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The low temperature electrical properties of some anisotropic crystals
Vol. 31, No. 12 ABSTRACTS OF ARTICLES TO BE PUBLISHED IN THE J. PHYS. CHEM. SOLIDS C.G.F. Stenger and A.J. Burggraaf, Twente University of Technology, Department of Chemical Engineering, Laboratory of Inorganic Chemistry and Materials Science, P.O. Box 217, 7500 AE Enschede, The Netherlands. The phase diagram of electrically poled, tetragonal PLZT materials has been investigated. In the higher La concentration range, a tetragonal, so-called/3-phase occurs, which has no clear FE properties. The transition to the FE t phase has first order character and takes place only after a strong electric field has been applied to the material. The energetics of the/3t -~ FEt transition were investigated in several ways. The heat-effects associated with this transition have a small value of 6 - 2 0 cal moF ~ , dependent on composition. The transition/It ~ FEt is accompanied by a relatively large activation energy AG2. The AG2 (T) curve shows a minimum for materials, which do not show a spontaneous transition to the FE t phase. This minimum value of AG 2. (1--2.5 cal mo1-1 ) is large in comparison to the average thermal energy k T and prevents the spontaneous transition from the/3 t phase to the FEt phase. Received 30 October 1978 Revised 4 May 1979
9.
COMPARATIVE STUDY OF THE STRUCTURES OF USUAL NON STOICHIOMETRIC, AND STOICHIOMETRIC/3 ALUMINA SINGLE CRYSTALS
G. Collin, J.P. Boilot, Ph. Colomban, R. Com6s, Chimie Appliqu6e de l'Etat Solide ENSCP 11, rue P. et M. Curie 75005 Paris, France; and Physique des Solides, Universit6 Paris-Sud, 91405 Orsay, France. The average structures of non-stoichiometric/3Ag N S 11 A12Oa -- 1.25 (Ag20) and stoichiometric/3Ag S 11 Al2Oa -- 0.95 Ag20/3 alumina are determined by X-ray diffraction technics (R factors 4 and 5% respectively). In both compounds Ag* ions are localized on two offcenters Beevers-Ross positions (BRD) very close to one another and with almost equal occupation factors. The evolution from BAgN S to/3Ag S occurs through the decrease of the occupation factor of the anti-BeeversRoss site and the disappearance of the Frenkel defect. A long range ordered superstructure in/3Ag S with the lattice constants ax/3 -- ax/3 -- c (P6a/m is observed at room temperature and found to arise from the in layer Ag and O ions). The BRD and oxygen ions are ordered on off-centered positions around an empty aBR site. The complementary structure reflections are interpreted in a twinned model with two types of domains, for the in layer ions. Received 11 January 1979
10.
iii
MAGNETISM AND HYPERFINE INTERACTIONS OF S~Fe, lSlEu, lSSGd, S61Dy, l~Er AND l~eYb IN RM4A] 8 COMPOUNDS (R = Rare Earth or Y , M = Cr, Mn, Fe, Cu) I. Feiner and I. Nowik, Racah Institute of Physics, The Hebrew University, Jerusalem, Israel.
M6ssbauer and magnetic susceptibility studies of sixty tetragonal RM4A1a compounds (R = 4f, M = 3d element), show a wide variety of magnetic phenomena in the behaviour of 3d transition elements. The rare earths order antiferromagnetically at temperatures below 10 to 30 K in all compounds. The 3d elements, however, all behave differently. Fe in RFe4AI s has a localized moment (effective moment of 4.4/~a) and orders independently of the rare earth sublattice. Mn in RMn4A! s has also a localized moment ('-, 1 # a ) but orders only when the rare earths order. Cr in RCr4AIa has no moment of its own, but it has an induced moment (0.1 ~B) by its magnetic rare earth neighhours. Cu in RCu4AI8 is nonmagnetic. The M6ssbauer studies of lSIEu, lSSGd, l~tDy, 166Er, 17°Yb and a STFe probe yield all hyperfme interaction parameters including the orientation of the hypert'me field relative to the crystallographic c-axis. In addition, the studies yield the Ce, Eu and Yb valencies in the various compounds. Eu in EuFe4Al s and in EuMn4A1s and Yb in YbCr4A1 s are in a mixed valent state. Received 26 January 1979
11.
DISLOCATION-PHONON INTERACTION S. Crowley, N. Flytzanis and V. Celli, Department of Physics, University of Virginia, Charlottesville, VA 22901, U.S.A.
The recent result that uniform screw dislocation motion can be sustained by an applied stress s ( 10-s initiates a study of the influence of intrinsic, low energy atomic vibrations on the dislocation. This dislocationphonon interaction is examined for two types of interatomic potentials in a crystal with an anisotropic slip system. For realistic interatomic potentials, we find that, in the presence of an appropriate phonon, uniform motion can occur at velocities v ~ 0.50 (in units of the speed of sound) with zero externally applied stress, or even against the direction of motion favored by such a stress. Received 11 October 1978
12.
