Structure evolution and large strain response in BNT–BT lead-free piezoceramics modified with Bi(Ni0.5Ti0.5)O3

Abstract

The composition and temperature-dependent structure, phase stability, strain behavior, dielectric, ferroelectric (FE), piezoelectric, and pyroelectric properties of lead-free Bi(Ni0.5Ti0.5)O3(BNiT)–modified 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (BNT–BT–xBNiT, 0 ≤ x ≤ 0.06) have been systematically investigated. The correlation between ferroelectric-to-relaxor transition temperature TF-R and depolarization temperature Td was unraveled based on temperature-dependent the stability of electrically induced long-range ferroelectric order and piezoelectricity. The phase diagram was established and the relationship between the phase structure and the electrical properties of the BNT–BT–xBNiT system has been clarified. As the BNiT content increases, the destabilization of the FE order resulting in a degradation of the remanent polarization, coercive field, Td and TF-R, is accompanied by a large electric-field-induced strain of 0.35% at 60 kV/cm with normalized strain Smax/Emax = 590 pm/V at around critical composition of x = 0.035. The Raman-spectra analysis, macroscopic properties, thermal depolarization results, and temperature-dependent relationships of both polarization and strain manifested that the observed large strain for the investigated system is contributed by a reversible field-induced relaxor to FE phase transformation.