The self-diffusion (D0) and isotope diffusion (D*) coefficients of oxygen in YBa2Cu3O6+x were calculated at 600 to 1200K, for 0 < x < 1. The Monte Carlo simulation was performed with due regard for both the interaction of oxygen ions at lattice sites in the basal planes of YBa2Cu3O6+x 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 of interaction between oxygen ions at the lattice sites. It was found that an increase in the oxygen content led to a decrease in the diffusion coefficients D0 and D*, an increase in the effective activation energies for diffusion by 0.3 to 0.5eV, and 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