The effect of hydrostatic pressure on the ionic conductivity of some crystals with the flourite structure
Oberschmidt, James Michael
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https://hdl.handle.net/2142/25535
Description
Title
The effect of hydrostatic pressure on the ionic conductivity of some crystals with the flourite structure
Author(s)
Oberschmidt, James Michael
Issue Date
1980
Doctoral Committee Chair(s)
Lazarus, David
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
hydrostatic pressure
ionic conductivity
crystals
fluoride structure
activation volumes
extrinsic vacancy motion
Language
en
Abstract
The effect of hydrostatic pressure on the ionic conductivity of
CaF2 SrF2 BaF2 CdF2 SrCl2 PbF2 PbCl2 PbBr2 and PbI2 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 consis-
tent with the dominance of Frenkel defects in all cases except PbCl2 and PbBr2. where large formation volumes were observed. indicating Schottky defects.
High pressure phase transitions in PbF2 SrCl2 and PbI2 were observed by the change in sample resistance across the transition. Transition temperature and pressure data are presented for pressures to 0.55 CPa and temperatures to near the melting point in PbIz to 850 K for PbF2 and to 1050K for SrCl2. The transition temperature is observed to increase linearly with increasing pressure at high temperatures for both PbF2 and SrCt2 but considerable hysteresis is observed in the transition at low temperatures. The transition in PbI2 occurs at approximately 0.39 GPa and
is observed to be essentially temperature independent.
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 PbCl2 and PbBr2. 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 (0 ~ lO-3 ohm-1cm-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.
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