A new oxygen-deficient perovskite, SrCuO2.5, was prepared at 950 degrees C and 100 kbar pressure in a multianvil apparatus. Rietveld profile analysis, using X-ray powder diffraction data, was employed for the structural determination. SrCuO2.5, is orthorhombic, Pbam (No. 55), Z = 4, a = 5.424(2) Angstrom, b = 10.837(4) Angstrom, and c = 3.731(1) Angstrom, which is related to the perovskite subcell by root 2a(p) x 2 root 2a(p) x a(p), where a(p) is the simple cubic perovskite lattice parameter. It consists of corner-shared CuO5 square pyramids with oxygen vacancy ordering in the CuO2 layers. The ordered oxygen vacancies create parallel pseudo-hexagonal tunnels where the Sr atoms reside, forming SrO10 polyhedra. Structural features with respect to oxygen vacancies, superstructures, and distortions are analogous to the type of ordering observed in Sr2CuO3+delta. Superconductivity was not observed in SrCuO2.5 down to 5 K. (C) 1996 Academic Press, Inc.
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