Epitaxial strain dependence of band gaps in perovskite oxynitrides compared to perovskite oxides
Year: 2018
Type: article
Abstract: Perovskite oxynitrides are a promising class of materials for photocatalytic water splitting due to their small band gaps and suitably aligned band edges. Recently, epitaxially strained perovskite oxynitrides started to attract interest due to the possibility to engineer the anion order and ferroelectric distortions. However, contrary to perovskite oxides there have been no studies on the band-gap evolution in perovskite oxynitrides with epitaxial strain. Here, we investigate, using density functional theory calculations, the influence of epitaxial strain on the band gaps of two different perovskite oxynitrides and compare our results with perovskite oxides. As opposed to cubic oxides where both compressive and tensile strains narrow the band gap, we find that the anion order leads to nondegenerate N $2p$ bands already at zero strain, which leads to opposite and anion order-dependent evolutions of the band gap under compressive and tensile strain. Furthermore, we find that in perovskite oxynitrides polar distortions increase the band gap by up to 1 eV for 4% strain whereas for perovskite oxides the increase is only about 0.1 eV for the same amount of strain. The reason for this difference is the larger ionic radius and smaller electronegativity of nitrogen leading to larger ferroelectric distortions and a stronger dependence of the band gap on the distortion amplitude. These results imply that ferroelectric distortions are strongly detrimental to light absorption and that their suppression, for example, above a critical temperature, should result in a marked decrease in the band gap and enhanced absorption of visible light.
Source: BORIS (University Library Bern)
Institution: University of Bern
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3099931297