Effects of La-doping on microstructure, dielectric and piezoelectric properties of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ lead-free ceramics

Lead-free (Ba_0.85Ca_0.15)_1−xLa_2/3xTi_0.90Zr_0.10O₃ + 1 mol% MnO₂ ceramics have been prepared an ordinary sintering technique and the effects of La-doping on the microstructure, dielectric and piezoelectric properties of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ were studied. All the ceramics possess a pure perovskite structure, indicating that La ions are incorporated into Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ lattices to form a lead-free solid solution. The ceramics are transformed from coexistence of orthorhombic and tetragonal phases to pseudocubic phase with the doping level of La increasing. After the doping of La, grain growth is inhibited, ferroelectric-paraelectric phase transition temperature (T _C) is decreased and the degree of diffuse phase transition is increased. The ferroelectricity of the ceramics is weakened after the addition of La. Unlike donor-doped lead zirconate titanate ceramics, the piezoelectric properties of the ceramics are degraded after the partial substitution of La³⁺ for (Ba_0.85Ca_0.15)²⁺ because of the weakness or disappearance of coexistence of orthorhombic and tetragonal phases near room temperature. The (Ba_0.85Ca_0.15)_1−xLa_2/3xTi_0.90Zr_0.10O₃ + 1 mol% MnO₂ ceramic with x = 0 exhibit the optimum piezoelectric properties: d ₃₃ = 277 pC/N and k _p = 30.3 %, respectively.