Ion mobility in alpha-PbF2: a computer simulation study

Computer simulation studies of the F--ion motion in pure and KF-doped alpha -PbF2 an described. The aliovalent doping introduces vacancies into the cr ystal lattice which promote a significant degree of ionic motion, as witnes sed by nuclear magnetic resonance and conductivity measurements. The simula tions, using polarizable ionic potentials that have already been shown to r eproduce the properties of the superionic conducting beta -phase of PbF2, g ive results which are consistent with these experimental data. A detailed s ite-hopping analysis is used to clarify the mechanism of the vacancy-promot ed ionic motion, which differs markedly from the mechanism responsible for the facile ion diffusion in the beta -phase.