An investigation of the Tl–Te–I system and crystal structure of the Tl5Te2I

Article abstract of DOI:10.1016/j.jallcom.2016.06.054

The phase relations in the Tl–Te–I system have been experimentally investigated over the entire concentration range mainly by thermal analysis (DTA), X-ray diffraction (XRD) applied to equilibrated alloys. The isothermal section at 300?K, liquidus surface projection and the phase diagrams of the six isopleth sections have been constructed. The homogeneity ranges and primary crystallization fields for the all phases, as well as, the character and temperature of non- and monovariant equilibria were determined in the system. The crystal structure of the Tl₅Te₂I compound has been determined by single crystal X-Ray diffraction. It is found to be stoichiometric and isostructural which crystallize in the In₅Bi₃structure type with four formula units in the tetragonal system, space group I4/mcm, а?=?9.001(2); c?=?13.291(4) ?.

Full text of DOI:10.1016/j.jallcom.2016.06.054

Journal of Alloys and Compounds 688 (2016) 997e1005
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
An investigation of the TleTeeI system and crystal structure of the
Tl5Te2I
,
b
,
*
a
c
Dunya M. Babanly a, Ziya S. Aliev a
, Samira Z. Imamaliyeva , Fco. Javier Zúniga ,
~
Gotzon Madariaga c, Dilqam B. Tagiyev a
a Institute of Catalysis and Inorganic Chemistry, Azerbaijan National Academy of Science, Baku, Azerbaijan
b Institute of Physics, Azerbaijan National Academy of Science, Baku, Azerbaijan
c Departamento de Física de la Materia Condensada Facultad de Ciencia y Tecnología, Universidad del País Vasco, Bilbao, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The phase relations in the TleTeeI system have been experimentally investigated over the entire con-
centration range mainly by thermal analysis (DTA), X-ray diffraction (XRD) applied to equilibrated alloys.
The isothermal section at 300 K, liquidus surface projection and the phase diagrams of the six isopleth
sections have been constructed. The homogeneity ranges and primary crystallization fields for the all
phases, as well as, the character and temperature of non- and monovariant equilibria were determined in
the system. The crystal structure of the Tl5Te2I compound has been determined by single crystal X-Ray
diffraction. It is found to be stoichiometric and isostructural which crystallize in the In5Bi3 structure type
with four formula units in the tetragonal system, space group I4/mcm, а ¼ 9.001(2); c ¼ 13.291(4) Å.
© 2016 Elsevier B.V. All rights reserved.
Received 17 December 2015
Received in revised form
20 May 2016
Accepted 7 June 2016
Available online 11 June 2016
Keywords:
Ternary system
Thallium tellurides
Tellurium iodides
Ternary thallium iodides
Phase diagram
Crystal growth
Crystal structure
1. Introduction
range. Also, here we provide details of the crystal growth and the
crystal structure of Tl5Te2I compound. Although the crystal system
The Tl-based chalcogenide and chalcogen-halides alloys are
very important materials for thermoelectric and photoelectric
conversation despite of toxicity of thallium derivatives limits their
application in the devices working in ambient condition [1e3]. On
the other hand, recently found that some thallium-based ternary
chalcogen-halides are very promising materials for efficient X-ray
and lattice parameters of the this compounds were determined in a
powder XRD study in our previous research paper, here we
examine full single crystal structure data which has not been re-
ported for this compounds to date.
This work is a part of systematic investigation of the ternary
thallium-chalcogen-halogen systems. In our previous works, phase
equilibria and thermodynamic properties of the subsystems Tl-TlI-S
[6], Tl-TlI-Se [7] and Tl-TlI-Te [8,9] were investigated. A number of
isopleth and isothermal sections, as well as, projections of liquidus
surfaces were constructed within these quasi-ternary systems.
Several homogeneity fields of the intermediate phases were fixed
and their fundamental thermodynamic functions were determined
experimentally from the EMF data.
and g-ray detection [4,5]. This caused extensive research on the Tl-
based binary and more complex chalcogenide systems in order to
develop novel preparative methods and growth of their single
crystals. In particular, to examine the formation of new interme-
diate phases, as well as varying and tuning properties of parent
phases in such systems, it is necessary to investigate the phase
relationships and to plot respective phase diagrams. The primary
task of this work is to investigate the phase relationships and to plot
phase diagram of the Tl-Te-I system over the entire concentration
We open this paper with reviewing the literature data on this
system and compounds in it, follow with the description of the
experimental procedure, and then discuss our results on the phase
equilibria, isopleth sections, liquidus surface and crystal structure
of Tl5Te2I.
