Advances in lead-free piezoelectric materials for sensors and actuators

Abstract

Piezoelectrics have widespread use in today's sensor and actuator technologies. However, most commercially available piezoelectric materials, e.g., Pb [Zr(x)Ti(1-x)] O(3) (PZT), are comprised of more than 60 weight percent lead (Pb). Due to its harmful effects, there is a strong impetus to identify new lead-free replacement materials with comparable properties to those of PZT. This review highlights recent developments in several lead-free piezoelectric materials including BaTiO(3), Na(0.5)Bi(0.5)TiO(3), K(0.5)Bi(0.5)TiO(3), Na(0.5)K(0.5)NbO(3), and their solid solutions. The factors that contribute to strong piezoelectric behavior are described and a summary of the properties for the various systems is provided.

Keywords: ceramics; electromechanical; ferroelectrics; piezoelectrics.

Figure 1.

Morphotropic phase boundary in PZT, reproduced from Jaffe et al. [8].

Figure 2.

Polymorphic phase transitions in barium titanate single crystals observed through changes in the unit cell parameters [32], spontaneous polarization [33], and dielectric constant [15], reproduced from the respective sources.

Figure 3.

Schematic of the pseudo-cubic NBT perovskite structure. The structure illustrated is locally ordered on the A-site (Bi, Na), although the extent of ordering is not well known. The oxygen atoms are not shown for clarity and their positions are instead represented by the oxygen octahedra.

Figure 4.

Polarization of KBT measured at temperatures of (a) 100 °C, (b) 200 °C, (c) 240 °C, and (d) 260 °C, reproduced from Hiruma et al. [39].

Figure 5.

Dielectric constant of [Li_x (Na_0.5K_0.5)_1−x]NbO₃ measured as a function of temperature for several Li concentrations, reproduced from Guo et al. [45].

Figure 6.

Schematic of the crystal structure of BFO, showing the direction of spontaneous polarization (P_s) as well as the antiferromagnetic ordering (displayed in the grey plane), reproduced from Chu et al. [51].

Figure 7.

Electromechanical coupling factor of [Bi_0.5(Na_1−xK_x)_0.5] TiO₃ as a function of KBT concentration (x), reproduced from Sasaki et al. [54].

Figure 8.

Phase diagram of NBT-BT showing the MPB between the ferroelectric rhomboheral phase and the ferroelectric tetragonal phase, reproduced from Takenaka et al. [58].

Figure 9.

Polarization (a) and strain (b) loops of 0.93 NBT-0.05 BT-0.02 KNN ceramics at several temperatures, reproduced from Zhang et al. [67].