Abstract
Highly porous structures consisting of niobium nanoparticles (Nb NPs) are prepared using magnetron sputtering and inert gas aggregation method. Alongside the thermally-driven evolution of nanoparticle morphology, the microstructural genesis is probed in-situ by x-ray diffraction for the temperature range up to 800 degrees C.
The asdeposited Nb NPs are formed by the Nb core and NbOx shell. The elevated temperature triggers the gradual oxidation that proceeds until 200 degrees C.
Above this point the structure is fully amorphous. Further increase of the temperature to 450 degrees C leads to a transition to the crystalline TT-Nb2O5 phase, which hexagonal structure was solved in the current study.
The subsequent rise of the temperature to 600 degrees C results in the conversion to the orthorhombic T-Nb2O5 phase. Up to this state, the size of nanoparticles corresponds to the size of crystallites.
The annealing above 600 degrees C causes coalescence of NPs with the formation of hundreds-of-nanometers large structures.