* Corresponding author. Institute of Catalysis and Inorganic Chemistry, ANAS, H.
Javid ave. 113, Baku, AZ1143, Azerbaijan.
E-mail address: ziyasaliev@gmail.com (Z.S. Aliev).
http://dx.doi.org/10.1016/j.jallcom.2016.06.054
0925-8388/© 2016 Elsevier B.V. All rights reserved.

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D.M. Babanly et al. / Journal of Alloys and Compounds 688 (2016) 997e1005
1.1. Review of the literature data
the corresponding melting point of compounds, whereas the
temperature of the cold zone was about 400 K. After the main
portion of iodine had reacted the sealed silica ampoules were
relocated into the hot zone; the melt was stirred at this tempera-
ture by shaking. TlI and TeI4 directly crystallize from liquid ac-
cording to phase diagrams [13], so these were cooled in the
switched-off furnace. Incongruently melting TlI3 and TeI were
annealed for 500 h at 20 K below the corresponding peritectic
temperatures.
The phase relationships in the Tl-TlI-Te subsystem of the Tl-Te-I
system have been reported in detail and its liquidus surface pro-
jection, numerous isopleth sections, as well as, isothermal section
at 300 K were plotted in our previous works [8,9] and in Ref. [10].
Peresh et al. [11] was examined the quasi-binary TlI-TeI4 section
and found only one ternary Tl2TeI6 compound in this system
melting congruently at 700 K.
Quasi-binary boundary sections of the Tl-Te-I system are very
well studied. For the Tl-Te boundary system, four compounds have
been reported; they are Tl2Te, Tl5Te3, TlTe, and Tl2Te3. The former
two melt congruently at 698 K and 726 K, respectively, whereas the
latter two decompose upon melting at 573 K and 511 K, respectively
[12,13]. In the Tl-I system three stable binary phases, TlI, Tl3I4 and
TlI3 were identified. The former melts congruently at 715 K and has
a polymorphous transition at 452 K whereas other two phases melt
incongruently by peritectic reactions at 533 and 403 K, respectively
[13,14]. Te-I system has two stable intermediate phases, TeI4 and TeI
which form through dystectic and peritectic reactions at 553 and
459 K, respectively [13,15].
Table 1 displays the crystal structure information for the all
compounds in the Tl-Te-I system. Herein, it should be noted that
the crystal structure of the Tl3I4 compound have not been revealed
to date. On the other hand, another thallium iodide, namely Tl2I3
was recently confirmed by Shiojiri et al. [16] (see Table 1.)
The first measurements of lattice parameters of Tl5Te2I were
performed in our previous research by means of powder XRD [9].
The tetragonal system, with the space group I4/mcm was found for
this compound. But, the full crystal structures data of this com-
pound was not reported elsewhere.
Considering some divergence of published data on the inter-
mediate composition between TlI and TlI3, we have set up special
experiments on the synthesis of Tl2I3 and Tl3I4 by reaction of
powdered TlI with elemental iodine. Syntheses were carried out in
the evacuated quartz ampoules placed in a two-phase horizontal
furnace. A “cold” zone (~300 K) was a source of iodine vapor, and a
“hot” zone (~500 K) was a main reaction area. The fine powders of
thallium monoiodide were in the “hot” zone and continuously feed
up with iodine. During process the substances in the reaction zone
were stirred by periodically rotation of the ampoules along the
longitudinal axis. After the full use of iodine, the ampoule inserted
into the “hot” zone, kept at 500 K for 200 h and cooled in the
switched off furnace.
The powder X-ray analysis of the obtained sample showed, that
the specimen of the composition Tl2I3 has a quite pure diffraction
pattern (Fig. 1) identical with that obtained in Ref. [16]. However,
the diffraction pattern of the Tl3I4 display the reflection lines of
both Tl2I3 and most intense lines of the low-temperature modifi-
cation of
a
TlI (2
q
¼ 26.73; 2
q
¼ 33.25ꢀ). The DTA heating spectrums
of the respective samples display two endothermic peaks which
corresponding to Tl2I3 e at 535 and 650 K; Tl3I4 e 535 and 673 K.
