The phase equilibria in the Tl-S-I system and electrical properties of the Tl6SI4 and TlS compounds

Article abstract of DOI:10.1016/j.jallcom.2018.10.220

The phase equilibria in the ternary Tl-S-I system were investigated experimentally by means of powder X-ray diffraction (PXRD) and differential thermal analysis (DTA). Five isopleth sections, liquidus surface projection and room temperature isothermal sec

Full text of DOI:10.1016/j.jallcom.2018.10.220

Accepted Manuscript
The phase equilibria in the Tl-S-I system and electrical properties of the Tl SI and
6 4
TlS compounds
Dunya M. Babanly, Ziya S. Aliev, Qorkhmaz M. Huseynov, Salim M. Asadov, Solmaz
N. Mustafaeva, Dilgam B. Tagiyev
PII:
S0925-8388(18)33894-5
10.1016/j.jallcom.2018.10.220
JALCOM 48038
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 17 May 2018
Revised Date: 15 October 2018
Accepted Date: 17 October 2018
Please cite this article as: D.M. Babanly, Z.S. Aliev, Q.M. Huseynov, S.M. Asadov, S.N. Mustafaeva,
D.B. Tagiyev, The phase equilibria in the Tl-S-I system and electrical properties of the Tl SI and TlS
6 4
compounds, Journal of Alloys and Compounds (2018), doi: https://doi.org/10.1016/j.jallcom.2018.10.220.
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ACCEPTED MANUSCRIPT
The phase equilibria in the Tl-S-I system and electrical properties of the Tl6SI4 and TlS
compounds
Dunya M. Babanlya,b, Ziya S. Alievc,d, Qorkhmaz M. Huseynove,
Salim M. Asadova, Solmaz N. Mustafaevad , Dilgam B. Tagiyeva
aInstitute of Catalysis and Inorganic Chemistry ANAS, Baku, Azerbaijan, AZ1143
bFrench - Azerbaijani University (UFAZ), Baku, Azerbaijan, AZ1010
cAzerbaijan State Oil and Industry University (ASOIU), Baku, Azerbaijan AZ1010
dInstitute of Physics, ANAS, Baku, Azerbaijan, AZ1143
eNakhchivan Branch of the Azerbaijan National Academy of Sciences, Nakhchivan,
Azerbaijan, AZ7000
*Corresponding author: dunyababanly2012@gmail.com
Abstract
The phase equilibria in the ternary Tl-S-I system were investigated experimentally by means of
powder X-ray diffraction (PXRD) and differential thermal analysis (DTA). Five isopleth
sections, liquidus surface projection and room temperature isothermal section were constructed
based on experimental data. dc-and ac-electric properties of the TlS and Tl6SI4 crystals were
studied within the temperature and frequency ranges from 120 K to 300 K and from 50 kHz to
35 MHz, respectively. The hopping mechanism for charge transfer over the localized states near
the Fermi level was established at low temperatures and high frequencies for these compounds.
The density and energy scatter of the states which are located in the vicinity of the Fermi level as
well as the average time and distances of jumps were estimated for the title compounds.
Keywords: chalcohalides; phase equilibria; ternary systems; radiation detectors; electric
measurements; localized states.
1. Introduction
Chalcogenides and chalcohalides of Group III-V metals are of potential interest as
prospective materials for new generation of electronic and spintronic devices thanks to their wide
range of electronic properties such as semiconducting, thermoelectric, photoelectric ones, etc. [1,
2]. The binary and ternary thallium containing phases take an important place among these
materials with outstanding electronic properties [3-10] in spite of toxicity of thallium
compounds.
The Tl–S–I system belongs to a group of alloy systems considered as promising materials
for efficient X-ray and γ-ray detection, e.g., the ternary compound Tl6SI4 displays a higher figure

