Semiconducting layered technetium dichalcogenides: insights from first-principles

Abstract

The structures and properties of layered technetium dichalcogenides TcX₂ (X = S, Se, Te) have been investigated using density functional theory. The equilibrium structures of TcSe₂ and TcTe₂, adopting distorted Cd(OH)₂-type unit cells similar to TcS₂, are reported for the first time at the atomic level, along with their electronic properties. In contrast to previous X-ray diffraction analyses, calculations reveal that stoichiometric TcTe₂ is not isomorphous to the high-temperature monoclinic phase β-MoTe₂. All three compounds are found to be semiconductors with calculated band gaps of 0.9 eV for TcS₂, 0.8 eV for TcSe₂, and 0.3 eV for TcTe₂. The thermal properties of these TcX₂ compounds have also been predicted using phonon frequencies calculated with density functional perturbation theory.