In₄Pb_5.5Sb₅S₁₉: A Stable Quaternary Chalcogenide with Low Thermal Conductivity

Transition-metal-based chalcogenides are a series of intriguing semiconductors with applications spanning various fields because of their rich structure and numerous functionalities. This paper reports the crystal structure and basic physical properties of a new quaternary chalcogenide In4Pb5.5Sb5S19. The crystal structure of In4Pb5.5Sb5S19 was determined by both powder and single-crystal X-ray diffraction techniques. In4Pb5.5Sb5S19 crystallizes in the monoclinic system with I2/m space group, and the structure parameters are a = 26.483 Å, b = 3.899 Å, c = 32.696 Å, and β = 111.86°. The polyhedral double chains of Sb3+ and Sb/Pb2+ as the main cations are parallel to each other and form a Jamesonite-like mineral structure through the short chain links of the distorted In, Pb, and Sb polyhedron. In4Pb5.5Sb5S19 exhibits a moderate experimental band gap of 1.42 eV, indicating its potential for application in solar cells and photocatalysis. In addition, In4Pb5.5Sb5S19 exhibits good ambient stability, and differential scanning calorimetry tests demonstrate that it is stable up to 892 K in a nitrogen atmosphere. Moreover, In4Pb5.5Sb5S19 exhibits extremely low thermal conductivity (0.438-0.478 W m-1 K-1 ranging from 300 to 700 K) compared with binary counterparts such as PbS and In2S3. Future chemical manipulation via elemental doping or defect engineering may make the title compound a potential thermoelectric or thermal insulating material.