16 - High power piezoelectric materials

Abstract

Heat generation is one of the significant problems in piezoelectrics for high power density applications. In this chapter, we review first the loss mechanisms in piezoelectrics, followed by the experimental techniques to measure dielectric, elastic and piezoelectric losses separately. Second, heat generation processes for various drive conditions are discussed. Heat generation at off-resonance is attributed mainly to intensive dielectric loss tan δ′ (i.e., Polarization (P) – Field (E) hysteresis loss), not to mechanical loss, while the heat generation at resonance originates mainly from the intensive mechanical loss tan ϕ′. Third, the maximum vibration velocity and the mechanical quality factor (an amplification factor of the impedance or displacement of a piezoelectric at its resonant status) are discussed in terms of driving voltage level. Fourth, practical high power ‘hard’ Pb(Zr,Ti) O3 (PZT)-based materials are introduced, which exhibit vibration velocities more than 1m/s, leading to the power density capability 10 times that of commercially available ‘hard’ PZTs. We propose an internal bias field model to explain the low loss and high power origin of these materials, which are suitable for actuator (ultrasonic motor) applications. We also describe ‘semi-hard’ materials based on PZT–Pb(Zn,Nb)O3–Pb(Ni, Nb)O3, with reasonable electromechanical coupling k factors, which are suitable for piezoelectric transducers. Finally, using a low temperature sinterable ‘semi-hard’ PZT, we demonstrate high power multilayer piezoelectric transformers with Cu or Ag internal electrodes.