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Conductivity relaxations in single crystals of sodium chloride containing suzuki phase precipitates
iv 12.
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS OPTO-ELECTRONIC PROPERTIES OF GALLIUM CHALCOGENIDES V.P. Gupta and V.K. Srivastava, Department of Physics, University of Roorkee, Roorkee-1 247672, India.
A study of opto-electronic properties of gallium chalcogenides (GAS, GaSe and GaTe) is presented here. An investigation in to the various effective charge parameters (Zeee, e*, e~ and e~) and their correlation with ionicity have been done. The energy dependence of optical effective charge parameter (neff) have been discussed with respect to the band structure of respective chalcogenides. The low frequency optical dielectric constants (e,) have been derived using reflectivity data and the obtained values of e~ have been found in agreement with the values obtained using Moss relation as also with the reported experimental data. The difference in the arrangement of fundamental structures of GaS and GaSe on one hand and GaTe on the other hand does not seem to effectively change the opto-electronic properties and the fundamental structure (which is common in all the three chalcogenides) is mainly responsible for determining these properties. The effect of surface conditions on the values of ne~~ and e~ have been evaluated for GaTe. Using derived values of neff and e~ the value of Penn gap have been determined. The Penn gap thus obtained is shown to be in agreement with the reflectivity data. In passing we also show that essentially the Varshni formula explain fairly well the temperature dependence of the energy gap for gallium chalcogenides and the constants involved are evaluated.
Received 11 July 1980 Revised 24 April 1981 13.
MECHANISMS OF SPIN-LATTICE RELAXATION OF VK AND RELATED CENTERS G. Corradi, Research Laboratory for Crystal Physics of the Hungarian Academy of Sciences, Budapest, H-1502 Budapest, P.O.B. 132, Hungary; and V.S. Vikhnin, Yu.S. Gromovoi and I.M. Zaritskii, Institute of Semiconductors of the Ukrainian Academy of Sciences, Kiev, USSR
An experimental and theoretical investigation of the spin-lattice relaxation (SLR) mechanisms of V~-centers in alkali and alkaline earth halides has been carried out. It has been shown that at low temperatures the main role in SLR is played by rapidly relaxing centers (RRC). In some cases, however, an intrinsic one-phonon SLR process due to modulation of both the isotropic and anisotropic hyperfme (HF) interaction seems to be
Vol. 40, No. 9
important. At higher temperatures SLR can be explained by an anharmonic Raman process with the participation of the resonant molecular vibrational (RMV) mode of the VK-center. In this SLR process, similarly to the lowtemperature intrinsic process, the spin-phonon coupling is due to the modulation of the HF interaction. Deviations from the Debye phonon spectrum and the local anharmonicity of VK-centers turn out to be important. The SLR of several other hole and interstitial type centers in alkali halides has also been investigated and their SLR mechanisms are discussed.
Received 15 May 1980 Revised 24 April 1981 14.
MAGNETIC STRUCTURE OF VsSs Satoru Funahashi, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, 319-11, Japan; and Hiroshi Nozaki and Isao Kawada, National Institute for Researches in Inorganic Materials, 1-1, Namiki, Sakura-mura, Ibaraki-ken, 305, Japan.
The magnetic structure of VsSs has been investigated by neutron diffraction at low-temperature. Two single crystals (sample 1 and sample 2) grown by the same procedure gave considerably different results. Sample 1 was found to have an incommensurate structure, while sample 2 was found to have simple colfinear antiferromagnetic structure consistent with magnetic measurements. Although the positions of the magnetic diffraction peaks of sample 1 were close to those of sample 2, the neutron intensity behavior was quite different and the detailed structure could not be determined in the case of sample 1. In both samples, the magnitude of the moments was evaluated to be much larger than the value estimated from NMR.
Received 19 February 1981 15.
CONDUCTIVITY RELAXATIONS IN SINGLE CRYSTALS OF SODIUM CHLORIDE CONTAINING SUZUKI PHASE PRECIPITATES N. Bonanos and E. Lilley, Materials Science Division, School of Engineering and Applied Sciences, University of Sussex, Falmer, Sussex, England.
