Orbitally Driven Anomalous Thermal Transport Under High Pressure in Gallium Nitride

ABSTRACT Extreme conditions such as high pressure offer opportunities for innovative materials design and applications. For over a century, studies on thermal transport in crystals under high hydrostatic pressure have shown that lattice thermal conductivity generally exhibits a monotonic increase with pressure. In this study, based on state‐of‐the‐art first‐principles calculations, we report that in wurtzite gallium nitride (GaN), the thermal conductivity exhibits a pressure‐driven nonmonotonic variation. Detailed analysis attributes the nonmonotonic variation to the competition between lattice anharmonicity and heat conduction channels (how often the phonons scatter with each other, revealing phonon transport pathways), and the pressure‐enhanced phonon anharmonicity dominates the decreasing thermal conductivity under high pressure exceeding 20 GPa. The examination of the electronic structures reveals that pressure alters orbital hybridizations and thus changes bonding polarization, leading to the pressure‐enhanced lattice anharmonicity. This work not only deepens understanding of the fundamental physical properties of materials under high pressure but also provides theoretical guidance for novel thermal management materials design.