Improvement in temperature stability and modified polymorphic phase transition of La-doped (Na_(0.52)K_(0.44)Li_(0.04)) Nb_(0.8)Ta_(0.2)O_3 lead-free piezoelectric ceramics

摘要

Lead-free ceramics (Na_(0.52)K_(0.44)Li_(0.04))_(1-3x)La_ xNb_(0.8)Ta_(0.2)O_3 (KNLNT-Lax, x = 0.00-125 mol%) were prepared by traditional method. The piezoelectric proprieties and the polymorphic phase transition behaviors around the room temperature were investigated. The results show that high density (ρ~95%) and outstanding piezoelectric performance (d_(33)≥200 pC/N, k_p≥40%) were obtained with 0.5-0.75 mol% La doping. By the research of temperature dependent ε_r, △f_c/f_(r20)·c and k_p, we acquired the extended and mild polymorphic phase transition region, and obvious improvement of temperature stability in - 50-80 ℃ with the maximum derivation d(△f_r/f_(r20) ·c)_(max) less than 2%, as the La doping content exceeds 0.5 mol%. The possible mechanism of enhanced properties and temperature stability was analyzed. Both excellent piezoelectric and temperature stability characteristics make the La-doped KNLNT ceramics feasible for practical applications.