Proton conduction in glass -: an impedance and infrared spectroscopic study on hydrous BaSi2O5 glass

Hydrous barium disilicate glasses (BaSi2O5) Containing 2.75 and 3.54 wt% dissolved water (corresponding to a molar concentration of hydrogen atoms of 11.1 and 14.2 mol/l, respectively) were synthesized by high temperature fusion in an internally heated gas pressure vessel. Near-infrared spectroscopy gives evidence that both OH groups and H2O molecules are present in the glasses. The maximum intensity in the range of OH stretching vibrations is at 2800 cm(-1) indicating strong hydrogen bonding in the glasses. Electric conductivity measurements were carried out at temperatures up to 523 K without significant alteration of the sample. At higher temperatures, OH groups are converted to molecular H2O and water diffuses out of the sample resulting in a continuous decrease of the conductivity. An activation energy of 87 kJ/mol was derived for the dc conductivity in the unaltered glasses similar to the activation energy for bulk water diffusion in other silicate glasses. Because the dry barium disilicate glass is an electrical insulator at experimental conditions, we infer that the dc conductivity of the hydrous glasses is due to proton conduction. (C) 2002 Elsevier Science B.V. All rights reserved.