Mora-Fonz, D; Kaviani, M; Shluger, AL; (2020) Disorder-induced electron and hole trapping in amorphous TiO₂. Physical Review B , 102 (5) , Article 054205. 10.1103/PhysRevB.102.054205.

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Abstract

Thin films of amorphous (a) - TiO₂ are ubiquitous as photocatalysts, protective coatings, photo-anodes, and in memory applications, where they are exposed to excess electrons and holes. We investigate trapping of excess electrons and holes in the bulk of pure amorphous titanium dioxide, a - TiO₂, using hybrid density-functional theory (h-DFT) calculations. Fifty 270-atom a - TiO₂ structures were produced using classical molecular dynamics and their geometries fully optimized using h-DFT simulations. They have the density, distribution of atomic coordination numbers, and radial pair-distribution functions in agreement with experiments. The calculated average a - TiO₂ band gap is 3.25 eV with no states splitting into the band gap. Trapping of excess electrons and holes in a - TiO₂ is predicted at precursor sites, such as elongated Ti–O bonds. Single electron and hole polarons have average trapping energies (E_{T}) of - 0.4 eV and - 0.8 eV, respectively. We also identify several types of electron and hole bipolaron states and discuss their stability. These results can be used for understanding the mechanisms of photo-catalysis and improving the performance of electronic devices employing a - TiO₂.

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