In situ synchrotron X-ray diffraction for actuation in sodium bismuth titanate relaxor ferroelectrics.

Sodium bismuth titanate-based (NBT-based) ergodic relaxor ferroelectrics have garnered significant attention for actuator applications due to their fully reversible electrostrain behavior. In general, it is believed that the electrostain originates from three main aspects: electric field-induced phase transitions with volume changes, non-180° domain switching, and lattice stretching without volume changes. However, the individual contribution remains to be quantitatively understood. In this work, in situ synchrotron X-ray diffraction in different integration directions is performed to quantify the contributions of electric field-induced phase transition and non-180° domain switching to electrostrain for NBT-based ergodic relaxor ferroelectrics under external electric field. The calculated total strain is 0.41%, in which 0.038% results from volume strain related to the electric field-induced phase transition, while 0.127% is due to induced ferroelastic domain structures. The rest 0.245% is attributed to lattice stretching. The volume change caused directly by phase transition has a very limited effect on electrostrain, while the indirect effect of phase transition on strain (the domain switching of the ferroelectric phase) has a relatively large effect on electrostrain. This innovative work offers theoretical insights for optimizing NBT-based relaxor ferroelectric materials for actuator applications, contributing to better control of electrostrain.