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.