Structure and thermal stability of novel fluorophosphate glasses

Article abstract of DOI:10.1016/j.jallcom.2004.07.071

A systematic investigation on glass formation in the PbF ₂-InF₃-BaHPO₄ ternary system has been carried out. These glasses have characterized by IR spectra, Raman spectra and differential thermal analysis. The results show that the structure of these glasses is mainly affected by BaHPO₄ and InF₃ contents. With decreasing BaHPO₄ content, the glass structure gradually transforms from metaphosphate to polyphosphate. When InF₃ content is low, it mainly acts as network modifier, when its content is high; it enters glass matrix and forms In(O,F)₆ groups connecting the polymerized phosphorus oxygen species. PbF₂ mainly acts as network modifier in this system. Systematic variations of the glass transition temperature and the thermal stability index agree well with these results. The most stable glass with ΔT = 230 °C and S = 21.79 K is obtained.

Full text of DOI:10.1016/j.jallcom.2004.07.071

Journal of Alloys and Compounds 391 (2005) 151–155
Structure and thermal stability of novel fluorophosphate glasses
a,b,∗
a,c
a,b
a
Hongtao Sun
, Liyan Zhang , Shiqing Xu , Shixun Dai ,
a
a
a
Junjie Zhang , Lili Hu , Zhonghong Jiang
a
Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800, PR China
b
Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China
c
School of Material Science and Engineering, Jinan University, Jinan 250022, PR China
Received 8 July 2004; accepted 23 July 2004
Available online 30 October 2004
Abstract
A systematic investigation on glass formation in the PbF
ized by IR spectra, Raman spectra and differential thermal analysis. The results show that the structure of these glasses is mainly affected by
BaHPO and InF contents. With decreasing BaHPO content, the glass structure gradually transforms from metaphosphate to polyphosphate.
When InF content is low, it mainly acts as network modifier, when its content is high; it enters glass matrix and forms In(O,F) groups con-
necting the polymerized phosphorus oxygen species. PbF mainly acts as network modifier in this system. Systematic variations of the glass
2 3 4
–InF –BaHPO ternary system has been carried out. These glasses have character-
4
3
4
3
6
2
◦
transition temperature and the thermal stability index agree well with these results. The most stable glass with ꢀT = 230 C and S = 21.79 K
is obtained.
©
2004 Elsevier B.V. All rights reserved.
Keywords: Fluorophosphate glasses; Structure; IR spectra; Raman spectra
1
. Introduction
2. Experimental
Fluorophosphate glasses have received great attention and
The starting materials used for preparation of the glasses
were In2O3 (99.99%), PbF2 (AR) and BaHPO4 (AR). InF3
was synthesized from corresponding oxide, In2O3, with
ammonium bifluoride NH4HF2 as fluorinating agent, as
described elsewhere [2]. The typical batch compositions
(mol%) listed in Table 1 were prepared by conventional melt-
ing and quenching method. About 20 g batches of the well
are the subject of intense research mainly because of their
wide transmission range from the ultraviolet to the infrared
regions, possible doping levels with rare earth ions exceeding
2
1
3
1
0 /cm , low linear and non-linear refractive index, and high
damage threshold as desirable for laser host materials [1,2].
The technological importance of fluorophosphate glasses
make it in increasing demand for the development of new
glasses with specific characteristics. In this paper, we develop
a novel fluorophosphate glass in the PbF2–InF3–BaHPO4
system. We investigate the structure of these glasses by IR
spectra and Raman spectra, and report glass formation abil-
ity in this system in order to define glass compositions stable
enough to give bulk samples, preforms and hopefully optical
fiber.
