite host: Two-step route to the alkali-metal-halide layered perovskite (Li x Cl)LaNb2O7  

International Nuclear Information System (INIS)

A two-step topotactic route is used to construct lithium halide layers within a perovskite host. Initially RbLaNb2O7 is converted to (CuCl)LaNb2O7 by ion exchange and then reductive intercalation with n-butyllithium is used to form (Li x Cl)LaNb2O7. The copper metal byproduct from the reduction step is removed by treatment with iodine. Rietveld refinement of neutron powder diffraction data revealed that an alkali-halide double layer with LiO2Cl2 tetrahedra forms between the perovskite slabs. Compositional studies indicate that the range for x in (Li x Cl)LaNb2O7 is 2?x<4, which appears consistent with the neutron data where only one lithium site was found in the structure. - Graphical abstract: Alkali-halide layers can be constructed within a layered perovskite host via a two-step topochemical process

137

Elementary processes of photolysis in lead halide crystals  

Energy Technology Data Exchange (ETDEWEB)

Emission spectra from PbCl{sub 2} crystals doped with various amount of Tl{sup +} ions have been measured at 4.8 K by varying the excitation photon energy. Two additional emission bands appear in the green region (G{sub 1} at 2.48 and G{sub 2} at 2.39 eV) with excitation in the low energy tail region of the excitonic absorption band. The G{sub 1}- and G{sub 2}-emissions show behavior similar to the intrinsic ultraviolet (UV at 3.78 eV) and blue-green (BG at 2.62 eV) emission, respectively, in their excitation spectra, temperature dependence and thermal quenching effect. By quenching the crystal from 620 K to room temperature, the intensities of the UV- and G{sub 1}-emissions are diminished drastically while those of the BG- and G{sub 2}-emissions are maintained. The G{sub 1}- and G{sub 2}-emissions are related to the [Tl{sup 0}(Cl{sup -}){sub 3}+hole] center and the [(PbTl){sup 2+}+hole] center corresponding to the [Pb{sup +}(Cl{sup -}){sub 3}+hole] center for the UV-emission and [(Pb{sub 2}){sup 3+}-STEL +hole] center for the BG-emission in the host crystal, respectively. A well-defined excitation band for the G{sub 1}-emission is established through spectral decomposition of the observed emission spectra. This means that the Tl{sup +}-related excitons maintain a rather strong localized nature leading to luminescence specific to the doped Tl{sup +} ion. The role of the anion vacancy will be discussed in relation to the lattice relaxation and the photolysis processes.

Nakagawa, H. E-mail: nakagawa@wbase.fuee.fukui-u.ac.jp; Terakami, M.; Yasuda, K

2001-10-01

138

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

139

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)

140

Purification growth of orthorhombic molybdenum trioxide crystals from alkali-metal-containing Mo-sources  

Science.gov (United States)

Transparent and colourless ?-MoO 3 crystal platelets have been prepared in vapour phase from various alkali-metal-containing molybdenum sources. With XRD technique, it is evident that the ?-MoO 3 is the only crystalline phase in the as-grown crystals. Furthermore, FTIR and elemental analysis results reveal that alkali metals are not intercalated in the layered crystal lattice of ?-MoO 3. Factors that lead to the success of this purification growth are identified. In view of its simplicity, this method can be efficiently used for laboratory preparation of high quality ?-MoO 3 crystals from low-grade molybdenum sources.

Zeng, H. C.

1999-06-01

 
 
 
 
141

Potential Advantage of Multiple Alkali Metal Doped KNbO3 Single Crystals  

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

Hideo Kimura

2014-06-01

142

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.)

143

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

Science.gov (United States)

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

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

2014-06-01

144

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)

145

Alkali reduction of graphene oxide in molten halide salts: production of corrugated graphene derivatives for high-performance supercapacitors.  

Science.gov (United States)

Herein we present a green and facile approach to the successful reduction of graphene oxide (GO) materials using molten halide flux at 370 °C. GO materials have been synthesized using a modified Hummers method and subsequently reduced for periods of up to 8 h. Reduced GO (rGO) flakes have been characterized using X-ray-diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR), all indicating a significantly reduced amount of oxygen-containing functionalities on the rGO materials. Furthermore, impressive electrical conductivities and electrochemical capacitances have been measured for the rGO flakes, which, along with the morphology determined from scanning electron microscopy, highlight the role of surface corrugation in these rGO materials. PMID:25337832

Abdelkader, Amr M; Vallés, Cristina; Cooper, Adam J; Kinloch, Ian A; Dryfe, Robert A W

2014-11-25

146

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

International Nuclear Information System (INIS)

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

147

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.)

148

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

Science.gov (United States)

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

Kido, Yoshiaki; Okazawa, Tetsuaki

149

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

150

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

Science.gov (United States)

The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ?0.5–2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s?1 at pH 6 and 5 s?1 at pH 8 in contrast to 6 s?1 at pH 6 and 2 s?1 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher for B. 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 80°C, less than the ?50 minutes at 80°C for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH?8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization. PMID:24915287

Brander, S?ren; Mikkelsen, J?rn D.; Kepp, Kasper P.

2014-01-01

151

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

152

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

153

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.)

154

Residual gas analysis of volatile impurities in halide precursors for scintillator crystals  

Science.gov (United States)

Alkaline-earth halides can be made into bright scintillators if purity is maintained during synthesis and growth. In order to investigate precursor purity, beaded halide precursors were heated under vacuum and evolved gas was assessed by residual gas spectroscopy. These precursors included cesium chloride, lithium chloride, yttrium chloride, cerium chloride, strontium iodide, europium iodide, barium bromide, and europium bromide. Water and CO2 desorption, sulfur release, argon release, and halide dissociation was observed in samples. Triply-oxidized precursors showed multiple paths to decomposition. The data inform approaches toward purification and growth.

Swider, S.; Motakef, S.; Datta, A.; Higgins, W. M.

2013-09-01

155

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) 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.

156

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

Science.gov (United States)

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

Naghavi, S. Shahab; Tosatti, Erio

2014-08-01

157

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

International Nuclear Information System (INIS)

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

158

A Combined Metal-Halide/Metal Flux Synthetic Route towards Type-I Clathrates: Crystal Structures and Thermoelectric Properties of A8 Al8 Si38 (A=K, Rb, and Cs).  

Science.gov (United States)

Single-phase samples of the compounds K8 Al8 Si38 (1), Rb8 Al8 Si38 (2), and Cs7.9 Al7.9 Si38.1 (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

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

Energy Technology Data Exchange (ETDEWEB)

We show for the first time that irradiation at room temperature of alkali iodide crystals by fast heavy ions ({sup 40}Ar{sup 14+} ions of 5.53 MeV/A at a fluence of 10{sup 13} ions/cm{sup 2}) leads to the formation of V-type defects. By means of UV visible optical absorption and resonant Raman scattering measurements, we have identified I{sub 3}{sup -}, I{sub 5}{sup -} and (I{sub 2}){sub n} in Kl and only I{sub 3}{sup -} and I{sub 5}{sup -} in RbI irradiated under similar conditions. These preliminary results are consistent with previous investigations obtained in iodide crystals after exposure to X or {gamma} rays at room temperature. (orig.).

Rzepka, E.; Wery, J.; Lefrant, S. (Lab. de Physique Cristalline, Univ. de Nantes, 44 (France)); Ramstein, B.; Tamisier, R.; Hourdequin, E. (Lab. de Physique Nucleaire de Nantes, Univ. de Nantes, 44 (France)); Bouffard, S. (C.I.R.I.L., 14 - Caen (France))

1992-02-01

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

Relation between interatomic distances and sizes of ions in molecules and crystals.  

Science.gov (United States)

Bond lengths and dissociation energies in alkali halides and alkaline earth oxides and fluorides have been analysed. Ions are considered as static deformable spheres, where an essential part of the electron density is concentrated. In molecules, they are compressed. Moving from molecules to crystals, the bond lengths are extended to such an extent that closed electron shells of ions in alkali halide crystals are separated by distances of approximately 20 pm owing to weakened Coulomb attractive forces acting in opposite directions in a crystal. Short-range repulsion is important only within a few surface layers. Some ionic radii are approximately estimated. PMID:12324689

Ignatiev, Viktor

2002-10-01

162

Crystal structure of the novel haloalkane dehalogenase DatA from Agrobacterium tumefaciens C58 reveals a special halide-stabilizing pair and enantioselectivity mechanism.  

Science.gov (United States)

A novel haloalkane dehalogenase DatA from Agrobacterium tumefaciens C58 belongs to the HLD-II subfamily and hydrolyzes brominated and iodinated compounds, leading to the generation of the corresponding alcohol, a halide ion, and a proton. Because DatA possesses a unique Asn-Tyr pair instead of the Asn-Trp pair conserved among the subfamily members, which was proposed to keep the released halide ion stable, the structural basis for its reaction mechanism should be elucidated. Here, we determined the crystal structures of DatA and its Y109W mutant at 1.70 and 1.95 Å, respectively, and confirmed the location of the active site by using its novel competitive inhibitor. The structural information from these two crystal structures and the docking simulation suggested that (i) the replacement of the Asn-Tyr pair with the Asn-Trp pair increases the binding affinity for some halogenated compounds, such as 1,3-dibromopropane, mainly due to the electrostatic interaction between Trp109 and halogenated compounds and the change of substrate-binding mode caused by the interaction and (ii) the primary halide-stabilizing residue is only Asn43 in the wild-type DatA, while Tyr109 is a secondary halide-stabilizing residue. Furthermore, docking simulation using the crystal structures of DatA indicated that its enantioselectivity is determined by the large and small spaces around the halogen-binding site. PMID:24770384

Guan, Lijun; Yabuki, Hideya; Okai, Masahiko; Ohtsuka, Jun; Tanokura, Masaru

2014-10-01

163

Stability diagrams for complexes in molten mixtures of halide salts  

International Nuclear Information System (INIS)

The stability of local fourfold coordination for divalent and trivalent metal ions in liquid mixtures of polyvalent metal halides and alkali halides is classified by means of structural coordinates obtained from properties of the elements. In parallel with earlier classifications of compound crystal structures and molecular shapes, the elemental properties are taken from first-principles calculations of valence electron orbitals in atoms, in the form of (i) the nodal radii of Andreoni, Baldereschi and Guizzetti or (ii) the pseudo-potential radii of Zunger and Cohen. As a third alternative we also consider a classification based on Pettifor's phenomenological chemical scale of the elements. The alternative structural classification schemes that are developed from these elemental properties are very successful in distinguishing molten mixtures in which the available experimental evidence indicates stability of ''complexes'', i.e. long-lived fourfold coordination of polyvalent metal ions. (author). 55 refs, 3 figs

164

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

165

Rare-Earth Tri-Halide Methanol-Adduct Single-Crystal Scintillators for Gamma Ray and Neutron Detection - 8/17/09  

Energy Technology Data Exchange (ETDEWEB)

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, Lynn A [ORNL; Wisniewski, D. [Institute of Physics, Nicolaus Copernicus University, Toru?, Poland; Neal, John S [ORNL; Bell, Zane W [ORNL; Ramey, Joanne Oxendine [ORNL; Kolopus, James A [ORNL; Chakoumakos, Bryan C [ORNL; Custelcean, Radu [ORNL; Wisniewska, Monika [Environmental College, Bydgoszcz, Poland; Peña, K. E. [Oak Ridge National Laboratory (ORNL)

2009-01-01

166

Silver halide lasers and amplifiers: Nd ion diffusion in AgBr crystals  

Science.gov (United States)

The luminescence of silver bromide crystals doped with rare earth ions (Nd3+) was investigated in the visible and near IR spectral ranges. The emission, excitation, and absorption spectra, as well as the kinetic parameters, were measured over a broad temperature range. Crystal doping was produced by growing in the melt and by a diffusion method. A novel method for measuring the diffusion profile of rare earth ions in AgBr crystals, based on the luminescence distribution of the dopant, was proposed. The luminescence parameters of AgBr:Nd crystals doped by the diffusion method were compared with these for crystals doped by adding Nd3+ to the melt. The spectroscopy parameters of Pr3+ and Er3+ ions in AgBr crystals doped in the melt were also investigated. The Judd-Ofelt analysis was applied to the rare-earth doped crystals, and transition rates, branching ratios, and quantum efficiencies were calculated. Good agreement between theory and experiment was obtained.

Nagli, Lev; German, Alla; Katzir, Abraham

1998-06-01

167

Metal-ion-doped silver halide crystals and fibers: I. Luminescence experiments  

Science.gov (United States)

The luminescence of silver bromide crystals doped with rare earth ions (Nd3+, Pr3+, and Er3+) was investigated in the visible and near infrared spectral ranges. The emission, excitation, and absorption spectra, as well as the kinetic parameter, were measured over a broad temperature range. The Judd-Ofelt analysis was applied to the rare-earth doped crystals, and transition rates, branching ratios, and quantum efficiencies were calculated. Good agreement between theory and experiment was obtained.

Oron, Ram; Bunimovich, David; Nagli, Lev; Katzir, Abraham; Hardy, Amos A.

1998-01-01

168

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

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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....

Bastiani, M.; D Innocenzo, V.; Stranks, Sd; Snaith, Hj; Petrozza, A.

2014-01-01

169

Middle infrared luminescence of rare earth ions in silver halide crystals  

Science.gov (United States)

Middle infrared laser systems for countermeasures against heat seeking missiles are currently under development. These systems, based on optical parametric oscillators, are complex, bulky and expensive. Middle-infrared fiber lasers emitting in the 3-5?m spectral region may provide an attractive alternative to the systems under development. We have investigated luminescence of silver bromide-chloride crystals and fibers doped with rare earth ions (e.g. Pr 3+, Tb 3+ and Nd 3+) in the near and middle infrared spectral ranges. The emission, excitation, and absorption spectra, as well as the kinetic parameters, were measured over a broad temperature range. The crystal doping was produced by growing from the melt. No significant differences were found between the luminescence properties in bulk crystals and in fibers. The Judd Ofelt analysis was applied to the doped crystals, and the transition rates, branching ratios, and quantum efficiencies were calculated. Good agreement was obtained between theory and experiment. The strong middle-infrared luminescence and the kinetic parameters of these crystals make them good candidates for the fabrication of fiber lasers in the 4-5.5?m spectral range.

Brodetzki, G.; Gayer, O.; Lyakhovsky, I.; Nagli, L.; Katzir, A.

2006-05-01

170

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-11-15

171

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

2014-07-01

172

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

International Nuclear Information System (INIS)

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

173

Alkali metal ion templated transition metal formate framework materials: synthesis, crystal structures, ion migration, and magnetism.  

Science.gov (United States)

Four transition metal formate coordination polymers with anionic frameworks, namely, Na[Mn(HCOO)3], K[Mn(HCOO)3], Na2[Cu3(HCOO)8], and K2[Cu5(HCOO)12], were synthesized using a mild solution chemistry approach. Multitemperature single-crystal (100-300 K) and powder X-ray diffraction studies of the compounds reveal structures of large diversity ranging from cubic chiral Na-Mn formate to triclinic Na-Cu formate. The structural variety is caused by the nature of the transition metals, the alkali metal ion templation, and the versatility of the formate group, which offers metal-metal coordination through three different O-C-O bridging modes (syn-syn, syn-anti, anti-anti) in addition to metal-metal bridging via a single oxygen atom. The two manganese(II) compounds contain mononuclear, octahedrally coordinated moieties, but the three-dimensional connectivity between the manganese octahedra is very different in the two structures. The two copper frameworks, in contrast, consist of binuclear and mononuclear moieties (Na-Cu formate) and trinuclear and mononuclear moieties (K-Cu formate), respectively. Procrystal electron density analysis of the compounds indicates one-dimensional K(+)-ion conductivity in K-Mn and K-Cu, and the nature of the proposed potassium ion migration is compared with results from similar analysis on known Na(+) and K(+) ion conductors. K-Mn and Na-Mn were tested as cathode materials, but this resulted in poor reversibility due to low conductivity or structural collapse. The magnetic properties of the compounds were studied by vibrating sample magnetometric measurements, and their thermal stabilities were determined by thermogravimetric analysis and differential thermal analysis. Despite structural differences, the metal formates that contain the same transition metal have similar magnetic properties and thermal decomposition pathways, that is, the nature of the transition metal controls the compound properties. PMID:25233266

Eikeland, Espen; Lock, Nina; Filsø, Mette; Stingaciu, Marian; Shen, Yanbin; Overgaard, Jacob; Iversen, Bo Brummerstedt

2014-10-01

174

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

DEFF Research Database (Denmark)

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

Eikeland, Espen; Lock, Nina

2014-01-01

175

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.)

