Superconductivity in (Sr, Ba)B3Si3 clathrate compounds

Extensive research has been conducted to explore sodalite clathrate compounds of groups 3 and 4, with various metal guest atoms, following the successful synthesis of XB3C3 (X = Sr, La) compounds. While the requirement for synthesis is still challenging. Here, using an efficient structure prediction method coupled with density functional theory, we investigated the stable phases and properties of MB3Si3 (M = Mg, Ca, Sr, and Ba) at both ambient and high pressure. Remarkably, our predictions uncover the presence of Pm-3n-SrB3Si3 and Pm-3n-BaB3Si3 compounds with clathrate-based sodalite structures, wherein the framework is composed of covalent B-Si bonds. Notably, compared to the elemental phases, BaB3Si3 has a negative enthalpy of formation at 1 atm, indicating the synthesis might be realized under conditions of ambient pressure. Additionally, according to calculations using electron–phonon coupling, the Pm-3n phase of SrB3Si3 and BaB3Si3 both have critical temperatures of 6.0 K and 3.9 K at atmospheric pressure, respectively, which show superconducting properties. Our research contributes to the understanding of Type-VII clathrate structure of alkaline-earth metal borosilicide that exhibit superconductivity.