Glass formation in the HgBr2-PbBr2-CsBr ternary

Article abstract of DOI:10.1134/S0036023609020223

Results of investigation of glass formation in the HgBr₂- PbBr₂-CsBr system are presented. The glass formation region has been outlined. Characteristic temperatures have been determined by differential thermal analysis, and the ratio

Full text of DOI:10.1134/S0036023609020223

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 2, pp. 294–298. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © I.Ya. Zaitseva, I.S. Kovaleva, V.A. Fedorov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 2, pp. 338–343.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Glass Formation in the HgBr2–PbBr2–CsBr Ternary
I. Ya. Zaitseva, I. S. Kovaleva, and V. A. Fedorov
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
Received February 14, 2008
Abstract—Results of investigation of glass formation in the HgBr2–PbBr2–CsBr system are presented. The
glass formation region has been outlined. Characteristic temperatures have been determined by differential ther-
mal analysis, and the ratio Tg/Tm and factor HR have been calculated for vitreous samples of the HgBr2–PbBr2–
CsBr ternary.
DOI: 10.1134/S0036023609020223
Increased interest observed currently to bromide investigated three samples with compositions close to
ternary eutectics Ö2, Ö3, and Ö4 (Fig. 1). Quenching of
these samples showed that they are vitreous [3]. In [4],
we presented the results of the investigation of glass
formation along three joins: of the HgBr2–PbBr2–CsBr
ternary system CsHgBr3–CsPbBr3 (1), Cs2HgBr4–
CsPbBr3 (2), and CsHg2Br5– CsPbBr3 (3). Quenching
gave glassy samples in the following ranges: along
join 1, over the whole concentration range; along
join 2, within 8.7–100 mol % CsPbBr3; and along
join 3, within 0–40 and 70–100 mol % CsPbBr3. The
compositions of the most stable glasses along joins 1–3
were near the eutectic compositions, which confirmed
the relation of the liquidus temperature with the glass-
forming tendency in systems.
compounds in both crystalline and vitreous states is due
to the possibility of their use in IR optics because of
their transparency in the far-IR spectral region (above
20 µm) [1]. We choose to study the ternary system con-
sisting of mercury, lead, and cesium bromides because
cations of heavy metals shift the absorption band edge
to a long-wavelength region, which is important to the
use of such materials in IR engineering.
The purpose of this work was to investigate glass
formation in the HgBr2–PbBr2–CsBr ternary system.
We previously investigated interactions in binary sys-
tems bordering the HgBr2–PbBr2–CsBr system. In the
HgBr2–CsBr and PbBr2–CsBr systems, compounds
CsHg2Br5, CsHgBr3, Cs2HgBr4, CsPb2Br5, CsPbBr3, and
Cs4PbBr6 are formed; two of them (CsPb2Br5 and
Cs4PbBr6) melt incongruently. As a result of the investi-
gation of interactions in the mentioned ternary system,
we outlined the fields of primary crystallization of
phases, determined the coordinates of ternary invariant
points, and lined isotherms [2]. These data were used in
the investigation of glass formation in the ternary sys-
tem since it is known that samples with the composi-
tions close to eutectic ones have a larger ability to glass
formation. First, we investigated glass formation in
binary systems bordering the HgBr2–PbBr2–CsBr ter-
nary system. Upon quenching samples to an ice–water
mixture at ~100–150 K/s in the CsBr–HgBr2 system,
we obtained glasses in the concentration range of 46–
76 mol % HgBr2; in the CsBr–PbBr2 system, in the
concentration range of 50–95 mol % PbBr2; and in the
HgBr2–PbBr2 system, no glasses were obtained. Of the
six ternary compounds of the HgBr2–PbBr2–CsBr sys-
tem, only two, namely, Cs2HgBr4 and Cs4PbBr6, were
not obtained in a vitreous state. To determine glass for-
mation in the HgBr2–PbBr2–CsBr ternary system, we
To restrict the glass formation region in the HgBr2–
PbBr2–CsBr ternary system, in this work, we addition-
ally studied three joins, namely, the polythermal iso-
concentration join with 40 mol % HgBr2 (4), HgBr2–
CsPbBr3 (5), and CsHgBr3–PbBr2 (6), as well as
some samples of the ternary system.
EXPERIMENTAL
To investigate glass formation in the HgBr2–PbBr2–
CsBr system, as starting substances, we used HgBr2
synthesized as in [5], high-purity grade PbBr2, and
chemically pure grade CsBr dried at 100°ë to remove
trace water. The melting points of HgBr2, PbBr2, and
CsBr determined by DTA were 245, 360, and 640°ë,
respectively. The CsPbBr3 and CsHgBr3 compounds
necessary for the investigation of glass formation along
joins 5 and 6 were prepared from dried mercury, lead,
and cesium bromides in silica cells evacuated to a resid-
ual pressure of 10–3 Pa at 640°ë for 1 day under stirring,
annealed for 3 days at 200°ë, and then cooled in the
294