176

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

177

Origin of radiative transitions from metastable minima of the excited state of Sn2+vsub(c)- centres in alkali halides  

International Nuclear Information System (INIS)

The dependence of electronic wave functions on the coordinates of not totally symmetric vibrations and the hyperfine interaction are considered theoretically as the possible reasons of the radiative decay of the metastable minima of the sp excited state of Sn2+vsub(c) centres in KCl crystals. It is shown that the dependence of electronic wave functions on the coordinates of not totally symmetric vibrations, which leads to the dynamical lowering of symmetry and removal of forbiddenness for radiative transition from metastable minima (deviation from the Condon approximation), is the main reason of the radiative decay. Taking into account also the mixing of the functions of the radiative and metastable minima by the hyperfine interaction, a 1 to 10% shortening of decay time tau is expected at the transition from natural tin (containing 16% of Sn119) to pure isotope Sn119. A comparison of the decay times is performed which are measured at 2 and 4.2 K for Asub(T) luminescence of Sn2+vsub(c) centres in KCl crystals doped with tin having different isotopic abundance. The values of tau in KCl:SnCl2 and KCl:119SnCl2 crystals are shown to differ to about 4%, whereas in KCl crystals doped with the isotope 119Sn the decay time is always shorter than that in KCl with natural tin. This result, being the first experimental observation of the influence of the hyperfine interaction on luminescence decay kinetics of impurity centres in the crystals, is in good agreement with the theory. (author)

178

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

DEFF Research Database (Denmark)

The effect of alkali-silicate glassy matrix as replacement for feldspar in soft and hard porcelain compositions was studied. SEM and X-ray diffraction analysis were used to evidence phase evolution. For each composition, the influence of soaking time was evaluated. The difference in chemical composition (amount of alkali and alumina) between the two types of porcelain studied influenced the final microstructure: density, pore size and shape, and mullite content. Quartz dissolution was more important in soft porcelain where the mullitization was limited by the low amount of alumina compared to hard porcelain. Replacing the feldspar by alkali-silicate glassy matrices with similar chemical composition, the amount of secondary mullite and mechanical properties increased in both soft and hard compositions.

Boccaccini, Dino

2009-01-01

179

Nonmetal-metal transition in molten potassium-potassium halide solutions  

International Nuclear Information System (INIS)

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

180

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

 
 
 
 
181

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

International Nuclear Information System (INIS)

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

182

Comparative crystal-chemical analysis of binary compounds and d-block metal halides containing tetrahedral anions  

International Nuclear Information System (INIS)

Using the TOPOS structural topological program package, comparative topological analysis was performed for binary compounds and 35 d-metal halides with tetrahedral anions MX4 (M = d-metal; X = F, Cl, Br, I), which belong to 20 topological types. Atomic networks in the structures of twelve d-metal halides and nine topological types of binary compounds were found to be similar. Most variants of structural similarity found for these compounds are also typical for other anhydrous inorganic salts: orthosilicates, sulfates, molybdates, nitrates, carbonates and borates. The topological analysis of ionic matrixes (sublattices) in the structures of d-metal halides shows that 11 of 20 topological types have at least one matrix with close packing topology. The effect of ion sizes on the topology and structure-forming role of the corresponding matrices is discussed

183

Influence of alkali reagents on phase formation and crystal morphology of hydrothermally derived lead titanate  

Science.gov (United States)

The influence of three different alkali reagents, i.e. ammonium hydroxide, sodium hydroxide and potassium hydroxide, on phase formation and crystallite morphology of lead titanate prepared under mild hydrothermal conditions was investigated. The formation of three different phases of lead titanate including tetragonal perovskite, tetragonal body-centered and cubic phases, which showed preference to different types of bases, was discussed. The relation between phases and morphology of the hydrothermally derived lead titanate was illustrated. The formation mechanism of lead titanate when various mixtures of ammonium-alkali hydroxide were employed was also discussed. The transmission electron microscopic technique was also employed in the investigation of a typical hydrothermally derived sample revealing the presence of a pyrochlore phase, otherwise undetected by the XRD technique.

Rujiwatra, Apinpus; Thammajak, Nirawat; Sarakonsri, Thapanee; Wongmaneerung, Rewadee; Ananta, Supon

2006-03-01

184

Investigations of structure and morphology of the AlN nano-pillar crystal films prepared by halide chemical vapor deposition under atmospheric pressure  

Science.gov (United States)

Aluminum nitride (AlN) prepared under atmospheric pressure using a halide chemical vapor deposition method has been examined by means of a variety of analytical techniques. Scanning electron microscopic observations showed that the crystals deposited onto a Si(100) substrate have hexagonal pillar structure. Based on the X-ray diffraction and X-ray pole-figure analyses, it was deduced that the each AlN pillar crystal grows with a different rotation angle around the axis. Transmission electron diffraction showed that they are of single-like form. This was also confirmed by the selected area electron diffraction image as well. It was found that the diameter of pillar which constitutes an AlN film was significantly dependent upon the ratio of NH3/AlCl3 used as source materials and the growth temperature.

Takahashi, Naoyuki; Matsumoto, Yoriko; Nakamura, Takato

2006-04-01

185

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

186

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)

187

Thermoluminescence of gamma irradiated barium doped KCl : KBr mixed crystals  

International Nuclear Information System (INIS)

The thermoluminescence (TL) of alkali halides under various parameter have been studied. The divalent impurity ions can strongly affect the mechanical properties of alkali halide crystals. Mixed crystals of ? irradiated barium doped KCl:KBr have been characterized by measuring the thermoluminescence. Two peaks are observed in the TL intensity with increasing composition of KBr in KCl, the TL intensity increases and attains a saturation value for a particular composition of KBr and KCl. It is due to the increase in the number of luminescence centres and concentration quenching with increasing composition of KCl and KBr, because the mixed crystals of critical composition contain higher number of vacancies which produces larger number of colour centres. (author)

188

Ultrasound velocity in dissolving alkali halide melts  

Energy Technology Data Exchange (ETDEWEB)

Ultrasound velocities in the molten exsolving mixtures (LiF + CsCl, LiF + KBr, LiF + RbBr, LiF + CsBr, LiF + KI, LiF + RbBr, and LiF + CsBr) were obtained along the saturation line over a wide temperature range using the acoustic method. The temperature dependences of properties far away from the critical temperature are close to linear and the temperature and composition factors are highly correlated. The difference between the magnitudes of sound velocity for the coexisting phases increases with the radii of ions in the mixtures. The linearity of the temperature dependence of the velocity, which is typical for all systems at relatively low temperatures, is violated when approaching the critical point of mixing, mainly due to sharp changes of the light phase state. Our results suggested a classical (mean-field) critical behavior of ionic melts.

Stepanov, Victor P., E-mail: v.stepanov@ihte.uran.r [Institute of High-Temperature Electrochemistry, Russian Academy of Sciences, Ural Division, S. Kovalevskaya Str. 22, Yekaterinburg 620990 (Russian Federation); Minchenko, Vladimir I. [Institute of High-Temperature Electrochemistry, Russian Academy of Sciences, Ural Division, S. Kovalevskaya Str. 22, Yekaterinburg 620990 (Russian Federation)

2011-03-15

189

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

190

Alkali and alkaline-earth metal amidoboranes: structure, crystal chemistry, and hydrogen storage properties.  

Science.gov (United States)

Alkali- and alkaline-earth metal amidoboranes are a new class of compounds with rarely observed [NH2BH3](-) units. LiNH2BH3 and solvent-containing Ca(NH2BH3)2 x THF have been recently reported to significantly improve the dehydrogenation properties of ammonia borane. Therefore, metal amidoboranes, with accelerated desorption kinetics and suppressed toxic borazine, are of great interest for their potential applications for hydrogen storage. In this work, we successfully determined the structures of LiNH2BH3 and Ca(NH2BH3)2 using a combined X-ray diffraction and first-principles molecular dynamics simulated annealing method. Through detailed structural analysis and first-principles electronic structure calculations the improved dehydrogenation properties are attributed to the different bonding nature and reactivity of the metal amidoboranes compared to NH3BH3. PMID:18847204

Wu, Hui; Zhou, Wei; Yildirim, Taner

2008-11-01

191

Crystal hydrates of alkali metal isopolyvanadate molybdates or tungstates as thermosensitive resistor materials or catalysts of trimethylphenol oxidation and method of their preparation  

International Nuclear Information System (INIS)

Crystal hydrates of alkali metal isopolyvanadate molybdates or tungstates of the Msub(2)Vsub(12-y)Ehsub(y)Osub(z)xnHsub(2)O composition (M-alkali metal; Eh-Mo or W; 0.5 < y <= 4; 31 <= z <= 33) are prepared by V(S) oxide interaction with the solution containing alkali metal molybdate or tungstate in the stoichiometric relation to V and to 200 g/l hydrogen peroxide at 1-10 deg C for 0.5-1 hour, the following heating of the reacting mass to 60-80 deg C, holding for 0.5-1 hour at this temperature and drying of the product at normal or high temperature. Compounds with 1 <= y <= 3 and 31.5 <= z <= 32.5 are recommended as catalysts

192

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

193

Novel alkali metal amidogallates as intermediates in ammonothermal GaN crystal growth  

Science.gov (United States)

Single crystals of lithium tetra-amidogallate, Li[Ga(NH2)4], were obtained from the reaction of Ga metal and LiNH2 in supercritical ammonia at a pressure of 250 MPa and temperature of 400 °C. Two structural modifications were characterized by single crystal X-ray diffraction: a=5.849(1) Å, b=12.640(3) Å, c=6.858(1) Å, ?=92.56(3)°, Z=4, space group P21/n; a=6.005(1) Å, b=7.394(2) Å, c=6.005(1) Å, ?=103.51(3)°, Z=2, space group P21. Disodium tetra-amidogallate amide, Na2[Ga(NH2)4]NH2 (a=11.748(2) Å, b=6.681(1) Å, c=9.665(2) Å, Z=4, space group Pnma), was grown ammonothermally (p=130 MPa, T=580 °C) as single crystals in the course of synthesizing wurzite GaN employing NaNH2 as an ammono-basic mineralizer. Like known Na[Ga(NH2)4], all three novel compounds contain isolated tetra-amidogallate ions [Ga(NH2)4]- as constituents and likely candidates for dominant dissolved gallium-containing species in ammonothermal GaN synthesis and crystal growth under ammono-basic conditions, accomplishing the material transport. Raman spectroscopy data for Li[Ga(NH2)4] in both modifications as well as Na2[Ga(NH2)4]NH2 are provided and discussed.

Zhang, Shiyu; Alt, Nicolas S. A.; Schlücker, Eberhard; Niewa, Rainer

2014-10-01

194

Sulfate separation from aqueous alkaline solutions by selective crystallization of alkali metal coordination capsules  

International Nuclear Information System (INIS)

Self-assembly of a tris(urea) anion receptor with Na2SO4 or K2SO4 yields crystalline capsules held together by coordinating Na+ or K+ cations and hydrogen-bonding water bridges, with the sulfate anions encapsulated inside urea-lined cavities. The sodium-based capsules can be selectively crystallized in excellent yield from highly competitive aqueous alkaline solutions (?6 M Na+, pH 14), thereby providing for the first time a viable approach to sulfate separation from nuclear wastes.

195

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

196

Growth of KCl1–xBrx Mixed Crystals with Different Composition Percent and Study of KBr Concentration Effect on Optical Characteristics of Mixed Crystals  

Directory of Open Access Journals (Sweden)

Full Text Available In the present research, mixed crystals KCl1–xBrx (x = 0.1, 0.3, 0.5, 0.7 & 0.9 were grown by Czochralski method. Then some analysis such as chemical etching, XRD, and absorbing spectrum were established on the irradiated crystals by ?-ray. The results of this research show that configuration of defects in mixed crystals in contrast with pure crystals is different. Somehow that type and percentage of cumulative composition cause to changing in lattice parameter and lattice defect density in alkali halide crystals and finally change optical properties of crystal.

Sajad Shahmaleki

2012-06-01

197

Ternary halides: novel NLO compounds for LWIR  

Science.gov (United States)

We carried out studies to identify, synthesize, purify and grow crystals of a novel class of halides for nonlinear optical applications. Tl3PbBr5, Tl4PbI6, Tl4HgI6 and Tl3PbI5, were synthesized by reacting binary halides and crystals were grown. Optical quality was evaluated by fabricating cm size crystals. The homogeneity of bulk crystal was evaluated by studying transparency, etchpit and X-ray rocking curve and 2?-? scans. These halides have transparency from visible to far-IR wavelength region. The material of the compounds of Tl3PbBr5 composition showed self-poling during the growth.

Singh, N. B.; Suhre, D. R.; Green, K.; Fernelius, N.; Hopkins, F. K.

2005-08-01

198

Single-crystal growth, alkali metal ordering, and superconductivity in La{sub 2-x}M{sub x}CuO{sub 4}(M = Na, K)  

Energy Technology Data Exchange (ETDEWEB)

Single crystals of La{sub 2-x}M{sub x}CuO{sub 4}, where M is Na or K, have been prepared by precipitation from molten NaOH at 320{degrees}C or from molten KOH at 450{degrees}C. The composition of several individual crystals as determined by wavelength-dispersive X-ray fluorescence analysis averaged to La{sub 1.88}Na{sub 0.12}CuO{sub 4} and La{sub 1.79}K{sub 0.21}CuO{sub 4}. Iodometric titrations of polycrystalline samples with identical compositions showed that the formal oxidation states for the Cu atoms are +2.19 and +2.31, respectively. On the basis of the analysis of single-crystal X-ray diffraction data, it has been determined that the alkali metal doped lanthanum copper oxides crystallize in a new structure type that this distinct from the analogous phases containing alkaline earth metal ions. The space group is Pr/nmm, and lattice parameters are a = 3.766(1) {angstrom}, c = 13.215(5) {angstrom} for the Na-doped material and a = 3.7708(7) {angstrom}, c = 13.321(2) {angstrom} for the K-doped material. In these phases, the alkali metal ions are ordered in the rock-salt blocks, and the Cu atoms are displaced out of the plane toward the alkali metal ions. Despite this distortion of the CuO{sub 2} planes, both phases exhibit superconductivity, near 26 and 6 K, respectively.

Stoll, S.L.; Stacy, A.M. [Lawrence Berkeley Lab., CA (United States); Torardi, C.C. [Du Pont Company, Wilmington, DE (United States)

1994-06-22

199

Measurement of the index of refraction of ?m crystals by a confocal laser microscope - Potential application for the refractive index mapping of ?m scale  

Science.gov (United States)

A conventional laser microscope can be used to derive the index of refractivity by the ratio of geometrical height of the transparent platelet to the apparent height of the normal incident light for very small crystals in the wide size range. We demonstrate that the simple method is effective for the samples from 100 ?m to 16 ?m in size using alkali halide crystals as a model system. The method is also applied for the surface fractured micro-crystals and an inclined crystal with microscopic size regime. Furthermore, we present two-dimensional refractive index mapping as well as two-dimensional height profile for the mixture of three alkali halides, KCl, KI, and NaCl, all are ?m in size.

Kimura, Keisaku; Sato, Seiichi

2014-05-01

200

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

 
 
 
 
201

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

202

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

203

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)

204

Metal-halide mixtures for latent heat energy storage  

Science.gov (United States)

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

Chen, K.; Manvi, R.

205

Metal-halide mixtures for latent heat energy storage  

Science.gov (United States)

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

Chen, K.; Manvi, R.

1981-01-01

206

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

207

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

208

Crystal structure and luminescent and thermochromic properties of tellurium (IV) halide complexes with N,N'-diphenylguanidine  

International Nuclear Information System (INIS)

Complexes of tellurium (IV) bromide and chloride with N,N-diphenylguanidine are synthesized. Compounds are characterized by the data of element analysis, roentgenography, luminescent spectroscopy and spectroscopy of diffuse reflection. Crystal structures of bis(N,N'-diphenylguanidinium) hexachlorotellurate(IV) and bis(N,N'-diphenylguanidinium) hexabromotellurate(IV) are determined. In isostructural complexes layers of [TeHal6]2- anions and [C13H13N3H]+ cations are joined by hydrogen bonds N-H...Hal (Hal - Cl, Br) and are associated into three-dimension framework by Van-der-Waals forces. Electronic and geometric aspects determining peculiarities of spectral-luminescent behaviour of complexes investigated at 77 and 300 K are discussed

209

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

Science.gov (United States)

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

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

2012-10-01

210

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

International Nuclear Information System (INIS)

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

211

Alkali metals in beryl and their role in the formation of derivative structural motifs: Comparative crystal chemistry of vorobyevite and pezzottaite  

Science.gov (United States)

The crystal structures of high-alkali beryl, i.e., vorobyevite Cs0.08Na0.42(H2O)0.18 + y × [Al2(Be2.35Li0.65)Si6O18], ( a = 9.2102(14) Å, c = 9.2179(14) Å, space group P6/ mcc, Z = 2, ?calcd= 2.74 g/cm3) and pezzottaite Cs0.75Na0.23(H2O)0.24[Al2Be2Li(Si6O18)] ( a = 15.955(3) Å, c = 27.810(8) Å, space group, R bar 3 c, Z = 18, ?calcd= 3.13 g/cm3), are determined at a temperature of 100 K. It is confirmed that, at a high lithium content in minerals of the beryl group, lithium is selectively incorporated into Be tetrahedra. The positive charge deficit due to the replacement of Be2+ cations by Li+ cations is compensated by incorporating large alkali cations into the “zeolite” channel. It is shown that, when the lithium content becomes close to unity per the corresponding formula, the Li and Be atoms are ordered and the rhombohedral structure of pezzottaite is formed. It is proposed to retain the historical name vorobyevite for the lithium- and cesium-containing variety of beryl with a disordered distribution of Be and Li atoms.

