Kinetics of YBa₂Cu₃O_xFormation and Crystal Defects in PMP-Processed Superconductor

Kinetic characters of the 123 phase formation and changes in microstructure at the peritectic reaction front during preparing PMP YBCO superconductors have been investigated. It has been found that the formation of 123 phase undergoes four different stages, i.e. the incubation period, nucleation, a fast and slow growing of 123 phase. In reaction process, 211 phase is first dissolved into the liquid phase consisting of CuO-rich 011 phase to form the supersaturate liquid with excess yttrium, 123 phase nucleate at the place where the cation ratio is near 123 phase from not only inhomogeneously, but also homogeneously, then fast grows. When yttrium in the liquid phase is consumed, the slow rate growing will appear due to the long diffusion of yttrium required in later 123 phase growing . The maximum allowable growth rate of 123 phase does not follow Cima's expression deduced from the Y-diffusion-controlled mechanism. The high dense planer defects are formed from the local excess atoms inserting into 123 phase crystal lattice.