High-power properties and miniature ultrasonic motor of (Sr,Ca)2NaNb5O15 piezoelectric ceramics

We investigated the high-power properties of lead-free piezoelectric ceramics with (Sr,Ca)2NaNb5O15 (SCNN), and clarified the properties of miniature cantilever-type ultrasonic motor of array-type multilayer piezoelectric ceramics of SCNN (SCNN–A–MLPC) as the lead-free-piezoelectric application. The jump phenomena of SCNN ceramics with constant-voltage driving produced mirror-reversed images relative to those of Pb(Zr,Ti)O3-based (PZT) ceramics. The nonlinear behavior was caused by the hard-spring effect of SCNN ceramics which possess notable elastic properties among the piezoelectric materials. Under high vibration velocity with constant-motional-current driving, SCNN ceramics showed that the temperature rise was lower than that of PZT ceramics and the degradation of the quality factor was limited, resulting in a gradual increase in the equivalent mechanical resistance. SCNN ceramics have superior high-power properties. The cantilever-type ultrasonic motor was fabricated using SCNN–A–MLPC and the driving properties were evaluated. The output power of the motor increased linearly with increasing input power up to 110 mW without heat generation. The output power density was high in comparison with that of the commercialized motor of PZT ceramics. Furthermore, the refined motor with build in preload mechanism was fabricated and the driving properties were evaluated. The motor was able to rotate with 200 rpm and 40 μN m at 2.6 Vp−p. 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.