Thermally-driven morphogenesis of niobium nanoparticles as witnessed by in-situ x-ray scattering

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 °C. The as-deposited Nb NPs are formed by the Nb core and NbOx shell. The elevated temperature triggers the gradual oxidation that proceeds until 200 °C. Above this point the structure is fully amorphous. Further increase of the temperature to 450 °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 °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 °C causes coalescence of NPs with the formation of hundreds-of-nanometers large structures.