The comparison of the DTA and XRD data with the known phase
diagram of the Tl-I system [13] suggests that the intermediate
thallium iodide has a composition of Tl2I3 and melts by peritectic
reaction at 535 2 K.
The crystal structures of Tl2TeI6 have been determined using
powder XRD [17]. It crystallizes in the monoclinic space group P21/c
and belongs to the monoclinic - K2TeBr6 structure type (see
Table 1). Compared with the high symmetry prototype A2BX6
structure of some ternary halides, this structure exhibits the strong
distortion of the TlI6 octahedral.
The ternary Tl2TeI6 compound was synthesized by melting
appropriate amounts of the pre-synthesized TlI and TeI4 in
vacuum-sealed silica ampoule at ~750 K. The DTA results have
shown that this compound melts at 645 K which is quite below
than that shown in Ref. [11] (700 K). Nevertheless, powder XRD
data and calculated crystal lattice parameters of this compound are
agreed well with the results given by Peresh [11].
All investigated samples (total mass, 0.5 g) were prepared from
initial elemental components or preliminary synthesized com-
pounds. After melting most of the alloys were annealed at 20e30 K
below the solidus for 800e1000 h.
2. Experimental details
2.1. Synthesis
Elements of high purity (Tl, 99.999 mass %, Alfa Aesar; Te, 99.999
mass %, Alfa Aesar; I, 99.9 mass % resublimed pearls, PA-ACS) were
used as starting components of synthesis.
Thallium and tellurium iodides were synthesized following a
specially designed method that takes into account high volatility of
iodine. The syntheses were performed in an inclined two-zone
furnace, the hot zone kept at a temperature 20e30 K higher than
2.2. Crystal growth
A single crystalline ingot of Tl5Te2I was grown from melt by the
Table 1
Crystal structure information of the compounds of the system Tl-Te-I.
Compounds
Structure
Space group
Lattice parameters, Å
Reference
Monoclinic
Tetragonal
Tetragonal
Monoclinic
Cubic
a ¼ 15.662; b ¼ 8.987; c ¼ 31.196
a ¼ 8.929; c ¼ 12.620
[20]
[21]
[22]
[21]
[23]
[24]
[25]
[16]
[26]
[27]
[28]
[17]
Tl2Te
Tl5Te3
TlTe
C2/c
I4/mcm
I4/mcm
Cc
Fm3m
Pm3 m
Pnma
-
C12/m1
P1
a ¼ 12.953; c ¼ 6.175
a ¼ 17.413, b ¼ 6.552, c ¼ 7.910
a ¼ 6.940
Tl2Te3
a
TlI
TlI
b
Cubic
a ¼ 4.198
TlI3
Tl2I3
TeI
Orthorhombic
Hexagonal
Monoclinic
Triclinic
Rhombic
Monoclinic
a ¼ 9.436; b ¼ 10.599; c ¼ 6.419
a ¼ 6.188; c ¼ 13.412
a ¼ 15.383; b ¼ 4.182; c ¼ 8.201
a ¼ 9.952; b ¼ 7.995; c ¼ 8.201
a ¼ 13.635; b ¼ 16.793; c ¼ 14.624
a ¼ 7.765(2), b ¼ 8.174(2),
c ¼ 13.756(5)
TeI4
Tl2TeI6
Pnma
P21/c

D.M. Babanly et al. / Journal of Alloys and Compounds 688 (2016) 997e1005
999
Fig. 1. XRD pattern of Tl2I3. Red lines shows the data of [16].
vertical BridgmaneStockbarger method using co-melting appro-
priate quantities of the pre-synthesized TlI and Tl2Te in a conical-
bottom quartz ampoule, which was sealed under a vacuum better
than 10ꢁ4 Pa.
temperature on a STOE StadiVari diffractometer. The structure was
refined using as starting model that of Tl5Te3; refinement per-
formed with the program system JANA2006 [18]. All atoms were
refined with occupancies according with the stoichiometric for-
mula, anisotropic thermal displacement parameters and without
any constrain. Images of chemical structure were visualized using
VESTA software [19]. Full crystal structure details, data collection
and structure refinement details are summarized in Table 2. Atomic
parameters are listed in Table 3.
