A new class of ion substitution to achieve high electrostrain under low electric field in BNT‐based ceramics

Abstract

AbstractFor Bi0.5Na0.5TiO3 (BNT)‐based materials, the effective way of composition modification to solve the drawback of considerable remanent strain (Srem) and achieve high electrostrain appeals intensive research interest, which often accompanies by a high electric field threshold to trigger the transition from ergodic relaxor (ER) state to ferroelectric (FE) state. Here, a unipolar electrostrain of 0.40% with the high normalized strain d33*(=Smax/Emax) of 793 pm/V under a low electric field of 5 kV/mm is firstly reported in rare‐earth Ce‐modified 0.935Bi0.5Na0.5TiO3–0.065BaTiO3 ceramics. Through the A‐ and B‐sites substitution with donor characteristic of multivalent Ce ion, two modification effects (i.e., compositional disorder and A‐site vacancy) are induced to weaken the A–O bonds and break the long‐range order. Microscopically, the proportion among three coexisted space groups (R3c, P4mm, and P4bm) changes in an opposite law when Ce concentration or poling electric field is served as variable, respectively. The domain size degrades after doping, but there still coexist small‐sized polar regions and labyrinth‐type domains in the optimal compound, wherein better reversibility is proved compared with undoped specimen from writing domain mode. As a result, the good reversibility and low electric field threshold (i.e., low‐energy barrier) to integrate relaxor state into FE state are ascribed to the coexistence of three phases and the coexistence of small‐sized polar regions and labyrinth‐type domains. This work not only enlarges the class of ion substitution other than the familiar substitution ions to achieve high electrostrain but also supplies a simple and propagable way to improve the relatively high electric field threshold through understanding the intrinsic mechanism of Ce ion.