Semiconducting and superconducting Mo–Ga frameworks: total energy and chemical bonding

Abstract

Endohedral Ga clusters filled with Mo are building units of homologous Mo₈Ga₄₁, Mo₆Ga₃₁, and Mo₄Ga₂₁-based compounds – a rich family of strongly coupled superconductors showing hints of multigap superconductivity. The crystal structures of Mo₈Ga₄₁, Mo₆Ga₃₁, and Mo₄Ga₂₁ can be derived from the simple cubic lattice of PtHg₄-type MoGa₄. Here, we construct the superconducting Mo₄Ga₂₁ structure type starting from the electron-precise MoGa₄ cubic framework and report the electronic structures of MoGa₄, Mo₄Ga₂₁, Mo₄Ga₂₀Sb, and Mo₄Ga₂₀Te. The valence electron count of 18 e⁻ per Mo atom, which defines the optimum band filling in MoGa₄, separates the bonding and antibonding Mo–Ga interactions within the Mo₄Ga₂₁ structure type. Total energy calculations reveal that Mo₄Ga₂₀Sb and Mo₄Ga₂₀Te superconductors with critical temperatures of T_c = 6.6 K and 4.6 K, respectively, are favorable in energy with respect to the parent MoGa₄ cubic framework, where semiconducting properties are expected.