Yakubovich, O. V.; Pekov, I. V.; Steele, I. M.; Massa, W.; Chukanov, N. V.

2009-05-01

212

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

213

On certain features of crystal structure and properties of alkali metal 6,8-dinitro- and 6,8,10-trinitro-1,4-dioxaspiro[4.5]deca-6,9-dienides  

International Nuclear Information System (INIS)

Specific features of crystal structure of alkali metals (M = Li, Na, K, Rb, Cs) spirocyclic complexes in the title have been studied by the methods of microscopy and crystallography. Methods of thermal decomposition of the complexes in the air, depending on cation nature, have been ascertained. 6 refs.; 4 figs.; 4 tabs

214

VUV excitation and electronic decay of rubidium halide molecules  

International Nuclear Information System (INIS)

Previously we reported an interionic Auger decay following the VUV resonant excitations of the metal atom in the alkali halide molecules. Opening and closing of the spectator Auger decay channel was found to strongly influence the lineshape of the participator decay transitions, an effect attributed to the changes in the lifetime of the VUV-excited state. In this work, the VUV excitation and the following electronic decay of the resonant states of rubidium halides is studied. A series of electron spectra have been measured at photon energies around the 4p ? nl resonance excitation region. Experimental results and the theoretical modelling of the excitation and decay spectra are presented

215

Optical properties and radiation damages of cerium fluoride crystals doped with alkali-earth and rare-earth elements  

International Nuclear Information System (INIS)

The most essential contribution in the investigation of CeF3 crystals having the goal to construct high precision electromagnetic calorimeters has been done by Crystal Clear Collaboration. Study of optical properties and radiation damages of Cerium Fluoride crystals doped with Ca, Ba, Sr, La, Nd, Zr and Hf in the wide range of concentrations has been performed with the goal to obtain high optical transparency of crystals at different cumulative doses under ?-irradiation. Time decay curves and relative light yields of scintillators as a function of doping level were measured using X-ray excitation of samples and single photon counting method

216

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

Directory of Open Access Journals (Sweden)

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

Robert Salchner

2014-01-01

217

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

Science.gov (United States)

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

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

2012-04-01

218

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

Energy Technology Data Exchange (ETDEWEB)

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

Akdeniz, Z. (International Centre for Theoretical Physics, Trieste (Italy) Istanbul Univ. (Turkey). Dept. of Physics); Tosi, M.P. (Trieste Univ. (Italy). Dipt. di Fisica Teorica Argonne National Lab., IL (USA))

1988-11-01

219

Electrochemistry of plutonium in molten halides  

International Nuclear Information System (INIS)

The electrochemistry of plutonium in molten halides is of technological importance as a method of purification of plutonium. Previous authors have reported that plutonium can be purified by electrorefining impure plutonium in various molten haldies. Work to eluciate the mechanism of the plutonium reduction in molten halides has been limited to a chronopotentiometric study in LiCl-KCl. Potentiometric studies have been carried out to determine the standard reduction potential for the plutonium (III) couple in various molten alkali metal halides. Initial cyclic voltammetric experiments were performed in molten KCL at 1100 K. A silver/silver chloride (10 mole %) in equimolar NaCl-KCl was used as a reference electrode. Working and counter electrodes were tungsten. The cell components and melt were contained in a quartz crucible. Background cyclic voltammograms of the KCl melt at the tungsten electrode showed no evidence of electroactive impurities in the melt. Plutonium was added to the melt as PuCl/sub 3/, which was prepared by chlorination of the oxide. At low concentrations of PuCl/sub 3/ in the melt (0.01-0.03 molar), no reduction wave due to the reduction of Pu(III) was observed in the voltammograms up to the potassium reduction limit of the melt. However on scan reversal after scanning into the potassium reduction limit a new oxidation wave was observed

220

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

 
 
 
 
221

Crystal structures and magnetic properties of alkali-metal lanthanide oxides A{sub 2}LnO{sub 3} (A = Li, Na; Ln = Ce, Pr, Tb)  

Energy Technology Data Exchange (ETDEWEB)

We have prepared alkali-metal lanthanide oxides A{sub 2}LnO{sub 3} (A = Li, Na; Ln = Ce, Pr, Tb). Li{sub 2}PrO{sub 3} crystallizes orthorhombically with space group Cmmm. The Pr atoms are octahedrally coordinated by six oxygen atoms and the edge-sharing PrO{sub 6} octahedra are aligned along the c-axis. Na{sub 2}LnO{sub 3} (Ln Ce, Pr, Tb) crystallizes monoclinically with space group C2/c. The Ln and Na atoms at z {approx} 0.25 and 0.75 are octahedrally coordinated by six oxygen atoms and these octahedra share edges forming slabs in the a-b planes. The resultant Na atoms are located between these slabs. Magnetic susceptibility and specific heat measurements indicate that all of these compounds except for Ce compounds order antiferromagnetically at low temperatures. The Neel temperatures for Li{sub 2}PrO{sub 3}, Na{sub 2}PrO{sub 3}, and Na{sub 2}TbO{sub 3} are 6.5, 4.6, and 38.3 K, respectively.

Hinatsu, Yukio [Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810 (Japan)]. E-mail: hinatsu@sci.hokudai.ac.jp; Doi, Yoshihiro [Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810 (Japan)

2006-07-20

222

Distinctive features of automated pulling of large scintillation alkali iodides single crystals without oxygen-containing impurities  

Science.gov (United States)

An influence of carbonate, sulphate- and borate ions on radiation resistance (RR) of CsI(Tl) crystals has been studied. The data demonstrate that borate ions affect the RR as well as other oxygen containing impurities (OI). Trace amounts of borate ions lead to colouring of the crystal under gamma rays, and decreasing of its light output. The method of purifying the melt of OI in the process of automated pulling of crystals by treating it with those high-melting metals, which generate insoluble oxides in the melt is suggested. Crystals, pulled out of the purified melt are highly resistant towards radiation and do not contain absorption bands in the IR spectrum, which is a distinctive feature of borate, carbonate and sulphate ions.

Zaslavsky, B. G.

2000-09-01

223

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

224

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2005-04-15

225

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

International Nuclear Information System (INIS)

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

226

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

227

Detection of alkali metal ions in DNA crystals using state-of-the-art X-ray diffraction experiments  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The observation of light metal ions in nucleic acids crystals is generally a fortuitous event. Sodium ions in particular are notoriously difficult to detect because their X-ray scattering contributions are virtually identical to those of water and Na+…O distances are only slightly shorter than strong hydrogen bonds between well-ordered water molecules. We demonstrate here that replacement of Na+ by K+, Rb+ or Cs+ and precise measurements of anomalous differences ...

Tereshko, Valentina; Wilds, Christopher J.; Minasov, George; Prakash, Thaza P.; Maier, Martin A.; Howard, Andrew; Wawrzak, Zdzislaw; Manoharan, Muthiah; Egli, Martin

2001-01-01

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

Electrorefining of zirconium metal in alkali chloride and alkali fluoride fused electrolytes  

International Nuclear Information System (INIS)

The electrorefining of zirconium metal in alkali halide melts has been investigated. Variables affecting the electrodeposition process such as the composition of the electrolyte, the current density, and the configuration of the electrodes were studied. Two types of electrolytes were used: the alkali chloride-rich and the alkali fluoride-rich electrolytes. The various electrolytes are considered in terms of their ability to complex the soluble zirconium ions, a property which is important for the electrodeposition of coherent metal deposits from these melts. Crystalline zirconium metal of good quality has been obtained from fluoride melts containing NaF, LiF, and either ZrF4 or K2ZrCl6 at about 7500C

230

Optical properties of halide and oxide scintillators  

Science.gov (United States)

Knowledge of optical properties of scintillators is important both for the optimization of scintillator systems and the development of new materials particularly ceramic scintillators. Recent theoretical developments, especially new density functionals that enable accurate prediction of band gaps, have made it possible to perform quantitative calculations of the optical properties of scintillator materials. We used these techniques to obtain optical properties of a large number of high light output halide scintillators. These calculations showed that many halide scintillators have remarkably little optical anisotropy and may be good candidates for development as ceramic scintillators. These include materials such as CaI2:Eu2+ that have very high light output and other favorable properties but are difficult to develop due to crystal growth issues. We review some of our recent results and present new results for CeCl3.

Singh, David J.

2011-09-01

231

Optical properties of halide and oxide scintillators  

Energy Technology Data Exchange (ETDEWEB)

Knowledge of optical properties of scintillators is important both for the optimization of scintillator systems and the development of new materials particularly ceramic scintillators. Recent theoretical developments, especially new density functionals that enable accurate prediction of band gaps, have made it possible to perform quantitative calculations of the optical properties of scintillator materials. We used these techniques to obtain optical properties of a large number of high light output halide scintillators. These calculations showed that many halide scintillators have remarkably little optical anisotropy and may be good candidates for development as ceramic scintillators. These include materials such as CaI{sub 2}:Eu{sup 2+} that have very high light output and other favorable properties but are difficult to develop due to crystal growth issues. We review some of our recent results and present new results for CeCl{sub 3}.

Singh, David J [ORNL

2011-01-01

232

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

233

Bleaching of F-type centres in alkali halides  

International Nuclear Information System (INIS)

Bleaching of the F band in KCl occurs on pulsing with 532 nm laser light. The bleaching is accompanied by the appearance of an absorption on the red side of the F band. Both bleaching and absorption are transient phenomena, and no permanent bleaching or absorption is observed. The same exponential lifetime of about 5?S was obtained for both bleaching and absorption, and all the features were found to be independent of both temperature (between 200 and 300 K) and the intensity of the analysing light. This eliminates the possibility of a trapped species, such as F-, being responsible. The phenomena are qualitatively different from the bleaching observed at low light intensity, where bleaching of the F band is accompanied by formation of F-, which is thermally stable below 250 K. The most likely explanation of the results is that the high concentration of conduction band electrons following the laser pulse allows formation of free or quasi-free electron pairs, e2-, which decay back into F centres on a time scale which is long compared with that for individual electrons. (author)

234

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. PMID:24835317

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

2014-01-01

235

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

Science.gov (United States)

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

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

2011-04-01

236

Alkali metal nitrate purification  

Science.gov (United States)

A process is disclosed for removing contaminants from impure alkali metal nitrates containing them. The process comprises heating the impure alkali metal nitrates in solution form or molten form at a temperature and for a time sufficient to effect precipitation of solid impurities and separating the solid impurities from the resulting purified alkali metal nitrates. The resulting purified alkali metal nitrates in solution form may be heated to evaporate water therefrom to produce purified molten alkali metal nitrates suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of purified alkali metal nitrates.

Fiorucci, Louis C. (Hamden, CT); Morgan, Michael J. (Guilford, CT)

1986-02-04

237

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

Directory of Open Access Journals (Sweden)

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

David T. Moore

2014-07-01

238

Quantum chemical simulation of the self-trapped hole in ?-Al2O3 crystals  

Science.gov (United States)

Atomistic simulations of hole self-trapping in a pure corundum crystal have been undertaken using three different approaches. The inward Jahn-Teller displacement of two O atoms (on which 80% of the hole density is concentrated), accompanied by the outward displacement of the two nearest Al atoms, gives the energetically most favorable configuration, thus suggesting a self-trapped-hole (STH) model analogous to that in alkali halides (VK center). The optical absorption of STH and three possible kinds of thermally activated hops are discussed in relation to experimental data.

Jacobs, P. W. M.; Kotomin, E. A.

1992-08-01

239

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

Science.gov (United States)

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

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

2014-09-01

240

Growth and characterization of multiphased mixed crystals of KCl, KBr and KI:1. Growth and X-ray diffraction studies  

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) x (KBr) y - x (KI)1- y crystals for various values of x and y by the melt method and physically characterized. Bulk composition of the crystals was measured using the measured density and refractive index values. X-ray diffraction analysis indicates the existence of two phases in the mixed crystals. Thermal parameters were determined using the X-ray powder diffraction intensity data

 
 
 
 
241

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

A complex rare-earth rich aluminoborosilicate glass has been proved to be a good candidate for the immobilization of new high level radioactive wastes. A simplified seven-oxides composition of this glass was selected for this study. In this system, sodium and calcium cations were supposed in other works to simulate respectively all the other alkali (R+=Li+, Rb+, Cs+) and alkaline-earth (R'2+=Sr2+, Ba2+) cations present in the complex glass composition. Moreover, neodymium or...

Quintas, Arnaud; Caurant, Daniel; Maje?rus, Odile; Charpentier, Thibault; Dussossoy, Jean-luc

2009-01-01

242

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

Energy Technology Data Exchange (ETDEWEB)

A complex rare-earth rich alumino-borosilicate glass has been proved to be a good candidate for the immobilization of new high level radioactive wastes. A simplified seven-oxides composition of this glass was selected for this study. In this system, sodium and calcium cations were supposed in other works to simulate respectively all the other alkali (R{sup +} = Li{sup +}, Rb{sup +}, Cs{sup +}) and alkaline-earth (R{sup 2+} = Sr{sup 2+}, Ba{sup 2+}) cations present in the complex glass composition. Moreover, neodymium or lanthanum are used here to simulate all the rare-earths and actinides occurring in waste solutions. In order to study the impact of the nature of R{sup +} and R{sup 2+} cations on both glass structure and melt crystallization tendency during cooling, two glass series were prepared by replacing either Na{sup +} or Ca{sup 2+} cations in the simplified glass by respectively (Li{sup +}, K{sup +}, Rb{sup +}, Cs{sup +}) or (Mg{sup 2+}, Sr{sup 2+}, Ba{sup 2+}) cations. From these substitutions, it was established that alkali ions are preferentially involved in the charge compensation of (AlO{sub 4}){sup -} entities in the glass network comparatively to alkaline-earth ions. The glass compositions containing calcium give way to the crystallization of an apatite silicate phase bearing calcium and rare-earth ions. The melt crystallization tendency during cooling strongly varies with the nature of the alkaline-earth. (authors)

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

2008-07-01

243

Oxoeuropates of alkali metals  

International Nuclear Information System (INIS)

Full text: There are only few works on the study of M-Eu-O (M=Na-Cs) system. This is owing to extreme hygroscopicity and high volatility of alkali metal oxides used in the reaction with europium oxide. The use of other compounds such as nitrates and carbonates is undesirable because the chemical activity of these substances is not sufficient. Only data on the oxides with MEuO2 composition have been reported up till now. But the single-crystal X-ray diffraction was studied only for RbEuO2 . Reliable data on caesium oxoeuropates are not present. The use of alkali metal peroxide or superoxide in considerable abundance in the solid-state synthesis is a new and promising method for synthesis of transition metal sophisticated oxides with alkaline cations. This method allows us to get appropriate compounds in a short time with a good yield even at not-too-high temperatures. Heating Eu2O3 with Na-2O2, KO2 and CsO2 at about 500 deg C led to formation of yellow-green products. The reaction with caesium superoxide passed most intensively and was accompanied by high exothermal effect. The obtained substances differed in their X-ray powder diffraction parameters from the known ones. Absorption 151Eu Moessbauer spectra were single lines with the following parameters of isomer shift (?) relative to Eu2O3 and the width at half height (?): ?=0.33±0.03 mm.s-1, ?(?): ?=0.33±0.03 mm.s-1, ?=2.53?0.06 mm.s-1 for sodium europate; ?=0.16±0.03 mm.s-1, ?=2.95±0.05 mm.s-1 for potassium one and ?=0.18±0.03 mm.s-1, ?=2.92±0.09 mm.s-1 for caesium derivative. The synthesis of the compounds was lasting only a few seconds and no europium oxide was found in the products. However some heating had to be continued to crystallize the substance well. In this case the narrowing of the lines was seen in the Moessbauer spectra and X-ray patterns. The isomer shifts value prove that europium is trivalent in these compounds. Broadening of the Moessbauer lines for potassium and caesium europates is indicative of quadrupole interactions

244

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

245

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

246

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

CERN Document Server

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

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

2000-01-01

247

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

248

Structure and optical properties of high light output halide scintillators  

Science.gov (United States)

Structural and optical properties of several high light output halide scintillators and closely related materials are presented based on first-principles calculations. The optical properties are based on the Engel-Vosko generalized gradient approximation and the recently developed density functional of Tran and Blaha. The materials investigated are BaBr2 , BaIBr, BaCl2 , BaF2 , BaI2 , BiI3 , CaI2 , Cs2LiYCl6 , CsBa2Br5 , CsBa2I5 , K2LaBr5 , K2LaCl5 , K2LaI5 , LaBr3 , LaCl3 , SrBr2 , and YI3 . For comparison results are presented for the oxide CdWO4 . We find that the Tran Blaha functional gives greatly improved band gaps and optical properties in this class of materials. Furthermore, we find that unlike CdWO4 , most of these halides are highly isotropic from an optical point of view even though in many cases the crystal structures and other properties are not. This general result is rationalized in terms of halide chemistry. Implications for the development of ceramic halide scintillators are discussed.

