Nanotwinning induced decreased lattice thermal conductivity of high temperature thermoelectric boron subphosphide (B₁₂P₂) from deep learning potential simulations

Highlights

• A deep learning potential for B₁₂P₂ crystal is developed.

• The phonon transport is greatly suppressed by twin boundaries in B₁₂P₂ crystal.

• The elastic moduli aren't significantly changed after introducing twin boundaries.

Abstract

Boron subphosphide (B₁₂P₂) is a promising high temperature thermoelectric material due to its good thermal stability, and chemical inertness. However, the thermal properties of B₁₂P₂ have not been well revealed so far. Here, we first develop a deep learning potential for B₁₂P₂ based on quantum mechanical calculations. Then the isotropic lattice thermal conductivity (LTC) of crystalline B₁₂P₂ is predicted to be 39.70 ± 4.38 W/m⋅K from molecular dynamics simulations using this deep learning potential. The LTC exhibits the relationship of κ_L∼1/T in the temperature range of 300 ∼ 1500 K. More important, a twin boundary strategy is proposed to reduce the LTC of B₁₂P₂. In nanotwinned B₁₂P₂, the phonon transport in all directions is significantly suppressed by twin boundaries (TBs) with the isotropic LTC of 15.85 ± 2.70 W/m⋅K, especially in the direction normal to the TB plane. The decrease of vibrational density of states and phonon participation ratio due to TBs' phonon scattering is the main reason of the low LTC in nanotwinned B₁₂P₂. In addition, the elastic moduli (B and G) of B₁₂P₂ crystal decrease by less than 7% after inducing TBs, which suggests that the mechanical properties are not significantly affected by TBs. Overall, this work enriches our understanding of the thermal properties of B₁₂P₂ and offers a promising approach, i.e., introducing TBs, to design high-performance thermoelectric materials.