Ion mobility in α-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 crystal lattice which promote a significant degree of ionic motion, as witnessed by nuclear magnetic resonance and conductivity measurements. The simulations, using polarizable ionic potentials that have already been shown to reproduce the properties of the superionic conducting beta -phase of PbF2, give results which are consistent with these experimental data. A detailed site-hopping analysis is used to clarify the mechanism of the vacancy-promoted ionic motion, which differs markedly from the mechanism responsible for the facile ion diffusion in the beta -phase.