过渡金属对Mg2Ni氢化物电子结构和热力学稳定性影响:第一性原理研究

摘要

The electronic structures and thermodynamic stabilities of Mg2Ni1-χMχ (M=Mn, Fe, Co, Ni, Cu, χ=0.25) alloys and their hydrides Mg2Ni1-χMχH4 were investigated by plane-wave pseudo-potential approach based on the density functional theory. It is found that the calculated cell parameters of Mg2NiH4 and Mg2Ni1-χMχ alloy are in good agreement with the experimental results. For Mg2Ni1-χMχH4, the interaction between Mg-H bonds is ionic bond, while the interactions between Ni-H and M-H are covalent bonds, which are stronger than that of Mg-H bonds. The Ni-H bond strength is almost unchanged when Ni is partially replaced by Mn, Fe and Co, and the Ni-H bond strength is weakened when Ni is partially substituted by Cu, which may be one of the reasons for causing the reduced structure stability of Mg2Ni0.75Cu0.25H4. The calculated formation enthalpies of Mg2Ni0.75M0.25H4 (M=Mn, Fe, Co, Ni, Cu) are -57.7, -61.5, -61.4,63.4 and 41.6 kJ/mol, respectively, which are in good agreement with the experimental results.%采用基于密度泛函理论(DFT)的平面波赝势(PW-PP)方法,计算并分析了Mg2Ni1-xMx(M=Mn,Fe,Co,Ni,Cu,x=0.25)合金及其氢化物Mg2Ni1-xMxH4的电子结构和热力学稳定性.计算结果表明:Mg2NiH4和Mg2Ni1-xMx 的晶胞参数与实验值吻合较好.对Mg2Ni1-xMxH4的电子结构分析发现:氢化物中的Ni-H和M-H键为共价键、Mg-H键为离子键,且Ni-H与M-H键的相互作用强于Mg-H键的.Mn、Fe和Co的部分替代对Ni-H键的相互作用影响较小,而Cu的替代则减弱了Ni-H键的相互作用,这可能是Cu替代后氢化物结构稳定性降低的一个原因.计算了Mg2Ni0.75M0.25H4 (M=Mn,Fe,Co,Ni,Cu)的生成焓,分别为-57.7、-61.5、-61.4、63.4和41.6kJ/mol,与实验值吻合较好.