DIFFUSION-CONTROLLED PLASTIC-DEFORMATION OF YBA2CU3OX

Steady-state creep experiments have been performed on polycrystalline YBa2Cu3Ox in the temperature range of 850-970 degrees C, as a function of oxygen partial pressure (P-O2). The results, when combined with a reanalysis of previous deformation studies, indicate that contrary to the previous conclusion that the activation energy was a function of P -O2, there are two different temperature regimes characterized by P-O2 -independent activation energies of 675 and 1100 kJ/mol for low and hi gh temperatures, respectively. This is interpreted in terms of two ind ependently operating rate-controlling mechanisms: grain-boundary diffu sion and lattice diffusion. Diffusion coefficients have been derived b y comparing experimental data and theoretical models.