Ultra-low thermal conductivity of AgBiS2 via Sb substitution as a scattering center for thermoelectric applications

AgBiS2 is a promising thermoelectric material, because of its environmentally compatible composition. In this study, a process of the solvothermal method followed by spark plasma sintering was applied to the preparation of AgBiS2 and AgBi1-xSbxS2 (x = 0.5-1) materials. The prepared samples were characterized by various techniques. The results revealed the significant and beneficial role of antimony-substituted sample (AgBi0.5Sb0.5S2). The multiphase of AgSbS2 (73.70%), Ag3SbS3 (22.59%), and Bi2S3 (3.71%) were found by Rietveld refinement technique. The optical properties showed the narrow direct bandgap of similar to 0.83 eV which can be helpful to transport the charge carriers easily. AgBiS2 and AgBi1-xSbxS2 (x = 0.5-1) have grain boundaries due to the presence of multiphase in the samples. The numerous interfaces and grain boundaries were known as a disordered arrangement of atoms, which remarkably enhanced the phonon scattering. It leads to low thermal conductivity of 0.21 Wm(-1) K-1 at 333 K in AgBi0.5Sb0.5S2 sample; it has the phases such as cubic-AgSbS2 (73.70%), rhombohedral-Ag3SbS3 (22.59%), and orthorhombic-Bi2S3 (3.71%). The plausible reason for low thermal conductivity was predicted as the occurrence of phonon scattering mechanism at grain boundaries of the multiphases.