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of merit than the Cd0.9Zn0.1Te (CZT) crystals which is a current state-of-the-art material for
room-temperature operation in X- and γ-ray detection [11-16].
In order to select novel functional materials and to develop chemical foundations of the
synthesis conditions, it is crucially important to study the respective phase diagrams. In
particular, the synthesis of non-stoichiometric or incongruently melting phases and growth of
their single crystals requires the knowledge on the phase diagrams.
The phase equilibria and thermodynamic properties of the systems Tl-TlX-Q (X=Cl, Br, I;
Q=S, Se, Te) have been carefully investigated in our previous works [3-7]. A number of isopleth
and isothermal sections, as well as the liquidus surface projections were constructed. The
homogeneity fields of all the intermediate phases were determined and their fundamental
thermodynamic functions were calculated from EMF measurements data.
Here, we present a further study of the Tl–S–I ternary system in order to reveal the phase
relationships over the entire composition range to provide more accurate experimental data for
pure and high-quality materials.
The phase equilibria in the system Tl–S–I were investigated by several authors [4, 17-21] so
far. The formation of the congruently melting (715 K) Tl6SI4 and Tl3SI which are stable within
640-670 K temperature range was reported in Ref. [17]. According to [18], Tl6SI4 melts
congruently at 710 K and has ~4 mol% homogeneity area (~2 mol % according to [19]). The
eutectics contain 7 and 45 mol% Tl2S and form at 685 and 665 K, respectively [18]. These data
slightly differ from those given in [17] reporting 10 and 45 mol% Tl2S at 694 and 670 K,
respectively.
The synthesis and single crystal growth methods and conditions, dissociation characteristics
as well as other properties of the Tl6SHal4 were reported elsewhere [19, 20].
The phase equilibria in the Tl-TlI-S subsystem of the title ternary system were investigated
experimentally in our previous work [5]. The primary crystallization areas of Tl6SI4 and Tl3SI, as
well as types and coordinates of all non- and monovariant equilibria in the Tl-TlI-S subsystem
were correctly determined. The fundamental thermodynamic properties of the Tl6SI4 were
accurately calculated from EMF measurements data.
Natural defects present in Tl6SI4 single crystals were studied by low-temperature
photoluminescence (PL) and photoconductivity (PC) measurements by Peters and co-authors
[21]. Large emission band localized at 1.64 eV was observed at low temperatures in the PL
measurements. The deep donor level located at 0.46 eV below the conduction-band edge was
detected in PC measurements, which agrees well with PL spectroscopy data.
The phase diagrams of the boundary binary systems Tl-S, Tl-I are adopted from Ref. [22]
whereas, the S-I one is taken from [23].

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The system Tl-S includes binary compounds Tl2S, Tl4S3, TlS, Tl2S5 and Tl2S3 [22]. Tl2S
melts congruently at 728 K whereas, Tl4S3, TlS, and Tl2S5 compounds form by peritectic
reactions at 570, 505 and 397 K, respectively. Tl2S3 decomposes by the solid phase reaction
Tl2S3→TlS+Tl2S5 at ~370 K.
So far, three binary compounds, namely - TlI, TlI3 and Tl3I4 were found in the Tl-I system
[22]. Thallium monoiodide melts congruently at 715 K and undergoes the TlII↔TlIII polymorph
transformation at 451 K. TlI3 and Tl3I4 are formed by peritectic reaction at 402 K and 533 K,
respectively.
The S–I system was reported to be a simple eutectic system [23]. The eutectic is located at
338 K and contains ~ 80 at.% S.
Crystal lattice parameters of all phases in the Tl-S-I system are summarized in the Table 1.
2. Experimental
2.1. Synthesis
High purity elemental components (Tl, 99.999%, Alfa Aesar; S, 99.999%, Alfa Aesar; I,
99% resublimed pearls, PA-ACS) were used for the synthesis of starting compounds.
Because of thallium and its compounds are often toxic and quickly oxidized, working with
them in laboratory conditions requires a special attention and caution. Therefore, we used
protective gloves and laboratory coats both during the sample preparation and measurements
processes. The samples are weighed as quickly as possible using an analytical balance to
minimize oxidation in air and were then accurately placed into quartz ampoules.
Tl2S was prepared from the stoichiometric amounts of the corresponding elements by one-
step melting in vacuum-sealed silica tubes (~10-2 Pa) at 800 K, followed by furnace cooling. TlS
(503 K) and Tl4S3 (570 K) were slowly cooled after fusing and then annealed for 500 h at 470±5
K and 540±5 K, respectively, because of their incongruent melting character.
Thallium iodides were synthesized by a specially designed method due to high volatility of
iodine at high temperatures. The synthesis was performed in an inclined two-zone furnace. The
optimal temperature of the hot zone was 20÷30 K higher than the corresponding melting point of
the compound, whereas the stable temperature of the cold zone was kept at 400 K. After the most
of iodine had reacted, the ampoule was relocated into the hot zone. The melt was incessantly
stirred at this temperature by shaking of ampoules. As thallium monoiodide forms by dystectic
reaction, it was cooled in the switched-off furnace. However, incongruently melting thallium
triiodide was further annealed for 500 h at temperature 20 K lower than the corresponding
peritectic temperature.

