Superconducting Properties and Phase Stability of REBa₂Cu₃O_7-x (RE=Nd, Gd, Dy) Superconductors during Continuous Cooling and Isothermal Heat Treatment

Abstract

The phase transformation of REBa₂Cu₃O_7-x (RE=Nd, Gd, Dy) was investigated using isothermal heat-treatment and continuous cooling in air. During continuous cooling, the REBa₂Cu₃O_7-x (RE=123) superconducting phase with well-distributed REBa₂Cu₃O_7-x (RE=211) was obtained at a cooling rate of 0.001&degC /s. Single phase RE-123 (Nd, Gd, Dy) was stable at 1050&degC, 1000&degC, and 950&degC during isothermal heat-treatment, respectively. Above these temperatures the RE-211 phase existed within the RE-123 grains. The RE-123, RE-211, BaCu₂O₂, and CuO phases coexisted at 50&degC below the partial melting temperature for each respective rare-earth RE-123. The variations in the phase transformation and lattice parameters on the rare-earth elements were explained by the different ionic radiis of the elements. The superconducting properties of each specimen heat-treated at the optimum condition were compared with the magnetic characteristics.