Zr-Nb二元合金电子结构的第一原理计算

发布时间：2018-05-29 06:46

本文选题：Zr合金 + 结合能　；参考：《辽宁大学》2017年硕士论文

【摘要】：Zr合金因具有非常好的耐腐蚀性,抗氧化性能,低的热中子吸收截面积,以及较高的力学性能等一直被广泛的应用到核工业中。Nb拥有良好热导率、较高的熔点和极强耐腐蚀性等特性,是很重要的合金元素,Nb作为锆合金的合金化元素,能够对锆合金中产生的少量有害杂质达到一定的清除作用,提高锆合金抗腐蚀性,并可降低锆合金的吸氢量,所以Nb非常适合做核反应堆的合金化元素。对加入锆合金中Nb的不同浓度及占位而言,研究其中腐蚀机制的影响,并研发新型Zr-Nb合金,模拟计算结果将对新型锆铌合金材料性能在微观上的深刻认识以及对各个领域的广泛应用与推广都具有很大的参考价值和重要意义。本论文使用基于密度泛函理论的第一原理的VSAP软件包,首先计算了Zr和Nb不同晶胞大小的结合能和电子结构,然后计算了Nb不同浓度及占位下Zr-Nb二元合金的晶体结构和电子结构,最后计算了Zr、Nb晶体中杂质三种近邻下的相互作用能。重要结论如下:(1)在计算Nb不同浓度及占位下Zr-Nb二元合金的晶体结构和电子结构之前,分别计算了Zr晶体的2×2×2超胞和3×3×3超胞,以及Nb晶体的单胞和2×2×2超胞的晶格常数和结合能,计算结果与实验值符合的很好。利用计算结果绘制了态密度图。(2)Zr-Nb合金稳定性:Zr-Nb合金晶格常数整体随着Nb含量的增加呈现逐渐变小的趋势,在Nb相同浓度且不同占位下的构型中Zr14Nb2-(3)、Zr13Nb3-(1)、Zr12Nb4-(3)、Zr52Nb2-(2)、Zr51Nb3-(4)、Zr50Nb4-(5)稳定性相对最好,即Zr-Nb合金中Nb元素更倾向于聚集分布;Zr-Nb合金电子结构:在Zr-Nb合金导带、价带以及费米能级处的电子结构主要由Zr的d轨道和Nb的d轨道电子同时提供;耐腐蚀性最强的构型为Zr14Nb2-(3)、Zr13Nb3-(3)、Zr12Nb4-(1)、Zr52Nb2-(2)、Zr51Nb3-(4)和Zr50Nb4-(7)。(3)向Zr晶体中掺杂Nb杂质时,两个原子之间表现出相互吸引,说明在Zr晶体中的Nb杂质有聚集的趋势;向Nb晶体中掺杂Zr杂质时,两个原子之间表现出相互吸引,且这种吸引力随着距离的增大先增大后减小,从相互作用能的数值大小上看,这种相互作用的差异不是很明显。
[Abstract]:Zr alloys have been widely used in nuclear industry because of their excellent corrosion resistance, oxidation resistance, low thermal neutron absorption area and high mechanical properties. Because of its high melting point and extremely strong corrosion resistance, Nb is an important alloying element of zirconium alloy, which can remove a small amount of harmful impurities produced in zirconium alloy and improve the corrosion resistance of zirconium alloy. It can reduce hydrogen absorption of zirconium alloy, so NB is very suitable for alloying element in nuclear reactor. For the different concentration and occupation of NB in zirconium alloy, the effect of corrosion mechanism was studied, and a new type of Zr-Nb alloy was developed. The simulation results will be of great reference value and significance to the microcosmic understanding of the new zirconium and niobium alloy material and the wide application and popularization of the new zirconium and niobium alloy materials in various fields. In this paper, the binding energy and electronic structure of Zr and NB cell size are calculated by using the first principle VSAP software package based on density functional theory (DFT). Then the crystal structure and electronic structure of Zr-Nb binary alloy with different NB concentration and occupation were calculated. Finally, the interaction energy of three kinds of impurity in ZrNb crystal was calculated. The important conclusions are as follows: (1) before calculating the crystal structure and electronic structure of Zr-Nb binary alloy with different NB concentrations and sites, the lattice constants and binding energies of 2 脳 2 脳 2 supercell and 3 脳 3 脳 3 supercell of Zr crystal and 2 脳 2 脳 2 supercell of NB crystal are calculated, respectively. The calculated results are in good agreement with the experimental values. According to the calculated results, the stability of Zr-Nb alloy is gradually decreasing with the increase of NB content. The stability of Zr-Nb alloy is relatively best in the same NB concentration and different sites. The stability of Zr14Nb _ 2-ZR _ (13) NB _ (3) and Zr _ (12) NB _ (3) Nb _ (2) and Zr _ (51Nb _ (3) O _ (4) Nb _ (4) B _ (50) NB _ (5) is relatively best. That is to say, the NB element in Zr-Nb alloy is more inclined to aggregate and distribute the electronic structure of Zr-Nb alloy. The electronic structure at the conduction band, valence band and Fermi level of Zr-Nb alloy is mainly provided by the d orbital of Zr and d orbital electron of NB. The most corrosion-resistant configurations are Zr14Nb _ 2-Nb _ (3) and Zr _ (13) NB _ (3) and Zr _ (52) NB _ (2-N) ~ (2 +) and Zr _ (50 NB _ (4) ~ (7) ~ (7) ~ (3) Zr crystals, which indicate that the NB impurities in Zr crystals tend to aggregate, and the NB impurities in Zr crystals tend to be aggregated when doped with NB impurity in Zr crystals, and when Zr is doped into Zr crystals, the two atoms exhibit a mutual attraction between the two atoms, which indicates that there is a tendency of aggregation of NB impurities in Zr crystals, and when Zr is doped in Zr crystals, the two atoms exhibit mutual attraction. The two atoms exhibit mutual attraction and the attraction increases first and then decreases with the increase of distance. From the value of the interaction energy the difference of the interaction energy is not obvious.
【学位授予单位】：辽宁大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.414

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