High piezoelectric properties of (Ba_,Ca)TiO₃-0.04LiF ceramics sintered at a low temperature

Lead-free piezoelectric ceramics are strongly needed to replace the lead-based piezoelectric ceramics with increasing environmental concerns. Barium titanate (BaTiO₃) systems are one of the most promising candidates due to excellent electrical properties. However, the sintering temperature for traditionally sintered BaTiO₃ ceramics are about 1300°C, which restricts the applications of BaTiO₃ ceramics. It is necessary to develop high piezoelectric properties of BaTiO₃ based ceramics which are able to sinter at low temperature. The (Ba_0.94Ca_x)Ti_0.94O_δ-0.04LiF (x = 0.00 ~ 0.05 mol) ceramics were synthesized by a conventional sintering method at 1050°C. All the samples show high relative densities over 90%. X-Ray Diffraction pattern indicated that the crystallographic structure of the samples (x = 0.00 and 0.01 mol) are orthorhombic phase and changes to pseudocubic one with increasing Ca content to x = 0.03 mol. Two-phases with orthorhombic and pseudocubic symmetries coexisted at x = 0.02 mol, which contributes the excellent properties, in which the piezoelectric constant d ₃₃ = 361 pC/N, the planar electromechanical coupling coefficient k_p = 41.2%, the Curie temperature Tc = 70°C, the temperature of phase transition T _O-PC = 34°C near the room temperature, the relative permittivity ε _r = 4028 and the remanent polarization P _r = 9.39 μC/cm².