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

Lead-free piezoelectric (1 - x)Bi-0.5(Na0.78K0.22)(0.5)TiO3-xK(0.5)Na(0.5)NbO(3) (BNKT-xKNN, 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 (epsilon(m)) decreased. The addition of KNN destabilized the ferroelectric order of BNKT ceramics exhibiting a pinched-type hysteresis loop with low remnant polarization (11 mu C/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 similar to 434 pm/V. This enhancement is attributed to the coexistence of ferroelectric and non-polar phases at room temperature. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.