Phase equilibrium in the system Tl2Te-TlBr-TlI and thermodynamic properties of the solid solution Tl5Te2Br xI1-x

Article abstract of DOI:10.1016/j.jallcom.2013.07.092

The Tl₂Te-TlBr-TlI system was investigated by means of the DTA and XRD analyses and microhardness and EMF measurements. Several polythermal and isothermal sections and the projection of the liquidus surface were constructed. The fields of prima

Full text of DOI:10.1016/j.jallcom.2013.07.092

Accepted Manuscript
Phase equilibrium in the system Tl Te–TlBr–TlI and thermodynamic properties
2
of the solid solution Tl Te Br I
5 2 x
1–
x
Dunya M. Babanly, Sara M. Bagheri, Andrei V. Shevelkov, Ziya S. Aliyev
PII:
S0925-8388(13)01717-9
DOI:
http://dx.doi.org/10.1016/j.jallcom.2013.07.092
JALCOM 29016
Reference:
To appear in:
Received Date:
Revised Date:
Accepted Date:
13 March 2013
3 July 2013
14 July 2013
Please cite this article as: D.M. Babanly, S.M. Bagheri, A.V. Shevelkov, Z.S. Aliyev, Phase equilibrium in the
system Tl Te–TlBr–TlI and thermodynamic properties of the solid solution Tl Te Br I
2 5 2 x
, (2013), doi: http://
x
1–
dx.doi.org/10.1016/j.jallcom.2013.07.092
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Phase equilibrium in the system Tl2Te–TlBr–TlI and thermodynamic properties of
the solid solution Tl5Te2BrxI1–x
Dunya M. Babanly,a, * Sara M. Bagheri, b Andrei V. Shevelkov,c, * Ziya S. Aliyev b
a Institute of Chemical Problems of ANAS, Baku, Azerbaijan
b Baku State University, General and Inorganic Chemistry Department, Azerbaijan
c Lomonosov Moscow State University, Department of Chemistry, Russia
* Corresponding authors
H.Javid, 32, Baku, Azerbaijan, e-mail: babanly_mb@rambler.ru (D.M. Babanly)
Leninskie Gory 1-3, Moscow 119991, Russia, e-mail: shev@inorg.chem.msu.ru (A.V. Shevelkov)
Abstract.
The Tl2Te–TlBr–TlI system was investigated by means of the DTA and XRD analyses and
microhardness and EMF measurements. Several polythermal and isothermal sections and the
projection of the liquidus surface were constructed. The fields of primary crystallization, as well
as types and coordinates of non- and monovariant equilibriums were determined. It was
established that the system is characterized by formation of the continuous solid solution (γ-
phase) between the Tl5Te2Br and Tl5Te2I (Tl5Te3 structure type) iso-structural compounds. The
homogeneity field of γ-phase in the Tl5Te2Br–Tl5Te2I section penetrates the Tl2Te–Tl5Te2Br–
Tl5Te2I subsystem and occupies its large part. The partial molar thermodynamic functions
(ΔG,ΔH,ΔS) of thallium were calculated for the Tl5Te2BrxI1-x (for x = 0.2; 0.4; 0.6; 0.8) solid
solution based on the results of the EMF measurements.

