Effects of BiNbO₄ on the microstructure and dielectric properties of BaTiO₃-based ceramics

The microstructure and dielectric properties of ternary system BaTiO₃ (BT)–Bi_0.5Na_0.5TiO₃ (BNT)–BiNbO₄ were investigated. In the case of 1 mol% BNT addition, the Curie point (T _c) of BaTiO₃ was increased from 130 to 140 °C. The dielectric constant peak at T _c was markedly depressed with the addition of BiNbO₄, whereas an enhancement in the dielectric constant at lower temperature was observed. The addition of BiNbO₄ improved the temperature dependence of the dielectric constants of BaTiO₃-BNT system ceramics and the temperature coefficient of capacitance curves satisfied the EIA X8R specification with 3–4 mol% BiNbO₄. The dielectric constant peak at T _c was suppressed evidently due to over high-sintering temperature. As the BiNbO₄ content was increased, the Curie point progressively moved to lower temperatures. SEM indicated that fine and homogeneous grains were observed with 1 mol% BiNbO₄ addition. However, secondary phase grains appeared with increasing the BiNbO₄ content, which were identified as Ba₂TiO₄, NaBiTi₂O₆, and BaTiNb₄O₁₃ by XRD. Moreover, the proportion of the secondary phase grains increased as the BiNbO₄ content increased.