Unveiling the microscopic origin of anomalous thermal conductivity in amorphous carbon
2025-06-06
Amorphous carbons pose fundamental questions, including incomprehensible phase transformations, microtopology identification, and origins of anomalous properties. However, transition pathways from low-density, high-sp 2 structures to high-density, high-sp 3 forms remain poorly understood, within which thermodynamical behaviors are practically unexplored. Here, we investigated the phase transition and thermal transport properties of a recently reported amorphous carbon phase, amorphous diaphite (a-DG). The continuous transformation pathway of a-DG is characterized by distinctive heterogeneous microstructural evolutions across a wide density range. We observed anomalous thermal conductivities in a-DG, which initially decrease and then increase with the density and sp 3 /sp 2 ratio, deviating markedly from previously reported trends. This anomaly originates from changes in phonon mean free path and phonon lifetime at the medium-frequency range (7 to 30 terahertz), dictated by the unique two-stage microtopological transition. These findings challenge conventional views of thermal conductivity in amorphous carbons, and, in a wider context, our mechanistic understanding provides fundamental insights into phase transitions and thermodynamic mechanisms of other amorphous materials.