A Rosen-type piezoelectric transformer employing lead-free K0.5Na0.5NbO3 ceramics

Lead-free K0.5Na0.5NbO3–K5.4Cu1.3Ta10O29– MnO2 (KNN–KCT–Mn) ceramics have been prepared by a conventional ceramic sintering technique. The ceramics show excellent piezoelectric properties for application in power devices, and the optimum properties measured are as follows: piezoelectric constant d33 = 90 pC/N, planar electromechanical coupling factor kp = 0.40, mechanical quality factor Qm = 1900, remanent polarization Pr = 11.8 lC/cm2, coercive field Ec = 0.85 kV/mm. A Rosentype piezoelectric transformer with a dimension of 21 mm · 6 mm · 1.2 mm was fabricated using the KNN– KCT–Mn ceramics. Properties of the piezoelectric transformer operating in the first and second modes have been characterized. For the first mode, the transformer has a maximum output power of 0.7 W with a temperature rise of 14 C. For the second mode, the maximum output power of the transformer is 1.8 W with a temperature rise of 33 C. KNN–KCT–Mn ceramics have shown to be a potential lead-free candidate to be used in high-voltage– low-current devices.