Delayed thermal depolarization of Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3 by doping acceptor Zn~(2+) with large ionic polarizability

摘要

In this paper, (Bi_(0.5)Na_(0.5))_(0.94)Ba_(0.06)Ti_(1-x)Zn_xO_3 ceramics (0 ≤ x ≤ 0.06) were prepared by the solid oxide reaction route. The doping of Zn~(2+) into Bi_(0.5)Na_(0.5)TiO_3-6BaTiO_3 delays the crossover from nonergodic to ergodic states, and the thermal depolarization temperature T_d is delayed from 85 °C for pure samples to 120 °C for samples doped by 6% Zn~(2+), as confirmed by temperature-dependent dielectric and ferroelectric measurements. It suggests that the variation of the T_d could be ascribed to the reformation of the long-range ferroelectric order due to the large ionic polarizability of Zn~(2+). The high ionic polarizability of Zn~(2+) can result in a large dipole moment of BO_6 octahedra, thus strengthening the coherence of neighboring dipoles and suppressing the ferroelectric-relaxor transition. These results improve our understanding on the thermal depolarization of Bi_(0.5)Na_(0.5)TiO_3-based ferroelectrics.