New glasses within the Tl2O-Ag2O-TeO2 system: Thermal characteristics, Raman spectra and structural properties

Article abstract of DOI:10.1016/j.materresbull.2010.09.024

Within the Tl₂O-Ag₂O-TeO₂ system, a large glass-forming domain was evidenced and is presented for the fist time. Densities, glass transition (T_g) and crystallization (T_c) temperatures of the relevant glasses were measured. A structural approach of these glasses as functions of the composition was performed using Raman scattering. The Raman spectra were analysed in terms of the structural modifications induced by the Tl₂O and Ag₂O modifiers. It has clearly evidenced a phase separation inherent in tellurite glasses with low valence cations (as Tl⁺ and Ag⁺). The glasses would be constituted of two phases only: one of pure TeO₂ and one of pure ortho-tellurite M₂TeO₃ (M = Ag, Tl) with the statistically mixed Ag-Tl cationic composition.

Full text of DOI:10.1016/j.materresbull.2010.09.024

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Materials Research Bulletin 45 (2010) 1816–1824
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Materials Research Bulletin
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New glasses within the Tl2O–Ag2O–TeO2 system: Thermal characteristics,
Raman spectra and structural properties
a
a
a
a
D. Linda a,b, M. Dutreilh-Colas a, , D. Hamani , P. Thomas , A. Mirgorodsky , J.-R. Duclere ,
*
`
O. Masson a, M. Loukil b, A. Kabadou b
a Laboratoire Science des Proce´de´s Ce´ramiques et de Traitements de Surface, UMR 6638 CNRS, Centre Europe´en de la Ce´ramique, 12 rue Atlantis, 87068 Limoges Cedex, France
b
´
Laboratoire des Sciences des Materiaux et d’Environnement, S Route de Soukra km 4, 3038 Sfax, Tunisia
A R T I C L E I N F O
A B S T R A C T
Article history:
Within the Tl2O–Ag2O–TeO2 system, a large glass-forming domain was evidenced and is presented for
the fist time. Densities, glass transition (Tg) and crystallization (Tc) temperatures of the relevant glasses
were measured. A structural approach of these glasses as functions of the composition was performed
using Raman scattering. The Raman spectra were analysed in terms of the structural modifications
induced by the Tl2O and Ag2O modifiers. It has clearly evidenced a phase separation inherent in tellurite
glasses with low valence cations (as Tl+ and Ag+). The glasses would be constituted of two phases only:
one of pure TeO2 and one of pure ortho-tellurite M2TeO3 (M = Ag, Tl) with the statistically mixed Ag–Tl
cationic composition.
Received 31 March 2010
Received in revised form 3 September 2010
Accepted 15 September 2010
Available online 20 October 2010
Keywords:
A. Glasses
A. Oxides
ß 2010 Elsevier Ltd. All rights reserved.
C. Differential scanning calorimetry
C. Raman spectroscopy
D. Lattice dynamics
1. Introduction
lattices [4–7]. Thus, it was evidenced that
g-TeO2 is the closest
crystalline structure to pure TeO2 glass [7,8].
Tellurium dioxide-based glasses are currently considered as
promising materials for nonlinear optical applications. They have
various advantageous properties as malleability, homogeneity in a
wide range of composition, chemical stability, weak absorption
coefficients, high linear and nonlinear refractive indices and a large
transparency window which spreads from the visible to the
The ab-initio-theory-based studies unequivocally indicate an
exceptionally high nonlinear susceptibility value of pure TeO2
glass (19.68 (10ꢀ21 m2/V2)). This peculiarity should be attributed
to a strong delocalization of the electronic dielectric response
occurring within polymerized –Te–O–Te– chains rather than to the
local polarization of a lone electronic pair related to the 5s orbital
of tellurium atoms as customarily proclaimed [3,9].
infrared region out to 7
mm [1]. Therefore, some substantial
literature has been devoted to the studies of such glasses during
the last decade. Many binary and ternary phase diagrams were
investigated and the existence of large glass-forming domains was
evidenced for most of them [1].
