Low driving field-induced large strain in MnO2-modified 0.76Bi1/2Na1/2TiO3-0.24SrTiO3 lead-free piezoceramics

MnO2-modified 0.76Bi(1/2)Na(1/2)TiO(3)-0.24SrTiO(3) (BNT-24ST) lead-free piezoceramics were synthesized by a conventional solid-state method. The introduction of MnO2 influences the phase structure and increases the grain size. Increasing the MnO2 content shifts the ferroelectric-relaxor transition temperature to below room temperature. This leads to a transition from ferroelectric behavior to ergodic-relaxor behavior. A large electrostrain of 0.18% and a normalized strain (S-max/E-max) of 902 pm/V with an ultra-low driving field of 2 kV/mm are achieved for the 0.25 wt% MnO2 doped BNT-24ST. A temperature-insensitive S-max/E-max of above 610 pm/V from room temperature to 90 degrees C is achieved at 4 kV/mm. This is attributed to the modification by MnO2 and the low poling field. Excellent mechanical performance of Young's modulus E similar to 127.4 GPa and fracture toughness K-IC similar to 1.38 MPa.m(1/2) are also obtained, which are better than those reported for PZT-based ceramics. The results indicate the BNT-24ST with MnO2 ceramic is a promising candidate for piezoactuator applications. (C) 2020 Elsevier B.V. All rights reserved.