Current Developments and Prospective of Lead-Free Piezoelectric Ceramics

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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, $d_{33}$, and a high Curie temperature, $T_{\text{c}}$, or a depolarization temperature, $T_{\text{d}}$ (${>}200$ °C). For BaTiO3-based solid solutions, ($1-x$)BaTiO3–$x$(Bi0.5K0.5)TiO3 (BT–BKT100$x$) ceramics, $T_{\text{c}}$ increases with increasing amount of $x$. The BT–BKT20 + MnCO3 (0.1 wt %) ceramic shows a high $T_{\text{c}}$ greater than 200 °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–$c$BaTiO3 [BNBK (100$a$/100$b$/100$c$)] 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, $Q_{\text{m}}$, 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 °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($x$)] ($1\leqq x\leqq 2$), displays the high $Q_{\text{m}}$ value ($=13500$) in (p)-mode at $x=1.25$. For resonator applications, (Sr1-xCax)2Bi4Ti5O18 (SCBT) ($0\leqq x\leqq 0.5$) ceramics are suitable.
2008-05-25

Current Developments and Prospective of Lead-Free Piezoelectric Ceramics

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