Hydrogen Effects on Ion-induced Luminescence of Li2ZrO3

Full text of publication follows: Lithium zirconate (Li2ZrO3 ) is one of the most attractive candidates for solid breeder materials because of its good characteristics of tritium release and chemical stability. It is important issue to clarify the irradiation effects and the behavior of hydrogen isotopes of these materials. In this study, the dynamic irradiation effects and the relation between oxygen vacancies and hydrogen in Li2ZrO3 were examined by in situ measurement of ion induced luminescence and ion beam compositional analysis. Samples used were sintered Li2ZrO3 pellets of 8 mm diameter and 1 mm thickness. Protons and helium ions in the energy range 0.2 to 2 MeV were irradiated to samples in a vacuum chamber with pressure of 10-5 Pa at room temperature and ion induced luminescence was simultaneously measured through a synthesized silica window. The typical ion flux density was 1 x 1016 ions/sec/m2 and the maximum fluence was 2 x 1019 ions/m2. For the depth profiling of hydrogen concentration, elastic recoil detection analysis was carried out with 2.8 MeV helium ions. Backscattering spectrometry was used with helium ions and protons to measure the concentration depth profiles of zirconium and of light elements, respectively. The intensity of ion induced luminescence at around 2.9 eV attributed to oxygen vacancies monotonically decreased with increasing the irradiation fluence. From analysis of incident energy dependence of the decrease rates, the production and annihilation of the luminescent centers can be explained by the nuclear collisions rather than electronic excitation of the incident ions. The luminescent intensity depends on the hydrogen concentration in samples; higher luminescent intensity was obtained for sample with lower hydrogen concentration. This indicates that the luminescent center was transformed into non-luminescent one by trapping of hydrogen. Meanwhile, the elemental composition of the Li2ZrO3 was remarkably changed by the pre-treatment of the sample. After exposing samples to the air for 100 hours, the hydrogen concentration in the samples became 4 times larger than that in the sample as prepared. In case of the humid air, the zirconium concentration was drastically reduced and lithium carbonate was formed on the near surface layer. (authors)