First-principles GGA+Ustudy of the different conducting properties in pentavalent-ion-doped anatase and rutile TiO2

The electronic properties of pentavalent-ion (Nb 5+ , Ta 5+ , and I 5+ ) doped anatase and rutile TiO 2 are studied using spin-polarized GGA + U calculations. Our calculated results indicate that these two phases of TiO 2 exhibit different conductive behavior upon doping. For doped anatase TiO 2 , some up-spin-polarized Ti 3d states lie near the conduction band bottom and cross the Fermi level, showing an n-type half-metallic character. For doped rutile TiO 2 , the Fermi level is pinned between two up-spin-polarized Ti 3d gap states, showing an insulating character. In addition to the Nb (Ta)-doped anatase TiO 2 , we propose that the I-doped anatase TiO 2 can also be a potential transparent conducting oxide, which is worthy of further experimental verification. These findings clarify the long-standing controversy of whether GGA + U calculation can successfully predict the conducting property in the Nb (Ta)-doped anatase phase and the insulating property in the rutile phase. Moreover, our results show that the symmetry breaking can cause a metal-insulating transition in pentavalent-ion-doped anatase TiO 2 , though this symmetry breaking may not occur spontaneously because of the relatively high energy barrier.