◦
mixed raw materials were melted at 1000–1100 C for 15 min
in covered aluminium oxide crucibles in an electronic fur-
nace. Then the melt was cast into a preheated stainless steel
mould and annealed at the glass transition temperature. Sam-
ples were divided according to their appearance into three
types: glasses, partially crystalline samples, and crystalline
samples. Differential thermal analysis (DTA) was carried
out to determine the glass transition temperature (Tg), the
crystallization onset temperature (Tx), and the maximum of
exotherm (Tp) of the glasses. The accurate temperature is
◦
◦
∗
± 2 C and the heating rate was 10 C/min. Thermal stability
factors ꢀT and S were calculated from the temperatures Tg,
Corresponding author. Tel.: +86 21 5991 0994; fax: +86 21 3991 0393.
E-mail address: htsun2003@eyou.com (H. Sun).
0
925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2004.07.071

1
52
H. Sun et al. / Journal of Alloys and Compounds 391 (2005) 151–155
Table 1
Batch composition, F/P ratios , and appearance of melted samples
a
Sample
Batch composition (mol%)
BaHPO4 PbF2 InF3
F/P ratiosa Appearance
P65Pb35
P65Pb30In5
P65Pb25In10 65
P65Pb20In15 65
P65Pb15In20 65
P60Pb40
P60Pb35In5
P60Pb30In10 60
P60Pb27In13 60
P60Pb25In15 60
P60Pb20In20 60
65
65
35
30
25
20
15
40
35
30
27
25
20
50
45
40
30
0
5
10
15
20
0
1.08
1.16
1.24
1.3
1.38
1.34
1.42
1.5
1.56
1.58
1.66
2
Brown
Colorless
Colorless
Colorless
Colorless
Brown
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
60
60
5
10
13
15
20
0
5
10
20
P50Pb50
P50Pb45In5
P50Pb40In10 50
50
50
Fig. 2. IR absorption spectra from the P65Pb35−xInx (x = 0, 5, 10, 15) glasses.
3.2. IR spectra
2.1
2.2
2.4
P50Pb30In20 50
a
Ratios calculated from nominal compositions.
The IR spectra of samples containing 65 mol% BaHPO4
are shown in Fig. 2. The IR spectra of the P Pb glass
65
35
is characterized by bands at ∼1269, 1087, 887, 728, and
Tx, and Tp according to the following relations: ꢀT = Tx − Tg
and S = (Tx − Tg) (Tp − Tx)/Tg [3]. A Thermo Nicolet NEXU
FT-IR spectrophotometer was used for IR spectra by us-
ing pressed KBr pellets containing 4 wt% of powdered glass
samples. Raman measurements on samples were performed
on a Labram-1B Raman spectrometer using a He–Ne laser
−
1
5
19 cm . The bands have been assigned based on previ-
−1
ous work [4–6] as follows: ∼1269 cm band is thought to
be attributable to the asymmetric stretching of P O groups
and/or the asymmetric stretching vibrations of O P O
−
1
−
groups, ∼1087 cm
band to stretching of ionic P O
−
1
groups, ∼887 cm band to asymmetric stretching of lin-
(632.8 nm) for excitation.
−1
ear metaphosphate chains (P O P), ∼728 cm
band to
symmetric stretching of P O P groups of small metaphos-
−
1
phate rings and ∼519 cm band to bending vibration of
3
. Results and discussion
P O bonds. Glass consisting of metaphosphate has bands at
−
1
∼
1295, 1110, 910, and 520 cm ; pyrophosphate has bands
3
.1. Glass-forming region
−1
at ∼1110, 910, and 520 cm ; orthophosphate has bands at
−
1
∼
1075 and 520 cm [7].
Systematic investigations have been implemented in the
With the increase of InF3 content, the band inten-
PbF2–InF3–BaHPO4 system. Fig. 1 shows the glass-forming
region, which is broad and near to the PbF2–BaHPO4 bi-
nary side. The clear glasses can be obtained in the limits of
the glass-forming region. Some glasses are transparent and
colorless in appearance, while others have brown color as
described in Table 1.
−1
sity at ∼1269 cm gradually decreases and disappears in
−1
P Pb In10 glass, whereas the ∼1087 cm
band inten-
65
25
sity increases and it also shifts towards higher wavenumber.
