La BH8 : Towards high-Tc low-pressure superconductivity in ternary superhydrides

In the last five years a large number of new high-temperature superconductors have been predicted and experimentally discovered among hydrogen-rich crystals, at pressures, which are way too high to meet any practical application. In this paper, we report the computational prediction of a hydride superconductor, La BH₈ , with a T_c of 126 K at a pressure of 50 GPa, thermodynamically stable above 100 GPa, and dynamically stable down to 40 GPa, an unprecedentedly low pressure for high-T_c hydrides. La BH₈ can be seen as a ternary sodalite-like hydride, in which a metallic hydrogen sublattice is stabilized by the chemical pressure exerted by the La-B scaffolding, which achieves a more efficient packing of atoms than in binary sodalite hydrides thanks to the combination of elements with very different sizes. The proposed aufbau principle may be exploited to design high-T_c hydrides that survive at even lower pressure, through a careful choice of the elements.