Abstract
Solid-state oxidation–reduction of a nonstoichiometric Nb12O29(NbO2.417) with monoclinic cell was studied using a JEOL 4000 EX HRTEM equipped with a gas reaction cell in which the oxide was oxidized and then reduced by sequentially introducing O2and H2. The oxidation yielded other block structures with higher oxygen content. The first step of the oxidation mechanism, involving formation oflamellardefects of composition Nb11O27(NbO2.450), could be elucidated with great certainty. Nb10O25(a metastable polymorph of NbO2.500) was formed as a final stage of the oxidation process. Subsequent reduction led to a nearly ordered Nb12O29phase suggesting that such an oxidation-reduction reaction is a reversible process. When Nb12O29was directly reduced, NbO was found to grow on the surface of the crystal.
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