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 κL based on the temperature jump caused by TBs obstructed heat flow. These models provide the basis for developing robust and efficient thermoelectric materials.