1. Introduction
Chalcogenides and chalcogen-halides of heavy p elements possess high-performance
semiconductor properties making them perspective matrices for the creation of various types of
new functional materials [1, 2]. It was recently reported that some wide gap thallium chalcogen-
halides can be used for ionized radiation detection at X-ray and γ-ray regimes; they have a higher
merit than the current state of the art material for room temperature operation, CdZnTe (CZT) [3,
4]. Other thallium derivatives display rather high thermoelectric figure-of-merit [5].
Although the toxicity of thallium and its compounds limits possible utilization of thallium-
based materials to some niche applications, the search for new multicomponent
nonstoichiometric phases based on thallium chalcogen-halides remains an important task. Not
only new materials can emerge but also proofs of concepts might be received and underline
physics established. In particular, this may be important for the phases with sizable homogeneity
ranges, for which the property optimization may depend on the controllable synthesis of the
required composition. In most cases, the choice for a correct synthetic approach requires detailed
investigation of phase equilibriums in the corresponding systems.
In this paper, we focus on the phase equilibriums that involve ternary Tl5Te2X (X = Br, I)
phases. The literature data on the Tl–Te–X (X = Br, I) systems show that the quasi-binary
sections TlX–Tl2Te are characterized by formation of the Tl5Te2X type ternary compounds [6–9].
These compounds crystallize in the Tl5Te3 type tetragonal structure (space group I4/mcm) with a
complete segregation of tellurium and halogen atoms [10]. Tl5Te3 and its ternary analogues such
as Tl9BiTe6, Tl9SbTe6, and Tl4PbTe3 are known to display perspective thermoelectric properties
[11–13]. Given the striking similarity of the crystal structures of these compounds and Tl5Te2X
(Figure 1), one can expect similar properties for the latter phases, although Tl5Te3 differ from
other phases in that they do not follow simple valence rules for Zintl compounds [14, 15].
In our preliminary works we have studied phase equilibriums in the systems Tl5Te3–
Tl9BiTe6–Tl5Te2Cl(Br,I) [16–18], Tl5Se2I–Tl5Te2I [19], Tl2Se–Tl2Te–TlBr(TlI), and Tl2Se–TlBr–
TlCl(TlI) [20], which enabled us to obtain some data on the phase equilibriums involving the
Tl5Te2X and Tl5Se2X compounds. We have also found that nonstoichiometric phases with the
Tl5Te3-type tetragonal structure form in these systems.
Here we report the results of the complete investigation of the phase equilibriums in the
quasi-ternary system Tl2Te-TlBr-TlI (A).

1.1. Review of the boundary binary systems.
Binary compounds belonging to the system (A) are well characterized [21–26].
Tl2Te melts congruently at 698K [21] and crystallizes in the monoclinic system, space
group C2/c, with the unit cell parameters а = 15.662; b = 8.987; c = 31.196 Å, β=100.7610, z =
44 [22]. Thought the crystal structure is unexpectedly very complex, the absence of Tl–Tl and
Te–Te interactions makes it possible to assign unambiguously oxidation states +1 and –2 for Tl
and Te, respectively.
TlBr melts congruently at 763 K and has a cubic crystal structure of the CsCl type, a =
3.984 Å [23]. TlI also melts congruently at 715 K and undergoes the α-TlI ⇔ β-TlI polymorph
transformation at 451 K [24]. The low-temperature modification α-TlI crystallizes in the
orthorhombic space group Cmcm with the unit cell parameters a = 4.57, b = 12.92, c = 5.24 Å, z
= 4, whereas the high-temperature modification β-TlI crystallizes in the cubic system similar to
TlBr, with а = 4.201 Å and z=1 [25, 26].
The boundary quasi-binary sections of the system (A) were studied in detail. The Tl2Te–
TlBr [9] and Tl2Te–TlI [7] systems are characterized by formation of ternary compounds
Tl5Te2Br and Tl5Te2I that melt with decomposition by synthectic reaction, respectively at 750 K
and 775 K. The immiscibility field in the system Tl2Te–TlBr at the synthectic temperature of 750
K ranges from ~15 to 92 mol% Tl2Te [9], whereas in the system Tl2Te–TlI it ranges from ~20 to
80 mol% Tl2Te [7]. It was established that both ternary compounds have wide homogeneity
fields that ranges from 66.6 to 87 mol % Tl2Te (Tl5Te2Br) and from 66 to 92 mol % Tl2Te
(Tl5Te2I).
The quasi-binary system TlBr–TlI is characterized by formation of unlimited solid solutions
between Tl(I) bromide and the high-temperature modification of Tl(I) iodide [27].
2. Experimental
2.1. Synthesis
The elements of high purity were used as starting materials: thallium 99.999%, tellurium
99.999%, iodine 99.9%. Iodine was purified three times by sublimation before use. Binary
(Tl2Te, TlBr, TlI) and ternary (Tl5Te2Br, Tl5Te2I) compounds were synthesized from the finely
grinded elements.

