Mg_(17)Al_(12)、Al_2Ca、Al_2Nd、Al_2Er金属间化合物稳定性与电子结构关系的第一性原理研究

Relationship between Structural Stabilities and Electronic Structures of Mg_(17)Al_(12), Al_2Ca, Al2_Nd and Al_2Er Intermetallic Compounds Studied by First-principles

采用基于密度泛函理论的Castep程序软件包,优化了Mg_(17)Al_(12)、Al_2Nd、Al_2Er及Al_2Ca等相的晶胞结构,计算了化合物的形成热、结合能和态密度等,分析了化合物结构稳定性与其电子结构的内在联系。结果表明:4种化合物的形成热和结合能均为负值,且化合物的合金化能力和结构稳定性强弱顺序依次为Al_2Er、Al_2Nd、Al_2Ca、Mg_(17)Al_(12)。态密度结果表明,Al_2Er和Al_2Nd具有较强结构稳定性的主要原因是:(1)在费米面低能级区,Al 3p轨道分别与Nd 4f、5d和Er 4f、5d轨道价电子发生强烈杂化作用;(2)Al_2Nd和Al_2Er成键电子数较多;(3)这_2种化合物的电子参与成键能力较大。电荷密度结果表明:Mg_(17)Al_(12)、Al_2Ca、Al_2Nd和Al_2Er中均存在金属键、离子键、共价键,4种化合物中Al_2Er、Al_2Nd共价键较强,Al_2Ca离子键最强,Mg_(17)Al_(12)中以较强的金属键为主。

The relationship between structural stabilities and electronic structures of Mg17Al12, Al2 Ca, Al2 Nd and Al2 Er intermetallic compounds was investigated by Castep module based on the density functional theory. The heats of formation, cohesive energies and densities of states（DOS） of these compounds were calculated and the crystal structures were optimized. Results show that the heats of formation and cohesive energies are all negative. The Al2 Er has the strongest alloying ability and structural stability, then Al2 Nd, thirdly Al2 Ca and finally Mg17Al12. The calculated DOS of all the compounds in this study shows that Al2 Er and Al2 Nd exhibit the stronger structural stabilities and the reasons can be deduced as follows：（1） Serious hybridization occurs in the valence electrons between Al3 p and Er4 f, Al3 p and Er5 d, Al3 p and Nd4 f, Al3 p and Nd5 d orbits in the lower energy region below Fermi level.（2） The bonding electrons of Al2 Nd and Al2 Er are more than Al2 Ca and Mg17Al12.（3） The bonding abilities of Al2 Nd and Al2 Er are stronger. Moreover, the calculations of density of charge indicate that all of these compounds contain metallic, ionic and covalent bonds. In these compounds, Al2 Er and Al2 Nd have the stronger covalent bonds than Al2 Ca and Mg17Al12, while the Al2 Ca has the strongest ionic bonds and the Mg17Al12 is dominated by the metallic bond.