SURFACE CHEMICAL-STATES OF BARIUM-TITANATE - INFLUENCE OF SAMPLE PROCESSING

The composition and chemistry of the near-surface region of BaTiO3 hav e been studied using x-ray photoelectron spectroscopy (XPS). It is fou nd that the Ba3d photoelectron peak shows two chemical states, one of which is attributed to the bulk perovskite and the other to a special surface state unrelated to contamination. The bulk component is reduce d and the surface component increases when the material is annealed at high temperatures (either in reducing or oxidizing atmosphere). Both the components are unaltered if the sample is exposed to air, solvents , or water: processes that lead to adsorption of impurities. The surfa ce peak, therefore, attributed to a relaxation related and not contami nation-related state, has been compared with those in other Ba-contain ing oxides. The oxygen photoelectron peak consists of a normal perovsk ite peak typical of most titanates and a higher energy component clear ly related to surface contamination. Annealing in reducing atmosphere results in drastically different optical and electrical properties, an d in chemical reduction of some Ti4+ ions to Ti3+. The overall stoichi ometry, however, does not change with annealing atmosphere. These resu lts have been discussed in light of our current understanding of this and other related oxides.