Addition of small amounts of BiFeO3 to (Li,K,Na)(Nb,Ta)O3 lead-free ceramics: Influence on phase structure, microstructure and piezoelectric properties

A small amount of BiFeO3 (BF) was incorporated into lead-free Li0.03(Na0.53K0.48)0.97Nb0.8Ta0.2O3 (LKNNT) piezoceramics for the purpose of property improvement via phase structure control. It was found that the addition of BF not only induced a series of phase transformations from orthorhombic to tetragonal and further to pseudocubic in LKNNT ceramics, but also enhanced its sintering densification behavior. Even tiny amount of BF addition down to 0.5 mol% could change the room-temperature phase structure from a dominant orthorhombic state to the coexistence of orthorhombic and tetragonal phases, resulting in peak piezoelectric properties of d33*∼340 pm/V, kp ∼ 47.0%. When the amount of BF was increased to 0.75 mol%, the tetragonal phase became dominant in the modified LKNNT ceramics, which exhibited excellent temperature stability, despite its slightly lowered piezoelectric coefficients.