Influence of surface morphology and surface area on release behavior of hydrogen isotopes in LiNbO_3

摘要

Surface processes have profound influence on tritium release behavior in ceramic breeder materials. In this paper, the release behavior of hydrogen isotopes in LiNbO_3 is studied by thermal desorption spectroscopy (TDS) with focusing on the influence of the surface morphology and surface area. It is found that the amount of surface hydroxyl groups is proportional to the specific surface area and can be decreased by smoothing the surface roughness through heating pretreatment at high temperatures. The isotope exchange reaction between the surface hydroxyl groups and water molecules residue in the system is discussed and turns out to proceed fast. The release behavior of hydrogen isotopes in LiNbO_3 is compared with that in Li_2TiO_3 studied in our previous work. It reveals that LiNbO_3 and Li_2TiO_3 have similar surface environment and similar concentration of surface hydroxyl groups with the level of 10~(20) m~(-2). The formation mechanism of hydroxyl groups on the surface is discussed and a model to explain the experimental observations is proposed.