Influencing factors of helium bubble growth in erbium tritides: Grain size and impurity element

Abstract

The influencing factors of helium bubble growth in the erbium tritides were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The Er tritide films with different grain size and Hf impurity content were fabricated by electron beam vapor deposition and magnetron sputtering evaporation. The helium bubble grows along the {111} preferential orientation in the Er deuteride with a columnar grain structure, while the helium bubble grows as spherical shape in the Er tritide with a nano-sized grain structure. The residual stress is proposed as the major reason affecting the helium bubble growth behavior in the Er tritide, and the helium bubbles tend to grow as spherical shape under compressive stress. The helium bubble size increases slowly with the aging time once the nucleation in the Er tritide. With addition of Hf impurity in the Er tritide, the helium bubble size changes to be smaller and the instantaneous helium release fraction is lower at least by an order of magnitude than pure Er tritide. The above results demonstrate that the grain size and impurity element are two key factors affecting the helium bubble growth in the Er tritide.