Dielectric, ferroelectric and field-induced strain behavior of K0.5Na0.5NbO3-modified Bi0.5(Na0.78K0.22)0.5TiO3 lead-free ceramics

Abstract Lead-free piezoelectric (1 − x )Bi 0.5 (Na 0.78 K 0.22 ) 0.5 TiO 3 – x K 0.5 Na 0.5 NbO 3 (BNKT– x KNN, x = 0–0.10) ceramics were synthesized using a conventional, solid-state reaction method. The effect of KNN addition on BNKT ceramics was investigated through X-ray diffraction (XRD), dielectric, ferroelectric and electric field-induced strain characterizations. XRD revealed a pure perovskite phase with tetragonal symmetry in the studied composition range. As the KNN content increased, the depolarization temperature ( T d ) as well as maximum dielectric constant ( ɛ m ) decreased. The addition of KNN destabilized the ferroelectric order of BNKT ceramics exhibiting a pinched-type hysteresis loop with low remnant polarization (11 μC/cm 2 ) and small piezoelectric constant (27 pC/N) at 3 mol% KNN. As a result, at x = 0.03 a significant enhancement of 0.22% was observed in the electric field-induced strain, which corresponds to a normalized strain ( S max / E max ) of ∼434 pm/V. This enhancement is attributed to the coexistence of ferroelectric and non-polar phases at room temperature.