Single crystals of NaCI containing volume fractions of up to 28% of the Suzuki phase Cd [] Na6Cls have been subjected to a.c. electrical measurements over a range of frequencies (I 0-107 Hz). Complex modulus plots and modulus spectra reveal two distinct electrical relaxations arising in the matrix, and the precipitates. The Maxwell layer model and the Maxwell-Wagner
Vol. 40, No. 9
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS
model for dispersions of two phases are used to separate the two ionic conductivities. The activation energy for ionic conduction in the Suzuki phase is found to be 0.93 + 0.05 eV, which is in agreement with a previously reported value obtained on polycrystalline Cd [] Na6C1a. Received 21 November 1980
16.
THE ABSORPTION, MAGNETIC CIRCULAR DICHROISM AND EMISSION OF EU 2÷ IN CUBIC ELPASOLITES Asok K. Banerjee and Robert W. Schwartz, Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, U.S.A.
The absorption, magnetic circular dichroism (MCD) and emission/excitation spectra of some 4/"7 --> 4 f 6 5 d transitions in Eu 2÷ in several hexachloro and hexabromoelpasolites have been measured. Data were collected between 5 and 300 K and up to energies of 42 000 cm -~. The absorption and MCD were satisfactorily interpreted using a coupling scheme that treats the d-electron crystal field as being much greater than the f-electron spin-orbit coupling and essentially ignores other interactions. Received 20 March 1981
17.
PROPRIETES ELECTRONIQUES ET ELECTROGALVANIQUES DU SELENIURE D'ARGENT/3: DOMAINE D'EXISTENCE Gaston Bonnecaze and Albert Lichanot, Laboratoire de Chimie Organique Physique, Facult6 des Sciences Exactes et Naturelles, Avenue Philippon, 64000 Pau, France; and Simon Gromb, Laboratoire de Chimie Physique, Universit6 des Sciences et Techniques du Languedoc, Place Eugene Bataillon, 34060 Montpellier, France.
A study of the electronic and electrogalvanic properties ofl3 silver setenide has been performed on polycrystalline samples whose non-stoichiometry is controlled by coulometric titration with the cell Ag/RbAg4Is/Ag2+~Se/Pt. The adoption of an electronic model according to which the Frenkel defects of the silver sublattice are completely ionised allows us to compute independently the non-stoichiometry with the two formulae/5 = [Ag°] -- [Vj, g] and 6 = n - - p . The homogeneity range has been drawn at positive temperatures and the formation enthalpy of the Frenkel defects is H~ = 0.40 eV. Received 14 November 19 81
18.
SHUBNIKOV-DE HAAS EFFECT IN n-CdSnAs2 J.J. Neve, C.F.J. de Meijer and F.A. Blom, Department of Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs2 have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5 T. The electron concentration of the samples ranged from 2 x 1017 to 2 x 101acm -3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E~ = 0.30 eV, a spin-orbit splitting A = 0.50 eV, a crystal field splitting parameter 5 = -- 0.09 eV, and an interband matrix element P = 8.5 x 10 -8 eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration. Received 30 March 1981
19.
ETUDE PAR RMN DE LA STRUCTURE DYNAMIQUE DE L'ALANATE NaaAIH6 Jean Senagas et Anne Marie Villepastour, Laboratoire de Chimie du Solide du CNRS, Universit6 de Bordeaux I, 351, cours de la Lib6ration, 33405 Talence Cedex, France; et Bernard Bonnetot, Laboratoire de Physico-Chimie Min6rale associ6 au CNRS No. 116, INSA, 20, Avenue Albert Einstein, 69621 Villeurbanne Cedex, France.
A low-temperature wide-line NMR study has allowed a determination of the AI-H bond lengths in cryolitetype Na3A1H6. It was found from the thermal behavior of the proton lines that the IA1H6[ 3- octahedra reorient around a C4 axis. Starting below 170 K, this rotation can be hindered by lattice defects. Above room temperature it becomes isotropic and a quick protonic exchange appears. The thermal narrowing of the linewidth and the T~ and T~p relaxation times lead to activation energies of about 0.38 eV for axial rotation and 0.51 eV for protonic exchange. The minimum in 7"1 is in good agreement with the exchange model. Absorption phenomena, as well as partial decomposition of Na3A1H6 during the heat treatments, explain the presence of small amounts of mobile hydrogen. Received 5 February 19 81
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS OPTO-ELECTRONIC PROPERTIES OF GALLIUM CHALCOGENIDES V.P. Gupta and V.K. Srivastava, Department of Physics, University of Roorkee, Roorkee-1 247672, India.
