Phase studies on the quasi-binary thallium(I) telluride-gallium(III) telluride system

Article abstract of DOI:10.1016/j.tca.2011.02.006

The phase diagram for the quasi-binary Tl₂Te-Ga ₂Te₃ system was constructed based on the results of phase studies by both common thermal analysis and X-ray diffraction. Numerical values of the phase transition temperatures

Full text of DOI:10.1016/j.tca.2011.02.006

Thermochimica Acta 518 (2011) 53–58
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journal homepage: www.elsevier.com/locate/tca
Phase studies on the quasi-binary thallium(I) telluride–gallium(III) telluride
system
∗
Igor Mucha, Katarzyna Wiglusz, Zbigniew Sztuba, Wieslaw Gawel
Department of Analytical Chemistry, Wroclaw Medical University, Szewska 38, 50-139 Wroclaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 August 2010
Received in revised form
The phase diagram for the quasi-binary Tl Te–Ga Te system was constructed based on the results of
2
2
3
phase studies by both common thermal analysis and X-ray diffraction. Numerical values of the phase
transition temperatures at different alloy compositions within the whole concentration range were listed.
The diagram was compared with another diagram for the same system published earlier by other authors.
The study produced substantial evidence corroborating the formation of two new chemical compounds.
2
0 December 2010
Accepted 4 February 2011
Available online 19 February 2011
©
2011 Elsevier B.V. All rights reserved.
Keywords:
Thallium–gallium telluride system
Quasi-binary phase diagram
Thermal analysis
1
. Introduction
The components of the system thallium(I) telluride–indium(III) tel-
luride form two ternary compounds [2,3]: at 42.9 mol% In Te3 (i.e.
2
The thallium(I) telluride–gallium(III) telluride system was for-
4Tl Te·3In Te ) melting incongruently at 1021.4 K and 54.5 mol%
2
2
3
merly examined by Babanly and Kuliyev [1]. In their studies
they employed differential thermal analysis (DTA) as the main
experimental method, while X-ray diffraction (XRD) and micro-
hardness measurement were used as auxiliary ones. The authors
published phase diagram for this system presented in Fig. 1. It
followed from the diagram that the system components formed
two chemical compounds: at 25 mol% Ga Te (i.e. 3Tl Te·Ga Te or
In Te (i.e. 5Tl Te·6In Te ) melting congruently at 1044.9 K. From
2
3
2
2
3
the comparison of the data [1] and [3] it may be seen that the
analogy is rather poor, unless the data [1] are precisely determined.
These were reasons why we decided to reexamine the
Tl Te–Ga Te system by common thermal analysis (TA), a method
2
2
3
that appeared [4] to be more accurate than others. X-ray diffraction
was also employed to obtain complementary information.
2
3
2
2
3
Tl GaTe ) incongruently melting at 691 K, and at 50 mol% Ga Te
3
3
3
2
(
i.e. Tl Te·Ga Te or TlGaTe ) melting congruently at 1048 K. The
2
2
3
2
2
. Experimental
latter was rather a phase of variable composition (␥). Both the com-
pounds formed terminal solid solutions ␣ with Tl Te 5 mol% wide
and ␤ with Ga Te3 20 mol% wide, respectively.
2
2.1. Materials
2
The paper [1] was published more than thirty years ago when
the level of the experimental technique was certainly lower com-
pared with the present state. Consequently, the results reported
earlier might be of lower accuracy as it was many times showed by
us, e.g. [2,3], while only reliable phase diagrams may serve as a base
of searching for new materials with favorable physico-chemical
properties.
The components of the system examined, i.e. thallium tel-
luride and gallium telluride, were prepared from high-purity
elements: thallium 99.9 mass%, gallium 99.9 mass% and tellurium
9
9.99 mass% (all from Aldrich Chemical Co.). The metal tellurides
were synthesized by simple fusion of stoichiometric quantities of
the elements, weighed with an accuracy of ± 0.0001 g, in quartz
tubes in a purified argon atmosphere (5 N pure, BOC Gazy, Poznan)
and then stirred for 15 min at a temperature about 100 K higher
than the melting point of the respective metal telluride.
On the other hand, we studied earlier the Tl Te–In Te sys-
2
2
3
tem [2,3], analogous to the system Tl Te·Ga Te , accordingly, the
2
2
3
phase diagram of the latter should resemble that of the former.
2.2. Apparatus and measurements
∗ Corresponding author.
E-mail address: gawel@cheman.am.wroc.pl (W. Gawel).
The phase studies on the Tl Te–Ga Te system were made by
TA method, employing a quartz apparatus designed for phase and
2
2
3
0
040-6031/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2011.02.006

