Creep and diffusion in high $\mathit{T}_\mathrm{c}$ superconductors

Data from steady-state creep and tracer diffusion tests are presented for the high-$T_{\rm c}$, superconductors YBa$_2$Cu$_3$O$_x$, and Bi$_2$Sri$_{1.7}$CaCu$_2$O$_y$ 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$_2$Cu$_3$O$_x$