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 h010i 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.