Abstract
A series of single phase materials with tetragonal triple-perovskite structure and nominal compositions of La 4- x Ca x Ba 3Cu 7O y (0.50⩽ x⩽1.375) was prepared by the solid state reaction method. Due to the differences in the size and valence between tha Ca ions and La ions, increasing the Ca substitution for La resulted in a decrease in unit cell axes, volume and the oxygen stoichiometry. A rapid decrease in the T c was observed when the a-axis was larger than 0.38 nm indicating the importance of the r Cu-O distance in the copper-oxygen planes for the superconductivity. Evidence of hole doping was observed by Ca substitution till x=1.00 which had the highest T c and a maximum hole concentration in the La 4- x Ca x Ba 3Cu 7O y superconductors.
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