Differences in the thermal stability of REBa₂Cu₃O_{7 −<i>x</i>}(RE = Y, Nd) thin films investigated by high temperature<i>in situ</i>observation and melt-texture growth

Abstract

Following the increasing interest in the high thermal stability of REBa2Cu3O7 − x (RE-123, RE = rare earth) thin films as seed materials, thermal stabilities of Y-123 and Nd-123 thin films were investigated by two methods: high temperature in situ microscopy and the melt growth process. A monotonic dependence of thermal stability on RE solubility in the Ba–Cu–O liquid was observed. The thermal stability of RE-123 films was found to strongly depend on the melting growth process, which is predominated by the melting rate of the RE-123 phase. Under the assumption of quasi-equilibrium, a simplified model of solute transport was suggested. The correlation between the solute inflow and outflow indicates that the melting rate of RE-123 is proportional to the growth rate of the RE2BaCuO5 (RE-211) phase and the ratio of the concentration difference between the RE-211 growth front and the RE-123 melting border. We conclude that an Nd-123 thin film is more unstable than a Y-123 thin film because of the higher melting rate, resulting from a higher growth rate of the RE-211 phase and a higher concentration difference ratio.