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As there are some disagreemets between the published data on existing intermediate phase
between TlI and TlI3, we have synthesized two alloys, Tl2I3 and Tl3I4, using TlI and iodine.
Syntheses were carried out in the evacuated quartz ampoules placed in a two-zone horizontal
furnace. A “cold” zone (~300 K) was a source of iodine vapor, while a “hot” zone (~500 K) was
used as the reaction area. The fine sintered powder of the thallium monoiodide was in the “hot”
zone and continuously reacted with iodine. During the process, substances in the reaction area
were stirred by continuous rotation of the ampoules along the longitudinal axis. After the
complete adsorption of iodine by the thallium monoiodide occured, the ampoule was placed into
the “hot” zone and kept at 500 K for 200 h, then cooled down in the switched-off furnace.
The PXRD analysis of the Tl2I3 alloy shows that its XRD pattern displays diffraction lines
identical with that observed in [28]. However, the diffraction pattern of the Tl3I4 contains the
most intense lines of the low-temperature modification of TlI (2θ=26.73; 2θ=33.250) together
with the reflections of Tl2I3. The DTA heating curves of the obtained samples contain thermal
effects corresponding to the transformation of Tl2I3 (535 and 650 K) and Tl3I4 (535 and 673 K).
The comparison of the DTA (Fig. 1a) and PXRD data (Fig. 2a) with the Tl-I phase diagram [22]
confirm that the intermediate thallium iodide is the Tl2I3 and that it melts peritectically at 535±2
K.
The ternary Tl6SI4 compound was synthesized by melting appropriate amounts of the pre-
synthesized TlI and Tl2S in the vacuum-sealed quartz ampoule at ~750 K. The heating curve of
Tl6SI4 consists of only visible peak corresponding to its melting temperature (Fig. 1b).
All the investigated samples (total weight, 0.5 g) were prepared from initial elements or
preliminary synthesized compounds. After the melting process, most of the alloys were annealed
at 20-30 K below the solidus temperature for 800-1000h.
2.2. Analysis by DTA and PXRD
DTA and PXRD were used to examine the alloy samples. Thermal analyses of the annealed
alloys were carried out using a NETZSCH 404 F1 Pegasus system. The measurements were
performed from room temperature up to 800 K depending on sample composition with a heating
and cooling rate of 10 K min–1. Temperatures of thermal effects were taken mainly from the
heating curves.
The PXRD analyses were performed on a Bruker D8 ADVANCE diffractometer with the
Cu-Kα1 radiation. The lattice parameters were refined using the Topas V4.2 software. PXRD
confirmed that the pre-synthesized binary and ternary compounds were phase-pure, and the unit
cell parameters perfectly agreed with the literature data. The PXRD pattern of the Tl6SI4
compound was indexed and lattice parameters were calculated. It was confirmed that Tl6SI4

