Effects of La-doping on microstructure, dielectric and piezoelectric properties of Ba_(0.85)Ca_(0.15)Ti_(0.90)Zr_(0.10)O_3 lead-free ceramics

摘要

Lead-free (Ba_(0.85)Ca_(0.15))_(1-x)La_(2/3x)Ti_(0.90)Zr_(0.10)O_3 + 1 mol% MnO_2 ceramics have been prepared an ordinary sintering technique and the effects of La-doping on the microstructure, dielectric and piezoelectric properties of Ba_(0.85)Ca_(0.15)Ti_(0.90)Zr_(0.10)O_3 were studied. All the ceramics possess a pure perovskite structure, indicating that La ions are incorporated into Ba_(0.85)Ca_(0.15)Ti_(0.90)Zr_(0.10)O_3 lattices to form a lead-free solid solution. The ceramics are transformed from coexistence of orthorhombic and tetragonal phases to pseu-docubic phase with the doping level of La increasing. After the doping of La, grain growth is inhibited, ferroelectric-para-electric phase transition temperature (T_c) is decreased and the degree of diffuse phase transition is increased. The ferro-electricity 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 La~(3+) for (Ba_(0.85)Ca_(0.15))~(2+) because of the weakness or disappearance of coexistence of orthorhombic and tetragonal phases near room temperature. The (Ba_(0.85)Ca_(0.15))_(1-x)La_(2/3x)Ti_(0.90)Zr_(0.10)O_3 + 1 mol% MnO_2 ceramic with x = 0 exhibit the optimum piezoelectric properties: d_(33) = 277 pC/N and k_p = 30.3 %, respectively.