5
4
I. Mucha et al. / Thermochimica Acta 518 (2011) 53–58
Fig. 1. Phase diagram for the system Tl2Te–Ga2Te3.
According to [1].
Table 1
cryometric studies at high temperatures, described in detail in
5]. The vessel was filled with the pure argon to prevent sam-
The phase transition temperatures at different alloy compositions within the whole
concentration range of the system Tl2Te–Ga2Te3.
[
ple oxidation. The phase transition temperatures of the samples
were determined using a Pt/Pt, Rh thermopile calibrated at the
freezing points of standards (lead, zinc, aluminium, potassium chlo-
ride and silver). The molten samples (no less than 28 g) were
vigorously stirred throughout the experiments with a quartz stir-
rer to maintain equilibrium conditions of crystallization of the
melts. The cooling rate was 0.8–1.2 K/min, and the accuracy of
measurement was ± 0.5 K. The thermopile was connected to a
Fluke 45 dual display multimeter, which was connected to a
computer for the processing and display of the experimental
data.
No.
Comp.
Temp. (K)
No.
Comp.
(mol% Ga2Te3)
Temp. (K)
(
mol% Ga2Te3)
1
2
3
4
5
6
7
8
9
0.00
0.98
1.99
2.76
5.00
6.07
6.07
8.02
8.02
9.74
9.74
10.78
10.78
12.58
12.58
14.35
15.54
16.10
16.55
17.46
17.46
17.89
18.60
19.62
20.82
20.82
22.92
22.92
23.12
25.70
25.70
25.73
27.20
27.20
29.82
29.82
687.5
705.4
707.5
709.1
710.9
710.2
677.6
704.9
680.0
698.6
680.8
694.7
680.9
691.6
684.0
685.4
682.1
772.1
686.7
890.0
826.1
678.2
687.0
869.0
928.5
688.6
902.3
686.4
895.0
926.5
683.4
953.7
964.8
685.4
937.5
930.3
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
36.00
38.77
44.37
46.80
46.80
52.20
54.45
56.61
56.91
59.09
59.35
60.13
61.65
62.15
64.02
64.40
64.87
66.72
66.95
68.23
68.23
68.95
69.10
71.06
71.06
71.84
73.95
74.22
74.22
75.45
75.45
77.55
77.55
80.36
80.36
83.40
961.5
987.6
1005.0
1018.4
1013.4
1029.6
1034.5
972.1
1029.0
973.4
1020.2
1008.0
973.4
1001.2
975.4
999.1
1010.5
987.7
973.8
997.7
984.3
979.7
979.5
975.3
965.3
965.5
974.7
987.2
968.2
1004.3
996.3
1011.7
975.3
1020.5
973.8
1029.7
10
To confirm the results obtained by TA, use was also made of
the XRD method. Alloy samples with compositions 2, 8, 25, 35,
11
12
1
1
1
1
3
4
5
6
4
7, 54.5, 65 and 85 mol% Ga Te3 were prepared by melting and
2
mixing appropriate quantities of components in quartz tubes in a
pure argon atmosphere. The solidified samples were powdered in
an Analysette 3 Spartan pulverisette 0 vibration mill (Fritsch) and
homogenized for 7 days under vacuum at 650 K, then quenched in a
cooling bath (ice + methanol). The XRD examinations of the alloys as
well as of the pure components (Tl Te and Ga Te ) were performed
17
18
19
20
21
2
2
3
using a Siemens D5000 diffractometer.
22
2
2
3
4
3
. Results
25
2
2
2
2
6
7
8
9
The experimental results, i.e. the temperatures of crystalliza-
tion of different alloys, obtained by TA are summarized in Table 1
These data enabled the precise phase equilibrium diagram to be
.
30
31
delineated for the thallium(I) telluride–gallium(III) telluride sys-
tem (Fig. 2). The constructed phase diagram was checked by the
XRD examination aimed at identifying phase compositions of dif-
3
3
3
2
3
4
ferent Tl Te + Ga Te alloys.
2
2
3
35
36
Both the TA and the XRD data evidenced two new chemical
compounds Tl19GaTe11 and Tl10Ga12Te23 (not found earlier [1])

