Formation Mechanism of FePt Nanoparticles Synthesized via Pyrolysis of Iron(III) Ethoxide and Platinum(II) Acetylacetonate

Abstract

In this study the mechanism for the formation of FePt nanoparticles (NPs) via the pyrolysis of iron(III) ethoxide [Fe(OEt) 3 ] and platinum(II) acetylacetonate [Pt(acac) 2 ] is investigated. We have recently reported that monodispersed equiatomic FePt NPs with a mean diameter of 4.5 nm and a narrow composition distribution were successfully synthesized by this route. However, control of the mean size and further narrowing of the size distribution have not yet been achieved. In the present study, we systematically examined variability in the particle size D p, size distribution σ, and atomic composition of the NPs with changing synthetic conditions such as reaction temperature, rate of temperature increase, and total amounts and input molar ratios of precursors and capping agents. As a result, D p was varied from 1.8 to 6.8 nm, the best size distribution σ achieved was 16%, and the Fe content of the NPs varied from 29 to 51 atomic %. On the basis of the experimental results, we determined the following important aspects of the reaction mechanism: (i) The FePt NPs are rapidly formed at 250−297 °C by the allelocatalytic decomposition of precursors. (ii) The formation of FePt NPs is dominated by nucleation of Pt followed by a slow growth process of Fe (and Pt) atoms. (iii) Fe and Pt atoms are stabilized by oleic acid and oleylamine, respectively.