Su Jin-Yang, Yang Wen, Zhu Jia-Hong, Wang Wei-Hua, Li Kun, Liu Shu-Ping, Li Yong-Tang
School of Applied Science, Taiyuan University of Science and Technology, Taiyuan 030024, Shanxi, P. R. China.
Phys Chem Chem Phys. 2020 Dec 7;22(46):27206-27213. doi: 10.1039/d0cp04209a.
The tritium release behavior of the Li2TiO3 crystal has become an important index to evaluate its comprehensive performance as a solid breeder material in nuclear fusion reactors. The tritium diffusion on the surface (surface diffusion) and diffusion from the inside to the surface (hopping diffusion) in Li2TiO3 crystals with a 1/3-Li(001) surface are systematically investigated by the first-principles method. Possible adsorption sites, diffusion pathways and energy barriers of surface diffusion and hopping diffusion have been calculated and analyzed, respectively. Tritium atoms are found to diffuse preferentially along the [100] direction on the surface and two equivalent pathways across the surface were identified. The obtained activation energies are about 0.50 eV for surface diffusion and 1.56 eV for hopping diffusion. The local density of states and Bader charge for typical surface diffusion and hopping diffusion pathways are calculated and analyzed. The results reveal that the tritium (T) atom bonds with neighboring oxygen (O) atoms during the surface diffusion, while the T-O interaction is significantly weakened in the hopping diffusion which results in the higher activation energy than that of surface diffusion. In combination with our previous work, a complete tritium diffusion model for the Li2TiO3 crystal is proposed and the corresponding tritium diffusion coefficients are obtained. Our obtained activation energies are in the same range as previous experimental data and could provide theoretical support for the future related experiments.
Li2TiO3晶体的氚释放行为已成为评估其作为核聚变反应堆中固体增殖材料综合性能的重要指标。采用第一性原理方法系统研究了具有1/3-Li(001)表面的Li2TiO3晶体表面的氚扩散（表面扩散）以及从内部到表面的扩散（跳跃扩散）。分别计算并分析了表面扩散和跳跃扩散可能的吸附位点、扩散路径和能垒。发现氚原子在表面优先沿[100]方向扩散，并确定了两条穿过表面的等效路径。表面扩散的活化能约为0.50 eV，跳跃扩散的活化能为1.56 eV。计算并分析了典型表面扩散和跳跃扩散路径的局域态密度和巴德电荷。结果表明，氚（T）原子在表面扩散过程中与相邻的氧（O）原子键合，而在跳跃扩散中T-O相互作用显著减弱，导致其活化能高于表面扩散。结合我们之前的工作，提出了Li2TiO3晶体完整的氚扩散模型，并得到了相应的氚扩散系数。我们得到的活化能与之前的实验数据在同一范围内，可为未来相关实验提供理论支持。
