Current developments and prospective of lead-free piezoelectric ceramics

Abstract

The dielectric, ferroelectric and piezoelectric properties of perovskite ferroelectric and bismuth layered-structured ferroelectric (BLSF) ceramics are described being superior candidates for lead-free piezoelectric materials to reduce environmental damage. Perovskite-type ceramics seem to be suitable for actuator and high-power applications that require a large piezoelectric constant, d33, and a high Curie temperature, Tc, or a depolarization temperature, Td (>200°C). For BaTiO 3-based solid solutions, (1 - x)BaTiO3-x(Bi 0.5K0.5)TiO3 (BT-BKT100x) ceramics, T c increases with increasing amount of x. The BT-BKT20 + MnCO 3 (0.1 wt%) ceramic shows a high Tc greater than 200°C and an electromechanical coupling factor of k33 = 0.35. In the case of a(Bi1/2Na1/2)TiO3-b(Bi1/2K 1/2)TiO3-cBaTiO3 [BNBK (100a/100b/100c)] solid solution ceramics, d33 is 191 pC/N for BNBK (85.2/2.8/12). KNbO 3 (KN)-based ceramics are also a candidate for lead-free piezoelectrics. In Mn-doped KN ceramics, a higher k33 of 0.507 is obtained for KN + MnCO3 (0.1 wt%). On the other hand, BLSF ceramics seem to be excellent candidates as piezoelectric sensors for high temperatures and ceramic resonators with a high mechanical quality factor, Qm, and a low temperature coefficient of resonance frequency, TC-f. The k33 value of the donor (Nb)-doped and grain-oriented (HF) Bi4Ti 3-xNbxO12 (BITN-x) ceramic is 0.39 for x = 0.08 and is able to keep the same stable value up to 350°C. Nd(0.01) and V(0.75) co-doped Bi4Ti3O12 ceramics, BNTV(0.01,0.75), show a relatively low TC-f. Bi3TiTa09 (BTT)-based solid solution, Srx-1Bi4_xTi 2-xTaxO9 [SBTT2(x)] (1 ≤ x ≤ 2), displays the high Qm value (= 13500) in (p)-mode at x = 1.25. For resonator applications, (Sr1-xCax)2Bi4Ti 5O18 (SCBT) (0 ≤ x ≤ 0.5) ceramics are suitable. © 2008 The Japan Society of Applied Physics.