Ceramics-Silikáty 54, (3) 258 - 262 (2010)

High-temperature capacitor materials were prepared in a BaTiO₃ (BT)-Bi_0.5Na_0.5TiO₃ (BNT)-BiNbO₄ (BN)-Nb₂O₅ system. The effects of BN and Nb₂O₅ on the dielectric properties and microstructure of 5 mol% BNT-doped BT ceramics were investigated. The dielectric constant peak at T_C was suppressed with the addition of BN, whereas an enhancement in the dielectric constant at lower temperatures was observed. In the case of 3 mol% BN addition, the temperature characteristic of capacitance satisfied the EIA X8R specification (-55 to 150°C, ΔC/C_25°C less than ±15 %). Scanning electron microscope and X-ray diffraction analyses suggested that a small amount of secondary phases existed in all the samples and the proportion of the secondary phases decreased with the addition of BN. When Nb₂O₅ was added to BT–BNT–BN ceramics, the dielectric constant at higher temperatures was markedly enhanced with an increase in Nb₂O₅ content. Therefore, the high-temperature specification (-55 to 200°C, ΔC/C_25°C less than ±15 %) is met when 3 mol% BN and 4 mol% Nb₂O₅ was added to 5 mol% BNT-doped BT ceramics, with a dielectric constant greater than 1200 and a dielectric loss lower than 1.5 %.