Thermally Stable Concentrated Solutions of Molecular Hydrogen in Bulk Lithium Silicate Glass

This paper is aimed at studying the effect of Li cationson thethermal stability of concentrated solid solutions of molecular hydrogenin the Li2O & BULL;6SiO(2)-0.39H(2) andLi(2)O & BULL;6SiO(2)-0.25H(2) compoundssynthesized at pressures of 7.5 and 6.6 GPa and a temperature of 280 & DEG;C. The decomposition of the solutions was examined by Ramanscattering under isothermal annealing at 21-70 & DEG;C andby hot hydrogen desorption into a pre-evacuated volume at 0-97 & DEG;C. The activation energies E (a) =(0.419 & PLUSMN; 0.019) and (0.411 & PLUSMN; 0.06) eV/H-2 of hydrogendesorption from the near-surface layer of the samples with 0.39H(2) and 0.25H(2), respectively, determined by Ramanspectroscopy were higher than E (a) = (0.16 & PLUSMN; 0.02) eV/H-2 previously determined for hydrogenatedpure silica glass. This suggests the occurrence of a "Kubas"or similar interaction between the lithium cations and hydrogen molecules.The interaction leads to a large decay time constant of & tau; =3220 s at room temperature compared to & tau; = 3 s for the hydrogensolutions in pure silica glass. The hot desorption showed that thediffusion activation energy was higher than 0.51 eV and also had agreat impact on the stability of the hydrogen solutions in bulk lithiumsilicate glass, which additionally increased the decay time constants several times.