Site identification of protons in SrTiO3: Mechanism for large protonic conduction

It is found that the proton is strongly absorbed in heavily Sc-doped SrTiO3. Neutron-diffraction measurements were performed using single crystals. The O-H distance is found to be about 1.2 Angstrom and the proton concentration is estimated to be about 2 mol% for SrTi0.98Sc0.02O3. Protonic conduction was observed in Sc-doped SrTiO3 by ac-conductivity measurements in wet air, while the hole conductivity was observed in dry air. The proton is bound by the oxygen ion as if the proton makes the hydrogen bond between two oxygen ions, which might be responsible for the high protonic conductivity in this material.