Phase behavior, proton concentration, and conductivity of La2Ce2O7 doped with Y, Ho, Er, Tm, or Yb

Abstract

AbstractLa2Ce2O7 is a fluorite‐type oxide, showing almost pure oxide ion conduction in dry oxygen atmosphere. Under wet oxygen atmosphere, protons are introduced into La2Ce2O7 through hydration reaction, making the material proton‐conducting. However, compared with the oxide ion conductivity, the proton conductivity is negligibly small in La2Ce2O7. Here we report the effect of doping trivalent rare earth cations R3+ (R = Y, Ho, Er, Yb, or Tm) and elevating partial pressure of water vapor on the proton concentration and conductivity of La2Ce2O7. The samples show single fluorite phases with the doping level up to 0.2, and the solubilities of these dopants were within 0.2–0.3 in La2Ce2O7. The proton concentration increased by doping, due to higher amount of hydratable oxygen vacancies, and statistical coordination of oxide ions surrounded by R3+ in addition to La3+. The sample with the Y content (x) of 0.05 showed the highest conductivity at 600°C among La2(Ce1−xYx)2O7−δ (x = 0–0.3) samples, possibly due to the balance between the improved hydration ability and decreased mobility of protons with the increasing Y doping level. Then, the dopant content was fixed to 0.05, and La2(Ce0.95R0.05)2O7−δ (R = Y, Ho, Er, Tm, or Yb) was prepared. It was found that as the water vapor partial pressure increased, the proton concentration and conductivity increased regardless of the dopants. Y‐doped La2Ce2O7−δ ha the highest proton concentration and conductivity.