Origin of composition-insensitive electrostrictive coefficient and continuous decrease of domain wall density in (1-x)NaNbO3-xBaTiO3 lead-free ferroelectrics

Perovskite ferroelectric ceramics with giant electrostrictive coefficient Q33 have attracted much attention due to their high strain response with ultralow hysteresis. In this work, the electrostrictive properties as well as domain morphology of the lead-free (1−x)NaNbO3-xBaTiO3 (NN-xBT) (0.10 ≤ x ≤ 0.27) system were investigated systematically. A composition-insensitive Q33 of 0.0406 m4/C2 is identified in the NN-xBT ceramics (0.15 ≤ x ≤ 0.27). An ab initio computation indicates that transverse Q12 would play an important role in understanding of the composition-insensitive Q33. Furthermore, distinctively banding domains and inhomogeneous distribution of nanodomains were observed in NN-xBT by piezoresponse force microscopy. A continuous decrease of domain wall density was identified with respect to the increase of x. This study would not only deepen our understanding of the origin of composition-insensitive Q33 in NN-BT and other related systems, but also provide a way to enhance the Q33, i.e., by forming the solid solutions with end members, which possess high Q12.