Phase equilibria in the Tl-TlCl-Te system and thermodynamic properties of the compound Tl5Te2Cl

Article abstract of DOI:10.1134/S0036023611030065

The Tl-Te-Cl system was studied in the Tl-TlCl-Te composition region by differential thermal analysis, X-ray powder diffraction, and emf and microhardness measurements. A series of polythermal sec- tions, an isothermal section at 400 K, and a projection of the liquidus surface of the phase diagram were con- structed. The ternary compound Tl₅Te₂Cl characterized by a wide homogeneity region and incongruent melting by a syntectic reaction at 708 K was shown to exist. This compound was found to crystallize in tetragonal lattice (space group I4/mcm) with the parameters a = 8.921 ?, c = 12.692 ?, and Z = 4. Wide phase separation regions were also found in the system, including a three-phase separation region in the Tl-TlCl-Tl₂Te sub- system. Regions of primary crystallization of phases, and the types and coordinates of in-and monovariant equilibria in the T-x-y diagram were determined. From emf measurement data, the standard thermody- namic functions of formation and the standard entropy were calculated for the compound Tl₅Te₂Cl, as follows: =ΔG₀ ²⁹⁸ 355.9 ± 1.1 kJ/mol, =ΔH₀²⁹⁸ 377.1 ± 5.0 kJ/mol, andΔS₀²⁹⁸ = 474.1 ± 6.8 J/(mol K). Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036023611030065

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 3, pp. 442–449. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © D.M. Babanly, Z.S. Aliev, F.Ya. Dhafarli, M.B. Babanly, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 3, pp. 483–489.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Phase Equilibria in the Tl–TlCl–Te System and Thermodynamic
Properties of the Compound Tl5Te2Cl
D. M. Babanly, Z. S. Aliev, F. Ya. Dhafarli, and M. B. Babanly
Baku State University, Baku, Azerbaijan
eꢀmail: babanly_mb@rambler.ru
Received July 7, 2009
Abstract—The Tl–Te–Cl system was studied in the Tl–TlCl–Te composition region by differential thermal
analysis, Xꢀray powder diffraction, and emf and microhardness measurements. A series of polythermal secꢀ
tions, an isothermal section at 400 K, and a projection of the liquidus surface of the phase diagram were conꢀ
structed. The ternary compound Tl5Te2Cl characterized by a wide homogeneity region and incongruent meltꢀ
ing by a syntectic reaction at 708 K was shown to exist. This compound was found to crystallize in tetragonal
lattice (space group I4/mcm) with the parameters a = 8.921 Å, c = 12.692 Å, and Z = 4. Wide phase separation
regions were also found in the system, including a threeꢀphase separation region in the Tl–TlCl–Tl2Te subꢀ
system. Regions of primary crystallization of phases, and the types and coordinates of inꢀ and monovariant
equilibria in the
T–x–y diagram were determined. From emf measurement data, the standard thermodyꢀ
namic functions of formation and the standard entropy were calculated for the compound Tl5Te2Cl, as folꢀ
0
0
0
lows:
= 355.9 1.1 kJ/mol,
= 377.1 5.0 kJ/mol, and
= 474.1 6.8 J/(mol K).
S298
−ΔG298
−ΔH298
DOI: 10.1134/S0036023611030065
This work continued our physicochemical study of
The Tl5Te2Cl–Tl5Te3 system is also nonꢀquasiꢀ
thallium chalcohalides [1–7] and presented new binary and is characterized by the formation of continꢀ
results on phase equilibria and thermodynamic propꢀ uous solid solutions [12]. Its interesting specific feaꢀ
erties of the Tl–Te–Cl system in the Tl–TlCl–Te ture is that the formation of solid solutions is comꢀ
composition region.
We failed to find any published data on the Tl–Te–
Cl system.
Previously [8–12], we investigated the Tl–Te–Cl
system over various polythermal sections. In particular
bined with the presence of a wide immiscibility region.
The primary crystallization of solid solutions in the
composition region 0–65 mol % Tl5Te3 occurs by a
monovariant syntectic reaction.
