压力场驱动下反钙钛矿结构Mn3Cu1-xAxN(C) (A=Ge, Sn)化合物中巨相变熵—巨压热效应的研究

反钙钛矿化合物中一些材料具有大的相变熵，如果把这些巨大的相变熵转换为热效应，在固态制冷技术方面将有广阔应用前景。反钙钛矿化合物的相变熵中由反常晶格变化引起的晶格熵占据了绝大部分，其余部分几乎都是磁相变熵。这些材料晶格熵与负热膨胀性质相关联，而负热膨胀又和反铁磁结构相关联，应用磁场很难影响反铁磁相进而引导出晶格熵。针对这一问题，本课题提出利用压力场诱导晶格熵和磁相变熵，将反钙钛矿化合物中巨大的相变熵转变为巨压热效应。选取具有巨相变熵的Mn3Cu1-xAxN(C) (A=Ge, Sn)系列化合物作为压热效应研究对象，通过调节Mn3Cu1-xAxN(C) 材料中Cu、Ge、Sn的含量，可以改变材料的负热膨胀行为、磁结构从而调控材料的压热效应。利用中子衍射技术测量压力下材料晶体结构、磁结构的演化规律，阐明反钙钛矿化合物中巨压热效应机理。

The phase transitions evolve giant entropy change in some antiperovskite compounds. If the giant phase transition entropy can be transformed into giant barocaloric effect, these materials will have broad applications in solid-state refrigeration. Most of the entropy is lattice entropy and other entropy is almost magnetic entropy in antiperovskite compounds. The lattice entropy is related to the negative thermal expansion (NTE) which is related to antiferromagnetic (AFM) structure. Hence, the lattice entropy can’t be induced by magnetic field. To solve this problem, this project through applying pressure field to induce the lattice and magnetic entropy. Therefore, it is expected that the giant entropy caused by phase transitions can be transformed into giant barocaloric effect. We study the barocaloric effect in Mn3Cu1-xAxN(C) (A=Ge, Sn) compounds with giant phase transition entropy. By adjusting the content of Cu, Ge, Sn in Mn3Cu1-xAxN(C), the negative thermal expansion behaviors and magnetic structures of these materials are changed. Consequently, the barocaloric effect of them can be controlled by this method. The evolution of the crystal and magnetic structures of these materials under pressure field are studied by neutron diffraction. According to these researches, we clarify the mechanism of giant barocaloric effect in antiperovskite compounds.