Proton Conduction in La0.9Sr0.1Ga0.8Mg0.2O3-α

The conduction behavior of La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3- α ceramics was investigated using electrochemical methods under various atmospheres in the temperature range of 600−1000 °C. The proton conduction in La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 - α ceramics is the first time it has been discovered in a hydrogen-containing atmosphere. The hydrogen concentration cell using La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 - α as an electrolyte showed stable electromotive forces close to the theoretical ones calculated from Nernst's equation, indicating the ion nature of the conduction. An isotope effect on the conductivity was observed using D 2 O−Ar instead of H 2 O−Ar as the atmosphere. The proton conduction in the specimen was directly confirmed by an electrochemical hydrogen permeation (hydrogen pumping) experiment. In a hydrogen atmosphere, La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 - α was found to be an excellent proton conductor, with a proton conductivity of σ H + = 1.4 × 10 - 2 to 1.4 × 10 - 1 S cm - 1 and a proton transport number of t H + > 0.99, which are comparable to those of proton-conducting BaCeO 3 -based oxides and Ba 3 Ca 1.18 Nb 1.82 O 9 - α . In a water-vapor-containing air atmosphere, the specimen was found to be a mixed-ion (proton + oxide ion) conductor, and the proton and oxide-ion transport numbers were about 0.05−0.20 and 0.95−0.80, respectively, whereas in dry oxygen-containing atmospheres, the specimen was a pure oxide-ion conductor.