Surface chemical states of barium titanate: Influence of sample processing
- PDF / 494,368 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 67 Downloads / 183 Views
The composition and chemistry of the near-surface region of BaTiO3 have been studied using x-ray photoelectron spectroscopy (XPS). It is found that the Ba3J 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 reduced 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 surface peak, therefore, attributed to a relaxation related and not contamination-related state, has been compared with those in other Ba-containing oxides. The oxygen photoelectron peak consists of a normal perovskite peak typical of most titanates and a higher energy component clearly related to surface contamination. Annealing in reducing atmosphere results in drastically different optical and electrical properties, and in chemical reduction of some Ti 4+ ions to Ti 3 + . The overall stoichiometry, however, does not change with annealing atmosphere. These results have been discussed in light of our current understanding of this and other related oxides.
I. INTRODUCTION BaTiO3 can, in many ways, be called the "model ferroelectric" material. Several of its bulk properties have therefore been widely investigated in the past for ferroelectric, piezoelectric, and optoelectronic type behavior.1'2 More recently, there has been a renewal of interest in this material because of its useful electrooptic properties, including photoferroelectric3 and photorefractive4 effects. Most active device applications eventually involve thin film forms, maybe even nanosize components, and an understanding of the near-surface region becomes important, but the current state of knowledge about the surface of this material is still very limited. There have been some recent studies that address the issues of interfacial composition, defect energies, space charge, and segregation," but there is very little information available on surface chemical states of the ions involved and how they interact with other phases. Photoelectron spectroscopic studies of this solid have mostly involved valence band studies in relation to band structure calculations.8 Therefore, their focus has been on those 0-100 eV peaks that represent the valence band structure. Only recently have some investigators9 discussed the core level peaks of Ti 4+ and O 2 ions in fractured BaTiC>3 in comparison to T1O2 electronic states. The surface chemistry of the Ba 2+ ion in this material, which is an important aspect both in terms of electronic defects and surface reactivity, does not seem to have been discussed in any of the earlier articles. 1502
J. Mater. Res., Vol. 10, No. 6, Jun 1995
We present in this article a surface specific study of BaTiO3 and discuss some changes that can arise from processing. Special emphasis is given to the chemical states of Ba.
Data Loading...