I. Mucha et al. / Thermochimica Acta 518 (2011) 53–58
55
Table 1 (Continued )
4. Discussion
No.
Comp.
mol% Ga2Te3)
Temp. (K)
No.
Comp.
(mol% Ga2Te3)
Temp. (K)
(
4.1. New ternary compounds found in the system Tl2Te–Ga2Te3
37
38
39
40
41
42
31.62
31.62
31.62
31.89
31.89
33.69
969.2
965.2
943.4
970.9
676.7
968.9
79
80
81
82
83
84
85.58
85.58
88.12
90.83
98.18
100.00
1036.8
973.7
1045.6
1052.0
1059.5
1065.0
The first of the compounds found by us, was formed with a
component molar ratio Tl Te:Ga Te = 19:1 (or 19Tl Te·Ga Te ), to
2
2
3
2
2
3
which the formula Tl19GaTe may be ascribed. This compound
11
composition was evidenced by both the maximum (at 5.0 mol%
Ga Te ) on the liquidus line corresponding to congruent melting of
2
3
the compound at 710.9 K and the arrangement of the experimental
points corresponding to the eutectic at 14.4 mol% Ga Te , melting
2
3
at 684.0 K. The points may be observed only at compositions higher
than 5.0 mol% Ga2Te3.
The other compound was formed at 54.5 mol% Ga2Te3, its com-
ponent molar ratio being Tl2Te:Ga2Te3 = 5:6 (5Tl2Te·6Ga2Te3), to
which a formula Tl10Ga12Te23 may be ascribed. Rather sharp max-
and confirmed the existence of terminal solid solutions ␣ and
reported in [1]. Thereby it was shown, that the compounds
Tl GaTe and TlGaTe [1] had not been formed in the system under
␤
3
3
2
consideration.
Fig. 2. Phase diagram for the system Tl2Te–Ga2Te3 (this work).

5
6
I. Mucha et al. / Thermochimica Acta 518 (2011) 53–58
Fig. 3. The X-ray diffraction patterns of some Tl2Te + Ga2Te3 alloys.
imum on the liquidus line corresponding to a congruent melting of
the compound at 1034.5 K lies exactly (confirmed several times)
at 54.5 mol% Ga Te . Moreover, the experimental points corre-
Taking into account the maximal error in the graphical deter-
mination of the coordinates of the characteristic points of the
phase diagram, the compositions of the eutectics are given
with an accuracy of ± 1 mol%. The eutectic coordinates were
determined from intersection points of the eutectic transition
line and respective two liquidus lines in the phase equilibrium
diagram.
2
3
sponding to the next eutectic (at 71.1 mol% Ga Te ) melting at
2
3
9
75.3 K, appear just above the compound composition. These two
facts unequivocally determine the compound composition. Conse-
quently, it may be stated that the compound at 50.0 mol% Ga Te3
2
(
TlGaTe ) reported in [1] does not exist.
The compositions of the examined alloys were calculated from
the masses of the components taken. There was no need to analyze
the samples after each measurement series was completed as the
mass loss due to evaporation of a more volatile component was
negligible (did not exceed 0.05 mass%).
2
4
.2. Accuracy of measurements
The TA method (the cooling curve technique) employed in
this work, enabled the melting temperatures of the compounds,
eutectics and pure components to be determined with a good accu-
racy of ± 0.5 K. The only exception is some parts of the liquidus line
on either side of the compound Tl1 Ga Te (54.5 mol% Ga Te )
where the experimental points are scattered. Undoubtedly this is a
result of supercooling liquid alloys even in spite of vigorous stirring.
In the metal chalcogenide alloys such phenomenon may frequently
appear as they easily form glasses [6,7] which results in consider-
able increasing viscosity of a melt.
4.3. XRD examinations
The XRD patterns of the pure components and those of the alloys
homogenized at 650 K are presented in Fig. 3. As it will be shown
later, the XRD patterns entirely corroborate the results described
above.
From comparison of the XRD pictures of pure Tl Te (Fig. 3(a))
and the alloy containing 2 mol% Ga Te3 (Fig. 3(b)), it can be seen
0
12
23
2
3
2
2
that the peaks in the latter figure are shifted compared to the for-

