| The effect of hydrostatic pressure on the ionic conductivity of CaF(,2), SrF(,2), BaF(,2), CdF(,2, )SrC(, 2), PbF(,2), PbC (,2), PbBr(,2) and PbI(,2) has been studied for pressures up to 0.6 GPa and temperatures up to near the melting point. The activation volumes for extrinsic vacancy motion were obtained from the effect of pressure on the conductivity of doped and oxygen contaminated samples. The formation volumes of intrinsic defects were calculated from measured activation volumes at high temperatures. The defect formation volumes are found to be uniformly small and consistent with the dominance of Frenkel defects in all cases except PbC (,2) and PbBr(,2), where large formation volumes were observed, indicating Schottky defects.(,).;The temperature dependence of the ionic conductivity has also been studied in all of the above materials. Good agreement with published results is obtained except in the cases of PbC (,2) and PbBr(,2). The differences in those two cases are attributed to differences in the fitting procedure used to analyze the data.;A large frequency dependence of the measured conductivity at high temperatures ((sigma) (TURN) 10('-3)ohm('-1)cm('-1)) is found to exist in all crystals with the fluorite structure. The observed frequency dependence is attributed either to polarization at the electrode interface or to an inherent dielectric response of the material resulting from many-body interactions, or a combination of these two effects.;High pressure phase transitions in PbF(,2), SrC (,2) and PbI(,2) were observed by the change in sample resistance across the transition. Transition temperature and pressure data are presented for pressures to 0.55 GPa and temperatures to near the melting point in PbI(,2), to 850 K for PbF(,2) and to 1050 K for SrC (,2). The transition temperature is observed to increase linearly with increasing pressure at high temperatures for both PbF(,2) and SrC (,2), but considerable hysteresis is observed in the transition at low temperatures. The transition in PbI(,2) occurs at approximately 0.39 GPa and is observed to be essentially temperature independent. |
