LOCAL PHASE-SEPARATION IN TL-BASED OXIDE SUPERCONDUCTORS

We present the results of the analysis of Cu K-edge X-ray absorption f ine structure (XAFS) on Tl2Ba2CUO6, which show a complex Cu-O pair dis tribution function with multiple Cu-O bondlengths in the CuO2 planes, implying local phase separation in this material. Based on these resul ts we propose a model of the local structure of these Tl-based superco nductors. We present the formalism used to extract a pair distribution function from XAFS from a model interatomic potential, associating a dynamic time scale to fluctuations between different bond lengths. The se copper-oxygen bondlengths are compared with those found in Bi2Sr2Ca Cu2O8+y, La1.85Sr0.15Cu2O4, and YBa2Cu3O7.