Control of mixed protonic and electronic conductivity by mixing rare-earth ortho-borates

In order to develop mixed protonic and electronic conductors, we proposed a novel concept for material design that enables to control partial conductivities by fabricating solid solutions of protonic and electronic conductors. In this work, Sr-doped LaBO3 and Sr-doped CeBO3 were chosen as model compounds conducting protons and electron holes, respectively. Solid solutions of the above borates, Sr-doped La1 − xCexBO3, were prepared, and their electrical conductivities were investigated in 8.5 × 102–4.2 × 103 Pa of p(H2O) and 1.0 × 10–1.0 × 105 Pa of p(H2) at 1073 K. From the experimental results of the gas partial pressure dependences of the conductivities, major charge carrier species were identified as a function of x. It was found that proton was the major charge carrier when x < 0.2 while the contribution of the electron hole conduction became remarkable as x increased above 0.2. The contribution of the electron hole conduction can be interpreted by the percolation model.