The purpose of the study was to investigate the formation of the crystal structure of hexagonal boron nitride (h-BN) nanoparticles obtained by the chemical-thermal method using two-stage heat treatment. Boric acid and urea were used as starting precursors, enabling ammonia-free synthesis conditions. It is shown that the first thermal stage at 600 °C under a nitrogen atmosphere leads to the formation of a predominantly amorphous BN-containing precursor, whereas the second stage at 1000 °C in an N2/H2 atmosphere promotes crystallization of a highly ordered hexagonal h-BN phase. The morphology and particle size distribution were examined by transmission electron microscopy, while the phase composition and crystal structure were analyzed by X-ray diffraction followed by Rietveld refinement. The obtained h-BN nanoparticles exhibit a narrow size distribution of 2–10 nm and a high degree of crystallinity (up to ~99%). Structural modeling and electron density analysis performed using the VESTA software confirm the formation of a layered hexagonal h-BN lattice with an interplanar spacing of approximately 3.3 Å. The results highlight the critical role of the two-stage thermal treatment and gas atmosphere in controlling the crystallinity and structural ordering of h-BN nanoparticles.
Abdurakhmonov et al. (Fri,) studied this question.