Zhang Ying, Yao Mingguang, Du Mingrun, Yao Zhen, Wang Yan, Dong Jiajun, Yang Zhenxing, Sundqvist Bertil, Kováts Éva, Pekker Sándor, Liu Bingbing
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.
College of Science, Civil Aviation University of China, Tianjin 300300, China.
J Am Chem Soc. 2020 Apr 22;142(16):7584-7590. doi: 10.1021/jacs.0c01703. Epub 2020 Apr 14.
According to the laws of thermodynamics, materials normally exhibit contraction or expansion along the directions of the applied pressure or tension. Here, we show that a man-made cocrystal of a metallofullerene and highly energetic cubane, with strained sp bonding, may exhibit an anomalous negative compressibility. In this cocrystal, the freely rotating fullerene ScN@C acts as a structural building block while static cubane molecules fill the lattice interstitial sites. Under high pressure, ScN@C keeps stable and preserves the crystalline framework of the materials, while the cubane undergoes a progressive configurational transformation above 6.5 GPa, probably promoted by charge transfer from fullerene to cubane. A further configurational change of the cubane into a low-density configuration at higher pressure results in an anomalous pressure-driven lattice expansion of the cocrystal (∼1.8% volume expansion). Such unusual negative compressibility has previously only been predicted by theory and suggested to appear in mechanical metamaterials.
根据热力学定律，材料通常会沿外加压力或拉力的方向表现出收缩或膨胀。在此，我们表明，一种具有应变sp键的金属富勒烯与高能立方烷的人工共晶体可能表现出反常的负压缩性。在这种共晶体中，自由旋转的富勒烯ScN@C充当结构构建单元，而静态的立方烷分子填充晶格间隙位置。在高压下，ScN@C保持稳定并保留材料的晶体框架，而立方烷在6.5 GPa以上会发生渐进的构型转变，这可能是由富勒烯向立方烷的电荷转移所促进的。在更高压力下，立方烷进一步转变为低密度构型，导致共晶体出现反常的压力驱动晶格膨胀（体积膨胀约1.8%）。这种不寻常的负压缩性此前仅在理论上被预测，并被认为会出现在机械超材料中。
