FCTO100. It presents, at room temperature, a cubic
structure belonging to the space group Ia
(#206),
with 16 molecules per unit cell (Z = 16). In this
structure the copper, titanium and iron are
localized in Wyckoff Positions 8b and 24d, where
oxygen is in site 48e (Table 2). The results of the
refinements carried out for CRFO100 and
FCTO100 structures are collected in the Table 3.
In the X-ray diffraction patterns of the
composites, we observe the presence of extra peaks
at (2θ): 29,88º; 33,98º e 34,74º, that probably are
associated to the fuse material used in the sintering
procedure.
In Figures 2(b) and 2(c) we have the
graphical criteria for the global view of the
CRFO66 and CRFO34. The refinement analysis of
the composites Z = 83, 50, 17 were carried out but
will not be presented in this paper. The major
numerical criteria of fit for this analyze were R
WP
,
S
Gof
and d
DW
(see Table 4).
From a purely mathematical point of view,
R
WP
is the most meagniful of the R’s because the
numerator is the residual being minimized [15]. As
show in the Tables 3 and 4, based on this criterion,
the refinement that more progressed was that for
the phase FCTO100. The value of the Durbin-
Watson d-statistic (d
DW
) shows the serial
correlation of the refinement, where an ideal value
should be around 2 [19-22], indicative of
insignificant serial correlation in the refinement
process. However, as shown in Tables 3 and 4, the
assigned standard deviations should not be
accurate. This is an expected result associated to
the presence of little amount of extra phases,
probably associated to fuse material used in the
sintering procedure of the ceramic. On the other
hand, the obtained values of S
Gof
around 1.0 are
showing that the models were adequate and,
because this, the refinement is presenting good
results.
In Table 5 we have the quantitative phase
analysis (QPA), without internal standard, of the
samples obtained from the refinement procedure.
One can observe that the QPA is in good agreement
for the composition of each composite phase in the
samples of CRFOZ for Z = 83, 66, 50, 34, 17. The
Rietveld´s method was successfully applied for
determination of the quantitative phase abundances
of the composite materials. In this procedure only
the phases CRFO100 and FCTO100 were
considered. The existence of extra phases is
probably the responsible for the observed variance
of the results. This is an extra confirmation of the
quality of the refinement of the X-ray diffraction
measurements.
Scanning Electron Microscopy
The morphology of the samples was
investigated by the Scanning Electron Microscopy
(SEM). In Figures 3(a)-(d) we have micrographs of
samples CRFO100, CRFO66, CRFO34 and
FCTO100, respectively.
For the CRFO100 (Fig. 3(a)) sample one
can notice a large variety of morphologies,
predominantly aggregates and polygonal shapes.
The sintering procedure appears to lead to a good
densification of the sample. For the CRFO66 (Fig.
3(b)) and CRFO34 (Fig. 3(c)) samples, polygonal
shapes for the grains are observed and wide grain
size distribution. For the FCTO100 (Fig. 3(d))
sample we observe a wide grain size distribution
with long cylindrical grains.
In Figure 4 and Table 6 we have the
electron-dispersive X-ray analysis (EDXS) for all
the studied samples. In the EDXS analysis, all the
peaks associated to main elements of the
composites like iron, chromium, copper, titanium,
and oxygen were observed. The bismuth and
carbon peaks are very weak in our present analysis,
and will not be considered in the following
examination.
Table 7 presents the values of each element
obtained from the EDXS analysis, together with the
nominal value used in the samples preparation. The
data obtained from the EDXS analysis is in good
agreement with the initial (nominal) values.
57
Fe Mössbauer Spectra
The experimental data were fitted using a
transformed pattern method of hyperfine field and
quadrupole splitting, in order to investigate the
influence due the great number of iron
microenvironments, characteristic of CRFO-FCTO
composites. We have used a set of 60 Lorentzians
to fit the experimental data. Figures 5, 6(a) and
6(b) show the Mössbauer spectra, the respective
quadrupole splitting and magnetic field pattern
distributions for CRFO(Z)-FCTO(100-Z) samples,
with Z =100, 83, 66, 50, 34, 17 and 0, respectively.
All the composites spectra can be interpreted as the
superposition of a broad sextet and a doublet. We
observe that at extremes of the interval considered,
the experimental spectra are respectively a
magnetic sextet (CRFO100) and a doublet
(FCTO100). The Mössbauer spectra for
intermediate mixtures of CRFO100 and FCTO100,
indicates a composition of individual spectra,
proportional to the amounts of the Fe ion-probe in
this compounds: This supports the hypothesis that