The specially designed method based on the phase diagram of
the system has been used in order to control the crystallization
process from two immiscible liquid phases L1 þ L2. In this method,
the liquid phase L1 was in dynamic equilibrium with another liquid
phase L2 and the compositions of the coexisting liquid phases al-
ways constant at the given temperature. During very slow crys-
tallization from the L1, the phase L2 gradually dissolves in L1, and
provides constancy of its composition, consequently, forms the
Tl5Te2I by the syntectic reaction occurs at 775 K according to phase
diagram. In the growing process, the ampoule was held in the “hot”
zone (~850 K) of two-zone tube furnace for 12 h for a complete
melting of the composition. Then, the charged ampoule moves
from the “hot” zone to the “cold” zone with the required rate
1.0 mm per hr. The temperature of the “cold” zone was 700 K. In this
way, the single crystal ingot with average dimensions of 1.5 cm in
length and 0.7 cm in diameter was obtained.
3. Results and discussion
To obtain a complete illustration of phase equilibria in the Tl-Te-
I system, we have prepared and investigated a number of alloys
along the vertical sections TlI-TeI4, Tl2TeI6-9Te, Tl2TeI6-9I, TlI-TeI, 9/
5Tl2I3-Tl2TeI6, and 1.25TlI3-TeI4 as well as, several more samples
inside from the TlI-Te-I concentration triangle.
2.3. Analysis
Table 2
Crystal data and refinement results.
Differential thermal analysis (DTA) and X-ray powder diffraction
(XRD) was employed to check the purity of the synthesized starting
compounds and analyze the samples in order to plot phase
diagrams.
Chemical formula
Mr
Crystal system, space group
Tl5Te2I
1404
Tetragonal, I4/mcm
293
9.001 (2), 13.291 (4)
1076.9 (5)
4
Temperature (K)
a, c (Å)
DTA was carried out with a TERMOSKAN-2 device equipped
with chromelealumel thermocouple. The temperature was
measured by Chromel-Alumel thermocouples. The measurements
were performed between room temperature and 800 K depending
V (Å3)
Z
Radiation type
Mo Ka
84.36
m
(mmꢁ1
)
on the composition of the alloys with a heating rate of 5 K minꢁ1
.
Crystal size (mm)
Diffractometer
Absorption correction
0.2 ꢂ 0.1 ꢂ 0.03
STOE StadiVari
Numerical
0.009, 0.146
11363
933
317
0.102
0.911
0.054, 0.062, 1.38
933
15
8.58, ꢁ4.82
Temperatures of thermal effects were taken mainly from the
heating spectrums.
T
min, Tmax
The XRD analysis was done with the Bruker D8 ADVANCE
diffractometer using the Cu-Ka1 radiation. The lattice parameters
were refined using the Topas V3.0 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 pattern for Tl2TeI6
was indexed using Topas V3.0 software.
No. of measured reflections
No. of used reflections
Observed reflections [I > 3
s
(I)]
Rint (obs.)
(sin
R[F2 > 3
No. of reflections
No. of parameters
Drmax
Drmin (e Åꢁ3
q/
l
)max (Åꢁ1
s
)
(F2)], wR(F2), S
,
)
Single crystal X-ray diffraction data collected at room

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D.M. Babanly et al. / Journal of Alloys and Compounds 688 (2016) 997e1005
Table 3
meaning that the number of atoms in initial components is
equalized.
Fractional atomic coordinates and equivalent isotropic displacement parameters for
the Tl5Te2I structure.
Atom
Wyckof
x
y
z
Ueq.(Å2)
3.1.1. The section TlI-TeI4
Tl1
Tl2
I1
16(i)
4(c)
4(a)
h(8)
0.35484(8)
0
0
0.14515(8)
0
0
0.1506(1)
0
0.25
0
0.0474(3)
0.0399(6)
0.0408(9)
0.0359(6)
This system (Fig. 2) was first reported by Peresh and co-authors
[11]. During the present investigation for selected alloys we have
detected that melting point for the Tl2TeI6 and its eutectic co-
ordinations with both starting compounds are disagree with those
reported in Ref. [20]. Consequently, we undertook the complete
study of this section. That enabled us to build its Tex diagram
(Fig. 3), which shows substantial differences from that reported
previously [11]. Apparently, the only ternary intermediate phase,
Tl2TeI6 is in eutectic equilibria with both parent compounds and
melts congruently at 654 K which is quite below temperature than
that found as 700 K in Ref. [11]. The eutectics contain approximately
20 mol% TeI4 and 77 mol% TeI4 and crystallize at 610 and 535 K,
respectively.
