Theoretical studies on the strong phonon coherence in the type-5 penta-PbN8 sheet

Abstract

Inspired by the recent prediction of the stable penta-PbN₈ sheet, which realizes the mathematical model known as the type-5 pentagonal tiling pattern from the perspective of materials, we have explored its lattice thermal transport properties. Using first-principles calculations combined with the unified theory of thermal transport, we found that penta-PbN₈ possesses a low lattice thermal conductivity at room temperature with the value of 4.61 (5.23) W m⁻¹ K⁻¹ along the x(y)-direction and a dominant contribution of 3.32 (3.84) W m⁻¹ K⁻¹ from the corresponding phonon coherence. Based on a detailed study of the phonon dispersion, phonon–phonon scattering, and phonon coherence, we further demonstrated that the intrinsic strong anharmonicity caused by the unique atomic configuration with a buckled geometry and the large atomic mass differences in this type-5 penta-sheet significantly enhance the phonon scattering rate and phonon coherent lifetime, leading to low lattice thermal conductivity with a high proportion contributed by phonon coherence. Our study demonstrates that the diverse patterns in the penta-sheet family lead to rich features in phonon transport.