Current Developments and Prospective of Lead-Free Piezoelectric Ceramics

The dielectric, ferroelectric and piezoelectric properties of pervoskite ferroelectric and bismuth layered-structured ferroelectric (BLSF) ceramics are described being superior candidates for lead-freee piezoelectric materials to reduce environmental damage. Pervoksite-type ceramics seem to be suitable for actuator and high-power applications that require a large piezoelectric constant, d(33), and a high Curie temperature, T-c, or a depolarization temperature, T-d (>200 degrees C). For BaTiO3-based solid solutions, (1-x)BaTiO3-x(Bi0.5K0.5)TiO3 (BT-BKT100x) ceramics, T-c increases with increasing amount of x, The BT-BKT20 + MnCO3 (0.1 wt%) ceramic shows a high T-c greater than 200 degrees C and an electromechanical coupling factor of k(33) = 0.35. In the case of a (Bi1/2Na1/2)TiO3-b(Bi1/2K1/2)TiO3-cBaTiO(3) [BNBK(100a/100b/100c)] solid solution ceramics, d(33) is 191 pC/N for BNBK (85.2/2.8/12). KNbO3 (KN)-based ceramics are also a candidate for lead-free piezoelectrics. In Mn-doped KN ceramics, a higher k(33) 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, Q(m), and a low temperature coefficient of resonance frequency, TC-f. The k(33) value of the donor (Nb)-doped and grain-oriented (HF) Bi4Ti3-xNbxO12 (BITN-x) ceramic is 0.39 for x = 0.08 and is able to keep the same stable value up to 350 degrees C. Nd(0.01) and V(0.75) co-doped Bi4Ti3O12 ceramics, BNTV(0.01, 0.75), show a relatively low TC-f. Bi3TiTaO9 (BTT)-based solid solution, (Srx-1Bi4-xTi2-xTaxO9 [SBTT2(x)] (1 <= x <= 2), displays the high Q(m) value (= 13500) in (p)-mode at x = 1.25. For resonator applications, (Sr1-xCax)(2)Bi4Ti5O18 (SCBT) (0 <= k <= 0.51) ceramics are suitable.