Cu K edge X-ray absorption spectra of La2SrCu2O6-type superconductor

Crystal structures have been refined using X-ray diffraction data acid X-ray absorption near edge structures (XANES) have been measured for La1.85-xNdxCa1.15Cu2O6+delta, and for La1.9Sr1.1-xCaxCu2O6+delta to investigate the relation between local structures around Cu ions and superconductivity in La2SrCu2O6-type cuprate superconductor. The superconducting transition temperature, T-c, decreases with increasing x and with constant oxygen content (6 + delta) in the former cuprate, acid it increases with increasing x and with decreasing (6 + delta). Structural refinements using X-ray diffraction data reveal that mixed occupations of La, Nd, Ca ions in the former cuprate and of La, Sr, Ca ions in the latter cuprate at their own sites increase with decreasing T-c. The refinements also reveal the aspect ratio of CuO5 pyramids in both cuprates with decreasing T-c. The analyses of XANES spectra for both cuprates indicate that the former cuprate has non-defective CuO2 conductive layers regardless of the composition, x, From these results, it is concluded that T-c is suppressed by the mixed occupation of the cations and/or by the deformation of CuO5 pyramid in La2SrCu2O6-type cuprate superconductors. (C) 1998 Elsevier Science B.V. All rights reserved.