Insight into vertical piezoelectric characteristics regulated thermal transport in van der Waals two-dimensional materials

The urgent demand of extreme (ultra-high/low) thermal conductivity materials is triggered by the high-power device, where exploring the theories and mechanisms of regulating thermal transport properties plays a key role. Herein, we elaborately investigate the effect of vertical (out-of-plane) piezoelectric characteristics on thermal transport, which is historically undiscovered. The different stacking-order (AA and AB) bilayer boron nitride (Bi-BN) in two-dimensional (2D) materials are selected as study cases. By performing state-of- the-art first-principles calculations, it is found that the polarization charge along the out-of-plane orientation ascends significantly with the increasing piezoelectric response in AB stacked Bi-BN (Bi-BN-AB) followed by the enhanced interlayer B-N atomic interactions. Consequently, the amplitude of phonon anharmonicity in Bi-BN-AB increases larger than that in the AA stacked Bi-BN (Bi-BN- AA), resulting in the dramatic weakening of the thermal conductivity by 20.34% under 18% strain. Our research reveals the significant role of the vertical (out-of-plane) piezoelectric characteristic in regulating thermal transport and provides new insight into accurately exploring the thermal transport performance of 2D van der Waals materials.