STRUCTURAL STUDY OF SR2CUO3+DELTA BY NEUTRON POWDER DIFFRACTION

Average crystal structures of superconducting Sr2CuO3+delta synthesized under high pressure and nonsuperconducting Sr2CuO3+delta synthesized at ambient pressure from a hydroxometallate precursor were refined from neutron powder diffraction data. A simplified model was used to fit the modulated superstructures. Both compounds have an oxygen-deficient La2CuO4-type tetragonal T structure with oxygen vacancies located in the Cu02 planes, not in the Sr2O2 layers. This result raises important questions regarding the nature of superconductivity in Sr2CuO3+delta reported to be a 70 K superconductor.