LOCAL LATTICE INSTABILITY OF CUO2 PLANE IN LA1.85SR0.15CUO4 BY POLARIZED CU K EDGE ABSORPTION

The temperature dependence of the local structure of the CuO2 plane in La1.85Sr0.15CuO4 has been studied by in-plane polarized Cu K edge extended X-ray absorption fine structure (EXAFS). The high signal-to-noise ratio in the E parallel to ab EXAFS allows us to separate the contributions of Cu-O(planar), Cu-O-Cu and Cu-La/Sr shells and to study their temperature dependence in the low-temperature orthorhombic (LTO) phase. We have observed an anomalous behavior of the local structure below 100 K with clear anomalies at similar to T-c (35 K) and T* (similar to 1.6T(c)) that are not expected on the basis of the average structure. These results suggest that the structure of the CuO2 plane is non-homogeneous and it shows anomalous changes at T* and T-c.