MOLECULAR-DYNAMICS STUDY OF THE EFFECT OF DOPING AND DISORDER ON DIFFUSION IN GADOLINIUM ZIRCONATE

We present the results of molecular dynamics (MD) simulations of gadol inium zirconate (Gd2Zr2O7), an oxide fast ion conductor with the pyroc hlore structure. Calculations of mean temperature dependent diffusion coefficients are used to obtain activation energies for diffusion whic h are compared with values obtained from static lattice calculations a nd from conductivity measurements. Simulations of yttrium and gadolini um doped zirconia were performed as a test of the potential parameters and the results compare well with experiment. The gadolinium zirconat e simulations show no diffusion for the ordered material which is cons istent with static lattice calculations. But appreciable diffusion is predicted for the simulations which incorporate cation disorder or dop ing with calcium where the present results agree well with those from static lattice simulations and from experimental observations. We fmd that diffusion occurs only by the 48f sites, in line with previous com putational and experimental studies. An increase in the activation ene rgy for diffusion with doping level suggests that dopant/vacancy and d efect-defect interactions become significant at the higher level of do ping. (C) 1998 Elsevier Science B.V. All rights reserved.