The boundary constituents Tl–Te and Tl–TlCl of
[8], we synthesized a new thallium tellurochloride, the Tl–TlCl–Te system have been investigated in a
Tl5Te2Cl, which melts with decomposition by a syntecꢀ number of works. According to the diagram [13],
tic reaction at 708 K and crystallizes in the tetragonal the compounds Tl5Te3, TlTe, and Tl2Te3 form in the
Т–х
lattice (space group
I
4/mcm) with the parameters
a
=
Tl–Te system. The first of them melts congruently at
726 K, and the other two melt incongruently at 573
and 511 K, respectively. The compounds Tl5Te3 and
TlTe crystallize in a tetragonal lattice with the unit cell
8.921 = 12.692 Å, and Z
Å,
с
= 4 [8].
The TlCl–Te quasiꢀbinary system [9] is characterꢀ
ized by a wide phase separation region and monotectic
equilibrium at 717 K. The eutectic is degenerate near
TlCl.
The polythermal sections TlCl–TlTe [10], TlСl–
Tl2Te3, and Tl5Te2Cl–Tl(TlTe) [11] are nonꢀquasiꢀ
binary because of the incongruent melting of one or
both of the initial compounds. However, they are staꢀ
ble in the subsolidus region; that is, their alloys consist
parameters
group 4/mcm [14] and
16 [15] (or = 18.229
group 42/nmc [16]), respectively. Tl2Te3 has a monoꢀ
clinic structure with = 17.413 = 6.552
7.910 = 133.6 = 4, and space group Cc [14].
Along with the described compounds, the phase
a
= 8.929
Å
a
Å
,
c
= 12.620 Å,
= 12.950 = 6.175 Å,
= 6.157 = 32, space
Z = 4, space
I
Å,
c
Z =
a
,
c
Å, Z
P
a
Å,
b
Å, c =
Å,
β
°, Z
of twoꢀphase mixtures of the initial phases. In the diagram [17] shows the compound Tl2Te, which melts
Tl5Te2Cl–TlTe system, a wide (to ~20 mol % TlTe) congruently at 698 K. It was shown that this compound
region of Tl5Te2Clꢀbased solid solutions was found forms a eutectic with Tl5Te3 at 695 K and ~34 at % Te.
[11]. In all of the described sections, there are wide These data [17] were later confirmed [18, 19]. Howꢀ
miscibility gaps where liquid separates into two liquid ever, doubt was cast upon the existence of the comꢀ
phases and, in the Tl5Te2Cl–Tl section, even into three pound Tl2Te [20] until the publication [21] appeared
liquid phases.
where, by analyzing 1989 diffraction reflections, it was
442

PHASE EQUILIBRIA IN THE Tl–TlCl–Te SYSTEM
443
established that this compound crystallizes in a monoꢀ Tl–TlCl–Te system. To bring the alloys to equilibꢀ
clinic lattice and is of its own structural type (space rium, they were annealed at temperatures 20–30 K
group С2
/
°
С
,
а
= 15.662
Z
Å
,
b
= 8.987
Å
,
c
= 31.196
Å
,
below the solidus temperature for 500–1000 h.
We performed differential thermal analysis with an
NTRꢀ72 pyrometer with Chromel/Alumel thermoꢀ
couples, Xꢀray powder diffraction with a Philips
β
= 100.7
, and = 4). It was stated [21] that the Tl2Te
crystal lattice contains not only regions characteristic
of Tl5Te3, but also regions (layers) that comprise only
thallium atoms and involve Tl–Tl bonds.
X’Pert MPD diffractometer (Cu
K
radiation), and
α
1
Phase equilibria in the Tl–Cl system were studied
in the T–TlCl3 composition region, and a Т–х diaꢀ
gram was constructed [22]. It was found that the comꢀ
pound TlCl melts congruently at 703 K, and the Tl–
TlCl subsystem is of a monotectic type and is characꢀ
terized by almost complete immiscibility in the liquid
state. The eutectic is degenerate near thallium.
measurements of microhardness with a PMTꢀ3
microhardness meter (load 20 g) and the emf of conꢀ
centration circuits of the type
(–)Tl(solid)/liquid electrolyte
(1)
+
Tl+/(Tl–Te–Cl)(solid)(+)
within the temperature range 300–430 K. The electroꢀ
lyte was a glycerol KCl solution containing ~0.5 wt %
TlCl. The left electrode was made from metallic thalꢀ
lium, which does not directly interact with glycerol
[24], and the right electrodes were made from prelimiꢀ
narily synthesized equilibrium alloys in the Tl–TlCl–Te
EXPERIMENTAL
For our studies, we synthesized the compounds
Tl2Te, TlCl, and Tl5Te2Cl and alloys of different comꢀ
positions in the Tl–TlCl–Te system. Tl2Te was syntheꢀ
sized by directly alloying highꢀpurity constituent eleꢀ
ments in an evacuated (to ~10–2 Pa) quartz ampoule.
