Evolution of phase structure and giant strain at low driving fields in Bi-based lead-free incipient piezoelectrics

• Nb-doped BNBT–SZ ceramics were prepared by conventional solid state method.
• A giant normalized strain of 825 pm/V at 4 kV/mm was achieved.
• A large strain of 0.20% triggered at a relatively low field of 3 kV/mm.
• Highest strain obtained in BNT-based ceramics at such a low driving field.
• Ferroelectric to ergodic-relaxor phase transition occurred with Nb-doping.

Lead-free 0.99[(Bi0.5Na0.5)0.935Ba0.065Ti(1–x)NbxO3]–0.01SrZrO3 (BNBTNb100x–SZ, with Nb100x = 0–1) ceramics were prepared by the conventional mixed oxide route. X-ray diffraction and Raman scattering was utilized for the structural evolution of Nb-modified BNBT–SZ ceramics at average and short-scale localized structure. Temperature dependent dielectric properties showed ferroelectric–ergodic relaxor (FE–ER) transition in Nb-modified BNBT–SZ ceramics by producing a significant disruption of the long-range FE order. A giant normalized strain of 825 pm/V at 4 kV/mm was achieved at Nb1.0. Interestingly, at a relatively low applied field of 3 kV/mm, the Nb0.75 sample displayed a large electric field-induced strain (EFIS) response of 0.20%, which is highest value obtained in non-textured lead-free BNT-based ceramics at such low driving field. The structural distortion induced by doping and electric poling is correlated with the dielectric, ferroelectric and EFIS response, and the evolution of giant strain was ascribed to reversible field induced phase transition from ER–FE phase.

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