Two-dimensional ferroelasticity in van der Waals β’-In2Se3

Abstract

Two-dimensional (2D) materials exhibit remarkable mechanical properties, enabling their applications as flexible and stretchable ultrathin devices. As the origin of several extraordinary mechanical behaviors, ferroelasticity has also been predicted theoretically in 2D materials, but so far lacks experimental validation and investigation. Here, we present the experimental demonstration of 2D ferroelasticity in both exfoliated and chemical-vapor-deposited β’-In2Se3 down to few-layer thickness. We identify quantitatively 2D spontaneous strain originating from in-plane antiferroelectric distortion, using both atomic-resolution electron microscopy and in situ X-ray diffraction. The symmetry-equivalent strain orientations give rise to three domain variants separated by 60° and 120° domain walls (DWs). Mechanical switching between these ferroelastic domains is achieved under ≤0.5% external strain, demonstrating the feasibility to tailor the antiferroelectric polar structure as well as DW patterns through mechanical stimuli. The detailed domain switching mechanism through both DW propagation and domain nucleation is unraveled, and the effects of 3D stacking on such 2D ferroelasticity are also discussed. The observed 2D ferroelasticity here should be widely available in 2D materials with anisotropic lattice distortion, including the 1T’ transition metal dichalcogenides with Peierls distortion and 2D ferroelectrics such as the SnTe family, rendering tantalizing potential to tune 2D functionalities through strain or DW engineering.

Structural Phase Transition and In-Situ Energy Storage Pathway in Nonpolar Materials: A Review

“…Benefiting from the antiparallel arrangement of electric dipoles within sublattices, null polarization is obtained on the unit cell scale. Typical AFE systems include PbZrO 3 , AgNbO 3 , NaNbO 3 , HfO 2 [64][65][66][67][68][69][70][71][72] and recently reported 2D van der Waals AFE β'-In 2 Se 3 [73,74]. From the perspective of lattice dynamics, the emergence of antiferroelectricity is a consequence of competing lattice instabilities [10,11], which are manifested by delicate structural orders [66,75].…”

Intercalation-driven ferroelectric-to-ferroelastic conversion in a layered hybrid perovskite crystal

“…Angle-resolved polarized optical microscopy images are shown in Figs. 3b–d and S9 ; the intensity contrast is caused by the changing orientation of the optical axes of the ferroelastic domain relative to the polarized light direction, thus allowing the spontaneous strain direction in each ferroelastic domain to be determined 45 , 46 . Based on this, we can deduce that the strain axis has C 3V symmetry, with three equivalent strain axes that are 120° apart.…”

“…Meanwhile, newly nucleated domains B are created. The expansion of B domain can be explained by the fact that its spontaneous strain direction may be aligned at a smaller angle to the direction of the applied stress 46 . After removing the external bending stress, a reversible switching from bright A domain to dark B domain occurs (Fig.…”

Ferroelastic–Ferroelectric Multiferroicity in van der Waals Rhenium Dichalcogenides

“…The onset strain of domain reconstruction is ≈1%, which is much lower than that of other materials. [ 26 ] Second, the Raman shift shows hysteresis according to external strain owing to the energetically degenerated orientation states. Third, the plateau of the Raman shift is observed after the onset of domain reconstruction.…”