Phase diagram and electrostrictive effect in BNT-based ceramics

In this work, phase diagram for the (Bi0.5Na0.5)TiO3-KNbO3-SrTiO3 ternary system has been constructed and analyzed based on macroscopic properties and structure analysis and pseudocubic (0.92−x)BNT-0.08KN-xST (0≤x≤0.07) ceramics have been fabricated and investigated. A morphotropic phase boundary between the ferroelectric rhombohedral and relaxor pseudocubic phases at around critical composition was proposed, resulting in large strain response. The polarization hysteresis loops, strain hysteresis loops and S-P2 curves demonstrate electrostrictive behavior of all studied samples. A very high electrostrictive strain (~0.148%) with a high electrostrictive coefficient Q11 of 0.0236 m4 C−2 is obtained for the 0.90BNT-0.08KN-0.02ST composition, which was entirely comparable to the well-known electrostrictive material Pb(Mg1/3Nb2/3 )O3 and attributed to the formation of relaxor pseudocubic phase developed by the SrTiO3 substitution. Meanwhile, the electrostrictive coefficient exhibited a highly temperature-insensitive behavior, indicating that the investigated system is suitable for high-precision positioning devices and solid-state actuators.