A First Principles Investigation of Native Interstitial Diffusion in Cr2O3

TL;DR

This study uses first principles DFT calculations to analyze native interstitial defects and their diffusion mechanisms in Cr2O3, revealing species-dependent mobility and complex diffusion pathways.

Contribution

It provides detailed insights into the defect structures, charge states, and diffusion mechanisms of interstitials in Cr2O3 using first principles calculations.

Findings

Interstitials are more mobile than vacancies.

Cr interstitials diffuse via a two-step process involving defect complexes.

O interstitials diffuse through bond switching, with high mobility in negative charge states.

Abstract

First principles density functional theory (DFT) investigation of native interstitials and the associated self-diffusion mechanisms in {\alpha}-Cr2O3 reveals that interstitials are more mobile than vacancies of corresponding species. Cr interstitials occupy the unoccupied Cr sublattice sites that are octahedrally coordinated by 6 O atoms, and O interstitials form a dumbbell configuration orientated along the [221] direction (diagonal) of the corundum lattice. Calculations predict that neutral O interstitials are predominant in O-rich conditions and Cr interstitials in +2 and +1 charge states are the dominant interstitial defects in Cr-rich conditions. Similar to that of the vacancies, the charge transition levels of both O and Cr interstitials are located deep within the bandgap. Transport calculations reveal a rich variety of interstitial diffusion mechanisms that are species, charge, and orientation dependent. Cr interstitials diffuse preferably along the diagonal of corundum lattice in a two step process via an intermediate defect complex comprising a Cr interstitial and an adjacent Cr Frenkel defect in the neighboring Cr bilayer. This mechanism is similar to that of the vacancy mediated Cr diffusion along the c-axis with intermediate Cr vacancy and Cr Frenkel defect combination. In contrast, O interstitials diffuse via bond switching mechanism. O interstitials in -1 and -2 charge states have very high mobility compared to neutral O interstitials.