ABSTRACTS OF ARTICLES TO APPEAR IN J. PHYS. CHEM. SOLIDS SILVER ATOM CENTER IN a-QUARTZ P.H. Davis and i.A. Well, Department of Chemistry and Chemical Engineering, University of Saskatchewan, Saskatoon, Sask. S7N OWO, Canada.
A new paramagnetic center,A Ag—Si’ in silverdiffused a-quartz is described and its spin-Hamiltonian parameters are presented. The center is formulated as a silver atom (S = 1/2) situated in a c-axis channel, bonded weakly to a normal silicon cation, with four oxygen anions as neighbors. A is created by X-irradiation, and is unstable at room temperature.
Vol. 25, No. 12
respect to one particular lattice parameter, leaving invariant all internal distances in the polyatomic ions. Received 11 July 1977 Revised 4 January 1978
MODEL OF INSTABILITIES IN PdHX AND PdDX K.L. Ngai and T.L. Reinecke, Naval Research Laboratory, Washington, D.C. 20375, U.S.A.
Received 27 September 1977
ELASTIC PROPERTIES OF DILUTE PALLADIUM—HYDROGEN SOLID SOLUTIONS R.J. Farraro and Rex B. McLellan, Department of Materials Science, William Marsh Rice University, Houston, TX 77001, U.S.A.
A thin-line pulse-echo technique has been used to measure the variation of the Young’s modulus of superpure palladium as a function of temperature and hydrogen concentration. The resulting measurements have been analyzed so as to yield approximate information relating to the change to be expected in the partial thermodynamic functions of the system due to the lattice relaxation at constant pressure. Received 21 November 1977 Revised 4 January 1978
EXPANSION OF THE MADELUNG PARAMETER IN TERMS OF MULTIPOLE MOMENTS AND AS A FUNCTION OF THE RATIO OF TWO LATTICE PARAMETERS P. Herzig and A. Neckel, Institut für Technische Elektrochemie der Technischen, Universität Wien, Getreidemarkt 9, A-1060 Vienna, Austria.
A method is derived to expand the Madelung parameters non-cubic crystals as in a function the ratio of twoof lattice parameters and terms ofof multipole moments. Only one expansion of this kind is necessary to evaluate the Madelung constants for a series of compounds of one type of structure either containing polyatomic ions or spherical ions at positions slightly varying from one compound to the other. This method also allows the minimisation of the lattice energy with
The instability and inhomogeneity of the PdHX and PdDX systems is discussed. A simple model based on the existence of more than one local electronic and ionic configuration is proposed, and the results of this model are shown to be consistent with several important lattice properties ofand these systems a difference between the Pd—H Pd—D forceincluding constants. Received 18 July 1977
SIMULTANEOUS DIFFUSION OF CALCIUM AND STRONTIUM IN KC1 SINGLE CRYSTALS H. Machida and W.i. Fredericks, Department of Chemistry, Origon State University, Corvallis, OR 97331, U.S.A.
Concentration dependent diffusion coefficients for 45Sr21’ in purified KCI were measured using a sectioning method. KC1 was purified by an ion exchange—C1 2—HC1 process and the crystals grown under 1/6 atmosphere of HC1. The tracers were purified on small disposable ion exchange columns to remove precessor and daughter impurities prior to use in a diffusion anneal. Isothermal diffusion anneals were made in the temperature range from 451 to 669°C.At temperatures above 580°C(the lowest melting eutectic in this system) diffusion was from a vapor source; below 580°Csurface deposited sources were used. The saturation diffusion coefficients, enthalpies and entropies of impurity—vacancy associations were calculated using the common ion model for simultaneous ofdiffusion divalent ions in alkali halides. In KC1 thediffusion saturation coefficients D8(Ca) and D8(Sr) are given by 2/sec (1) Ds(Ca) = 9.93 x l0~exp(— 0.592 eV/kT)cm and D~(Sr) = 1.20 x l0~exp(— 0.871 eV/kT)cm2/sec (2) for calcium and strontium, respectively. The Gibbs free energy of association of the impurity vacancy complex in KU for calcium can be represented by
Vol. 25, No. 12 ~g(Ca)
ABSTRACTS OF ARTICLES TO APPEAR IN J. PHYS. CHEM. SOLIDS
0.507 eV + (2.25 x i0’-~eV/K)T
wave and the change in its velocity due to an external temperature gradient in piezoelectric semiconductors. The numberical results have been presented for a typical
case of indium antimonide. The present analysis is valid in the low frequency region only (i.e., ql 1).
and that for strontium by ~g(Sr)
0.575 eV + (2.90 x l0-’~eV/K)T.