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crystallizes in the Tl6HgBr4 type tetragonal symmetry with the crystal lattice parameters a=
9.1914(9), c = 9.6225(10) Å, and z = 4 which are very close to the literature data [17] (Fig. 2b).
2.3. The dc- and ac-conductivity measurements
The dc-electrical measurements were performed in the temperature range from 120 to 286 K
for the title compounds placed into a cryostat having a temperature stabilization system. The
silver conductive paste was served as a contact material. The thickness of the examined crystals
and the contact area were 100–120 µm and ~2×10–2·cm2, respectively. The dc electric field
applied to the sample varied in the range of 8×102÷ 1.25×104 V/cm.
The samples for the ac-electric measurements were prepared in the form of parallel plate
capacitors. Silver conductive paste served as capacitor plates in this case. The thickness of the
samples was 0.1 cm, and the plate area was 0.1 cm2. The conductivity of the TlS and Tl6SI4
crystals was measured by the resonance technique. The frequency range of the ac electric field
was 5×104–3.5×107 Hz. All the ac-electric measurements were carried out at 300 K. The
amplitude of the ac electric field applied to the samples corresponded to the ohmic region of the
current–voltage characteristics.
3. Results and discussion
A full scheme of phase equilibria in the Tl-S-I system has been obtained based on
experimental and reference data on the boundary binary Tl-S [22], Tl-I [22], S-I [22] systems
and Tl-S-I sub-system [6].
For the convenience of comparison, the quasi- and non-quasi-binary isopleth sections are
expressed using the normalized compositions, meaning that the number of atoms in initial
components is equal.
3.1. The quasi−binary system TlI–S
The system is characterized by the monotectic and eutectic equilibria (Fig. 3). A wide two-
phase liquation field L2+L3 covering the area from 2 to 97 at.% S is observed at monotectic
L2↔L3+(TlI)II equilibrium (m4) temperature (712K). The horizontal line at 450 K reflects the
(TlI)I↔(TlI)II polymorphic transition. The coincidence of the thermal effects at around 450 K for
pristine TlI and alloys indicates a negligible solubility range for both modifications of this
compound. The crystallization process finishes at 385 K by the eutectic L3↔(TlI)I+S reaction
(e9) and consequently, system transfers into (TlI)I+S two-phase state. The X-ray analysis further
confirms this transformation by the appearance of the diffraction lines belonging to the low-
temperature modification of thallium monoiodide and elemental sulfur (Fig. 4).

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3.2. The 300 K isothermal section of the Tl-S-I system
The PXRD data for the selected samples of the TlI-I-S subsystem and literature data [7, 18-
22] allowed us to plot the isothermal section of the Tl-S-I system at 300 K (Fig. 5). The only one
ternary compound, namely Tl6SI4, has been found in this system. The thallium monoiodide,
which is the most thermodynamically stable compound of the system, is in equilibrium with all
phases except of the Tl4S3 phase. On the other hand, all three thallium iodides are in tie line
connection with elemental sulfur. This leads to the formation of the three-phase areas in the Tl-
S-I system.
3.3. The liquidus surface projection of the Tl-S-I system
The liquidus surface projection of the system is illustrated in the Fig. 6 while the types and
coordinates of all non- and monovariant equilibria are summarized in Tables 2 and 3. The
liquidus surface consists of twelve primary crystallization fields. The primary crystallization
fields of thallium, sulfur and Tl2S5, as well as several equilibrium points and curves are found to
be degenerated at the thallium and sulfur corners of the concentration triangle. These areas are
represented by blow-ups in Figs. 6 a,b,c.
The largest primary crystallization area in the system belongs to high-temperature
modification of the thallium monoiodide (TlI)II. This area covers most of non- and mono-variant
equilibria in the Tl-S-I system (Tables 1 and 2). The ternary Tl6SI4 compound has also a wide
primary crystallization area, which allows to growing its large single crystals from non-
stoichiometric melts. The primary crystallization field of the Tl3SI compound (M3P6U7e2M2U5)
exists in a narrow temperature interval from 640 to 670 K [6] (Fig. 6). Despite the fact that this
compound decomposes by the Tl3SI→Tl2S+Tl6SI4 solid-state reaction [17] along the section
Tl2S-TlI, its decomposition occurs by transition reactions U5 and U7 (Table 2) beyond this
section. The notable feature of the Tl-S-I system is the presence of two wide L1+L2 and L2+L3
immiscibility regions (L1 is the melt based on metallic thallium, L2 is the liquid solution of
sulfides, iodides and thallium triiodide, L3 is the melt based on of sulfur and iodine). The L1+L2
area almost entirely covers the Tl-Tl2S-TlI subsystem, however, the L2+L3 area takes a
considerable part at the center of the composition triangle. The latter liquation area comes from
/
/
quasi-binary TlI-S section (Fig. 3), then it penetrates into the iodine- (m4M5K2M5 m4 ) and
/
/
sulfur–rich (m4M5K2M5 m4 ) areas (Fig. 6). The primary crystallization fields of all the phases
are bordered by the monovariant curves (Table 3) and nonvariant points (Table 2). The
monovariant eutectic and peritectic curves are transformed into the nonvariant monotectic
equilibria upon the intersection with immiscibility areas (See Fig. 6 and Table 3, the conjugate
/
/
/
/
/
pairs of M1M1 , M2M2 , M3M3 , M4M4 , M5M5 points).

