Xenon ion sputtering-induced oxygen vacancy evolution and dielectric insulation degradation in alumina ceramics

Abstract

Alumina ceramic is a critical insulating material used in the grid components of ion thrusters; however, it undergoes degradation under prolonged ion sputtering. This study simulates the accelerated aging process of ion thruster grid operating conditions by sputtering 95% Al2O3 ceramics with a 1200 eV Xe+ ion beam to investigate the evolution of oxygen vacancy defects and the degradation characteristics of the insulation performance. This work correlates oxygen vacancy defects with insulation failure using photoluminescence (PL) spectroscopy, grazing incidence x-ray diffraction (GIXRD), and vacuum flashover measurements. GIXRD results reveal a significant decrease in surface crystallinity after 8 h of sputtering, from over 95% to less than 60%. PL analysis (λex=325nm) identified F centers (404 nm), F22+ centers (shifting from 440 to 466 nm), and F2 centers (504 nm) as the primary oxygen vacancy defects. Their intensities increase with prolonged sputtering time, indicating a rise in the concentration of oxygen vacancy defects. Vacuum flashover tests demonstrate significant insulation degradation. The characteristic flashover voltage (U63.2%) decreases by 33.2% after 4 h and by 37.4% after 8 h compared to the original samples, respectively. The initial flashover voltage (Ufirst) exhibits an even more pronounced decrease, dropping by 53.1% after 8 h. We attribute this degradation to the preferential sputtering of lighter oxygen atoms, leading to the formation of oxygen vacancy defects that promote surface charge accumulation and local electric field distortion. These findings establish a quantitative relationship between the evolution of oxygen vacancy defects and dielectric breakdown in ion radiation environments, providing valuable guidance for the design of durable insulators in aerospace systems.