Abstract
The crystal structure of a Ba-Y-Cu-O superconductor was refined by the Rietveld analysis of X-ray powder diffraction data. This material is orthorhombic with lattice parameters a = 3.8845 Å, b = 3.8293 Å, and c = 11.6926 Å. Possible space groups are P222, Pmm2, and Pmmm. Metal atoms have essentially the same configuration as that in the perovskite-type structure. A structural model is proposed in which an oxygen atom at (0, 0, 1/2) is deficient.