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

In this research, we investigated the real structure and thermal evolution of niobium nanoparticles. The nanoparticles we studied were prepared using a magnetron-based gas aggregation cluster source (Haberland-type gas) from a high-purity Nb target in an argon atmosphere.

The phase composition, morphology, and the real structure of nanoparticles (i.e., the size and shape distributions, lattice parameters, lattice defects, and size of coherently diffracting domains) were investigated by a combination of small angle X-ray scattering, X-ray diffraction, and electron microscopies. In order to describe the thermal stability and evolution of the nanoparticles, a critical issue for all elevated temperature applications, the in-situ SAXS and XRD experiments were performed under the air atmosphere up to 800 °C.

As prepared, spherical nanoparticles with a mean particle size of approximately 25 nm contained pure BCC-phase Nb in the core with a thin 1.5 nm oxide shell at the surface. The size of coherently diffracted domains corresponds to the mean nanoparticle size, implying that, in the initial state, each nanoparticle is formed by one crystallite. At temperatures up to 200 °C, the nanoparticles’ phase composition and internal structure do not significantly change. Above 200 °C, the amorphization of nanoparticles occurs consequently, followed by the nucleation and creation of crystalline TT-Nb2O5 phase at around 450 °C. The hexagonal structure of this phase was solved in the current study from the powder diffraction pattern. Increasing the temperature to 600 °C results in conversion to the orthorhombic T-Nb2O5 phase and in the coalescence of individual nanoparticles. A detailed description of the thermal evolution of the microstructural parameters will be shown and discussed during the webinar.

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Materials Chemistry and Physics 277 (2022) 125466: https://doi.org/10.1016/j.matchemphys.2021.125466