Singh, David J.

2010-10-01

249

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

International Nuclear Information System (INIS)

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

250

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

International Nuclear Information System (INIS)

We have investigated the optical absorption spectra of the CsBr:Au- crystals irradiated with an ultraviolet (UV) light. Before the UV-light irradiation, the absorption bands associated with the isolated Au- ion (monomer) are observed in the energy region of UV. After a slight UV-light irradiation, the absorption intensities of the monomer bands decrease and the absorption bands due to paired Au- ions appear around the monomer bands. Furthermore, UV-light irradiation on the CsBr:Au- crystals brings about the appearance of several new absorption bands in the visible region. From the analogy with the aggregation of the F centers in alkali halide crystals, the new absorption bands are attributed to the aggregate centers of the Au- ions. They can also be regarded as the CsAu nanocluster constructed from the Cs+ cations and the Au- anions. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

251

Coloration dependence in the thermoluminescence properties of the double doped NaCl single crystals under gamma irradiation  

International Nuclear Information System (INIS)

In this work the behaviour of calcium manganese doped NaCl single crystals under gamma irradiation is reported. Various single crystals of NaCl doped with Ca and Mn have been irradiated at different doses with ionising radiation. The production of defects has been correlated to the increase in the intensity of the thermo luminescent glow curve as a function of doses. The glow curves intensity as a function of doses shows the potential use of these materials as dosimeters. Optical properties of such crystals after irradiation with gamma rays have also been studied; results have shown their potentiality as a good detector and optical store memory devices. Since the creations of colour centres by photons with energy less than the band gap energy has been detected also in ns2-ion doped alkali halides. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

252

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

International Nuclear Information System (INIS)

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

253

Crystal structures of native and xylosaccharide-bound alkali thermostable xylanase from an alkalophilic Bacillus sp. NG-27: structural insights into alkalophilicity and implications for adaptation to polyextreme conditions.  

Science.gov (United States)

Crystal structures are known for several glycosyl hydrolase family 10 (GH10) xylanases. However, none of them is from an alkalophilic organism that can grow in alkaline conditions. We have determined the crystal structures at 2.2 Angstroms of a GH10 extracellular endoxylanase (BSX) from an alkalophilic Bacillus sp. NG-27, for the native and the complex enzyme with xylosaccharides. The industrially important enzyme is optimally active and stable at 343 K and at a pH of 8.4. Comparison of the structure of BSX with those of other thermostable GH10 xylanases optimally active at acidic or close to neutral pH showed that the solvent-exposed acidic amino acids, Asp and Glu, are markedly enhanced in BSX, while solvent-exposed Asn was noticeably depleted. The BSX crystal structure when compared with putative three-dimensional homology models of other extracellular alkalophilic GH10 xylanases from alkalophilic organisms suggests that a protein surface rich in acidic residues may be an important feature common to these alkali thermostable enzymes. A comparison of the surface features of BSX and of halophilic proteins allowed us to predict the activity of BSX at high salt concentrations, which we verified through experiments. This offered us important lessons in the polyextremophilicity of proteins, where understanding the structural features of a protein stable in one set of extreme conditions provided clues about the activity of the protein in other extreme conditions. The work brings to the fore the role of the nature and composition of solvent-exposed residues in the adaptation of enzymes to polyextreme conditions, as in BSX. PMID:16823036

Manikandan, Karuppasamy; Bhardwaj, Amit; Gupta, Naveen; Lokanath, Neratur K; Ghosh, Amit; Reddy, Vanga Siva; Ramakumar, Suryanarayanarao

2006-08-01

254

Charged-soft-sphere potentials for trivalent metal halides  

International Nuclear Information System (INIS)

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

255

Structure and properties of lanthanide halides  

Science.gov (United States)

Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl 3 type structure. These scintillating alloys exhibit high luminosity and proportional response, making them the first scintillators comparable to room temperature semiconductors for gamma spectroscopy; Ce(III) activated lanthanum bromide has recently enabled scintillating gamma ray spectrometers with < 3% FWHM energy resolutions at 662 keV. However brittle fracture of these materials impedes development of large volume crystals. Low fracture stress and perfect cleavage along prismatic planes cause material cracking during and after crystal growth. These and other properties pose challenges for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Recent progress on basic structure and properties of the lanthanide halides is reported here, including thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. Observations including reversible hydrate formation under atmospheric pressure, loss of stoichiometry at high temperature, anisotropic thermal expansion, reactivity towards common crucible materials, and crack initiation and propagation under applied loads are reported. The fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. Analysis of the symmetry and crystal structure of this system suggests possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. This proposed failure mechanism and its implications for scale up to large diameter crystal growth are also discussed.

Doty, F. P.; McGregor, Douglas; Harrison, Mark; Findley, Kip; Polichar, Raulf

2007-09-01

256

The solvent extraction of alkali metal ions with ?-diketones  

International Nuclear Information System (INIS)

This work was undertaken to investigate effects of solvent and chelating-agent on the solvent extraction of alkali metal ions by seven ?-diketones, acetylacetone (Acac), benzoylacetone (BzA), dipivaloylmethane (DPM), dibenzoylmethane (DBM), thenoyltrifluoloacetone (TTA), benzoyltrifluoroacetone (BFA) and hexafluoroacetylacetone (HFA), and to separate lithium from alkali metals. The extraction of alkali metals increase with increasing donor power of the solvent: i.e., benzene Na>K>Rb>Cs, which is also the order in which the adduct formation of these ?-diketone chelates with donor solvents increase. The adduct formations between ?-diketone chelates of alkali metals and donor solvents markedly enhance the solubilities of the chelates in solvents and, consequently, the extractabilities of alkali metals with ?-diketones. Lithium was extracted with TTA in ether at such a low base concentration that sodium, potassium, rubidium and cesium were hardly extracted, and this enabled to separate lithium from other metals by the use of rubidium hydroxide (0.02 M). An attempt has been made to isolate alkali metal ?-diketone chelates and some chelates have been obtained as crystals. The infrared absorption bands arising from C=O and C.=C of TTA shift to lower frequencies in the alkali metal chelates with TTA, and consequently, ?-diketones is suggested to coordinate to alkali metal as a bidentate ligand. (JPN)

257

Application of halides to the production of pure molybdenum  

International Nuclear Information System (INIS)

Studies of the sublimation of molybdenum halides and the possible use of this process to obtain high purity metal are reported. The effect of impurities on the sublimation of molybdenum dioxydichloride was investigated. Equilibria in the molybdenum-iodine system were examined and the conditions for the chemical transport of molybdenum in the presence of iodine were determined. On the basis of these studies a method of producing high purity molybdenum is proposed which invovles the successive sublimation and vacuum reduction of the halides followed by zone recrystallization of the metal in a vacuum. High purity molybdenum was obtained in which the impurity content was at or below the limits of detection by mass spectrometry (less than 3x10-5%). The ratio rho298/rhosub(4.2) of the electrical resistance at room temperature to that at liquid helium temperature was 50000 for the best molybdenum single crystals obtained using this technique. (Auth.)

258

Correlations between entropy and volume of melting in halide salts  

International Nuclear Information System (INIS)

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

259

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

CERN Document Server

The theory of the dislocation motion in the periodic potential relief of the crystal lattice (the Peierls-Nabarro barriers) is reviewed. On the basis of the kink mechanism the temperature dependence of the flow stress is described for a wide class of materials. The theory of quantum mechanical dislocation tunnelling through the Peierls-Nabarro barriers is extended and compared with experimental data on the plasticity of alkali halides, BCC and HCP metals at low temperatures. The behavior of the flow stress at the range of athermic anomalies is modeled by changing the mechanism of the dislocation motion from the thermally activated hopping over the barriers to the quantum tunnelling through them. Some results of previous calculations are represented in a more explicit convenient for applications form. The pronounced effect of the switching between the normal and the superconducting states on the flow stress of metals is explained on the basis of the change in the dissipative properties of the electron subsyste...

Petukhov, B V

2007-01-01

260

Alkali metal oxides trapped by diethylzinc.  

Science.gov (United States)

Reactions of alkali metal hydroxides with neat diethyl zinc lead to the formation of oxo-centered clusters M2O(ZnEt2)n (M = Na, n = 3 or M = K, Rb, n = 4). These molecules crystallize in highly symmetric space groups, forming extended structures supported by weak M-H interactions. We discuss the mechanistic implications and relationship of these structures to known (oxo)organozincates. PMID:24975282

Miller, L Zane; Shatruk, Michael; McQuade, D Tyler

2014-08-18

 
 
 
 
261

Alkali and Halogen Chemistry in Volcanic Gases on Io  

CERN Document Server

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

Schaefer, L

2004-01-01

262

Nonlinear refractive index of optical crystals  

International Nuclear Information System (INIS)

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

263

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

Science.gov (United States)

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

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

2009-11-01

264

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

265

Methods of recovering alkali metals  

Energy Technology Data Exchange (ETDEWEB)

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

Krumhansl, James L; Rigali, Mark J

2014-03-04

266

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

267

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.)

268

Chlor-Alkali Technology.  

Science.gov (United States)

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

Venkatesh, S.; Tilak, B. V.

1983-01-01

269

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

Science.gov (United States)

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

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

2012-07-01

270

Halide transport in Xenopus oocytes.  

Science.gov (United States)

1. Radioisotopes and intracellular microelectrodes were used to characterize the permeability of Xenopus oocytes to chloride and other halides. 2. Uptake of 36Cl had a half-time for equilibration of approximately 3 h, with an initial rate of Cl- entry corresponding to a permeability coefficient of 3.9 x 10(-7) cm/s, and an equilibrium uptake of 36Cl of 33 mM. 3. Replacement of bathing Na+ by K+ depolarized the oocytes from -46 to -7 mV and stimulated influx approximately 3-fold. 4. Influx was linearly dependent on bathing [Cl-] and was temperature dependent with an activation energy of 46 kJ/mol. Influx of 125I of 36Cl was not affected by the presence of equal concentrations of other halides or thiocyanate. These results are consistent with a channel-mediated entry mechanism. 5. Diphenylamine-2-carboxylate (DPAC) and 9-anthracene carboxylate (9-AC), blockers of Cl- channels in other cells, inhibited Cl- entry with dissociation constants (Kds) of approximately 5 x 10(-4) and approximately 10(-3) M, respectively. Inhibitors of Cl(-)-HCO3- exchange or Na(+)-K(+)-2Cl- co-transport did not affect Cl- influx. 6. Attempts to lower or raise intracellular Ca2+ with BAPTA or A23187, respectively, were also without effect on Cl- influx. 7. The halide selectivity sequence determined with isotopes was I- (3.2) greater than Br- (1.3) greater than Cl- (1.0). However, DPAC inhibited almost all of the 36Cl influx but only a small fraction of 125I influx. 8. Replacement of bathing Cl- by I- or Br-resulted in hyperpolarizations, from which the same selectivity sequence was determined. 9. Replacement of bathing Cl- by gluconate caused a marked depolarization, which was inhibited by DPAC and, less potently, by 9-AC. PMID:1822540

Katayama, Y; Widdicombe, J H

1991-11-01

271

New layered manganese oxide halides.  

Science.gov (United States)

The first layered manganese(III) oxide chlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2, have been synthesised; Sr2MnO3Cl adopts a K2NiF4 type structure with sheets of MnO5 square based pyramids linked through oxygen and separated by SrCl layers; it is the end member of a new family of Ruddlesden-Popper type manganese oxide halides which includes the three-layer member Sr4Mn3O8-yCl2 also reported herein. PMID:12120392

Knee, Christopher S; Weller, Mark T

2002-02-01

272

Equilibrium constants of reactions of displacement of halogens by other halogens from molten chlorides, bromides, and iodides of alkali metals  

International Nuclear Information System (INIS)

In electrochemical experiments cases occur when a halogen (chlorine, bromine, or iodine) electrode is immersed in a melt consisting of a mixture of two halides with different anions rather than an individual alkali halide. During the operation of such electrodes the composition of the electrolyte may alter as the result of such displacement reactions. The authors use an independent method for determining equilibrium constants of all exchange reactions of chloride, bromine, and iodine with molten lithium, sodium, potassium, rubidium, and cesium chlorides, bromides, and iodides

273

Fullerenes doped with metal halides  

International Nuclear Information System (INIS)

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

274

Multiplication of electronic excitations and prospects for increasing scintillation efficiency in wide-gap crystals  

International Nuclear Information System (INIS)

A comparative analysis of the electron-hole (e-h) excitation mechanism of impurity luminescence has been performed for wide-gap oxides (WGO) and alkali halides crystals (AHC). A low quantum yield of scintillation in WGO with respect to that in AHC is connected with the high value of the average energy needed for the creation of an e-h pair in WGO. In AHC and many WGO, the width of a valence band Ev is smaller than the energy gap Eg and hot valence holes are not able to create any secondary e-h pairs. The Ev/Eg ratio that describes 'hole losses' in scintillators is 1.5-2.0 times higher in WGO than in CsI. The scenario of the two-step transformation of an e-h pair or an anion exciton into two emitted photons in ?-Al2O3:Mg2+,Ti4+ has been considered

275

Reactions of diiminopyridine ligands with chalcogen halides.  

Science.gov (United States)

The reactions of the chalcogen halides (Ch = S, Se, Te) with a series of diiminopyridine (DIMPY) ligands were explored. It was determined through these studies that varying both the substitution on the ?-carbon and the chalcogen halide reagent afforded different products. If methyl groups were present on the ?-carbon, reactivity was observed through the eneamine tautomer to yield N,N',C-bound neutral chalcogen complexes. In the cases where H and C(6)H(5) groups were in the same position, N,N',N?-chelated chalcogen cations or dications were produced. Many of the reactions resulted in complex mixtures postulated to occur by the release of halogen decomposing the product or, for reactions with the CH(3) substituted ligand, uncontrollable reactivity with the eneamine tautomer. This is the first report of reactions of sulfur and selenium halides with the ubiquitous diiminopyridine ligands and only the second example for a tellurium halide. PMID:22339169

Martin, Caleb D; Ragogna, Paul J

2012-03-01

276

Chlor-alkali electrolysis  

International Nuclear Information System (INIS)

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

277

Electrical conductivity anisotropy in alkali feldspar at high pressure  

Science.gov (United States)

Magnetotelluric studies have shown that electrical conductivity in the crust is highly anisotropic. Knowledge of the anisotropy of crustal minerals, such as feldspar and quartz, is essential to interpreting this phenomenon. Feldspars are the most abundant minerals in the earth's crust, and thus, the electrical conductivity of feldspars may help in understanding of the bulk conductivity of the crust. The electrical conductivities of single-crystal and polycrystalline feldspars have been previously studied, but few studies have considered the electrical conductivity of single alkali feldspars. In this study, we investigated the electrical conductivity of alkali feldspars at different orientations under high temperatures and pressures through several heating and cooling cycles. The starting materials were natural alkali feldspar minerals collected from Beijing, China. The samples contain 65 % potassium-rich host (microcline) and 30 % sodium-rich exsolution lamellae (albite), as well as ~5% minor phases. The impedance spectrum measurements were carried out in a high-pressure cubic-anvil apparatus.All complex impedance measurements were performed at 1 GPa using a Solartron 1260 impedance phase analyzer. Impedance arcs representing crystal conductivity occur in the frequency range of ~10^3-10^6 Hz. The electrical conductivity of alkali feldspars increased with increasing temperature. The highest electrical conductivities in alkali feldspars were measured along the a-axis, with somewhat lower conductivities along the b-axis and the lowest conductivities along the c-axis, suggesting minor anisotropy. The activation enthalpies ranged from 100 to 110 kJ/mol. The electrical conductivity of alkali feldspar is mildly anisotropic, with an anisotropy factor of approximately 2. The minor anisotropy in conductivity for alkali feldspar may not account for the anisotropy of the crust. This work is supported by the Important Field Knowledge Innovation Program (KZCX2-YW-QN608), National Natural Science Foundation of China (No. 40774036)

Wang, D.; Yu, Y.

2013-12-01

278

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

279

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.)

280

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

 
 
 
 
281

Calcium phosphate cements with strontium halides as radiopacifiers.  

