Abstract
In presented work we investigated the real structure and thermal evolution of niobium nanoparticles. Studied nanoparticles were prepared by magnetron-based gas aggregation cluster source (Haberland type GAS) from high purity Nb target in 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 combination of small angle x-ray scattering, x-ray diffraction and electron microscopy. In order to describe the thermal stability and evolution of nanoparticles, a critical issue for all its 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 mean particle size of 21.6 nm contained pure bcc Nb phase in the core with thin 0.9 nm oxide shell at the surface. The size of coherently diffracted domains corresponds to the mean nanoparticle size, which implicates that at initial state each nanoparticle is formed by one crystallite.
At the temperatures up to 200°C the phase composition and internal structure of nanoparticles does not significantly change. Above 200°C the amorphisation of nanoparticles occurs consequently followed by nucleation and creation of crystalline niobium oxides at around 450°C.
The detailed description of thermal evolution of microstructural parameters is shown and discussed in our work.