Deformation twinning merits attention because of its intrinsic importance as a mode of energy dissipation in solids. Herein, through the atomistic electron microscopy observations, the size-dependent twinning mechanisms in refractory body-centered cubic molybdenum nanocrystals (NCs) under tensile loading are shown. Two distinct twinning mechanisms involving the nucleation of coherent and inclined twin boundaries (TBs) are uncovered in NCs with smaller (diameter < ≈5 nm) and larger (diameter > ≈5 nm) diameters, respectively. Interestingly, the ultrahigh pseudo-elastic strain of ≈41% in sub-5 nm-sized crystals is achieved through the reversible twinning mechanism. A typical TB cross-transition mechanism is found to accommodate the NC re-orientation during the pseudo-elastic deformation. More importantly, the effects of different types of TBs on the electrical conductivity based on the repeatable experimental measurements and first-principles calculations are quantified. These size-dependent mechanical and electrical properties may prove essential in advancing the design of next-generation flexible nanoelectronics.

中文翻译：

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钼纳米晶尺寸依赖变形孪晶介导的伪弹性和可变电导率

变形孪生值得关注，因为它作为固体能量耗散模式的内在重要性。在此，通过原子电子显微镜观察，显示了在拉伸载荷下难熔体心立方钼纳米晶体 (NCs) 中尺寸依赖性孪晶机制。在分别具有较小（直径 < ≈ 5 nm）和较大（直径 > ≈ 5 nm）直径的 NC 中，发现了两种不同的孪生机制，涉及相干和倾斜孪晶界 (TB) 的成核。有趣的是，亚 5 nm 尺寸晶体中 ≈41% 的超高伪弹性应变是通过可逆孪生机制实现的。发现了一种典型的 TB 交叉过渡机制，以适应伪弹性变形期间的 NC 重新定向。更重要的是，基于可重复的实验测量和第一性原理计算，量化了不同类型的 TB 对电导率的影响。这些与尺寸相关的机械和电气特性可能被证明对于推进下一代柔性纳米电子产品的设计至关重要。