Te2
0.6594(2)
0.1594(2)
XRD data confirm the phase diagram of this system. The XRD
pattern for the alloy having 33.3 mol% TlI4 (Fig. 3) displays
completely new diffraction peaks which are characteristic for
Tl2TeI6. The XRD patterns for all other intermediate alloys display
peaks of the
a
TlI þ Tl2TeI6 and Tl2TeI6þTeI4 mixtures in the con-
centartion ranges of <33.3 and >33.3 mol% TeI4, respectively. In-
tensity of the peaks varies with composition change according to
the phase diagram.
3.1.2. The sections Tl2TeI6e9Te and Tl2TeI6e9I
Both sections are of simple eutectic type (Fig. 4 a, b). The eutectic
compositions lie at 3 and 67 mol% Tl2TeI6 and temperatures of 520
and 385 K. The accuracy of the eutectics coordinates were deter-
mined by using the method of the Tamman triangle constructed
from the values for the endothermic thermal effects of the alloys.
The combined analysis of all our experimental data and the
results found in the literature on the phase equilibrium in the
boundary systems [12e15] enabled us to construct the self-
consistent phase diagram of the Tl-Te-I system.
Fig. 2. Phase diagram of the system TlI-TeI4.
3.1. The quasi-binary sections
The Tl-Te-I system is represented by three quasi-binary sections.
In order to easy comparison, all quasi and non-quasi-binary
isopleth sections are expressed using normalized compositions,
Fig. 3. XRD patterns of several samples along the section TlI-TeI4.

D.M. Babanly et al. / Journal of Alloys and Compounds 688 (2016) 997e1005
1001
Fig. 4. Phase diagram of the system Tl2TeI6-9Te (a) and Tl2TeI6-9I (b).
Fig. 6. The liquidus surface projection of the Tl-Te-I system. Primary crystallization
fields of phases: 1, d; 2, aTlI; 3, Tl2I3; 4, TlI3; 5, Tl2TeI6; 6, TeI4; 7, TeI; 8, Te; 9, Tl2Te3; 10,
Fig. 5. Isothermal section at 300 K.
TlTe; 11, I2.
3.2. The isothermal section at 300 K
equilibrium lines and invariant points (see Tables 5 and 6). The
primary crystallization fields of thallium, -phase based on Tl2Te
and some invariant and monovariant equilibria are degenerated.
The primary crystallization fields of the -phase based on Tl5Te3
and Tl5Te2I, Tl2TeI6 and tellurium are very large and occupy major
part of the total area of the Tl-Te-I triangle. The crystallization of
former two phases takes place by the monotectic reactions in a
wide concentration range. Several wide immiscibility fields (L1þL2;
L1þL3; L2þL3; L1þL2þL3) were observed in this system formed by a
different combination of three liquids phases based on thallium (L1)
The isothermal section of the system (Fig. 5) illustrates the solid
state phase equilibrium at room temperature. Two ternary com-
pounds were detected in this system: Tl5Te2I and Tl2TeI6. The
a
d
former one has a wide homogeneity range (d-phase) while latter
one is a stoichiometric compound. Apparently, both thallium
monoiodide and Tl2TeI6 play a key role in the formation of these
areas in the system. The tie lines connect the coexisting thallium
monoiodide with both ternary compounds, TlTe and Tl2Te3, as well
as, with elemental tellurium, while, Tl2TeI6 is in equilibrium with
elemental tellurium, iodine and tellurium iodides. The interaction
of these and other phases in the system leads to the formation of
various two- and three-phase regions. Ultimately, four two-phase
regions and twelve three-phase regions were experimentally
determined at 300 K.
and bTlI (L2), as well as, tellurides and tellurium (L3). These fields
cover a large part of the liquid surface. The specific feature of this
system is the presence of a triple aliquation (the triangle MTM/TMT//)
with invariant syntectic equilibrium (see Table 5, #38). The mon-
ovariant eutectic (e5) and syntectic (c and c/) curves from the TlI-
Tl2Te quasi-binary system pass through these immiscibility fields
and transform to invariant monotectic equilibria M1M/1, M2M2/ and
MтM/т,М/т (see Table 5).