Of a series of TeO2–MnOk binary systems systematically
investigated at the SPCTS laboratory, a special attention was paid
to the case M = Tl. The phase diagrams were obtained and analyzed
under equilibrium and non-equilibrium conditions, and a large
The nature of the aforementioned optical properties of TeO2-
based glasses is of special interest regarding both fundamental
science and applied aspects. Numerous attempts were made to
clarify the role of the structural constitution in those properties
[2,3]. In our laboratory, extensive studies of TeO2 glassy and
crystalline phases were undertaken during the last 10 years
glassy domain was found. Three stable (Tl2TeO3,
a-Tl2Te2O5,
Tl2Te3O7) and one metastable ( -Tl2Te2O5) crystalline compounds
b
[10–12] were revealed and their structures determined. The
existence of a high-temperature polymorph of Tl2TeO3 was
recently evidenced in [13].
The central points of these investigations were the nonlinear
optical properties of the thallium tellurite glasses. Thus it was
found that:
including the lattice-dynamical analysis of the
a, b, and g-TeO2
(i) their third-order nonlinear susceptibility coefficient can be
50–100 times higher than that of SiO2;
´
´
* Corresponding author at: Centre Europeen de la Ceramique, Science des
Proce´de´s Ce´ramiques et de Traitements de Surface, UMR 6638 CNRS, 12 rue Atlantis,
87068 Limoges Cedex, France. Tel.: +33 05 87 50 23 80, fax: +33 05 87 50 23 09.
E-mail address: maggy.colas@unilim.fr (M. Dutreilh-Colas).
(ii) such value tends to increase upon Tl2O component addition
(about 480 ꢁ 10ꢀ23 m2/V2, measured at 0.8
mm) [14,15]. This
0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2010.09.024

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D. Linda et al. / Materials Research Bulletin 45 (2010) 1816–1824
1817
effect is not ordinary. Actually, as a rule, the addition of a
modifier causes the TeO2 framework to depolymerize into
island-type isolated complex anions [TenOm]2(mꢀ2n)ꢀ, thus
decreasing the susceptibility value [16]. Exceptions to this rule
are the glasses in which the modifier contains highly
polarisable cations, in particular Tl+ [15];
NaCl (temperature about ꢀ14 8C). Glass-forming region was
determined by optical inspection of the obtained products (which
were in the case of glassy samples transparent) and by using X-ray
diffraction (D5000 Siemens diffractometer, Sol-X detector, Cu K
a
radiation, step size = 0.048).
Glass transition (Tg) and crystallization (Tc) temperatures were
measured by heat flux differential scanning calorimetry (Netztsch
STA 409 apparatus). The powdered samples (ꢂ30 mg) were
introduced into platinum crucibles and the DSC curves were
recorded between 20 and 500 8C using a heating rate of 10 8C/min
and under nitrogen atmosphere. The glass transition temperature
was taken at the inflection point of the slope change of the
calorimetric signal associated with this transition. The crystalliza-
tion temperature was taken (when an exothermic peak was
observed) at the intersection of the slope of this exothermic peak
with the baseline. The densities of glassy samples were measured
on finely ground powders by helium pycnometry (Accupyc 1330
pycnometer).
(iii) the Raman gain coefficient of the glasses can be up to 58 times
that of a standard Corning 7980-2F fused silica [17].
However, TeO2–Tl2O glasses materials were found relatively
brittle and characterized by a low thermal stability. To overcome
this drawback, maintain the good non-linear characteristics of the
glasses, and even enlarge the scope of their interesting optical
properties, the Tl2O–MxOy–TeO2 ternary systems were recently
investigated at our laboratory. In particular, quite satisfactory
results relating the thermo-mechanical stability were achieved by
adding TiO2 to thallium tellurite system [18].