THE LOW TEMPERATURE ELECTRICAL PROPERTIES OF SOME ANISOTROPIC CRYSTALS
iv
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN THE J. PHYS. CHEM. SOLIDS Vol. 31, No. 12 Robert Shelby and John Fontaneila, Physics Department, U.S. Naval Academy, Annapolis, MD 21402, U.S.A.; and Carl Andeen, Physics Department, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
The principal complex dielectric constants have been studied at audio frequencies over the temperature range 5.5-380 K for wquartz, sapphire, magnesium fluoride, and calcite. For some samples, the imaginary part of the dielectric constant revealed the presence of dipolar or thermally activated loss mechanisms which are attributed to trace impurities. The effects of these impurities are considered in arriving at values of the real part of the dielectric constants for each of the materials.
Received 5 March t979 13.
INVESTIGATIONOF THE ELECTRONIC STRUCTURE OF Lat_x(M2+)xCrOa, Cr2Oa AND La20 a BY X-RAY PHOTOELECTRON SPECTROSCOPY W.-Y. Howng and R.J. Thorn, Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.
The electronic structures of lanthanum chromites, pure and doped with magnesium and strontium, have been studied in comparison with Cr2Os and La203 through the use of X-ray photoelectron spectroscopy. The main peaks and satellites of inner and outer electrons are properly assigned. The band structure of LaCrOs is determined by using the XPS data and a calculation based on point charge model. The partially filled Cr(3d) band is localized. The conduction is mainly extrinsic. The measured Fermi-level is close to the valence band indicating a low activation energy in agreement with the results of conductivity measurements.
Received lOJuly 1978 Revised 4 May 1979
14.
QUADRUPOLESPLITTING AND GROUND STATE IN FeS AND NiS (Fe s~) A. Leclerc and M.G. Townsend, Department of Energy, Mines and Resources, Ottawa, Canada.
From a M6ssbauer study of an oriented single crystal of Nio.9~ S (2% Fe sT) at 298 K (above the metal-insulator transition at "~ 230 K) the sign of the quadrupole splitting in Fe s~ is determined to be positive; this contrasts with a negative sign found for FeS and Feo.93S. A tentative model is presented that is consistent with these results and with magnetic anisotropy data.
Received 30 August 1978 15.
ANALYSISOF THE DIELECTRIC BEHAVIOUR OF TRANSITION METAL OXIDES Jal Shanker and V.P. Gupta, Department of Physics, Agra College, Agra 282002, India.
The transition metal oxides (TMO) viz. MnO, CoO and NiO crystallize in cubic face centred sodium chloride structure above their Noel temperatures in paramagnetic phase. These crystals possess two atoms per primitive unit cell, the bonding between them being largely ionic. The elastic behaviour of these crystals is very interesting as they show large Cauchy deviation Cn-C44 with empirical relation Cn ~ 2C44 for MnO and CoO and C44 -~ 2C12 for NiO. The high frequency (e.,) and low frequency (eo) dielectric constants, and the difference between the two are very large for the TMO. Thus the TMO show interesting deviations from the typical ionic crystals viz. alkali halides.
Received 11 October 1978
9.
COMPARATIVE STUDY OF THE STRUCTURES OF USUAL NON STOICHIOMETRIC, AND STOICHIOMETRIC/3 ALUMINA SINGLE CRYSTALS
G. Collin, J.P. Boilot, Ph. Colomban, R. Com6s, Chimie Appliqu6e de l'Etat Solide ENSCP 11, rue P. et M. Curie 75005 Paris, France; and Physique des Solides, Universit6 Paris-Sud, 91405 Orsay, France. The average structures of non-stoichiometric/3Ag N S 11 A12Oa -- 1.25 (Ag20) and stoichiometric/3Ag S 11 Al2Oa -- 0.95 Ag20/3 alumina are determined by X-ray diffraction technics (R factors 4 and 5% respectively). In both compounds Ag* ions are localized on two offcenters Beevers-Ross positions (BRD) very close to one another and with almost equal occupation factors. The evolution from BAgN S to/3Ag S occurs through the decrease of the occupation factor of the anti-BeeversRoss site and the disappearance of the Frenkel defect. A long range ordered superstructure in/3Ag S with the lattice constants ax/3 -- ax/3 -- c (P6a/m is observed at room temperature and found to arise from the in layer Ag and O ions). The BRD and oxygen ions are ordered on off-centered positions around an empty aBR site. The complementary structure reflections are interpreted in a twinned model with two types of domains, for the in layer ions. Received 11 January 1979
10.
iii
MAGNETISM AND HYPERFINE INTERACTIONS OF S~Fe, lSlEu, lSSGd, S61Dy, l~Er AND l~eYb IN RM4A] 8 COMPOUNDS (R = Rare Earth or Y , M = Cr, Mn, Fe, Cu) I. Feiner and I. Nowik, Racah Institute of Physics, The Hebrew University, Jerusalem, Israel.
