Local structural changes are studied occurring during transformation from a
morphous to nanocrystalline phases of Fe8.5Zr7B6Cu2, Fe73.5Cu4Nb3S15.5B7 an
d Fe6.6Cr8Cu4Nb3Si13B9 alloys. The nanocrystalline state of a formerly amor
phous alloy was achieved by heat treatment at temperatures between 420 and
600 degreesC. The high-resolution transmission electron microscopic images
have shown the average size of the Fe and Fe(Si) nanograins in nanocrystall
ine alloys ranging from 5 to 15 nm in alloys at different stages of crystal
lisation. X-Ray absorption spectra at the K-edge of Fe, Cu and Cr atoms for
nanocrystalline alloys measured using synchrotron radiation have shown a d
ifferent local structure, namely the structure bcc Fe around Fe atoms, fcc
Cu around Cu atoms and amorphous around Cr atoms. The growth of fcc Cu clus
ters before the nucleation of bcc Fe grains in nanocrystalline alloys was o
bserved. It can be considered as a basic mechanism responsible for nanocrys
talline grain formation. The FEFF8 program was used for calculations of X-r
ay absorption spectra up to about 260 eV above the Fe K-edge for bcc Fe met
al and Fe3Si compound in terms of self-consistent muffin-tin potential appr
oximation and full multiple scattering approach. The theoretical spectra we
ll explained the experimental result that the amplitude of EXAFS oscillatio
ns in Fe,Si was considerably decreased by the presence of Si atoms in compa
rison to that for Fe metal. (C) 2001 Elsevier Science B.V. All rights reser
ved.