Composition‐ and Temperature‐Dependent Large Strain in (1− <i>x</i> )(0.8Bi _0.5 Na _0.5 TiO ₃ –0.2Bi _0.5 K _0.5 TiO ₃ )– <i>x</i> NaNbO ₃ Ceramics

Abstract

Ternary solid solutions of (1 − x )(0.8Bi 0.5 Na 0.5 TiO 3 –0.2Bi 0.5 K 0.5 TiO 3 )– x NaNbO 3 (BNKT– x NN) lead‐free piezoceramics were fabricated using a conventional solid‐state reaction method. Pure BNKT composition exhibited an electric‐field‐induced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric‐to‐relaxor temperature T F‐R shifted down below room temperature as the substitution of NN , a compositionally induced nonergodic‐to‐ergodic relaxor transition was presented, which featured the pinched‐shape polarization and sprout‐shape strain hysteresis loops. A strain value of ~0.445% (under a driving field of 55 kV/cm) with large normalized strain of ~810 pm/V was obtained for the composition of BNKT –0.04 NN , and the large strain was attributed to the reversible electric‐field‐induced transition between ergodic relaxor and ferroelectric phase.