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Abstract
La1.85Sr0.16Ca0.99Cu2O5.93 + δ becomes a superconductor if synthesized under high O2 pressure at temperatures higher than 970°C although it is not superconducting when sintered in air or 1-atm O2. The crystal structure is determined by Rietveld analysis of X-ray diffraction data as a function of O2 pressure during synthesis. The relationship between crystal structure and superconductivity is discussed based on the structure analysis and measured superconducting properties. The ordering of La and Ca sites increases and Cu-O interatomic distance in the CuO2 plane decreases with increasing O2 pressure during synthesis. These changes may also contribute to the superconductivity of this compound in addition to the contribution from the increase in hole density by the synthesis at high O2 pressure.