Our last activity in that field concerns the influence of the Ag2O
modifier introduced into Tl2O–TeO2 glasses. Indeed, according to
previous reports on silver-doped phosphate glasses [19], it is
expected that Tl2O–Ag2O–TeO2 glasses would show some inter-
esting photoluminescent properties (without loosing their initial
high non-linearity), resulting from the presence of silver cations.
Some results of structural studies of silver tellurite glasses and
of some metal-oxide silver tellurite ternary glasses have been
already published [1,20–22]. More or less large glassy domains
were found with respect to the melting and quenching conditions.
In particular, a glassy domain was revealed in a range 0–46 mol%
AgO0.5 in Ref. [21]. In analyzing neutron diffraction and Raman
spectra data, the authors concluded that a progressive depolymer-
isation of the TeO2 glass structure occurs with increasing modifier
oxides content. This depolymerisation is characterized by the
transformation of the TeO4 disphenoids into TeO3 units [20–22].
Such a structural change is a trivial fact for MxOy–TeO2 glasses [11].
One of the rare exceptions is the case M = Ti for which the Ti–O
bond distances in the glassy structure are very close to the Te–O
ones. Consequently, the Te–O–Te bridges are just replaced by Te–
O–Ti ones and the glass framework is conserved [18].
The Raman spectra of powder sample were recorded in the 80–
1000 cmꢀ1 range and in back-scattering mode at 514.532 nm using
a
T64000 Jobin-Yvon spectrophotometer operating in triple
subtractive configuration (1800 grooves/mm) associated to
a
liquid nitrogen-cooled CCD detector. Measurements were per-
formed at low power (<10 mW on the surface of the sample) of the
excitation line, in order to avoid any damage of the glasses. The
scattered light was collected through a microscope objective (50ꢁ
LWD) and confocal filtering (0.1 mm). The spectral resolution was
about 2.5 cmꢀ1 at the exciting line. All samples were measured
three times to check the reproducibility of spectra and to enhance
the accuracy of the data by accumulation.
The Raman measurements of bulk sample were carried out on
an inVia Reflex Raman spectrometer of the Renishaw Company at
514 nm. The spectra were recorded in a linefocus mode (in order to
minimize the damage of the samples) centred to 500 cmꢀ1 over a
time of 1 s with the diffraction grating of 1800 grooves/mm
(spectral resolution about 2.7 cmꢀ1). The laser power at the sample
level and through an objective 50ꢁ was 20 mW.
A stable silver tellurite crystalline phase was detected in the
Ag2O–TeO2 phase diagram, Ag2TeO3 [23]. This phase exits in two
3. Results and analysis
polymorphic forms,
a metastable orthorhombic form which
3.1. Glass formation
transforms irreversibly into the monoclinic stable variety above
573 K [24].
To the best of our knowledge, no crystalline compound and no
glass have been evidenced within the binary Ag2O–Tl2O system.
We can only indicate some investigations of ternary systems (see
e.g., the study of silver–thallium borate glasses [25]).
A large glass forming domain observed within the Tl2O–Ag2O–
2 system is presented in Fig. 1. The glasses are all yellow, the
T[()$DFIGT] eO
Our present work was initially aimed at the determination of
the glass formation domain within the Tl2O–Ag2O–TeO2 ternary
system which has never been explored. Then, the thermal
behaviour of the glasses including the measurements of the
glass-transition (Tg) and crystallization (Tc) temperatures was
studied and the evolution of the glassy structure with increasing
modifier component was analysed by using Raman spectroscopy.
The results obtained are presented and discussed in this paper.
2. Experimental
Glassy samples were prepared by first melting at 800 8C in air
for 15 min in platinum crucibles intimate mixtures of high purity
Tl2CO3 (Aldrich, 99.9%), Ag2O (99.9%) and home-made TeO2. The
former was prepared by decomposition, at 550 8C, of commercial
H6TeO6 (Aldrich, 99.9%). The decomposition of Tl2CO3 (CO2
evaporation) was ensured during the melting. The melts (2 g for
the bulk samples and 200 mg for the powder samples) were then
fast-quenched in a freezing mixture consisting of ice, ethanol and
Fig. 1. Glass forming domain at 800 8C under ice-quenching conditions within the
Tl2O–Ag2O–TeO2 system.

