Phase equilibria in the Tl2Te-SnTe-Bi2Te3 system

Article abstract of DOI:10.1134/S0036023611120254

phase equilibria in the Tl₂Te-SnTe-Bi₂Te₃ system were studied by differential thermal analysis (DTA), X-ray powder diffraction, and microhardness measurements. Some polythermal sections and isothermal (at 600 and 800 K) se

Full text of DOI:10.1134/S0036023611120254

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 12, pp. 1981–1987. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.B. Babanly, V.P. Zlomanov, F.N. Guseinov, G.B. Dashdyeva, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 12, pp. 2069–2075.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Phase Equilibria in the Tl Te–SnTe–Bi Te System
2
2
3
a
b
a
a
M. B. Babanly , V. P. Zlomanov , F. N. Guseinov , and G. B. Dashdyeva
a
Baku State University, Baku, Azerbaijan
eꢀmail: Babanly_mb@rambler.ru
Moscow State University, Moscow, Russia
b
Received July 7, 2010
Abstract—phase equilibria in the Tl Te–SnTe–Bi Te system were studied by differential thermal analysis
2
2
3
(
DTA), Xꢀray powder diffraction, and microhardness measurements. Some polythermal sections and isoꢀ
thermal (at 600 and 800 K) sections of the phase diagram and a projection of the liquidus surface were conꢀ
structed. It was shown that the system is characterized by the formation of solid solutions with the Tl Te
5
3
structure (
Their homogeneity regions were determined. The liquidus surface consists of the primary crystallization
fields of the ꢀ, , and phases and the compounds SnBi Te4 and SnBi Te7. The liquidus of the phase
1ꢀ, γ'2
δ
) and solid solutions based on SnTe ( 1
γ
), Tl Te (
α
), Bi Te (
β
), and two TlBiTe2 ( 2
γ
and γ'2 ) phases.
2
2
3
β
γ
ꢀ
δ
α
2
4
is degenerate. The primary crystallization fields of phases were determined, and the types and coordinates of
inꢀ and monovariant equilibria were found.
DOI: 10.1134/S0036023611120254
Tellurides of heavy
p elements, in particular, tin, [10–12], and have monoclinic [13], cubic, and rhoꢀ
bismuth, and thallium, are narrowꢀgap semiconducꢀ mobohedral [10, 12] structures, respectively.
tors and are considered to be promising matrix phases
for producing new thermoelectric materials [1, 2]. A
way to increase the efficiency of thermoelectric mateꢀ
rials is to sophisticate their composition and structure
The boundary elements of system A were studied in
a number of works. The Tl Te –SnTe system is characꢀ
2
terized by the formation of the congruently melting (at
8
28 K) ternary compound Tl SnTe with a wide
4 3
[
3]. For the directed search and development of scienꢀ
homogeneity region (12–35 mol % SnTe) [14, 15].
This compound and its base solid solutions based
( phase) crystallize in a tetragonal structure of the
tific principles of production of new multicomponent
telluride phases based on the above elements, it is reaꢀ
sonable to study phase equilibria in relevant systems.
δ
Tl Te type (space group
I4/mcm). The unit cell
5
3
The Tl–Sn–Bi–Te system is interesting because parameters of Tl SnTe are
a
= 8.82 Å, = 13.01 Å,
b
4
3
not only the binary compounds Bi Te3, SnTe, and and
Z
= 4 [16].
2
Tl Te3, but also the ternary compounds Tl BiTe ,
5
9
6
In the Tl Te–Bi Te system, the congruently melting
2
2
3
TlBiTe , SnBi Te4, and SnBi Te7 in this system have
2
2
4
compounds Tl BiTe6 (at 815 K) and TlBiTe2 (at 830 K)
9
good thermoelectric properties [1, 2, 4–6]. In this
context, we studied phase equilibria in this quaternary
system in some concentration planes: Tl Te –
form [17, 18]. Tl BiTe has a tetragonal structure of the
9
6
Tl Te3 type (
a
= 8.855 Å, c = 13.048 Å, and Z = 2) [17,
5
5
3
1
9] and forms a continuous series of solid solutions
Tl SnTe –Tl BiTe [7], SnTe–TlBiTe –Te [8], and
4
3
9
6
2
with Tl Te [17]. TlBiTe has two crystalline phases: the
2
2
Tl Te–SnTe–TlBiTe [9].
Т–х–у
diagrams were conꢀ
2
2
lowꢀtemperature orthorhombic phase at 780 K transꢀ
forms to the highꢀtemperature variableꢀcomposition
disordered phase, which melts with an open maximum
structed for these systems. In the first of these systems,
unlimited solid solutions with a tetragonal structure of
the Tl Te type (
δ
phase) were found to form [7]. In the
second system, there are a ternary eutectic and wide
regions of solid solutions based on SnTe ( 1 phase) and
TlBiTe ( phase) [8]. In the Tl Te–SnTe–TlBiTe2
5
3
[
20].
The results of numerous studies of the SnTe–Bi Te
3
γ
2
system before 1991 were generalized [21]. However,
data on the number and composition of species in sysꢀ
tem Are contradictory. A new detailed investigation of
γ
2
2
2
system, wide fields of
γ
1ꢀ,
γ
2ꢀ, and
δ
solid solutions
were found and their homogeneity regions were deterꢀ
mined [9].
the SnTe–Bi Te3 system was performed [4], and a
2
phase diagram was compiled using all the available
published data. According to this diagram, in the sysꢀ
tem there are three ternary compounds, SnBi Te ,
In this work, we presented the full pattern of phase
equilibria in the Tl Te–SnTe–Bi Te system (system
2
2
3
2
4
A) in the
Т–х–у
coordinates.
SnBi Te7, and SnBi Te10, which have tetradymiteꢀlike
4
6
The binary compounds Tl Te, SnTe, and Bi Te3 structures and melt with decomposition by peritectic
2
2
melt congruently at 698, 1080, and 858 K, respectively reactions at 873, 863, and 855 K, respectively.
1981

