X-ray photoelectron spectroscopy of amorphous and quasiamorphous phases of BaTiO3 and SrTiO3

Nonpolar amorphous and polar quasiamorphous phases of substrate-supported BaTiO3 and SrTiO3 were studied with x-ray photoelectron spectroscopy (XPS) to characterize the structural and chemical changes accompanying the transformation of the former into the latter. It was found that there are two spectral features distinguishing the amorphous from the quasiamorphous films: (1) an extra peak in the valence band spectra of amorphous films and (2) a satellite line in the XPS O 1s spectra of the amorphous films. On the basis of literature data, we suggest that both these features may be interpreted as originating from an oxygen-oxygen chemical bond. During the thermally driven transformation of an amorphous into a polar quasiamorphous phase, the oxygen-oxygen chemical bond breaks, leading to volume expansion and the development of inhomogeneous in-plane mechanical stress.