SUPERCONDUCTIVITY AND CRYSTAL STRUCTURE OF LaBa2−xCaxCu3O7

Abstract

The samples with nominal composition LaBa2−xCaxCu3O7 (x=0, 0.5, 1.0, 1.5, 2.0) have been prepared by solid state reactions and studied by x-ray diffraction method and transmission electron microscopy. The substitution of Ba by Ca results in the decrease of the cell volume, increase of the structural orthorhombic distortion and appearance of the c/3 translation domain. Of the five samples studied only those with x=0, 1.0, and 1.5 are superconductors. The x=0 sample shows onset temperature 90 K, the zero resistance temperature 45 K and a weak diamagnetic effect. The x=1.5 sample shows zero resistance at 72 K and sustantial diamagnetic effect. The relation between the crystal structure and superconductivity is discussed.