Field-induced strain behavior for potassium sodium bismuth titanate ceramics

Data are reported for the dielectric, piezoelectric, electrostrictive, and ferroelectric properties of potassium-substituted sodium bismuth titanate, [(K_xNa_1-x)_0.5Bi_0.5]TiO₃. For the morphotropic phase boundary composition x = 0.2, relaxor-type behavior was observed at room temperature with piezoelectric (effective d₃₃₃ = 325 ldr10^-12 m/V) and ferroelectric properties (P_R = 25 muC/cm², E_c = 30 kV/cm). A transition to a relatively frequency-independent, diffuse phase transformation region occurred with increasing temperature, with no remanent strain or coercive field. Above the transition temperature, the field-induced strain was consistent with contributions from elec-trostriction and field-induced piezoelectricity (M₃₃₃₃ = 1.9 ldr 10^-16 m²/V² and d₃₃₃ = 81ldr10^-12 m/V at 100degC). Information is given for the temperature dependence of properties, e.g., 0.14% strain induced at 50 kV/cm at 200degC. Higher potassium content x = 0.6 stabilized the ferroelectric piezoelectric region to temperatures above 200degC, with a relatively stable (d₃₃₃ = 150-145 ldr 10^-12 m/V between 25degC and 200degC. Pb-free KNBT ceramics appear competitive with PZT, especially for higher temperature electromechanical applications.