GLASS FORMATION IN THE HgBr2–PbBr2–CsBr TERNARY
CsBr
295
640°
Cs PbBr
4
6
p
1
P
3
e
4
e
5
Cs HgBr
435°
2
4
E
4
E
e
3
3
CsPbBr
570°
CsHgBr
3
310°
3
E
2
e
2
CsHg Br
250°
2
5
CsPb Br
2
5
P
1
P
2
e
E
1
1
p
2
e
6
HgBr e
M
PbBr
2
2
7
245°
mol %
360°
Fig. 1. Phase diagram of the HgBr –PbBr –CsBr ternary system in equilibrium and nonequilibrium states (glass-formation region
2
2
is hatched).
switched off furnace. The melting points of CsPbBr3 temperatures tg, tc, and tm (°C), which are the glass-tran-
and CsHgBr3 determined by DTA were 570 and 310°ë, sition temperature, crystallization temperature, and
melting point, respectively. DTA was performed on a
pyrometer with Pt–Pt/Rh thermocouples, the reference
was Al2O3, the heating rate was 8–10 K/min, and tem-
perature was determined accurate to 5°ë.
respectively. The synthesis of samples along joins 4–6
and other samples situated in different parts of the
HgBr2–PbBr2–CsBr phase diagram, was performed in
Stepanov vessels evacuated to a residual pressure of
10–3 Pa by the above-described procedure. The sample
weight was 1 g. Glasses in the bulk were prepared via
heating the synthesized samples to a temperature
exceeding the melting point by 50–70°ë, held at this
temperature for 30 min, and quenched in iced water
mixture with NaCl at about –10°C. The quenching rate
was ~100–150 K/s. Quenched samples were often yel-
low with color intensity depending on the composition.
Some samples were obtained in the vitreous state, and
some in the crystalline state. Glass formation was
RESULTS AND DISCUSSION
To determine the glass-formation regions in the
HgBr2–PbBr2–CsBr system, we investigated three non-
quasi-binary joins: polythermal isoconcentration join
containing 40 mol % HgBr2 (4), HgBr2–CsPbBr3 (5),
CsHgBr3–PbBr2 (6), as well as some other samples with
the compositions in various parts of the HgBr2–PbBr2–
detected both visually (as transparency and conchoidal CsBr ternary phase diagram. Let us consider the results
fracture) and by DTA via determining the characteristic obtained along each of joins.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 2 2009

