Dielectric, ferroelectric and field-induced strain behavior of K_(0.5)Na_(0.5)NbO_3-modified Bi_(0.5)(Na_(0.78)K_(0.22))_(0.5)TiO_3 lead-free ceramics

摘要

Lead-free piezoelectric (1 — x)Bi_(0.5)(Na_(0.78)K_(0.22))_(0.5)TiO_3-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 (ε_m) decreased. The addition of KNN destabilized the ferroelectric order of BNKT ceramics exhibiting a pinchcd-typc 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.