Valence selective DAFS measurements of Mn in La1/3Ca2/3MnO3

The manganese perovskite system La1-xCaxMnO3 displays a complex phase diagr am of structural, magnetic, and transport properties with varying Ca concen tration. At x = 2/3 and at low temperature, the system is antiferromagnetic with Mn4+ and Mn3+ ions occupying special positions in a charge-ordered su pperlattice. The charge ordering transition at about 260 K is characterized by the appearance of satellite peaks around certain strong normal lattice reflections. The normal lattice reflections are due to scattering from plan es containing Mn4+ and Mn3+ ions in nearly stoichiometric proportion, howev er the superlattice reflections are due to scattering from planes containin g only Mn4+ ions. By measuring Diffraction Anomalous Fine-Structure spectra on a superlattice reflection and its associated normal lattice reflection, it is possible to isolate absorption-like spectra for the two Mn sites. Du e to the weak intensity of these superlattice reflections, we were unable t o obtain high quality near-edge spectra for the superlattice reflection mea sured. However, the data offer useful information about the local electroni c structures of the two Mn ions.