Electrical Properties and Depolarization Temperature of (Bi_1/2Na_1/2)TiO₃–(Bi_1/2K_1/2)TiO₃ Lead-free Piezoelectric Ceramics

TLDR

The study determined the depolarization temperature, Td, by analyzing the temperature dependence of dielectric and piezoelectric properties. The authors investigated the piezoelectric properties of BNKT solid solutions (x = 0.50–0.98) with a focus on depolarization temperature, Td. Near the morphotropic phase boundary, the BNKT ceramics exhibited excellent piezoelectric performance (k33 = 0.56, d33 = 157 pC/N) but low depolarization temperatures (≈174 °C), whereas the BNKT70 composition showed a favorable combination of high d33 (126 pC/N), dynamic d33 (214 pm/V), and a higher Td (206 °C), making it a promising lead‑free actuator material.

Abstract

The piezoelectric properties of a solid solution of the binary system, x(Bi1/2Na1/2)TiO3–(1-x)(Bi1/2K1/2)TiO3 [BNKT100x; x=0.50–0.98] were investigated, focusing on depolarization temperature, Td. Fine piezoelectric properties in lead-free piezoelectric ceramics were obtained near the morphotropic phase boundary (MPB) composition between the rhombohedral and tetragonal structures, and the highest electromechanical coupling factor, k33, and piezoelectric constant, d33, were 0.56 for BNKT84 and 157 pC/N for BNKT80, respectively. However, the Td of BNKT80 was low (174 °C). The Td of the MPB composition was low, and the Td near the MPB composition was sharply decreased. It is thought that BNKT70 is a candidate composition for lead-free actuator applications owing to its relatively large piezoelectric constant, d33 (126 pC/N), dynamic d33 (214 pm/V), and high depolarization temperature, Td (206 °C). In this study, we determined depolarization temperature, Td, from the temperature dependence of dielectric and piezoelectric properties.