Structural and property investigations of Strontium Galloniobate

Structural, thermogravimetric and conductivity studies have been performed on the cubic perovskite Sr2GaNbO6 in the initial assessment of its potential as a solid oxide fuel cell anode material. Electron diffraction, PXRD and TEM pointed at alternate B site ordering of gallium and niobium. On overnight reduction at 1000 degreesC, a 3% decrease in lattice parameter,vas observed with a corresponding colour change from white to pale blue. Buoyancy corrected TGA analysis of structural oxygen removal accompanying partial niobium reduction from 5(+) to 4(+) and the effect of surface area suggested a process controlled initially by surface exchange kinetics and ultimately by bulk diffusion to crystallite surfaces. Fitted TGA mass loss data gave an estimate of maximum niobium reduction to result in stoichiometry Sr2GaNbO5.88. Conductivity increased between four and two orders of magnitude in the temperature range 200-1000 degreesC, respectively, when measured under air and then 5% dry hydrogen by AC impedance spectroscopy. Results from DC measurements under variable pO(2) at 934 degreesC concurred with the impedance data and also highlighted extensive n-type behaviour at log pO(2) < - 15. (C) 2002 Published by Elsevier Science B.V.