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

The conduction behavior of La0.9Sr0.1Ga0.8Mg0.2O3-alpha ceramics was investigated using electrochemical methods under various atmospheres in the temperature range of 600-1000 degrees C. The proton conduction in La0.9Sr0.1Ga0.8Mg0.2O3-alpha ceramics is the first time it has been discovered in a hydrogen-containing atmosphere. The hydrogen concentration cell using La0.9Sr0.1Ga0.8Mg0.2O3-alpha 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 D2O-Ar instead of H2O-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, La0.9Sr0.1Ga0.8Mg0.2O3-alpha was found to be an excellent proton conductor, with a proton conductivity of sigma(+)(H) = 1.4 x 10(-2) to 1.4 x 10(-1) S cm(-1) and a proton transport number of t(H)(+) > 0.99, which are comparable to those of proton-conducting BaCeO3-based oxides and Ba3Ca1.18Nb1.82O9-alpha. 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.