A study of opto-electronic properties of gallium chalcogenides (GAS, GaSe and GaTe) is presented here. An investigation in to the various effective charge parameters (Zeee, e*, e~ and e~) and their correlation with ionicity have been done. The energy dependence of optical effective charge parameter (neff) have been discussed with respect to the band structure of respective chalcogenides. The low frequency optical dielectric constants (e,) have been derived using reflectivity data and the obtained values of e~ have been found in agreement with the values obtained using Moss relation as also with the reported experimental data. The difference in the arrangement of fundamental structures of GaS and GaSe on one hand and GaTe on the other hand does not seem to effectively change the opto-electronic properties and the fundamental structure (which is common in all the three chalcogenides) is mainly responsible for determining these properties. The effect of surface conditions on the values of ne~~ and e~ have been evaluated for GaTe. Using derived values of neff and e~ the value of Penn gap have been determined. The Penn gap thus obtained is shown to be in agreement with the reflectivity data. In passing we also show that essentially the Varshni formula explain fairly well the temperature dependence of the energy gap for gallium chalcogenides and the constants involved are evaluated.
Received 11 July 1980 Revised 24 April 1981 13.
MECHANISMS OF SPIN-LATTICE RELAXATION OF VK AND RELATED CENTERS G. Corradi, Research Laboratory for Crystal Physics of the Hungarian Academy of Sciences, Budapest, H-1502 Budapest, P.O.B. 132, Hungary; and V.S. Vikhnin, Yu.S. Gromovoi and I.M. Zaritskii, Institute of Semiconductors of the Ukrainian Academy of Sciences, Kiev, USSR
An experimental and theoretical investigation of the spin-lattice relaxation (SLR) mechanisms of V~-centers in alkali and alkaline earth halides has been carried out. It has been shown that at low temperatures the main role in SLR is played by rapidly relaxing centers (RRC). In some cases, however, an intrinsic one-phonon SLR process due to modulation of both the isotropic and anisotropic hyperfme (HF) interaction seems to be
Vol. 40, No. 9
important. At higher temperatures SLR can be explained by an anharmonic Raman process with the participation of the resonant molecular vibrational (RMV) mode of the VK-center. In this SLR process, similarly to the lowtemperature intrinsic process, the spin-phonon coupling is due to the modulation of the HF interaction. Deviations from the Debye phonon spectrum and the local anharmonicity of VK-centers turn out to be important. The SLR of several other hole and interstitial type centers in alkali halides has also been investigated and their SLR mechanisms are discussed.
Received 15 May 1980 Revised 24 April 1981 14.
MAGNETIC STRUCTURE OF VsSs Satoru Funahashi, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, 319-11, Japan; and Hiroshi Nozaki and Isao Kawada, National Institute for Researches in Inorganic Materials, 1-1, Namiki, Sakura-mura, Ibaraki-ken, 305, Japan.
The magnetic structure of VsSs has been investigated by neutron diffraction at low-temperature. Two single crystals (sample 1 and sample 2) grown by the same procedure gave considerably different results. Sample 1 was found to have an incommensurate structure, while sample 2 was found to have simple colfinear antiferromagnetic structure consistent with magnetic measurements. Although the positions of the magnetic diffraction peaks of sample 1 were close to those of sample 2, the neutron intensity behavior was quite different and the detailed structure could not be determined in the case of sample 1. In both samples, the magnitude of the moments was evaluated to be much larger than the value estimated from NMR.
Received 19 February 1981 15.
CONDUCTIVITY RELAXATIONS IN SINGLE CRYSTALS OF SODIUM CHLORIDE CONTAINING SUZUKI PHASE PRECIPITATES N. Bonanos and E. Lilley, Materials Science Division, School of Engineering and Applied Sciences, University of Sussex, Falmer, Sussex, England.
