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

Reports measurements of the electrical conductivity and 19 F nuclear magnetic resonance (NMR) relaxation times T 1 , T 2 , T 1 rho and T 1D in BaF 2 single crystals over a temperature range 300K-1200K. The dominant process responsible for the 19 F 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.