BaPb2Ga6Q12 (Q = S, Se): The first two compounds in the Ba–Pb-Ga-Q (Q = S, Se) systems

Abstract

The first two metal chalcogenides in the systems Ba–Pb-Ga-Q (Q = S, Se), namely BaPb₂Ga₆Q₁₂ (Q = S, Se), have been synthesized successfully via high-temperature solid-state reaction for the first time. They are isotypic and crystallize in the cubic space group Pa $\bar{3}$. Their three-dimensional frameworks are composed of corner-sharing Ga₃Q₉ (Q = S, Se) clusters which are made up of corner-sharing GaQ₄ (Q = S, Se) tetrahedra, PbQ₆ polyhedron and charge-balanced Ba²⁺ cations. From the UV–Vis–NIR diffuse reflectance spectra, it can be seen that the band gaps of BaPb₂Ga₆S₁₂ and BaPb₂Ga₆Se₁₂ are 2.60 eV and 2.0 eV, respectively. Thermal analyses show that BaPbGa₆Q₁₂ melt incongruently but have good thermal stability (1079 K for the sulfide and 1068 K for the selenide). Electronic structures and densities of states are investigated by first-principles calculations, and the results indicate that BaPb₂Ga₆Q₁₂ have indirect band gaps and their band gaps are mainly determined by Pb²⁺ cations and GaQ₄ tetrahedra.