Difference of electronic structures between SrTiO3 and BaTiO3

X-ray photoemission spectroscopy (XPS) measurements were performed on SrTiO 3 and BaTiO3 single crystals with monochromated Al K alpha radiation. Valen ce band (VB) spectra of as-fractured SrTiO3 and BaTiO3 crystals exhibit two peaks arising from the O 2p pi and O 2p sigma bonding orbitals, From a par tial density of states (PDOS) calculation, it is found that O 2p orbitals f airly hybridize with Ba 5p orbitals, while do not almost hybridize with ato mic orbitals of Sr atom. This indicates that the nature of the chemical bon ding of Ba-O in BaTiO3 is more covalent than that of Sr-O in SrTiO3.