Protonic conduction in Sr-doped (La1−xSmx)PO4

High temperature protonic conduction in 1 mol% Sr-doped (La1−xSmx)PO4 (x=0.3, 0.5 and 0.7) with the monazite structure (S. G.: P21/n) was investigated. The conductivities of the materials under wet atmosphere were considerably higher than those under dry atmosphere. From the conductivity measurements under H2O- and D2O-containing atmospheres, it was found that the magnitude of H/D isotope effect was 1.2–1.4. These results indicated that protonic conduction was dominant in the materials under wet atmosphere. The p(H2O) dependencies of the conductivities were discussed in terms of the defect equilibria, and, as a result, higher Sm content in 1 mol% Sr-doped (La1−xSmx)PO4 seemed more preferable for proton dissolution.