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The electronic strain polarizability constants of the alkali halides
iv
ABSTRACTS OF ARTICLES TO BE PUBUSHED IN THE J. PHYS. CHEM. SOUDS
14.
FARADAY ROTATION IN THE PRESENCE OF DEEP REPULSIVE TRAPS D.P. Bhattacharya, Department of Physics, B.K.C. College, Calcutta 700-035, India; and Z.S. Kachlishvill, Department of Solid State Physics, Thilisi State University, Thilisi, USSR.
16.
THERMAL PROPERTIES OF SMOKY QUARTZ AT VERY LOW TEMPERATURES J. Chaussy, J. Le G. Gilchrist, J.C. Lasjuanias and M. Saint-Paul, Centre de Recherches sur les Trés Basses Temperatures, CNRS, BY. 166 X, 38042 Grenoble CCdex, France; and R. Nava, Instituto Venezolano de Investigaciones Cientificas, Centro de Fisica, Apartado 1827, Caracas Venezuela.
The Faraday rotation is investigated in the general
.
case for any mechanism of the energy and momentum scattering of hot electrons in the strong and weak magnetic field limits and under the condition when the free carriers are captured by deep repulsive traps. For some definite scatteringmechanisms the investigations are carried out in the presence of any finite value of the magnetic field. The possibility of using the results for the estimation of some of the semiconductor parameters and for the determination of the dominant scattering mechanism is discussed. The calculations are carried out assuming a parabolic law of dispersion and a scalar effective mass. Received 5 July 1978 Revised 1 March 1979 15.
TEMPERATURE DEPENDENCE OF THE ELASTIC CONSTANTS OF ALUMINUM J.L. Talon, Department of Structural Properties of Materials, The Technical University of Denmark, Building 307, DK-2800 Lyngby, Denmark; and A. Wolfenden, Physics and Engineering Laboratory, Department of Scientific and Industrial Research, Lower Hutt, New Zealand.
The single crystal elastic constants of aluminum have been measured using a piezoelectric composite oscillator from room temperature to just 20K below the melting point. The elastic moduli differ remarkedly from previous high temperature results. but match in well with previous cryogenic results. Over the temperature range investigated the isothermal bulk modulus and the two there moduli have a simple exponential dependence on isobaric volume, and the cryogenic data indicate this dependence may be preserved down to absolute zero. As has been found previously for a wide range of materials, the isothermal bulk modulus and the shear modulus (c11 c12)/2 appear to be continuous functions of vol—
ume through the melting expansion, and melting seems to find its origin in the mechanical instability associated with this shear modulus vanishing at the volume of the melt at the freezing point. GrUneisen’s parameter divided by the molar volume is very nearly independent of isobaric volume. Recieved 26 January 1979
Vol. 31, No.4
The existence of a distribution of low-lying energy levels associated with holes trapped at substitutional aluminium impurities is confirmed by measurements of low temperature specific heat and dielectric loss. A large linearly temperature-dependent contribution to the specific heat is observed at temperatures below 1 K, down to 30 mK. A localization temperature describing the width of the distribution of the energy levels is estimated to vary between 3 and 6K. We determined the thermal conductivity down to 30 inK and attribute the decrease below the boundary.
.
scatteringvalue to irradiation damage generally, arguing that it is not attributable to resonant scattering.
Received 21 December 1978 Revised 15 February 1979 17.
THE ELECTRONIC STRAIN POLARIZ ABILITY CONSTANTS OF THE ALKALI HAUDES Howard Coker, Department of Chemistry, University of South Dakota, Vermilion, SD 57069, U.S.A.
The electronic strain polarizabiity constants of the alkali halides have been calculated. The cation contributions are negligibly small. Several empirical forms were used for the description of the variation of the halide ion polarizabiity with density. A model due to Wilson and Curtis was found to give results higher than the experimental strain polarizability constants by a nearly constant factor of 1.8 ±0.1, a fact permitting prediction of the strain polarizabiity constants and P(afl/aP)T for the alkali halides for which experimental values are not available. A modification of the Wilson— Curtis model was found to give much better agreement, and the agreement improved monotonely with decreasing internal forces. The dispersions of the strain polarizability constants at 5893 A from the static values range from 2% for the fluorides to 7% for the iodidies. Values of (alnvo/alnp)T, upon which these dispersions depend, have been obtained for all twenty alkali halides. Refinement of the modified Wilson—Curtis model must await improved van der Waals’ constants. Recently proposed sets of van der Waals’ constants may be rejected in favor
Vol.31, No.4 ABSTRACTS OF ARTICLES TO BE PUBUSHED IN THE J. PHYS. CHEM. SOLIDS of the classic values of Mayer. Vacuum ultraviolet spectral evidence is used to discount the contention that the cation polarizabilities in the alkali halides are greatly reduced from their free-ion values, Received 2 June 1978 Received 9 March 1979 18.
COMPARAISON DE LA METHODE CNDO ET DE MODELES ANALYTIQUES POUR LA DETERMINATION DE LA POLARIZABILITE DE PETITS AMAS UNEAIRES Pierre Joyes, Laboratoire de Physique des Solides, Assoc~au CNRS, Bâtiment 510, Université Paris-Sud, 91405 Orsay, France.
