The structural origin of extraordinary plasticity in polycrystalline semiconductors with low symmetry

Ductile polycrystals are usually metals with high-symmetry structures that provide multiple slip systems to coordinate the synergetic deformation of adjacent grains. However, while exceptional plasticity was recently discovered in a series of low-symmetry semiconductors, their deformation mechanism remains mysterious. Here, taking monoclinic Ag₄SSe as a case study, we show that the inherent high-symmetry anion sublattice with a quasi-body-centered cubic (bcc) structure is embedded in the monoclinic matrix. This, coupled with the highly diffuse cations, results in multiple slip systems and is responsible for the superior plasticity as normally unexpected in low-symmetry structures. We observe typical slip systems conforming with those of the bcc structure by experiment. This finding clarifies the deformation mechanism of Ag₂S-based low-symmetry semiconductors and sheds light on future exploration of ductile inorganic semiconductors.