High pressure synthesis and electrical properties of BaTiO_3−xF_x

Abstract

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−x F _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 atx=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−x F _x were in the range from 4Ωcm for x=0.05 to 3OΩcm forx=0.1 at 300 K and the relationship between Inϱ and 1000 T⁻¹ was linear. The thermoelectric powers at 300 K were −250μV K⁻¹ forx=0.05 and −130μVK⁻¹ forx=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.