Science.gov (United States)

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

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

2014-02-01

282

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

283

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

284

Defects in anisotropic silver halide microcrystals studied with transmission electron microscopy  

Science.gov (United States)

For more than 100 years silver halide microcrystals, where the halide is chloride or bromide, are used as the light-sensing element in photographic films. The combination of properties, like high sensitivity, high resolution and excellent image quality, leads to its dominant use in the imaging industry. Only with the development of the CCD camera in recent years a valuable alternative was found. Yet the image quality is still inferior to silver halide films. Therefore it is believed that the silver halides will still play an important role in the 21st century. Despite the progress over the last 100 years, there is still room for improvement and therefore the silver halides are still intensively investigated. One part of the research deals with the production of homogeneous populations of silver halide crystals with a specific morphology. This thesis reports the results of an investigation of the defect structure in populations of tabular silver halide crystals. The influence of these defects on the morphology of the crystals and the photographic properties is discussed. The technique used for this investigation is transmission electron microscopy (TEM), which is suitable to visualise, to localise and to characterise the defects completely. The samples have been investigated mainly in plan view, but also in edge view. The samples for the edge-view investigation have been prepared with ultramicrotomy. First the growth mechanisms of tabular AgCl and AgBr crystals with {100} surfaces are studied. It is shown that in both cases a limited number of mixed dislocations with an a/2 Burgers vector, lying in the (001) plane induce the tabular growth. The origin of these defects has been determined and the relation with the anisotropic growth is explained. Next, the growth of AgCl crystals with {111} faces is investigated. Using similar growth conditions as for AgBr, a large number of globular crystals are produced and the growth mechanism of these globular crystals is discussed. It is shown that the presence of twins on a {111} type of plane that is not parallel with the tabular plane is responsible for the thickness growth. Further, the introduction of a mixed bromo-iodide shell with high iodide concentration in an AgBr {111} tabular crystal population is investigated. Different incorporation methods are compared and their influence on the defect structure and the thickness of the crystals is discussed and related to the incorporation kinetics of the iodide. The crystals have also been studied in edge view. This showed the location of the parallel twins and the shell with high iodide concentration. The shell with low iodide concentration and the stacking faults, on the other hand, were not recognised in edge view. In the last chapter of this thesis, the formation of silver filaments during development of AgBr {111} tabular crystals is investigated. The evolution of the filament growth and the defect structure are investigated. It is shown that a large number of parallel twins and stacking faults formed on {111} type planes are present in the majority of the filaments. Further the influence of thickness of the tabular crystals on the filament morphology and on the colour of the developed film is discussed. It is argued that the compactness of the filaments is the major difference between the samples.

van Renterghem, Wouter

2001-12-01

285

IR analysis of polyvinylidene fluoride doped with transition metal halides  

Science.gov (United States)

Pure and doped polyvinylidene fluoride (PVDF) films were prepared by casting. Films with various concentrations of transition metal halides TMHs (AlCl3, ZnCl2, and CoCl2) were prepared. The microstructure and physical properties of these films were studied by IR analysis. The two factors affecting the interaction between the PVDF and MHs are (i) the dopant weight fraction (Hc) (0.05% -30%) by weght, and (ii) precasting time (tpc) which is the time during which the PVDF pellets are maintained solved with the halides added before casting. From the IR quantitative analysis, it is evident that the addition of the three MH to the undoped PVDF film makes ?-phase as the dominant crystalline structures in the doped films without the need for mechanical drawing treatment. The precasting time plays a role for new crystalline structures to appear which becomes strong for CoCl2 doping, moderate in ZnCl2 doping and weak in AlCl3 doping. This phase is maximum for the relatively low doping levels AlCl3. This result is extremely important hence the ?-phase is that one which is electrically active compared with the other two phases and it is needed in all the samples used in the useful applications of the PVF2 films. Remembering, that ?-phase is obtained in the crystallization from melt samples by the uneasy mechanical stress and elevated temperature, it becomes evident the importance of the present result.

El Hefnawy, Somia M.; Aboelkher, Mervet M.; Abdelkader, H.

2009-05-01

286

Influence of the surface roughness of silver halide fibers on their transmission in the near infrared  

Science.gov (United States)

Silver halide crystals are highly transparent from the visible to the mid-infrared, but fibers extruded from these crystals have low transmission in the near infrared in the spectral range 1-3 ?m. We found that this low transmission is partly due to surface roughness and that it can be highly improved by treatment with potassium cyanide solution. Using the Rayleigh criteria for a simple planar waveguide model, we showed that the attenuation due to surface roughness is theoretically dependant on the square of the roughness and on the inverse square of wavelength. Experimentally, the measured surface attenuation indeed follows this behavior. The reduced attenuation in the near infrared is crucial, especially for applications such as the development of silver halide fiber lasers.

Israeli, S.; Katzir, A.

2012-07-01

287

Synthesis of methyl halides from biomass using engineered microbes.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2009-01-01

288

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

International Nuclear Information System (INIS)

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

289

About the F center in cesium halides  

International Nuclear Information System (INIS)

The energy levels for the F center in cesium halides are determined. The point ion method and the ion size correction are applied. Vacancy-centered trial wave functions of three types are used. The structure of NaCl and the CsCl are considered in the calculations. It is concluded that some investigations probably used the NaCl structure in their calculations for cesium halides. For wave functions of the Gourary-Adrian type it is found that the Bartram et al. method can not be applied for values of the empirical parameter ? ? 0.53. Others papers are discussed. (author)

290

Upgrading platform using alkali metals  

Energy Technology Data Exchange (ETDEWEB)

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

Gordon, John Howard

2014-09-09

291

Configuration and migration of point defects in alkali metals  

International Nuclear Information System (INIS)

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

292

Elastic properties of alkali-feldspars  

Science.gov (United States)

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

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

2013-12-01

293

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)

294

Crystal Electrostatic Energy  

CERN Document Server

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

Ivanchin, Alexander

2010-01-01

295

crystal  

Science.gov (United States)

The polarized absorption, emission spectra and decay time measurements of Pr3+-doped CaYAlO4 single crystal have been performed at room temperature. Based on the Judd-Ofelt theory, the spectroscopic parameters , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr3+:CaYAlO4 is a promising candidate for visible solid-state laser emission.

Lv, Shaozhen; Wang, Yan; Zhu, Zhaojie; You, Zhenyu; Li, Jianfu; Gao, Shufang; Wang, Hongyan; Tu, Chaoyang

2014-07-01

296

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-10-15

297

Unraveling halide hydration: A high dilution approach  

Science.gov (United States)

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

Migliorati, Valentina; Sessa, Francesco; Aquilanti, Giuliana; D'Angelo, Paola

2014-07-01

298

Experimental determination of partition coefficients for Rb, Sr, and Ba between alkali feldspar and silicate liquid  

International Nuclear Information System (INIS)

velopment of sector zoning, and Or content of the alkali feldspar. These factors severely limit the use of partitioning of these elements in alkali feldspar as geothermometers. The technique for measuring growth rates utilized here combined with measurement of trace element depletion in diffusion boundary layers adjacent to the alkali feldspar crystals makes it possible to estimate diffusivities for Ba and Sr. These estimates suggest a difference of 2 orders of magnitude between diffusivities for Ba and Sr in a vapor-saturated melt and those measured for a dry obsidian glass. (author)

299

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.)

300

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

Science.gov (United States)

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

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

2005-06-01

 
 
 
 
301

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

International Nuclear Information System (INIS)

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

302

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

Science.gov (United States)

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

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

2012-12-13

303

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

Science.gov (United States)

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

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

2014-11-01

304

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

Science.gov (United States)

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

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

2004-05-01

305

Equation-of-state data for CsCl-type alkali halides  

Science.gov (United States)

Energy-dispersive x-ray diffraction (EDXD), with synchrotron radiation and diamond anvil cells (DAC), is used with different pressure sensors to determine the lattice parameters and equations of state (EOS) at room temperature, and pressures up to typically 40 GPa, for KBr, KI, RbCl, RbBr, RbI, CsCl, and CsBr. A comparison with previous literature data obtained by various techniques, and for different ranges of pressure indicates that all of the data fit to a recently proposed `simple' first-order EOS form.

Köhler, U.; Johannsen, P. G.; Holzapfel, W. B.

1997-06-01

306

Equation-of-state data for CsCl-type alkali halides  

International Nuclear Information System (INIS)

Energy-dispersive x-ray diffraction (EDXD), with synchrotron radiation and diamond anvil cells (DAC), is used with different pressure sensors to determine the lattice parameters and equations of state (EOS) at room temperature, and pressures up to typically 40 GPa, for KBr, KI, RbCl, RbBr, RbI, CsCl, and CsBr. A comparison with previous literature data obtained by various techniques, and for different ranges of pressure indicates that all of the data fit to a recently proposed 'simple' first-order EOS form. (author)

307

Equation-of-state data for CsCl-type alkali halides  

Energy Technology Data Exchange (ETDEWEB)

Energy-dispersive x-ray diffraction (EDXD), with synchrotron radiation and diamond anvil cells (DAC), is used with different pressure sensors to determine the lattice parameters and equations of state (EOS) at room temperature, and pressures up to typically 40 GPa, for KBr, KI, RbCl, RbBr, RbI, CsCl, and CsBr. A comparison with previous literature data obtained by various techniques, and for different ranges of pressure indicates that all of the data fit to a recently proposed 'simple' first-order EOS form. (author)

Koehler, U.; Johannsen, P.G.; Holzapfel, W.B. [Fachbereich Physik, Universitaet GH Paderborn, D-33095 Paderborn (Germany)

1997-06-30

308

Stabilization of the interstitial center by divalent impurities in alkali halides  

International Nuclear Information System (INIS)

Studies are made on the growth of the Hayes-Nichols band and the D3 band in Ca2+-doped KBr by X-irradiation at liquid helium temperature, by subsequent thermal annealing and by irradiation with an electron pulse between liquid nitrogen and dry ice temperatures. It is shown that the Hayes-Nichols band is an impurity band created predominantly by the treatments described above and concluded that the Hayes-Nichols center is an H center stabilized by the pair of a divalent impurity and a positive ion vacancy. The height of the D3 band is proportional to the square of the height of the Hayes-Nichols band during irradiation at liquid nitrogen and dry ice temperatures, suggesting that the D3 center is a di-H center stabilized by an impurity-vacancy pair. It is pointed out that the reaction rate to form a D3 center by adding an H center to a Hayes-Nichols center is larger by an order of magnitude than that to form a Hayes-Nichols center by adding an H center to an impurity-vacancy pair. (author)

309

The aluminum electrode in AlCl3-alkali-halide melts.  

Science.gov (United States)

Passivation phenomena have been observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and omega to the minus 1/2 power. Upon cathodic polarization, dendrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/sq cm at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/sq cm were measured.

Holleck, G. L.; Giner, J.

1972-01-01

310

Shear viscosity of molten alkali halides from equilibrium and nonequilibrium molecular-dynamics simulations  

Science.gov (United States)

The shear viscosity of molten NaCl and KCl was calculated through equilibrium (EMD) and nonequilibrium molecular-dynamics (NEMD) simulations in the canonical (N,V,T) ensemble. Two rigid-ion potentials were investigated, namely, the Born-Mayer-Huggins-Tosi-Fumi potential and the Michielsen-Woerlee-Graaf-Ketelaar potential with the parameters proposed by Ladd. The NEMD simulations were performed using the SLLOD equations of motion [D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984)] with a Gaussian isokinetic thermostat and the results are compared with those obtained from Green-Kubo EMD (N,V,T) simulations and experimental shear viscosity data. The NEMD zero strain rate shear viscosity, ?(0), was obtained by fitting a simplified Carreau-type equation and by application of mode-coupling theory, i.e., a ?-?1/2 linear relationship. The values obtained from the first method are found to be significantly lower than those predicted by the second. The agreement between the EMD and NEMD results with experimental data is satisfactory for the two potentials investigated. The ion-ion radial distribution functions obtained with the two rigid-ion potentials for both molten salts are discussed in terms of the differences between the two models.

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

2005-06-01

311

Selective endo and exo binding of alkali metals to corannulene.  

Science.gov (United States)

The ion size matters: the structures of corannulene monoanions crystallized with Cs(+) and Rb(+) ions in the presence of [18]crown-6 reveal the intrinsic binding preferences of alkali metals and allow evaluation of the bowl deformation caused by negative charge distribution and metal binding. The large cesium cation coordinates exclusively to the concave face of C(20) H(10)(-), whereas the smaller rubidium cation exhibits convex binding. PMID:21748832

Spisak, Sarah N; Zabula, Alexander V; Filatov, Alexander S; Rogachev, Andrey Yu; Petrukhina, Marina A

2011-08-22

312

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

313

Alkali-vapor laser-excimer pumped alkali laser  

International Nuclear Information System (INIS)

Based on the research internal and overseas, the principle of the excimer pumped alkali laser (XPAL) is explained, and the advantages and disadvantages of the XPAL are analyzed. Taking into consideration the difficulties that the diode pumped alkali laser (DPAL) meets on its development, the ability to solve or avoid these difficulties of XPAL is also analyzed. By summing up the achievements of the XPAL, the possible further prospect is proposed. The XPAL is of possibility to improve the performance of the DPAL. (authors)

314

crystal  

Science.gov (United States)

An eye-safe Raman laser is realized with BaTeMo2O9 (BTM) nonlinear crystal for the first time. By using a diode-end-pumped acousto-optically Q-switched Nd:YVO4 laser as the pumping source, the BTM crystal converts the fundamental laser at 1,342 nm to first-Stokes laser at 1,531 nm successfully. With an incident power of 10.8 W and a pulse repetition rate of 25 kHz, the average output power at 1,531 nm is obtained to be 0.83 W, corresponding to a diode-to-Stokes conversion efficiency of 7.7 %. The pulse width is 11 ns, and the peak power is 3.0 kW.

Bai, Fen; Wang, Qingpu; Tao, Xutang; Li, Ping; Zhang, Xingyu; Liu, Zhaojun; Shen, Hongbin; Lan, Weixia; Gao, Liang; Gao, Zeliang; Zhang, Junjie; Fang, Jiaxiong

2014-08-01

315

Crystals  

...cfm Interests: scientific materials research and learning information management and dissemination; multidisciplinary scientific research repositories; human and automated scientific metadata generation; scientific information classification and thesaurus; electronic scientific communication Contribution: Special Issue: Metal-Organic Frameworks (MOFs): Energy and Informatics Dr. Alberta Bonanni Institute for Semiconductor and Solid State Physics, Johannes Kepler University, Altenbergerstr. 69, A4040 Linz, Austria Tel. +43 732 2468 9664; Fax: +43 732 2468 9696 Website: http://magicspin.jku.at Interests: crystal growth; ...

316

Waste form development for immobilization of radioactive halide salt generated from pyrometallurgical reprocessing  

International Nuclear Information System (INIS)

Pyrometallurgical process will generate chloride salt waste which contains alkali and alkaline earth metal fission products. This waste is nuisance because it is hard to be vitrified. The authors have developed a simple dry process to synthesize sodalite, Na8(AlO2)6(SiO2)6)Cl2, which is a natural occurring mineral that contains halide salt stably in its three-dimensional cage structure. In this study, synthetic reaction was studied with various salt mixing ratio, temperature and time to synthesis in order to obtain leach resistant product without any further treatment. The sodalite synthesized by 200 hr''s heating of stoichiometric mixing at 1073 K was found to have higher leach resistance than conventional vitrified form. (author)

317

Polarized XANES study of the importance of inter-block vis-à-vis intra-block coupling in evolution of Tc in halide-molecule-intercalated Bi2Sr2CaCu2O8-? single crystals  

Science.gov (United States)

In addition to doping in the lattice that affects the intra-block coupling, intercalated molecules sit in between the consecutive basal planes, thereby increasing the effective length of the c-axis. This, in turn, must lead to a decrease in inter-block coupling. Both the doping and intercalation have been reported to affect the evolution of Tc in a system, implying the inherent importance of both types of coupling. In the latter case, the resulting depression of Tc is ascribed to transfer of charge between the intercalate and the host CuO2 plane. Most interesting studies in this regard pertain to use of I2, HgI2 and HgBr2 molecules as intercalates for the Bi2Sr2CaCu2O8+y system. Earlier reports mostly claim that the host CuO2 plane in Bi2Sr2CaCu2O8+y invariably becomes overdoped whichever the intercalate, thereby leading to a fall in Tc. In this paper, we examine these claims in the case of Bi2Sr2CaCu2O8+y single crystals by measuring the number of itinerant holes before and after intercalation by making polarization-dependent soft-x-ray absorption measurements at the O K and the Cu L3 edges. Our results do support the earlier claims on overdoing of the CuO2 plane in the case of iodine intercalate but are not in agreement with those in the case of the HgI2 intercalate.

Singhal, R. K.; Saini, N. L.; Dalela, B.; Dalela, S.; Choy, J. H.; Chaturvedi, D.; Sekhar, B. R.; Jain, D. C.; Garg, K. B.; Lin, Hong-Ji; Hou, T. Y.; Chen, C. T.

2002-07-01

318

Interactions of polar alkali dimers  

Science.gov (United States)

The effects of external electric static fields on the interactions of polar alkali diatoms for the purposes of alignment is investigated for a variety of trapping geometries and external field strengths. We also present new results for the dispersion and induction van der Waals coefficients calculated using the sum over states method of time dependent density functional transition moments. Additionally the static electric moments and polarizabilities for each heteronuclear alkali diatom have been calculated. These new results are used to accurately model the interactions between polar alkali molecules in the long range by a van der Waals expansion up to R-8. We find that strong alignment of specific heteronuclear diatoms is possible with strong but physically realizable external electric fields.

Byrd, Jason; Montgomery, John, Jr.; Cøté, Robin

2011-06-01

319

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

International Nuclear Information System (INIS)

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

320

Theoretical characterization of dihydrogen adducts with halide anions.  

