Biomedical Engineering Reference
In-Depth Information
as well as Cu
2+
EPR signal intensity dependence on the substitution degree
of Cu
2+
(I) in Y
1
Ba
2
Cu
3
O
7
x
by Fe atoms. The results showed [45] that
EPR signals correspond to Cu
2+
(I) in the chains and not to the Cu
2+
(II) in
the CuO
2
planes.
Analysis of EPR signals for polymer-ceramic nanocomposites showed
that Cu
2+
(I) EPR signals depend on the binder. Figure 9.16 shows Cu
2+
(I)
EPR spectra for Y
1
Ba
2
Cu
3
O
6.97
and polymer-ceramic nanocomposites with
various polymeric binders: polystyrene (ps), polymethylmetacrylate
(PMMA) and polyethylene (PE). The results demonstrate that the particles
of the layered ceramic feature nanocomposite structures, where the ceramic
grains are the precursors of the macromolecules. The addition of a polymer
changes the valence state of Cu
2+
(I), as demonstrated by curves 1-4 of Fig.
9.16. This indicates intermolecular interaction between the Y
1
Ba
2
Cu
3
O
0.67
ceramic grains and elements of the polymer chains. Such an interaction can
be explained by the intercalation of some elements or fragments of the
macromolecules into the layered structure of the ceramic. During such an
intercalation, superposition of the unpaired electron of the Cu
2+
(I) 3d
x2-y2
orbital with the orbital of corresponding elements in the polymer chains
occurs. As a result, the Cu
2+
(I) EPR response is altered because of the
change of the valence state of Cu
2+
(I).
It is interesting to elucidate whether the intensity of the Cu
2+
(I) EPR
signal is dependent on the filling rate (on the fraction of binder in the
ceramic, for example). To answer this question, polymer-ceramic nano-
composites were investigated with various Y
1
Ba
2
Cu
3
O
6.97
:SHMPE ratios:
100:0; 99:1; 97:3; 95:5; 93:7; 90:10 and 80:20 (in accordance to their mass
%). The obtained data are presented in Fig. 9.17. Curves 1-6 of the figure
demonstrate that the intensity of the EPR output signal depends on the
binder content. It is interesting to note that a bigger shift is observed for
smaller quantities of additive (SHMPE) (curves 2 and 3) and compared with
the pure ceramic (curve 1). Further increase of the binder content reduces
the signal intensity (curves 4-6).
9.7
The use of metal-complex polymer binders to
enhance the SC properties of polymer-ceramic
nanocomposites
Doping of some atoms into a ceramic's lattice structure is one technique
presently used in the search for new superconducting (SC) ceramic
nanocomposites in order to enhance the onset of the SC transition
temperature. As such, the use of metal-complex polymers as binders has
been explored as a possible method for regulating both the critical transition
temperature and the width of the SC state.
