Probing the intrinsic phonon transport properties of the SnTe thermoelectric material

Based on the Boltzmann transport theory combined with first-principles calculations, we analyze the lattice anharmonicity of SnTe and the respective contributions of the lattice thermal conductivity (κ_L) from six different phonon modes. The Grüneisen parameter (γ), three-phonon scattering phase space (SPS), phonon lifetime (τ), and phonon velocity (v) were obtained quantitatively. These calculations indicate that large τ with maximum value of 104 ps and high v of 4800 m/s for acoustic branches make the acoustic modes a major contributor to the high κ_L of SnTe (～78% for acoustic branches and ～22% for Optical branches). Further, the dependence of κ_L on phonon mean free path shows that designing nanostructures with characteristic length of less than 14.5 nm could be an effective way to decrease the κ_L. In addition, we employed high-temperature gradient directional solidification technique to grow the SnTe single crystal and the measured κ_L vaules of the single crystal match reasonably with the theoretical calculation results.