Tl2Te was prepared from the stoichiometric amounts of the corresponding elements by one-
step melting in vacuum-sealed silica ampoules (~10-2 Pa) at 750 K, followed by cooling in the
switched-off furnace.
TlI was synthesized following a specially designed method that takes into account high
volatility of iodine. The synthesis was performed in an inclined two-zone furnace, with the hot
zone kept at a temperature 20–30 K higher than the corresponding melting point of TlI (698),
whereas the temperature of the cold zone was about 400 K. After the main portion of iodine had
reacted, the ampoule was relocated in such a manner that the product could melt at 720 K. The
melt was stirred at this temperature by shaking the furnace and then cooled with the furnace.
TlBr was prepared by an indirect method reported in the literature [28]. At first, metallic
thallium was dissolved in the dilute sulfuric acid (~10 mol. %) at 350 K to get the Tl2SO4
solution. Then diluted HBr was added into a hot 2% Tl2SO4 solution until complete precipitation
of TlBr. Yellowish green TlBr was separated from the mother liquor and washed with icy
distilled water. The product was dried over KOH in a desiccator at 380-400 K and stored in the
dark to prevent its decomposition.
Ternary compounds Tl5Te2Br and Tl5Te2I were synthesized by melting appropriate amounts
of the synthesized TlBr, TlI and Tl2Te in vacuum-sealed quartz ampoules. These compounds
decompose by a synthectic reaction upon melting [8]. Accordingly, the tubes containing melts
were cooled slowly to 730 K and held at this temperature for ~800 h.
Most of the samples having masses of 1 g were prepared for further investigation from the
binary and ternary compounds described above. After determining the solidus temperature, the
sintering temperatures were adjusted to be 20-30 K below the solidus. Thus, the samples were
annealed for 800-1000 h at 670 K.
2.2. Analysis
X-ray powder diffraction (XRD), measurement of microhardness, and differential thermal
analysis (DTA) were used to characterize the samples.
The XRD analysis was performed on a Bruker D8 ADVANCE diffractometer with the Cu-
Kα1 radiation. The lattice parameters were refined using the TopasV3.0 software. XRD
confirmed that the pre-synthesized binary and ternary compounds were phase-pure, and that the
unit cell parameters perfectly matched the literature data for binary compounds. The powder
XRD patterns for Tl5Te2Br and Tl5Te2I were indexed (Figure 2) using Topas V3.0 software. The

following unit cell parameters were obtained from the least-squares refinements. It is confirmed
that both compounds crystallize in the tetragonal Tl5Te3 structure type with the space group
I4/mcm and the following unit cell parameters: a = 8.980(2), c = 12.932(3) Å, z = 4 for Tl5Te2Br;
a = 9.026(1), c = 13.324(3) Å, z = 4 for Tl5Te2I.
Microhardness measurements were performed with a microhardnessmeter PMT-3, the
typical loading being 20 g.
For the DTA measurements, the NTR-72 device equipped with two chromel–alumel
thermocouples was used. The ramp rate was 5 Km–1. Temperatures of thermal effects were taken
mainly from the heating curves. The melting points of the pre-synthesized ternary compounds
were measured and found to be in excellent agreement with the literature data.
2.3. EMF measurements
For the electromotive force (EMF) measurements, the following concentration chains were
assembled:
(–) Tl (solid) / glycerin + KI + TlI / [Tl–Te–Br–I] (solid) (+)
(1)
In the chains of type (1), “metallic” thallium was used as the left electrode, while
equilibrium alloys of the system Tl2Te–TlBr–TlI were exploited as the right electrodes. A
saturated glycerin solution of KI with the addition of 0.1 mass % TlI was used as an electrolyte.
The electrodes prepared by pressing the alloys in the form of pellets with the mass of 0.5 g were
assembled and placed in a tubular furnace; the temperature was stabilized at 350K for 40–50 h.
EMF was measured by the compensation method in the temperature range of 300–400 K with the
accuracy of 0.1 mV, using the high-resistance universal B7-34A digital voltmeter. In each
experiment the first reading was performed approximately 30 h after the start of the experiment
and then 4–5 h after reaching the desired temperature, which ensures the achievement of
equilibrium. Considered equilibrium were the EMF readings that varied by no more than 0.5 mV
regardless of the direction of the temperature change at repeated measurements at a given
temperature. In order to eliminate the contribution of the thermopower, all contacts and leads
were kept at the same temperature. The reversibility of the assembled concentration chains and
the reproducibility of the results were controlled by checking the mass of the electrodes before
and after the measurements and further confirmed by the chemical analysis of selected electrodes
after the measurements. It was shown that the composition and mass of the electrodes remained
constant during the experiment.

