We studied the dynamics of dissolved water in aluminosilicate glasses with the compositions NaAlSi{sub 3}O{sub 8}{center_dot}0.3H{sub 2}O, NaAlSi{sub 3}O{sub 8}{center_dot}1.3H{sub 2}O and Ca{sub ...0.5}AlSi{sub 3}O{sub 8}{center_dot}1.3H{sub 2}O using quasielastic neutron scattering. As shown by near-infrared spectroscopy on these samples, H{sub 2}O molecules are the predominant hydrous species in the water-rich glasses whereas OH groups bound to tetrahedrally coordinated cations are predominant at low water contents. Backscattering and time-of-flight methods were combined to investigate motional correlation times in the range between 0.2 ps and 2 ns. For the water-rich glasses an elastic scan between 2 K and 420 K shows that the dynamical processes set in at lower temperatures in the Ca-bearing glass than in the Na-bearing glass. This is corroborated by the broadening of the inelastic spectra S(Q,{omega}). The shape of the scattering function S(Q,t) suggests a distribution of activation barriers for the motion of hydrous species in the disordered structure of the glass. The distribution is narrower and the average activation energy is smaller in the Ca-bearing glass than in the Na-bearing glass. No indication for dynamics of hydrous species was found at temperatures up to 520 K in the water-poor glass NaAlSi{sub 3}O{sub 8}{center_dot}0.3H{sub 2}O containing dissolved water mainly in the form of OH groups. It is concluded that H{sub 2}O molecules are the dynamic species in the above-mentioned time regime in the water-rich glasses. The dynamic process is probably a rotation of H{sub 2}O molecules around their bisector axis.
In recent years, nanocrystalline materials have considerably attracted the interest of the materials research community 1–4. Single-phase materials with an average particle diameter of less than 50 ...nm exhibit new or at least enhanced chemical and physical properties when compared to their coarse-grained counterparts. For example, they show new mechanical 5–8, electrical 9–13, magnetic 14–19, optical 20–24, catalytic 25, 26, and/or thermodynamic 27–29 features. In ion conducting nanocrystalline materials, an enhancement of the diffusivity of small cations and anions like Li+ and F−, or even larger anions like O2−, is often observed 2–4, 30–41. The diffusivity is additionally influenced by admixing an ionic insulator to the conducting phase 4, 42–47.
