Impedance spectroscopy and piezoelectric property of LiF-doped PZN–PZT low-temperature sintering piezoelectric ceramics

Low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn1/3Nb2/3)O3–0.7Pb(Zr0.49Ti0.51)O3 with LiF and Sm2O3 additives were fabricated by a conventional solid-state reaction. In view of the possible defects caused by LiF doping, the as-sintered specimens were annealed in oxygen to enhance grain size and piezoelectric properties. X-ray diffraction revealed that Sm2O3 and LiF were dissolved in the lattices, forming a pure perovskite structure. Scanning electron microscopy showed that the grain size decreased with increased LiF amount. Hysteresis-loop studies indicated that increased LiF led to ferroelectricity deterioration. Impedance spectroscopy and activation-energy analyses revealed decreased oxygen vacancies after annealing in oxygen. Energy-dispersive spectrometry revealed that fluorine volatilized during annealing in oxygen. Thus, the decreased amounts of FO and VO were presumed responsible for the improved piezoelectric properties. Upon doping 1 mol% LiF, sintering temperature decreased from 1125 to 950 °C. Annealing in oxygen greatly improved the piezoelectric properties from d33 = 252 pC/N and Kp = 0.53 to d33 = 403 pC/N and Kp = 0.56, respectively.