Stabilization of the gamma phase in Fe–Pt alloy nanoparticles with low Pt contents prepared by chemical synthesis method

Nanometer-sized particles (nanoparticles) of Fe–Pt alloy having less than 25 at.% Pt were prepared by a chemical synthesis method which Sun et al. recently reported. In this method, iron pentacarbonyl (Fe(CO)5) and platinum acetylacetonate (Pt(acac)2) are used as raw materials for the component metals. Crystal structure and phase transformation of the alloy nanoparticles were examined by transmission electron microscopy and electron diffraction, and chemical composition by energy-dispersive X-ray spectroscopy as well. As a result, it was found that even the γ phase nanoparticles with an average composition of Fe–5.4 at.% Pt did not show any martensitic transformation upon cooling from an austenitizing temperature to room temperature. This marked stabilization is discussed from a thermodynamic point of view, referring to previous work on Fe–Ni and Au–Cd alloy nanoparticles.