Creep and diffusion in high Tc superconductors

Data from steady-state creep and tracer diffusion tests are presented for the high- $T_{\rm c}$, superconductors YBa 2Cu 3O x, and Bi 2Sri 1.7CaCu 2O y Both compounds exhibit oxygen nonstoichiometry and possess orthorhombic, layered perovskite crystal structures in which Cu occupies the B sites and the other cations occupy the A sites. For each, the A-site cations diffuse most slowly. For every species that has been measured, diffusion is much faster in the ab-plane than in the c-direction. At low stresses, both superconductors deform by diffusional creep with the ratecontrolling species being a A-site cation in YBa 2Cu 3O x