Release behavior of hydrogen isotopes thermally absorbed in lithium niobate

To elucidate the release behavior of hydrogen isotopes from ternary lithium oxides, thermal desorption spectroscopy and infrared absorption spectroscopy were conducted with LiNbO3, in which deuterium had been absorbed by heating at 1073 K in D2O vapor at 100 Pa. The release behavior was simulated based on a diffusion model. Characteristic deuterium releases of three types were found: (1) release by isotope exchange reaction of surface –OD− with a H2 or H2O molecule in the atmosphere, (2) release as HDO by recombination with surface hydroxyls (–OD− and –OH−) on the surface, and (3) release as HDO or D2O by recombination with surface hydroxyls from the bulk at high temperatures. Release (1) occurred at room temperature, but release (2) occurred at about 600 K. The temperature range at which release (3) takes place depends on the diffusion path length: the plate specimen thickness and the grain specimen size.