Difference of Electronic Structures between SrTiO3 and BaTiO3

X-ray photoemission spectroscopy (XPS) measurements were performed on SrTiO3 and BaTiO3 single crystals with monochromated Al Kα radiation. Valence band (VB) spectra of as-fractured SrTiO3 and BaTiO3 crystals exhibit two peaks arising from the O 2pπ and O 2pσ bonding orbitals. From a partial density of states (PDOS) calculation, it is found that O 2p orbitals fairly hybridize with Ba 5p orbitals, while do not almost hybridize with atomic orbitals of Sr atom. This indicates that the nature of the chemical bonding of Ba-O in BaTiO3 is more covalent than that of Sr-O in SrTiO3.