Superconductivity Transition in High-Tc Y-Ba-Cu-O Mixed-Phase System

Abstract
We report the results of temperature dependence of the resistivity in Y-Ba-Cu-O mixed-phase system for several samples with different composition and sintered at different temperatures. Two types of compounds were investigated, which have the nominal composition (Y1-x Ba x )2CuO4-δ(Type I) or Y1-y Ba y CuO3-δ(Type II) with x=0.45 or 0.40, y=0.6 and δ undetermined. Superconductivity transition was observed in all the samples around 90 K, although it was incomplete at 78 K in some Type I-samples. In a Type II-sample with nominal composition Y0.4Ba0.6CuO3-δ, in addition to this transition which is completed at 87 K, sharp reduction of resistivity was observed around 150 K, suggesting a possible existence of a new phase with higher T c in this system.

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