Intrinsically Minimal Thermal Conductivity in Cubic I−V−VI2 Semiconductors

We report measurements of the thermal conductivity of high-quality crystals of the cubic $mathrm{I}mathrm{text{ensuremath{-}}}mathrm{V}mathrm{text{ensuremath{-}}}{mathrm{VI}}_{2}$ semiconductors ${mathrm{AgSbTe}}_{2}$ and ${mathrm{AgBiSe}}_{2}$. The thermal conductivity is temperature independent from 80 to 300 K at a value of approximately $0.70text{ }text{ }mathrm{W}/mathrm{mK}$. Heat conduction is dominated by the lattice term, which we show is limited by umklapp and normal phonon-phonon scattering processes to a value that corresponds to the minimum possible, where the phonon mean free path equals the interatomic distance. Minimum thermal conductivity in cubic $mathrm{I}mathrm{text{ensuremath{-}}}mathrm{V}mathrm{text{ensuremath{-}}}{mathrm{VI}}_{2}$ semiconductors is due to an extreme anharmonicity of the lattice vibrational spectrum that gives rise to a high Gr”uneisen parameter and strong phonon-phonon interactions. Members of this family of compounds are therefore most promising for thermoelectric applications, particularly as $p$-type materials.