Current status and prospects of lead-free piezoelectric ceramics

Dielectric, ferroelectric and piezoelectric properties of perovskite ferroelectric and bismuth layer-structured ferroelectric (BLSF) ceramics are described as superior candidates for lead-free piezoelectric materials to reduce environmental damages. Perovskite type ceramics seem to be suitable for actuator and high power applications that are required a large piezoelectric constant, d(33) (> 300 pC/N) and a high Curie temperature, T-c (> 200 degrees C). For BaTiO3 (BT)-based solid solutions, that is, (1 - x)BaTiO3 - x(Bi0.5K0.5)TiO3 [BTBK - 100x] ceramics, the T-c increases with increasing the amount of x. BTBK-20 + MnCO3 0.1 wt.% ceramic shows the high T, than 200 degrees C and the electromechanical coupling factor, k(33) = 0.35. In the case of a(Bi1/2Na1/2)TiO3 - bBaTiO(3) - c(Bi1/2K1/2)TiO3 [BNBK (100a/100b/100c)] solid solution ceramics, the d(33) and T-c are 191 pC/N and 301 degrees C for the BNBK (85.2/2.8/12), respectively. On the other hand, BLSF ceramics seem to be excellent candidates as piezoelectric sensors for high temperatures and ceramic resonators with high mechanical quality factor and low temperature coefficient of resonance frequency (TC-f(r)). Donor-doped Bi4Ti3O12 ceramics such as Bi4Ti3-xNbxO12 [BITN-x] and Bi4Ti3-xO12 [BITV-x] show high T-c than 650 degrees C. The k(33) value of the grain-oriented (HF) BITN-0.08 ceramic is 0.39 and is able to keep the same value up to 350 degrees C. Bi3TiTaO9 (BTT)-based solid solution system, Srx-1Bi4-xTi2-xTaxO9 [SBTT2(x)] (1 <= x <= 2), displays the high Q(m) value (=13500) in (p)-mode at the x = 1.25 composition. (c) 2005 Elsevier Ltd. All rights reserved.