296
t , t ,
ZAITSEVA et al.
with PbBr2 percentage increasing from 2 to 8 mol %;
T /T
g
c
g
m
,°C
∆t, t
for 10 mol % PbBr2, tg increases to 115°ë. The ratio
Tg/Tm gradually increases from 0.51 at 2 mol % PbBr2
to 0.65 at 10 mol % PbBr2. We succeeded to obtain the
values of tc, ∆t, and HR only for the sample with a com-
position of 2 mol % PbBr2 (∆t = 90°ë, HR = 0.4). The
values of ∆t and HR, which are considered as character-
istics of devitrification, indicate that glass is moderately
stable to crystallization.
m
HR
400
300
200
100
Join HgBr2–CsPbBr3 (5) was investigated over the
entire concentration range. Glasses were prepared in
the range from 60 to 100 mol % CsPbBr3 (Fig. 3). For
the samples with 60 and 90 mol % CsPbBr3, tg is virtu-
ally constant and equals 75–80°ë. A maximum value of
tg = 175°ë corresponds to the CsPbBr3 compound. The
abrupt increase in tg for CsPbBr3 is possibly associated
with the structural rearrangement of glass. The ratio
Tg/Tm in the range of 60–90 mol % CsPbBr3 initially
decreases from 0.5 to 0.42; then, at 100 mol % CsPbBr3,
its value increases to 0.54. We succeeded to obtain the
values of tc, ∆t, and HR only for the sample with the
composition of 60 mol % CsPbBr3. Low values of ∆t
and HR (45°ë and 0.14) indicate that this glass in the used
quenching mode is formed, but can easily crystallize.
t
t
g
c
∆t
t
m
T /T
g
m
HR
0.8
0.6
0.4
Join CsHgBr3–PbBr2 (6) was also investigated
over the entire concentration range. Glasses were pre-
pared in the concentration range from 0 to 25 mol %
PbBr2. After quenching, the samples of compositions of
29 and 33.3 mol % PbBr2 were mixtures of glass and a
crystalline phase, and with more than 33.3 mol %
PbBr2, quenched samples were crystalline. The results
obtained for glasses along join 6 are presented in Fig. 4.
The value of tg has a minimum for 5 mol % PbBr2 5 (tg =
50°ë). In the concentration range of 10–25 mol %
PbBr2 tg, is almost invariable and equals 80–75°C. The
drop of tg in the range from 0 to 10 mol % PbBr2 can
be explained by the phase transition α-CsHgBr3
β-CsHgBr3. The ratio Tg/Tm varies insignificantly, in the
limits of 0.57–0.67. The minimum of Tg/Tm (0.57) is
also apparently associated with the phase transition in
PbBr2. The values of tc, ∆t, and HR (155°ë, 105°ë, and
0.75) are maximal for the sample with 5 mol % PbBr2.
This can be explained by the fact that CsHgBr is
obtained in a vitreous state upon cooling, while the
addition of a small amount of PbBr2 exerts the stabiliz-
ing effect on glass, which is expressed in a large value
of ∆t and especially HR (0.75). As a result, two factors
compete, namely, the stabilizing effect of PbBr2 on
CsHgBr3, which enhances glass formation and facili-
tates the preparation of glasses more stable to crystalli-
zation, and the existance of the phase transition inhibit-
ing the glass formation in this concentration region.
0.2
0
0
5
10
mol %
15
PbBr
2
CsBr
Fig. 2. t , t , ∆t, t , T /T , and H vs. PbBr percentage
g
c
m
g
m
R
2
along the 40 mol % HgBr join (4).
2
Isoconcentration join at 40 mol % HgBr2 (4) was
investigated over the whole concentration range. In the
mentioned quenching mode, glass formation was
detected in samples containing 2 to 10 mol % PbBr2.
Samples containing 15 and 20 mol % PbBr2 were mix-
ture of crystals and glass. The glass-forming ability of
materials and stability of glasses can be characterized
by variuos methods. We used the method taking into
account the values of characteristic temperatures (tg, tc, tm),
∆t = tc – tg, the ratio Tg/Tm, and the Hruby factor HR =
(tc – tg)/(tm – tc), and studied the appearance of samples.
The results obtained for glass along join 4 are presented
in Fig. 2 as the composition dependences of character-
istic temperatures tg, tc, tm, and ∆t and the ratio Tg/Tm and
HR. tg initially somewhat increases from 60 to 70°ë
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 2 2009

