Quenched-in fcc fluorite-type materials in the Bi2O3-Er2O3-PbO system were annealed in air at 500 and 600 degrees C for up to 2000 h. Each material experienced a conductivity-lowering structural transformation, thus making them unsuitable for use in SOFCs. For example, the materials (BiO1.5)(0.80)(ErO1.5)(0.20-x)(PbO)(x), x = 0.03, 0.06 and 0.09, underwent a fluorite-type to tetragonal transformation during annealing at 500 degrees C due to (100) oxide-ion vacancy ordering, and the rate of conductivity decay at 500 degrees C increased with increasing Pb2+/Er3+ ratio. (C) 2008 Elsevier B.V. All rights reserved.