Electrical properties and ¹⁸O tracer diffusion in (Bi_0.5Na_0.5)TiO₃ ceramics doped with CuO and Nb₂O₅

抄録

(Bi_0.5Na_0.5)TiO₃ [BNT] ceramics can be sintered at low temperatures of 940 °C with CuO addition. This is believed to reduce Bi³⁺ volatilization and improve the quality of BNT-based ceramics by lowering the number of oxygen vacancies. However, there is no direct evidence that low-temperature sintering prevents the formation of oxygen vacancies. In this study, the formation of oxygen vacancies by ¹⁸O tracer diffusion and the additive effect of CuO on this formation in BNT ceramics were examined using secondary ion mass spectrometry (SIMS). In addition, Nb₂O₅, which acts as a donor, was added to the CuO-doped BNT ceramics. The formation of oxygen vacancies was discussed, and the electrical properties were clarified. As a result, the volume diffusion coefficients D of the BNT ceramics with 0.5 wt % CuO (Cu0.5) were 2.0 × 10⁻¹¹ cm²/s. This value is equivalent to pure BNT, which means that for BNT ceramics, CuO acts as an acceptor, suggesting that BNT ceramics still contain many oxygen vacancies. On the other hand, the D of ¹⁸O in Cu0.5 added 0.4 wt % Nb₂O₅ was 3.5 × 10⁻¹⁵ cm²/s, indicating that the formation of oxygen vacancies is suppressed. Moreover, Nb₂O₅ enhanced the poling treatment and the coercive field E_c decreased, indicating a softening trend.