1982
BABANLY et al.
Tl Te
2
α
X
Tl BiTe6
9
I–SnBi Te4
2
II–SnBi Te
4
7
δ
80
20
δ
+
γ
2
Tl SnTe
4
3
6
0
40
δ
+
γ
+
γ
1
2
γ
2
TlBiTe2
γ
+
δ
1
γ
+
γ
1
2
40
60
β
+
γ
+
γ
1
2
β
+
γ
2
20
80
γ
+ II
1
γ
1
γ
+ I
β
+
γ
1
1
γ
+ I + II
1
SnTe
20
40
60
80
Bi Te3
2
mol %
Fig. 1. Isothermal section of the T–x–y diagram of system A at 600 K.
SnBi Te forms a continuous series of solid solutions
6
10
with Bi Te3
.
2
L + I
T, K
L + γ1 + II
L
P2
EXPERIMENTAL
8
50
28
The initial binary and ternary compounds for
studying system A were synthesized by alloying the
corresponding elemental components of high purity in
8
L + I + II
–
2
L + γ1
evacuated (
∼
10 Pa) and sealed quartz ampoules at
γ
L + 1
+ II
L +
δ
7
50 K (Tl Te), 1150 K (SnTe), and 900 K (TlBiTe2,
2
8
00
50
Bi Te , Tl SnTe3, and Tl BiTe6), which somewhat
2
3
4
9
L + γ1
+
δ
exceeded their melting points, with subsequent slow
cooling. The individuality of the synthesized comꢀ
pounds was checked by differential thermal analysis
(DTA) and Xꢀray powder diffraction.
γ
1
δ
7
Alloys in system A were also prepared by alloying
the initial tellurides in evacuated quartz ampoules.
Alloys in the sections Tl SnTe –SnBi Te , Tl SnTe –
γ
+
δ
1
γ
1
+ II
4
3
4
7
4
3
Bi Te , SnBi Te –TlBiTe2, and Tl Te–SnBi Te and
2
3
4
7
2
4
7
alloys outside these sections were prepared. To bring
the alloys to a state that would be maximally close to
the equilibrium state, samples were subjected to long
thermal annealing. For this purpose, 1ꢀg cast nonhoꢀ
mogenized alloy samples were ground to powder, careꢀ
fully stirred, and compacted into pellets, after which
they were annealed at 600 or 800 K for 1000 h. The
1
.5Tl SnTe 20
4
40
60
mol %
80
SnBi Te
4 7
3
Fig. 2. Polythermal section 1.5Tl SnTe –SnBi Te of the
phase diagram of system A.
4
3
4
7
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

