Positron annihilation lifetime spectroscopy (PALS) has indicated that Nb2O5‐doped TiO2 samples treated
in either Ar or air at 1400°C for 48 h are both charge‐compensated by Ti vacancies, but with statistically significant differences between the results. A Ta2O5‐doped
air‐sintered TiO2 sample also showed behavior similar to the Nb2O5‐doped air‐sintered TiO2.
In addition, Nb2O5‐doped SnO2 samples sintered in air at 1400°C for 1 h showed evidence of Sn
vacancy cluster formation, with no indications of Sn2+ compensation from ultraviolet irradiation studies. PALS studies of air‐sintered ZrO2 did not show any
evidence of Zr vacancies after doping with Nb2O5.