Intermediate-Temperature Proton Conduction in Al[sup 3+]-Doped SnP[sub 2]O[sub 7]

-doped proton conductors were prepared by controlling the initial composition of the reactants [ , , and ]. with displayed conductivities approximately two orders of magnitude lower than , while those of with exhibited conductivities at a maximum of 1.99 times higher. However, because the conductivity values of with were not stable, the optimal value of in was determined to be 2. Partial substitution of for in led to an increase in the conductivity up until . As a result, the conductivity reached at , at , and at when the and values were 0.05 and 2, respectively. A hydrogen concentration cell with this material demonstrated that the ionic transport number was , and a fuel cell using this material demonstrated that the dc conductivity was comparable to the ac conductivity.