Origin of the different conductive behavior in pentavalent-ion-doped anatase and rutile TiO$_2$

TL;DR

This study uses spin-polarized GGA+U calculations to explain why pentavalent-ion doping results in metallic behavior in anatase TiO$_2$ and insulating behavior in rutile TiO$_2$, aligning with experimental observations.

Contribution

It reveals the fundamental electronic differences caused by doping in anatase and rutile TiO$_2$, providing insights into their distinct conductive properties.

Findings

Doped anatase TiO$_2$ shows n-type half-metallic behavior.

Doped rutile TiO$_2$ remains insulating with Fermi level between gap states.

Results explain experimental differences in electronic transport.

Abstract

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+\emph{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 3\emph{d} states lie near the conduction band bottom and cross the Fermi level, showing an \emph{n}-type half-metallic character. For doped rutile TiO$_2$, the Fermi level is pinned between two up-spin-polarized Ti 3\emph{d} gap states, showing an insulating character. These results can account well for the experimental different electronic transport properties in Nb (Ta)-doped anatase and rutile TiO$_2$.