Shibazaki Yuki, Kono Yoshio, Shen Guoyin
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, 980-8578, Sendai, Japan.
International Center for Young Scientists, National Institute for Materials Science, 1-1 Namiki, 305-0044, Tsukuba, Ibaraki, Japan.
Sci Rep. 2019 May 17;9(1):7531. doi: 10.1038/s41598-019-43954-5.
Amorphous diamond, formed by high-pressure compression of glassy carbon, is of interests for new carbon materials with unique properties such as high compressive strength. Previous studies attributed the ultrahigh strength of the compressed glassy carbon to structural transformation from graphite-like sp-bonded structure to diamond-like sp-bonded structure. However, there is no direct experimental determination of the bond structure of the compressed glassy carbon, because of experimental challenges. Here we succeeded to experimentally determine pair distribution functions of a glassy carbon at ultrahigh pressures up to 49.0 GPa by utilizing our recently developed double-stage large volume cell. Our results show that the C-C-C bond angle in the glassy carbon remains close to 120°, which is the ideal angle for the sp-bonded honey-comb structure, up to 49.0 GPa. Our data clearly indicate that the glassy carbon maintains graphite-like structure up to 49.0 GPa. In contrast, graphene interlayer distance decreases sharply with increasing pressure, approaching values of the second neighbor C-C distance above 31.4 GPa. Linkages between the graphene layers may be formed with such a short distance, but not in the form of tetrahedral sp bond. The unique structure of the compressed glassy carbon may be the key to the ultrahigh strength.
由玻璃态碳高压压缩形成的非晶金刚石，作为具有诸如高抗压强度等独特性能的新型碳材料而备受关注。先前的研究将压缩玻璃态碳的超高强度归因于从类石墨sp键合结构到类金刚石sp键合结构的结构转变。然而，由于实验上的挑战，目前尚无对压缩玻璃态碳键结构的直接实验测定。在此，我们利用最近开发的双级大体积细胞成功地通过实验测定了高达49.0吉帕超高压力下玻璃态碳的对分布函数。我们的结果表明，玻璃态碳中的C-C-C键角在高达49.0吉帕时仍接近120°，这是sp键合蜂窝结构的理想角度。我们的数据清楚地表明，玻璃态碳在高达49.0吉帕时保持类石墨结构。相比之下，石墨烯层间距离随着压力增加而急剧减小，在高于31.4吉帕时接近第二近邻C-C距离的值。石墨烯层之间的连接可能以如此短的距离形成，但不是以四面体sp键的形式。压缩玻璃态碳的独特结构可能是其超高强度的关键。