PHASE EQUILIBRIA
1983
T, K
L
850
800
750
8
28
L +
β
L + γ'2
L +
δ
e4
γ
L + 1
E2
'2
L +
β
+
γ'2
γ
1
+
+
γ
L + γ1
+
γ
'2
δ
E1
β
+ γ'2
β
γ
+
γ'2
1
γ
L + 1
+
δ
δ
γ
+
γ
1
2
β
γ
+
γ
+
1
2
β
+
γ
1
β
+
γ
+
γ
γ
+
δ
1
2
1
20
40
60
80
2
Bi Te3
1/3Tl SnTe
4
3
mol %
Fig. 3. Polythermal section 1/3Tl SnTe –Bi Te of the phase diagram of system A.
4
3
2
3
alloys annealed at 600 K were cooled in a switchedꢀoff
The phase equilibria were investigated by DTA
furnace, and the alloys annealed at 800 K were (HTPꢀ72 pyrometer, Chromel/Alumel thermocouꢀ
quenched in cold water.
ples), Xꢀray powder diffraction (DRONꢀ2 diffractoꢀ
Table 1. Invariant equilibria in the Tl Te–SnTe–Bi Te system
2
2
3
Composition, mol %
Point in Fig. 6
Equilibrium
T, K
Tl Te
Bi Te
2
2
3
D1
D2
L
L
Tl SnTe3
66.67
90
–
828
815
4
Tl BiTe
10
9
6
*
D
L
L
L
L
L
L
L
γ'2
50
50
–
825–830
778
3
e1
e2
e3
e4
γ
1
+
δ
51
γ'2
+
δ
74
26
70
42
23
763
γ
'
+
β
30
815
2
γ
γ
+
γ2
'
42
815
1
1
E1
E2
P1
P2
P3
P4
P5
+
′
2
+
δ
65.5
755
γ
β
+
γ
1
+
γ'2
18
–
–
–
5
65
65
74
805
873
863
853
840
820
L + γ1
SnBi Te4
2
L + SnBi Te
SnBi Te
2
4
7
L + SnBi Te
β
78.5
70
4
7
L + SnBi Te4
γ
1
+ SnBi Te
4 7
2
L + SnBi Te
γ
1
+
β
11
69
4
7
*
Note: For explanation of the point D , see the text.
3
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

1984
BABANLY et al.
the
beyond the SnTe–TlBiTe2 and Tl SnTe –Tl BiTe
6
γ
1,
γ
2, and
δ
homogeneity regions significantly go
T, K
4
3
9
quasiꢀbinary sections on both sides. The homogeneity
region of the phase occupies a considerable (>90%)
part of the Tl Te–Tl SnTe –Tl BiTe elementary triꢀ
L + I
δ
L
γ
L + I + 1
2
4
3
9
6
γ
P2
50 P4
angle. The unit cell parameters of the
vary almost linearly along the sections SnTe–TlBiTe2
= 6.327–6.465 and Tl SnTe –Tl BiTe (
8.821–8.854 = 13.01–13.05
There are wide twoꢀphase regions of the
1ꢀ and phases
δ
8
8
8
L + γ1
L +
γ
'1
830
(
a
Å
)
4
3
9
a =
6
L +
β
+
γ
γ
L + 1
+ II
P5
1
Å
,
c
Å).
γ
1
phase
both with
γ2ꢀ and
δ
solid solutions, and with all the
00
50
E2
γ
'2
L +
β
+ γ'2
phases of the SnTe–Bi Te3 boundary system. This gives
2
rise to three phase regions in the system:
γ
+
+ SnBi Te +
1 2 4
γ
+ δ,
1
2
β
+
γ
+
γ'2
β
+ γ'2
1
β
+
γ
+
γ
2,
β
+
γ
+ SnBi Te , and
γ
1
1
4
7
β
+
γ
1
E
*
SnBi Te7.
4
γ
In Fig. 1 two regions near Tl Te
identified. Alloys in the
,
α
and
region consist of a monoꢀ
clinic phase with the Tl Te structure [13]. An
Х, have been
2
2
α
β
γ
+
γ
+ γ'2
1
β
+
γ
2
α
+
δ
2
β
+
γ
+
1
2
twoꢀphase region was not detected. Therefore, we
assume that there is morphotropic phase transition
α ↔ δ in the system. Equilibrium alloys in the region
1
/3SnBi Te 20
4
40
60
80
TlBiTe2
7
Х
contain not only the
αꢀ
and
δ
phases, but also a
mol %
metallic phase based on thallium. This rare phenomeꢀ
non, which was also observed in the Tl Te–SnTe
boundary system, was explained previously [14, 15].
2
Fig. 4. Polythermal section SnBi Te –TlBiTe of the
4
7
2
phase diagram of system A.
To revise the primary crystallization regions of
phases and the coordinates of inꢀ and monovariant
meter, Cu
K radiation), and microhardness measureꢀ equilibria, we constructed a number of polythermal
α
ments (PMTꢀ3 microhardness meter, load 20 g).
sections of the Т–х–у diagram of the system under
investigation (Figs. 2–5). These sections are conveꢀ
niently considered together with Figs. 1–7 and Tables 1
and 2.
RESULTS AND DISCUSSION
The experimental results and published data on the
Section Tl SnTe –SnBi Te (Fig. 2) in the subsoliꢀ
4
3
γ
4
7
γ
boundary systems and the Tl Te–SnTe–TlBiTe2 sysꢀ
2
dus intersects the
+
δ
and
+ SnBi Te twoꢀphase
1
1 4 7
tem enabled us to determine the total selfꢀconsistent
pattern of phase equilibria in system A (Figs. 1–7;
Tables 1, 2).
regions, which are separated by the region of the
γ
1
phase. The liquidus consists of three branches correꢀ
sponding to the primary crystallization of and
δꢀ
γ
1
Isothermal section of the phase diagram at 600 K phases, and the compound SnBi Te4. The horizontal
2
(
Fig. 1). A characteristic feature of this system is that line at 840 K characterizes the invariant peritectic
Table 2. Monovariant equilibria in the Tl Te–SnTe–Bi Te system
2
2
3
Curve in Fig. 6
Equilibrium
Temperature range, K
e1E1
e E
L
L
L
γ
1+
δ
778–755
763–755
815–755
815–805
815–805
873–840
863–840
853–830
830–820
840–820
820–805
γ'2
+
δ
2
1
1
2
2
e E
γ
1
+
γ'2
4
e E
L
L
γ'2
+
β
3
e E
γ
1
+
γ'2
4
P1P4
P2P4
P3K
L + γ1
SnBi Te
2
4
L + SnBi Te
SnBi Te
2
4
7
4
7
L + SnBi Te
β
4
KP5
L
L
L
SnBi Te7 +
4
β
P4P5
P5E2
γ
+ SnBi Te
4 7
1
1
γ
+
β
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