−1
These two bands gradually form a new band at ∼1134 cm
.
These facts clearly indicate that the glass structure gradu-
ally transforms from metaphosphate to pyrophosphate struc-
−1
ture. The large broadening and shifting of the ∼1087 cm
band also indicates the formation of fluorophosphate unit of
P2(O,F)7 since it has been found to be caused by the over-
lapping of stretching vibration of O P F bond (appears at
−
1
−1
−
∼
1140 cm ) with the ∼1112 cm band of P O group
−
1
[
7]. Gradual shifting of ∼887 cm band, with the increase
of InF3 content, towards higher wavenumber indicates the
formation of F P F bonds as a result of breaking of linear
metaphosphate chains (P O P), because the F P F stretch-
−1
ing vibrations have been found in the 750–1050 cm range
8]. This agrees well with the results reported by Fuxi and
Haiyan [9] and Wasylak and Czerwosz [10]. The slight shift-
[
−
1
ing of ∼728 cm
band to higher wavenumber with in-
creasing InF3 content also indicates the decrease of chain
length, because it has been previously observed in phosphate
Fig. 1. Glass-forming region in the PbF2–InF3–BaHPO4 system. Composi-
tions are expressed in mol%.

H. Sun et al. / Journal of Alloys and Compounds 391 (2005) 151–155
153
Fig. 5. Raman spectra from the P65Pb35−xInx (x = 5, 15) glasses.
Fig. 3. IR absorption spectra from the P60Pb40−xInx (x = 0, 5, 10, 15) glasses.
to 50 mol% is the complete disappearance of the bands at
−
1
∼
1269 and 1254 cm . As mentioned previously the bands
glasses that as chain length decreases, the symmetric stretch-
ing P O P band increases in frequency [11]. It is interesting
−
1
at ∼1115, 909, 729 cm may be attributed to fluorophos-
phate unit of P2(O,F)7 groups, F P F stretching vibrations,
symmetric stretching of P O P groups, respectively. The
529 cm band may be caused by the overlapping of In–F
stretching vibration with bending vibration of P O, and/or
−
1
that, with the increase of InF3 content, the ∼519 cm band
intensity increases and slightly shifts to higher wavenumber.
This might be the result of the overlapping of In–F stretching
−
1
∼
−
1
vibration (appears at ∼509 cm ) [12] with the bending vi-
In(O,F) vibration. All these facts clearly indicate that these
glasses have pyrophosphate-like structure. With the increase
6
bration of P O [13]. On the other hand, it could be tentatively
assigned to the formation of In(O,F) vibrational mode when
6
3+
of InF3 content or F/P ratio, the intensity of bands at ∼1115,
InF3 content is high, suggesting that the In acts as a net-
−
1
9
09, 729, 529 cm increases, which indicates that the ad-
work forming cation to form a structure similar to Al(O,F) in
6
dition of fluorides leads to rupturing of long metaphosphate
chains and more formation of short structure fragments of
P2(O,F)7 and F P F.
the aluminium fluorophosphate glasses [4]. Those small frag-
ments, such as P2(O,F)7 groups and F P F, may be linked
up to a greater extent by the In(O,F) polyhedral, which leads
6
to strengthening of the glass network. Compared with Fig. 2,
the glasses with 60 mol% BaHPO4 in Fig. 3 have the similar
bands and transformation tendency with the increase of InF3
content, except for the band intensity.
3.3. Raman spectra
The Raman spectra of glasses containing 65, 60, 50 mol%
BaHPO4 are shown in Figs. 5–7. The Raman spectra of the
Fig. 4 shows IR spectra of P Pb In and P Pb30In20
50
45
5
50
−1
glasses, characterized by bands at ∼1115, 909, 729,
P65Pb30In5 glass is characterized by a band at ∼1160 cm
,
−1
−1
5
29 cm . Compared with Fig. 2 and Fig. 3, the most no-
two weak shoulders at ∼1229 and 1054 cm , a strong
−
1
−1
ticeable change as decreasing BaHPO4 content from 60
band at ∼691 cm , a broad band at ∼493 cm , and a
1
−
medium band at ∼322 cm . The shoulders at ∼1229 and
Fig. 4. IR absorption spectra from the P50Pb50−xInx (x = 5, 20) glasses.
