The activation volume for type-I dipoles in lanthanum-doped strontium fluoride

Abstract
The audio-frequency complex dielectric constant has been measured for lanthanum-doped strontium fluoride at pressures up to 0.4 GPa over the temperature range 240-260K. Consequently the reorientation of a Type-I dipole (substitutional rare-earth and nearest-neighbour interstitial fluorine charge compensator) has been studied. The activation volume for the motion is found to be 3.26 cm3 mol-1. For comparison, a theoretical value of 3.29 cm3 mol-1 is calculated using Flynn's dynamical diffusion model (1972). In addition, the thermal expansion coefficient of the activation volume is found to be negative and the compressibility is about an order of magnitude larger than that of the bulk material.