Chemistry Reference
In-Depth Information
Fig. 4.27 4.2 K Mössbauer
spectrum under 6 T of FeF
3
nanostructured powder
ground for 48 h and its
decomposition with
speromagnetic (up) and
antiferromagnetic (middle)
structures attributed to grain
boundaries and crystalline
grains, respectively [
165
]
-12
-6
0
6
12
V (mm/s)
The proportions of each component have to be derived from the fitting model
which does describe the Mössbauer spectra recorded at different temperatures, for
different grinding times and milling conditions. It is clearly established that the
evolution of the crystalline component decreases when the grinding time increases
at the expense of the grain boundaries whereas the estimated proportions are found
to be rather similar to those estimated from X-ray diffraction patterns, assuming
spherical grains.
Furthermore, in-field Mössbauer spectrum was recorded in presence of an
external magnetic field of 6T oriented parallel to the c-beam on the 48 h ground
powder. As illustrated in Fig.
4.27
, the decomposition into 2 components which
gives rise to a good description of the hyperfine structure, is fairly consistent with
previous conclusions. Indeed, one component is unambiguously attributed to the
antiferromagnetic crystalline grains through the value of the hyperfine field and the
significant increase of intermediate line intensities (close to 3:4:1:1:4:3) while the
second one results from a speromagnetic structure as in the case of the amorphous
varieties, allowing to be assigned to the presence of grain boundaries. The pro-
portions of these two structural components which derive from their respective
absorption area, assuming the same values of recoilless factors [
167
], are con-
sistent with those estimated from series of zero field Mössbauer spectra [
165
], and
those from X-ray diffraction and solid state
19
F,
69
Ga and
71
Ga applied to ball-
milled ionic GaF
3
[
168
].