3.3. The liquidus surface projection
Three isopleth sections TlI-TeI, 9/5Tl2I3-Tl2TeI6 and 1.25TlI3-TeI4
were studied in order to determine the coordinates of invariant
points, particularly the immiscibility areas (Figs. 7e9). As stated
above, for the purpose of easy comparison with isothermal section
The liquidus surface of the Tl-Te-I system consists of eleven
fields corresponding to the primary crystallization of binary and
ternary phases, as well as, elemental components (Fig. 6). All these
primary crystallization fields are bordered by various monovariant

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D.M. Babanly et al. / Journal of Alloys and Compounds 688 (2016) 997e1005
Table 4
of TlI is clearly fixed at 450 K in all alloys within this region. As a
result of this process the
TlI þ Tl2TeI6þTe three-phase region is
Geometric parameters (Å) for Tl5Te2I.
a
formed in the range of 0e66.7 mol% TeI. This section crosses the
Tl2TeI6eTe section at 66.7 mol% TeI. After primary crystallization in
the 66.7e100 mol% compositional range, the monovariant crys-
tallization of Tl2TeI6þTe eutectic occurs by the reaction #29. Crys-
tallization finishes by the invariant transition U3 at 450 K.
Subsequently, the three-phase Tl2TeI6þTeI þ Te region were found
in the subsolidus.
Atoms
d
Tl1dTl1i
Tl1dTl1ii
Tl1dTe2iii
Tl1dTe2
Tl1dI1
3.696 (2)
3.716 (2)
3.1930(2)
3.397 (2)
3.695 (2)
3.323 (2)
3.385 (2)
Tl2dI1
Tl2dTe2iv
Symmetry codes: (i) -x þ 1, -y, z; (ii) -x þ 1, y, -z þ 1/
2; (iii) y, -x þ 1, z; (iv) x-1, y, z.
3.4.2. The section 9/5Tl2I3-Tl2TeI6
This section is stable below the solidus. i.e., consists of mixture
of initial compounds, but entirely it is non quasi-binary due to the
incongruent melting character of the Tl2I3 (Fig. 8). The liquidus
section is represented by two curves of the primary crystallization
and liquidus surface, the isopleths sections are expressed using the
normalized compositions.
of
bTlI and Tl2TeI6. Then, in the 0e5 and 5e100 mol% Tl2TeI6
compositional ranges the
b
TlI þ Tl2TeI6 eutectic mixture and Tl2I3
3.4. Isopleth sections
crystallize monovariantly and peritectically by the reactions #16
and #17, respectively. The crystallization of all samples along the
section finishes by the invariant transition reaction U4 at 525 K.
3.4.1. The section TlI-TeI
The comparison of this section (Fig. 7) with the liqiudus surface
projection clearly shows that the liquidus curves from left to right
belongs to primary crystallization of the
b
TlI, Tl2TeI6 and telliruim.
3.4.3. The section 1.25TlI3-TeI4
Horizontal line at 560 K and curve alight towards invariant eutectic
point E3 reflects the monovariant eutectic equilibrium #24 (see
Table 6). The thermal effects at 512 K reflect the crystallization of
the invariant eutectic E3, whereas the polymorphous modification
This section reflects all the equilibria in the iodine-rich area of
the phase diagram (Fig. 9). This section passes through the two
three-phase areas and crosses the quasi-binary Tl2TeI6-9I section.
The liquidus section is represented by three curves of the primary
Table 5
Invariant equilibria in the Tl-Te-I system.
No.
Point in Fig. 6.
