NiMnGa基Heusler合金的多卡性能研究

Solid-state refrigeration is a new type of eco-friendly and high efficient refrigeration technology. This refrigeration technology is designed based on the caloric effect of solid-state transformation materials. The presentation of multicaloric effect provides a new approach to enhance the caloric properties of solid-state refrigerant and broaden the space for the interaction of different forms of energy. Thus, the multicaloric effect has gained a lot of attention recently. Among NiMn-based Heusler alloys, NiMnGa-based alloys show more advantages in the investigation of multicaloric effect and application in solid-state refrigeration due to the cooperative effect of magnetic and structural transformations. However, NiMnGa-based alloys with such cooperative effect are scarce at room temperature and their multicaloric effect has not been studied. In this project, we propose to explore more systems with such cooperative effect at room temperature. In these systems, the quantitative relation of transformation entropy change and magnetostructural coupling strength will be investigated on the basis of a phenomenological Landau model combined with comprehensive experimental studies. This quantitative relation can provide theoretical basis for developing excellent multicaloric materials. Besides, the elastocaloric effect of NiMnGa-based alloys under bias magnetic fields will be investigated and the influencing mechanism of magnetic field on elastocaloric effect in materials with cooperative effect will be revealed. With the framwork of this project, the develpment of magnetostructural transformation materials with cooperative effect and their multicaloric effect should be actively promoted.

固态制冷是绿色环保、高效节能的新型制冷技术，其原理是利用固态相变材料的热效应进行制冷。多卡效应的提出为固态制冷材料热性能的改善和不同能量形式相互干预空间的扩宽提供了新的途径，因此受到了人们的广泛关注。NiMn基Heusler合金中具有磁结构协同相变特征的NiMnGa基合金在多卡效应研究和固态制冷应用方面具有明显优势。但是相变温度在室温的磁结构协同相变材料体系目前较少且该类材料的多卡效应研究还尚未开展。本项目拟以探索NiMnGa基室温磁结构协同相变材料体系为基础，结合系统的实验表征和唯象的朗道理论模拟深入探究磁结构协同相变材料中相变熵变和磁结构耦合强度的定量关系，为开发多卡性能优异的制冷材料提供理论依据。同时，本项目拟通过研究NiMnGa基合金在偏置磁场下的弹热效应揭示磁结构协同相变材料中磁场对弹热效应的影响机制，积极推动室温磁结构协同相变材料及其多卡效应的研究进展。

固态制冷是绿色环保、高效节能的新型制冷技术，其原理是利用固态相变材料的热效应进行制冷。Ni-Mn-Ga基Heusler合金的磁结构相变具有两个协同特性：（1）晶格振动熵变和磁熵变协同贡献于相变熵变；（2）结构和磁性对磁场和应力场具有协同响应。磁结构相变的协同特性有利于高相变潜热的获得和多场联合调控热效应的实现。目前，磁结构协同相变材料体系只有Ni-Mn-Ga-X(X=Ni,Cu,In)，亟需开发新的材料体系。同时，磁结构协同相变材料中磁结构相变的协同特性和相变潜热、热效应之间的关联关系也有待进一步研究。. 在本项目支持下，项目实施人通过元素掺杂开发了Ni-Mn-Ga-X(X=Sn,Sb,Ti)磁结构协同相变材料新体系，并总结了磁结构协同相变材料的开发策略：对价电子浓度和晶胞体积实施联合调控；通过对Ni-Mn-Ga基合金的相变熵变进行量化研究揭示了磁结构相变的协同特性可以使合金表现出高相变潜热；通过对Ni-Mn-Ga-Cu合金的磁热效应进行基于朗道相变理论的唯象模拟明确了磁结构相变的协同特性和显著磁热效应之间的强烈依赖关系；通过研究发现Ni51.0Mn20.8Ga22.4Cu5.8合金的磁结构相变和磁热效应具有优异的循环稳定性。本项目的研究成果丰富了磁结构协同相变材料及其磁热效应的理论体系，为设计具有高潜热和高磁热性能的磁结构协同相变材料提供了理论基础，在推动磁结构协同相变材料在固态制冷应用方面具有重要指导意义。