The alloying temperature was 750 K.
TlCl was produced according to a published proceꢀ
dure [23]. Initially, metallic thallium was dissolved at
~350 K in dilute (~7–10 mol %) sulfuric acid to obtain
system in the composition region TlCl–Tl2Тe–Тe
.
The emf was measured by a compensation method
with a V7ꢀ34A highꢀresistance digital voltmeter. Cirꢀ
cuits of type (1) were produced and the emf was meaꢀ
sured according to published procedures [2, 3, 25].
a
Tl2SO4 solution. To a boiling 2% Tl2SO4 solution,
dilute HCl was added until the precipitation was comꢀ
pleted. After cooling the mother liquor, TCl was withꢀ
drawn, washed with ice distilled water, and dried for a
long time in a drying cabinet at 390–400 K.
RESULTS AND DISCUSSION
Processing of the total experimental data set
obtained from the above sections and a series of the
additional alloys using the Т–х diagrams of the boundꢀ
The ternary compound Tl5Тe2Cl was produced by
alloying the TlCl and Tl2Te obtained as described
above in the required ratio in an evacuated quartz
ampoule. Because of the syntectic melting of this
compound [8], the melts consist of two separating liqꢀ
uid phases. Therefore, heterogeneous mixtures conꢀ
taining TlCl and also phases based on Tl5Тe2Cl and
Tl2Te crystallize from melts even on slow cooling.
Therefore, according to our previous data [8], the
completeness of interaction was reached by slow (for
~5 h) cooling to 700 K and treatment at this temperaꢀ
ture for ~300 h.
ary systems Tl–Te [17], Tl–TlCl [22], and TlCl–Te
[9] and the previously examined inner sections [8, 10–
12], provides a complete selfꢀconsistent pattern of
phase equilibria in the Tl–TlCl–Te system (Figs. 1–7,
Table 1).
Figure 1 presents the Т–х diagram [8] of the TlCl–
Tl2Te quasiꢀbinary system together with the results of
the measurements of microhardness and the emf of
circuits of type (1). In the system the Tl5Te2Cl ternary
compound forms, which melts incongruently at 708 K
by a syntectic reaction. At the syntectic temperature,
the phase separation region extends from ~7 to 85 mol %
Tl2Te. A eutectic between TlCl and Tl5Te2Cl is at
~3 mol % Tl2Te and 692 K. The compound Tl5Te2Cl
forms a series of solid solutions with Tl2Te which
undergoes a morphotropic phase transition from the
The compounds synthesized were identified by difꢀ
ferential thermal analysis and Xꢀray powder diffracꢀ
tion.
By alloying the initial compounds and elemental
tellurium and thallium in various ratios in evacuated
quartz ampoules, we prepared alloys in the sections
Tl2Тe–[Tl2Cl], Tl2Тe–[TlТeCl], and Tl5Тe2Cl–Тe
(here and hereinafter, bracketed compounds are hetꢀ
erogeneous alloys taken as “components”) and also a
series of additional samples in the Tl–TlCl–Te comꢀ
position region. The compositions of the additional
samples were chosen based on the phase diagram of
the Tl–Te boundary binary system [17] and the data
Tl5Te3 (
ture at ~90
The Xꢀray powder diffraction patterns of TlCl–
Tl2Te alloys from the phase homogeneity region virꢀ
δ
phase) structure to the Tl2Te (
α
phase) strucꢀ
%
Tl2Te [8].
δ
tually coincide with the Tl5Te2Cl diffraction pattern and
contain no reflection lines representing Tl2Te (Fig. 2).
