The electronic contribution significantly
dominates thermal transport
for most pure metallic systems, while the phononic (lattice) contribution
remains relatively small. We report four metallic materials, namely
cubic BeCo, BeNi, BeRh, and BeHf, which are screened by our recent
deep learning approach from Open Quantum Materials Database, all possessing
large phonon bandgaps and phonon anomaly features. Employing first-principles
calculations to solve the phonon Boltzmann transport equation, we
report that at room temperature, the phononic thermal conductivity
of these Be–X compounds is exceptionally high, rivaling that
of diamond. Specifically, the thermal conductivities are 2117 W/mK
for BeCo, 2243 W/mK for BeNi, 2368 W/mK for BeRh, and 1600 W/mK for
BeHf. This remarkable thermal performance is attributed to the large
phonon bandgaps and phonon anomaly features present in these materials.
Furthermore, when electron–phonon coupling is accounted for,
the phononic thermal conductivities of the Be–X compounds experience
a reduction by approximately 2 orders of magnitude. Notably, BeHf
presents an exceptional case, with its phononic thermal conductivity
measured at 68 W/mK. This value is several times to an order of magnitude
higher than the typical range observed in most metals and metallic
systems, which generally lies between 2 and 18 W/mK. Quantitative
analysis of phonon lifetime, Eliashberg spectral function, and Fermi
surface show that the Be–X systems have strong electron–phonon
coupling which originates from their Fermi surface nesting. However,
the phonon anomalies of BeHf are shallower, which weakens the electron–phonon
coupling and results in the abnormally high phononic thermal conductivity
of BeHf. This research enhances our comprehension of various heat
conduction phenomena in crystals, particularly offering a method to
identify new materials with phonon-mediated thermal transport in metals
and metallic systems for innovative applications in the future.