Fig. 2: Evolution of the stripy twin domain in GeSe under tensile loading and unloading strains.
From: Reversible shuffle twinning yields anisotropic tensile superelasticity in ceramic GeSe
a, High-resolution TEM snapshots taken along the <001> zone axis of the GeSe sample (sample B) under the loading and unloading strains. b,c, The FFT pattern (c) of the HRTEM image (b) corresponding to the region containing a twin domain. The scale bar in the FFT pattern is 5 nm−1. d–f, HAADF-STEM image (d), corresponding structural model (e) and simulated HAADF-STEM image (f) of a twin boundary. Here HRTEM and HAADF-STEM images of sample B, obtained via the PTP method, reveal twinning behaviour in the first cycle and atomic-resolution details of twinning structure formed in the subsequent cycle. g, Top: the energy profile of the twinning transformation pathway at different strain values. Arrows indicate the energy saddle points. The inset schematic illustrates the bond breakage and formation during twinning/detwinning in GeSe under uniaxial strain along the zigzag direction. Here the energy of the initial state is set as zero energy. Bottom: the corresponding distance changes of Ge1–Se1 and Ge1–Se2 atoms during the twinning process. d1 and d2 represent the bond lengths of Ge1–Se1 and Ge1–Se2, respectively. The bond length for GeSe without strain is calculated to be 2.60 Å. h, The final energy, twinning barrier and detwinning barrier as a function of strain.
