B-site donor and acceptor doped Aurivillius phase Bi₃NbTiO₉ ceramics

The electrical properties of B-site donor and acceptor doped Aurivillius phase Bi₃NbTiO₉-based ceramics have been investigated. The effect of donor and acceptor doping on the dielectric constant, coercive field, dc conductivity and piezoelectric constant are presented. The band gap of Bi₃NbTiO₉ (BNTO) is about 3.4 ± 0.2 eV, determined from high-temperature dc conductivity measurements. All of the ceramics are ferroelectrics with high Curie points (∼900 °C). In acceptor doped ceramics, a low-temperature peak in the dielectric loss tangent is explained in terms of a Debye-type relaxation that results from an oxygen ion-jump mechanism. The activation energy for the relaxation is calculated as 0.93 ± 0.05 eV. The reduction of the piezoelectric constant below 500 °C is produced by depolarization, which is produced by the switching of thermally unstable non-180° domain walls.