Enhancing phonon thermal conductivity in the semiconducting electride Sc₂C via interstitial lattice electrons

Sc₂C is a recently synthesized novel semiconducting electride characterized by electrons residing in well-defined interstitial lattice sites rather than being localized within atoms. While extensive research has been carried out to explore its novel properties, such as reversible, high-capacity hydrogen storage and electrochemical storage, existing literature lacks a precise characterization of its electronic states and thermal transport mechanism, which is a critical prerequisite for a comprehensive understanding of its electronic properties. In this work, we investigate the phonon thermal conductivity (κ) of Sc₂C by incorporating the Hubbard U correction to accurately describe its electronic structure using first-principles calculations and the linearized Boltzmann transport equation. We find that the Hubbard U correction significantly enhances κ compared to calculations performed without it. Moreover, we unveil a key competition mechanism: while the Hubbard U correction slightly suppresses four-phonon (4ph) lifetime, it drastically increases the three-phonon (3ph) lifetime. The competition between 3ph and 4ph scattering ultimately leads to the enhanced thermal conductivity. Additionally, the in-plane κ exhibits high sensitivity to boundary scattering at length scales below 200 nm. This work clarifies the role of electronic correlation in modulating the thermal transport properties of electride-based nanodevices.