Received 14 November 1977 8.
THE LATTICE ENERGY OF MAGNESIUM HYDRIDE C.M. Stander and R.A. Pacey, Council for Scientific and Industrial Research, National
Received 29 August 1977 11.
The lattice energy of MgH2 has been calculated using the Born—Mayer model. The result is U0 = 2906.5 ki mol’ which may be compared with the 1. This Born—Haber cycle value of 2721.3 kJ mol difference indicates that there is an appreciable covalent contribution to the bonding. The importance of the zeropoint energy contribution to the lattice energy in the case of the light metal hydrides is discussed. Received 7 November 1977 ELECTRICAL PROPERTIES OF a-MnS H.H. Heikens, C.F. van Bruggen and C. Haas, Laboratory of Inorganic Chemistry, Materials Science Center of the University, Nijenborgh 16, 9747 AG Groningen, The Netherlands.
Electrical data including thermoelectric power, Hall effect and resistivity on iodine-grown crystals of p-type a-MnS are reported. A study of the temperature dependences reveals that occursofbythe 3’Dthe andconductivity that the mobility in not a 3d-band (Mnactivated. Photoelectron spectra holes is thermally confirm the 3d character of the top of the valence band. Accurate analysis of the electrical.data gives a satisfactory explanation of the extrinsic and intrinsic behaviour; the simultaneous presence of donors (substitutional iodine) and acceptors (manganese vacancies) is responsible for the observed phenomena. Received 10 November 1977 10.
AMPLIFICATION AND CHANGE IN VELOCITY OF ACOUSTIC WAVES DUE TO EXTERNAL TEMPERATURE GRADIENT IN PIEZOELECTRIC SEMICONDUCTORS S.S. Sharma, Department of Physics, Indian Institute of Technology, New Delhi 110029, India; and S.P. Singh, Ludwig Boltzmann Institut für Festkorperphysik, Kopernikusgasse 15, 1060 Wien, Austria.
Using hydrodynamic equations we calculate the attenuation/amplification coefficient of an acoustic
RAMAN SCATTERING STUDY OF THE LOW TEMPERATUREPHASE OF AMMONIUM NITRATE H.C. Tang and B.H. Torrie, Department of Physics, University of Waterloo, Waterloo, Ontario, Canada.
Physical Research Laboratory, Pretoria, Republic of South Africa.
Raman spectra NH4NO3 and ND4NO3 recorded from roomoftemperature down to 11have K. Abeen sluggish transition from phase IV to phase V was clearly observed but no evidence was found for another low temperature phase. Large splitting of the v 3 mode indicates that the interionic interaction between NHZ and NO~is rather strong in both phases. A possible mechanism for the transition involving coupled modes is discussed. Received 7 September 1977 Revised 30 December 1977 12.
MAGNETIC PROPERTIES OF V5S8 SINGLE CRYSTALS H. Nozaki, M. Umehara, Y. Ishizawa and M. Saeki, National Institute for Researches in Inorganic Materials, Sakura-mura, Niihari-gun, Ibaraki, Kurakake, 300-31, Japan; T. Mizuguchi, Faculty of Science, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo, 171, Japan; and M. Nakahira, Okayama College of Science. Laboratory for Solid State Chemistry, 1-1, Ridai-cho, Okayama, 700, Japan. The magnetic properties of V
5S8 single crystals have been investigated by susceptibility and torque measurements. The susceptibilities parallel and perpendicular to the magnetic easy axis show a remarkable anisotropy below the Néel temperature of 32 K and are nearly along the c axis of the monoclinic lattice, being inclined at an angle of 9.6 ±1.0°from the c axis toward the a axis. The torque curves, measured up to 24.4 kOe at liquid helium temperature, diviate from the usual form of a sine function with increasing magnetic field. The analysis of theze torque curves suggests that spin flopping may occur at 43 kOe, a comparatively low critical field. Using these experimental results, a localized d-electron model for a particular site of the