Time-of-flight neutron diffraction of nanocrystalline powders of nonstoichiometric niobium carbide NbC$_{0.77}$

The evolution of the microstructure of nonstoichiometric niobium carbide NbC$_{0.77}$ powders subjected to high-energy ball milling has been investigated using time-of-flight neutron diffraction. It has been found that the nanocrystalline powders prepared by milling have a microinhomogeneous structure and contain two clearly identified fractions that differ from each other by the sizes of their particles. One fraction has a particle size of less than 60 nm, whereas the particle size of the second fraction exceeds 250 nm. The average size of coherent scattering regions and the value of microstrains in nanocrystallites, which accounts for the anisotropy of strain-induced distortions, have been estimated.