Rare earth effect on conductivity and stability properties of doped barium indates as potential proton-conducting fuel cell electrolytes

Substitution of In by several rare earth elements in the proton conductor BaIn0.8Ti0.2O2.6 square(0.4) were carried out to form BaIn(0.6)Ti(0.2)Ln(0.2)O(2.6)square(0.4) (Ln=Gd, Dy, Ho, Er, Yb, Lu) perovskite type series. Pure phases have been prepared by solid state reaction at 1350 degrees C in air and studied by TGA, XRD and EIS. All compounds react at low temperature with water vapor to incorporate protons with a maximum volume variation of 3% and are chemically stable under moisture and 3% CO2 atmosphere at 600 degrees C. At high temperature the conductivity is mainly anionic (sigma(O2-) approximate to 0.01 S cm(-1) at 700 degrees C) and below 600 degrees C proton conductivity is observed. The best level of H+ conductivity was found for Ln = Yb, (at 400 degrees C, sigma(H+) = 1.7 x 10(-3) S cm(-1)). For this family of compounds, it is shown that the proton conductivity level at 400 degrees C (which corresponds approximately to the maximum of conductivity) is correlated to the Goldschmidt factor. It is also found that good protonic conductors at low temperature are also good anionic conductors at high temperature. (C) 2012 Elsevier B.V. All rights reserved.