Metal oxynitrides: Tuning the properties of oxides by nitrogen incorporation - new syntheses approaches using TaON as a model material

Oxynitrides of transition metals, alkaline earth metals, and rare earth metals have been intensively studied in recent years as a group of materials designed to expand and refine the properties of oxides. Differences in polarizability, electronegativity, and anion charge of nitrogen and oxygen induce changes in the properties of oxides by nitrogen incorporation and expand the possibilities of tuning physical and chemical properties concerning the most used strategy of cation substitution. However, exploratory research with mixed anion chemistries is limited by the sensitivity of these materials to synthesis conditions. Here, we present syntheses approaches of oxynitrides using TaON (an n-type semiconductor for solar water splitting) as a model material. By combining pulsed laser deposition (PLD) of a Tantalum source (Ta or Ta₂O₅), with rapid thermal processing (RTP, annealing by high-intensity Halogen lamps), a systematic study of the nitrogen incorporation into the lattice was performed. By optimization of the N₂ and O₂ pressures in the PLD and RTP systems, attaining the desired anion stoichiometry is feasible, and the ability of RTP to enable amorphous to crystalline transitions without preferential anion loss is demonstrated.