High-throughput structure searches for ambient-pressure superconductors in boron-carbon clathrates

Boron–carbon (B–C) clathrates have attracted much attention in recent years due to their excellent sp3 hybridized B–C covalent bonds and distinctive electronic properties. Here, we conduct systematic high-throughput structural searches for ambient-pressure superconductors in B–C clathrates. Twenty-one stable X2B8C4 clathrates are identified, among which superconductivity is found in X2B8C4 (X = Rb, Ca, Sr, Ba, La, and Ce) clathrates with superconducting transition temperatures of 34, 21, 17, 16, 13, and 10 K, respectively. The calculated results indicate that the superconductivities of main-group and transition metal-doped B–C clathrates are influenced by the amount of charge transferred from the metal to the B–C frameworks and the metallicities of the guest metal atoms. The high Tc value of the Rb2B8C4 superconductor originates from the strong metallicity and large atomic radius of the Rb atom, which squeezes the B–C cages and strengthens the electron–phonon coupling (EPC) interactions, thereby enhancing superconductivity. The present results enrich the databases of B–C clathrate superconductors and offer a viable strategy for design and synthesis of high-temperature superconductors at ambient pressure.