Surface diffusion of nickel in metal oxide high-temperature superconductors

Temperature dependence of Ni diffusion coefficient and effect of grain size, composition, intrinsic disordering, variable deformations on diffusion were investigated in YBa2Cu3O7-x and (Bi0.8Pb0.2)2Ca2Sr2Cu3O10 high-temperature superconductors. In both systems diffusion is characterized by rapid and slow components with close values of activation energies Δ in the temperature range 200 to 5000C. However in system 123 transition from two-component diffusion to one-component diffusion with Δ jump at 4000C is observed. The jump temperature and Δ value of high-temperature diffusion depend on grain size and action of super sound deformations. The discovered behaviour of the diffusion coefficients is explained by surface mechanisms of migration of Ni atoms. (author)