【摘要】 A15型Nb₃Al金属间化合物与Nb₃Sn类似，但其具有更好的应力应变容许特性和高场临界电流密度（J_c）.由于Nb₃Al晶格原子排列的有序度较差，其超导性能对晶格完整性不敏感，且Al含量对Nb₃Al成相及T_c有较大的影响.因此对相结构的研究对Nb₃Al超导性及热学性质的影响具有理论和实际意义.本文采取第一性原理以及热力学理论计算方法，对Nb₃Al的结构进行晶格相结构转变、原子位移以及热力学性质等系统计算研究.结果发现晶格相结构转变的势垒高于原子的位移势垒，且晶格相结构的转变温度高于Nb₃Al的熔化温度.与Nb原子扩散位移相比，Al原子具有更低的位移势垒，且Al原子的“位移温度”低于熔化温度，为1070 K.对于Nb原子位移势垒，通过统计方法得到Nb原子的“位移温度”为2333 K,与实验中得到的Nb₃Al熔化温度2306 K吻合较好，此计算结果表明高温下Nb₃Al的制备主要体现为Al原子的位移，而Nb原子对该化合物的相结构稳定性具有更重要作用.计算结论为更好地理解Nb₃Al制备过程中微观结构演化及扩散反应提供一定的理论依据.更多还原

【Abstract】 The A15-type conventional superconductor Nb₃Al alloy has higher superconducting properties and is less sensitive to strain than that of industrialized superconductor Nb₃Sn.Due to the imperfect order of Nb₃Al lattice, its superconductivity is not sensitive to lattice integrity, and Al content has a great influence on Nb₃Al phase formation and T_c.Therefore, the study of the phase structure on the superconductivity and thermal properties of Nb₃Al has theoretical and preparation significance.In this paper, the lattice phase structure transformation, atomic displacement, and thermodynamic properties of Nb₃Al were systematically studied by using the first principles and thermodynamic theoretical methods. The results showed that the potential barrier of lattice phase transformation was higher than the atomic displacement barrier energy, and the transformation temperature of the lattice phase was higher than the melting temperature of Nb₃Al. Compared with the diffusion displacement of the Nb atom, the Al atom had a lower displacement barrier, and the "displacement temperature" of the Al atom was 1070 K, lower than the melting temperature. The "displacement temperature" of the Nb atom was 2333 K using the statistical method, which was in well agreement with the Nb₃Al melting temperature 2306 K in the experiment. The calculations showed that the preparation of Nb₃Al at high temperature was mainly realized by the diffusion displacement of Al atoms, and Nb atoms played a more important role in the phase stability of this alloy. The calculation results provided a theoretical basis for better understanding the microstructure evolution and diffusion reaction in the preparation of Nb₃Al.更多还原