Fabrication and piezoelectric properties of (K0.5Na0.5)NbO3-based ceramics doped with Bi-perovskites

The effect of the addition of Bi-perovskites to (Li_0.04K_0.52Na_0.44)(Nb_0.84Ta_0.1Sb_0.06)O₃ (LF4) ceramics was studied to improve the properties of lead-free piezoelectrics. Ceramics with the relative density above 96% were successfully obtained by a solid state reaction process. The changes in lattice parameters indicated that the vacancy concentration at the A-site of the perovskite structure and the tetragonality of the crystal lattice were reduced with the addition of BiFeO₃. The addition of BiFeO₃ changed the LF4 to a soft-piezoelectric. The electrical insulation of the LF4 was improved with the addition of BiFeO₃, which made a full poling possible under high electric fields. A few mol% of BiFeO₃ was effective to improve the remanent polarization of the LF4 ceramics and a piezoelectric d₃₃ constant of about 358 pm/V was obtained in the 0.4 mol% doped ceramics.