First-principles study of helium-vacancy complexes in Be12Ti.

• The microstructures of helium bubbles in Be 12 Ti are studied detailedly. • The stabilities of helium bubbles are investigated by the calculations of solution energies. • The nucleation and growth mechanism of helium bubbles in Be 12 Ti are elaborated. First-principles calculations have been conducted to study the stability of He-vacancy clusters and the trapping behavior of vacancies for He atoms in Be 12 Ti. We considered the various metastable microstructures of four types of He-vacancy clusters, and the most stable configurations were determined by the calculations of solution energy. Some He-vacancy clusters in Be 12 Ti have specific geometrical shape, and grow along specific crystal plane. For example, three types of He 2 V clusters (two He atoms trapped by vacancy) form dumbbell-shaped structure, three He atoms of He 3 V clusters (three He atoms trapped by vacancy) are located in the specific crystal plane. The solution energies of four types of clusters increase with the increase of number of He atoms, and the increasing rate is basically identical. The solution energies of He n V B e 1 clusters are always the largest, and the solution energies of the He n V T i clusters are always the smallest, which mainly attribute to the larger vacancy volume and perfect spatial symmetry of Ti vacancies. The binding energies of a single He atom with He n V (n =0-3) clusters are all positive, and the segregation of He atoms on the inner surface of the vacancy is closer to the center of the vacancy, indicating that the He-vacancy has a stronger trapping ability for He atoms. The present research results provide a theoretical foundation of vacancy trapping mechanism for He atoms in Be 12 Ti, which is extremely important for the nucleation and growth mechanism of He bubbles in Be 12 Ti. [ABSTRACT FROM AUTHOR]