Gilbert C A, Smith R, Kenny S D, Murphy S T, Grimes R W, Ball J A
Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, UK.
J Phys Condens Matter. 2009 Jul 8;21(27):275406. doi: 10.1088/0953-8984/21/27/275406. Epub 2009 Jun 12.
Point and small cluster defects in magnesium aluminate spinel have been studied from a first principles viewpoint. Typical point defects that occur during collision cascade simulations are cation anti-site defects, which have a small formation energy and are very stable, O and Mg split interstitials and vacancies. Isolated Al interstitials were found to be energetically unfavourable but could occur as part of a split Mg-Al pair or as a three atom-three vacancy Al 'ring' defect, previously observed in collision cascades using empirical potentials. The structure and energetics of the defects were investigated using density functional theory (DFT) and the results compared to simulations using empirical fixed charge potentials. Each point defect was studied in a variety of supercell sizes in order to ensure convergence. It was found that empirical potential simulations significantly overestimate formation energies, but that the type and relative stability of the defects are well predicted by the empirical potentials both for point defects and small defect clusters.
从第一性原理的角度对铝酸镁尖晶石中的点缺陷和小团簇缺陷进行了研究。碰撞级联模拟过程中出现的典型点缺陷是阳离子反位缺陷，其形成能小且非常稳定，还有O和Mg分裂间隙原子及空位。发现孤立的Al间隙原子在能量上是不利的，但可能作为分裂的Mg-Al对的一部分出现，或者作为三原子-三空位Al“环”缺陷出现，此前在使用经验势的碰撞级联中观察到过这种缺陷。使用密度泛函理论（DFT）研究了缺陷的结构和能量，并将结果与使用经验固定电荷势的模拟结果进行了比较。为确保收敛，对各种超胞尺寸下的每个点缺陷进行了研究。结果发现，经验势模拟显著高估了形成能，但对于点缺陷和小缺陷团簇，经验势能很好地预测缺陷的类型和相对稳定性。