Science.gov (United States)

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 nu(H-H) and in general the perturbation of the hydrogen molecule in complexes are much greater in the complexes with anions (Delta nu(H-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 Delta nu 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, 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 H(2) in storage materials. PMID:16784275

Vitillo, Jenny G; Damin, Alessandro; Zecchina, Adriano; Ricchiardi, Gabriele

2006-06-14

 
 
 
 
321

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)

322

Mechanical filter for alkali atoms  

CERN Document Server

A device for separating gases of different mass is discussed. Such a device could be used in a laser-driven spin exchange source of polarized hydrogen atoms to reduce the contamination of alkali atoms. A Monte Carlo simulation has shown that the suggested apparatus based on a commercial turbo pump could reduce by a factor of 10-15 the concentration of the alkali-metal atoms in the hydrogen flow from a laser driven polarized source. This would greatly enhance the effective polarization in hydrogen targets.

Toporkov, D K

2000-01-01

323

A negative ion source for alkali ions  

International Nuclear Information System (INIS)

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 5750C. (orig.)

324

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

325

Exciton emissions in alkali cyanides  

International Nuclear Information System (INIS)

The emissions of Alkali Cyanides X irradiated at low temperature were measured. In addition to the molecular (Frenkel Type) exciton emissions, another emitting centre was found and tentatively assigned to a charge transfer self trapped exciton. The nature of the molecular exciton emitting state is discussed. (Author)

326

Anionic halide···alcohol clusters in the solid state.  

Science.gov (United States)

The cationic (1,3,5-triazapentadiene)Pt(II) complexes [1](Cl)2, [2](Cl)2, [3](Br)2, and [4](Cl)2, were crystallized from ROH-containing systems (R = Me, Et) providing alcohol solvates studied by X-ray diffraction. In the crystal structures of [1-4][(Hal)2(ROH)2] (R = Me, Et), the Hal(-) ion interacts with two or three cations [1-4](2+) by means of two or three or four contacts thus uniting stacked arrays of complexes into the layers. The solvated MeOH or EtOH molecules occupy vacant space, giving contacts with [1-4](2+), and connects to the Hal(-) ion through a hydrogen bridge via the H(1O)O(1S) H atom forming, by means of the Hal(-)···HOR (Hal = Cl, Br) contact, the halide-alcohol cluster. Properties of the Cl(-)···HO(Me) H-bond in [1][(Cl)2(MeOH)2] were analyzed using theoretical DFT methods. PMID:25192004

Gushchin, Pavel V; Kuznetsov, Maxim L; Haukka, Matti; Kukushkin, Vadim Yu

2014-10-01

327

Structure and Chemistry in Halide Lead-Tellurite Glasses  

Energy Technology Data Exchange (ETDEWEB)

A series of TeO2-PbO glasses were fabricated with increasing fractions of mixed alkali, alkaline earth, and lanthanide chlorides. The glass and crystal structure was studied with Raman spectroscopy, nuclear magnetic resonance (NMR), X-ray diffraction, and electron microscopy. As the chloride fraction increased, the medium-range order in the glass decreased up to a critical point (~14 mass% of mixed chlorides), above which the glasses became phase-separated. Resulting phases are a TeO2/PbO-rich phase and a crystalline phase rich in alkali chlorides. The 125Te NMR indicates, contrary to previous studies, that Te site distribution did not change with increased concentrations of M+, M2+, and M3+ cations, but rather is controlled by the Te/Pb molar ratio. The 207Pb NMR shows that two Pb species exist and their relative concentration changes nearly linearly with addition of the mixed chlorides, indicating that the additives to the TeO2-PbO glass are accommodated by changing the Pb species. The 23Na and 35Cl NMR indicate that Na and Cl are distributed in the single-phase glass phase up to the critical point, and at higher concentrations partition to crystalline phases. Transmission electron microscopy shows that the sample at the critical point contains ~10 nm seed nuclei that increase in size and concentration with exposure to the electron beam.

McCloy, John S.; Riley, Brian J.; Lipton, Andrew S.; Windisch, Charles F.; Washton, Nancy M.; Olszta, Matthew J.; Rodriguez, Carmen P.

2013-02-11

328

Photoexcitation, photoionisation and photofragmentation of molecular rubidium halides  

International Nuclear Information System (INIS)

Photoionisation and photofragmentation of molecular rubidium halides following photoexcitation in the vacuum ultraviolet region are investigated. For this purpose total and partial ion yield spectra are measured from the vapours of RbF, RbCl, RbBr and RbI. Two different decay channels - spectator and participator type - are studied in different rubidium halide molecules. It is demonstrated that the opening of the spectator channel takes place at different excitation energies, depending on the halide atom in the molecule

329

Structure peculiarities of mixed alkali silicate glasses  

International Nuclear Information System (INIS)

The thermal porperties and structure of alkali and mixed alkali (Li, Na, K) silicate glasses by means of differential scanning calorimetry (DSC), the positron annihilation method, X-ray fluorescence and infrared (300-30 cm-1) spectroscopy were studied. Introduction of different alkali cations in glass results in nonadditive change in their electron structure (bond covalence degree growth) and the thermal behaviour. The different manifestations of mixed alkali effect can be explained by the lessening of long distance Coulomb interactions and strengthening the short-range forces in the mixed alkali glasses. (orig.)

330

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

331

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

Science.gov (United States)

...Definitions concerning metal halide lamp ballasts and fixtures. 431.322 Section...INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide lamp ballasts and fixtures. Ballast...

2010-01-01

332

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

333

Synthesis of Cyclic Aza-Ether Compounds and Studies of Their Use as Anion Receptors in Non-Aqueous Lithium Halide Salt Solutions  

Energy Technology Data Exchange (ETDEWEB)

A series of new anion receptors, based on cyclic aza-ether compounds, have been synthesized. In all of these cyclic aza-ether compounds, the electron-withdrawing group CF{sub 3}SO{sub 2} was attached to each of the nitrogen atoms. When used as additives, all of them can significantly increase the ionic conductivity of lithium halide salts in THF solutions. This is due to the complexation between these compounds and halide anions. Ionic conductivity studies show that the complexation behavior is related to both the ring structure of the cyclic compounds and the characteristics of the halide anions. X-ray diffraction data show that the diffraction patterns of the complex crystals are different from the pure cyclic aza-ether compounds. New Bragg peaks representing a large d-spacing ({approx}15 {angstrom}) are observed for the complex crystals which provides a clear evidence for complexation.

Lee, H. S.; Sun, X.; Yang, X. Q.; McBreen, J.; Callahan, J. H.; Choi, L. S.

1999-11-01

334

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

335

FTIR Studies of Internal Water Molecules of Bacteriorhodopsin: Structural Analysis of Halide-bound D85S and D212N Mutants in the Schiff Base Region  

Science.gov (United States)

Bacteriorhodopsin (BR), a membrane protein found in Halobacterium salinarum, functions as a light-driven proton pump. The Schiff base region has a quadropolar structure with positive charges located at the protonated Schiff base and Arg82, and counterbalancing negative charges located at Asp85 and Asp212 (Figure 1A). It is known that BR lacks a proton-pumping activity if Asp85 or Asp212 is neutralized by mutation. On the other hand, binding of C1- brings different effects for pumping functions in mutants at D85 and D212 position. While C1--bound D85T and D85S pump C1-, photovoltage measurements suggested that C1--bound D212N pumps protons at low pH. In this study, we measured low-temperature FTIR spectra of D85S and D212N containing various halides to compare the halide binding site of both proteins. In the case of D85S, the N-D stretching vibrations of the Schiff base were halide-dependent. This result suggests that the halide is a hydrogen-bond acceptor of the Schiff base, being consistent with the X-ray crystal structure. On the other hand, no halide dependence was observed for vibrational bands of the retinal skeleton and the Schiff base in the D212N mutant. This result suggests that the halide does not form a hydrogen bond with the Schiff base directly, unlike the mutation at D85 position. Halide-dependent water bands in the Schiff base region also differ between D85S and D212N. From these results, halide binding site of both proteins and role of two negative charges in BR will be discussed.

Shibata, Mikihiro; Kandori, Hideki

2007-12-01

336

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

337

Transient photocurrent measurements in alkali chalcogenide ternary compound semiconductors  

International Nuclear Information System (INIS)

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. (paper)

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

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

340

The coacervation of aqueous solutions of tetraalkylammonium halides  

International Nuclear Information System (INIS)

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

 
 
 
 
341

Metal-rich gadolinium hydride halides  

International Nuclear Information System (INIS)

Preparation, structures, and thermal behaviour of gadolinium hydride halides GdXH/sub n/ (X = Cl, Br, I; 0.7 2, and GdX3 in sealed Ta ampoules to 900 0C and 950 0C. The arrangement of the heavy atoms corresponds to the 3 slab (X-Gd-Gd-X) structures of ZrCl and ZrBr. Besides these, a new stacking variant containing only 2 slabs in the identity period (2s-GdBrH/sub 0.69/ and 2s-GdIH/sub 0.80/; nomenclature of niobium dichalcogenides) is found. (author)

342

Energy levels and predissociation in mercuric halides  

International Nuclear Information System (INIS)

Electron energy-loss spectra were obtained over an extended energy-loss range (approximately 5 to 15 eV) for incident electron energies of 200 eV and scattering angles of 20 in the mercuric halides HgBr2 and HgCl2. Under these conditions of impact energy and scattering angle, the energy-loss spectra correspond closely to optical absorption spectra, though the energy-loss spectra extend to much higher energies than previous photoabsorption spectra, and reveal many more excited states of these molecules than had previously been observed. This preliminary report gives raw spectra and tentative identifications of the principal features of these spectra

343

Oxidative addition of Pd(0) and Pt(0) with aromatic halides: Material for second-harmonic generation  

Science.gov (United States)

The use of M(PEt3)2(X) (M = Pd, Pt; X = Br, I) as donors in donor-acceptor benzene systems yields material suitable for second-harmonic generation. These compounds can be prepared in moderate yields from oxidative addition of Pd(0) and Pt(0) complexes with the appropriate phenyl halides. The structure of trans-Pt(PEt3)2(I)(?-nitrophenyl) has been determined; it crystallizes in the space group Cmc21.

Tam, Wilson; Calabrese, J. C.

1988-02-01

344

Photodissociation of OH- ions in RbCl crystals  

International Nuclear Information System (INIS)

Experiments utilizing optical absorption tecniques in the visible and ultraviolet spectral regions have been performed to study the primary and secondary defects from the photodissociation of the OH- ion in RbCl crystals, over the 77 to 300 K temperature range. It was observed that the basic mechanism of the OH- photodissociation is the same as the other alkali halides doped with OH-. Due to the presence of the CN- molecular impurity in one of the samples used, it has been observed that these ions interact with the OH- impurities changing the photodissociation process. The experimental observation of OH- photodissociation in RbCl: OH- + CN- allowed us to propose new aggregated defects. These defects are complex centers in the form of [OH- . CN-] characterized by an eletronic absorption at 1940 A and a vibrational-rotational absorption at 2165 cm-1, and in the form [O- . CN-] with a characteristic eletronic absorption at 2040 A. One property of the complex center [OH- . CN-] observed is that it allows photodissociation of the OH- impurity, by X and UV irradiation, at room temperature producting U and [O- . CN-] centers. The additive coloration of the RbCl: OH- + CN- also showed that it's possible to obtain U centers directly from the OH- dissociation in the presence of CN- impurities

345

Crystal structures of native and xylosaccharide-bound alkali thermostable xylanase from an alkalophilic Bacillus sp. NG-27: Structural insights into alkalophilicity and implications for adaptation to polyextreme conditions  

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Crystal structures are known for several glycosyl hydrolase family 10 (GH10) xylanases. However, none of them is from an alkalophilic organism that can grow in alkaline conditions. We have determined the crystal structures at 2.2 Å of a GH10 extracellular endoxylanase (BSX) from an alkalophilic Bacillus sp. NG-27, for the native and the complex enzyme with xylosaccharides. The industrially important enzyme is optimally active and stable at 343 K and at a pH of 8.4. Comparison of the structur...

Manikandan, Karuppasamy; Bhardwaj, Amit; Gupta, Naveen; Lokanath, Neratur K.; Ghosh, Amit; Reddy, Vanga Siva; Ramakumar, Suryanarayanarao

2006-01-01

346

Europium-doped barium halide scintillators for x-ray and ?-ray detections  

Science.gov (United States)

Single crystals of undoped or europium-doped barium chloride, bromide, and iodide were investigated under x-ray and ?-ray excitations. The Eu2+-related x-ray excited luminescence found in the Eu-doped barium halides occurs at 402, 404, and 425nm for the chloride, bromide, and iodide, respectively. BaCl2:Eu2+ shows the best scintillation properties of the systems investigated. The light yield is about 20000±2000photonsperMeV of absorbed ?-ray energy, the energy resolution for the 662keV photopeak is 8.8%±0.9%, and the scintillation decay time is 390±40ns.

Selling, J.; Birowosuto, M. D.; Dorenbos, P.; Schweizer, S.

2007-02-01

347

Surface characterization of alkali-treated coals  

Energy Technology Data Exchange (ETDEWEB)

The surface interactions of alkali with coal and mineral matter have been studied by electron spectroscopy for chemical analaysis (ESCA) to establish a basis for predicting the relative reactivity of alkali with sulphur during coal beneficiation processes. The speciation of sulphur in coals doped with various alkali salts was determined and quantified after heating the mixtures to 648 K in air or N{sub 2}, then washing with water. Organic and pyritic sulphur on the surface react with alkali when heated, and the sulphide or oxidized sulphur product can then be washed from the coal. The extent of reaction between the alkali salt and surface sulphur is governed by the size of the cation and the electronic properties of the anion; larger alkali cations are more effective in promoting the reactivity of surface sulphur, as are anions with stronger nucleophilic properties. 14 refs., 2 figs., 5 tabs.

Baltrus, J.P.; Diehl, J.R.; D' Este, J.R.; Ladner, E.P. (USDOE Pittsburgh Energy Technology Center, PA (USA))

1990-01-01

348

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

International Nuclear Information System (INIS)

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

349

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

Science.gov (United States)

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

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

2013-04-01

350

Regenerable activated bauxite adsorbent alkali monitor probe  

Science.gov (United States)

A regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC exhaust gases.

Lee, Sheldon H. D. (Willowbrook, IL)

1992-01-01

351

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

Energy Technology Data Exchange (ETDEWEB)

We have investigated the optical absorption spectra of the CsBr:Au{sup -} crystals irradiated with an ultraviolet (UV) light. Before the UV-light irradiation, the absorption bands associated with the isolated Au{sup -} ion (monomer) are observed in the energy region of UV. After a slight UV-light irradiation, the absorption intensities of the monomer bands decrease and the absorption bands due to paired Au{sup -} ions appear around the monomer bands. Furthermore, UV-light irradiation on the CsBr:Au{sup -} crystals brings about the appearance of several new absorption bands in the visible region. From the analogy with the aggregation of the F centers in alkali halide crystals, the new absorption bands are attributed to the aggregate centers of the Au{sup -} ions. They can also be regarded as the CsAu nanocluster constructed from the Cs{sup +} cations and the Au{sup -} anions. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Kawai, Taketoshi; Yamano, Asuka [Department of Environmental Sciences, Faculty of Science, Osaka Women' s University, Daisen-cho 2-1, Sakai City, Osaka 590-0035 (Japan)

2006-02-01

352

An EPR investigation of Ag0 and Ag2+ in irradiated single crystal of potassium fluoride doped with silver fluoride  

International Nuclear Information System (INIS)

The electron paramagnetic resonance absorption spectra of a singly ionized diatomic fluoride molecule-ion F2-, atomic silver Ag0, and divalent silver Ag2+ contained in single crystals of potassium fluoride were re-examined at X-band wavelengths. The F2- and Ag0 centers are produced simultaneously by ?-irradiation at liquid nitrogen temperature. The divalent silver Ag2+ centers are formed by subsequently warming the irradiated samples to room temperature for a few hours and then cooling to 77 K. All field-strength positions of resonance-absorption lines observed at low temperatures were satisfactorily predicted by computer simulation. The high degree of resolution exhibited by the spectra is due in part to the large nuclear magnetic moment of fluorine and in part to the fact that spectral lines in KF are narrow compared to those of similar systems in other alkali halide crystals. For atomic silver, the hexafluoride cluster is cubic. By contrast, the divalent silver center is tetragonally distorted along a crystal cube edge as a consequence of the Jahn-Teller effect

353

A EPR Investigation of Atomic Silver and Divalent Silver in Irradiated Single Crystal of Potassium Fluoride Doped with Silver Fluoride  

Science.gov (United States)

The electron paramagnetic resonance absorption spectra of a singly ionized diatomic fluoride molecule -ion F_2^-, atomic silver Ag^0 and divalent silver Ag ^{2+} contained in single crystals of potassium fluoride have been re-examined at X-band wavelengths. The F_2^- and Ag^0 centers are produced simultaneously by gamma-irradiation at liquid nitrogen temperature. The divalent silver Ag^{2+} centers are formed by subsequently warming the irradiated samples to room temperature for a few hours and then cooling to 77 K. All field strength positions of resonance absorption lines observed at low temperatures have been satisfactorily predicted by computer simulation. The high degree of resolution exhibited by the spectra is due in part to the large nuclear magnetic moment of fluorine and in part to the fact that spectral lines in KF are narrow compared to those of similar systems in other alkali halide crystals. For an atomic silver, the hexafluoride cluster is cubic. By contrast, the divalent silver center is tetragonally distorted along a crystal cube edge as a consequence of the Jahn-Teller effect. Unexpected splittings of the central lines in the resonance absorption spectrum of divalent silver are observed and interpreted as being due to second order perturbation effects.

