Fabrication and characterization of Na0.5K0.5NbO3-CuNb2O6 lead-free step-down piezoelectric transformers

Lead-free (Na0.5K0.5)NbO3 (NKN) ceramics doped with 1 mol% CuNb2O6 (01CN) ceramics were prepared using the conventional mixed oxide method at a sintering temperature of 1075 degrees C. NKN + 1 mol% CuTa2O6 (NKN-01CN) ceramics sintered at 1075 degrees C exhibit excellent "hard" piezoelectric properties of k(p) = 40%, k(t) = 45%, and k(33) = 57%, with ferroelectric property E-c = 23 kV/cm. The mechanical quality factor (Q(m)) is extraordinarily high (1933) and the temperature stability is excellent (Temperature coefficient of frequency (TCF) = -154 ppm/degrees C). The piezoelectric transformer (PT) was fabricated on NKN-01CN lead-free substrates, and the electrical characteristics were investigated. The devices were simplified into an equivalent circuit and analyzed using the MATLAB software package. The simulation results matched the experimental results. By reversing the input and the output, the step-down PT can be easily fabricated using a simple disk-type structure. A maximum efficiency of 93% with a voltage gain of 0.12 was measured, which was in good agreement with the simulation results (a maximum efficiency of 98.7% with a voltage gain of 0.13) for the step-down mode. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624579]