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3.4. Isopleth sections
The phase diagrams of the Tl2I3-S, TlI3-S, TlI-[SI] and Tl0.5S0.5-I systems (Figs.7-10)
intersect all the phase regions in the Tl-S-I system and include the majority of non- and
monovariant equilibria. Comparative analysis of these phase diagrams with Fig. 6 and Table 2
and 3 shows excellent agreement between them.
3.4.1.The isopleth section Tl2I3-S
This section is stable in the subsolidus area (Fig. 7), however, it is entirely non-quasi binary
due to incongruent melting character of the Tl2I3. The liquidus of this system consists of only one
curve corresponding to the primary crystallization of thallium monoiodide. The comparison of
the Fig. 6 and 5 shows that the (TlI)II crystallizes in a wide composition range from ~5 to 95
at.% S by monovariant monotectic reaction. The thermal effect at 525 K reflects the nonvariant
monotectic equilibrium (see Table 2, point M5). The polymorphic transition of thallium
monoiodide occurs at 450 K. Finally, the crystallization in the Tl2I3-S section finishes by the U7
transition reaction at 355 K.
3.4.2.The isopleths section TlI3-S
This section is also featured by the formation of a large immiscibility region (Fig.8). High-
temperature modification of thallium monoiodide primarily crystallizes from L2, L3 and L2+L3
liquid phases. Then, the crystallization process continues by monotectic reaction M5 and finishes
by the formation of the three-phase area L2+L3+Tl2I3. When decreasing the temperature, the L2
phase completely crystallizes into Tl2I3 and then forms two-phase area L3+Tl2I3. In the 0-80 at.%
S compositional range, crystallization occurs by peritectic reaction P5U8 (Table 3) whereas, it
continues by the eutectic scheme of L↔Tl2I3+S within the 80-100 at.% S compositional range.
The crystallization ends by a transition equilibrium (see Table2, U8) at 345K and the system
transforms into the TlI3+S two-phase state (Fig.8).
3.4.3.The isopleth section TlI-[SI]
The liquidus of the system (Fig.9) consists of four curves according to the primary
crystallization of the (TlI)II, Tl2I3, TlI3 and iodine. The liquidus curve of the (TlI)II is almost
completely miscible, however, the liquidus of the Tl2I3 partially passes through the immiscibility
L2+L3 region. The primary crystallization of the TlI and Tl2I3 takes place by monovariant
monotectic reactions L2↔L3+(TlI)II and L2↔L3+Tl2I3, respectively at 27-98 mol% and 20-27
mol% TlI (Table 3).
The horizontal lines at 525 and 475 K reflect the nonvariant monotectic reaction (M5) (Table
2) and the end of the monovariant monotectic reaction L2↔L3+Tl2I3, respectively. The reaction

