Temperature‐Insensitive Large Strain of (Bi _1/2 Na _1/2 )TiO ₃ –(Bi _1/2 K _1/2 )TiO ₃ –(K _0.5 Na _0.5 )NbO ₃ Lead‐Free Piezoceramics

Abstract

The effect of (K 0.5 Na 0.5 )NbO 3 (KNN) addition on the ferroelectric behavior of (Bi 1/2 Na 1/2 )TiO 3 –(Bi 1/2 K 1/2 )TiO 3 (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 ∼0.48% (corresponding to a large signal d 33 of ∼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 ∼250 pm/V up to 200°C was achieved.