Quenching effects on depolarization temperature and ¹⁸O tracer diffusion in (Bi_0.5Na_0.5)TiO₃ ceramics with acceptor and donor additives

Abstract

Lead-free ferroelectric and piezoelectric ceramics, (Bi_0.5Na_0.5)TiO₃ (BNT), with Mg and Nb additives were prepared and the concentration of oxygen vacancies as the ¹⁸O tracer diffusion of these ceramics were clarified by secondary ion mass spectroscopy (SIMS). Moreover, the samples were quenched after sintering to examine the depolarization temperature T_d, and then their electrical properties were investigated. As a result, the obtained values of volume diffusion coefficient D of BNT doped with 0.4 wt % Mg and 0.4 wt % Nb were determined to be 9.2 × 10⁻¹¹ and 1.1 × 10⁻¹³ cm²/s, respectively. The oxygen vacancy concentration increased with the amount of Mg added and decreased with that of Nb added. Moreover, quenching increased T_d by ∼50 °C in BNT with the Mg additive (Mg x) and ΔT_d also increased. Thus, the effect of quenching was promoted by Mg x. On the other hand, the T_d of BNT with the Nb additive (Nb y) also increased despite the low concentration of oxygen vacancies. This is because the D of pure BNT (no additives) was revealed found to be 2.5 × 10⁻¹¹ cm²/s, that is, pure BNT originally contained a high concentration of oxygen vacancies. The concentration was maintained even after quenching, then D showed 1.8 × 10⁻¹¹ cm²/s. In addition, the electromechanical coupling factor k₃₃ of the quenched ceramics remained similar to that of the ordinarily fired samples of BNT with the Mg and Nb additives.