CRYSTAL-GROWTH MECHANISM OF YBA2CU3OY SUPERCONDUCTORS WITH PERITECTIC REACTION

Directional steady-state solidification, the zone melting method from a prtial molten state, in which Y2BaCuO5 (211) and liquid coexist in equilibrium, were performed under several different experimental conditions. The effect of process parameters and Pt-doping on the solidified structure of the YBa2Cu3Oy (123) phases was also investigated. Results indicated that higher G/R(G: temperature gradient; R: growth rate) values were preferable for continuous growth. The sample grown at 1 mm/h possessed a large faceted solid/liquid interface and the volume fraction of the 211 phase particles decreased drastically from the liquid to the 123 phase solids at the interface. The results lead us to the conclusion that the necessary solute for the peritectic reaction is provided from 211 particles to a 123 interface through a liquid. Based on this idea, we developed a simple solidification model which agrees with the experimental results. From our investigation of Pt-doping, we tentatively concluded that Pt-doping causes the product of DGAMMA (D: diffusivity; GAMMA: Gibbs-Thomson coefficient) to reduce and result in a decrease of the 123 cell spacing.