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 ~ 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.