LaTiO2N nanopowders (NPs) with low surface defect density via nitridation of flame made NPs retaining simple perovskite structure

Abstract

This work introduces a novel route to perovskite LaTiO₂N nanopowders (NPs) via nitridation of perovskite LaTiO₃ NPs in an NH₃ gas flow at 1050 °C/NH₃/15 h, in which a simple perovskite structure (ABX₃) is retained during nitridation. The LaTiO₃ NP is formed with a trace of a second phase in a precursor oxide NP (LTO-4/3) produced using liquid-feed flame spray pyrolysis (LF-FSP) of a metallo-organic ethanol solution with La/Ti = 4/3. The characterization of the resulting powders allows for a comparison with LaTiO₂N NPs synthesized by the nitridation of the La₂Ti₂O₇ precursor oxide NP (LTO-1) with a perovskite slab structure (A₂B₂X₇) also prepared by LF-FSP of a La/Ti = 1 solution. Williamson–Hall plots suggest that the as-produced LaTiO₂N from LTO-1 offers a quite small but effective crystallite size of 16–18 nm with almost no lattice spacing fluctuations, while LaTiO₂N from LTO-4/3 presents a larger effective crystallite size of 50–52 nm with some lattice spacing fluctuations. UV-vis diffuse reflectance analysis reveals that, unlike LaTiO₂N from LTO-1, the spectra of LaTiO₂N from LTO-4/3 show a quite low absorption background above the wavelength of the optical absorption edge (∼580 nm), suggesting good crystallinity with a very low surface defect density. Both oxynitride NPs appear to offer utility as inorganic pigments with different colours, while LaTiO₂N NPs from LTO-4/3 have advantages for various applications, including potential as a visible-light-driven water splitting photocatalyst.