The Tl5Te2Cl microhardness remains constant
(
~1340 MPa), regardless of the composition in the
on the previously [8–12] investigated sections in the TlCl–Tl5Te2Cl region, and monotonically increases to
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

444
BABANLY et al.
(c)
(b)
I
E
, mV
(а)
(b)
(300 K)
400
417
6000
4000
300
230
2000
H, mPa
1450
0
1400
4000
3000
2000
1000
0
1300
T
, K (а)
l
l + l
1 2
50
, deg
1
20
30
40
60
80
70
l
2
2
θ
708
C
703
700
l +
2
δ
l +
1
δ
Fig. 2. Xꢀray powder diffraction patterns for (a) the comꢀ
pound Tl Te Cl and (b) the alloy containing 85 mol %
Tl Te in the TlCl–Tl Te section.
692
5
2
693
2
2
690
e
3
δ
TlCl + Tl Te Cl
2
α
2
Tl5Тe2Cl and the
twoꢀphase equilibria with TlCl and also with TlTe and
elemental thallium.
Phase equilibria in complex polythermal sections
(Figs. 4–6) are conveniently analyzed together with a
δ
phase on its basis are involved in
680
TlCl
20
40
mol %
60
80 Tl Te
2
projection of the Т–х–у diagram (Fig. 7).
Fig. 1. (a)
Т
–
х
, (b)
Η
–
х, and (c)
Е–
х
diagrams of the
TlCl–Tl Te system
.
2
[Tl2Cl]–Tl2Te section (Fig. 4) contains a wide
~10–80 mol % Tl2Te) region where the liquids sepaꢀ
(
rates into three liquid phases l1 + l2 + l3, which is adjaꢀ
cent to l1 + l2 and l2 + l3 twoꢀphase fields (where l1, l2,
and l3 are liquid solutions based on metallic thallium,
TlCl, and tellurides, respectively). The horizontal lines at
505 and 575 K represent a polymorphic transition and
melting of metallic thallium. The thermal events at 690
and 700 K, respectively, characterize the fourꢀphase
monotectic (М1) and syntectic (СT) equilibria (Figs. 4, 7;
Table 1). Below the solidus, this section intersects three
~1420 MPa within the composition range 66.7–
90 mol % Tl2Te. At high Tl2Te concentrations, the microꢀ
hardness slightly decreases from 1450 to ~1420 MPa
(Fig. 1b).
The emf continuously increases from 230 mV for
the pure Tl2Te [28] to 417 mV for the stoichiometricꢀ
composition phase Tl5Te2Cl and then remains conꢀ
stant. This indicates that each of the alloys within the
Tl5Te2Cl–Tl2Te composition region consists of a single
phase (Fig. 1c).
phase fields: Tl1 +
α, TlI +
δ
, and TlI + TlСl + .
δ
Tl5Te2Cl–Te section (Fig. 5) describes phase equiꢀ
libria in the TlCl–Tl2Te–Te composition region. In the
subsolidus region, this section intersects five phase
Isothermal section of the Tl–TlCl–Te system at
Т
≤
500 (Fig. 3) demonstrates the locations of phase
K
regions below the solidus line, in particular, the presꢀ
ence of a wide homogeneity region of Tl5Te2Clꢀbased
fields (δ,
δ
+ TlTe, + TlCl + TlTe, TlCl + Tl2Te3 +
δ
Te, and Tl2Te3 + TlCl + Te), which is in full agreement
with the diagram of solidꢀphase equilibria (Fig. 3).
The data on this section allow one to revise the locaꢀ
tions of the of primary crystallization and immiscibilꢀ
ity regions, the run of monovariant equilibrium curves,
and the coordinates of a number of nonvariant points
of the Tl–TlCl–Te system (Fig. 7; Table 1).
alloys (
δ
phase). It is seen that the phase homogeneꢀ
δ
ity region extends considerably beyond the TlCl–
Tl2Te section toward an excess of tellurium and has the
shape of a wide continuous band for a variableꢀcomꢀ
position phase based on Tl5Te3 in the Tl–Te binary sysꢀ
tem (34.5–38.5 at % Te [17]).
