  The control of the crystalline phases of the nanoparticles grown in a
direct-current transferred-arc plasma-assisted reactor is reported. The
crystalline phases of the as synthesized nanoparticles are shown to critically
depend on the operating gas pressure. The paper reports about the change in the
crystalline phases of three distinct compounds namely aluminium oxide (Al2O3),
aluminium nitride (AlN) and iron oxide (FexOy). The major outcome of the
present work is that the phases having higher defect densities are more
probable to form at the sub-atmospheric operating pressure. The variations in
the crystalline structures are discussed on the basis of the equilibrium defect
density formed during the homogeneous nucleation. The as synthesized
nanoparticles were examined by X-ray diffraction analysis and transmission
electron microscopy. In addition, the confirmatory analysis for the crystalline
phases of the as synthesized iron oxides was carried out with the help of
Mossbauer spectroscopy.