Yu, Cheng

354

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

355

The unexpected properties of alkali metal iron selenide superconductors  

Energy Technology Data Exchange (ETDEWEB)

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

Dagotto, Elbio R [ORNL

2013-01-01

356

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.)

357

Characterization of Waste Poly(Ethylene-Terephthalate after Alkali Treatment  

Directory of Open Access Journals (Sweden)

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

Reš?ek, A.

2011-07-01

358

40 CFR 721.4740 - Alkali metal nitrites.  

Science.gov (United States)

...2010-07-01 false Alkali metal nitrites. 721.4740 ...Substances § 721.4740 Alkali metal nitrites. (a) Chemical...are nitrites of the alkali metals (Group IA in the periodic classification of chemical...

2010-07-01

359

40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.  

Science.gov (United States)

...Substituted halogenated pyridinol, alkali salt. 721.8900 Section 721.8900 ...Substituted halogenated pyridinol, alkali salt. (a) Chemical substances and significant...substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and...

2010-07-01

360

Metal halide-group III halide gas complexes with emphasis on aluminum chloride  

International Nuclear Information System (INIS)

The thermodynamics of the presently known gas complexation reactions between metal halides and group III halides are treated in a self-consistent manner. By focusing on aluminum chloride as a complexing agent, certain systematic trends are revealed. The partial pressures of the gaseous complexes display shallow minima near 8000K whenever the complex molecules involve more than one molecule of AlCl3. Increasing the aluminum chloride pressure from 1 atm. to 103 atm. decreases somewhat the differences in the partial pressures among the various gaseous complexes which span two to three orders of magnitude. The methods developed for characterizing the complexes, and their structures as well as some applications of gas complexation are discussed

 
 
 
 
361

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

362

Vibrational Spectroscopy of Sodium Halide and Hydrogen Halide Aqueous Solutions: Application to Atmospheric Aerosol Chemistry  

Science.gov (United States)

Heterogeneous reactions on the surfaces of atmospheric aerosols play an important role in atmospheric chemistry. These reactions are capable of converting alkyl and hydrogen halides (common constituents of marine boundary aerosols) into active halogen compounds. Fundamental questions still remain concerning surface species and reaction mechanisms pertaining to marine boundary aerosols. The first step in beginning to understand these heterogeneous reactions is to determine how ions in solution affect the structure of water at the interface. Vibrational sum frequency generation spectroscopy is used to examine the air-liquid interface of sodium halide and hydrogen halide (i.e. strong acid) solutions. In addition, comparison of the bulk water structure to that of the interface is accomplished using Raman spectroscopy. The hydrogen-bonding environment at the surface of NaCl is found to be similar to that of the air-water interface. In contrast, the interfacial water structure of NaBr, HCl, and HBr solutions is significantly altered from that of neat water. In the bulk, NaCl, NaBr, HCl, and HBr solutions disturb the hydrogen-bonding network of neat water. A comparison between the corresponding salts and acids show that the salts produce greater disorder (i.e. less coupling of the water symmetric stretching modes) in the bulk water structure.

Levering, L. M.; Liu, D.; Allen, H. C.

2003-12-01

363

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

364

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

365

A T-shaped selenenyl halide.  

Science.gov (United States)

The title selenenyl halide complex, 3-iodo-2-phenyl-3H-3-selenaindazole, C(12)H(9)IN(2)Se, has an almost planar conformation and a nearly ideal T-shape for the Se(INC) moiety [Se-I 2.8122 (12), Se-C 1.881 (7) and Se-N2 2.051 (6) A; C-Se-N 79.6 (3), C-Se-I 96.8 (2) and N-Se-I 176.17 (17) degrees ]. This arrangement, together with the two selenium lone pairs, leads to a distorted trigonal-bipyrimidal geometry about the Se atom. Intermolecular interactions are largely limited to stacking forces. PMID:15263218

Majeed, Z; McWhinnie, W R; Lowe, P R

2000-03-15

366

Soft scorpionate coordination at alkali metals.  

Science.gov (United States)

Reported here are the single-crystal X-ray structure analyses of bis-?-methanol-?(4)O:O-bis{[hydrotris(3-phenyl-2-sulfanylidene-2,3-dihydro-1H-1,3-imidazol-1-yl)borato-?(3)H,S,S'](methanol-?O)sodium(I)}, [Na2(C27H22BN6S3)2(CH4O)4] (NaTm(Ph)), bis-?-methanol-?(4)O:O-bis{[hydrotris(3-isopropyl-2-sulfanylidene-2,3-dihydro-1H-1,3-imidazol-1-yl)borato-?(3)H,S,S'](methanol-?O)sodium(I)}-diethyl ether-methanol (1/0.3333/0.0833), [Na2(C18H28BN6S3)2(CH4O)4]·0.3333C4H10O·0.0833CH3OH (NaTm(iPr)), and a novel anhydrous form of sodium hydrotris(methylthioimidazolyl)borate, poly[[?-hydrotris(3-methyl-2-sulfanylidene-2,3-dihydro-1H-1,3-imidazol-1-yl)borato]sodium(I)], [Na(C12H16BN6S3)] ([NaTm(Me)]n). NaTm(iPr) and NaTm(Ph) have similar dimeric molecular structures with ?(3)H,S,S'-bonding, but they differ in that NaTm(Ph) is crystallographically centrosymmetric (Z' = 0.5) while NaTm(iPr) contains one crystallographically centrosymmetric dimer and one dimer positioned on a general position (Z' = 1.5). [NaTm(Me)]n is a one-dimensional coordination polymer that extends along the a direction and which contains a hitherto unseen side-on ?(2)-C=S-to-Na bond type. An overview of the structural preferences of alkali metal soft scorpionate complexes is presented. This analysis suggests that these thione-based ligands will continue to be a rich source of interesting alkali metal motifs worthy of isolation and characterization. PMID:24816005

Rajesekharan-Nair, Rajeev; Lutta, Samuel T; Kennedy, Alan R; Reglinski, John; Spicer, Mark D

2014-05-01

367

Method of handling radioactive alkali metal waste  

International Nuclear Information System (INIS)

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

368

Purification and Characterization of an Extracellular, Thermo-Alkali-Stable, Metal Tolerant Laccase from Bacillus tequilensis SN4  

Science.gov (United States)

A novel extracellular thermo-alkali-stable laccase from Bacillus tequilensis SN4 (SN4LAC) was purified to homogeneity. The laccase was a monomeric protein of molecular weight 32 KDa. UV-visible spectrum and peptide mass fingerprinting results showed that SN4LAC is a multicopper oxidase. Laccase was active in broad range of phenolic and non-phenolic substrates. Catalytic efficiency (kcat/Km) showed that 2, 6-dimethoxyphenol was most efficiently oxidized by the enzyme. The enzyme was inhibited by conventional inhibitors of laccase like sodium azide, cysteine, dithiothreitol and ?-mercaptoethanol. SN4LAC was found to be highly thermostable, having temperature optimum at 85°C and could retain more than 80% activity at 70°C for 24 h. The optimum pH of activity for 2, 6-dimethoxyphenol, 2, 2?-azino bis[3-ethylbenzthiazoline-6-sulfonate], syringaldazine and guaiacol was 8.0, 5.5, 6.5 and 8.0 respectively. Enzyme was alkali-stable as it retained more than 75% activity at pH 9.0 for 24 h. Activity of the enzyme was significantly enhanced by Cu2+, Co2+, SDS and CTAB, while it was stable in the presence of halides, most of the other metal ions and surfactants. The extracellular nature and stability of SN4LAC in extreme conditions such as high temperature, pH, heavy metals, halides and detergents makes it a highly suitable candidate for biotechnological and industrial applications. PMID:24871763

Sondhi, Sonica; Sharma, Prince; Saini, Shilpa; Puri, Neena; Gupta, Naveen

2014-01-01

369

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

International Nuclear Information System (INIS)

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

370

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

371

Catalytic effect of halide additives ball milled with magnesium hydride  

Energy Technology Data Exchange (ETDEWEB)

The influence of various halide additives milled with magnesium hydride (MgH{sub 2}) on its decomposition temperature was studied. The optimum amount of halide additive and milling conditions were evaluated. The MgH{sub 2} decomposition temperature and energy of activation reduction were measured by temperature programmed desorption (TPD) and differential scanning calorimetry (DSC). The difference in catalytic efficiency between chlorides and fluorides of the various metals studied is presented. The effects of oxidation state, valence and position in the periodic table for selected halides on MgH{sub 2} decomposition temperature were also studied. The best catalysts, from the halides studied, for magnesium hydride decomposition were ZrF{sub 4}, TaF{sub 5}, NbF{sub 5}, VCl{sub 3} and TiCl{sub 3}. (author)

Malka, I.E.; Bystrzycki, J. [Department of Advanced Materials and Technologies, Military University of Technology, Kaliskiego 2, 00-908 Warsaw (Poland); Czujko, T. [Department of Advanced Materials and Technologies, Military University of Technology, Kaliskiego 2, 00-908 Warsaw (Poland); CanmetENERGY, Hydrogen Fuel Cells and Transportation Energy, Natural Resources (Canada)

2010-02-15

372

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

373

Three distinct cadmium coordination polymers with a multidentate tripyridyl-substituted triazole tecton regulated by halide anions  

Science.gov (United States)

Three distinct Cd(II) coordination polymers [Cd3(L434)2Cl6]n (1), [Cd(L434)2Br2]n (2), and [Cd2(L434)2I4(H2O)2]n (3) have been designed and synthesized with a versatile building block 3,5-bis(4-pyridyl)-4-(3-pyridyl)-1,2,4-triazole (L434) by altering the Cd(II) halides of reaction systems. Single crystal X-ray diffraction reveals that 1-3 display different zigzag, box-like, and ladder-like 1D polymeric motifs, respectively. Moreover, aromatic stacking interactions are observed in all these structures to extend and/or stabilize the supramolecular lattices. Their thermal stabilities and fluorescent properties have also been explored. Significantly, the regular variation in structural patterns and photoluminescence properties of 1-3 can be properly ascribed to the diversification of halide anions.

Chen, Jing; Wu, Na; Li, Cheng-Peng

2013-11-01

374

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.)

375

X-ray-absorption spectroscopic investigation of alkali and alkaline earth catalysts in coal gasification. Final report, January 1987-September 1989  

International Nuclear Information System (INIS)

The structures of alkali and alkaline-earth metal catalyst species in lignite and polymer chars and during pyrolysis pretreatment and char gasification have been investigated using ambient and newly-developed, in situ XAFS spectroscopic techniques. The XAFS data, which were obtained at the Stanford Synchrotron Radiation Laboratory, were supplemented by char characterization and reactivity measurements made at the Pennsylvania State University. The findings of the investigation are as follows: (i) the catalytic species, as introduced to the char or lignite, is an atomically-dispersed, metal-ion-oxygen-anion complex, and remains a metal-oxygen complex throughout pyrolysis and gasification; (ii) the catalyst species transforms to a bulk oxide species during pyrolysis pretreatment; (iii) during gasification, the catalyst species rapidly transforms to bulk alkali carbonate in the case of the alkali-metal species and slowly to calcium oxide in the case of the calcium species; (iv) higher catalyst loadings results in an increased number of catalytic sites, rather than any structural variation of the catalyst site due to concentration effects; and (v) reaction of alkali with aluminosilicates (from clays) or silica is the major catalyst poisoning reaction, unless the coal is demineralized in which case the alkali may react with residual halide from HCl or HF used to clean the coal. Such poisoning reactions were not demonstrated for calcium-oxygen speciescium-oxygen species

376

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

377

Oxygen mobility in alkali feldspars  

International Nuclear Information System (INIS)

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

378

Halide and proton binding kinetics of yellow fluorescent protein variants.  

Science.gov (United States)

A T203Y substitution in green fluorescent protein causes a red shift in emission to yield a class of mutants known as yellow fluorescent protein (YFP). Many of these YFP mutants bind halides with affinities in the millimolar range, which often results in the chromophore pK values being shifted into the physiological range. While such sensitivities may be exploited for halide and pH sensors, it is desirable to reduce such environmental sensitivities in other studies, such as in Förster resonance energy transfer probes to measure conformational changes within fusion proteins. Venus and Citrine are two such variants that have been developed with much reduced halide sensitivities. Here we compare the kinetics of halide binding, and the coupled protonation reaction, for several YFP variants and detect slow kinetics (dissociation rate constants in the range of 0.1-1 s(-1)), indicative of binding to an internal site, in all cases. The effective halide affinity for Venus and Citrine is much reduced compared with that of the original YFP 10C construct, primarily through a reduced association rate constant. Nuclear magnetic resonance studies of YFP 10C confirm halide binding occurs on a slow time scale (<4 s(-1)) and that perturbations in the chemical shift occur throughout the sequence and structure. PMID:23514090

Seward, Harriet E; Basran, Jaswir; Denton, Roanne; Pfuhl, Mark; Muskett, Frederick W; Bagshaw, Clive R

2013-04-01

379

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-05-15

380

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

International Nuclear Information System (INIS)

The DC Conductivity and Differential Thermal Analysis of glasses with composition (30?x)Li2O?xV2O5?20Bi2O3?50B2O3(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 (Tg) and crystallization temperature (Tx). 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

 
 
 
 
381

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

Science.gov (United States)

The DC Conductivity and Differential Thermal Analysis of glasses with composition (30-x)Li2O?xV2O5?20Bi2O3?50B2O3(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 (Tg) and crystallization temperature (Tx). 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.; Dahiya, M. S.; Agarwal, A.

2014-04-01

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

Cluster harvesting by successive reduction of a metal halide with a nonconventional reduction agent: a benefit for the exploration of metal-rich halide systems.  

Science.gov (United States)

The preparation of thermally labile compounds is a great temptation in chemistry which requires a careful selection of reaction media and reaction conditions. With a new scanning technique denoted here as Cluster Harvesting, a whole series of metal halide compounds is detected by differential thermal analysis (DTA) in fused silica tubes and structurally characterized by X-ray powder diffraction. Experiments of the reduction of tungsten hexahalides with elemental antimony and iron are presented. A cascade of six compounds is identified during the reduction with antimony, and five compounds or phases are monitored following the reduction with iron. The crystal structure of Fe2W2Cl10 is reported, and two other phases in the Fe-W-Cl system are discussed. PMID:23718691

Ströbele, Markus; Mos, Agnieszka; Meyer, Hans-Jürgen

2013-06-17

384

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

385

Dielectric properties of quenched and x-ray irradiated triglycine sulphate single crystals later excited with laser light  

International Nuclear Information System (INIS)

It was reported earlier from this laboratory that, if X-ray or ?-ray irradiated alkali halide crystals were subsequently excited with laser light, interesting changes were observed in their colour centre phenomena and dielectric properties. The results suggested that laser excitation also produces defects in these solids. The work was extended later to other materials. X-ray or ?-ray irradiation of ferroelectrics such as BaTiO3 and KNbO3 showed that the dielectric constant (K) and loss (tan ?) are reduced only at low frequencies. In this letter we present the results of detailed investigations on the effect of X-ray irradiation (and subsequent laser excitation) on the dielectric constant (K) and loss (tan ?) of quenched triglycine sulphate (TGS) single crystals. The frequency range studied was 102-106 Hz and the temperature range 30-80oC. At constant temperature, K decreased with increasing frequency, reaching a constant value at 105 Hz; tan ? also decreased with increasing frequency. The results obtained at different temperatures for a given frequency showed a peak in the value of both K and tan ? at 49oC, the Curie temperature for TGS. An explanation of these observations is offered in terms of the possible lattice defects produced by the laser excitation. (author)

386

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

Directory of Open Access Journals (Sweden)

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

Ting Zhang

2010-06-01

387

Alkali content of alpine ultramafic rocks  

Science.gov (United States)

The lower limit of abundance of sodium and potassium in ultramafic rocks is less than the threshold amount detectable by conventional analytical methods. By a dilutionaddition modification of the flame-spectrophotometric method, sodium and potassium have been determined in 40 specimens of alpine ultramafic rocks. Samples represent six regions in the United States and one in Australia, and include dunite, peridotite, pyroxenite, and their variably serpentinized and metamorphosed derivatives. The median value found for Na2O is 0.004 per cent, and the range of Na2O is 0.001-0.19. The median value for K2O is 0.0034 per cent and the range is 0.001-0.031 per cent. Alkali concentrations are below 0.01 per cent Na2O in 28 samples and below 0.01 per cent K2O in 35. Derivation of basalt magma from upper-mantle material similar to such ultramafic rocks, as has been postulated, is precluded by the relative amounts of sodium and potassium, which are from 200 to 600 times more abundant in basalt than in the ultramafic rocks. Similar factors apply to a number of other elements. No reasonable process could produce such concentrations in, for example, tens of thousands of cubic miles of uniform tholeiitic basalt. The ultramafic rocks might have originated either as magmatic crystal precipitates or as mantle residues left after fusion and removal of basaltic magma. Injection of ultramafic rocks to exposed positions is tectonic rather than magmatic. ?? 1965.

