金属基负热膨胀新化合物探索及机理研究

物质的热胀冷缩是自然界普遍现象，热膨胀系数不匹配对材料、航空航天、精密仪器等领域具有重要的影响。负热膨胀化合物为调控材料热膨胀性能提供了契机。本项目以金属基负热膨胀化合物为中心，围绕磁结构与晶格热收缩物性关联研究主线，通过化学元素替代、外场调控等途径增强磁性转变速率，以实现将常见的正热膨胀化合物转变为负热膨胀化合物的研究目标，进而探索和发展负热膨胀新体系。在具有急剧磁性转变特征的物质中开展负热膨胀新体系探索，如在具有强烈的磁有序-无序转变、局域磁矩减少、变磁性转变、短程磁有序等磁性转变的物质。以不同类型磁性负热膨胀体系为研究对象，如反铁磁Mn3Ge、铁磁(Hf,Nb)Fe2、亚铁磁TbCo2和具有倾斜磁结构的La(Fe,Al)13等，借助同步辐射和中子散射大科学装置以及第一性原理计算等方法，揭示磁性负热膨胀的复杂机理。该项目将有利于拓展金属基负热膨胀新体系，加深对磁性负热膨胀机理的理解。

It is a common phenomenon in nature that compounds expand on heating and contract on cooling. The mismatch of thermal expansion coefficient has an important influence on materials, aerospace, precision instruments and other fields. Negative thermal expansion (NTE) materials provide an opportunity to control the thermal expansion performance. In this project, metal-based NTE compounds are taken as the center, and the relationship between magnetic structure and lattice thermal shrinkage properties is studied. The rate of magnetic transition is enhanced through chemical element substitution and external field, so as to realize the research goal of transforming common positive thermal expansion compounds into NTE compounds, and then explore and develop new NTE systems. Exploring new NTE systems in materials with sharp magnetic transition, such as materials with strong magnetic order-disorder transition, the reduction of local magnetic moment, metamagnetic transition, short-range magnetic order transition and so on. Different types of magnetic NTE systems, such as antiferromagnetic Mn3Ge, ferromagnetic (Hf,Nb)Fe2, ferrimagnetic TbCo2 and La(Fe,Al)13 with canting magnetic structure, are studied. The complex mechanism of magnetic NTE is revealed by means of synchrotron radiation, neutron scattering and first principles calculations. The project will help to expand the new metal-based NTE system, and deepen the understanding of magnetic NTE mechanism.