Ultrahigh Thermal Conductivity of θ -Phase Tantalum Nitride

Extracting long-lasting performance from electronic devices and improving their reliability through effective heat management requires good thermal conductors. Taking both three- and four-phonon scattering as well as electron-phonon and isotope scattering into account, we predict that semimetallic $\ensuremath{\theta}$-phase tantalum nitride ($\ensuremath{\theta}\text{\ensuremath{-}}\mathrm{TaN}$) has an ultrahigh thermal conductivity ($\ensuremath{\kappa}$), of 995 and $\text{820 }\mathrm{W}\text{ }{\mathrm{m}}^{\ensuremath{-}1}\text{ }{\mathrm{K}}^{\ensuremath{-}1}$ at room temperature along the $a$ and $c$ axes, respectively. Phonons are found to be the main heat carriers, and the high $\ensuremath{\kappa}$ hinges on a particular combination of factors: weak electron-phonon scattering, low isotopic mass disorder, and a large frequency gap between acoustic and optical phonon modes that, together with acoustic bunching, impedes three-phonon processes. On the other hand, four-phonon scattering is found to be significant. This study provides new insight into heat conduction in semimetallic solids and extends the search for high-$\ensuremath{\kappa}$ materials into the realms of semimetals and noncubic crystal structures.