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 BaTiO3-based solid solutions, (1-x)BaTiO3–x(Bi0.5K0.5)TiO3 (BT–BKT100x) ceramics, Tc increases with increasing amount of x. The BT–BKT20 + MnCO3 (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(Bi1/2K1/2)TiO3–cBaTiO3 [BNBK (100a/100b/100c)] solid solution ceramics, d33 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 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) Bi4Ti3-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. Bi3TiTaO9 (BTT)-based solid solution, Srx-1Bi4-xTi2-xTaxO9 [SBTT2(x)] (1≦x≦2), displays the high Qm value (=13500) in (p)-mode at x=1.25. For resonator applications, (Sr1-xCax)2Bi4Ti5O18 (SCBT) (0≦x≦0.5) ceramics are suitable.

Phase transformations during HLnTiO4 (Ln=La, Nd) thermolysis and photocatalytic activity of obtained compounds

“…The first stage from the beginning of heating (Table 1, step 1) is surface water evaporation with 0.23% weight loss for HNdTiO 4 and more than 0.71% for HLaTiO 4 which is more hygroscopic like most La-containing compounds. After that four main thermal effects are presented.…”

“…Until present time perovskite-like compounds are actively studied as materials with wide range of important physical and chemical properties, such as super-conductivity [1], colossal magnetoresistance [2], ferroelectricity [3,4], catalytic and photocatalytic activity [5][6][7], thermochemical properties [8] and electrochemical properties [9]. In recent years, there has been a constant interest in using the soft chemistry methods for development of new layered perovskitelike compounds with specified physicochemical properties, as well as design of these materials based on perovskite structure [10][11][12][13][14].…”

Lead-Free Ferroelectric Ceramics with Perovskite Structure

“…On the other hand, solid solutions of BTO with ferroelectrics of higher Curie temperature have been studied in order to increase the T C of the system; unfortunately, although the T C increases, the effects on the dielectric properties are undesirable. In the solid solution 0.80BTO-0.20(K 0.5 Bi 0.5 )TiO 3 the T C reaches a value around 240°C, but the relative permittivity at room temperature and at the T C , has lower values than the pure BTO (Haertling, 1999;Takenaka, 2008). The colossal permittivity observed in BTO, is attributed to an interfacial polarization and is achieved in nanomaterials by the activation of a high number of carriers and their trapping at the interfaces (Guillemet-Fritsch et al, 2008).…”

“…As in the case of BTO, there have been efforts to improve the piezoelectric response of NBT by the substitution of one or more of its ions. Different authors have studied solid solutions of NBT with BTO, K 0.5 Bi 0.5 TiO 3 (Takenaka et al, 2008) and KNN (Nagata et al, 2003;Yao et al, 2009;. All these attempts try to exploit the morphotropic or polymorphic phase boundaries, where it is known that an improvement of dielectric and piezoelectric properties exist.…”

Effect of sintering condition on the microstructure and electrical properties of lead-free (Na0.5K0.5)NbO3- Bi0.5(Na0.83K0.17)0.5TiO3ceramics

“…NKN ceramics sintered by ordinary sintering show relatively lower values (k p =25%) due to difficulty in the processing of dense ceramics by ordinary sintering [2]. This issue has received significant attention and has been thoroughly investigated [3][4][5].…”