Ultra-low lattice thermal conductivity in two-dimensional ZrTe5, HfTe5, and ZrHfTe10.

Employing first-principles calculations, self-consistent phonon theory, and the Boltzmann transport equation, we systematically investigate the lattice thermal transport properties of two-dimensional transition metal pentatellurides, including ZrTe5, HfTe5, and the ordered substitutional derivative ZrHfTe10. Our results reveal that the monolayer structures exhibit significantly reduced thermal conductivity when compared to their bulk counterparts. In particular, the cross-substitution of Zr/Hf atoms in monolayer ZrHfTe10 further enhances phonon anharmonic scattering by breaking structural symmetry and introducing elemental inhomogeneity. This enhancement induces notable phonon softening, reduced group velocities and higher phonon scattering rates at high temperature. As a result, monolayer ZrHfTe10 achieved an ultra-low lattice thermal conductivity of 2.87 W m-1 K-1 at room temperature, which is 17% (19%) lower than that of ZrTe5 (HfTe5). This study elucidates the synergistic modulation of thermal transport by dimensional confinement and compositional engineering, providing a theoretical foundation for the application of transition metal pentatellurides in thermal management.