Electrical and mechanical properties of proton conducting SrCe_0.95Yb_0.05O3-α

Yb3+-doped ceramic strontium cerate of exactly the composition SrCe0.95Yb0.05O3−α was prepared, having a relative density of 99.0 (± 0.3%). Great care was taken to obtain homogeneous, carbonate free material. Analysis are made of the X-ray powder diffraction pattern of the as-prepared dense ceramic, resulting in the orthorhombic unit cell parameters a = 6.997(2) Å, b = 12.296(3) Å, c = 8.588(2) Å, Z = 8 and dx = 5.806(2) g cm−3. Bending strength values of the ceramic in non-proton and proton conducting state are found to be 177 and 194 MPa respectively. The ceramic kept under proton conducting conditions for 500 h at 300 °C to 800 °C in a N2 flow containing 155 mbar water vapour and 245 mbar H2, have shown to remain chemically and structurally stable. Impedance spectroscopy measurements of the bulk conductivity of the proton conducting ceramic revealed an activation energy of 53.2 kJ mol−1 and a preexponential factor of 359.1 (Ω cm)−1 K. In the non-proton conducting state the ceramic is mainly oxygen ion vacancy conducting, which indicates that charge compensation on substituting Yb+3 in SrCeO3 takes place by oxygen ion vacancies.