负热膨胀材料为解决热膨胀问题带来了契机，然而大多数负热膨胀化合物属于陶瓷或粉体材料，因力学性能差、导热系数低等固有缺陷限制了其实际应用。金属材料具有良好应用价值，目前已知的具有负热膨胀性的金属体系却十分稀少，并且其热膨胀性调控较难。本项目拟选取高居里温度RE2(Fe,Co)17（RE=稀土元素）基化合物作为研究对象，通过RE和Fe/Co位置的取代制备出几种热膨胀性可调的稀土基金属材料。利用同步辐射、中子衍射等手段研究晶体结构和磁结构；采用磁性/非磁性元素取代，进行热膨胀改性，研究稀土4f磁矩对负热膨胀性的特殊贡献；通过施加原位磁场，探索磁性对负热膨胀性的影响。研究结果将进一步深化对稀土磁性化合物热膨胀性的认识，为设计和开发具有“理想”热膨胀性的新型金属功能材料提供新的途径。

Negative thermal expansion (NTE) materials are likely to solve the problems caused by thermal stress. However, most NTE materials reported are in the forms of ceramics or powders, which have poor mechanical property and low thermal/electric conductivities, limiting their real applications. The metallic materials can effectively avoid such shortcomings, but very few NTE materials are found in metals and their thermal expansions are difficult to control. This project aims to search for metallic NTE materials in RE2(Fe,Co)17 –based intermetallic compounds which have high magnetic Curie temperatures, and to control their thermal expansions by chemical modifications. The crystal and magnetic structures will be analyzed with methods such as synchrotron radiation and neutron diffraction. The role of magnetism plays in NTE will be exploited by in-situ magnetic field experiment and the mechanism of NTE in RE2(Fe,Co)17 –based compounds will be further developed. The present study will be helpful in understanding the nature of rare earth-based magnetic compounds and pave ways for designing multifunctional materials with desirable thermal expansion property.