High Strain Response and Dielectric Properties of Bi1/2(Na0.78K0.22)1/2TiO3 Ceramics Doped with (Fe1/2Nb1/2)4+

Environmentally friendly piezoceramics Bi1/2(Na0.78K0.22)1/2Ti1-x(Fe1/2Nb1/2)xO3 (BNKT-FN) with FeNb (FN) ratios 0, 0.01, 0.02, 0.03 and 0.04 were synthesized via conventional solid-state reaction (CSSR). X-ray diffraction (XRD) analysis revealed that the FN complexes were completely dissolved in BNKT perovskite and the structural transition occurred from ferroelectric to relaxor state. The average grain sizes for x = 0, 0.01, 0.02, 0.03 and 0.04 were found to be 0.34 μm, 0.35 μm, 0.38 μm, 0.32 μm and 0.39 μm, respectively. It is observed that the grain size increased with the addition of FN, except for x = 0.03. The coercive field (Ec) and remnant polarization (Pr) of the system were decreased with increasing FN concentration and the highest Ec of 21.1 kV/cm and Pr of 29.2 μC/cm2 were noted for the base pure sample. In addition, the increase of FN content steadily broadened the dielectric anomaly at maximum dielectric constant temperature (Tm) in the BNKT-FN system. Consequently, unipolar normalized strain (Smax/Emax) was found to be enhanced monotonically achieving the highest value of around 654 pm/V (x = 0.02). These properties suggest that the investigated system could be a promising eco-friendly candidate for piezoelectric actuators and many other applications requiring high piezoelectric induced strain.