L10 Ordering of Ultrasmall FePt Nanoparticles Revealed by TEM In Situ Annealing

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• 作者：Micha毛l Delalande ; Maxime J.-F. Guinel ; Lawrence F. Allard ; Anastasia Delattre ; R茅my Le Bris ; Yves Samson ; Pascale Bayle-Guillemaud ; Peter Reiss
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：March 29, 2012
• 年：2012
• 卷：116
• 期：12
• 页码：6866-6872
• 全文大小：559K
• 年卷期：v.116,no.12(March 29, 2012)
• ISSN：1932-7455

文摘

The transformation of 鈮? nm equiatomic FePt nanoparticles from the disordered cubic A1 to the ordered tetragonal L1₀ phase was studied by means of high-resolution transmission electron microscopy coupled with in situ heating experiments. In accordance with ex situ annealing experiments, a transition temperature of around 500 掳C was determined. Diffusion is enhanced at surfaces and plays a dominant role in the ordering process. Hence, the ordering of the crystallographic structure starts at the surface of the nanoparticles and propagates toward their center, resulting in complete ordering within some minutes, for temperatures above 600 掳C. Unlike the generally assumed lower limit of ordering (3.5 nm), we demonstrate that ultrasmall (less than 3 nm) FePt nanoparticles can also be fully transformed to the L1₀ phase. The well-controlled and precise stoichiometry (Fe_50聽at.%Pt_50聽at.%) and the homogeneous composition of these particles both play a major role in their successful phase transformation.