Superelastic ferroelectric micropillar with large hysteresis and super-durability

Hysteresis and durability are generally on the opposite sides of a trade-off for superelastic materials. We herein break this trade-off and report that BaTiO ₃ (BT) micropillars present size-dependent superelasticity and possess simultaneous large hysteresis and super-durability, sustaining up to 10 ⁸ superelastic cycles without functional degradation and structural failure. TEM results reveal that the as-fabricated BT pillars are composed of inner BT crystal part and surface BT amorphous layer. In addition, it is found that after high temperature annealing, the BT pillar with cross sectional side length d of 2 µm loses superelasticity. Based on these results, a model was developed to explain the size dependent behavior of BT pillars by considering the constitutive behavior difference of BT crystal and BT in amorphous phase, and their interaction during compressive stress loading and unloading. The super-durability was attributed to the small ferroelastic switching stress, which are much smaller than the dislocation nucleation activation stress and the compression strength of BT pillars, and the moderate mismatch stress between different ferroelectric variants as well as the stress relaxation by the high surface area of the small volume BT pillar. These discoveries enable ferroelectric micropillars many promising applications such as microdampers, and also provide significant insight into developing superelastic materials with enhanced durability.