Using ac conductivity and the concentration cell emf method, conductivity contributions from protons, native ions, and electrons have been measured as a function of temperature (560" to 1156°C) in wet oxygen/air for the cubic systems YzOJ + 1 mol% MgO, Sm203 + 1 mol% CaO, Gd203 + 1 mol% CaO, and Y Y b 0 3 + 5 mol% CaO. All exhibit significant proton conductivities as well as native-ion and electronic conductivities at all temperatures. In wet atmospheres and reduced temperatures, the oxides dissolve protons to compensate for the acceptor doping, at the expense of native positive defects. This dissolution of protons seems to be relatively more favorable in oxides of smaller rare-earth cations (e.g., Y3+ and Yb3+). On the other hand, larger cations (e.g., Sin3+ and Gd3+) give higher proton mobilities. As compared to oxides of the true lanthanides with similar cationic radii, yttrium-containing oxides have lower proton mobilities. [

Composite electrodes of La 0.8 Sr 0.2 MnO 3 (LSM) / La 28-x W 4+x O 54+3x/2 (x=0.85, "LWO56") on LWO56 electrolytes have been characterized by use of electrochemical impedance spectroscopy vs pO 2 and temperature from 900 ⁰C, where LWO56 is mainly oxide ion conducting, to 450 ⁰C, where it is proton conducting in wet atmospheres. The impedance data are analyzed in a model which takes into account the simultaneous flow of oxide ions and protons across electrolyte and electrodes, allowing extraction of activation energies and pre-exponential factors for the partial electrode reactions of protons and oxide ions. One composite electrode was infiltrated with Pt nanoparticles with average diameter of 5 nm, lowering the overall electrode polarization resistance (R p ) at 650 ⁰C from 260 to 40 Ω cm 2 . The Pt-infiltrated electrode appears to be rate limited by surface reactions with activation energy of ~90 kJ mol -1 in the low temperature proton 2 transport regime and ~150 kJ mol -1 in the high temperature oxide ion transport regime. The charge transfer reaction, which makes a minor contribution to R p , exhibits activation energies of ~85 kJ mol -1 for both oxide ion and proton charge transfer.

Lanthanum phosphate (LaPO 4 ) powders were synthesized by precipitation with and without excess of phosphate and sintered at 1450• C. Bulk and surfaces of different origin and treatments were investigated using powder x-ray diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy. The XPS data are reported and interpreted in some detail, and they indicate that phosphate excesses do remain in surfaces and appear to be accompanied by sodium accumulated in the surface from an unknown source. It is likely that grain boundaries are similarly phosphate enriched and a generally higher electrical conductivity of phosphate-excess LaPO 4 samples is discussed in view of this.