Nous étudions dans quelle mesure une technique analytique donne une precision comparable aux calculs seif-consistents de Chimie Quantique (CNDO) lorsque l’on se propose de determiner la polarisabiité F(k) de petits amas d’environ cent atomes. Las systèmes o~i nous effectuons ce type de contrôle sont les molecules h~othétiques H76 et H~oü les atomes sont equidistants et disposes scion une chalne fermée. Notre conclusion est qu’il existe un bon accord (a la fois pour la valeur absolue et pour l’allure de la courbe) entre les valeurs CNDO et celles de la méthode analytique RPA.L’écart qui subsiste entre les deux courbes est di essentiellement au fait que dans la méthode RPA on néglige les interactions d’échange. On montre aussi que la courbe CNDO presente des particularites dues a la degénérescence dans le spectre de niveaux d’energie’ Ces effets n’altèrent pas l’accord mentionné plus haut car us sont limités a quelques valeurs de k (~k~ 5) et localisés autour de
V
k = 38 pour H~et de k = 0 pour H%. Ils sont dus dam le premier cas a la formation spontanCe d’une onde de charge de vecteur d’onde k = 38 et dans le deuxième cas a un terme de depolarisation qui n’apparaitrait pas Si, par exemple, les transitions k = 1 et k = 1 n’Ctaient pas exactement dCgCnérées. Nous Ctendons de plus notre trailtement analytique au cas N = 1014 et montrons de queUe façon évoluent les valeurs de FRpA(k) lorsque N-~00• —
Received 18 December 1978 Revised 1 March 1979 19.
TEMPERATURE DEPENDENCE OF FLUORESCENCE DECAY RATES OF MONOVALENT-CATION URANYL NITRATES A.F. Leung and K.K. Tsang, Department of Physics, The Chinese University of Hong Kong, Hong Kong. Fluorescence decay rates, fluorescence and absorp-
tion spectra of seven mono-valent-cation uranyl nitrates, XUO2(N03)3 where I = Ag, NH.1, K, Rb and Cs and Y2 UO2(N03)4 where Y = K and (CH3)4N, have been measured. The temperature dependence of fluorescence decay rates can be explained by assuming that the fluorescent level is always in thermal equilibrium with another level at higher energy. The decay rates are correlated and the ionic radii of the mono-valent-cations and the differences in normal coordinates of the ground and excited states. Received 15 May 1978 Revised 2 March 1979
ABSTRACTS OF ARTICLES TO BE PUBUSHED IN THE J. PHYS. CHEM. SOUDS
14.
FARADAY ROTATION IN THE PRESENCE OF DEEP REPULSIVE TRAPS D.P. Bhattacharya, Department of Physics, B.K.C. College, Calcutta 700-035, India; and Z.S. Kachlishvill, Department of Solid State Physics, Thilisi State University, Thilisi, USSR.
16.
THERMAL PROPERTIES OF SMOKY QUARTZ AT VERY LOW TEMPERATURES J. Chaussy, J. Le G. Gilchrist, J.C. Lasjuanias and M. Saint-Paul, Centre de Recherches sur les Trés Basses Temperatures, CNRS, BY. 166 X, 38042 Grenoble CCdex, France; and R. Nava, Instituto Venezolano de Investigaciones Cientificas, Centro de Fisica, Apartado 1827, Caracas Venezuela.
The Faraday rotation is investigated in the general
.
case for any mechanism of the energy and momentum scattering of hot electrons in the strong and weak magnetic field limits and under the condition when the free carriers are captured by deep repulsive traps. For some definite scatteringmechanisms the investigations are carried out in the presence of any finite value of the magnetic field. The possibility of using the results for the estimation of some of the semiconductor parameters and for the determination of the dominant scattering mechanism is discussed. The calculations are carried out assuming a parabolic law of dispersion and a scalar effective mass. Received 5 July 1978 Revised 1 March 1979 15.
TEMPERATURE DEPENDENCE OF THE ELASTIC CONSTANTS OF ALUMINUM J.L. Talon, Department of Structural Properties of Materials, The Technical University of Denmark, Building 307, DK-2800 Lyngby, Denmark; and A. Wolfenden, Physics and Engineering Laboratory, Department of Scientific and Industrial Research, Lower Hutt, New Zealand.
The single crystal elastic constants of aluminum have been measured using a piezoelectric composite oscillator from room temperature to just 20K below the melting point. The elastic moduli differ remarkedly from previous high temperature results. but match in well with previous cryogenic results. Over the temperature range investigated the isothermal bulk modulus and the two there moduli have a simple exponential dependence on isobaric volume, and the cryogenic data indicate this dependence may be preserved down to absolute zero. As has been found previously for a wide range of materials, the isothermal bulk modulus and the shear modulus (c11 c12)/2 appear to be continuous functions of vol—
ume through the melting expansion, and melting seems to find its origin in the mechanical instability associated with this shear modulus vanishing at the volume of the melt at the freezing point. GrUneisen’s parameter divided by the molar volume is very nearly independent of isobaric volume. Recieved 26 January 1979
Vol. 31, No.4
The existence of a distribution of low-lying energy levels associated with holes trapped at substitutional aluminium impurities is confirmed by measurements of low temperature specific heat and dielectric loss. A large linearly temperature-dependent contribution to the specific heat is observed at temperatures below 1 K, down to 30 mK. A localization temperature describing the width of the distribution of the energy levels is estimated to vary between 3 and 6K. We determined the thermal conductivity down to 30 inK and attribute the decrease below the boundary.
