Systematic Mn d-configuration change in the ${\mathrm{La}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Ca}}_{\mathrm{x}}$${\mathrm{MnO}}_3$ system: A Mn K-edge XAS study

Systematic Mn K-edge x-ray-absorption spectroscopy (XAS) measurements on samples of ${\mathrm{La}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Ca}}_{\mathrm{x}}$ ${\mathrm{MnO}}_3$ are reported. Detailed results on the chemical shift and pre-edge feature spectral strength (both indicators of the Mn d-hole count) are discussed. The overall chemical shift across the series is compared to standard materials and is consistent with the identification of the endpoint perovskites with the ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ states. The detailed compositional dependence of the chemical shift and the 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 from this behavior for x values less than x≈0.2. Careful x-ray-diffraction measurements of the lattice parameter variation are also found to manifest changes near x≈0.2 and the chemical shift results are shown to scale with the lattice parameter results. Additional XAS results on air prepared and oxygen annealed samples reveal a variation in the chemical shift response to excess oxygen across this series. These XAS results are discussed in terms of the important Mn d-hole count variation across this system.