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

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41.6 kJ/mol,与实验值吻合较好。

Effects of transitional metal on electronic structure and thermodynamic stability of Mg2Ni hydride:A first-principle investigation

The electronic structures and thermodynamic stabilities of Mg2Ni1-xMx(M=Mn,Fe,Co,Ni,Cu,x=0.25) alloys and their hydrides Mg2Ni1-xMxH4 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-xMx alloy are in good agreement with the experimental results.For Mg2Ni1-xMxH4,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.