Studies on surface composition and chemical states of calcium manganites

This paper describes investigations on atomic composition and chemical states of sintered calcium manganites discs in surface and near surface regions. The atomic composition was determined by 3.05 MeV 16O(α, α)16O resonance elastic scattering while the chemical states by, X-ray photoelectron spectroscopy (XPS). The specimens examined included undoped and donor (Y3+, Bi3+) doped CaMnO3, and Ca-excess and Mn-excess manganites namely Ca2MnO4 and CaMn2O4 respectively. Calcium manganite powder used in the preparation of discs was synthesized by a wet chemical method. X-ray diffraction (XRD) results indicated that all the discs are monophasic except CaMn2O4, which contained ∼98% requisite manganite. The atomic compositions of undoped specimens are close to the stoichiometric value while Y3+ and Bi3+ doped specimens are deficient in Mn and O respectively. The O deficiency may be responsible for comparatively higher electrical conductivity of Bi3+ doped specimen. Some of the specimens were also examined subsequent to their annealing in low PO2 atmosphere. This treatment produced significant compositional and structural modifications in the near surface regions. Mn(2p) electrons have identical binding energies in the sintered discs; therefore the valence states of Mn could not be discerned. However lesser binding energies of these electrons in annealed CaMnO3 indicated the existence of Mn(II)/Mn(III) in the specimen.