Synthesis and Structure of A New Perovskite, SrCuO2.5

Abstract A new oxygen-deficient perovskite, SrCuO 2.5 , was prepared at 950°C and 100 kbar pressure in a multianvil apparatus. Rietveld profile analysis, using X-ray powder diffraction data, was employed for the structural determination. SrCuO 2.5 is orthorhombic, Pbam (No. 55), Z = 4, a = 5.424(2) Â, b = 10.837(4) Â, and c = 3.731(1) Â, which is related to the perovskite subcell by $\root{2}$ a p × 2$\root{2}$ a p × a p , where a p is the simple cubic perovskite lattice parameter. It consists of corner-shared CuO 5 square pyramids with oxygen vacancy ordering in the CuO 2 layers. The ordered oxygen vacancies create parallel pseudo-hexagonal tunnels where the Sr atoms reside, forming SrO 10 polyhedra. Structural features with respect to oxygen vacancies, superstructures, and distortions are analogous to the type of ordering observed in Sr 2 CuO 3+δ . Superconductivity was not observed in SrCuO 2.5 down to 5 K.