We investigated why the nonlinear behaviors of (Bi,Na,Ba)(Ti,Mn)O3 (BNBTM) ceramics and (Sr,Ca)2NaNb5O15 (SCNN) ceramics occur in comparison with Pb(Zr,Ti)O3-based (PZT) ceramics by evaluating their high-power properties with the distinction between mechanical nonlinearity and temperature dependence of properties. The equivalent stiffness of PZT decreased with increasing vibration velocity and sample temperature. However, the equivalent stiffnesses of BNBTM and SCNN did not depend on vibration velocity, they decreased and increased linearly with an increase in sample temperature, respectively. The nonlinear behavior of PZT originated from the soft-spring effect through which the mechanical nonlinearity was induced and the temperature dependence of stiffness was enhanced. On the other hand, it appeared that the nonlinear behaviors of BNBTM and SCNN originated from the apparent soft- and hard-spring effects through which the temperature dependence of stiffness was induced. The temperature characteristic of elasticity is important for controlling the high-power properties.

The nonlinear behaviors and high-power properties of two lead-free piezoelectric ceramics – (Bi1/2Na1/2)0.85Ba0.15Ti0.98Mn0.02O3 (BNBTM) and Sr1.9Ca0.1NaNb5O15 (SCNN) – were clarified by comparison of their mechanical characteristics using the continuous driving method. BNBTM ceramics exhibited jump phenomena with constant-voltage driving that were similar to those found in Pb(Zr,Ti)O3-based (PZT) ceramics. The jump phenomena of SCNN ceramics produced mirror-reversed images relative to those of BNBTM ceramics. Their nonlinear behaviors were caused by the soft-spring effect and hard-spring effect, respectively. Among the piezoelectric materials, SCNN ceramics possess notable elastic properties. With increasing vibration velocity, their rise in temperature was lower than that of PZT ceramics; in particular, the temperature of SCNN ceramics was lower than that of BNBTM ceramics. The quality factor of BNBTM ceramics gradually decreased and that of SCNN ceramics showed a broad peak. The degradation of the quality factor was thus limited, resulting in a gradual increase in the equivalent mechanical resistance.

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The properties of miniature cantilever-type ultrasonic motors using lead-free array-type multilayer piezoelectric ceramics of (Sr,Ca)2NaNb5O15 (SCNN) developed using the design rule were investigated under high input power by comparison with the high-power properties of SCNN ceramics. The frequency dependence of the revolution speed reflected the nonlinear behavior of SCNN ceramics with the hard-spring effect and showed a mirror-reversed image relative to that of the motor of Pb(Zr,Ti)O3 (PZT) ceramics. The output power increased linearly with increasing input power up to 110 mW without heat generation, and the driving properties were almost the same as the expectations under low input power. The output power density characteristics of the motors were high in comparison with those of the commercialized motors of PZT ceramics. It appeared that the motors have a high potential as an environmental friendly piezoelectric device with excellent properties, reflecting the high-power properties of SCNN ceramics.

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