Single crystals of NaCI containing volume fractions of up to 28% of the Suzuki phase Cd [] Na6Cls have been subjected to a.c. electrical measurements over a range of frequencies (I 0-107 Hz). Complex modulus plots and modulus spectra reveal two distinct electrical relaxations arising in the matrix, and the precipitates. The Maxwell layer model and the Maxwell-Wagner
Vol. 40, No. 9
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN J. PHYS. CHEM. SOLIDS
model for dispersions of two phases are used to separate the two ionic conductivities. The activation energy for ionic conduction in the Suzuki phase is found to be 0.93 + 0.05 eV, which is in agreement with a previously reported value obtained on polycrystalline Cd [] Na6C1a. Received 21 November 1980
16.
THE ABSORPTION, MAGNETIC CIRCULAR DICHROISM AND EMISSION OF EU 2÷ IN CUBIC ELPASOLITES Asok K. Banerjee and Robert W. Schwartz, Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, U.S.A.
The absorption, magnetic circular dichroism (MCD) and emission/excitation spectra of some 4/"7 --> 4 f 6 5 d transitions in Eu 2÷ in several hexachloro and hexabromoelpasolites have been measured. Data were collected between 5 and 300 K and up to energies of 42 000 cm -~. The absorption and MCD were satisfactorily interpreted using a coupling scheme that treats the d-electron crystal field as being much greater than the f-electron spin-orbit coupling and essentially ignores other interactions. Received 20 March 1981
17.
PROPRIETES ELECTRONIQUES ET ELECTROGALVANIQUES DU SELENIURE D'ARGENT/3: DOMAINE D'EXISTENCE Gaston Bonnecaze and Albert Lichanot, Laboratoire de Chimie Organique Physique, Facult6 des Sciences Exactes et Naturelles, Avenue Philippon, 64000 Pau, France; and Simon Gromb, Laboratoire de Chimie Physique, Universit6 des Sciences et Techniques du Languedoc, Place Eugene Bataillon, 34060 Montpellier, France.
A study of the electronic and electrogalvanic properties ofl3 silver setenide has been performed on polycrystalline samples whose non-stoichiometry is controlled by coulometric titration with the cell Ag/RbAg4Is/Ag2+~Se/Pt. The adoption of an electronic model according to which the Frenkel defects of the silver sublattice are completely ionised allows us to compute independently the non-stoichiometry with the two formulae/5 = [Ag°] -- [Vj, g] and 6 = n - - p . The homogeneity range has been drawn at positive temperatures and the formation enthalpy of the Frenkel defects is H~ = 0.40 eV. Received 14 November 19 81
18.
SHUBNIKOV-DE HAAS EFFECT IN n-CdSnAs2 J.J. Neve, C.F.J. de Meijer and F.A. Blom, Department of Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs2 have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5 T. The electron concentration of the samples ranged from 2 x 1017 to 2 x 101acm -3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E~ = 0.30 eV, a spin-orbit splitting A = 0.50 eV, a crystal field splitting parameter 5 = -- 0.09 eV, and an interband matrix element P = 8.5 x 10 -8 eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration. Received 30 March 1981
19.
ETUDE PAR RMN DE LA STRUCTURE DYNAMIQUE DE L'ALANATE NaaAIH6 Jean Senagas et Anne Marie Villepastour, Laboratoire de Chimie du Solide du CNRS, Universit6 de Bordeaux I, 351, cours de la Lib6ration, 33405 Talence Cedex, France; et Bernard Bonnetot, Laboratoire de Physico-Chimie Min6rale associ6 au CNRS No. 116, INSA, 20, Avenue Albert Einstein, 69621 Villeurbanne Cedex, France.
A low-temperature wide-line NMR study has allowed a determination of the AI-H bond lengths in cryolitetype Na3A1H6. It was found from the thermal behavior of the proton lines that the IA1H6[ 3- octahedra reorient around a C4 axis. Starting below 170 K, this rotation can be hindered by lattice defects. Above room temperature it becomes isotropic and a quick protonic exchange appears. The thermal narrowing of the linewidth and the T~ and T~p relaxation times lead to activation energies of about 0.38 eV for axial rotation and 0.51 eV for protonic exchange. The minimum in 7"1 is in good agreement with the exchange model. Absorption phenomena, as well as partial decomposition of Na3A1H6 during the heat treatments, explain the presence of small amounts of mobile hydrogen. Received 5 February 19 81