X-ray photoelectron study of the valence state of iron in iron-containing single-crystal (BiFeO3, PbFe1/2Nb1/2O3), and ceramic (BaFe1/2Nb1/2O3) multiferroics

Fe2p, Fe3p, and Fe3s X-ray photoelectron spectra (XPS) are measured with high resolution in single-crystal multiferroics BiFeO3 and PbFe1/2Nb1/2O3, as well as in reference samples Fe2O3, FeSO4 center dot 7H(2)O, FeC2O4 center dot 2H(2)O. The spectra are assigned based on an isolated-ion approximation calculation. Single-crystal multiferroics and Fe2O3 are shown to have the Fe ions only in the Fe3+ valence state. Ceramic samples of BaFe1/2Nb1/2O3 with various relative Fe2+/Fe3+ abundances are synthesized in various conditions. An approximate method to determine the Fe2+/Fe3+ ratio in a sample is suggested. The method is based on the fitting of the sample's 2p XPS with a superposition of Fe2+ and Fe3+ 2p spectra. An effect of temperature regimes of sintering and annealing on the Fe2+/Fe3+ ratio is demonstrated. (C) 2010 Elsevier B.V. All rights reserved.