Plastic/ductile inorganic van der Waals (vdW) thermoelectric semiconductors offer transformative advantages for high-performance flexible thermoelectric devices, which can displace the self-charge system of wearable electronics. However, the chemical origin of their plasticity remains unclear. Here, it is reported that the exceptionally large plastic strain of the bulk SnSe₂ crystal results from its polytype conversion under an external force. The SnSe₂ single crystal consists of a large-period polytype with 18R low-symmetry structure rather than the trigonal and hexagonal-phase that are frequently observed in the polycrystalline specimen. In situ applied pressure to the specimen drives a phase transition from low to high-symmetry, that is, from 18R to 4H, and finally to 2H-SnSe₂. First principle calculations corroborate that the dynamic phase transition is a pressure-activated process and only 15 MPa pressure erases their energy gaps, consistent with experimentally measured strain–stress curves. This dynamic phase transition results in superior and near isotropic plasticity along the direction parallel and perpendicular to the cleavage plane.

中文翻译：

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动态相变导致热电 SnSe2 单晶具有非凡的塑性变形能力

塑料/延展性无机范德华 (vdW) 热电半导体为高性能柔性热电器件提供了变革性优势，可以取代可穿戴电子产品的自充电系统。然而，其可塑性的化学起源仍不清楚。据报道，块状SnSe ₂晶体异常大的塑性应变是由于其在外力作用下的多型转变所致。SnSe ₂单晶由具有18R低对称结构的大周期多型体组成，而不是在多晶样品中经常观察到的三角相和六方相。对样品施加原位压力会驱动从低对称性到高对称性的相变，即从 18R 到 4H，最后到 2H-SnSe₂ . 第一原理计算证实，动态相变是一个压力激活的过程，只有 15 MPa 的压力就能消除它们的能隙，这与实验测量的应变-应力曲线一致。这种动态相变导致沿着平行和垂直于解理面的方向具有优异且接近各向同性的塑性。