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 In₄Pb_5.5Sb₅S₁₉. The crystal structure of In₄Pb_5.5Sb₅S₁₉ was determined by both powder and single-crystal X-ray diffraction techniques. In₄Pb_5.5Sb₅S₁₉ 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. In₄Pb_5.5Sb₅S₁₉ exhibits a moderate experimental band gap of 1.42 eV, indicating its potential for application in solar cells and photocatalysis. In addition, In₄Pb_5.5Sb₅S₁₉ exhibits good ambient stability, and differential scanning calorimetry tests demonstrate that it is stable up to 892 K in a nitrogen atmosphere. Moreover, In₄Pb_5.5Sb₅S₁₉ 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.