氧在钒中基本热力学行为的第一性原理研究

Basic thermodynamic property of oxygen in vanadium:A first-principles study

钒(V)是核聚变反应堆结构材料的重要候选材料。实验表明杂质氧(O)会对V的结构和力学性能产生极大的影响。采用基于密度泛函理论的第一性原理方法研究了O在V中热力学稳定性、扩散特性以及与缺陷空位的相互作用。O在V中易于占据八面体间隙位,其溶解能为-4.942 eV。O在间隙位的最佳扩散路径为八面体间隙位→四面体间隙位→八面体间隙位,扩散激活能为1.728 eV,在此基础上对不同温度下的扩散系数在文中给出了详细分析。O在V中与空位存在很强的吸引相互作用,1个O原子和2个O原子被空位捕获时的捕获能分别为-0.484 eV和-0.510 eV。当O原子的数量超过3,其捕获能变为正值0.382 eV,因此单空位最多能够结合2个O原子,这意味着"O_1-vacancy"和"O_2-vacancy"团簇在V中很容易形成。这些研究结果将对V基合金在核聚变反应堆中的最终应用具有一定的参考价值。

Vanadium （V） is identified as a promising candidate of the structural materials in fusion reactors. Experimental results have demonstrated that the impurity oxygen （O） has great influence on the structure and mechanical properties of V. Employing a first-principles method based on the density functional theory, we study the stability and diffusion property of impurity O as well as its interaction with defect vacancy in V. O atom is energetically favorable to occupy the octahedral insterstitial site with the solution energy of -4.942 eV. The intrinsic optimal diffusion route of O in the interstitial site is octahedral insterstitial site→tetrahedral insterstitial site→octahedral insterstitial site,and the diffusion activation energy is calculated to be 1.728 eV. The diffusion coefficients of O at the different temperature are systematically analyzed. We demonstrate that there is the strong attractive interaction between O and vacancy in V. The trapping energies of one and two O atoms are-0.484 eV and -0.510 eV, respectively. With the increase of the number of O atoms, the trapping energy of the third O becomes the positive value of 0.382 eV, meaning that vacancy cannot bind the additional O atom again. Thus, one vacancy can accommodate as many as two O atoms. It is revealed that the ＂O1-vacancy＂ and ＂O2-vacancy＂ clusters are easily formed in V. The current results can provide a very useful reference for V as a candidate structural material in a fusion reactor.