Effect of lattice occupation behavior of Li⁺ cations on microstructure and electrical properties of (Bi_1/2Na_1/2)TiO₃-based lead-free piezoceramics

The multisite occupation of Li⁺ cations in perovskite structure of (Bi_1/2Na_1/2)TiO₃-based solid solution is investigated, which is rarely reported in previous studies. The multisite occupation in relation to the Li₂CO₃ doping level has been demonstrated with the aid of the microstructure and temperature-dependent conductivity analysis: As the addition of Li₂CO₃ is below 0.75 mol. %, the introduced Li⁺ cations precede to enter the A sites of the perovskite lattice to compensate for the A-site deficiency stemming from the high-temperature sintering process. Once the addition exceeds 0.75 mol. %, the excess Li⁺ cations will occupy B sites to substitute for Ti⁴⁺ and give rise to the generation of oxygen vacancies. The proposed multisite occupation behavior of Li⁺ cations and its derivative effects, involving the clamping effect or grain size effect, have made the piezo-/ferroelectric performances of the 0.85BNT–0.10BKT–0.05BT ceramics optimized at the Li₂CO₃ addition of 1.0 mol.%:d₃₃ = 163 pC/N, P_r = 40.9 μC/cm2.