Temperature-driven n-p conduction type switching without structural transition in a Cu-rich chalcogenide, NaCu5S3

Functional Alkali Metal-Based Ternary Chalcogenides: Design, Properties, and Opportunities

The search for novel materials has recently brought research attention to alkali metal-based chalcogenides (ABZ) as a new class of semiconducting inorganic materials. Various theoretical and computational studies have highlighted many compositions of this class as ideal functional materials for application in energy conversion and storage devices. This Perspective discusses the expansive compositional landscape of ABZ compositions that inherently gives a wide spectrum of properties with great potential for application. In the present paper, we examine the technique of synthesizing this particular class of materials and explore their potential for compositional engineering in order to manipulate key functional properties. This study presents the notable findings that have been documented thus far in addition to outlining the potential avenues for implementation and the associated challenges they present. By fulfilling the sustainability requirements of being relativity earth-abundant, environmentally benign, and biocompatible, we anticipate a promising future for alkali metal chalcogenides. Through this Perspective, we aim to inspire continued research on this emerging class of materials, thereby enabling forthcoming breakthroughs in the realms of photovoltaics, thermoelectrics, and energy storage.

In4Pb5.5Sb5S19: 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.