PRESSURE AND TEMPERATURE DEPENDENCE OF THE STATIC DIELECTRIC CONSTANTS AND ELASTIC ANOMALIES OF ZnF2.

The static dielectric constants epsilon //a and epsilon //c of ZnF//2 have been studied in the range 4-296 degree K at zero pressure and in the pressure range 0-5 kbar at 296, 195, and 78 degree K. epsilon //a and epsilon //c exhibit normal temperature behavior. epsilon //c decreases with pressure as is normally the case. epsilon //a, on the other hand, exhibits an anomalous increase with pressure at room temperature. This anomalous increase is reduced with decreasing temperature and by 78 degree K has completely disappeared. The pressure and temperature results are combined with thermal expansion and compressibility data to evaluate the pure volume and the pure temperature dependence of the dielectric constants. The dielectric constants are described by a Clausius-Mossotti relation. The Szigeti effective charge ratios have been determined for the transverse optical (TA) modes along the left bracket 100 right bracket and c axes. These ratios are found to be rather small, being 0. 44 and 0. 54 for the two axes, respectively, suggesting that the bonding is partially covalent.