M2O3 = Al2O3, Ga2O3, Sc2O3, La2O3, Bi2O3 - Ceramics-Silikaty

Figure 1. Boundaries between one- and two-phase glass regions
in the systems TeO 2-B 2O 3-M 2O 3: M 2O 3= (1) Al 2O 3; (2) Ga 2O 3;
(3) Sc 2O 3; (4) La 2O 3; (5) Bi 2O 3.
The results of TEM observations show the
influence of the third component on the immiscibility
tendency in different tellurite-borate glasses. In our
previous works [5 - 8], the pronounced trend for cluster
formation in slowly cooled pure vitreous B 2O 3 (v-B 2O 3)
has been discussed. The presence of nano-scale
heterogeneities in v-B 2O 3 ranging in sizes between 1.5 -
2 nm was experimentally established by TEM data
[6, 7]. According to the classification of Zarzycki [9]
and Porai-Koshits [10], they were associated with the
thermal density fluctuations. By means of MM
computer simulation, we made an attempt to model the
cluster formation in borate network at the presence of
BO 3-groups and B 3O 6-boroxol rings [5, 7, 8]. The
addition of TeO 2, containing mainly TeO 3-groups,
stimulates the clustering at micro-scale level [5, 7] and
leads to appearance of metastable phase separation. In
this sense, the role of the third component should be
assigned to its influence on the formation of different
borate or tellurite complexes.
Some typical IR-spectra of chosen compositions in
binary and three component systems are shown in
figures 5 and 6. Their interpretation is based on IR data
analysis of borate glasses [11 - 15]. According to the
obtained IR-spectra the B 2O 3 participates as BO 3- (1380
and 1240 cm -1 ) and BO 4-groups (900 cm -1 ) in the
network of the binary tellurite glass, in spite the small
B 2O 3 amount in the composition (figure 5 - 1). Similar
spectra are obtained when La 2O 3 is added to TeO 2-B 2O 3
glass, but the intensity of the band at 1325 cm -1
increases at the expense of the band at 1215 cm -1 ,
leading to an increase in the tendency for formation of
superstructural units containing BO 3- and BO 4-groups
(figure 5 - 2). This trend is developed (1380, 1050 and
940 cm -1 ) for composition with higher B 2O 3 content
E. Kashchieva, M. Pankova, Y. Dimitriev
Figure 2. Immiscibility droplets and micro-aggregates in onephase
glass with composition 70TeO 2,20B 2O 3,10Bi 2O 3
(mol.%).
Figure 3. B 2O 3-enriched immiscibility droplets in the low layer
of two-phase glass with composition 20TeO 2,70B 2O 3,10 Ga 2O 3
(mol.%).
Figure 4. Microcrystals dispersed in amorphous matrix of glass
with composition 50TeO 2,30B 2O 3,20Al 2O 3 (mol.%).
112 Ceramics − Silikáty 45 (3) 111-114 (2001)