Hydrogen permeability in (CeO₂)_0.9(GdO_1.5)_0.1 at high temperatures

The atomic hydrogen (1/2H₂) permeability, J_H, in (CeO₂)_0.9(GdO_1.5)_0.1 (fluorite-type) was measured at 1800-800 K. Two tubular specimens (SP(L), SP(S)) of different lengths sintered at 1970 K in air were used to eliminate the permeation through supporting materials (Pt rings, alumina tube and alumina disk). The J_H was 2.81 × 10^-6-1.50 × 10^-8/mol h^-1 cm^-1, when it was assumed that P_H2=7.34 × 10³ Pa and P_H2O=2.28 × 10³ Pa outside of both specimens and that the Ar flow rates to the inside of SP(L) and SP(S) were 20.9 and 9.4-16.0 cm³ min^-1, respectively. LogJ_H decreased with decreasing temperature and was proportional to the inverse temperature at 1800-1100 and 1100-800 K, and the activation energies were 1.12 ± 0.01 and 0.18 ± 0.01 eV, respectively. (CeO₂)_0.9(GdO_1.5)_0.1 would be an electron-proton mixed conductor under H₂-H₂O atmosphere at high temperatures. The protonic conductivity was roughly calculated from the J_H and from the hydrogen partial pressures inside and outside the specimens, its values being 1.4 × 10^-4-7.2 × 10^-7/S cm^-1 and 1.2 × 10^-6/S cm^-1 at 1070 K.