Defects dipoles control strategy for temperature-insensitive piezoelectricity in the lead-free BiFeO₃-BaTiO₃ ceramics

The large and temperature-insensitive piezoelectric actuator coefficient (d(33)*) with small strain hysteresis and the enhanced piezoelectric sensor coefficient (d(33)) with high Curie temperature (T-C) are highly demanded in the real applications. The controlled design of defects engineering has been proved to be an effective way for the improvement of temperature strain stability (Delta d(33)*((T))) and reducing hysteresis (H-s) in piezoelectric ceramics. Two types of defect dipoles such as (Fe-Fe3+(2+)' -V-center dot center dot (O2)-) and (VBi3+''' -V-O2-(center dot center dot) ) are possible in the lead-free BiFeO3-BaTiO3 (BF-BT) ceramics that suppress their functional property. However, these defect dipoles can be inhibited in the Ba2+-site Sm3+-donor BF-BT engineered ceramics. Additionally, the valence and ionic radius difference of Sm3+ (1.24 angstrom) and Ba2+ (1.61 angstrom) becomes the origin of large lattice strain in the unit cell of BF-BT that leads to the maximum piezoelectric performance. Therefore, the enhanced d(33) (334 pC/N) and d(33)* (552 pm/V) with high T-C (454 degrees C) were obtained in the Ba2+-site Sm3+-donor BF-BT lead-free ceramics. Furthermore, the reduced H-s approximate to 18% and preferable temperature-insensitive piezoelectric strain, Delta d(33)*((T)) approximate to 10% in the temperature 25-125 C are highly encourageable in the lead-free ceramics. Hence, the defect dipoles controlling strategy helps to improve the functional properties and the concept presented here can be applied to design the lead-free piezoelectric material for real applications.