Low-Temperature Diffusion
of Oxygen through Ordered Carbon Vacancies in Zr<sub>2</sub>C<sub><i>x</i></sub>: The Formation of Ordered Zr<sub>2</sub>C<sub><i>x</i></sub>O<sub><i>y</i></sub>
- Publication date
- Publisher
Abstract
Investigations are performed on low-temperature oxygen
diffusion in the carbon vacancy ordered ZrC<sub>0.6</sub> and thus
induced formation of the oxygen atom ordered ZrC<sub>0.6</sub>O<sub>0.4</sub>. Theoretically, a superstructure of Zr<sub>2</sub>CO can
be constructed via the complete substitution of carbon vacancies with
O atoms in the Zr<sub>2</sub>C model. In the ordered ZrC<sub>0.6</sub>, 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<sub>0.6</sub>O<sub>0.4</sub>. Relative to the ordered
ZrC<sub>0.6</sub>, the Zr positions are finely tuned in the ordered
ZrC<sub>0.6</sub>O<sub>0.4</sub> 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<sub>0.6</sub> along
some special zone axes. Similar to the vacancies in ordered ZrC<sub>0.6</sub>, the ordering arrangement of O atoms in the ordered ZrC<sub>0.6</sub>O<sub>0.4</sub> is in nanoscale length, thus forming the
nano superstructural domains with irregular shapes