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D. Linda et al. / Materials Research Bulletin 45 (2010) 1816–1824
intensity of the colour decreasing with increasing Ag2O content.
For rich-Ag2O content the glasses become grey. Using such specific
quenching conditions as freezing mixture of ice, ethanol and NaCl
(temperature about -14 8C), the glass forming domain within the
TeO2–Ag2O binary system was slightly enlarged (0–45 mol%
AgO0.5) with respect to those reported in the literature [1,20–22].
3.2. Thermal properties and densities of glasses
The thermal characteristics and density of some glasses are
listed in Table 1. The samples are labelled as indicated in Fig. 1. The
variation with the composition of the density, glass transition and
crystallisation temperatures are shown in Fig. 2. The composition
Table 1
Glass-transition (Tg) and crystallisation (Tc) temperatures, thermal stability (Tc–Tg) and density of some glasses within the TeO2–Tl2O–Ag2O system (the samples are
numbered as labelled in Fig. 1).
No
Composition (mol%) TeO2–TlO0.5–AgO0
Tg
(
ꢃ5 8C)
Tc
(
ꢃ5 8C)
Tc–Tg
(
ꢃ5 8C)
Density (ꢃ0.05)
9
9
90–10–0
277
245
204
260
260
250
246
240
225
210
195
177
264
247
234
214
213
199
183
165
251
226
210
195
189
172
158
141
231
211
191
181
169
151
135
208
197
173
155
145
128
115
191
173
152
133
124
111
171
140
129
120
112
151
131
105
110
130
111
98
320
322
317
290
290
276
277
273
270
268
268
244
288
298
275
276
267
267
266
233
282
287
273
268
263
260
227
205
281
275
270
258
260
222
208
281
276
258
234
219
192
154
270
268
255
203
193
161
266
260
202
178
150
244
215
182
156
221
173
150
214
154
111
170
110
108
43
77
113
24
30
26
31
33
45
58
73
67
24
51
41
62
54
77
83
68
31
61
63
73
74
88
69
64
50
64
79
77
91
69
73
73
79
85
79
74
64
39
79
95
103
70
69
50
95
120
73
58
38
93
84
77
46
91
62
52
94
64
28
67
32
23
5.51
6.13
6.40
5.63
5.68
5.76
5.75
5.81
6.02
6.12
6.24
6.28
5.70
5.85
5.95
5.98
6.04
6.17
6.28
6.37
5.68
5.90
6.07
6.15
6.25
6.37
6.44
6.42
5.90
6.13
6.23
6.15
6.40
6.52
6.49
6.07
6.19
6.37
6.41
6.58
6.68
6.70
6.27
6.34
6.26
6.47
6.70
6.71
6.42
6.50
6.51
6.68
6.74
6.57
6.67
6.63
6.64
6.73
6.72
6.98
6.85
6.91
7.19
7.02
7.16
7.20
80–20–0
9
70–30–0
1
90–00–10
90–00–10
85–00–15
80–00–20
75–00–25
70–00–30
65–00–35
60–00–40
55–00–45
90–05–5
13
24
34
42
49
55
60
63
2
14
25
35
43
50
56
61
3
85–05–10
80–5–15
75–5–20
70–05–25
65–05–30
60–05–35
55–05–40
85–10–5
15
26
36
44
51
57
62
4
80–10–10
75–10–15
70–10–20
65–10–25
60–10–30
55–10–35
50–10–40
80–15–5
16
27
37
45
52
58
5
5–15–10
70–15–15
65–15–20
60–15–25
55–15–30
50–15–35
75–20–5
17
28
38
46
53
59
6
70–20–10
65–20–15
60–20–20
55–20–25
50–20–30
45–20–35
70–25–5
18
29
39
47
54
7
65–25–10
60–25–15
55–25–20
50–25–25
45–25–30
65–30–50
60–30–10
55–30–15
50–30–20
45–30–25
60–35–5
19
30
40
48
8
20
31
41
9
55–35–10
50–35–15
45–35–20
55–40–5
21
32
10
22
33
11
23
12
50–40–10
45–40–15
50–45–5
120
90
45–45–10
40–45–15
45–50–5
83
103
78
40–50–10
40–55–5
85

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D. Linda et al. / Materials Research Bulletin 45 (2010) 1816–1824
1819
a
b
6,8
6,6
6,4
6,2
6,0
5,8
5,6
5,4
280
260
240
220
200
180
160
140
120
100
0
5
10 15 20 25 30 35 40 45
0
5
10 15 20 25 30 35 40 45
mol % AgO
0.5
mol % AgO
0.5
10 % TlO0.5
20 % TlO0.5
30 % TlO0.5
c
340
320
300
280
260
240
220
200
180
160
140
0
5
10 15 20 25 30 35 40 45
mol % AgO
0.5
Fig. 2. Evolution with the Ag2O content of (a) the density r, (b, c) the glass transition (Tg) and crystallisation (Tc) temperatures, for some Tl2O–Ag2O–TeO2 glasses.
