Abstract
We report O and Ca K-edges x-ray absorption near edgestructure (XANES) spectra of Ba1-xCaxTiO3(x = 0.01 and 0.08), BaTiO3 and CaTiO3 and theelectronic structure of Ba0.875Ca0.125TiO3obtained by first-principles calculation. The characteristicfeatures in the O K-edge XANES spectra of these ferroelectricperovskites are influenced by the Ca concentration. They differsubstantially from those of the reference TiO2. The OK-edge spectra suggest that the combination of thealkaline-earth-metal oxides, CaO and/or BaO, with TiO2enhance the effective charge of the O ions. Thus, a largedipole moment may result from the displacement of the Ti ionfrom the centre of the TiO6 octahedron leading tocollective displacement of Ti ions through attractivedipole-dipole couplings and may give rise to ferroelectricity.In the Ca K-edge XANES spectra there is a pre-edge feature similar to those found in other 3d transition-metalperovskites, which may provide information about hole doping.
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