Gao Qilong, Wang Jiaqi, Sanson Andrea, Sun Qiang, Liang Erjun, Xing Xianran, Chen Jun
International Laboratory for Quantum Functional Materials of Henan, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China.
Beijing Advanced Innovation Center for Materials Genome Engineering and School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China.
J Am Chem Soc. 2020 Apr 15;142(15):6935-6939. doi: 10.1021/jacs.0c02188. Epub 2020 Apr 6.
Exploring isotropic negative thermal expansion (NTE) compounds is interesting, but remains challenging. Here, a new concept of "average atomic volume" is proposed to find new NTE open-framework materials. According to this guidance, two NTE compounds, AgB(CN) and CuB(CN), have been discovered, of which AgB(CN) exhibits a large NTE over a wide temperature range (α = -40 × 10 K, 100-600 K). The analysis by extended X-ray absorption fine structure spectroscopy and first-principles calculation indicate that (i) the NTE driving force comes from the transverse vibrations of bridge chain atoms of C and N, corresponding to the low-frequency phonon modes; and (ii) the same transverse vibration direction of C and N atoms is a key factor for the occurrence of strong NTE in AgB(CN). The present concept of "average atomic volume" can be a simple parameter to explore new NTE compounds especially in those open-framework materials.
探索各向同性负热膨胀（NTE）化合物很有趣，但仍具有挑战性。在此，提出了“平均原子体积”这一新概念以寻找新型NTE开放框架材料。根据这一指导原则，已发现了两种NTE化合物，即AgB(CN)和CuB(CN)，其中AgB(CN)在很宽的温度范围内表现出较大的NTE（α = -40×10⁻⁶ K⁻¹，100 - 600 K）。通过扩展X射线吸收精细结构光谱和第一性原理计算分析表明：（i）NTE驱动力来自C和N桥链原子的横向振动，对应于低频声子模式；（ii）C和N原子相同的横向振动方向是AgB(CN)中出现强NTE的关键因素。“平均原子体积”这一当前概念可以作为一个简单参数来探索新型NTE化合物，特别是在那些开放框架材料中。
