Thermal transport in amorphous materials involves a complex interplay between anharmonicity and atomic-scale dynamics, particularly across the glass transition. To elucidate the underlying mechanisms, we investigate the temperature dependence of thermal transport in amorphous ${\mathrm{Al}}_2{\mathrm{O}}_3$ by combining homogeneous nonequilibrium and equilibrium molecular dynamics (HNEMD and EMD) with the Wigner transport equation (WTE), complemented by structural and dynamical analyses. The thermal conductivity exhibits a significant nonmonotonic temperature dependence, increasing at low temperatures, showing a weak suppression in the glassy regime, and rising again above the glass transition temperature $T_g$. Below $T_g$, heat transport is primarily governed by vibrational excitations and is strongly modulated by anharmonic effects. The WTE framework further reveals that this behavior originates from a competition between two vibrational transport channels: population transport suppressed by anharmonic scattering, and coherence contributions enhanced by intermode coupling. Above $T_g$, strong atomic diffusion renders a purely vibrational description incomplete. EMD decomposition shows that atomic diffusion substantially enhances the kinetic contribution to heat transport. Meanwhile, strong anharmonic interactions give rise to a pronounced negative kinetic-potential cross correlation. This compensating effect, in turn, partially suppresses the rapid increase of the total thermal conductivity with temperature. Element- and coordination-resolved analyses further demonstrate that low-coordination oxygen species exhibit enhanced per-species dynamical activity, which plays a key role in strengthening the kinetic contribution to heat transport at high temperatures.

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• Glass transition
• Thermal transport
• Glasses
• Supercooled liquid
• Molecular dynamics