The X-ray photoelectron spectroscopy was applied to study a series of room temperature stabilised hexagonal barium titanate (h-BaTiO_3), which have been synthesized with solid-state reaction method by adding Ga~(3+) ions into the process of producing BaTiO_3. 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 Ti~(3+) ions, as a result of replacing Ti~(4+) with Ga~(3+), 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 BaTiO_3. These components stayed weak until the doping level reaches 20% and higher, and became stronger together with Ti~(3+) components (at lower binding energies than the corresponding Ti~(4+) peaks). These unexpected components may be attributed to the internal compressive stress due to the coexistence of Ba_2TiO_4 and BaTiO_3 as described in [J. Appl. Phys. 95, 219 (2004)].
展开▼
