Heavy-ion irradiation effects on electrical properties of yttrium oxide coatings

Ceramic coatings have been developed for nearly half a century to mitigate tritium leakage through steels and corrosion of the components in fusion reactor blanket systems. In recent years, irradiation effects of ceramic coatings on their characteristics and functions have been elucidated through heavy-ion irradiation tests. However, most of analytical methods used in these studies were destructive and time-consuming. In this study, yttrium oxide coatings were fabricated by radio-frequency magnetron sputtering, and the electrical impedance measurements were conducted for the coatings to develop a convenient approach for understanding of irradiation effects. The conductivity obtained from Nyquist plots showed lower values for the undamaged sample than for the damaged ones below 350 °C, while the relationship of the conductivity was reversed at 350 °C and higher temperatures. The ac conductivity of the undamaged sample showed a frequency dependence from 200 °C to 550 °C; however, that of the damaged ones did not show at 300 °C and lower temperatures and indicated a tendency similar to undamaged one above 300 °C. These tendencies of the conductivity at low temperatures were attributed to the partial recovery of the irradiation damage, while the remaining irradiation defects and/or irradiation-induced grain growth affected the electrical properties at higher temperatures. The electrical impedance spectroscopy methods have a potential to detect the influence of irradiation on the coating.