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

Abstract

The large and temperature-insensitive piezoelectric actuator coefficient (d33*) with small strain hysteresis and the enhanced piezoelectric sensor coefficient (d33) with high Curie temperature (TC) 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 (Δd33*(T)) and reducing hysteresis (Hs) in piezoelectric ceramics. Two types of defect dipoles such as (FeFe3+2+′ −VO2−••) and (VBi3+''' −VO2−••) 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 Å) and Ba2+ (1.61 Å) becomes the origin of large lattice strain in the unit cell of BF-BT that leads to the maximum piezoelectric performance. Therefore, the enhanced d33 (334 pC/N) and d33* (552 pm/V) with high TC (454 °C) were obtained in the Ba2+-site Sm3+-donor BF-BT lead-free ceramics. Furthermore, the reduced Hs ≈ 18% and preferable temperature-insensitive piezoelectric strain, Δd33*(T) ≈ 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.