The detailed description of the methods of assembling the electrochemical cell and carrying
out the EMF measurements is given elsewhere [29].
3. Results and discussion
The analysis of the summarized experimental results together with the literature data on the
boundary binary systems Tl2Te–TlBr(TlI) [6–9] and TlBr–TlI [27] allowed us to construct a self-
consistent diagram of the phase equilibrium in the quasi-ternary system Tl2Te–TlBr–TlI.
3.1. The polythermal section Tl5Te2Br–Tl5Te2I
The phase diagram of the system Tl5Te2Br–Tl5Te2I is shown in Figure 3, where the DTA
data, results of XRD, microhardness, and EMF for the selected compositions are indicated.
The system is non quasi-binary due to the synthectic melting character of the ternary
compounds Tl5Te2Br and Tl5Te2I.
As shown in Figure 3 the three-phase area L1+L2+γ is directly connected with the single γ-
phase. Two liquid phases L1 and L2 are used at the same time by the synthectic reaction L1+L2⇔γ
in the crystallization process of the γ-phase; therefore, the expected two-phase fields L1⇔γ and
L2⇔γ are degenerate.
The formation of the unlimited solid solution in this system is confirmed by the XRD
analysis, measurements of microhardness and EMF of concentration chains of type (1) (Table 1,
Figures 3 and 4).
The XRD data of the alloys after annealing for about 800 h at 700 K are presented in Figure
4. Apparently, all samples of the system Tl5Te2Br–Tl5Te2I have the same diffraction pattern.
Upon increasing the Tl5Te2Br content in alloys, the corresponding peak positions are shifted
towards higher angles. The dependence of the lattice parameters (a, c) on the composition obeys
the Vegard’s rule (Figure 3b).
The dependence of the microhardness upon the composition shows up as a curve with a flat
maximum (Figure 3c). The EMF values are the linear functions of the composition. The
isothermal E-x curve at 300 K is characterized by a monotonous change of EMF values with the
composition (Figure 3d). All these dependences are typical for the systems containing continuous
solid solutions.
Thus, the system Tl5Te2Br–Tl5Te2I is characterized by formation of the continuous
substitutional solid solution, despite of full immiscibility in the liquid state.
3.2. The isothermal section of the Tl2Te–TlBr–TlI quasi-ternary system at 300K

