Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase. Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase.

Domain wall motion and lattice strain dynamics of ferroelectrics at resonance were simultaneously measured by combining high-power burst excitation and in situ high-energy x-ray diffraction. The increased loss at high vibration velocity was directly related to the increased domain wall motion, driven by dynamic mechanical stress. A general relationship between the microstructural strain contributions and macroscopic electromechanical behavior was established, allowing the prediction of high-power stability of ferroelectric materials. The results indicate that the materials' stability during high-power drive is predominantly related to the basic chemical composition, while the piezoelectric hardening mechanisms mainly influence the small-signal behavior.

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Lead-free relaxor ferroelectrics are promising candidates for next-generation piezoelectric high-power devices, such as ultrasonic motors, transformers, and therapeutic ultrasonics. These applications require hard ferroelectrics with a broad operating temperature range. Recently, acceptor Zn2+ doping and composite formation with ZnO were proposed to induce hardening in Na1/2Bi1/2TiO3–BaTiO3 and simultaneously increase the depolarization temperature. Here, these two strategies are compared by studying the temperature dependence of electromechanical properties, ferroelectric loops, and nonlinear polarization harmonics. In the modified compositions, depolarization is associated with the shift of the ferroelectric-to-relaxor transition to higher temperatures, while the depolarization onset remains unchanged. This leads to broadening rather than translation of the depolarization region, accompanied by decoupling of the piezoelectric d33 and d31 coefficients. The temperature-dependent electromechanical response is stable for composites, while the Zn2+-doped samples exhibit strong temperature dependence akin to acceptor-doped Pb(Zr,Ti)O3. The thermal evolution of electromechanical coefficients is not related to the thermally induced decrease of the coercive/internal bias fields but instead to the ratio of irreversible-to-reversible nonlinear dynamics arising from displacements of domain walls or similar interfaces. The results demonstrate that mechanical stress-based hardening in the composites exhibits superior thermal stability, which can considerably improve the operational range of lead-free piezoelectric materials.