Thermal depoling process and piezoelectric properties of bismuth sodium titanate ceramics

TLDR

The authors fabricated stoichiometric and nonstoichiometric (Bi₀.₅Na₀.₅)TiO₃ ceramics by conventional processing and measured the piezoelectric properties of fully poled samples across all vibration modes and temperatures. The study found that BNT ceramics exhibit high conductivity caused by Bi vaporization, a tetragonal phase between 330–480 °C, depolarization, rhombohedral‑tetragonal transition, and dielectric‑maximum temperatures at 187 °C, ~300 °C, and 325 °C, respectively, and that three distinct thermal depoling processes occur at these temperatures, as evidenced by changes in strain, X‑ray patterns, and dielectric constant.

Abstract

Stoichiometric and nonstoichiometric (Bi0.5Na0.5)TiO3 (BNT) ceramics were prepared by a conventional ceramic fabrication process. This study revealed that the high conductivity of BNT ceramics is associated with Bi vaporization during sintering. An x-ray study revealed that a tetragonal phase exists in the temperature range between 330 and 480 °C in BNT ceramic as well as BNT single crystals. In addition, the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant were determined to be 187, approximately 300, and 325 °C, respectively, from the temperature dependences of dielectric properties using unpoled and poled specimens. The piezoelectric properties of all vibration modes and the temperature dependences of the piezoelectric properties were measured using fully poled BNT ceramics. It was also revealed that BNT ceramics exhibit three thermal depoling processes at Td, between Td and TR-T, and between TR-T and Tm from the effects of annealing on the field-induced strain, x-ray diffraction patterns, and dielectric constant of poled specimens.