The isothermal section of the system Tl2Te–TlBr–TlI (A) at 300 K (Figure 5) was
constructed based on the powder XRD and EMF measurements results. As shown in Figure 5 the
homogeneity field of γ-phase in the Tl5Te2Br–Tl5Te2I section penetrates into the Tl2Te–
Tl5Te2Br–Tl5Te2I subsystem. The fact that the γ-phase occupies large part of this subsystem is
not surprising because of an easy substitution of halide atoms, leading to the Tl5Te3 crystal
structure.
According to the XRD results (Figure 6), the samples of the Tl2Te-TlBr0.5I0.5 section
containing 66.7, 80, and 90 mol. % Tl2Te crystallize in the Tl5Te3 type tetragonal structure, but
the sample containing 95 mol% Tl2Te displays diffraction lines pertinent to Tl2Te. Based on
these results, it was shown that the two-phase α+γ field occupies a narrow composition area
(Figure 5).
3.3. The liquidus surface of theTl2Te–TlBr–TlI system
The liquidus surface of the Tl2Te–TlBr–TlI system (Figure 7) consists of three fields
corresponding to primary crystallization of α-, β-, and γ-phases. The liquidus surface of α-phase
occupies a very small area close to Tl2Te. The crystallization of β-phase from the liquid phase
takes place in the narrow composition range along the quasi-binary system TlBr–TlI.
/
/
The liquid surface of γ-phase is divided into two parts (C1C2p2p1 and e1e2C2 C1 ) by the
/
/
wide immiscibility area. Crystallization of γ-phase in the C1C2C2 C1 field occurs by the
monovariant synthectic L1+L2⇔γ reaction in the 750-775 K temperature range. The curves e1e3
and e2e3 reflect the monovariant eutectic equilibrium L ⇔ β+γ. This equilibrium is nonvariant at
the minimum point e3 (675 K). The monovariant peritectic L+γ⇔α equilibrium sets along the
curve p1p2 (Figure 7).
3.4.The non-quasi-binary polythermal sections
3.4.1. The polythermal section TlBr–Tl5Te2I
The polythermal section TlBr–Tl5Te2I (Figure 8) obviously reflects crystallization
processes in the TlBr–Tl5Te2Br–Tl5Te2I–TlI subsystem. Primary crystallization of γ-phase occurs
in the wide (0–92 mol % TlBr) composition range, while β-phase crystallizes from the TlBr-rich
liquid phase L1 in a narrow range. Crystallization of γ-phase in the region of 0–80 mol % TlBr
(immiscibility field) is accompanied by the monovariant synthectic reaction. Secondary
crystallization of β-phase from the L1+γ two-phase field is observed in the ~3–93 mol % TlBr

composition range. At 20 mol.% TlBr this process takes place at the constant minimum
temperature (675 K) and conforms to the point e3 on the liquidus surface (Figure 7).
3.4.2. The polythermal section TlBr0.5I0.5–Tl2Te
As shown in Figure 9, γ-phase primary crystallizes from the liquid in a wide (3–97 mol. %
Tl2Te) composition area. The immiscibility field ranges from 15 to 80 mol. % Tl2Te. In this area,
crystallization takes place by the L1+L2⇔γ monovariant synthectic reaction. Crystallization of
the alloys containing less than 66.7 mol. % Tl2Te is accompanied by the L⇔β+γ eutectic
reaction, upon which the system transforms into the two-phase β+γ state. In the alloys containing
66.7-90 mol % Tl2Te the liquid phase completely crystallizes to γ-phase. The α-phase based on
Tl2Te forms by the peritectic reaction L+γ⇔α at ~700 K.
Note that a monovariant synthectic, eutectic, and peritectic reactions in the system (A)
occur in a narrow temperature interval. Subsequently, thermal effects on the DTA curves of the
corresponding samples are practically isothermic. But the comprehensive analysis of the T-x-y
diagram shows that these thermal effects confirm the monovariant processes occurring in a
narrow temperature interval. Therefore, these intervals and the three-phase areas that correspond
to them are shown as dotted lines in Figures 8 and 9.
3.5. Thermodynamic properties of the solid solution Tl5Te2BrxI1–x.
The results of the EMF measurements of the chains of type (1) allowed calculating
thermodynamic properties of alloys of the section Tl5Te2Br–Tl5Te2I. The analysis showed the
linearity of the EMF dependences upon temperature for all alloys. Accordingly, the linear least-
square treatment of the data was performed and the results were expressed according to the
literature recommendations [29] as
1/ 2
2
⎡
⎢
⎣
⎤
⎥
⎦
2
SE
n
E = a + bT t
+ S2b
(
T − T
)
(2)
where n is the number of pairs of Е and Т values; SE and Sb are the error variances of the EMF
readings and b coefficient, respectively; T is the average of the absolute temperature; t is the
Student’s test. At the confidence level of 95% and n ≥ 20, the Student’s test is t ≤ 2 [29]. The
composed equations of the mode (2) are presented in Table 2.

