Valence state of cations in manganites Pr1-xCaxMnO3 (0.3 ≤ x ≤ 0.5) from X-ray diffraction and X-ray photoelectron spectroscopy

Polycrystalline Pr1-xCaxMnO3 (х = 0.3, 0.35, 04, 0.45, and 0.5) samples are synthesized by solid-state reaction method. Crystal structure of the samples is studied by X-ray diffraction method with Rietveld refinement. Diffraction patterns from all the samples are well indexed within the Pnma space group. It is shown that lattice parameters and unit cell volume decrease monotonically and O−Mn−O angles become closer to the ideal 180⁰ value upon the growth of x. Mn2p, Mn3s, Ca2p, Pr3d, Pr4d, and O1s X-ray photoelectron spectra are measured. Pr3d and Pr4d spectra are calculated in isolated ion approximation with approximate accounting for the charge transfer effect. Elemental compositions of samples are measured by the XPS method; they differ noticeably from the nominal ones. Charge compensation upon heterovalent Pr3+ → Ca2+ substitution is shown to realize via two mechanisms: creation of oxygen vacancies and formation of Mn4+ ions coexisting with Mn3+. Relative Mn4+/Mn3+ abundances are determined via decomposition of Mn2p and Mn3s XPS into contributions from the spectra of tri- and quadrivalent Mn ions. The amount of Mn4+ ions is shown to increase with Ca content x.