High electric field-induced relaxor to ferroelectric phase transition in (Bi 0.5 Na 0.3 K 0.2 )TiO 3 –SrTiO 3 –(Ba 0.8 Ca 0.2 )TiO 3 Pb-free piezoelectric ceramic

Electric field-induced phase transitions are the most important characteristics of relaxor, ferroelectric and anti-ferroelectric materials, while the origin of this behavior in relaxor materials is poorly understood. In the present study, an electric field dependent on the structural, the dielectric, and the ferroelectric properties of 0.7[(Bi 0.5 Na 0.3 K 0.2 )TiO 3 ]-0.2SrTiO 3 -0.1(Ba 0.8 Ca 0.2 )TiO 3 ](BNKT-ST-BCT) relaxor ceramic has been performed. In the absence of the poling effect, a normal transition from relaxor to para-electric phase occurs at Burns temperature T B ~ 100 °C. However, at high electric field of the poling ( E = 50 kV/cm, T = 80 °C, t = 15 min), two-step transitions were found: the first one is a ferroelectric–relaxor transition at depolarization temperature (T d ~ 100 °C), and the second one is a relaxor–para-electric transition at higher temperatures (T B = 150 °C). Increasing the Burns temperature by applying field is due to the residual polarization effect. At lower electric field ( E < 15 kV/cm), a relaxor behavior with pinched P–E loop was observed caused by man intrinsic effect, where ST induced phase transition from a non-polar incommensurate to a polar commensurately modulated crystal structure. The sample exhibited a relaxor–ferroelectric phase transition as manifested by a change of the domain structure from polar nano-region PNR with short-range order (SRO) to coarse ferroelectric Lamellar domain with long-range order (LRO) at high applied cycle of electric field above the domain switching field. The change of the domain structure is contributed to domain growth caused by domain wall displacement effect. These results were confirmed by XRD of poled ceramic at different poling conditions ( E = 0.0–58 kV/cm) near the phase transition temperature.