Jiang Xingxing, Wang Naizheng, Dong Liyuan, Molokeev Maxim S, Wang Shuaihua, Liu Youquan, Guo Shibin, Li Wei, Huang Rongjin, Wu Shaofan, Li Laifeng, Lin Zheshuai
Functional Crystals Lab, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
Mater Horiz. 2022 Aug 1;9(8):2207-2214. doi: 10.1039/d2mh00273f.
Negative and zero thermal expansion (NTE and ZTE) materials are widely adopted to eliminate the harmful effect from the "heat expansion and cool contraction" effect and frequently embrace novel fundamental physicochemical mechanisms. To date, the manipulation of NTE and ZTE materials has mainly been realized by chemical component regulation. Here, we propose another method by making use of the anisotropy of thermal expansion in noncubic single crystals, with maximal tunability from the integration of linear NTE, ZTE and positive thermal expansion (PTE). We demonstrate this concept in borate optical crystals of AEBO (AE = Ca or Sr) to make the light transmission temperature-independent by counterbalancing the thermal expansion and thermo-optics coefficient. We further reveal that such a unique thermal expansion behavior in AEBO arises from the synergetic thermal excitation of bond stretching in ionic [AEO] and rotation between covalent [BO] groups. This work has significant implications for understanding the thermal excitation of lattice vibrations in crystals and promoting the functionalization of anomalous thermal expansion materials.
负热膨胀和零热膨胀（NTE和ZTE）材料被广泛用于消除“热胀冷缩”效应的有害影响，并且常常涉及新颖的基本物理化学机制。迄今为止，NTE和ZTE材料的调控主要通过化学成分调节来实现。在此，我们提出了另一种方法，即利用非立方单晶中的热膨胀各向异性，通过线性NTE、ZTE和正热膨胀（PTE）的整合实现最大程度的可调性。我们在AEBO（AE = Ca或Sr）硼酸盐光学晶体中验证了这一概念，通过平衡热膨胀和热光系数使光传输与温度无关。我们进一步揭示，AEBO中这种独特的热膨胀行为源于离子型[AEO]中键拉伸的协同热激发以及共价型[BO]基团之间的旋转。这项工作对于理解晶体中晶格振动的热激发以及促进反常热膨胀材料的功能化具有重要意义。
