RbB3Si3: An Alkali Metal Borosilicide that is Metastable and Superconducting at 1 atm

The stability, electronic structure, and potential superconductivity in AB3Si3 (A = Na, K, Rb, and Cs) compounds that assume a clathrate-based sodalite structure whose framework consists of covalent B–Si bonds are investigated via first-principles calculations. This structure type has recently been predicted in a number of high-temperature superconducting hydrides, but these are only stable under megabar pressures. Herein, we predict a novel superconducting phase, RbB3Si3, that could be synthesized under pressures that are smaller by a factor of 10, ∼10 GPa, and quenched to atmospheric conditions. Electron–phonon coupling calculations predict that RbB3Si3 possesses a superconducting critical temperature, Tc, of 14 K at 1 atm. The dynamic stability of RbB3Si3 and CsB3Si3 at ambient pressure can be explained by considering the chemical pressure exerted on the B–Si framework that is caused by the size effect of the alkali metal atom.