Atomic and electronic structures of thallium-based III-V-VI₂ ternary chalcogenides: Ab initio calculations

The atomic and electronic structures of III-V-VI₂ ternary chalcogenides (III=Tl, V=Sb and Bi, and VI=Te, Se, and S) have been studied using ab initio electronic structure calculations. Most of these compounds are found to take rhombohedral structures as their lowest energy structures (except for TlSbS₂, which takes a triclinic structure), in agreement with experiments. There is a disagreement between theory and experiment in the case of TlSbSe₂, wherein our calculations identify a rhombohedral structure (as yet hypothetical), which has lower energy than a monoclinic one (given by experiment). Band-gap formation in these ternaries are controlled by a highly directional hybridization between the cation (Sb, Bi), anion (S, Se, Te), and Tl p states, and the electronic structure near the Fermi level is sensitive to the ordering on the cation sublattice.