High power density piezoelectrics are required to miniaturize devices such as ultrasonic motors, transformers, and sound projectors. The power density is limited by the heat generation in piezoelectrics, therefore, clarification of the loss mechanisms is necessary. This paper provides a methodology to determine the electromechanical losses, i.e., dielectric, elastic and piezoelectric loss factors in piezoelectrics by means of a detailed analysis of the admittance/impedance spectra. This method was applied to determine the piezoelectric losses for lead zirconate titanate ceramics and lead magnesium niobate-lead titanate single crystals. The analytical solution provides a new method for obtaining the piezoelectric loss factor, which is usually neglected in practice by transducer designers. Finite element simulation demonstrated the importance of piezoelectric losses to yield a more accurate fitting to the experimental data. A phenomenological model based on two phase-shifts and the Devonshire theory of a polarizable-deformable insulator is developed to interpret the experimentally observed magnitudes of the mechanical quality factor at resonance and anti-resonance.
Lead magnesium niobate–lead titanate (PMN–PT) single crystals are a suitable replacement over conventional PZT-based ceramics in transducer applications because of their large electromechanical coupling factors (k > 0.90) and piezoelectric constants (d > 1000 pC/N). For single crystals, it is possible to modify the performance by suitable selection of the orientation, and appropriate composition changes or doping can be utilized to improve the mechanical quality factor Q m. In this research, we report the piezoelectric loss performance in PMN–PT single crystals as a function of orientation, doping and vibration mode. The loss characteristics are based on mechanical quality factor Q m as well as the Q values at resonance (Q A) and anti-resonance (Q B). The Mn-doping resulted in almost twice the enhancement of the mechanical quality factor Q m and the maximum vibration velocity in comparison with the undoped samples.
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