Ba5Nb4O15 nanofibers with tailored nanofiber diameters are prepared via electrospinning, and treated in ammonia gas to synthesize niobate oxynitride nanofibers. Most importantly, the retain their fiber morphology during ammonolysis, diameter of converted fibers can be adjusted. Only a thorough characterization, including detailed Rietveld refinements, reveal that ammonolysis results not only Ba...