High temperature protonic conduction in Sr-doped La 2Si 2O 7

Abstract

Electrical conduction in the monoclinic lanthanum disilicate La 2Si 2O 7 was investigated in H 2O/O 2 (D 2O/O 2) and H 2O/H 2 (D 2O/D 2) atmospheres at 500–925 °C. It was found that La 2Si 2O 7 became to conduct protons under wet conditions by partially substituting Sr for La. From the H/D isotope effect and the partial pressure dependence of the conductivity, it was demonstrated that the protonic conduction in the Sr-doped La 2Si 2O 7 was considerably predominant both in wet oxidizing and in wet reducing atmospheres and that the contribution of electronic conduction to the total conductivity was minor. The conductivities of the 1 mol% Sr-doped La 2Si 2O 7 were 8×10 −7–2×10 −5 S cm −1 under moisturized conditions at 550–925 °C, and were relatively lower than the conductivities of the acceptor-doped LaPO 4 and LaBO 3. The partial pressure dependencies of the conductivity of the Sr-doped La 2Si 2O 7, however, seemed to essentially resemble to those of the acceptor-doped LaPO 4 and LaBO 3, indicating the similar proton dissolution and conduction mechanism in these oxoacid salts.