新型核燃料钍基氮/碳氮化物在压力下的晶体结构相变、物性及相变机理研究

The thorium based nitrides and carbonitrides, as the new type fuel of the Generation-IV nuclear reactors, have the advantages of high thermal conductivity, high melting point and high fission atom density. These materials have great application prospects. Crystal structure and phase transition are the basis for understanding the material properties and application. However, as a new type of nuclear fuel, the crystal structure and phase transition of thorium-based fuels have not been systematically studied compared with the uranium fuels that have been widely studied. By merging ab initio calculations and structural search methods of particle-swarm optimization algorithm, this project will systematically predict the crystal structures of thorium-based nitrides and carbonitrides under various chemical constituents and external pressures. The phase transition mechanism and structure evolution among the structures with the pressure increasing will be studied. Combined with our previous studies on thorium-based carbides, we will construct a component-pressure structural phase diagram of the Th-C-N system. Meanwhile, the physical properties, such as electronic structures, elastic properties, thermodynamic properties, etc., will be studied comprehensively in order to provide detailed theoretical basis for the subsequent research and practical application.

钍基氮化物和碳氮化物作为第四代核反应堆的新型核燃料，具有热导率高、熔点高、裂变原子密度高等优良性能，有着巨大的应用前景。晶体结构及其相变是理解材料特性、实现应用的基础，然而作为新型核燃料，与得到普遍研究的铀燃料相比，钍基燃料的晶体结构和相变一直缺乏系统的研究。本项目拟采用密度泛函理论结合结构搜寻方法粒子群算法，针对钍基氮化物和碳氮化物两类材料，在不同组分和压强下对其晶体结构进行预测，并研究各个结构间的相变机理和结构演化规律。结合我们已取得的钍基碳化物的研究成果，构建Th-C-N体系的组分-压强结构相图。同时，对其相关物性，比如电子结构、弹性性质、热力学性质等，进行研究，以期为后续的研究以及实际应用提供详细的理论依据。

晶体结构及其相变是理解材料特性、实现应用的基础，然而作为新型核燃料，与得到普遍研究的铀燃料相比，钍基核燃料的晶体结构和相变一直缺乏系统的研究。在本项目的支持下，开展了对新型核燃料钍基化合物Th-C-N、Th-N、Th-B-C、Th-Si等体系在高压环境下的结构相变和相变机理的研究。同时，我们对核燃料包壳材料Zr-C体系在高压环境下的晶体结构演化规律进行了研究。这些结果扩展了钍基和Zr-C材料的结构相图，这对于其实际应用至关重要。此外，在保证原计划顺利进行的情况下，课题组成员和合作者开展了对二维材料V2C和T2CO2 (T = Zr, Hf) MXene；BC3、C3N nanosheets和h-BN/BC3异质结的力学、电学以及储能等性能的研究，并且对二维材料表面吸附过渡金属团簇作为氮还原反应的高效催化剂的电催化性能进行了相关的研究。