Equilibrium
Composition, at.%
Tl
T,K
Te
1
2
3
4
5
6
7
8
D1
D2
D3
D4
D5
p1
p2
p3
p4
p5
U1
U2
U3
U4
U5
e1
e2
e3
e4
e5
e6
e7
e8
e9
e10
e11
E1
E2
E3
L 4 Tl2Te
L 4 Tl5Te3
66.7
62.5
50.0
e
33.3
37.5
e
698
723
715
553
645
573
511
533
401
458
568
505
450
525
390
695
497
363
451
710
707
610
535
520
383
385
491
445
512
360
380
680
714
712
775
708
695
755
L 4
bTlI
L 4 TeI4
L 4 Tl2TeI6
20
22.2
43.0
35.0
23.0
16.0
e
11.1
57.0
65.0
e
L þ
L þ TlTe 4 Tl2Te3
TlI 4 Tl2I3
d
4 TlTe
L þ
b
9
L þ Tl2I3 4 TlI3
L þ Te 4 TeI
e
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
46
L þ
d
4
b
TlI þ TlTe
TlI þ Tl2Te3
L þ Te 4 Tl2TeI6 þ TeI
L þ TlI 4 Tl2I3 þ Tl2TeI6
L þ Tl3I4 4 TlI3 þ Tl2TeI6
L 4
41.0
29.0
4.0
21.0
15.0
65.5
30.0
12.0
57.5
70.0
43.0
2.0
L þ TlTe 4
b
a
1.5
a
þ
d
34.5
70.0
e
L 4 Tl2Te3 þ Te
L 4 TlI3 þ I2
L 4 TeI þ TeI4
e
42.0
1.7
75.0
8.0
18.0
42.0
~1
L 4
L 4
L 4
b
b
b
TlI þ
d
50.8
12.5
31.0
7.0
15.0
e
TlI þ Te
TlI þ Tl2TeI6
L 4 Tl2TeI6 þ TeI4
L 4 Tl2TeI6 þ Te
L 4 TeI4 þ I2
L 4 Tl2TeI6 þ I2
<1
30.0
2.0
17.0
11.0
<1
69.5 (97.0)
51.0 (98.0)
48.0 (15.0)
54.5 (63.5)
51.5 (97.0)
51.0 (53.0)
57.0 (69.0; 94.0)
<1
L 4
b
TlI þ Tl2Te3 þ Te
68.0
41.0
41.0
1.0
<1
30.5 (3.0)
e
L 4 Tl2TeI6 þ TeI þ TeI4
L 4
b
TlI þ Tl2TeI6 þ Te
E4
E5
L 4 TlI3 þ Tl2TeI6 þ I2
L 4 Tl2TeI6 þ TeI4 þ I2
m1(m/1)
m2(m/2)
m3(m/3)
c(c/)
M1(M/1)
M2(M/2)
L
L
L
3 4 L1 þ Tl2Te
2 4 L1
2 4 L3
þ
þ
b
b
d
b
b
TlI
TlI
4.0 (70.0)
9.0 (27.5)
1.5 (1.0)
8.0 (40.0)
5.0 (27.0; 3.0)
L2 þ L3 4
L
L
2 4 L1
2 4 L3
þ
þ
TlI þ
TlI þ
d
d
Mт(M/т,М/т/
)
L2 þ L3 4 L1
þ
d

D.M. Babanly et al. / Journal of Alloys and Compounds 688 (2016) 997e1005
1003
Table 6
Monovariant equilibria in the TleTeeI system.
No.
Curve in Fig. 6.
Equilibrium
Temperature interval, K
1
2
3
4
5
6
7
8
c
c
М
М
т; c/М/т
L2 þ L3
L2 þ L3
4
4
d
d
d
d
b
b
775e755
775e695
755e708
755e680
714e708
712e695
710e708
710e695
695e568
573e568
568e505
511e505
505e491
497e491
707e491
630e252
533e525
525e390
401e390
390e360
450e445
363e360
385e360
610e512
707e512
520e512
451e445
535e445
520e450
458e450
535e380
383e380
385e380
2; c/М/2
МтМ1
М
;
М/T/М/1
L
L
L
L
L
L
L
2 4 L1
þ
þ
þ
þ
т/m1; М/т/m/1
3 4 L1
2 4 L1
2 4 L3
m2M1; m/2M/1
m3M2; m/3M/2
e5M1
TlI
TlI
d
2 4
2 4 L3
3 4
TlI þ
b
TlI þ
e5M2
þ
bTlI
9
M/2U1
p1U1
b
d
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
L3
L
þ
d
4 TlTe
TlI þ TlTe
U1U2
p2U2
U2E1
e2E1
e6E1
e7U4
p3U4
U4U5
p4U5
U5E4
U3E2
e3E4
3 4 b
L3 þ TlTe 4 Tl2Te3
L
L
L
3 4
3 4 Tl2Te3 þ Te
3 4
TlI þ Te
TlI þ Tl2TeI6
TlI 4 Tl2I3
b
TlI þ Tl2Te3
b
L 4
L þ
b
b
L 4 Tl2I3 þ Tl2TeI6
L þ Tl2I3 4 TlI3
L 4 TlI3 þ Tl2TeI6
L 4 Tl2TeI6 þ TeI
L 4 TlI3 þ I2
Fig. 8. Isopleth section 9/5Tl2I3-Tl2TeI6.
