In　this　study,　we　have　investigated　the　feasibility　of　forming　a　new　ionic　conducting　electrolyte　from　a　proton　conducting　phase,　BaCe0.8Y0.2O3-delta　(BCY),　and　an　oxygen　conducting　phase,　Ce0.8Gd0.2O1.9　(CDC).　in　order　to　decrease　the　reduction　of　Ce4+　ions　to　Ce3+　ions　in　reducing　atmospheres　at　high　temperatures.　BCY-GDC　composite　powders　(molar　ratio　1:1)　are　synthesized　via　a　one-step　citric　acid-nitrate　gel　combustion　method.　The　reaction　between　the　BCY　and　GDC　in　these　composite　powders　at　1550　degrees　C　results　in　the　formation　of　a　new　perovskite　phase　with　a　nominal　composition　of　BaCe1.6Y0.2Gd0.2O4.9-alpha.　The　conductivity　of　the　new　perovskite　phase　is　found　to　be　substantially　(similar　to　150%)　higher　than　that　of　the　composite　electrolyte　made　from　the　mixture　of　BCY　and　GDC　with　the　same　nominal　composition　as　the　new　perovskite　phase.　The　single　fuel　cells　with　the　new　perovskite　electrolyte　exhibit　better　electrochemical　performance　than　the　cells　with　the　composite　electrolyte　made　of　the　mixture　of　BCY　and　GDC.　The　maximum　power　density　of　single　cells　with　the　new　perovskite　electrolyte　can　reach　0.657　W　cm(-2)　at　700　degrees　C　using　humidified　hydrogen　(3%　H2O)　as　the　fuel.　This　maximum　power　density　is　similar　to　65%　higher　than　that　of　the　cells　with　the　BCY+GDC　composite　electrolyte.　(C)　2012　Elsevier　B.V.　All　rights　reserved.