I. Mucha et al. / Thermochimica Acta 518 (2011) 53–58
57
Fig. 4. Phase diagram for the system Tl2Te–In2Te3 [3].
mer which provides an evidence for the terminal solid solution
␣) on the Tl Te matrix. The region of the solid solution ␣ cov-
ure only, are shifted compared to the first one, which provides a
good evidence for a region of the terminal solid solution (␤) on
(
2
ers 5 mol% Ga Te3 only, i.e. up to the compound 19:1 because in
the Ga Te3 matrix, no more than 15 mol% wide at the (homoge-
2
2
Fig. 3(c) (8 mol% Ga Te ) the shift is no longer observed. Fig. 3(c)
almost entirely presents the XRD pattern of the compound 19:1
nization) temperature of 650 K. The last statement appears to be
quite consistent with the arrangement of experimental points cor-
responding to the eutectic (71.1 mol% Ga Te ) melting at 975.3 K.
2
3
(
Tl19GaTe11).
2
3
The X-ray diffraction patterns of the alloy samples of composi-
The points may be observed as far as 85.58 mol% Ga Te3 (Table 1,
2
tions of 25 mol% Ga Te3 (Fig. 3(d)), 35 mol% Ga Te3 (Fig. 3(e)) and
no. 80) which corroborates the solid solution existence above this
alloy composition.
2
2
4
7 mol% Ga Te (Fig. 3(f)) show superimposed peaks characteris-
2 3
tic of the compound Tl19GaTe11 (19:1) together with strong peaks
corresponding to the next compound Tl10Ga12Te23 (5:6), which is
clearly proved by the XRD pattern in Fig. 3(g) (54.5 mol% Ga Te ).
5. Conclusions
2
3
Accordingly, it may be inferred that no additional chemical com-
The results of the present study differ considerably from those
of [1] in some details, in both the composition of the chemical
pound is formed within the range 8–47 mol% Ga Te3 (as e.g. the
2
compound at 25 mol% Ga Te3 reported in [1]). At the same time in
compounds formed in the system Tl Te–Ga Te and the phase
2
2 2 3
Fig. 3(f) and (h) compared with Fig. 3(g), no shifts may be observed
of the peaks characteristic of the compound 5:6, from which it fol-
lows that there is no phase of variable composition (␥) reported in
transition temperatures. It should especially be noted that the for-
mer authors did not observe the maximum on the liquidus line at
5.0 mol% Ga Te , corresponding to congruent melting of the com-
2
3
[
1].
From comparison of the XRD pictures of pure Ga Te3 (Fig. 3(j))
pound at 710.9 K and determined inaccurately the composition of
the other compound as being 50 mol% Ga Te , while it was exactly
2
2
3
and the alloys containing 65 mol% Ga Te3 (Fig. 3(h)) and 85 mol%
54.5 mol% Ga Te .There are in the literature several reports (e.g.
2
2 3
Ga Te (Fig. 3(i)), it can be seen that the peaks in the latter fig-
[8,9]) on studying properties of the compound TlGaTe2 (exactly:
2
3