8
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M5 takes place with an excess of the L2 phase in the < 75 mol% TlI composition range whereas,
it occurs in >75 mol% TlI composition range with the excess of (TlI)II. Therefore, two three-
phase areas L2 +L3+Tl2I3 and L3+(TlI)II +Tl2I3 appear in the corresponding composition areas.
During the cooling, the latter three-phase mixture, the(TlI)II →(TlI)I polymorphic transition
occurs at 450 K followed by nonvariant transition reaction U7 (Table 2). The comparison of the
given isopleths with Figs. 5 and 6 show that, the crystallization process complete by the
nonvariant eutectic (E4) and transition (U8 and U7) reactions at 0-33, 33-67 and 67-100 mol% TlI
compositional ranges, respectively. Subsequently, the following three three-phase areas appear in
the subsolidus area: TlI3+I2+S, TlI3+Tl2I3+S and (TlI)I+ Tl2I3+S (Fig. 9).
3.4.4.The isopleth section Tl0.5S0.5 -I
This section (Fig.10) crosses six three-phase areas in the subsolidus area and contains the
most of non- and monovariant equilibria in the Tl-S-I system. The nature of the phase equilibria
along this section is comprehensively discussed in our previous work [6]. Crystallization features
of the alloys and phase equilibria in the iodine-rich area are qualitatively similar to the section
TlI-[SI] (Fig. 9).
3.5. The ac- and dc-conductivity of the TlS and Tl6SI4single crystals
The presence of the structural defects in thallium chalcogenides such as vacancies and
dislocations results in a high density of localized states near Fermi level. The localized states in
the band gap are responsible for most electronic processes occurring in semiconductors. Both dc
and ac charge transports in semiconductors at low temperatures and high frequencies proceed via
these localized states.
The experimental data obtained in dc-electric measurements indicate that the TlS single
crystal exhibits variable range of hopping conductivity over states lying in a narrow energy band
near Fermi level (Fig. 11) in the temperature range from 120 to 230 K. According to this type of
conductivity [33]
σ
exp[ −(T0 /T )1/ 4 ] ,
(1)
T =16/(N ka3 )
where
The density of states near Fermi level for TlS was calculated from the low-temperature dc-
conductivity measurements:
= 2.8×1020 eV–1 cm–3.
,
k
is the Boltzmann constant, is the localization radius.
al
0
F
l
NF
Frequency-dependent 300 K ac-conductivity of TlS crystal (Fig.12, a) follows the relation
0.8 at f 106 Hz. The observed 0.8 behavior in TlS attests to hopping transport
~
≥
~
f
σ ac
f
σ ac
through the localized in forbidden gap states [33]:

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
ν
4

π 3


2
2
F
5
l


ph 
σ
ac ( f ) =
e kTN a f ln
,
(2)


96
f




where
e
is the unit charge,
is the density of states near Fermi level,
is the
α
NF
al = 1/
α
localization radius,
charge carrier,
found for the Tl SI single crystal (Fig. 12, b). The Fermi level density of states (
α
is the exponent of the decay of the wave function
ψ ~
e− r of the localized
ν
is the phonon frequency. Similar frequency-dependent conductivity was also
ph
= 3.1 ×
NF
6
4
1019 eV–1 cm–3 for TlS and
= 2 × 1018 eV–1 cm–3 for Tl6SI4) have been evaluated. The
ν ph in
NF
the crystals under study was taken to be 1012 Hz [34]. The spread of energies near Fermi level
was calculated by following formula [35]:
∆W = 3/ 2
π
R3 NF
(3)
(∆W = 2.4×10-3 eV for TlS and 4.1× 10-2 eV for Tl6SI4), and the mean hop distance (R = 185 Å
for TlS and R = 180 Å for Tl6SI4) have been estimated by following formula [35]:
ν


1
ph




R =
ln
.
(4)
2α
f


4. Conclusion
Experimental data from DTA and PXRD measurements allowed us to obtain a self-
consistent description of phase relationships in the Tl-S-I system. The plotted phase diagram
presents valuable information useful to achieve controlled synthesis of the materials with desired
compositions and growth of bulk single crystals of the title compounds both from stoichiometric
and non-stoichiometric melts. Moreover, determination of the eutectic, peritectic and
polymorphic phase transformations, as well as the primary crystallization areas and the
homogeneity ranges of the existing phases allow to better understand the composition–structure–
properties relationships for Tl-S-I alloys.
From electric and high-frequency dielectric measurements, it was found that the dc- and
ac-conductivities of TlS and Tl6SI4 single crystals at low temperatures and high frequencies
indicate the hopping mechanism of the charge transfer over the states localized near Fermi level.
The density of the states at Fermi level is 3.1×1019 eV–1 cm–3 for TlS and 2×1018 eV–1 cm–3 for
Tl6SI4. The energy range (∆W) is found to be 2.4×10-3 eV for TlS and 4.1×10-2 eV for Tl6SI4.
The average hopping length is estimated as 185 Å for TlS and 180 Å for Tl6SI4.

