Crystal Structure Classification of Copper‐Based Sulfides as a Tool for the Design of Inorganic Functional Materials

Abstract

Research focusing on the interplay between structural features and transport properties of inorganic materials is of paramount importance for the identification, comprehension, and optimisation of functional materials. In this respect, Earth‐abundant copper sulfides have been receiving considerable attention from scientists as the urgency remains to discover and improve the efficiency of sustainable materials for energy applications. This proposed classification of copper sulfides, associated with p‐ and/or d‐block elements, is based on their crystallographic features and an analysis of their transport properties. It provides guidelines to help estimate some properties of new materials (type of main charge carriers, thermal conductivity, transport mechanisms, etc.) from consideration of only their chemical composition and crystal structure. The classification relies primarily on recent studies in the fields of thermoelectricity and photovoltaics as well as on crystal‐structure investigations.

Engineering Transport Properties in Interconnected Enargite‐Stannite Type Cu2+xMn1−xGeS4 Nanocomposites

“…Such low values are mainly attributed to their small grain sizes and their similar crystal structure. The values of 1.5–2 W m −1 K −1 at 700 K determined in Cu‐rich compounds ( x ≥ 0.3) are in agreement with the state‐of‐the‐art sphalerite derivative copper‐based sulfides [3] . The vibrational DOS of the tetragonal stannite‐type and orthorhombic enargite‐type phases, presented in Figure S14, exhibit similar features observed in other copper sulfides, [40, 42–44] notably including a low‐frequency manifold centered at about 2 THz (≈60 cm −1 ) involving mostly Cu displacement.…”

“…In contrast, the role of the structure and chemical bond on the thermoelectric properties of these materials is so far not really understood. A recent review of copper sulfides [3] shows that the thermoelectric properties of these systems are mainly observed for the sphalerite derivatives, while very little is known about the possible synthesis of thermoelectric wurtzite derivatives, in spite of the fact that, in both structural families, univalent copper exhibits the tetrahedral coordination and they differ only in the packing of such tetrahedra: fcc and hcp for sphalerite and wurtzite, respectively.…”

Engineering Transport Properties in Interconnected Enargite‐Stannite Type Cu2+xMn1−xGeS4 Nanocomposites

“…Such low values are mainly attributed to their small grain sizes and their similar crystal structure. The values of 1.5–2 W m −1 K −1 at 700 K determined in Cu‐rich compounds ( x ≥ 0.3) are in agreement with the state‐of‐the‐art sphalerite derivative copper‐based sulfides [3] . The vibrational DOS of the tetragonal stannite‐type and orthorhombic enargite‐type phases, presented in Figure S14, exhibit similar features observed in other copper sulfides, [40, 42–44] notably including a low‐frequency manifold centered at about 2 THz (≈60 cm −1 ) involving mostly Cu displacement.…”

RealizingzT>2 in Environment‐Friendly Monoclinic Cu2S—Tetragonal Cu1.96S Nano‐Phase Junctions for Thermoelectrics

“…Some Cu atoms are regular in bonding, and others show a pretty severe distortion in the triangle. The length of the Cu−S bond varies from 2.21 to 2.89 Å with an average of 2.33 Å [21] . As for tetragonal Cu 1.96 S, its unit cell is a = b =3.996 Å, c =11.287 Å, belonging to the space group of P 4 3 2 1 2 [19] .…”