TEMPERATURE-DEPENDENCE OF THE LOCAL-STRUCTURE IN SUPERCONDUCTING AND NONSUPERCONDUCTING TL2BA2CUOY STUDIED BY EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE

The local structure of Tl2Ba2CuOy (Tl2201) has been investigated by ''tended X-ray absorption fine structure (EXAFS) on the Cu K-edge. The result for the high-T(c) sample with T(c) = 70 K indicates a splitting of Cu-O bondlengths in the CuO2 plane, which shows a strong temperature dependence over a wide temperature range well above T(c), although the crystallographical symmetry of the unit cell is tetragonal. The splitting is evaluated from the filtered EXAFS by the beat-node method, and the maximum splitting distance is approximately 0.16 angstrom. The magnitude of the splitting abruptly decreases in the vicinity of T(c) by more than 10%. On the other hand, no splitting in the in-plane Cu-O bondlengths was observed in non-superconductor samples from room temperature down to 30 K. No apparent change of axial oxygen sites was observed. These facts strongly demonstrate that the local structural distortion in the CuO2 plane may directly relate to the superconductivity.