LOCAL STRUCTURE OF THE CHARGE ORDERED La0.5Ca0.5MnO3

Local lattice of the charge ordered La0.5Ca0.5MnO3 has been studied by temperature dependent Mn K-edge x-ray absorption measurements, using fluorescence detection method, to explore how the local lattice distortions are associated with the charge ordering in this system. The x-ray absorption near edge structure (XANES) reveals an abrupt change in the local MnO6 octahedral geometry across the charge ordering temperature. The extended x-ray absorption fine structure (EXAFS) analysis shows largely distorted MnO6 octahedra with coexisting Q3-type and Q2-type of Jahn-Teller (JT) modes at low temperature in the commensurate charge ordered phase. We find that small JT distortions persist also in the charge disordered phase at high temperature.