H/He interaction with vacancy-type defects in alpha-Al2O3 single crystals studied by positron annihilation
H/He interaction with vacancy-type defects in alpha-Al2O3 single crystals studied by positron annihilation
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通过正电子湮灭研究 H/He 与 α-Al2O3 单晶中空位型缺陷的相互作用
DOI：
10.1039/c6ra00612d
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发表时间：
2016
期刊：
影响因子：
3.9
通讯作者：
Wang Xiaolin
中科院分区：
文献类型：
--
作者：
Zhang Guikai;Xiang Xin;Yang Feilong;Liu Lang;Tang Tao;Shi Yan;Wang Xiaolin
为了探讨氚衰变产生的H和He与聚变反应堆中α-Al2O3的空位型缺陷作为氚渗透屏障（TPB）的相互作用，分别在纯Ar气、D2气和T2气中处理α-Al2O3单晶，并进行氚时效处理，然后结合DFT结果研究了α-Al2O3单晶的正电子湮灭寿命和可能导致正电子寿命组成的缺陷类型。与新鲜和ar退火样品相比，热氢化样品中形成了更多的单空位和空位团簇，表明氢的稳定作用；这与α-Al2O3在存在氢杂质时向导带最小值（CBM）移动的费米能级位置一致，导致VAl3−和[VAl3−-H +]2−变得更加稳定。对样品进行热退火，然后在室温下在T2气体中时效，单空位被轻微消除，表明He填充了空位。这与He原子占据Al空位是一致的，其中最容易形成HeAl3−，同时不断诱导更多的空位团簇，这表明Al - o键减弱，因此纳米硬度随着外部负载而降低。本研究首次证明了H可以稳定Al空位并填充He，这将为进一步的新型TPB设计提供机会。
To probe the interaction of H and He, produced by tritium decay, with vacancy-type defects of α-Al2O3 as a tritium permeation barrier (TPB) in fusion reactors, α-Al2O3 single crystals were treated in pure Ar gas, D2 gas and T2 gas with subsequent tritium aging, respectively, and then their positron annihilation lifetimes and the type of defects that may contribute to the observed positron lifetime components were studied, in combination with DFT results. More monovacancies and vacancy clusters were formed in the thermally hydrogenated samples when compared to the fresh and Ar-annealed samples, indicating the stabilizing effect of hydrogen; this was consistent with the Fermi level position of α-Al2O3 moving towards the conduction band minimum (CBM) in the presence of hydrogen impurities, resulting in VAl3− and [VAl3−–H+]2− becoming more stable, as observed by DFT calculations. The monovacancies were slightly eliminated when the samples were thermally annealed and then aged in T2 gas at room temperature, indicating that He filled the vacancies. This was consistent with it being favourable for He atoms to occupy Al vacancies, with HeAl3− forming most readily, whilst more vacancy clusters were continuously induced, suggesting that Al–O bonds weakened and thus nano-hardness decreased with an external load. This study provides the first evidence that Al vacancies can be stabilized by H and filled with He, which will provide further novel TPB design opportunities.