Ferroelectric Bi(Na,K)TiO3-based materials for lead-free piezoelectrics

A lead-free piezoelectric materials of Cu-doped Bi0.5(Na0.79K0.21)TiO3 (BNKT–xCu) have been synthesized using a conventional ceramic process. The addition of a small amount of CuO increased the d33-value up to 156 pC/N for BNKT–0.6Cu, while the large amout of CuO (>0.6 mol%) decreased it down to 80 pC/N for BNKT–2.0CuO. However, it was found that the mechanical quality factor (Qm) was not increased until the CuO content was less then 0.6 mol%, but it was significantly increased when CuO exceeded 0.6 mol%, resulting from the development of small defect. The inverse dielectric permittivity followed the Curie–Weiss law above the deviation temperature (Tdev.) at high temperatures for the BNKT–xCu. The thermal hysteresis for BNKT–xCu confirmed that with an increase in the amount of CuO addition, the variation of the temperature in dielectric permittivity maximum (Tm) increased gradually while the depolarization temperature (Td) decreased during the heating and the cooling cycles.