Enhanced electronic conductivity by controlled self-doping in pyrochlores

Abstract

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 Y₂Ti₂O₇. 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.