Destabilization of the ferroelectric order in Na0.5Bi0.5TiO3–6 wt% BaTiO3 ceramics through doping

One of the most promising candidates to replace lead-based compounds in actuator applications are Na0.5Bi0.5TiO3 (NBT)-based materials. K0.5Na0.5NbO3 (KNN)-modified NBT-BaTiO3 (NBT-BT) solid solutions exhibit giant large-signal strain–electric-field coefficients (Smax/Emax) exceeding 500 pm V−1. However, despite the promising properties of the ceramics reported in the literature, the synthesis of these materials remains challenging, leaving gaps in the understanding of the synthesis-property relationship. In this contribution, we investigate the microstructure and the electrical properties while changing the composition to destabilize the ferroelectric order in the material, which is the key to achieve large strain response. Measurements of dielectric and ferroelectric properties reveal that Na- or Ti-deficiency or excess of Bi decrease the ferroelectric-to-relaxor transition temperature and remnant polarization, indicating a destabilization of the ferroelectric order. Additionally, the use of KNO3 instead of K2CO3 as the potassium source in KNN results in an additional destabilizing effect on the ferroelectric order, which can be attributed to better incorporation of K+ into the perovskite structure. The results identify the key aspects of the synthesis of NBT-BT-KNN ceramics to obtain high Smax/Emax values.