(ΔG,ΔH,ΔS)
The partial molar functions of thallium
in the Tl5Te2BrxI1-x solid solution
(Table3) were calculated by known thermodynamic relations [29] taking into account the phase
state of alloys by using data from Table 2. The graphical dependences of the partial molar
functions of thallium on the composition for the section Tl5Te2Br–Tl5Te2I are plotted in Figure
10 based on the data of Table 3. As can be seen from Figure 10, the isotherms of ΔGTl , ΔHTl
and ΔSTl are continuous and monotonous functions of the composition in the homogeneous
range of the γ-phase.
It should be noted that the monotonous character of the concentration dependences of the
partial thermodynamic functions of thallium in the homogeneity region of γ-phase indicates that
formation of the solid solutions in the system Tl5Te2Br–Tl5Te2I is accompanied by minor
structural and energetic changes. Besides, it confirms that γ- phase belongs to the substitutional
type of solid solutions.
4. Conclusions
We have constructed the self-consistent phase diagram of the Tl2Te–TlBr–TlI system
applying various experimental methods. A wide range of the solid solution (γ-phase) that
crystallizes with the Tl5Te3 type structure is formed in the system. The homogeneity area of the γ-
phase occupies a large part (up to ~90mol% Tl2Te) of the Tl2Te–Tl5Te2Br–Tl5Te2I subsystem.
The change of the unit cell parameters along the section Tl5Te2Br–Tl5Te2I follows the Vegard’s
law. In spite of the formation of the unlimited solid solution the system is non-quasi-binary due
to the syntectic melting character of both ternary compounds.
The calculated partial thermodynamic functions of thallium in the homogeneity region of γ-
phase display the monotonous character of the concentration dependences, which indicates that
formation of the solid solutions in the Tl5Te2Br–Tl5Te2I system is accompanied by minor
structural and energetic changes.
Acknowledgment.
This work was supported by the Science Development Foundation of the President of the
Republic of Azerbaijan, grant no. EİF-2011-1(3)-82/69/4-M-50.
References

1.
2.
3.
4.
M.G. Kanatzidis, Semiconductors and semimetals 69 (2001), 51–100.
A.V. Shevelkov, Russ. Chem. Rev. 77 (2008) 1–19; Uspekhi Khimii 77 (2008) 3–21.
K. Biswas, M.H. Du, D.J. Singh, Phys. Rev. B 86 (2012) 144108.
S. Johnsen, Z.F. Liu, J.A. Peters, J.H. Song, S. Nguyen, C.D., H. Jin, A.J. Freeman, B.W.
Wessels, M.G. Kanatzidis, J. Am. Chem. Soc. 133 (2011) 10030–10033.
5.
6.
H. Matsumoto, K. Kurosaki, H. Muta, S. Yamanaka, J. Appl. Phys. 104 (2008) 073705.
E.Y. Peresh, V.B. Lazarev, O.I. Kornichuk, V.V. Tsigika, O.V. Petrushova, Z.Z. Kish,
E.E. Semrad, Inorganic Materials 29 (1993) 440–444.
7.
R.A. Aliyeva, D.M. Babanly, I.M. Babanly, I.I. Aliyev, J. Chem. Problems 4 (2004) 83–
88.
8.
D.M. Babanly, A.A. Najafova, M.I. Chiragov, M.B. Babanly, J. Chem. Problems 2 (2005)
149–151.
9.
D.M. Babanly, M.B. Babanly, Russ. J. Inorg. Chem. 55 (2010) 1620–1629.
10.
11.
12.
13.
14.
I. Schewe, P. Böttcher, H.G. von Schnering, Z. Kristallogr. 188 (1989) 287–298.
S. Yamanaka, A. Kosuga A., K. Kurosaki K, J. Alloys Compd. 352 (2003) 275–278.
B. Wölfing, C. Kloc, J. Teubner, E. Bucher, Phys. Rev. Lett. 86 (2001) 4350–4353.
X.M. Tao, P. Jund, R. Viennois, J.-C. Tédenac, J. Phys. Chem. A. 115 (2011) 8761–8766.
G.J. Miller, in: Chemistry, structure and bonding of Zintl phases and ions. Ed.: M. S.
Kauzlarich, VCH Publishers, New York, 1996.
15.
16.
A.V. Shevelkov, M.M. Shatruk, Russ. Chem. Bull. 50 (2001) 337–352.
D.M. Babanly, S.V. Askerova, I.M. Babanly, Yu.A.Yusibov, Inorganic Materials 46
(2010) 17–21.
17.
D.M. Babanly, S.V. Askerova, M.B. Babanly, Yu.A. Yusibov, Russ. J. Inorg. Chem. 56
(2011) 1118–1122.
18.
D.M. Babanly, S.V. Askerova, Z.S. Aliev, M.B. Babanly, Russ. J. Inorg. Chem. 56 (2011)
1833–1838.
19.
D.M. Babanly, T.G. Kasumova, Yu.A. Yusibov, Scientific reports of Azerb. Techn. Univ.
4 (2009) 110–114.
20.
D.M. Babanly, T.G. Kasumova, S.V. Askerova, Yu.A. Yusibov, M.B. Babanly, XI
International conference on crystal chemistry of intermetallic compounds, Lvov, Ukraine (2010).
Book of Abstracts, page 48.

