Glass Ceramics in the Ga2S3-GeS2-CsCl System
J. Phys. Chem. B, Vol. 113, No. 44, 2009 14579
5. Conclusions
Transparent and homogeneous Ga2S3-GeS2-CsCl glass
ceramics have been prepared from a base glass by appropriate
annealing. A structural study was carried out in function of heat
treatment time using X-ray diffraction and 133Cs and 71Ga solid-
state NMR. Both these techniques give a complementary point
of view on the structure and permit to follow the long- and the
short-range order in the structure during the heat treatment. Note
that NMR and XRD are quantitative tools which could permit
to measure the rate of the crystalline phase versus time. To
achieve this goal from the 71Ga NMR spectra, it is essential to
reconstruct properly the initial line shape observed in the base
glass. Some fundamental works are ongoing on that field.
One of the main results is that CsCl is very well incorporated
in the base glass, permitting to obtain totally transparent
materials in the visible range by fixing the electrons of the lone
pair of sulfur. Moreover, it was demonstrated that Ga plays the
role of the nucleating agent in the crystallization process in both
(Ga2S3)25-(GeS2)65 -CsCl10 and (Ga2S3)35-(GeS2)25-CsCl40
glass ceramics. The successful preparation of transparent
chalcohalide glass ceramics in the whole visible range combined
with the nucleation role of Ga demonstrated in the present work
are promising results in order to prepare rare earth ions doped
glass ceramics. Indeed, the final target of our investigations is
to generate a crystalline environment around the REI in order
to enhance their luminescence properties and REI are prefer-
entially located near Ga atoms in Ga containing chalcogenide
glasses.
Figure 10. (Ga2S3)35-(GeS2)25-CsCl40 glass ceramics labeled as GCx
with x the second heat treatment duration at 369 °C (in h). All of the
samples have been previously heat treated at 339 °C during 15 h
(nucleation step).
Figure 11. X-ray diffraction patterns of (Ga2S3)35-(GeS2)25-CsCl40
glass ceramics heat treated 15 h at T ) 339 °C (nucleation step) and
x h at T ) 369 °C (growth step), labeled as GCx with x ) 0, 1, 2, 3,
and 4, respectively. Crystalline GaS and Ga2S3 X-ray diffraction patterns
from the respective PDF cards no. 40-1030 and no. 84-1440 are also
presented.
Acknowledgment. The authors thank Dr. G. Tricot from the
University of Lille I (France) for carrying out 71Ga NMR
measurements on the 800 MHz Bruker spectrometer.
one-step isotherm heat treatment was sufficient to ceramize the
(Ga2S3)25-(GeS2)65-CsCl10 glass, a two steps process had to
be implemented to obtain homogeneous and reproducible
(Ga2S3)35-(GeS2)25-CsCl40 glass ceramics. Thus, glass ceramics
have been successfully prepared by heat treating the base glass
at Tg + 20 °C ) 339 °C during 15 h in a first time (nucleation
step) and at Tg + 50 °C ) 369 °C during 1 to 4 h (crystal
growth step). The obtained glass ceramics labeled as GCx with
x the duration of the second heat treatment are shown in Figure
10.
Ex situ X-ray diffraction (XRD) has been carried out on the
GCx glass ceramics to compare the crystallization process in
this composition to the one observed in (Ga2S3)25-(GeS2)65-
CsCl10 glass ceramics. The collected XRD patterns are presented
in Figure 11. The crystalline GaS and Ga2S3 XRD patterns
obtained from crystallographic database (PDF cards no. 40-1030
and no. 84-1440, respectively) are also depicted.
As for the (Ga2S3)25-(GeS2)65-CsCl10 glass ceramics, the
XRD patterns reveal the formation of Ga2S3 nanocrystals in the
GC2 and GC3 samples (2θ ) 29°, 50°, and 58°). However, a
slight difference is observed at the very beginning of crystal-
lization for the (Ga2S3)35-(GeS2)25-CsCl40 composition. Indeed,
while the GC0 XRD pattern is typical of an amorphous state, a
single sharp peak arises at 2θ ) 29° on the GC1 pattern. It can
be assumed from this result that a small amount of GaS
nanocrystals is first precipitated in the matrix before the
crystallization of the Ga2S3 phase. Nevertheless, XRD patterns
confirm here that the initiation of crystallization in the
Ga2S3-GeS2-CsCl glassy network also takes place around Ga
atoms. And even though the Ga2S3 phase does not seem to be
the first crystallizing phase in the (Ga2S3)35-(GeS2)25-CsCl40
glass, Ga2S3 nanocrystals are also precipitated at the beginning
of the crystallization process.
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