Dielectric and electromechanical properties of LiNbO₃-modified (BiNa)TiO₃-(BaCa)TiO₃ lead-free piezoceramics

The dielectric and electromechanical properties of LiNbO₃-modified (1-x) [0.91Na_0.5Bi_0.5TiO₃-0.09Ba_0.70Ca_0.30TiO₃]-xLiNbO₃ (abbreviated as (BiNa)TiO₃-(BaCa)TiO₃-LN) lead-free piezoceramics were investigated. The electrical properties revealed that the addition of LiNbO₃ (LN) induces a phase transition from a non-ergodic relaxor to an ergodic relaxor in the (BiNa)TiO₃-(BaCa)TiO₃-LN system. A large electrostrain of ∼0.418% with a normalized strain of ∼690 pm V^-1 at 6 kV mm^-1 was observed at the coexistence of the non-ergodic relaxor and ergodic relaxor phases for LN 0.020, where a field-assisted reversible phase transition between metastable ferroelectric and stable ergodic relaxor phases occurs. Subsequently, a gradual enhancement in the temperature stability of the dielectric constant was observed. At 3 mol.% LN, a nearly constant temperature and a frequency-invariant permittivity of ϵ_r ∼ 3300 over a broad temperature range of 147 °C-306 °C was observed along with small losses from room temperature up to 400 °C.