21.
22.
165.
23.
24.
M.M. Asadov, M.B. Babanly, A.A. Kuliyev, Inorganic Materials 13 (1977) 1137–1140.
R. Cerny, J.M. Joubert, Y. Filinchuk, Y. Feutelais, Acta. Crystallogr. A 58 (2002) 163–
M.A. Popova, T.I. Darvoid, M.A. Gurevich, Russ. J. Inorg. Chem. 11 (1966) 661–662.
Binary alloy phase diagrams, Ed. Massalski T.B., second edition. ASM International,
Materials park, Ohio. 2 (1990) 3589 p.
25.
26.
27.
28.
R.F. Rolsten. Iodide Metals and Metal Iodides, John Wiley and Sons, New York, 1961.
L.G.Schulz, Acta Crystallogr. 4 (1951) 487–489
I.I. Ilyasov, S.D. Dionisev, A.G. Bergman, Russ. J. Inorg. Chem. 7 (1962) 625–627.
Handbuch der Präparativen Anorganischen Chemie. Ed.: Brauer, G. Ferdinand Enke
Verlag. Stuttgart, 1975
29.
M.B. Babanly, Y.A. Yusibov. Electrochemical Methods in Thermodynamics of Inorganic
Systems. Baku, 2011, 306 p. (ISBN 978-9952-453-17-1).

Table 1. Some properties of the solid solutions in the system Tl5Te2Br–Tl5Te2I
Laticce
parameters, Å
c
E, mV
Composition
Tl5Te2Br
Tm,K
750
(300K)
Hμ, МPa
a
8.980(2)
12.932(3)
13.005(3)
1270
435
Tl5Te2Br0.8I0.2
Tl5Te2Br0.6I0.4
Tl5Te2Br0.5I0.5
Tl5Te2Br0.4I0.6
Tl5Te2Br0.2I0.8
Tl5Te2I
755
757-760
764-760
762-766
770
8.9749(1)
1325
1380
1360
1400
1330
1300
437
442
440
440
443
445
9.003(2)
13.106(2)
9.017(1)
9.026(1)
13.250(3)
13.324(3)
775

Table 2. Temperature dependencies of EMF for the chains of type (1) in the Tl5Te2Br–
Tl5Te2I system (Т = 300–400К)
1/ 2
Composition
S2
2
⎡
⎤
E
E,mV = a + bT t
+ S2b
(
T − T
)
⎢
⎣
⎥
⎦
n
1/ 2
1/ 2
Tl5Te2Br [9]
Tl5Te2Br0.8I0.2
Tl5Te2Br0.6I0.4
Tl5Te2Br0.4I0.6
Tl5Te2Br0.2I0.8
Tl5Te2I
1,7
⎡
⎤
435,5+ 0,003T 2
+ 5,3⋅10−5 (T −360,4)2
+ 4,7⋅10−5 (T −361,6)2
+ 3,2⋅10−5 (T −361,1)2
⎢
⎥
⎦
22
⎣
1,9
⎡
⎤
433,4 + 0,014T 2
⎢
⎥
⎦
24
⎣
1/ 2
1,3
⎡
⎤
434,7 + 0,018T 2
⎢
⎥
⎦
25
⎣
1/ 2
2,2
⎡
⎤
439,9 + 0,007T 2
+ 6,2⋅10−5 (T − 363,8)2
⎢
⎣
⎥
⎦
25
1/ 2
2,0
⎡
⎤
451,3− 0,026T 2
+ 5,1⋅10−5 (T −362,7)2
+ 3,9⋅10−5 (T −361,5)2
⎢
⎣
⎥
⎦
26
1/ 2
1,5
⎡
⎤
464,3− 0,062T 2
⎢
⎥
⎦
26
⎣

