The X-ray photoelectron spectroscopy was applied to study a series of room temperature stabilised hexagonal barium titanate (h-BaTiO3), which have been synthesized with solidstate reaction method by adding Ga3+ ions into the process of producing BaTiO3. The doping levels vary from 5% to 25% (0.05 <= x <= 0.25). The photoelectron spectra collected at different spots of the samples showed inhomogeneous occurrences of the atomic replacement. The inhomogeneity increases significantly at and beyond 20% of doping levels (x >= 0.2). The expected appearance of Ti3+ ions, as a result of replacing Ti4+ with Ga3+, was observed only when the Ga concentration is 20% or higher. In all of the samples we observed unexpected components at higher binding energies than the expected Ti(4+)2p(3/2) and Ti(4+)2p(1/2) peaks in BaTiO3. These components stayed weak until the doping level reaches 20% and higher, and became stronger together with Ti3+ components (at lower binding energies than the corresponding Ti4+ peaks). These unexpected components may be attributed to the internal compressive stress due to the coexistence of Ba2TiO4 and BaTiO3 as described in [J. Appl. Phys. 95, 219 (2004)].
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CHINESE JOURNAL OF PHYSICS 卷: 50 期: 6 特刊: SI 頁數: 926-931
