NMR relaxation, ionic conductivity and the self-diffusion process in barium fluoride

Abstract

Reports measurements of the electrical conductivity and 19F nuclear magnetic resonance (NMR) relaxation times T1, T2, T1 rho and T1D in BaF2 single crystals over a temperature range 300K-1200K. The dominant process responsible for the 19F spin relaxation is self-diffusion. The magnitude and temperature dependence of the relaxation times are satisfactorily interpreted using the Wolf theory. Absolute values of diffusion coefficients calculated from NMR relaxation data assuming a vacancy diffusion process are in excellent agreement (within 15%) with those calculated from ionic conductivity data using the Nernst-Einstein relation. From the temperature dependence studies, the diffusion parameters were determined. The formation enthalpy for a Frenkel pair was found to be 1.91 eV and migration enthalpies for free F- vacancies and F- interstitialcies were found to be 0.57 and 0.76 eV respectively.