The self-diffusion and isotope diffusion coefficients of O in YBa2Cu3O6+x were calculated at 600 to 1200K for x = 0 to 1. Monte Carlo simulations were performed while taking account of the interaction of O ions at lattice sites in the basal planes, and the interaction between a jumping ion at a saddle point and the environment. Equilibrium thermodynamic characteristics (including the phase diagram and the heat capacity) were calculated in terms of the Hamiltonian for interaction between O ions at the lattice sites. It was found that an increase in the O content led to a decrease in both diffusion coefficients, to an increase in the effective activation energies for diffusion by 0.3 to 0.5eV and to a decrease in the Haven ratio from 1 to ~0.5.

Mobility and Diffusion of Oxygen Isotopes in YBa2Cu3O6+x - Monte Carlo Simulation. M.Z.Uritsky, V.I.Tsidilkovski: Physics of the Solid State, 2003, 45[6], 1005-11