Structural and compositional variations in Ta3N5 produced by high-temperature ammonolysis of tantalum oxide

A series of samples of Ta3N5 (Cmcm, a = 3.89 Å, b = 10.22 Å, c = 10.28 Å) have been produced by high temperature ammonolysis of amorphous tantalum oxide under various temperature and heating time regimes. These were characterised by powder diffraction (x-ray and neutron), combustion microanalysis, thermogravimetric analysis and transmission electron microscopy. All samples were found to contain oxide in the 3-coordinate anion site and the b-axis length was sensitive to compositional variation. Samples heated for longer times at higher temperatures were anion deficient. The compositions of the samples have been related to their optical band gap UV-visible spectra. This work highlights the importance of careful compositional analysis when samples of nitride materials are produced for real-world applications