84
L. A. Frolova et al.
Fig. 5.2 Dependence of the
degree of inversion of spinel
(1), octahedral, and
tetrahedral distances as a
function of x
1000
(111)
(200)
(331)
(222)
(400)
(422)
(511)
(400)
(622)
I, arb.unit
900
800
700
600
500
400
300
200
100
0
5
1 5
2 5
3 5
4 5
5 5
6 5
x=0.25
x=0.75
x=1.0
x=0.5
75
2q
Fig. 5.3 XRD patterns of ferrite obtained at different ratios of components (Table 5.1)
the octahedral distances increase, since the cobalt (II) radius is 0.82 A and the iron
(III) is 0.64 A. The spinel degree of inversion is thus increasing.
XRD patterns corresponding to samples 1–4 with different molar ratios x have
diffraction peaks corresponding to spinel oxide systems of cobalt ferrite (Fig. 5.3).
All the main characteristic peaks of spinels are present on the diffractograms (220),
(311), (222), (400), (422), and (511). Moreover, with the increase in cobalt content,
the diffraction peaks are broadened, and their intensity decreases, which is due to
the presence of crystallization water.
There are also peaks corresponding to Fe 3 O 4 , for the compositions enriched in
iron. The calculations of the basic crystal-chemical parameters have shown that the
formation of a structure with an iron content higher than stoichiometric takes place