The dominating role in the formation of phase
The liquidus in the Tl5Te2Cl–Te section consists of
regions in the diagram of solidꢀphase equilibria is three curves corresponding to the primary crystallizaꢀ
played by TlCl, which is the most thermodynamically tion of TlCl, phase, and Te. In the composition
δ
stable compound in the Tl–Te–Cl ternary system. region 20–100 mol % Tl5Te2Сl, the melt separates into
This compound is characterized by stable tieꢀlines to two liquid phases (l1 + l2). From this twoꢀphase melt,
all phases, except Tl5Te3, which gives rise to Tl +
TlCl, TlCl + TlTe + , TlCl + TlTe + Tl2Te3, and TlCl + TlCl primarily crystallizes, and in the composition
Tl2Te3 + Te threeꢀphase regions. The compound region 85–100 mol % Tl5Te2Cl phase does. In the
δ
+
in the composition region ~20–85 mol % Tl5Te2Cl,
δ
,
δ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

PHASE EQUILIBRIA IN THE Tl–TlCl–Te SYSTEM
445
TlCl
40
20
Tl + δ + TlCl
I
δ
+ TlTe
TlCl + Tl Te + Te
2
3
δ
+ Tl
δ
I
α
+ Tl
I
α
TlTe
3 Te, at %
Tl
20
Tl2Te
Tl Te40
60
80
Te
α
+
δ
5
Tl2Te3
Fig. 3. Isothermal section of the phase diagram of the Tl–TlCl–Te system at 300 K.
composition region 0–20 mol % Tl5Te2Cl primarily This section, as well as Fig. 5, clearly demonstrates the
crystallizes from liquid l3 (Fig. 5).
curves of monovariant (М2Р3 Р3Р4
,
, Р4Е, and М3Е) and
nonvariant (М2 Р3 Р4, and Е) equilibria (Table 1). In
the subsolidus region, this section intersects seven
phase fields.
,
,
Tl2Te–[TlTeСl] section (Fig. 6). The pattern of
phase equilibria in this section is qualitatively similar
to that for the Tl5Te2Cl–Te section. This is because
both of the polythermal sections intersect the same
The liquidus surface of the Tl–TlCl–Te system
(Fig. 7) consists of five fields corresponding to the priꢀ
phase regions of the
directions. The liquidus consists of the curves of priꢀ
Т–х–у diagrams in different
mary crystallization of TlCl, the
δ
phase, TlTe, Tl2Te3,
and elemental tellurium. The liquidus surfaces of Tl2Te
mary crystallization of TlCl and the
δ
phase (Fig. 6).
T, K
T, K
l3
l2 + l3
l3
l1 + l2 + l3
l +
δ
+ TlCl
l2 + l3 +
l2 + l3
2
723
δ
l3 +
δ
700
M3
CT
700
690
l + Te
M2
+ TlCl
l2 + l3 + TlCl
700
600
500
698
δ
M1
l1 + l2 +
δ
l2 + l3 +
δ
l + TlCl
l +
δ
+ TlCl
l1 + l2 + TlCl
600
500
l + TlCl + Te
l +
δ
l + TlCl + TlTe
568
l + TlCl +
δ
575
505
P3
505
δ
P4
E
TlII
+
δ
TlII + TlCl +
TlI + TlCl +
20
δ
490
l + TlCl + Tl2Te3
TlCl + Tl2Te3 + Te
TlI +
δ
δ
TlCl + Tl2Te3+ TlTe
Tl Te Cl
5
80
60
mol %
40
20
Te
2
[Tl Cl]
2
40
mol %
60
80
Tl Te
2
Fig. 4. Polythermal section [Tl Cl]–Tl Te of the phase
Fig. 5. Polythermal section Tl Te Cl–Te of the phase diaꢀ
5 2
gram of the Tl–TlCl–Te system.
2
2
diagram of the Tl–TlCl–Te system.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

446
BABANLY et al.
