Anatase- and rutile-type Nb- and Ta-doped TiO${}_2$ compounds have different electronic properties. While doped anatase TiO${}_2$ is a transparent metallic material, doped rutile TiO${}_2$ behaves as a semiconductor. Density-functional calculations within the (semi)local-density approximation predict the metallization of both anatase and rutile TiO${}_2$ with Nb or Ta doping while the on-site Coulomb correction has prevented metallization in both systems. We present screened-hybrid-density-functional calculations of Nb- and Ta-doped TiO${}_2$. The calculations show that doped anatase TiO${}_2$ is metallic, and doped rutile TiO${}_2$ is a semicondutor with the in-gap state related to a Ti${}^{3+}$ species. The difference in the electronic states of the Nb- and Ta-doped TiO${}_2$ is clearly shown.

• Received 22 October 2011

DOI:https://doi.org/10.1103/PhysRevB.85.033104