.
scatteringvalue to irradiation damage generally, arguing that it is not attributable to resonant scattering.
Received 21 December 1978 Revised 15 February 1979 17.
THE ELECTRONIC STRAIN POLARIZ ABILITY CONSTANTS OF THE ALKALI HAUDES Howard Coker, Department of Chemistry, University of South Dakota, Vermilion, SD 57069, U.S.A.
The electronic strain polarizabiity constants of the alkali halides have been calculated. The cation contributions are negligibly small. Several empirical forms were used for the description of the variation of the halide ion polarizabiity with density. A model due to Wilson and Curtis was found to give results higher than the experimental strain polarizability constants by a nearly constant factor of 1.8 ±0.1, a fact permitting prediction of the strain polarizabiity constants and P(afl/aP)T for the alkali halides for which experimental values are not available. A modification of the Wilson— Curtis model was found to give much better agreement, and the agreement improved monotonely with decreasing internal forces. The dispersions of the strain polarizability constants at 5893 A from the static values range from 2% for the fluorides to 7% for the iodidies. Values of (alnvo/alnp)T, upon which these dispersions depend, have been obtained for all twenty alkali halides. Refinement of the modified Wilson—Curtis model must await improved van der Waals’ constants. Recently proposed sets of van der Waals’ constants may be rejected in favor
Vol.31, No.4 ABSTRACTS OF ARTICLES TO BE PUBUSHED IN THE J. PHYS. CHEM. SOLIDS of the classic values of Mayer. Vacuum ultraviolet spectral evidence is used to discount the contention that the cation polarizabilities in the alkali halides are greatly reduced from their free-ion values, Received 2 June 1978 Received 9 March 1979 18.
COMPARAISON DE LA METHODE CNDO ET DE MODELES ANALYTIQUES POUR LA DETERMINATION DE LA POLARIZABILITE DE PETITS AMAS UNEAIRES Pierre Joyes, Laboratoire de Physique des Solides, Assoc~au CNRS, Bâtiment 510, Université Paris-Sud, 91405 Orsay, France.
Nous étudions dans quelle mesure une technique analytique donne une precision comparable aux calculs seif-consistents de Chimie Quantique (CNDO) lorsque l’on se propose de determiner la polarisabiité F(k) de petits amas d’environ cent atomes. Las systèmes o~i nous effectuons ce type de contrôle sont les molecules h~othétiques H76 et H~oü les atomes sont equidistants et disposes scion une chalne fermée. Notre conclusion est qu’il existe un bon accord (a la fois pour la valeur absolue et pour l’allure de la courbe) entre les valeurs CNDO et celles de la méthode analytique RPA.L’écart qui subsiste entre les deux courbes est di essentiellement au fait que dans la méthode RPA on néglige les interactions d’échange. On montre aussi que la courbe CNDO presente des particularites dues a la degénérescence dans le spectre de niveaux d’energie’ Ces effets n’altèrent pas l’accord mentionné plus haut car us sont limités a quelques valeurs de k (~k~ 5) et localisés autour de
V
k = 38 pour H~et de k = 0 pour H%. Ils sont dus dam le premier cas a la formation spontanCe d’une onde de charge de vecteur d’onde k = 38 et dans le deuxième cas a un terme de depolarisation qui n’apparaitrait pas Si, par exemple, les transitions k = 1 et k = 1 n’Ctaient pas exactement dCgCnérées. Nous Ctendons de plus notre trailtement analytique au cas N = 1014 et montrons de queUe façon évoluent les valeurs de FRpA(k) lorsque N-~00• —
Received 18 December 1978 Revised 1 March 1979 19.
TEMPERATURE DEPENDENCE OF FLUORESCENCE DECAY RATES OF MONOVALENT-CATION URANYL NITRATES A.F. Leung and K.K. Tsang, Department of Physics, The Chinese University of Hong Kong, Hong Kong. Fluorescence decay rates, fluorescence and absorp-
tion spectra of seven mono-valent-cation uranyl nitrates, XUO2(N03)3 where I = Ag, NH.1, K, Rb and Cs and Y2 UO2(N03)4 where Y = K and (CH3)4N, have been measured. The temperature dependence of fluorescence decay rates can be explained by assuming that the fluorescent level is always in thermal equilibrium with another level at higher energy. The decay rates are correlated and the ionic radii of the mono-valent-cations and the differences in normal coordinates of the ground and excited states. Received 15 May 1978 Revised 2 March 1979