3
1
M3
T
, K
2
5
4
l2 + l3
l2
l2 + l3 +
δ
3
l2 + l3 + TlCl
717
700
600
500
7
M2
6
l+
δ
l + TlCl
l +
δ
+ TlCl
δ
10
568
P3
α
+
δ
505
P4
E
490
9
8
α
TlCl + Tl2Te3 + Te
Tl Te
2
80
60
mol %
40
20 [TlTeCl]
Fig. 6. Polythermal section Tl Te–[TlTeCl] of the phase diagram of the Tl–TlCl–Te system: Phase regions: (1) l + l , (2) l + l + TlCl,
2 3 2 3
2
(3) l + l + Te, (4) l + TlCl, (5) l + TlCl + Te, (6) l + TlCl + Te, (7) l + Te, (8) TlCl + TlTe + Tl Te , (9) l + TlCl + Tl Te , and
2 3 2 3 2 3
δ
(10) l + + TlTe.
(
α
)
and elemental thallium are degenerate. Noteworꢀ
'
'
), almost touches the Tl–Te
again (
e3M 2M 2P3P4EM 3
thy is an unusual form of the primary crystallization boundary system, after which it narrows again
field of TlCl (Fig. 7). On the left along the side of the
Tl–TlCl system, this field nearly reaches the thallium
*
'
(
).
M3M3e4
A characteristic feature of the Tl–TlCl–Te system
is the presence of wide regions of threeꢀphase melts,
namely, those based on metallic thallium (l1); TlCl
*
*
vertex of the concentration triangle (
), then sigꢀ
e5 E
*
*
**
nificantly narrows (
), and, broadening
E M1 M1 e3
TlCl
D3
e*4
1
m*2
m3'
e3
M3
M2
M*1
CT
C
40
A–Tl5Te2Cl
l1 + l2
l1 + l2 + l3
20
A
CT'
C
'
M2'
P3
M3'
P4
E
CT''
m3
Te
2
Tl
700
e2
m
1 D1
e1D2
P2
m1
'
P1
5
603
20
40
80
4
M*1*
m*2*
e5*
Te, at %
E
*
e6*
Fig. 7. Projection of the liquidus surface of the Tl–TlCl–Te system. Primary crystallization regions: (
1
) TlCl, (2) the
δ
phase
based on Tl Te Cl, ( ) TlTe, ( Tl Te , and ( ) Te. The dashed line is the TlCl–Tl Te quasiꢀbinary section.
3
4)
5
5
2
2
3
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

PHASE EQUILIBRIA IN THE Tl–TlCl–Te SYSTEM
Table 1. Invariant equilibria in the Tl–TlCl–Te system
447
Composition, at %
Te
Point in Fig. 7
D1
Equilibrium
T, K
Tl
Cl
66.67
62.5
50
33.33
37.5
–
–
–
698
723
703
695
493
692
l
Tl2 Te(α)
Tl5 Te3(δ)
TlCl
D1
D2
D3
e1
lD
lD
2
50
3
66
34
–
l
l
l
α
e2
31
69
Tl2Te3 + Te
TlCl + δ
e3
50.5
1.0
48.5
~50
~50
700
575
575
l
l
TlCl + Te
TlII + TlCl
TlII + α
*
e4
*
>99
>99
e5
*
l
l
e6
E
30.5
68.5
57
~1
490
573
508
568
505
TlCl + Tl2Te3 + Te
P1
P2
P3
P4
43
–
l +
l +
l +
l +
δ
TlTe
35
65
–
~1.5
~1
TlTe
δ
Tl2Te3
TlCl + TlTe
43.5
36
55
63
TlTe
TlCl + Tl2Te3
'
69.5(97)
~51(>99)
2.5(48.5)
52(>99)
50(53)
30.5(3)
–
–
681
700
717
690
687
l3
l2
l2
l2
l2
m1 m1
l1 + δ
(
)
*
**
m2 m2
~49(<1)
l1 + TlCl
(
)
95(3)
~1
2.5(48.5)
'
l3 + TlCl
m3 m3
(
)
*
**
47
M1 M1
l1 + TlCl + δ
l3 + TlCl + δ
(
)
'
3(43)
47(4)
M2 M2
(
)
49(13)
3(85)
48(2)
695
708
700
'
l2
l3 + TlCl + Te
Tl5Te2Cl(δ)
l1 + δ
M3 M3
)
(
C
(C
')
51(65)
2.5(30)
2(27;4)
46.5(5)
46(5;1)
l2 + l3
'
"
)
53(68;95)
CT CT;CT
l + l3
2
(
Note: The asterisks mark degenerate points; parenthesized are conjugate points and their corresponding compositions.
