Tailoring the anion stoichiometry and oxidation kinetics of vanadium (oxy)nitride by the control of ammonolysis conditions

Abstract

Higher N/O increases significantly the V(O,N) oxidation resistance.

The effect of ammonolysis conditions on the structural properties and oxidation kinetics of cubic niobium oxynitride

“…7 shows the SEM micrographs of the Nb 2 O 5 precursor as well as niobium oxynitride powders synthesized for 12 h as a function of temperature. From the SEM results, no significant morphological differences were observed, in good agreement with previous literature, 54 in which authors reported that the use of ammonolysis does not substantially influence the final morphology of the obtained powders.…”

“…The cation-vacancy mechanism of (eqn 7) cannot fulfill this requirement, as this equation infers a constant cation oxidation state of 3 + , with ammonolysis, as recently experimentally shown for vanadium oxynitrides. 28 An equivalent case to vanadium oxynitride is not seen in the current work, and, thus, cation vacancies alone cannot explain the measured stoichiometries of the present niobium oxynitride system.…”

“…4 and 5. One could predict that the formation of cation vacancies, (eqn 7), would suggest a strong decrease in lattice parameter on increasing oxygen content, as previously seen for the vanadium oxynitride system, 28 whilst (eqn 8, 9 and 10), may result in weaker lattice parameter changes, as the expansion of the lattice by oxygen incorporation may be partially offset by the reduction in lattice parameter expected by the oxidation of Nb 3+ to Nb 5+ , for charge compensation. To confirm these hypotheses, further experiments are recommended, which can provide higher sensitivity to the anion lattice, such as that of neutron diffraction.…”

“…27 As documented for other transition-metal oxynitrides, the experimental parameters utilized during this synthesis route can have great impact on the final oxynitride composition. 11,15,28,29 Among these experimental variables, temperature, dwell time, heating/cooling rates and flow rate of NH 3 are reported to be key parameters that can introduce significant variations in the final stoichiometry. 30 From a thermodynamic point of view, ammonia decomposition to nitrogen and hydrogen is predicted to start at low temperatures (∼200 °C), Fig.…”

Formation Mechanism of Passivation Layer under Air Exposure on TiZrV Non-Evaporable Getter Film

“…Figures – show the XPS results of the surface composition variation of the TiZrV NEG films after undergoing different storage periods when wrapped by aluminum foil. With prolonging the storage time under conditions set in this research, a significant change of the film surface layer has occurred: For the N 1s spectra, there were some amounts of N–H and AlN* were gradually formed apart from the moderate-screened γ-N 2 , well-screened γ-N 2 , and M-N For the C 1s spectra, C x H y − has undergone more significant changes in terms of structure and content compared to other carbonaceous compositions such as −COO–, − −CO–, ,, and carbides. , For the O 1s spectra, the content of oxides decreased greatly as C x H y increased significantly. For different metallic elemental p or d spectra, various kinds of oxides (TiO 2 , Ti 2 O 3 , ZrO 2 , and VO 2 ), hydroxyl groups (Ti-hydroxyl groups, Zr-hydroxyl groups, and V-hydroxyl groups), and carbides (TiC, ZrC*, and VC) were detected on the surface or in the surface layer of the film. …”