Unveiling the microscopic origin of anomalous thermal conductivity in amorphous carbon

ZT Zhang and J Luo and HA Wu and H Ma and YB Zhu, SCIENCE ADVANCES, 11, eadx5007 (2025).

DOI: 10.1126/sciadv.adx5007

Amorphous carbons pose fundamental questions, including incomprehensible phase transformations, microtopology identification, and origins of anomalous properties. However, transition pathways from low-density, high-sp2 structures to high-density, high-sp3 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 sp3/sp2 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.

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