Pretreatments and Sintering Behavior of Oxide Superconductors Y-Ba-Cu-O

Abstract

Sintering behavior of the high T_c oxide superconducting material, YBa₂Cu₃O_y, and its superconducting properties such as T_c and J_c have been studied. Particular attention has been paid to the mixing procedures of starting powders, the particle size of calcined powders, and the low temperature oxygen annealing.
In the calcined powder sintered for 3.1×10⁵ s at 1203 K, most voids are annihilated, the grains are coarsened up to about 100 μm in the long direction, and the density exceeds 90% of the ideal density. Full mixing of the starting powders considerably improves the density of sintered YBa₂Cu₃O_y, whereas ball milling of YBa₂Cu₃O_y powder degradates the improvement.
Resistivity of the sample in the normal conducting state increases with increasing sintering time, i.e. with increasing density; this behavior is attributed to difficulty in diffusing oxygen atoms into a high density YBa₂Cu₃O_y sample. Transmission electron microscope studies have often revealed the second phase along the grain boundary which is believed to reduce the critical current of polycrystalline bulk material YBa₂Cu₃O_y.