Fabrication of perovskite-type Ba(Sn_1−x Ta _x )O₃ ceramics and their power factors

Perovskite-type Ba(Sn_1−x Ta _x )O₃ (0.01 ≤ x ≤ 0.06) ceramics with high relative densities (92.7–94.4 %) were fabricated using the hot isostatic pressing (HIP) method at 1273 K and 196 MPa for 4 h in an atmosphere of argon gas. The lattice parameter decreased slightly with increasing x. From the XPS measurement, the Ta⁵⁺ ion was stable in Ba(Sn_1−x Ta _x )O₃ ceramics and the broad peak of the Ta4f level was the overlap between the Ta⁵⁺4f_5/2 and Ta⁵⁺4f_7/2 levels. Ba(Sn_1−x Ta _x )O₃ ceramics were n-type semiconductors, and their electrical resistivities increased with increasing x. The increase in the electrical resistivity was explained by impurity scattering due to the presence of the Ta ions. The absolute value of the Seebeck coefficient (S) increased with increasing temperature and x. The power factor (S ² σ), which was calculated from electrical conductivity (σ) and the Seebeck coefficient, was ca. 1.0 × 10⁻⁵ W m⁻¹ K⁻² at x = 0.01.