Fig. 6. Raman spectra from the P60Pb40−xInx (x = 5, 15) glasses.

1
54
H. Sun et al. / Journal of Alloys and Compounds 391 (2005) 151–155
The Raman spectra of glasses containing 50 mol%
BaHPO4 are characterized by bands or shoulders at ∼1095
and 1118, 1040 and 1059, 967 and 994, 741 and 736, 516 and
−
1
5
29, 336 and 341 cm . Compared with Figs. 6 and 7, the
shoulders appearing in Fig. 6 disappear completely in Fig. 7
and a new shoulder which is tentatively associated with sym-
metric stretching vibration of [PO4] with three non-bridging
−1
oxygen atom [11,14] appears at ∼967 and 994 cm . The
sources of other bands have been already discussed above and
they have no apparent changes with increasing InF3 content.
Allthesefactsindicatethattheseglasseshavepyrophosphate-
like structure.
Some literatures have mentioned the structural role of
Pb2+ in glass network by Raman spectra. Unfortunately, the
ways to interpret as well as the results are quite distinct
and even contradictory from one another. Liu and Chin [17]
suggest that the covalent Pb O bond is indeed present in
the metaphosphate as well as the polyphosphate structure.
However, it seems to be not a peak characteristic of the
Pb O bond in Figs. 5, 6 and 7, except a weak absorption
Fig. 7. Raman spectra from the P50Pb50−xInx (x = 5, 20) glasses.
−
1
054 cm 1 are attributable to asymmetric stretch of the PO2
unit and the isolated P (O,F)4 monomers, respectively [14].
−
1
The ∼1160 cm band is the dominant feature of the spec-
−
1
2+
tra, which has been assigned to the symmetrical stretching
band at ∼156 cm . Then we can suggest that Pb mainly
occupies the modifier sites in the PbF2–InF3–BaHPO4
glasses.
−
1
mode of the PO2 [14]. The ∼691 cm band is attributed to
the in-chain symmetric stretching modes along the P O P
−
1
chains, while the ∼493 cm band could be tentatively as-
−
1
signed to InOF vibrational modes [14,15]. The 322 cm
3.4. Characteristic temperature and glass stability
band is due to PO2 group deformation vibrations [16]. With
the increase of InF3 content, a decrease occurs in the inten-
The properties of the glasses can be understood on the ba-
−
1
sity of Raman bands at ∼1160 and 691 cm , at the same
sis of the structure discussed above. The glass transition tem-
perature (Tg) and the onset crystallization temperature (Tx)
were clearly observed in all the glasses indicated by the open
circles in Fig. 1. The characteristic temperature and stability
indices of some glasses are given in Table 2. The selection
of good glass compositions can be done on the basis of the
thermal stability indices, which are important factors for fiber
−
1
time, the ∼1160 cm band shifts to lower frequency while
−
1
the ∼691 cm band shifts to higher frequency. These facts
indicate a breaking of the P O P bond in the metaphosphate
chain structure and the consequent decrease in the number of
the P O P [11]. With the increase of InF3 content, the grad-
−
1
ual disappearance of the ∼1229 cm shoulder also indicates
the rupture of P O P chains, and the slight increase in the
◦
drawing [19]. In our glasses, the largest ꢀT value of 230 C
−
1
3+
intensity of the ∼493 cm band indicates that the In acts
as a network forming cation and leads to strengthening of the
glass network.
