Dielectric properties of Ba2+Doped bnt and bnt-pt ferroelectrics

Abstract

The dielectric properties and the microstructures in Ba doped Bi[subscript 0.5]Na[subscript 0.5]TiO₃ (BNT) and 0.90Bi[subscript 0.5]Na[subscript 0.5]TiO₃ – 0.10PbTiO₃ (0.90BNT-0.10PT) solid solutions were investigated as functions of %Ba and sintering temperature. In addition, a second phase of these systems was observed. Ba decreased grain size of BNT and increased the dielectric constant throughout the temperature range. 5% Ba lowered the first transition temperature from 170 ℃ to 72 ℃. As % Ba increased the dissipation factor also increased. The second phase at 15% Ba doped BNT lowered the dielectric constant (K’) at Curie temperature. Ba doped 0.90BNT-0.10PT also limited grain growth. With 5% Ba doped 0.90BNT-0.10PT, K’ increased both at Curie point and room temperature, the dissipation factor decreased and the first transition temperature lowered from 152 ℃ to 68 ℃. Further addition of Ba to 10 % and 15%, the K’ tended to decrease, the dissipation factor did not vary and the first transition temperature disappeared. Thus, the phase boundary was between 5-10% Ba. Compared with those of Ba doped BNT, the grain size of Ba doped 0.90BNT-0.10PT was larger, the K’ was higher and the first transition temperature was lower. For this research 5% Ba doped 0.90BNT-0.10PT gave the optimum dielectric properties for high temperature capacitor.