Origin of the high lattice thermal conductivity of beryllium among the elemental metals

From first-principles calculations we reveal that beryllium has the highest lattice thermal conductivity (${\ensuremath{\kappa}}_{\mathtt{ph}}$) among all elemental metals at room temperature. Specifically, the calculated ${\ensuremath{\kappa}}_{\mathtt{ph}}$ is 104(125) ${\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, contributing $\ensuremath{\sim}50$% (60%) to the total thermal conductivity along the $a(c$) axis, contrary to the common belief that ${\ensuremath{\kappa}}_{\mathtt{ph}}$ is negligible in metals. ${\ensuremath{\kappa}}_{\mathtt{ph}}$ reach the maxima with values of $\ensuremath{\sim}210 {\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$ for both axes at 125 K. The unusually high ${\ensuremath{\kappa}}_{\mathtt{ph}}$ is related to the weak three-phonon scattering with a dip in the intermediate-frequency region, which arises from its high Debye temperature and bunched phonon dispersions. Another consequence of the weak three-phonon scattering is the strong effect of higher-order (fourth-order) anharmonicity and electron-phonon coupling on ${\ensuremath{\kappa}}_{\mathtt{ph}}$. We also predict that ${\ensuremath{\kappa}}_{\mathtt{ph}}$ increases significantly with pressure, mainly due to the weakening of four-phonon scattering, and consequently exceeds the electronic contribution ${\ensuremath{\kappa}}_{\mathtt{e}}$ by more than one third in both axes at 20 GPa. Our work deepens the understanding of thermal transport in metals, and can benefit the search of metals with high thermal conductivity.