Anisotropic electron–phonon coupling and thermal transport in layered quaternary hydrides

Abstract

Electron–phonon coupling (EPC) and anisotropic thermal transport properties in a series of layered quaternary hydrides XYZH (X = Ba, Sr; Y = Al, Ga; Z = Si, Ge) are systematically investigated via first-principles calculations. These compounds form covalent H–Y–Z layers separated by weakly bonded X atoms. Despite pronounced structural anisotropy, charge transport exhibits unexpectedly weak directional dependence. In contrast, the lattice thermal conductivity exhibits relatively weak anisotropy, with high-frequency hydrogen-dominated optical phonons making unexpectedly substantial contributions to cross-plane heat conduction. EPC strength is found to be highly sensitive to carrier type and composition, being strongest for p-type carriers in AlSi-based systems due to the high electronic density of states near the valence band maximum. Notably, p-type doping induces markedly stronger EPC than n-type doping, leading to a greater reduction in lattice thermal conductivity. This study unveils the unique vibrational and electron–phonon coupling mechanisms in these layered hydrides, providing critical insights for their potential applications in thermal management.