High Power Piezoelectric Materials

Abstract

Heat generation is one of the significant problems in piezoelectrics for high-power density applications. In this article, we review the loss phenomenology in piezoelectrics first, including three losses, dielectric, elastic and piezoelectric losses, followed by heat generation analysis in piezoelectric materials for pseudo-DC and AC drive conditions. Heat generation at off-resonance is attributed mainly to intensive dielectric loss tanδ′, while the heat generation at resonance is mainly originated from the intensive elastic loss tanϕ′. Third, various experimental techniques (High Power Characterization System, HiPoCS) are introduced to measure dielectric, elastic and piezoelectric losses separately, including admittance/impedance spectrum analysis and burst/transient response method. Mechanical quality factors (QA at resonance and QB at antiresonance) are primarily measured as a function of vibration velocity. Fourth, loss mechanisms are discussed from the materials science viewpoint, in particular, from the domain dynamics models. The polarization angle dependence of losses in PZT’s and crystallographic orientation dependence of PMN-PT single crystal losses provide insightful domain dynamic models, including negative extensive piezoelectric loss tanθ. Then, practical high power “hard Pb(Zr,Ti)O3 (PZT)” based materials are described from four approaches: (1) ionic doping (acceptor doping creates hard PZTs), (2) material’s composition (higher Curie temperature ferroelectrics exhibit higher coercive field in general), (3) Pb-free piezoelectrics (crystallographic difference and lower thermal conductivity helps higher power density), and (4) grain size control (smaller grain specimens exhibit higher maximum vibration velocity). Piezo-ceramics with the maximum vibration velocities close to 1m/s (rms) are now available, which lead to the power density capability 10 times that of the commercially available hard PZTs. We proposed an “internal bias field model” to explain the low loss and high-power origin of these materials. Finally, we also introduce DC bias electric field and stress dependence of losses from the practical specimen driving technique viewpoint for the high-power applications.