Transport Properties of LaF3

Abstract

We report measurements of the lattice and bulk thermal expansion, fluorine nuclear magnetic resonance, and electrical conductivity of single-crystal La${\mathrm{F}}_{3}$ in the temperature range 300-1000\ifmmode^\circ\else\textdegree\fi{}K. In the lower portion of this temperature range, the measurements yield activation energies for the formation of Schottky defects of \ensuremath{\sim}0.07 eV and for fluorine ion diffusion of \ensuremath{\sim}0.45 eV. The activation energy for diffusion appears to decrease at higher temperatures. We propose a model for the crystal with low activation energy for the formation of neutral defects, and a higher energy for defect dissociation and diffusion. The apparent changes of activation energy are ascribed to the excitation of lattice vibrations near the Debye temperature.