The Use of Combinatorial Chemical Vapor Deposition in the Synthesis of Ti3-δO4N with 0.06 < δ < 0.25: A Titanium Oxynitride Phase Isostructural to Anosovite

Abstract

We employ, for the first time, a unique combinatorial chemical vapor deposition (CVD) technique to isolate a previously unreported transition-metal mixed-anion phase. The new oxynitride phase, Ti(3-delta)O4N (where 0.06 < delta < 0.25), is the first example of a complex titanium oxynitride and was synthesized within composition graduated films formed from atmospheric pressure CVD of TiCl4, NH3, and ethyl acetate. Characterization was performed by X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible spectra, and SQUID magnetometry. The material crystallizes in the Cmcm space group, with the ordered nitrogen ions stabilizing the orthorhombic analogue of the monoclinic anosovite structure, beta-Ti3O5. The lattice parameters are sensitive to composition, but were determined to be a = 3.8040(1) A, b = 9.6486(6) A, and c = 9.8688(5) A for Ti(2.85(2))O4N. Powder samples were prepared through delamination of the thin films for synchrotron X-ray diffraction and magnetic measurements. It is the first example of a new phase to be synthesized using such a combinatorial CVD approach and clearly demonstrates how such techniques can provide access to new materials. This metastable phase with unusual nitrogen geometry has proved to be elusive to conventional solid-state chemistry techniques and highlights the value of the surface growth mechanism present in CVD. Furthermore, the ease and speed of the synthesis technique, combined with rapid routes to characterization, allow for large areas of phase space to be probed effectively. These results may have major implications in the search for new complex mixed-anion phases in the future.