Proton conduction in glass – an impedance and infrared spectroscopic study on hydrous BaSi 2 O 5 glass H. Behrens a, * , R. Kappes a,b , P. Heitjans b a Institut f€ ur Mineralogie, Universit€ at Hannover, Welfengarten 1, D-30167 Hannover, Germany b Institut f€ ur Physikalische Chemie und Elektrochemie, Universit€ at Hannover, Callinstrasse 3-3a, D-30167 Hannover, Germany Received 19 September 2001; received in revised form 2 January 2002 Abstract Hydrous barium disilicate glasses (BaSi 2 O 5 ) 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 H 2 O mol- ecules 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 H 2 O 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. Ó 2002 Elsevier Science B.V. All rights reserved. 1. Introduction Water contents in synthetic glasses produced by 1 atm fusion are typically very low (0.1 wt%). By high pressure fusion or hydrothermal treatment of glasses, however, homogeneous glasses with water contents up to 20 wt% can be synthesized [1,2]. Depending on bulk composition and water con- tent such glasses may have a high thermal stability. For instance, NaAlSi 3 O 8 glasses with 4 wt% water can be heated to 573 K for several hours without water loss. Hydrous glass is a material with inter- esting properties. Due to selective absorption it may be used as a gate for radiation in the near and mid infrared. Furthermore, glasses with high con- centrations of OH groups are potential proton conductors. Water is dissolved in silicate glasses in the form of at least two different water species – OH groups and H 2 O molecules [1,3,4]. At water contents be- low 3 wt% OH groups are usually the dominating species. With increasing water content, molecular Journal of Non-Crystalline Solids 306 (2002) 271–281 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +49-511 762 8054; fax: +49- 511 762 3045. E-mail address: h.behrens@mineralogie.uni-hannover.de (H. Behrens). 0022-3093/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0022-3093(02)01190-0