Piezoelectric Properties of CuO-Doped (K,Na)NbO

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We report the piezoelectric properties of CuO-doped hydrothermal (K,Na)NbO<inf>3</inf>ceramics that can be applied as hard-type lead-free piezoelectric ceramics. To date, we have succeeded in synthesizing high-quality KNbO<inf>3</inf>and NaNbO<inf>3</inf>powders by the hydrothermal method, which is based on an ionic reaction at high temperature (around 210 °C) and pressure. Increasing both the piezoelectric constant d and the mechanical quality factor (Q_{\text{m}}) is important for resonance-type piezoelectric devices, such as ultrasonic motors and transformers. CuO doping into hydrothermal (K,Na)NbO<inf>3</inf>ceramics was examined to realize hard-type lead-free piezoelectric ceramics. By doping with 1.2 mol % CuO, Q_{\text{m}} was increased and the dielectric loss (\tan\delta) was decreased to 0.5%. The grain size was also influenced by the amount of CuO doping, which indicates that Q_{\text{m}} is related to the density. To achieve a higher Q_{\text{m}} value, the grain size is required to be less than 5 μm; however, excessive CuO doping leads to anomalous grain growth. Optimal piezoelectric properties were obtained for 1.2 mol % CuO-doped (K,Na)NbO<inf>3</inf>; k_{31} = 0.32, d_{31} = -44 pC/N, Q_{\text{m}}\ (\text{radial}) = 959, and \tan\delta = 0.5%. These characteristics showed that CuO doping with hydrothermal powders is effective for obtaining hard-type ceramics, and the mechanical quality factor is more than ten times higher than that of nondoped hydrothermal (K,Na)NbO<inf>3</inf>ceramics. Therefore, compared with the conventional solid-state method, we could succeed in obtaining hard-type ceramics by a simple and short process.
2013-07-25

Piezoelectric Properties of CuO-Doped (K,Na)NbO

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