Synthesis of niobium oxide nanopowders by field-crystallization-assisted anodization

Herein, for the first time, we demonstrate that a large quantity of niobium oxide nanopowders consisting of amorphous round shape nanoparticles and highly crystalline needle shape nanoparticles can be prepared by anodization of a niobium foil in ethylene glycol containing NH4F at a high voltage. FE-SEM, TEM, XRD measurements were performed to characterize the anodically prepared nanopowders and to reveal the formation mechanism. We ascribed the formation of niobium oxide nanopowders on the foil to field-crystallization induced breakdown of oxide film and chemical dissolution.