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 RE₂Ba₁Cu₁O₅ (RE-211) was obtained at the cooling rate of 0.001°C/s. Single phase of RE-123 (Nd, Gd, Dy) was stable at 1050°C, 1000°C, and 950°C during isothermal heat-treatment, respectively. Above these temperatures RE-211 phase existed within the RE-123 grains. The RE-123, RE-211, BaCu₂O₂, and CuO phases coexisted at 50°C below the partial melting temperature for each respective RE-123. The variations in the phase transformation and microstructure change on rare-earth elements were explained by the different ionic radii of the elements. The superconducting properties of each specimen heat-treated under the optimum conditions were compared with the magnetic characteristics.