Semiconducting and Superconducting Mo-Ga Frameworks: Total Energy and Chemical Bonding

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 Tc = 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.