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Acknowledgment
This work was partially supported by the Science Foundation of the State Oil Company of
Azerbaijan Republic (SOCAR project 12LR – AMEA. 2018) and by the Science
№
Development Foundation under the President of the Republic of Azerbaijan (SDFAR grant
EIF-BGM-4-RFTF-1+/2017-21/05/1-M-07).
№
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Table 1
Crystallographic data for the binary and ternary phases in the Tl-S-I system
Phase
Crystal
system
Space Crystal lattice parameters, Å
Group
z
Reference
a
b
C
Tl2S
Rhombohedral
Monoclinic
Tetragonal
R3
12.26
7.72
-
18.29
7.96
27
4
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
Tl4S3
TlS
P21 /c
P412121
12.98
7.803
6.66
-
29.55
6.538
12.92
-
32
4
Tl2S5
(TlI)I
(TlI)II
TlI3
Orthorhombic P212121
Orthorhombic Amma
16.70
5.251
4.198
9.436
6.188
9.176
4.582
4
Cubic
Pm3m
-
4
Orthorhombic Pnma
10.599
6.419
13.412
9.608
4
Tl2I3
Tl6SI4
Hexagonal
Tetragonal
-
-
-
-
P4/mnc
2

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Table 2
Nonvariant equilibria in the Tl-S-I system
Point in the
Figure 5
Equilibrium
Composition, аt%
T,K
S
I
D1
D2
33.3
-
-
50
728
715
L↔ Tl2S
L↔(TlI)II
D3
e1
e2
e3
e4
e5
e6
e7
e8
9.1
4.3
15
-
<1
<1
-
80
>99
-
<1
<1
>99
79
46
55
98
-
36.4
44
25
<1
-
<1
89
20
-
<1
<1
<1
<1
20
-
710
690
665
575
575
575
363
338
385
385
575
575
385
335
570
503
397
535
401
670
635
560
495
475
L↔
L↔(TlI)II+
γ(Tl6SI4)
γ
L↔γ+Tl3SI
L↔(TlI)II+TlII
L↔Tl2S+TlII
L↔γ+TlII
L↔ TlI3 + I2
L↔ S + I2
L↔ Tl2S5 + S
L ↔(TlI)I + S
L↔(TlI)II+γ+TlII
L ↔ Tl2S+γ+TlII
L↔ (TlI)I +Tl2S5 + S
L ↔ TlI3+I2+S
L+Tl2S↔Tl4S3
L+ Tl4S3↔TlS
L +TlS↔ Tl2S5
L + (TlI)II↔Tl2I3
L + Tl2I3↔ TlI3
e9
E1
E2
E3
E4
P1
P2
P3
P4
P5
P6
U1
U2
U3
U4
-
-
77
83
19
17
5
2
3
<1
<1
14
20
-
21
26
43
54
60
<1
98
85
79
L+Tl2S↔Tl3SI
L+Tl3SI ↔γ +Tl2S
L+ Tl2S ↔γ +Tl4S3
L+Tl4S3↔γ + TlS
L+γ↔(TlI)II +TlS
L+Tl3SI↔γ+Tl2S
L+TlS↔(TlI)I +Tl2S5
L + (TlI)I↔Tl2I3+S
L+Tl2I3↔ TlI3 +S
U5
U6
U7
U8
635
395
355
345
/
m1(m1 )
m2(m2 )
m3(m3)
m4(m4 )
m5(m5)
M1(M1)
M2(M2)
M3(M3)
M4(M4 )
M5(M5 )
32(4)
73(97)
-
2(97)
8.8(<1)
4(<1)
18(<1)
20(<1)
70(97)
73(14)
-
-
723
420
714
712
705
682
661
665
450
525
L2↔ L1+Tl2S
L2 ↔ L3 +TlS
L2↔ L1+(TlI)II
/
49(<1)
49(~1)
35(<1)
43(<1)
20(<1)
18(<1)
2(<1)
11(84)
/
L2↔ L3+(TlI)II
L2↔ L1+γ
L2↔ L1+(TlI)II+γ
L2↔ L1 +Tl3SI +γ
L2+ Tl2S ↔ L1+Tl3SI
L2+(TlI)II↔ L3+TlS
L2+(TlI)II↔ L3+Tl2I3
/
/
Note: Index I and II in the formulas indicates the low- and high-temperature modification of Tl and TlI,
respectively;
parenthesis.
γ - is the solid solution on the base of Tl6SI4. Conjugate points of the monotectic equilibria are given in

