SYSTEMATIC MN D-CONFIGURATION CHANGE IN THE LA1-XCAXMNO3 SYSTEM - A MN K-EDGE SAS STUDY

Systematic Mn K-edge x-ray-absorption spectroscopy (XAS) measurements on samples of La1-xCaxMnO3 are reported. Detailed results on the chemi cal shift and pre-edge feature spectral strength (both indicators of t he Mn d-hole count) are discussed. The overall chemical shift across t he series is compared to standard materials and is consistent with the identification of the endpoint perovskites with the Mn3+ and Mn4+ sta tes. The detailed compositional dependence of the chemical shift and t he strength of the pre-edge feature both indicate a uniform Ca-induced increase in the Mn d-hole count for x> 0,2 and an anomalous break fro m this behavior for x values less than x approximate to-0.2. Careful x -ray-diffraction measurements of the lattice parameter variation are a lso found to manifest changes near x approximate to 0.2 and the chemic al shift results are shown to scale with the lattice parameter results . Additional XAS results on air prepared and oxygen annealed samples r eveal a variation in the chemical shift response to excess oxygen acro ss this series. These XAS results are discussed in terms of the import ant Mn d-hole count variation across this system.