Superconductivity and Crystal Structure of LaBa2Cu3-xOy Compounds

The crystal structure of a sample which shows a superconducting transition onset temperature of 89 K and a transition width of 9 K is determined to be orthorhombic with oxygen-deficient triperovskite structure from Rietveld refinement of X-ray powder diffraction patterns. The crystal data are as follows: LaBa2Cu2.94O7, orthorhombic, space group Pmmm, a = 3.8829(1), b = 3.9342(4), and c = 11.810(1) Å. It is proposed that an orthorhombic structure is essential to the 90 K superconductivity of oxygen-deficient triperovskites and the T c of their tetragonal forms is around 60 K.