High temperature protonic conduction in LaBO₃ with the aragonite-type structure

Electrical conduction in lanthanum orthoborates LaBO₃ with the orthorhombic aragonite-type structure (S. G.: Pnam) was investigated by using conductivity measurements under 0.4-5 kPa of p(H₂O) and 0.01-100 kPa of p(O₂) at 500-930°C. From humidity dependence and H/D isotope effect of the conductivity, it was found that LaBO₃ exhibited dominantly protonic conduction under wet conditions by substituting Sr for La. Results of conductivity measurements under various p (H₂O) and p(O₂) suggested that the contribution of electron hole conduction became significant as temperature increased, p(O₂) increased and p(H₂O) decreased, although protonic conduction was estimated as predominant under the conditions used. The conductivities of the 1 mol% Sr-doped LaBO₃ were 1 × 10^-5 -2 × 10 ^-4 S cm^-1 under moisturized conditions at 500-930°C. The conductivity behaviors as well as the conductivity values of the Sr-doped LaBO₃ with the aragonite-type structure were quite similar to those of the acceptor-doped rare earth orthophosphates, indicating a similar proton conduction mechanism in these oxoacid salts.