Two-dimensional single-layer BiOI nanosheets: Lattice thermal conductivity and phonon transport mechanism

This paper conducts an in-depth study of the lattice thermal conductivity and phonon transport properties of two-dimensional single-layer BiOI nanosheets. Combining first-principles calculations and Boltzmann transport theory, we systematically analyzed the phonon group velocity, Greeneisen parameter, three-phonon scattering rate, and scattering phase space of single-layer BiOI nanosheets at different temperatures and other key physical quantities. Calculation results show that the intrinsic lattice thermal conductivity of single-layer BiOI nanosheets at room temperature was approximately 4.71 W<middle dot>m(-1)<middle dot>K-1, significantly decreasing to 1.74 W<middle dot>m(-1)<middle dot>K-1, as the temperature increased to 800 K. The out-of-plane acoustic (ZA), transverse acoustic (TA), and longitudinal acoustic (LA) phonon modes contribute almost equally to the lattice thermal conductivity in the studied temperature range. The physical origin of low lattice thermal conductivity is attributed to low phonon group velocity, strong phonon-phonon scattering process, and low Debye temperature. In addition, we also explored the electronic structure and confirmed that the single-layer BiOI nanosheet has semiconductor properties and an indirect band gap of approximately 2.16 eV.