The atomic hydrogen permeability, J(H), in fluorite-type (CeO2)(0.85)(CaO)(
0.15) was measured to confirm the influence of CaO concentration in CeO2 at
1050-1800 K. The decrease of J(H) with reducing temperature and the propor
tionality of log J(H) to inverse temperature are suggested. The estimated a
ctivation energies are 1.0(5) +/- 0.01, 1.3(5) +/- 0.02 and 0.2(2) +/- 0.04
eV at 1800-1400, 1400-1250 and 1250-1050 K, respectively. The J(H) of (CeO
2)(1 - X)(CaO)(X) decreases with increasing X and proportional to X-5/2 at
1800-1300 K under H-2-H2O atmosphere. H-2 is decomposed to 2H(+) and 2e(-)
on the surface of the specimen and they permeate it. They hop between oxyge
n ions and cerium ions, respectively. It would be difficult for H+ to cross
over Vo. which was produced by CaO, then J(H) decreased with increasing X.
(CeO2)(1 - X)(CaO)(X) would be the electron-proton mixed conductor under H
-2-H2O atmosphere at high temperatures. (C) 2001 Elsevier Science B.V. All
rights reserved.