Ionic conductivity, activation volumes, and frequency-dependent conductivity in crystals with the fluorite structure

Activation volumes were extracted from the effect of pressure on the ionic conductivities of CaF2, SrF2, BaF2, and CdF2. The activation volumes for motion of vacancies were measured in oxygen-contaminated samples and used to calculate defect-formation volumes from the activation volumes at high temperatures. The formation volumes are uniformly small and consistent with the dominance of Frenkel defects for temperatures up to 1400 K in the alkaline-earth fluorides. The CdF2 was found to contaminate badly at temperatures around 600 K, and become an electronic conductor. All of the crystals were found to exhibit frequency-dependent conductivities at high temperatures, attributable to electrode effects or bulk dielectric response of the material, or both. © 1980 The American Physical Society.