A series of samples with nominal composition of La3CaχBa4−χCu7Oy (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≤Tconset≤86 K. A Tc 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 rCu-O distance of ca. 1.94 Å in the Cu-O planes was the most appropriate value for superconductivity in the La3CaχBa4−χCu7Oy system.
