Mechanical softening of thermoelectric semiconductor Mg_2Si from nanotwinning

Abstract

Nanotwinning exhibits strengthening effects in many metals, semiconductors, and ceramics. However, we show from ab-initio calculations that nanotwins significantly decrease the strength of thermoelectric semiconductor Mg_2Si. The theoretical shear strength of nanotwinned Mg_2Si is found to be 0.93 GPa, much lower than that (6.88 GPa) of flawless Mg_2Si. Stretching the Mg-Si bond under deformation leads to the structural softening and failure of flawless Mg_2Si. While in nanotwinned Mg_2Si, the Mg-Si bond at the twin boundary (TB) is expanded to accommodate the structural misfit, weakening the TB rigidity and leading to the low ideal shear strength.

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