Lawrence Berkeley National Laboratory

Low thermal conductivity of BaAb ₂ SnSe ₄ is measured, which can be attributed to the weakly-bonded Ag–Ag dimers.

Engineering the thermal properties in solids is important for both fundamental physics ( e.g. electric and phonon transport) and device applications ( e.g. thermal insulating coating, thermoelectrics). In this paper, we report low thermal transport properties of four selenide compounds (BaAg ₂ SnSe ₄ , BaCu ₂ GeSe ₄ , BaCu ₂ SnSe ₄ and SrCu ₂ GeSe ₄ ) with experimentally-measured thermal conductivity as low as 0.31 ± 0.03 W m ⁻¹ K ⁻¹ at 673 K for BaAg ₂ SnSe ₄ . Density functional theory calculations predict κ < 0.3 W m ⁻¹ K ⁻¹ for BaAg ₂ SnSe ₄ due to scattering from weakly-bonded Ag–Ag dimers. Defect calculations suggest that achieving high hole doping levels in these materials could be challenging due to monovalent ( e.g. , Ag) interstitials acting as hole killers, resulting in overall low electrical conductivity in these compounds.