Proton conductivity in stoichiometric and sub-stoichiometric yittrium doped SrCeO3 ceramic electrolytes

The crystal structure and electrical properties of stoichiometric perovskite proton conductors SrCe1−xYxO3−δ (where x = 0.025, 0.05, 0.075, 0.1, 0.15, and 0.2 and δ = x/2) and substoichiometric Sr0.995Ce0.95Y0.05O3−δ have been investigated. The conductivities of the samples were measured as a function of the partial pressure of oxygen at 600 and 800 °C, and at two water vapor pressures imagePH2O=0.01 and 0.001 atm). A PO2 range of 1 atm (pure O2) to approximately 1 × 10−25 atm (N2/H2 mix) allowed for the separation of n-(electron), p-(hole), and i-(ionic) type conductivities. In the case of stoichiometric perovskite proton conductors, the unit cell volume (UCV) and calculated density decrease with increasing yttrium content. The ionic and p-type components of the conductivity show threshold effect with Y-doping, which may be related to the double substitution of Y on both A- and B-sites. A maximum ionic conductivity of 5 mS/cm is found at 10% Y, whereas p-type conductivity increases with increasing yttrium concentration. A conductivity component appearing at low oxygen partial pressures decreases with yttrium doping. The substoichiometric material showed a drop in unit cell volume of approximately 0.34 Å3 compared to its stoichiometric partner. The conductivity components of substoichiometric material are higher than the conductivities of corresponding stoichiometric material, being approximately 7 mS/cm for both PH2O levels.