MODEL FOR THE OXYGENATION OF THE YBA2CU3O7-X 90K SUPERCONDUCTOR

A model incorporating the thermodynamic equilibrium oxygen content, ox ygen in-diffusion, and oxide phases for the oxygenation of the YBaCu3O 7-x is described. For sintered polycrystals, grain growth and the resu lting grain size distribution are included. The model is used to calcu late the volume percent of each oxide phase for several processing con ditions of sintered specimens and is compared with available results o n the quantification of phases present. Such a comparison indicates th at as the concentration of impurity phases increases so does the conce ntration of the less oxygenated 123 phases, suggesting that impurities coating 123 grains act as oxygen indiffusion barriers. The model is a lso used to investigate the uniformity of the oxygen content in large twinned and detwinned single crystals such as have been used for measu ring superconductivity parameters.