GLASS FORMATION IN THE HgBr2–PbBr2–CsBr TERNARY
297
t , t ,
g
c
,°C
∆t, t
m
T /T
g
m
HR
600
t
t
g
c
∆t
t
m
T /T
g
m
500
HR
400
200
0.8
0.6
0.4
0.2
0
100
0
HgBr
50
60
70
mol %
80
90
100
CsPbBr
2
3
Fig. 3. t , t , ∆t, t , T /T , and H CsPbBr percentage along the HgBr –CsPbBr join (5).
g
c
m
g
m
R
3
2
3
In addition to the six investigated joins of the
HgBr2–PbBr2–CsBr ternary system, the possibility of
glass formation was investigated for the samples of
compositions presented in the table. However, all
quenched samples, except for one, were crystals. The
compositions and DTA results for quenched samples
are presented in the table.
For the sample obtained in the form of glass, we
determined ∆t = 75°ë, Tg/Tm = 0.54, and HR = 0.33.
In Fig. 1, along with the phase diagram of the
HgBr2–PbBr2–CsBr system in the equilibrium state
(lines of univariant equilibria and invariant points), we
present the generalized results of the investigation of
glass formation along the joins studied in [3, 4] and in
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 2 2009

298
t , t ,
ZAITSEVA et al.
this work. The glass-formation region (hatched in Fig. 1)
g
c
,°C
∆t, t
m
is considerable, is arranged along joins CsHgBr3–
CsPbBr3 (1), Cs2HgBr4–CsPbBr3 (2), and CsHg2Br5–
CsPbBr3 (3) (its boundary passes near the line of joint
isolation of these phases), and includes three ternary
eutectic points (Ö2, Ö3, and Ö4). The large extent of the
glass-formation region in the HgBr2–PbBr2–CsBr ter-
nary system is possibly associated with a large field of
primary separation of the CsPbBr3 compound, which
plays the role of glass former. The CsHgBr3, Cs2HgBr4,
and CsHg2Br5 compounds most probably play the role
of modifiers. The presence of binary and ternary eutec-
tics is the factor that promotes the glass formation.
t
t
g
c
T /T
HR
400
g
m
∆t
t
m
T /T
g
m
HR
200
300
100
As the most promising samples for preparing
glasses, we can mention the samples of compositions
48.7 mol % HgBr2–2.6 mol % PbBr2 –48.7 mol % CsBr
(∆t = 105°ë, Tg/Tm = 0.57, HR = 0.75), 59.6 mol %
HgBr2–5.3 mol % PbBr2–35.1 mol % CsBr (∆t =
105°ë, Tg/Tm = 0.63, HR = 1.24), 62.1 mol % HgBr2–
3.4 mol % PbBr2 –34.5 mol % CsBr (∆t = 90°ë, Tg/Tm =
0.67, HR = 1.125), and 51.9 mol % HgBr2 –11.1 mol %
PbBr2 –37.0 mol % CsBr (∆t = 75°ë, Tg/Tm = 0.64, HR =
0.625).
0.8
0.6
0.4
0.2
0
0
5
10
15
20
25
100
PbBr
CsHgBr
Therefore, glass formation has been investigated for
the HgBr2–PbBr2–CsBr ternary system for the first time,
and the extensive glass-formation region is found.
Complicating the composition via introduction of chlo-
rides and iodides, it is possible to obtain stable glasses
with high optical properties.
3
2
mol %
Fig. 4. t , t , ∆t, t , T /T , and H vs. PbBr percentage
along the CsHgBr –PbBr join (6).
g
c
m
g
m
R
2
3
2
DTA results for quenched samples of the HgBr2–PbBr2–CsBr
ternary system
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