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 attri- buted 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

14. QUADRUPOLE SPLITTING 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.93 S. A tentative model is presented that is consistent with these results and with magnetic anisotropy data.

13. INVESTIGATION OF 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 elec- trons 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 agree- ment with the results of conductivity measurements.

Received lOJuly 1978 Revised 4 May 1979

Received 30 August 1978

15. ANALYSIS OF 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 chlor- ide structure above their Noel temperatures in para- magnetic 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