Table 3. Relative partial thermodynamic functions of thallium in the solid solution of the
Tl5Te2Br–Tl5Te2I system at 298 K.
Composition
− ΔGTl
− ΔHTl
ΔSTl
(J⋅K−1 mol−1)
(kJ⋅mol−1)
Tl5Te2Br
Tl5Te2Br0.8I0.2
Tl5Te2Br0.6I0.4
Tl5Te2Br0.4I0.6
Tl5Te2Br0.2I0.8
Tl5Te2I
41.82 0.09
42.22 0.09
42.46 0.08
42.61 0.10
42.80 0.09
43.02 0.09
41.73 0.51
41.82 0.48
41.94 0.39
42.44 0.55
43.54 0.50
44.80 0.44
0.29 1.41
1.35 1.32
1.74 1.09
0.68 1.52
–2.51 1.38
–5.98 1.21

Figure Captions
Figure 1. Crystal structure of Tl5Te2Br (center) in comparison with the crystal structures of
Tl5Te3 (left) and Tl9SbTe6 (right). Color online.
Figure 2. Indexed XRD patterns for Tl5Te2Br (a) and Tl5Te2I (b). Color online.
Figure 3. Phase diagram (а), concentration dependence of the unit cell parameters (b),
microhardnesses (c), and EMF of the chains of type (1) at 300 K (d) for the system Tl5Te2Br–
Tl5Te2I.
Figure 4. XRD patterns for different compositions in the Tl5Te2Br–Tl5Te2I system: 1 –
Tl5Te2Br, 2 – 80% Tl5Te2Br, 3 – 50% Tl5Te2Br, 4 – 20% Tl5Te2Br, 5 – Tl5Te2I. Color online.
Figure 5. Isothermal section of the phase diagram of the Tl2Te–TlBr–TlI quasi-ternary
system at 300K.
Figure 6. XRD patterns for different compositions in the Tl2Te–TlBr0.5I0.5 section: 1 –
Tl2Te, 2 –95% Tl2Te, 3 – 90% Tl2Te, 4 – 80% Tl2Te, 5 – 66.7 % Tl2Te. Color online.
Figure 7. Projection of the liquidus surface of the Tl2Te–TlBr–TlI system. Primary
crystallization fields are marked by numbers: 1 – β , 2 – γ , 3 – α.
Figure 8. Polythermal section TlBr–Tl5Te2I of the Tl2Te–TlBr–TlI system
Figure 9. Polythermal section TlBr0.5I0.5–Tl2Te of the Tl2Te–TlBr–TlI system.
Figure 10. Dependence of the relative partial thermodynamic functions of thallium on the
composition in the Tl5Te2Br–Tl5Te2I system.

Fig. 1

Tl5Te2Br
Tl5Te2I
Fig. 2

Fig. 3

Fig. 4

Fig .5

Fig.6

Fig. 7

Fig. 8

Fig. 9

ΔSTl
J ⋅mol−1 ⋅K−1
2
0
-2
-4
-6
Tl5Te2Br
Tl5Te2I
20
40
60
80
mol%Tl5Te2I
41
42
43
ΔG
ΔH
44
45
ΔG(ΔH)Tl
kJ⋅mol−1
Fig. 10

Highlights
•
•
•
•
The Tl2Te–TlBr–TlI system is investigated.
The fields of primary crystallization are determined
Formation of the unlimited Tl5Te2I1-xBrx solid solution is established.
The partial molar thermodynamic functions of Tl in Tl5Te2BrxI1-x are calculated