Dielectric, ferroelectric and field induced strain properties of Nb-modified Pb-free 0.99Bi0.5(Na0.82K0.18)0.5TiO3–0.01LiSbO3 ceramics

• Nb-substituted Pb-free 0.99[Bi1/2(Na0.82K0.18)1/2TiO3]–0.01LiSbO3 (x = 0–0.05) ceramics were characterized.
• Single-phase ceramics formed for compositions with x ⩽ 0.025, showing its solubility limit.
• A large field induced strain (43%) was observed at d33∗ = 614 pm/V for the composition with x = 0.015.

The effect of Nb-substitution on the dielectric, electromechanical and piezoelectric properties of Pb-free 0.99[Bi1/2(Na0.82K0.18)1/2Ti1−xNbxO3]–0.01LiSbO3 (x = 0–0.05) piezoelectric ceramics has been investigated. X-ray diffraction analysis reveals the formation of single-phase perovskite structure with tetragonal symmetry for the compositions with x ⩽ 0.025. Both the dielectric constant and depolarization temperature decreased with an increase in Nb-content. Analysis of the electric-field-induced polarization and strain hysteresis loops indicated that Nb substitution disrupted the long range ferroelectric order of BNKT-LS ceramics. This degraded the remnant polarization, coercive field and piezoelectric coefficient d33 while the electric-field-induced strain increased (peaked at x = 0.015) to 0.43% corresponding to a normalized strain (d33∗) of 614 pm/V at a deriving field of 7 kV/mm. This abnormal strain enhancement may be attributed to the coexistence of ferroelectric (FE) and relaxor ferroelectric (RFE) phases.

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