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Table 3
Mono-variant equilibriaof the Tl-S-I system
Curve in the Figure 5
Equilibrium
Temperature intervals, K
e1M1
e1U4
e2M2
e2U1
690-682
690-475
665-661
665-635
670-665
670-635
570-560
635-560
503-495
560-495
495-475
475-470
470-450
535-525
525-355
385-355
355-345
401-345
363-335
338-335
345-335
723-665
714-682
705-682
705-661
665-661
712-450
712-525
450-420
525-470
L↔(TlI)II +
L↔(TlI)II +
γ
γ
L↔γ+Tl3SI
L↔γ+Tl3SI
L+Tl2S↔Tl3SI
L+Tl2S↔Tl3SI
L+Tl2S↔Tl4S3
L ↔ Tl2S+γ
P6M3
P6U1
P1U2
U1U2
P2U3
U2U3
U3U4
U4K1
K1M4
P4M5
L+ Tl4S3↔TlS
L↔γ +Tl4S3
L↔γ +TlS
L↔(TlI)II+TlS
L+(TlI)II↔TlS
L+(TlI)II↔Tl2I3
L↔(TlI)II+ Tl2I3
L↔(TlI)II+S
L↔Tl2I3+S
L+ Tl2I3↔TlI3
L↔ TlI3+I2
L↔ S+I2
L↔ S+ TlI3
L2↔ L1+Tl2S
L2↔ L1+(TlI)II
L2↔ L1+(TlI)II
L2↔ L1+γ
L2↔ L1 +Tl3SI
L2↔ L3+(TlI)II
L2↔ L3+(TlI)II
L2↔ L3+ TlS
L2↔ L3+ Tl2I3
/
M5 U7
e9U7
U7U8
P5U8
e6E4
e7E4
U8E4
m1M3
m3M1
m5M1
m5M2
M3M2
/
/
m4M4(m4 M4 )
/
/
m4M5(m4 M5 )
/
/
M4m2(M4 m2 )
M5K2(M5 K2)
/
Note: The labeling of phases is the same as in the Table 2. Degenerated monovariant equilibria near the Tl
and S corners of the concentration triangle are not represented. They can be easily determined from the Table 2 and
Fig.5.

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Figure Captions
Figure 1. DTA heating spectrum of: a) Tl2I3 and, b) Tl6SI4
Figure 2. PXRD patterns of the compounds: a) Tl2I3 and, b) Tl6SI4
Figure 3. The phase diagram of the TlI-S system
Figure 4. PXRD patterns for different compositions of the TlI-S system: blue; TlI, red; 50%
TlI+50% S, black; S (color online)
Figure 5. The 300 K isothermal section of the Tl-S-I system
Figure 6. The liquidus surface projection of the Tl-S-I system (color online). Primary
crystallization fields are: 1, Tl2S; 2, Tl4S3; 3, TlS; 4, Tl3SI; 5, Tl6SI4(γ); 6, (TlI)II; 7, Tl2I3; 8, TlI3;
9, I2; 10, Tl; 11, S and 12 , Tl2S5
Figure 7. The isothermal section Tl2I3 –S
Figure 8. The isopleth section TlI3-S
Figure 9. The isoplet section TlI-[SI]
Figure 10. The isopleth section Tl0.5S0.5 -I
Figure 11. Temperature dependence of the low-temperature conductivity of a TlS single crystal
Figure 12. Frequency-dependent 300 K ac-conductivity for the TlS (a) and Tl6SI4 (b)

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The self-consistent phase diagram of the Tl–S–I system is constructed
•
•
•
The existence of the wide immiscibility fields was revealed
dc-and ac-electric properties for the TlS and Tl6SI4 crystals were studied