Lead-free piezoceramics: from high piezoelectric coefficients to reliable devices

More than 15 years ago the seminal discoveries of high piezoelectric coefficients in various lead-free piezoceramic compositions triggered a period of extensive scientific research [1,2]. The efforts resulted in the... [ view full abstract ]

More than 15 years ago the seminal discoveries of high piezoelectric coefficients in various lead-free piezoceramic compositions triggered a period of extensive scientific research [1,2]. The efforts resulted in the development of a series of new materials and identification of novel physical mechanisms. Most noticeable electromechanical properties were demonstrated in compositions based on (K,Na)NbO₃, Na_1/2Bi_1/2TiO₃, BiFeO₃, and (Ba,Ca)(Ti,Zr)O₃, which seem to be good candidates for certain sensor, actuator, and transducer applications [3]. This is evidenced by the worldwide growing amount of reported prototype devices and the increasing interest by the industry. By now, several companies are offering lead-free piezoceramics or devices thereof, which is also attracting increased attention by the governmental regulation agencies [4]. The field thus seems to be entering the natural next stage, whereby the research focus is required to shift from the so called “primary properties” (e.g., piezoelectric coefficients) to other application-relevant aspects. These include reduction of materials´ costs, development of reproducible processing routes, ensuring suitable mechanical and thermal properties, and obtaining good fatigue resistance [5]. This contribution will briefly review the most prominent lead-free compositions, present the recent prototypes and commercially available products, and discuss the remaining open issues for future scientific research to support the implementation of lead-free piezoceramics into devices.

[1] Takenaka et al., Jpn J Appl Phys 30, 2236–2239 (1991). 

[2] Saito et al., Nature 432, 84–87 (2004).

[3] Rödel et al., J Eur Ceram Soc 35, 1659–1681 (2015).

[4] RoHS evaluation report: rohs.exemptions.oeko.info/.

[5] Koruza et al., J Materiomics doi: 10.1016/j.jmat.2018.02.001 (2018).