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

Abstract

The piezoelectric properties of a solid solution of the binary system, x(Bi 1=2 Na 1=2 )TiOx ¼ 0:50 { 0:98] were investigated, focusing on depolarization temperature, T d . 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, k 33 , and piezoelectric constant, d 33 , were 0.56 for BNKT84 and 157 pC/N for BNKT80, respectively. However, the T d of BNKT80 was low (174 C). The T d of the MPB composition was low, and the T d 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, d 33 (126 pC/N), dynamic d 33 (214 pm/V), and high depolarization temperature, T d (206 C). In this study, we determined depolarization temperature, T d , from the temperature dependence of dielectric and piezoelectric properties.

Progress in engineering high strain lead-free piezoelectric ceramics

“…The existence of an MPB between (Bi 1/2 Na 1/2 )TiO 3 and (Bi 1/2 K 1/2 )TiO 3 in the compositional range 16-20 mol% (Bi 1/2 K 1/2 )TiO 3 was later substantiated by Sasaki et al [57] based on structural studies indicating coexistence of rhombohedral and tetragonal phases as well as the corresponding compositionally dependant peaks in the dielectric, piezoelectric and electromechanical coefficients. More recent studies [58][59][60][61][62][63] • C) is higher than that of pure (Bi 1/2 Na 1/2 )TiO 3 as expected, however, the depolarization temperature (due to a polymorphic phase transformation to the intermediate pseudocubic phase) is quite low reaching a minimum (T d = 140…”

Determination of depolarization temperature of (Bi1/2Na1/2)TiO3-based lead-free piezoceramics

“…3,5 Nevertheless, one of the major drawbacks of these newly developed materials is the limited temperature regime in which the high performance is achieved. 2,4 For example, Bi 1/2 Na 1/2 TiO 3 -0.06BaTiO 3 (BNT-BT) loses piezoelectric properties around 100 C, 6 and Bi 1/2 Na 1/2 TiO 3 -0.2Bi 1/2 K 1/2 TiO 3 (BNT-BKT) has a similar polarization loss at $150 C. 7 K 0.5 Na 0.5 NbO 3 (KNN) shows a polymorphic phase transition (PPT) between orthorhombic and tetragonal structure at $200 C, above which the piezoelectric properties degrade. High performance in these lead-free ceramics is achieved by shifting the PPT to room temperature, which can be done by various dopants.…”

Polarization and leakage current properties of self-supported bismuth sodium titanate ceramic films deposited by aerosol deposition method

“…Takenaka et al have demonstrated that (Bi,Na)TiO 3 (BNT) is an attractive piezoelectric material 1)3) because it has a large spontaneous polarization. However, the piezoelectric properties of BNT are lost or drastically deteriorated above the depolarization temperature (T d ) at 200°C for BNT 4), 5) due to the structural phase transition from rhombohedral (R3c symmetry: ferroelectric) to tetragonal (P4bm symmetry: ferriferroelectric). 6) Recent investigations have focused on increasing the T d for solid solutions of BNT with other perovskite materials.…”