Anisotropic relaxations introduced by Cd impurities in Rutile TiO2: first-principles calculations and experimental support

TL;DR

This study combines first-principles calculations and experimental PAC measurements to investigate how Cd impurities induce anisotropic relaxations and alter the electric-field gradient orientation in TiO2.

Contribution

It provides the first combined theoretical and experimental analysis of impurity-induced relaxations and EFG changes in TiO2 with Cd impurities.

Findings

Strong anisotropic relaxations of oxygen neighbors predicted by calculations.

Change in EFG orientation from [001] to [110] confirmed experimentally.

V33 at the Cd site aligns with [110] or [1-10] axes.

Abstract

We present an ab initio study of the relaxations introduced in TiO2 when a Cd impurity substitutes a Ti atom and the experimental test of this calculation by a perturbed-angular-correlation (PAC) measurement of the orientation of the electric-field gradient (EFG) tensor at the Cd site. The ab-initio calculation predicts strong anisotropic relaxations of the nearest oxygen neighbors of the impurity and a change of the orientation of the largest EFG tensor component, V33, from the [001] to the [110] direction upon substitution of a Ti atom by a Cd impurity. The last prediction is confirmed by the PAC experiment that shows that V33 at the Cd site is parallel to either the [110] or the [1\bar{1}0] crystal axis.