【摘要】 负热膨胀（NTE）是一种反常的物理现象,已在合金和框架结构化合物等材料中被观察到,但NTE材料的种类仍然有限.本文合成了一种单轴NTE材料Zn（NCN）,该材料在c轴方向及在100～475 K下的热膨胀系数为-3.35×10^-6K^-1,而a轴和b轴方向则呈低热膨胀性,体积具有低的热膨胀系数[6.13×10^-6K^-1（100～475 K）].通过同步辐射X射线衍射、扩展X射线吸收精细结构和拉曼光谱等方法,研究了Zn（NCN）的NTE机理.结果表明,Zn—N键具有明显的横向振动,一些低频振动模Grüneisen参数为负值.直接的实验证据表明, N=C=N的横向振动以及准刚性ZnN4四面体的耦合旋转和扭摆导致了c轴方向的NTE.更多还原

【Abstract】 As an abnormal physical phenomenon,negative thermal expansion（NTE）has been observed in some materials like alloys and framework structure materials. However,the types of NTE materials are still limited. In this study,a uniaxial NTE material Zn（NCN）was synthesized. The coefficient of thermal expansion of the c-axis is-3.35×10^-6K^-1 of 100-475 K,while the a and b axes show low thermal expansion. The volume of Zn（NCN）has a low coefficient of thermal expansion(αvca. 6.13×10^-6K^-1 ,100-475 K). The NTE mechanism was revealed by joined methods of synchrotron X-ray diffraction,extended X-ray absorption fine structure spectroscopy,and Raman spectra. It is found that the Zn-N exhibits obvious transverse vibration. Some low frequency vibration modes show negative Grüneisen parameter. The direct experimental evidence reveals that the transverse vibration of N=C=N linkage and coupling rotation and twist of quasi rigid ZnN4tetrahedra result in the NTE in the c-axis.更多还原