  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
work, we report the computational prediction of a hydride superconductor,
LaBH$_{8}$, 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. LaBH$_{8}$ can be seen as a ternary
sodalite-like hydride, in which a metallic hydrogen sublattice is stabilized by
the chemical pressure exerted by the guest elements. The combination of two
elements with different atomic sizes in LaBH$_{8}$ realizes a more efficient
packing of atoms than in binary sodalite hydrides. A suitable choice of
elements may be exploited to further reduce the stabilization pressure to
ambient conditions.
