In-situ transmission electron microscopy observation of the helium bubble evolution in pre-irradiated fluorapatite during annealing

Abstract

The polycrystalline fluorapatite Ca10(PO4)6F2 ceramic synthesized by a standard solid-state sintering method was pre-irradiated with 80 keV He+ ions to a fluence of 5 × 1016 ions/cm2 at room temperature. After that, an in-situ annealing experiment was performed inside a transmission electron microscope to monitor the evolution of helium bubbles during heating to 723 and 823 K. Initially, no helium bubble formation was observed in the damage layers of the pre-irradiated samples. However, as the temperature increased, helium bubbles first became visible and then began coarsening, ultimately reaching an asymptotic radius during annealing. The migration and coalescence of helium bubbles in the fluorapatite matrix was complete at a temperature of 823 K, and its likely mechanism involved the existence of two different types of coalescing bubbles.