Supposed Versatile β-TaxOyNz Structures: DFT Studies

In the last decade, tantalum oxynitride material has been proposed as an interesting photo-catalyst for its spectral response extension in the visible light and good efficiency in water splitting process [1]. The electronic and structural properties of crystalline materials based on ß-TaON (baddeleyite-type) have been theoretically investigated (PBE, B3LYP) in the density functional theory (DFT). The effects of Ta-vacancies, together with changes of the stoichiometry ratio Ta:O:N, suggested from experimental literature, are investigated. The electronic properties are valued by changing N and O atom positions in the crystallographic TaON, to reach the most stable form. The ß-form of TaON is an n-type semiconductor when O prevails, while is a p-type semiconductor when N prevails. Consideration was given on the formation of acceptors or donors states related to the energetic positions. A structure with the best stability has also been found when a Ta-vacancy is formed in conjunction to an O increase. A model of the crystal structure that fully meets the experimentally observed properties (optical, structural and stoichiometric ratio) is proposed.