M6ssbauer and magnetic susceptibility studies of sixty tetragonal RM4A1a compounds (R = 4f, M = 3d element), show a wide variety of magnetic phenomena in the behaviour of 3d transition elements. The rare earths order antiferromagnetically at temperatures below 10 to 30 K in all compounds. The 3d elements, however, all behave differently. Fe in RFe4AI s has a localized moment (effective moment of 4.4/~a) and orders independently of the rare earth sublattice. Mn in RMn4A! s has also a localized moment ('-, 1 # a ) but orders only when the rare earths order. Cr in RCr4AIa has no moment of its own, but it has an induced moment (0.1 ~B) by its magnetic rare earth neighhours. Cu in RCu4AI8 is nonmagnetic. The M6ssbauer studies of lSIEu, lSSGd, l~tDy, 166Er, 17°Yb and a STFe probe yield all hyperfme interaction parameters including the orientation of the hypert'me field relative to the crystallographic c-axis. In addition, the studies yield the Ce, Eu and Yb valencies in the various compounds. Eu in EuFe4Al s and in EuMn4A1s and Yb in YbCr4A1 s are in a mixed valent state. Received 26 January 1979
11.
DISLOCATION-PHONON INTERACTION S. Crowley, N. Flytzanis and V. Celli, Department of Physics, University of Virginia, Charlottesville, VA 22901, U.S.A.
The recent result that uniform screw dislocation motion can be sustained by an applied stress s ( 10-s initiates a study of the influence of intrinsic, low energy atomic vibrations on the dislocation. This dislocationphonon interaction is examined for two types of interatomic potentials in a crystal with an anisotropic slip system. For realistic interatomic potentials, we find that, in the presence of an appropriate phonon, uniform motion can occur at velocities v ~ 0.50 (in units of the speed of sound) with zero externally applied stress, or even against the direction of motion favored by such a stress. Received 11 October 1978
12.
THE LOW TEMPERATURE ELECTRICAL PROPERTIES OF SOME ANISOTROPIC CRYSTALS
iv
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN THE J. PHYS. CHEM. SOLIDS Vol. 31, No. 12 Robert Shelby and John Fontaneila, Physics Department, U.S. Naval Academy, Annapolis, MD 21402, U.S.A.; and Carl Andeen, Physics Department, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
The principal complex dielectric constants have been studied at audio frequencies over the temperature range 5.5-380 K for wquartz, sapphire, magnesium fluoride, and calcite. For some samples, the imaginary part of the dielectric constant revealed the presence of dipolar or thermally activated loss mechanisms which are attributed to trace impurities. The effects of these impurities are considered in arriving at values of the real part of the dielectric constants for each of the materials.
Received 5 March t979 13.
INVESTIGATIONOF THE ELECTRONIC STRUCTURE OF Lat_x(M2+)xCrOa, Cr2Oa AND La20 a BY X-RAY PHOTOELECTRON SPECTROSCOPY W.-Y. Howng and R.J. Thorn, Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.
The electronic structures of lanthanum chromites, pure and doped with magnesium and strontium, have been studied in comparison with Cr2Os and La203 through the use of X-ray photoelectron spectroscopy. The main peaks and satellites of inner and outer electrons are properly assigned. The band structure of LaCrOs is determined by using the XPS data and a calculation based on point charge model. The partially filled Cr(3d) band is localized. The conduction is mainly extrinsic. The measured Fermi-level is close to the valence band indicating a low activation energy in agreement with the results of conductivity measurements.
Received lOJuly 1978 Revised 4 May 1979
14.
QUADRUPOLESPLITTING AND GROUND STATE IN FeS AND NiS (Fe s~) A. Leclerc and M.G. Townsend, Department of Energy, Mines and Resources, Ottawa, Canada.
From a M6ssbauer study of an oriented single crystal of Nio.9~ S (2% Fe sT) at 298 K (above the metal-insulator transition at "~ 230 K) the sign of the quadrupole splitting in Fe s~ is determined to be positive; this contrasts with a negative sign found for FeS and Feo.93S. A tentative model is presented that is consistent with these results and with magnetic anisotropy data.
Received 30 August 1978 15.
ANALYSISOF THE DIELECTRIC BEHAVIOUR OF TRANSITION METAL OXIDES Jal Shanker and V.P. Gupta, Department of Physics, Agra College, Agra 282002, India.
The transition metal oxides (TMO) viz. MnO, CoO and NiO crystallize in cubic face centred sodium chloride structure above their Noel temperatures in paramagnetic phase. These crystals possess two atoms per primitive unit cell, the bonding between them being largely ionic. The elastic behaviour of these crystals is very interesting as they show large Cauchy deviation Cn-C44 with empirical relation Cn ~ 2C44 for MnO and CoO and C44 -~ 2C12 for NiO. The high frequency (e.,) and low frequency (eo) dielectric constants, and the difference between the two are very large for the TMO. Thus the TMO show interesting deviations from the typical ionic crystals viz. alkali halides.
Received 11 October 1978