The effect of the Ca/Ba ratio on the superconductivity of the La 3Ca χBa 4−χCu 7O y system

Abstract

A series of samples with nominal composition of La 3Ca χBa 4−χCu 7O y (0≤χ≤4.00) was prepared by the conventional powder reaction method. Single-phase materials with triple-perovskite structure were obtained for χ≤1.25 samples of which the lattice parameters monotonically decreased with the increase of Ca substitution. Superconductivity was observed for χ≤3.50 samples with 37 K≤ T conset≤86 K. A T c plateau above 80 K was found in the 1.00≤χ≤1.25 samples with a-axis length of 3.879≥ a≥3.872 Å. In other words, an optimal r Cu-O distance of ca. 1.94 Å in the Cu-O planes was the most appropriate value for superconductivity in the La 3Ca χBa 4−χCu 7O y system.