and the highest S value of 21.79 K have been obtained. With
the substitution of InF3 for PbF2, it is observed that the Tg
values increase dramatically, while the evolution of ꢀT and
Compared with Fig. 5, the Raman spectra of glasses con-
taining 60 mol% BaHPO4 in Fig. 6 change significantly
with increasing InF3 content. The Raman spectra of the
P Pb In glass, which is characterized by bands at ∼1154,
Table 2
The characteristic temperatures and stability indices
6
0
35
5
◦
◦
◦
◦
−
1
Sample
T ( C) ± 2 T ( C) ± 2 T ( C) ± 2 ꢀT ( C) S (K)
g
x
p
6
1
89, 505, 341, 156 cm
067 cm , is similar to that of 65 mol% BaHPO4 glasses
and shoulders at ∼1213 and
−
1
P65Pb35
P65Pb30In5
P65Pb25In10 465
P65Pb20In15 468
P65Pb15In20 486
P60Pb40
P60Pb35In5
P60Pb30In10 415
P60Pb27In13 470
P60Pb25In15 475
P60Pb20In20 478
300
362
440
482
595
660
680
438
465
540
608
705
660
412
570
568
655
480
526
632
700
732
475
510
580
642
750
702
455
588
595
688
140
120
130
192
194
160
115
125
138
230
182
104
130
123
165
18.67
14.59
10.34
16.41
20.76
21.29
14.79
12.05
9.98
21.79
16
14.52
5.32
−
1
except for the ∼156 cm band attributable to Pb O bond
[
17]. The Raman spectra of the P Pb In glass is char-
60
25 15
−
1
acterized by weak shoulders at ∼1227, 1053 cm , bands at
−
1
∼
1111, 738, 510, and 341 cm . Videau et al. [18] suggested
278
350
that the symmetric stretching of O P O in P2(O,F)7 dimers
−
1
−1
has a band at ∼1080 cm , then the band at ∼1111 cm can
be tentatively assigned to the symmetric stretching of O P O
in P2(O,F)7 dimers. With increasing InF3 content, the band at
−
1
−1
∼
689 cm shifting to 738 cm indicates that the glass net-
P50Pb50
P50Pb45In5
P50Pb40In10 445
P50Pb30In20 490
308
440
work is ruptured heavily, and this is consistent with the results
of the IR spectra. The other bands are essentially unaffected
by the increasing InF3 content.
7.46
11.11

H. Sun et al. / Journal of Alloys and Compounds 391 (2005) 151–155
155
S values is not monotonous. The evolution of Tg for the In/Pb
Acknowledgements
substitution can be easily explained since the glass transition
involves the breaking of the chemical bonds. The bond en-
ergy of the In–F is much larger than that of Pb–F because
This work was financially supported by the Shanghai Sci-
ence and Technology Foundation (022261046) and ‘Qim-
ingxing’ Project of Shanghai Municipal Science and Tech-
nology Commission (04QNX1448).
3+
2
−2
the charge densities of In (z/a = 469 nm ) is larger than
that of Pb2 (z/a = 139 nm ), then the substitution of InF3
for PbF2 leads to the increase of the Tg values. At the same
time, the obvious increase of Tg also indicates a restructuring
of the network. The evolution of the ꢀT and S values may
be explained on the basis of the structural evolution. The ini-
tial decrease of the ꢀT and S values, with the substitution of
InF3 for PbF2, may be due to the weakening PbF2–BaHPO4
glass network ruptured by fluorine ions. With the increase
of InF3 content, the ꢀT and S values increase notably. This
+
2
−2
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mainly affected by BaHPO4 and InF3 contents. With decreas-
ing BaHPO4 content, the glass structure gradually transforms
from metaphosphate to polyphosphate. When the InF3 con-
tent is low, it mainly acts as network modifiers, when its con-
[
[
[
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6
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◦
sults. The most stable glass, P Pb In , with ꢀT = 230 C
60
25 15
and S = 21.79 K, is obtained, which is a promising material
for fiber drawing and laser glasses doped with RE ions.