Investigations on the chemical states of sintered barium titanate by X-ray photoelectron spectroscopy

This study describes the surface characterisation of sintered discs of polycrystalline barium titanate (BaTiO3) of different electrical properties resulting from doping with Sb5+ in different concentrations, by X-ray photoelectron spectroscopy (XPS). It involves the chemical state identification of the constituents of the ceramic and the surface contaminants. It is observed that the Ba (3d5/2) electron spectrum has two components with characteristic binding energies of 778.5 and 780 eV, respectively. It is indicative of the existence of Ba in two distinct chemical environments in the perovskite surfaces. Similarly, the O (1s) spectrum has two components. The component at 529.5 eV corresponds to the ceramic whereas the other at 531.4 eV is related to surface contamination. The Ba (3d5/2) and O (1s) spectra undergo considerable change on surface treatments such as abrasion and sputtering with Ar+ ions. In contrast, the Ti (2p3/2) spectrum has only one component at 457.7 eV and remains relatively unaltered on surface treatments. The relative intensity of the lower to higher energy components of Ba (3d5/2) spectra varies with the electrical nature of the specimens; it is about 1.15 for semi-conducting and >2 for dielectric pristine specimens, respectively. It indicates a direct correlation between the higher energy component and the semi-conducting properties of the ceramics. The abrasion of semi-conducting specimen leads to a considerable increase in the relative intensity of the higher energy component in the Ba (3d5/2) spectra. The increase is more significant for semi-conducting specimens. This observation has been explained on the basis of preferred orientation of ferroelectric domains on the abraded surfaces. The analysis of C (1s) and O (1s) spectra suggests that the abraded surfaces are prone to adsorption of atmospheric contaminants. Sputter etching of the sample with Ar+ ion bombardment, apart from removing the contaminants, induces alteration in surface layers. It is manifested in the modification of Ba spectra and reduction of some Ti4+ ions to Ti3+ ions.