High pressure synthesis and electrical properties of BaTiO_3-xF_x

The substitution of fluorine for oxygen in BaTiO₃ was investigated by the reaction of BaO₂, BaF₂, TiO₂ and Ti under the conditions of 3.0 GPa and 1300° C for 2 H. Batio_3-xF_x solid solutions were obtained as a single phase in the region of 0 ≤x≤0.1. The X-ray diffraction data showed that the symmetrical change from tetragonal to cubic form occurred at x=0.08 at room temperature. Also, the solid solutions were characterized by TG-DTA analysis, ESCA spectroscopy and diffusion reflectance spectroscopy. As a result, the existence of Ti³⁺ was verified. The electrical resistivities of BaTiO_3-xF_x were in the range from 4Ωcm for x=0.05 to 3OΩcm for x=0.1 at 300 K and the relationship between In ρ{variant} and 1000 T^-1 was linear. The thermoelectric powers at 300 K were -250 μV K^-1 for x=0.05 and -130 μVK^-1 for x=0.1. The electrical property of the solid solution was discussed on the basis of a conventional band model which involved localized donor levels associated with oxygen vacancies.