dependence of the glass density is shown in Table 1 and Fig. 2. The
density increases logically with increasing Tl2O and Ag2O content,
which is in a full correspondence with atomic weight of the adding
oxides. As for example the density increases from 5.51 to 7.2 for
90TeO2–10TlO0.5 and 55TlO0.5–5AgO0.5–40TeO2 glasses, respec-
tively. One observes for all the glassy samples a continuous
decrease of Tg and Tc with increasing concentration of both Ag2O
and Tl2O. These results suggest that the addition of a modifier
oxide like Ag2O leads to a progressive change from a highly
polymerized network in which the TeO4 disphenoids are linked
together via bridging-oxygen corners to a more depolymerised
network involving mainly TeO3 units with bridging and non-
bridging oxygen atoms.
The evolution of (Tc–Tg), which in fact characterizes the
thermal stability of glasses (see values in Table 1), is more
complex. It first slightly increases and then weakly decreases for
higher Ag2O content. So, the addition of Ag2O to TeO2–Tl2O
glasses leads to decrease their thermal stability (parameter we
have to take into account to elaborate glass pellets and to
process to Raman analysis), and that all the more as they are
richer in Tl2O.
following lines (AB) and (CD) of the phase diagram varying firstly z
and keeping y = 5 (AB) and then varying y and keeping x/z = 2.33
(CD) (see Fig. 1). As the spectra for y = 5, 10, 15, 20, 25 and 30 are
quite similar, only these recorded for y = 5 are presented in this
paper. The first line (AB) evidences the Tl2O influence and the
second one (CD) points out the Ag2O effect on the binary TeO2–Tl2O
system. The Raman spectra evolutions are given, respectively, in
Figs. 3 and 4. The spectra of the pure TeO2 glass, crystalline
structures
g-TeO2, Tl2TeO3 and Ag2TeO3 are added for better
understanding.
Each spectrum has been divided by its average value, to correct
intensity fluctuations which might originate from defocusing.
Possible laser intensity fluctuations are also corrected by this way.
Using the FOCUS program [26], Raman spectra have been
decomposed using Gaussian functions for all oscillators, except
for boson peak which has been simulated by using a lognormal
function.
During the decomposition procedure, the idea of a phase
separation within
a M2O–TeO2 glassy system, preliminary
illustrated in [6], was kept in mind (see Section 4). Therefore, it
was implied that the Raman spectra of the glasses under study
could be presented as a superposition of two spectra: that of
tellurium dioxide, and that of M–orthotellurite. Consequently, the
glass decomposition had to be based on the initial set of the
Gaussian oscillator parameters estimated from the spectra of pure
TeO2 and of pure Tl2TeO3 (or Ag2TeO3).
3.3. Vibrational spectra
The Raman spectra of the glasses within the ternary zTlO0.5
–
yAgO0.5–xTeO2 system were studied in our work along the two