Low-Temperature Diffusion of Oxygen through Ordered Carbon Vacancies in Zr₂C_x: The Formation of Ordered Zr₂C_xO_y

Abstract

Investigations are performed on low-temperature oxygen diffusion in the carbon vacancy ordered ZrC(0.6)and thus induced formation of the oxygen atom ordered ZrC(0.6)O(0.4). Theoretically, a superstructure of Zr(2)CO can be constructed via the complete substitution of carbon vacancies with O atoms in the Zr(2)C model. In the ordered ZrC(0.6), the consecutive arrangement of vacancies forms the vacancy channels along some zone axes in the C sublattice. Through these vacancy channels, the thermally activated oxygen diffusion is significantly facilitated. The oxygen atoms diffuse directly into and occupy the vacancies, producing the ordered ZrC(0.6)O(0.4). Relative to the ordered ZrC(0.6), the Zr positions are finely tuned in the ordered ZrC(0.6)O(0.4) because of the ionic Zr-O bonds. Because of this fine adjustment of Zr positions and the presence of oxygen atoms, the superstructural reflections are always observable in a selected area electron diffraction (SAED) pattern, despite the invisibility of superstructural reflections in ZrC(0.6) along some special zone axes. Similar to the vacancies in ordered ZrC(0.6), the ordering arrangement of O atoms in the ordered ZrC(0.6)O(0.4) is in nanoscale length, thus forming the nano superstructural domains with irregular shapes.

A Non-Thermal Plasma Route to Plasmonic TiN Nanoparticles

“…It is reasonable to expect that the high density of vacancies in the nitrogen-deficient particles makes them more susceptible to oxidation, with oxygen clearly diffusing within the core of the particles. This vacancy-induced oxidation mechanism has been reported for other refractory materials such as ZrC …”

“…This vacancy-induced oxidation mechanism has been reported for other refractory materials such as ZrC. 48 Role of Oxidation on the Plasmonic Response. We have investigated the role of oxidation on the plasmonic response of TiN particles by monitoring the changes in their optical properties after annealing in air.…”

On the stoichiometry of zirconium carbide

“…It is also possible for carbon or oxygen to occupy the octahedral interstitial vacancies of the Zr lattice 20,21 . The oxycarbide was shown to exhibit the exact same rock salt structure of ZrC x (see the Powder Diffraction File, PDF, 035 0784 22 ) with similar 23 or smaller cell parameters 21 . Gendre et al 17 observed that oxycarbides with C/Zr ≥ 0.8, have the same XRD pattern as ZrC x while oxycarbides with C/Zr ≤ 0.7 could instead display some additional zirconia peaks 17 .…”

First‐principles study of the thermal properties of Zr2C and Zr2CO

“…The space group for both Zr 2 C and Zr 2 CO is Fd $$\bar{3}$$ m . The crystal structures of Zr 2 C and Zr 2 CO, which are shown in Figure 1, were built based on Rietveld refinement of X‐ray diffraction patterns 21 . First‐principles calculations were employed to optimize the crystal structures and to calculate the second‐order elastic constants.…”

“…The crystal structures of Zr 2 C and Zr 2 CO, which are shown in Figure 1, were built based on Rietveld refinement of X-ray diffraction patterns. 21 First-principles calculations were employed to optimize the crystal structures and to calculate the second-order elastic constants. Phonon calculations were conducted with the finite displacement method.…”