Solid State Ionics 107 (1999) 107–117 www.elsevier.com / locate / ssi Proton conducting Ba Ca Nb O –H O: 3 1.18 1.82 8.73 2 pressure–compositions isotherms in terms of Fermi-Dirac statistics, concentration and fuel-cell measurements, and impedance spectroscopy a, a a b b a * B. Groß , St. Marion , K. Lind , D. Grambole , F. Herrmann , R. Hempelmann a ¨ ¨ Physikalische Chemie, Universitat des Saarlandes, D-66123 Saarbrucken, Germany b Forschungszentrum Rossendorf , D-01314 Dresden, Germany Abstract Thin films of Ba Ca Nb O , prepared in a sol-gel process by multiple dip-coating on silicon wafers, and powder 3 1.18 1.82 8.73 samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressure and temperature. The hydrogen content was determined ex situ at room temperature using nuclear resonance reaction analysis. From the resulting water vapour pressure–composition isotherms the absorption [ [ [ enthalpies D H , D H and the absorption entropy D S were calculated, using a two-site model, based on Fermi-Dirac O t statistics. On Ba Ca Nb O bulk material also impedance spectroscopy, concentration and fuel-cell measurements as 3 1.18 1.82 8.73 well as neutron diffraction were performed. From these data, taken together, the proton diffusion coefficient D could be H evaluated and compared to quasielastic neutron scattering results.  1999 Elsevier Science B.V. All rights reserved. 15 Keywords: N method; Thermodynamics; EMF; Impedance spectroscopy Materials: Ba Ca Nb O 3 1.18 1.82 8.73 1. Introduction vide an appropriate conductivity, puts high demands on interconnector materials. Proton conducting ma- The interest in fuel cells as an alternative energy terials might be able to replace the oxygen ion conversion technique is growing steadily. Today the conductors, because they need lower operating tem- solid electrolyte of fuel cells is usually the oxygen peratures in the range 6008C–8008C. In this tempera- ion conductor yttrium stabilised zirconia (YSZ), ture range conventional steel is a good and cheap which operates at temperatures of about 10008C. candidate for interconnectors. This high operating temperature, necessary to pro- Acceptor doped cerates and zirconates have been studied in the past, see for instance [1,2], as have ternary perovskite-type oxides like Ba SnInO and 2 5.5 *Corresponding author. Tel.: 149-681-302-2426; fax: 149- Ba SnYO [3]. For Ba Ca Nb O ceramics 681-302-4759. 2 5.5 3 1.18 1.82 8.73 E-mail address: gross@hal.pc.uni-sb.de (B. Groß) (BCN18) high proton conductivity was found [4]. 0167-2738 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0167-2738(99)00164-2