Structural evolution and bonding features of electron deficient copper chalcogenides

Abstract

A group of otherwise covalent ternary copper sulfides and selenides demonstrate metallic p-type conductivity and Pauli paramagnetism, which distinguishes them from semiconducting counterparts built up from the same elements. This difference originates from the electron deficiency delocalized over structural units of copper chalcogenides. Considering the significant technological importance of chalcogenide materials, we surveyed ternary copper sulfides and selenides with alkali and alkaline earth cations to provide insights into their crystal structures and transport properties. We found that the compositions and structures of many chalcogenides can be rationalized based on two 2D nets with honeycomb and square lattice net topologies, respectively. We have also shown how simple electron-orbital counts can be applied to metallic chalcogenides with formally charge unbalanced compositions and demonstrated that these compounds are indeed electron deficient. In agreement with experimental data and DFT calculations, such phases demonstrate metallic p-type conductivity.