Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

7C/2003G096

Local structures of nano-structured Fe clusters
Yu OKUNO1, Yoshiyuki HATTORI3, Yohko NOBUHARA1, Hiroshi NOGUCHI1,Takehisa KONISHI2, Hirofumi KANOH1, 2, Katsumi KANEKO*1, 2
1Graduate school of science, Chiba Univ., Inage, Chiba 263-8522, Japan2
Department of chemistry, Faculty of science, Chiba Univ., Inage, Chiba 263-8522, Japan
3
Institute of research and innovation, Takada, Kashiwa, Chiba 277-0861, Japan

Experimental
The FeCl3 were dissolved in the aqueous solution ofpoly(vinylalcohol) (PVA). The NaOH aqueous solution
3+
was pored into the mixed solution of Fe ions and PVApolymers at 353 K. The precipitations were obtained andwere separated by filtration. The precipitates were driedat room temperature after washing with distilled water.
The dried precipitates were heated at 973 K under
nitrogen gas flow. The nano-Fe has been obtained by the3+
thermal decomposition of Fe /PVA composites. TheXAFS measurements were performed on Fe K-edge atBL-7C beam line with transmission mode. Samples wereadjusted in a sufficient quality to give an edge jump. The
program code FEFF8 was used to calculate the theoreticalphase and amplitude for curve fitting.
Results and Discussion
The XANES spectrum of nano-Fe became abroadening compared with that of Fe foil, owing to aconsequence of the cluster-size distribution [2].
The
radial distribution functions (RSFs) calculated from theEXAFS signals for the Fe foil and the nano-Fe are shownin Figure 1. Although these RSFs show few peaks
coming from the scattering of neighboring Fe atoms, theintensity of the peaks in the nano-Fe was smaller than thatin the Fe foil, suggesting the decrease in the amplitude ofthe χ(k) related to the structural parameters. The170

Users' Reportstructural parameters are calculated from the EXAFS databy curve fitting the first peak of the RSF. Table 1 shows
the coordination number (N), nearest-neighborinteratomic distance (R), Debye-Waller factor (σ) of theFe foil and the nano- Fe. The σ value of the nano-Fe waslager than that of the Fe foil, suggesting the degradationof the structures in Fe clusters. The drastic decrease inthe N of the nano-Fe was also observed, owing to theformation of the very small clusters. Because small
clusters with nano-dimensions have a significant fractionof the atoms located on the surface, the RSF shows areduction in the coordination numbers.

Fe foilnano-FeFT amplitude

Introduction
The structural properties of nano-metals are of interestin the variety of fields in solid-state physics and chemistry.
Their structural properties influence on their physical andchemical properties, such as the enhancement of chemical
reactivity, the lowering of the melting temperature, andthe magnetic behavior. We have succeeded to synthesize
the metallic nickel colloids with nano-porosities [1]. The
XAFS studies on the nickel colloids have been performed
and have elucidated that the colloids have a characteristic
local structure. Recently, we also have synthesized thenano-structured iron clusters (nano-Fe) that are stable inatmosphere. The clusters are too small to characterize
their structures by diffraction techniques. The TEM
photographs of the clusters cannot be obtained, because
they are unstable under the irradiation of the electronbeam. In this work, we report an investigation on thestructural properties of nano-Fe by Fe K-edge XAFS
spectra.

0123R/Å

456Figure 1. The radial distribution functions of Fe foil andnano-Fe.
Table 1: The local structural parameters of Fe foil andnano-Fe.
22NR/ Åσ /Å
Fe foil
8.15
2.52
0.00443
Nano-Fe
2.73
2.510.00716

References[1] Y. Hattori et al., Adv. Matr. 15, 529 (2003).
[2] A. Balerna et al., Phys. Rev., B31, 5058 (1985).
* kaneko@pchem2.s.chiba-u.ac.jp