Hamilton, W.; Mountjoy, W.

1965-01-01

388

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)

389

Transcriptome Analysis of Alkali Shock and Alkali Adaptation in Listeria monocytogenes 10403S  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Alkali stress is an important means of inactivating undesirable pathogens in a wide range of situations. Unfortunately, Listeria monocytogenes can launch an alkaline tolerance response, significantly increasing persistence of the pathogen in such environments. This study compared transcriptome patterns of alkali and nonalkali-stressed L. monocytogenes 10403S cells, to elucidate the mechanisms by which Listeria adapts and/or grows during short- or long-term alkali stress. Transcription profile...

Giotis, Efstathios S.; Muthaiyan, Arunachalam; Natesan, Senthil; Wilkinson, Brian J.; Blair, Ian S.; Mcdowell, David A.

2010-01-01

390

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

Science.gov (United States)

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

2010-01-01

391

Color silver halide hologram production and mastering  

Science.gov (United States)

Color reflection holograms recorded with the Denisyuk geometry have been demonstrated by the recently formed HOLOS Corporation in New Hampshire. The Slavich red-green-blue (RGB) sensitized ultra-high resolution silver halide emulsion was used for the hologram recording. The employed laser wavelengths were 647 nm, 532 nm, and 476 nm, generated by an argon ion, a frequency doubled Nd:YAG, and a krypton ion laser, respectively. A beam combination mechanism with dichroic filters enabled a simultaneous RGB exposure, which made the color balance and overall exposure energy easy to control as well as simplifying the recording procedure. HOLOS has been producing limited edition color holograms in various sizes from 4' X 5' to 12' X 16'. A 30 foot long optical table and high power lasers will enable HOLOS to record color holograms up to the size of one meter square in the near future. Various approaches have been investigated in generating color hologram masters which have sufficiently high diffraction efficiency to contact copy the color images onto photopolymer materials. A specially designed test object including the 1931 CIE chromaticity diagram, a rainbow ribbon cable, pure yellow dots, and a cloisonne elephant was used for color recording experiments. In addition, the Macbeth Color Checker chart was used. Both colorimetric evaluation and scattering noise measurements were performed using the PR-650 Photo Research SpectraScan SpectraCalorimeter.

Bjelkhagen, Hans I.; Huang, Qiang

1997-04-01

392

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)

393

Calcium silicate hydrate: Crystallisation and alkali sorption  

Energy Technology Data Exchange (ETDEWEB)

Homogeneous single C-S-H gels has been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, R{sub d}, was introduced to express the partition of alkali between solid and aqueous phases at 25 deg. C. R{sub d} 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 R{sub d} indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant R{sub d} 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 R{sub d}, indicating enhancement of alkali binding. However, the dependence of R{sub d} on alkali concentration is non-ideal with composition. A two-sitemodel 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){sub 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, 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){sub 2} is exsolved and occurs as nano-sized crystallites. (author)

Hong, S

2000-07-01

394

Investigation of new alkali bismuth oxosulfates and oxophosphates with original topologies of oxo-centered units.  

Science.gov (United States)

Two new alkali bismuth oxosulfates, [Bi12O15]Li2(SO4)4 (I) and [Bi7K2O8]K(SO4)4 (II), have been synthesized by heating a mixture of Bi2O3, CuSO45H2O, and A2CO3 (A = Li, K), and characterized by single crystal XRD, transmission electron microscopy, and multiphoton SHG and IR spectroscopy. In the above formula the [BixOy] subunits denote the 3D-porous (I) or 1D-columnar (II) polycationic host-lattice formed of edge-sharing OBi4 or O(Bi,K)4 oxocenterd tetrahedra. The SO4(2-) groups and alkali ions are arranged into channels in the interstices leading to original opened crystal structures for these two first reported alkali oxo-bismuth sulfates. The strong adaptability of the oxocentered framework is demonstrated by the possibility of preparing single crystals of [Bi8.73K0.27O8]K1.54(PO4)4 (III) whose crystal structure is similar to those of II with disorder between OBi4 and O(Bi3,K) tetrahedra and different channel occupancy due to the aliovalent replacement of SO4(2-) for PO4(3-). PMID:25360515

Lü, Minfeng; Colmont, Marie; Huvé, Marielle; De Waele, Isabelle; Terryn, Christine; Aliev, Almaz; Mentré, Olivier

2014-11-17

395

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

396

Scaling behavior in the conductivity of alkali oxide glasses  

Energy Technology Data Exchange (ETDEWEB)

Although the frequency dependent conductivity, {sigma}({omega}), of ion-containing glasses displays power law dispersion ({sigma}({omega}) {approx} {omega}{sup n}) that can usually be described by a master curve, several findings have suggested that this scaling fails at low temperatures as indicated by a temperature dependence of the scaling exponent, n. The authors investigate this behavior in the frequency range between 1 Hz and 10{sup 6} Hz for a different materials including alkali metaphosphate glasses and a polymer. They identify two distinct regimes of conductive behavior, {sigma}{sub {vert_bar}} and {sigma}{sub {parallel}}. The first, {sigma}{sub {vert_bar}}, is strongly temperature dependent and appears to obey a master curve representation. The second, {sigma}{sub {parallel}}, exhibits only a weak temperature dependence with a roughly linear frequency dependence. A strong depression of {sigma}{sub {vert_bar}} occurs for the mixed alkali case, but {sigma}{sub {parallel}} is unaffected and occurs at roughly the same location in all the alkali compositions studied. They propose that {sigma}{sub {parallel}} does not arise from cation motion, but rather originates from a second mechanisms likely involving small distortions of the underlying glassy matrix. This assignment of {sigma}{sub {parallel}} is further supported by the roughly universal location of {sigma}{sub {parallel}}, to within an order of magnitude, of a variety of materials, including a polymer electrolyte and a doped crystal. Since {sigma}{sub {vert_bar}}(T) and {sigma}{sub {parallel}}(T {approx} const.) are viewed as separate phenomena, the temperature dependence of the scaling exponent is shown to result merely from a superposition of these two contributions and does not indicate any intrinsic failure of the scaling property of {sigma}{sub {vert_bar}}.

Sidebottom, D.L.; Green, P.F.; Brow, R.K.

1995-11-01

397

Design and construction of a copper-halide laser  

International Nuclear Information System (INIS)

The considerations necessary for the design and construction of an inexpensive, reliable copper halide laser are presented. A broad range of parameters which govern the output of the double-pulse copper-halide laser was studied. The laser has an optimum operating temperature which is different for each halide uCl, CuBr, CuI), but corresponds to a halide vapor pressure of about 0.1 torr for all three halides. At low repetition rates the highest laser output is achieved with helium as buffer gas. The laser output increases linearly with laser tube cross-section. As the tube diameter is increased, the dissociation energy must be increased, but not the excitation energy. A thyratron bias circuit has been developed which permits both dissociation and excitation pulses to be obtained from the same capacitor (with a small delay) without thyratron latch. Use of the single thyratron reduces the laser cost considerably. A laser tube with an operating life of many hundreds of hours has been designed. The description of a laser with an output of 0.5 mJ per pulse at repetition rates of up to 120 pulses per second is given. The design and construction of various components of this laser are given in detail. (authors)

398

Ultrafast Electron-Lattice Relaxation of Optically Excited Centers in Crystals  

Science.gov (United States)

The excited-state dynamics of a localized center (defect, molecule, cluster) in a nonconducting crystal is discussed, and the Pulse Model is introduced to study its temporal behavior on a scale from few femtoseconds to tens of picoseconds after ultrafast electronic excitation. The simple Pulse Model and a modified version, both elaborated few years ago by the authors, allow a numerical selfconsistent evaluation of the electron-phonon coupled dynamics during the relaxation, i.e. the values of position and momentum of the ions as well as of the wavefunction and energy of the electron as function of time. In particular the process of relaxation of the ions surrounding the center is related to the motion of the multimode wavepacket of lattice phonons generated by the ultrafast optical excitation of the center Numerical data for defects in alkali halides in the limit of strong electron-phonon coupling are presented in two cases: that of a non degenerate electronic excited state and that of a double degenerate excited state (Exe Jahn-Teller case). In the former case, we show that the decay time to the relaxed configuration is related to the autocorrelation time of the multimode phonon wavepacket coupled to the excited electron. In the second case, the Jahn-Teller case, we observe a process of dynamical trapping and hopping between distorted lattice configurations with features depending on the symmetry, electron-phonon coupling strength and temperature.

Terzi, Nice; Dominoni, Matteo

399

Radiation processes in ionic crystals and the problem of material study by radiation  

International Nuclear Information System (INIS)

To find ways for radiation-stable material search and production, a survey of some research works is given and investigations have been carried out on the effect of radiation upon defect generation in alkali halide crystals (AHC) within a wide range of dose rates and temperatures. It has been stated that fast electron-hole processes are responsible for the formation of primary defects and their simple aggregates both at high and low temperatures. At high absorbed doses (102-106 Mrad) radiation processes in AHC grow more complicated: radiation-induced decay of large colloidal centres goes on along with colour centre coagulations. Annealing of radiation defects at high temperatures (up to 1000 K) yields: 1) radiation-generated primary short-living defects (F-H pairs) which partially recombine during their lifetime due to radiation- stimulated diffusion; 2) spatially separated final products - long-living colloidal centres and halogen clusters. An increase of AHC radiation stability and decrease of radiolysis product yield (caused by induced radiation annealing and by inserting a stabilizing impurity into the AHC matrix) is shown to be possible. The possibility to use ionic compounds in molten salt reactors is analysed

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

Chemistry of gaseous lower valent actinide halides. Final technical report, August 1979-August 1985  

International Nuclear Information System (INIS)

The objective of this program was to provide accurate thermochemical information for key actinide-halide and oxyhalide systems, starting with uranium halides, so that the basic factors underlying the chemical bonding and chemical reactivity in these systems can be elucidated in a systematic way. Our principal focus was on the gaseous halides, mainly the lower valent halides, because these molecular species largely will define the high temperature chemistry in the nuclear applications of interest. 6 refs., 2 tabs

402

Substitution mechanism of alkali metals for strontium in strontium hydroxyapatite  

International Nuclear Information System (INIS)

Strontium hydroxyapatites substituted by alkali metals are synthesized by double decomposition method in basic medium. Structures of Sr9.50Na0.30(PO4)6(OH)1.30 (SrNaHAp) and Sr9.81K0.12(PO4)6(OH)1.74 (SrKHAp) are determined by X-ray powder diffraction. Both compounds are isotypic and crystallize in hexagonal system (space group P63/m) with the following cells: a=9.751(3) A and c=7.279(3) A for SrNaHAp and a=9.755(4) A and c=7.284(3) A for SrKHAp. Results are compared to those of Sr10(PO4)6(OH)2. According to the site occupancy factors, in SrNaHAp sodium is localized in site (I) and in SrKHAp potassium in site (II). Both structures contain vacancies in hydroxyl and metal sites. The mechanism of alkali metals substitution for strontium proposed explains the vacancies formation

403

Methyl halide emissions from greenhouse-grown mangroves  

Science.gov (United States)

Two mangrove species, Avicennia germinans and Rhizophora mangle, were greenhouse grown for nearly 1.5 years from saplings. A single individual of each species was monitored for the emission of methyl halides from aerial tissue. During the first 240 days, salinity was incrementally increased with the addition of seawater, and was maintained between 18 and 28‰ for the duration of the study. Exponential growth occurred after 180 days. Methyl halide emissions normalized to leaf area were measured throughout the study and varied dramatically. Emission rates normalized to land area (mg m-2 y-1), assuming a LAI = 5, yielded 82 and 29 for CH3Cl, 10 and 1.6 for CH3Br, and 26 and 11 for CH3I, for A. germinans and R. mangle, respectively. From these preliminary determinations, only CH3I emissions emerge as being of possible global atmospheric significance. This study emphasizes the need for field studies of methyl halide emissions from mangrove forests.

Manley, Steven L.; Wang, Nun-Yii; Walser, Maggie L.; Cicerone, Ralph J.

2007-01-01

404

Chemistry of gaseous lower-valent actinide halides  

International Nuclear Information System (INIS)

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

405

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

International Nuclear Information System (INIS)

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

406

Lattice strain across Na-K interdiffusion fronts in alkali feldspar: an electron back-scatter diffraction study  

Science.gov (United States)

Cation exchange experiments between gem quality sanidine and KCl melt produced chemical alteration of alkali feldspar starting at the grain surface and propagating inwards by highly anisotropic Na-K interdiffusion on the alkali sublattice. Diffusion fronts developing in b-direction are very sharp, while diffusion fronts within the a- c-plane are comparatively broad. Due to the composition dependence of the lattice parameters of alkali feldspar, the diffusion induced compositional heterogeneity induces coherency stress and elastic strain. Electron back-scatter diffraction combined with the cross-correlation technique was employed to determine the lattice strain distribution across the Na-K interdiffusion fronts in partially exchanged single crystals of alkali feldspar. The strain changes gradually across the broad fronts within the a- c-plane, with a successive extension primarily in a-direction conferring to the composition strain in unstressed alkali feldspar. In contrast, lattice strain characterised by pronounced extension in b-direction is localised at the sharp diffusion fronts parallel to b, followed by a slight expansion in a-direction in the orthoclase-rich rim. This strain pattern does not confer with the composition induced lattice strain in a stress-free alkali feldspar. It may rather be explained by the mechanical coupling of the exchanged surface layer and the mechanically strong substratum. The lattice distortion localised at the sharp diffusion front may have an influence on the diffusion process and appears to produce a self-sharpening feedback, leading to a local reduction of component mobilities.

Schäffer, Anne-Kathrin; Jäpel, Tom; Zaefferer, Stefan; Abart, Rainer; Rhede, Dieter

2014-11-01

407

Thallous and cesium halide materials for use in cryogenic applications  

International Nuclear Information System (INIS)

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

408

Silica enigma and ignorance in alkali  

International Nuclear Information System (INIS)

Si migration and K, Na alterations are two key problems for understanding the whole process of hydrothermal metallogenesis, but they have not attracted sufficient attention of geologists for a long time. It is impossible for us to know hydrothermal metallogenetic regularity actually without studying dequartzfication and alkali-introduction. Being distinct from common habitual thinking, it is considered that ore-forming elements are micro-amount, passive subordinate components in the flow of hydrothermal matter movement, and there is no metallogenesis for a certain element in nature. Except that the ore source is controlled by the uneven distribution ore-forming elements in the mantle and crust the same metallogenesis may almost lead to the formation of deposits of all elements. Principal active components in the hydrothermal matter system include alkali, silica and acid volatiles. The ternary system has determined the fate of release, activation, migration, precipitaion and concentration of ore-forming elements. Each member of the ternary system plays a different role in metallogenesis, having marvellous functional division of work. of these three members main control factor is alkali metal, whereas silica and acid are constrained by alkali. Acidic matter (including silica) and ore-forming elements are derivatives from activities of alkali metals

409

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

410

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)

411

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

412

EPR Study of Hole-Trapping at Cation Vacancies in Silver-Halides  

Science.gov (United States)

The hole-trapping at cation vacancies in silver halides is studied by means of electron paramagnetic resonance (EPR). The studied silver halide crystals were doped with trivalent Fe, and also with one of the divalent ions Ca, Cd, or Zn. The former dopant is to serve as a hole source upon sub-band-gap irradiation, while the latter increases the concentration of silver vacancies in the crystal. In AgCl, the photo-hole is observed to become self-trapped at a silver ion at a regular lattice site near a cation vacancy. The thermal stability of the resulting vacancy-perturbed self-trapped hole (STH) is found to be substantially enhanced by the presence of the nearby vacancy. Due to the close similarity of the EPR spectrum of the new centers to that of the normal STH, the existence of the vacancy-perturbed STH centers is further confirmed by isochronal annealing experiments. By comparing the intensities of the 20K STH spectra after annealing at successively higher temperatures, it is demonstrated that, in fact, there exist two types of vacancy-perturbed STH centers, one of which decays at 70K and the other survives up to a higher temperature (110K). In addition, by computer simulation, the position of the perturbing vacancy is determined to be located at the next-nearest-neighbor position for the less stable perturbed STH. On the other hand, in AgBr, no corresponding effects have been seen here. This result is in contrast to what is expected from Kanzaki's optical absorption experiments, in which an absorption line was assigned to a hole trapped near a cation vacancy in AgBr. The metastable nature of the self-trapped hole state in AgBr might probably provide explanation for the absence of such a resonance, even with the stabilizing effect of a nearby silver vacancy.

Kao, Chien-Teh

413