Zhang ZhongTing, Luo Jian, Wu HengAn, Ma Hao, Zhu YinBo
CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei 230027, China.
CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei 230027, China.
Sci Adv. 2025 Jun 6;11(23):eadx5007. 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-sp structures to high-density, high-sp 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/sp 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.
非晶碳带来了一些基本问题，包括难以理解的相变、微观拓扑结构识别以及异常性质的起源。然而，从低密度、高sp结构到高密度、高sp形式的转变途径仍知之甚少，其中热力学行为几乎未被探索。在此，我们研究了最近报道的一种非晶碳相——非晶透辉石（a-DG）的相变和热输运性质。a-DG的连续转变途径的特征是在很宽的密度范围内有独特的非均匀微观结构演变。我们在a-DG中观察到异常的热导率，其最初随密度和sp/sp比降低，然后升高，这与先前报道的趋势明显不同。这种异常源于中频范围（7至30太赫兹）声子平均自由程和声子寿命的变化，这是由独特的两阶段微观拓扑转变决定的。这些发现挑战了非晶碳中热导率的传统观点，并且在更广泛的背景下，我们的机理理解为其他非晶材料的相变和热力学机制提供了基本见解。
