Gao Qilong, Jiao Yixin, Sprenger Jan A P, Finze Maik, Sanson Andrea, Sun Qiang, Liang Erjun, Chen Jun
Key Laboratory of Materials Physics of Ministry of Education, School of Physics, Zhengzhou University, Zhengzhou 450001, China.
ZhongYuan Critical Metals Laboratory, Zhengzhou University, Zhengzhou 450001, China.
J Am Chem Soc. 2024 Aug 7;146(31):21710-21720. doi: 10.1021/jacs.4c05808. Epub 2024 Jul 25.
Exploring the relationship between thermal expansion and structural complexity is a challenging topic in the study of modern materials where volume stability is required. This work reports a new family of negative thermal expansion (NTE) materials, AM(CN) with A = Li and Na and M = B, Al, Ga, and In. Here, the compounds of LiB(CN) and NaB(CN) were only synthesized; others were purely computationally studied. A critical role of nonrigid vibrational modes and spiral acoustical modes has been identified in NaB(CN). This understanding has been exploited to design the colossal NTE materials of NaM(CN) (M = Al, Ga, In). A joint study involving synchrotron X-ray diffraction, Raman spectroscopy, and first-principles calculations has been conducted to investigate the thermal expansion mechanism. It has been found that the A atoms can either increase the symmetry of the crystal structure, inducing stronger NTE, or lower the crystal symmetry, thus resulting in positive thermal expansion. Conversely, the M-site atoms do not affect the crystal structure. However, as the radius of the M atoms increases, the ionic nature of the C-M bonds strengthens and the CN vibrations become more flexible, thereby enhancing the NTE behavior. This study provides new insights to aid in the discovery and design of novel NTE materials and the control of thermal expansion.
在需要体积稳定性的现代材料研究中，探索热膨胀与结构复杂性之间的关系是一个具有挑战性的课题。这项工作报道了一类新型的负热膨胀（NTE）材料，即A为Li和Na且M为B、Al、Ga和In的AM(CN)。在此，仅合成了LiB(CN)和NaB(CN)化合物；其他化合物则仅通过计算进行了研究。已确定非刚性振动模式和螺旋声子模式在NaB(CN)中起关键作用。基于这一认识，已设计出NaM(CN)（M = Al、Ga、In）的巨负热膨胀材料。开展了一项联合研究，涉及同步辐射X射线衍射、拉曼光谱和第一性原理计算，以研究热膨胀机制。研究发现，A原子既可以增加晶体结构的对称性，诱导更强的负热膨胀，也可以降低晶体对称性，从而导致正热膨胀。相反，M位原子不影响晶体结构。然而，随着M原子半径的增加，C - M键的离子性增强，CN振动变得更加灵活，从而增强了负热膨胀行为。这项研究为新型负热膨胀材料的发现与设计以及热膨胀的控制提供了新的见解。
