To improve the chemical stability of high temperature proton conductors based on barium cerate, electrolyte powders doped with different amounts of niobium were synthesized by the citrate-nitrate auto-combustion method. Pure single phases of BaCe0.9-xNbxY0.1O3-x (BCYN, 0.03 <= x <= 0.12) were obtained by thermal treatment at 1000 degrees C. Sintering at 1450 degrees C for 10 h produced dense pellets. X-ray absorption spectroscopy allowed to define the dopant ion insertion site and the co-dopant valency. Treatments in pure CO2 atmosphere at 700 degrees C for 3 h and subsequent XRD analysis were carried out to probe the chemical stability of the produced electrolytes. The influence of the presence of Nb5+ on conductivity has been investigated by electrochemical impedance spectroscopy (EIS) measurements. Polarization curves were acquired in the 400-750 degrees C temperature range. (C) 2011 Elsevier B.V. All rights reserved.