Ballistic-damage-induced size changes in equilibrium and under-pressurized Xe precipitates in amorphous silica

This work explores the behaviour of xenon precipitates in amorphous silica using a transmission electron microscope with in-situ ion implantation. The specimens were first implanted at high-temperature to form equilibrium Xe precipitates which were then cooled to room temperature to form under-pressurized precipitates. In-situ implantation and real-time monitoring at high and room temperature were used to study the behaviour of the equilibrium and under-pressurized precipitates, respectively. The study at high-temperature revealed that the precipitates grow under equilibrium conditions until saturation is reached. Subsequent to precipitate growth under equilibrium conditions, the specimens contain a mixture of equilibrium, under-pressurized and possibly over-pressurized precipitates in addition to voids. Unlike precipitates growth at high-temperature (873 K), under-pressurized precipitates, formed after cooling the specimen implanted at 873 K to room temperature, considerably shrank when subjected to further ion implantation. The shrinkage continued until a new equilibrium state defined by the room temperature density of the Xe precipitates was achieved. We discuss the growth and shrinkage of the precipitates in terms of the ballistic thermal spike which initiates Xe diffusion from the matrix into the precipitates at high-temperature and convective flow of the glass towards the under-pressurized precipitates and voids causing their shrinkage at room temperature.