e
11E4
L 4 Tl2TeI6 þ I2
e7E3
e6E3
e9E3
e4E2
e8E2
e9U3
p5U3
e8E5
L 4
L 4
b
b
TlI þ Tl2TeI6
TlI þ Te
3.5. Crystal structure of Tl5Te2I
L 4 Tl2TeI6 þ Te
L 4 TeI þ TeI4
L 4 Tl2TeI6 þ TeI4
L 4 Tl2TeI6 þ Te
L þ Te 4 TeI
The ternary compound Tl5Te2I is isostructural with Tl5Te3 [21]
with I atoms in the 4(a) Wyckoff sites replacing to Te2 atoms in
Tl5Te3. Although Te and I could not be distinguished in the struc-
tural analysis (because the same contrast against X-rays), we have
chosen the 4(a) Wyckoff position versus the 8(h) site because the
latter required a randomly occupancy 50% shared with Te atoms.
The structure can be described as layers of corner sharing TlTe4I2
octahedral (Tl2 central atom) with additional interstitial Tl1 atoms
with trigonal prism coordination. Octahedra consecutive along the
c-axis are rotated 45ꢀ relative to each other. A projection along the
[010] and [001] directions, and perspective view of the structure are
shown in Figs. 10e12. The substitution of Te1 by I increases the
interatomic distances with respect to Tl5Te3. Tl1 is coordinated by a
distorted trigonal prism of Te and Tl1-type atoms with shortest
distances between Tl1eTe2 (see Table 4) at 3.193(2) Å and 3.397(2)
Å (x2) and three Tl1 atoms at 3.696(2) Å and 3.716(2) Å (x3)
respectively. Tl2 has a regular octahedral coordination with four
L 4 Tl2TeI6 þ TeI4
L 4 TeI4 þ I2
e
e
10E5
11E5
L 4 Tl2TeI6 þ I2
crystallization of bTlI (0e10 mol % TeI4), Tl2TeI6 (10e80 mol % TeI4)
and TeI4 (80e100 mol% TeI4). The horizontals at 525 və 390 K,
respectively, reflect the invariant transition U1 and U2 equilibria. As
a result of the latter transition reaction, the L þ TlI3þTl2TeI6 three-
phase region appears in the system. The ternary TlI3þTl2TeI6þI2
eutectic primarily precipitates from the melt in the 0e40 mol % TeI4
compositional range at 360 K by the reaction #30.
The Tl2TeI6 þ I2 (e11E5 curve) and Tl2TeI6 þ TeI4 eutectics crys-
tallize monovariantly in the 40e100 mol% TeI4 compositional
range. Finaly, the quadriphase eutectic equilibrium appears at
380 K and concludes by the invariant reaction #31.
Fig. 7. Isopleth section TlI-TeI.
Fig. 9. Isopleth section 1.25TlI3-TeI4.

1004
D.M. Babanly et al. / Journal of Alloys and Compounds 688 (2016) 997e1005
Fig. 12. Perspective view of Tl5Te2I showing a layer of Tl5Te2I corner-sharing octahe-
dral. Color codes like in Fig. 11 and Tl1 atoms in lighter color.
Fig. 10. Structure of Tl5Te2I view along the [010] direction.
space group I4/mcm.
Acknowledgments
This work was supported by the Science Foundation of the State
Oil Company of Azerbaijan Republic (SOCAR), the Basque Country
ꢀ
Government, Departamento de Educacion, Universidades e Inves-
ꢀ
tigacion (project IT779-13; Grant N.o. IT-756-13), the Spanish
ꢀ
Ministerio de Ciencia e Innovacion (Grant No. FIS2010-19609-C02-
01).
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diffraction and it is confirmed that it crystallize in the In5Bi3
structure type with four formula units in the tetragonal system,

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