Enhanced electronic conductivity by controlled self-doping in pyrochlores.

Most 5d transition-metal (TM) pyrochlores exhibit metallic behavior, but 3d and 4d TM pyrochlores are generally electronic semiconductors or insulators. Here, we report a semiconductor-metal transition induced by introducing excess Ti metal as interstitials into Y(2)Ti(2)O(7). These Ti interstitials prefer anion vacant 8a sites or bridge sites between two neighboring cations along the <010> direction. Density functional theory calculations suggest that an increased electronic conductivity originates from the interplay between the extra Ti and its neighboring cations. These findings suggest a means for achieving metallic behavior in semiconducting pyrochlore oxides and tuning the electronic conduction in pyrochlores for their electrochemical applications in solid oxide fuel cells.