Ultralow thermal conductivity in the mixed-anion solid solution Sn2SbS2−xSexI3

Abstract

The mixed-anion compounds Sn₂SbS_2−xSe_xI₃ (x = 0, 0.2, 0.5) and Sn₂BiS₂I₃ were synthesized and characterized. Rietveld refinement, elemental analysis, and diffuse reflectance measurements indicate successful substitution of Se for S and potential for bandgap tunability. Thermal conductivity measurements reveal ultralow thermal conductivities as low as 0.22 W m⁻¹ K⁻¹ at 573 K within this family of compounds. Such exceptionally low thermal conductivities are anomalous when compared to the previously reported heavier Pb₂BiS₂I₃ (0.7 W m⁻¹ K⁻¹). Computational analysis in the form of electron localization function and Grüneisen parameter reveal Sn to be the most influential factor that controls the lattice thermal conductivity, due to its localized antibonding electrons and large contribution to structural anharmonicity.