Local structure of Ca dopant in BaTiO3 by Ca K-edge X-ray absorption near-edge structure and first-principles calculations

The local environment of Ca dopants in barium titanate, BaTiO3, is investigated by Ca K-edge X-ray absorption near-edge structure (XANES) spectroscopy. In conjunction with experiments, first-principles calculations by two methods are systematically made. The projector-augmented wave (PAW) method is used to optimize the local structure and obtain the formation energy. The augmented plane wave plus local orbitals method is adopted to obtain theoretical XANES spectra. A comparison between experimental and theoretical XANES spectra shows that Ca dopants are located at the Ba2+ sites forming Ca2+. Formation energy calculations of Ca doped BaTiO3 by the PAW method also give the same results. The Ca atom in BaTiO3 is off-centering in comparison with the Ba site in BaTiO3. The off-centering of Ca atom is newly revealed by the combination of XANES spectroscopy and first-principles DFT calculations.