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I. Mucha et al. / Thermochimica Acta 518 (2011) 53–58
alloy containing 50 mol% Ga Te ) since many years. The authors of
Comparison of another two analogous systems Tl Te–Sb Te
2 2 3
2
3
the reports stated that it was a phase with wide homogeneity area.
This statement indirectly confirms our results: if the compound
composition is 54.5 mol% Ga Te (5:6 or Tl10Ga12Te23), and we pre-
[10] and Tl Te–Bi Te [11] shows more clearly the respective sim-
ilarities and differences.
These examples are a confirmation of a rule that in such analo-
gous systems the tendency to compound formation increases with
increase in atomic weight of metal M.
2 2 3
2
3
pare the alloy 50.0 mol% Ga Te3 (because we suppose that this is
2
TlGaTe ), we will find that it is no pure TlGaTe2 but some region
2
covering the range up to 54.5 mol%. The composition 54.5 mol% will
be considered as a limit of a homogeneity area. Of course, the alloy
References
5
0 mol% Ga Te also embodies some crystal structure, thermody-
2 3
namic and electrical properties that may be studied and described
in publications.There are two possible reasons for the discrepan-
cies between the present data and those of [1]. The first is the
limitations of the differential thermal analysis employed by the
former authors. In the DTA method the samples are not stirred and
therefore the phase transformations occur under nonequilibrium
conditions. Unlike DTA, the TA method used in this study enabled
the solid and liquid phases to be in equilibrium on cooling due to
efficient stirring, which resulted in precise temperature measure-
ments of the phase transitions in the examined alloys. The other
reason is that the metal chalcogenide alloys may form glasses on
solidifying, which makes exact temperature measurement impos-
sible. The formation of glasses appears very easily when the liquid
sample is not stirred (as in DTA method).
[
1] M.B. Babanly, A.A. Kuliyev, Phase equilibriums in the thallium(I)
sulfide–gallium(III) sulfide, thallium(I) selenide–gallium(III) selenide,
and thallium(I) telluride–gallium(III) telluride systems, Khim. Khim. Tekhnol.
19 (1976) 1316–1318.
[
[
2] E. Zaleska, Z. Sztuba, I. Mucha, W. Gaweł, Electrochemical study of the quasi-
binary thallium(I) telluride–indium(III) telluride solid system, Electrochim.
Acta 52 (2007) 8048–8054.
3] Z. Sztuba, K. Wiglusz, I. Mucha, A. Sroka, W. Gaweł, Solid–liquid equilibria in
the quasi-binary thallium(I) telluride–indium(III) telluride system, Calphad 32
(2008) 106–110.
[4] W. Gaweł, Phase studies on the quasi-binary metal telluride systems, in: K.
S´ wi a˛ tkowski (Ed.), Metallurgy on the Turn of the 20th Century, Committee
of Metallurgy of the Polish Academy of Sciences, Publishing House AKAPIT,
Kraków, 2002, pp. 413–436.
[5] W. Gaweł, A. Górniak, Phase diagram and thermodynamic properties of the
system MnCl2-UCl4, prediction and investigation results, J. Nucl. Mater. 340
(
2005) 64–68.
[
[
[
6] E.V. Aleksandrovich,
Manifestation
of
peculiarities
of
the
It is worth comparing the phase diagrams for both the
Tl Te–In Te (Fig. 4) and the Tl Te–Ga Te (Fig. 2) systems as anal-
gallium–thallium–tellurium glasses structure on the DTA-thermograms,
Khim. Fizika Mezoskopiya 12 (2010) 204–208.
7] V.P. Khan, B.N. Perevozchikov, E.V. Aleksandrovich, Structural transformations
and electrical properties of glasses of the system Ga–Tl–Te, Neorg. Mater. 29
(1993) 1473–1476.
2
2
3
2
2
3
ogous. There are some considerable similarities between them. The
most important is that in either system one chemical compound
is formed of common formula 5Tl Te·6M Te (where M = Ga or
8] H. Matsumoto, K. Kurosaki, K. Muta, S. Yamanaka, Systematic investigation of
the thermoelectric properties of TlMTe2 (M = Ga, In or Tl), J. Appl. Phys. 104
2
2
3
In). Comparing melting temperatures of the compounds it may
(
2008) 073705–073710.
be stated that higher melting point of 5Tl Te·6In Te (1045.0 K)
[9] M.M. Gospodinov, I.Y. Yanchev, A.N. Mandalidis, A.N. Anagnastopoulos, Grown
and characterization of TlGaTe2, Mater. Res. Bull. 30 (1995) 981–985.
10] W. Gaweł, B. Fuglewicz, E. Zaleska, Phase diagram for the Tl2Te–Sb2Te3 system,
Pol. J. Chem. 63 (1989) 93–96.
2
2
3
is an indicative of greater tendency to compound formation in
[
the system Tl Te–In Te than in Tl Te–Ga Te (5Tl Te·6Ga Te
–
2
2
3
2
2
3
2
2
3
1
034.5 K), since the melting temperature of a compound is a mea-
2 2 3
[11] W. Gaweł, E. Zaleska, J. Terpiłowski, Phase diagram for the Tl Te–Bi Te system,
sure of a stability thereof. Another common feature of the two
J. Therm. Anal. 35 (1989) 59–68.
systems is forming terminal solid solutions ␣ and ␤.