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The electronic structure of La_3MgNi_ (14) and (110) of primary surface hydrogen

Author: ShaoShuang
Tutor: ZhangMinGang
School: Taiyuan University of Science and Technology
Course: Materials Science
Keywords: Hydrogen storage alloy First Principle La3MgNi14 electronicstructure surface adsorption
CLC: TG139.7
Type: Master's thesis
Year: 2012
Downloads: 31
Quote: 0
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Abstract


The new La-Mg-Ni system hydrogen storage alloy has excellent hydrogenstorage properties, It is hopeful to improve the cathode charge and dischargecapacity with its higher capacity. In this paper, a major phase La3MgNi14of theLa-Mg-Ni hydrogen storage alloy have been investigated, that provide help toimprove hydrogen storage properties of La-Mg-Ni hydrogen storage alloy andresearch hydrogen storage microscopic mechanism.In this paper, the CASTEP module which first-principles plane wavepseudo-potential method based on density functional theory was used, it wasstudied from electronic structure, Firstly, build different structures according toLa occupy the4f position, optimize the structures and calculate energy andformation heat, so as to get the most stable structure of the system. After that,investigate band structure, density of states and population of the stable structureas well as the microscopic electronic structure of Ce2Ni7-type La3MgNi14hydrogen storage alloy. The results show that: Ce2Ni7-type La3MgNi14tends tobe S1structure, in which lanthanums are scattered to each other; Band structureand density of states shows that the system have typical metallic, in combinationwith metallic bonds. The energy state of the system near Fermi level was mainlycontributed by Ni3d orbital. The contribution of the La atoms provided by-16eV5p orbital and-32eV6s orbital. The lowest energy state of the system wasobserved at the-42ev below the Fermi level, which contributed by Mg2p orbital.Population analysis provides an objective criterion for the bonding between atoms. The bond population and atomic population analysis showed that: InLa3MgNi14system, The bond of Ni-La is ionic bond, Mg-Ni dominated both theionic bond, covalent bond. Ni-Ni is covalent bond. In all of the four structuresNi-Ni is covalent bond, Ni-La is ionic bond. When the structure is centrosymmetric structure （S2, C2）, Mg-Ni bond is both covalent key and ionic bond,the stability of the structure was reduced because of the presence of ionic bonds.When the structure is an axisymmetrical structure （S1, C1）, Mg-Ni bond is onlycovalent bond exists, so the stability of the structure higher than thecentrosymmetric structure, S1structure with the average bond length of covalentbond average2.6767is less than the C1structure of2.6934, so that the S1structure is more stable.Research on metal surfaces of the hydrogen adsorption process is to be ableto study the hydrogen adsorption on metal surfaces. In this paper, the CASTEPmodule which first-principles plane wave pseudo-potential method based ondensity functional theory was used, the hydrogen atom in La3MgNi14 Crystal（110） surface adsorption was studied. The results show that: The DOS（density ofstates） of La3MgNi14（110） surface is similar with bulk DOS, however, theband gap width of （110） surface DOS has reduced, the conduction band aboveFermi level have a tendency to drift to the low energy level; Surface activity isalso higher than the activity of the bulk; The stability of distance of hydrogenatom adsorbs at various position between3to3.5; when the hydrogen atomsadsorbed in the crystal La3MgNi14（110） surface, the most stable structure is hydrogen atoms adsorbed on the La-Ni Longbridge, with the Mg-Ni long bridgesite next and Mg-La short bridge site minimum.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Other special nature of the alloy > Hydrogen storage alloy
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