Pressure-induced boron clathrates with ambient-pressure superconductivity

Element B in binary metal borides forms various polymetric configurations due to its electron-deficient nature. Here we predict a new pressure-stabilized boron clathrate structure, LaB8, that is recoverable under ambient conditions. Crystal structure searches and first-principles calculations predict a series of thermodynamically stable La-B compounds at high pressures. Besides known LaB4 and LaB6 compounds, trigonal LaB8 is predicted to be thermodynamically stable above 70 GPa. Its B atoms construct face-sharing B-26 cages, each surrounding a central La atom. The compound can be recovered to ambient conditions with the B-26 cages well preserved. Electron-phonon coupling calculations suggest that it is potentially superconducting with an estimated T-c of 5 K at 70 GPa, which increases to similar to 20 K at ambient pressure. The enhanced T-c is attributed to the increased B-derived electronic density of states at the Fermi level and to the softened E-u mode related to vibration of the B-26 cages.

Automated summary

Through crystal structure searches and first-principles calculations, a new pressure-stabilized boron clathrate structure, LaB8, is predicted to be thermodynamically stable above 70 GPa. The compound can be recovered under ambient conditions and is potentially superconducting, with an estimated T-c of 5 K at 70 GPa increasing to around 20 K at ambient pressure. This enhanced superconductivity is attributed to the increased B-derived electronic density of states at the Fermi level and the softened E-u mode related to vibration of the B-26 cages.