Zhang Guikai, Xiang Xin, Yang Feilong, Peng Xuexing, Tang Tao, Shi Yan, Wang Xiaolin
Institute of Materials, China Academy of Engineering Physics, 621908, Jiangyou, China.
Phys Chem Chem Phys. 2016 Jan 21;18(3):1649-56. doi: 10.1039/c5cp06496a. Epub 2015 Dec 17.
Little is known about hydrogen interaction with helium, an extrinsic defect, present in α-Al2O3 TPBs due to tritium decay and (n, a) reaction. Using density functional theory (DFT), the stability, structure and diffusion of He-related complexes at the different positions (VAl(3-), V, Oi(2-) and octahedral interstitial sites (OISs)) in α-Al2O3, as well as the interactions with H, are determined under H2-rich conditions. A He atom favors occupation of Al vacancies, the centers of OISs or forms a dumbbell around Al vacancies, forming Hei, HeAl(3-), Hei-HeAl(3-), V-Hei and Oi(2-)-He complexes, among of which HeAl(3-) forms most readily. VAl(3-) can attract He to form small stable He-HeAl(3-) clusters, whereas only a He atom is trapped by an OIS, V and Oi(2-). Hei is more likely to diffuse into VAl(3-) and V than diffuse along the c-axis from one OIS to another. Hi(+) trapping into HeAl(3-) and V-Hei is thermodynamically and kinetically feasible, whereas dissociation of Hei-H(+) is more feasible. Forms of H-He complex defects in α-Al2O3 are Hei, Hi(+), Hei-H(+), HeAl(3-)-H(+) and HO(+)-Hei. HeAl(3-) and V-Hei present will increase the activation energy of H migration in α-Al2O3, which is favored for low H transport of TPBs.
关于氢与氦（一种由于氚衰变和（n，α）反应而存在于α-Al2O3三相边界中的外在缺陷）之间的相互作用，人们了解甚少。利用密度泛函理论（DFT），在富氢条件下确定了α-Al2O3中不同位置（VAl(3-)、V、Oi(2-)和八面体间隙位置（OISs））与氦相关的复合物的稳定性、结构和扩散，以及它们与氢的相互作用。一个氦原子倾向于占据铝空位、OISs的中心或在铝空位周围形成哑铃状，形成Hei、HeAl(3-)、Hei-HeAl(3-)、V-Hei和Oi(2-)-He复合物，其中HeAl(3-)最容易形成。VAl(3-)可以吸引氦形成小的稳定的He-HeAl(3-)团簇，而只有一个氦原子被一个OIS、V和Oi(2-)捕获。Hei比从一个OIS沿c轴扩散到另一个OIS更有可能扩散到VAl(3-)和V中。Hi(+)捕获到HeAl(3-)和V-Hei在热力学和动力学上是可行的，而Hei-H(+)的解离更可行。α-Al2O3中氢-氦复合缺陷的形式有Hei、Hi(+)、Hei-H(+)、HeAl(3-)-H(+)和HO(+)-Hei。存在的HeAl(3-)和V-Hei将增加α-Al2O3中氢迁移的活化能，这有利于三相边界的低氢传输。
