Formation and stability of reduced TiO_x layers on anatase TiO_2(101): identification of a novel Ti_2O_3 phase

TL;DR

This study uses DFT calculations to identify a novel Ti2O3 phase on reduced TiO2 layers, which may influence the properties of black TiO2 in photocatalysis.

Contribution

It introduces a new csp-Ti2O3 phase with distinct structure and similar properties to known Ti2O3, expanding understanding of reduced TiO2 surfaces.

Findings

Identification of a new Ti2O3 phase on TiO2 surfaces

The csp-Ti2O3 phase is energetically close to α-Ti2O3

Potential role in black TiO2 photocatalytic properties

Abstract

We use density functional theory (DFT) calculations to investigate structural models consisting of anatase TiO2(101) slabs covered by reduced overlayers formed by (101) crystallographic shear planes (CSPs). Ab initio thermodynamics supports the stability of these structures under a wide range of experimental conditions. The overlayers are found to have Ti2O3 stoichiometry with a crystal structure different from the known corundum-like Ti2O3 (here denoted {\alpha}-Ti2O3) phase. DFT calculations predict this new "csp-Ti2O3" phase to be energetically close to {\alpha}-Ti2O3 and to have also a similar band gap. These results suggest a possible role of the csp-Ti2O3 phase in the properties of black TiO2, a promising photocatalytic material made of nanoparticles with a crystalline TiO2 core and a highly reduced TiOx shell that is capable of absorbing the whole spectrum of visible light.