A nanotwin-based physical model for designing robust layered bismuth telluride thermoelectric semiconductor

The inherent weak van der Waals (vdW) interaction of Bi₂Te₃ semiconductors results in inferior strength, limiting their micromachining into urgently needed thermoelectric microdevices for 5G and the Internet of Things. Here, we report the effect of twin boundary (TB) spacing λ and orientation θ on strength. A physical model of the inverse proportional function between λ and shear strength is developed based on the TBs hindered vdW layer slippage. Then, we establish a sine function model of θ and shear strength based on the bond strain characteristics. Notably, the shear strength (1.64 GPa) of nanotwinned Bi₂Te₃ with λ = 2.42 nm and θ = 80.54° is 2.5 times higher than that of the flawless single crystal. Moreover, we build a function model between λ and the lattice thermal conductivity κ_L based on the temperature jump caused by TBs obstructed heat flow. These models provide the basis for developing robust and efficient thermoelectric materials.