Applications of lead-free piezoelectric materials
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Introduction Piezoelectric materials enable the transformation between electrical and mechanical signals and can thus be used in actuators, sensors, and resonators. Individual applications require specific piezoelectric properties. For example, the most important parameter for an actuator is the piezoelectric coefficient (d), while the performance of a resonator will depend on the coupling coefficient (k) and the mechanical quality factor (Qm). Since the pioneering work by the Toyota Central R&D Lab., Inc. in 2004,1 piezoelectric properties of lead-free piezoceramics have rapidly improved. In parallel to academic research, intensive industrial development has been carried out worldwide, especially in Europe and Asia. In particular, ferroelectric ceramics based on (K,Na)NbO3 (KNN), (Bi1/2Na1/2)TiO3 (BNT), (Sr,Ca)2NaNb5O15 (SCNN), and (Ba,Ca)(Zr,Ti)O3 (BCZT) compositions have shown performance for individual applications comparable to those of state-of-the-art Pb(Zr,Ti)O3 (PZT) and thus are of considerable commercial interest.2 Despite the promising properties of the newly emerging lead-free compositions, a majority of the industrial players are still hesitant about implementation of these materials. This is mostly because the motivation to replace the wellestablished PZT with lead-free materials is, in most areas,
still low. However, this motivation may change in the near future due to the increasing amount of available lead-free products, emergence of new players on the market, increased environmental and health awareness of consumers, and expected changes in governmental regulations.3 In addition, further improvements of piezoelectric properties and other application-relevant aspects4 are expected to promote this development. In this article, we introduce the most prominent current applications and prototypes using lead-free piezoelectrics based on ferroelectric materials.
Lead-free products and prototype devices Actuator applications Actuators require piezoceramics with large electric-fieldinduced strain, a large blocking force (force produced in the fully clamped state), and, for many applications, a high Curie temperature (TC). These parameters predominantly define the actuator’s operational range and are adjusted according to individual device requirements. In 2012, Toshiba Tec Corporation (Japan), in cooperation with Hosei University (Japan), developed an inkjet printhead using the shear mode of KNN-based piezoceramics.5 Two poled piezoceramic plates with fine-patterned ink channels are glued in a tail-to-tail configuration to form multiple pressure chambers, as shown in Figure 1a. The piezoceramic
Kenji Shibata, SCIOCS Co., Ltd., Japan; [email protected] Ruiping Wang, National Institute of Advanced Industrial Science and Technology, Japan; [email protected] Tonshaku Tou, Honda Electronics Co., Ltd., Japan; [email protected] Jurij Koruza, Technische Universität Darmstadt, Germany; [email protected] doi:10.1557/mrs.2018.180
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• VOLUME 43 • AUGUST 2018 • www.mrs.org/bullet
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