Table 2. Equations of the temperature dependence of the emf in circuits of type (1) at 300–430 K
E
, mV =
a
+
bT tSE
(T)
Phase region in Fig. 3
Tl5Te2Cl + TlCl + TlTe
TlCl + TlTe + Tl2Te3
TlCl + Tl2Te3 + Te
420.4 + 0.0124
T
2[2.379/22 + 7.5
×
10–5 – 360.4)2]1/2
(T
431.6 + 0.020
T
2 [3.44/22 + 1.5
2 [2.55/22 + 8.2
×
×
10–4
10–5
(T
– 361.8)2]1/2
T
– 361.8)2]1/2
436.8 + 0.079
T
(
(l2); and
δ
phase, tellurides, and elemental tellurium rium l2 + l3
l1 + δat 700 K (Table 1). The formation of
the threeꢀphase separation field is due to the presence of
(l3). These regions occupy more than 90% of the area
of the concentration triangle of the Tl–TlCl–Te sysꢀ
tem. For the system, there is a wide field of threeꢀ
*
**
'
three wide separation regions (
m1m1, m2 m2
and CC')
,
along all of the sides of the concentration triangle of the
Tl–TlCl–Tl2Te subsystem.
'
"
(Fig. 7), which is surrounded by
phase melts:
CTCTCT
the corresponding twoꢀphase melt fields. The triangle
'
The immiscibility regions CC' and
m3m3
TlCl–Tl2Te and TlCl–Te quasiꢀbinary sections extend
in the
'
"
is characterized by invariant syntectic equilibꢀ
CTCTCT
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

448
BABANLY et al.
Table 3. Standard integral thermodynamic functions for the
Thus, the standard thermodynamic functions of
formation and the standard entropy for the compound
Tl5Te2Cl can be calculated from
compounds Tl5Te2Cl, TlCl, and TlTe
−ΔG2098
−ΔH2098
S2098
ΔZ 0 Tl Te Cl
Compound
(
)
5
2
kJ/mol
J/(mol K)
= 2ΔZTl + ΔZ 0 TlCl + 2ΔZ 0 TlTe ,
(
)
(
)
TlCl [29]
TlTe [28]
Tl5Te2Cl
185.0 0.8 208.3 3.0 111.5 0.2
44.5 0.4 43.9 0.5 115.9 1.6
355.9 1.1 377.1 5.0 474.1 6.8
where
Δ
Z
is
Δ
G,
Δ
H,
or
Δ
S, and
S 0 Tl Te Cl
(
)
5
2
= 2ΔS + 2S 0 Tl + S 0 TlCl + 2S 0 TlTe
(
)
(
)
(
)
Tl
respectively. In the calculations we used both our own
data on and published data on the correspondꢀ
ing thermodynamic characteristics of TlCl [29] and
TlTe [28] (Table 3) and the standard entropy of eleꢀ
mental thallium. Table 3 presents the calculation
results. The errors were found by the error accumulaꢀ
tion method,
deep into the concentration triangle of the TlCl–
Tl2Te–Te subsystem and form a wide continuous band
of twoꢀphase melts: l2 + l3. The eutectic curve originatꢀ
ing at point е3 intersects this twoꢀphase region. As a
ΔZ Tl
,
'
result, the horizontal line
characterized by
M 2M 2
invariant monotectic equilibrium forms (Table 1).
The phases in the immiscibility regions crystallize
by various monotectic and syntectic reactions (Fig. 7,
Table 1). Table 1 presents the types of invariant equiꢀ
libria and the coordinates of the corresponding points
for the Tl–TlCl–Te system.
The emf measurements not only confirmed the
solidꢀphase equilibrium diagram for the TlCl–Tl2Тe–
Тe subsystem but also allowed us to determine the
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found that, within each of the threeꢀphase regions
ТlCl–ТlТе– , ТlCl–ТlТе–Тl2Те3, and ТlCl–Тl2Те3–Те),
Е = a + bT tSE(T) [27]. We
(
δ
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relative partial molar functions of thallium at 298 K:
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ΔHTl = −(40.56 0.61) kJ mol,
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