On the spherical chromium oxide particulates via pulsed laser ablation at a very high power density in vacuum with a specified oxygen flow rate

Chromium oxide condensates nearly spherical in shape ranging from 0.1 to 0.2 micron in diameter were fabricated by laser ablation on a Cr target at a very high power density of 1.8×10¹² W/cm² for a very rapid heating and cooling effect. Analytical electron microscopic observations of such spherical particulates revealed three types: (1) α-Cr₂O₃ single crystal with ( $\bar{1}101),(\bar{1}012)$ and (1 $\bar{2}10)$ facets, (2) spinel-like Cr₃O₄ polycrystals with spherulitic texture, i.e. a rather corrugated solidification front, (3) recrystallized Cr₃O₄ polycrystals derived from type 2 by radiant heating. The microstructure and phase difference among the particulates can be attributed to a varied extent of supercooling under the influence of rather complicated Cr²⁺ solute trapping of the molten and solid phases in the Cr₃O₄?O pseudo-binary in vacuum. The chromium oxide condensates being spherical yet full of facets, with significant internal compressive stress up to ca. 3.4 GPa according to Raman shift, and with UV-absorbance close to violet light due to the presence of internal stress and/or Cr²⁺, may have potential optoelectronic and catalytic applications.