  We perform a high-throughput screening on phonon-mediated superconductivity
in ternary metal diboride structure with alkali, alkaline earth, and transition
metals. We find 17 ground states and 78 low-energy metastable phases. From fast
calculations of zone-center electron-phonon coupling, 43 compounds are revealed
to show electron-phonon coupling strength higher than that of MgB2. An
anti-correlation between energetic stability and electron-phonon coupling
strength is identified. We suggest two phases, i.e., Li3ZrB8 and Ca3YB8, to be
synthesized, which show reasonable energetic stability and superconducting
critical temperature.
