Temperature-Insensitive Large Strain of (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3-(K0.5Na0.5)NbO3 Lead-Free Piezoceramics

The effect of (K0.5Na0.5)NbO3 (KNN) addition on the ferroelectric behavior of (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3 (BNT-BKT) lead-free piezoceramics was investigated. Polarization and strain hysteresis loops indicate that the ferroelectric order is disrupted significantly with the addition of KNN as a replacement for BNT and the destabilization of the ferroelectric order is accompanied by an enhancement of the unipolar strain, which peaks at a value of similar to 0.48% (corresponding to a large signal d(33) of similar to 600 pm/V) at 1 mol% KNN content. This strain was analyzed as derived from an electrostrictive effect at lower electric fields and a converse piezoelectric effect at higher electric fields. By limiting the electric driving field to exclude the contribution from the converse piezoelectric effect, a temperature-insensitive large-field d(33) of similar to 250 pm/V up to 200 degrees C was achieved.