ThMn12型金属间化合物NdFe10-xCoxMo2有序化行为的热力学研究

从合金热力学的角度,采用四亚晶格热力学模型,辅助以第一性原理总能计算,研究了具有ThMn12原型结构的NdFe10-xCoxMo2金属间化合物中元素的占位有序化行为。结果表明,NdFe10-xCoxMo2系列合金中稀土原子Nd占据2a亚晶格,Mo占据50%的8i亚晶格,Fe和Co原子共同占据8f、8j和剩余50%的8i亚晶格,与实验结果相吻合。在三元合金中,Fe和Co原子的占位分数在8f和8j亚晶格上随温度变化不发生改变。而在四元合金中,由于Fe和Co原子在8f和8j亚晶格上局部固溶更有利于体系稳定,Fe和Co原子的占位分数在8f和8j亚晶格上随温度变化而发生变化。Co原子部分取代Fe原子而不影响体系的占位有序化行为。Fe与Co等成分的NdFe5Co5Mo2合金中Fe原子微弱趋向于占据8f亚晶格,而Co原子则微弱趋向于占据8j亚晶格。

On the Ordering Behavior of the ThMn12-Type Intermetallics NdFe10-xCoxMo2 by Using Thermodynamic Model

Based on the fundamental thermodynamic principles, the ordering behavior of the ThMn12-type intermetallics NdFe10-xCoxMo2 were studied using a general four-sublattice model supported with first-principles calculations. The results show that the 2a sublattices are occupied by the rare earth elements Nd exclusively, while the 50% of 8i sublattices are occupied by Mo atoms, 8f, 8j and the rest 50% of 8i sublattices are shared by Fe and Co atoms, which agreed well with the reported experimental results. Site occupancy fractions of Fe and Co atoms vary with temperature in the quaternary alloys due to the partial solid solution of Fe and Co atoms in sublattice 8f and 8j, while they keep constant in ternary alloys upon varying temperature. Co and Fe atoms can substitute each other without affecting the ordering behavior of the intermetallics. In the alloy NdFe5Co5Mo2, with an equal the content of Fe and Co, Fe atoms favor the occupancy of sublattice 8f, while Co atoms prefer the occupancy of sublattice 8j.