PHASE EQUILIBRIA
1985
T, K
900
850
800
750
700
650
L + I
L +
γ
+ I
1
P
L
P4
L +
L +
γ
P5
γ
+ II
1
1
e4
L + I + II
L +
δ
L +
γ
+
β
E2
1
L +
γ
+
+
γ
'2
1
L +
γ
+
δ
1
γ
γ
'2
1
E1
γ
+
γ
+
δ
1
2
L +
α
β
+
γ
+ II
1
α
δ
γ
1
+
δ
γ
1
+
γ
+
2
δ
β
+
γ
1
Tl Te
2
80
60
40
20
1/3SnBi Te
4 7
mol %
Fig. 5. Polythermal section Tl Te–1/3SnBi Te of the phase diagram of system A.
2
4
7
Tl Te
2
D2
80
2
e2
D1
E1
6
0
40
e1
D
*
3
e4
40
60
3
e3
1
20
80
E2
4
P5
P4
5
K
6
SnTe
P1
P2
P
380
min
2
Bi Te3
20
40
60
mol %
Fig. 6. Liquidus surface projection for system A. The primary crystallization fields: (
1)
γ
1, (2)
δ
, (3
)
γ '2 , (
4
) , (5) SnBi Te , and
β
4 7
(6
) SnBi Te . The dashed lines are substantially quasiꢀbinary sections.
2
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

1986
BABANLY et al.
Tl Te
2
L
Tl BiTe6
9
I–SnBi
II–SnBi Te
Te
2 4
4
7
80
20
δ
L
+δ
Tl SnTe
4
3
L
60
40
L
+ '2
γ
TiBiTe2
60
L
+
γ
1
40
β
+
γ
+ '2
γ
1
β
+ γ'
2
20
80
γ
+ II
1
γ
+
β
1
γ
1
γ
+ I
1
I
II
SnTe
20
40
60
Bi Te , mol %
80
β
Bi Te3
2
2
3
Fig. 7. Isothermal section of the T–x–y diagram of system A at 800 K.
equilibrium Р4 (Table 1; Fig. 7). Comparison of Fig. 2 crystallization regions of the
α
phase and the comꢀ
with Fig. 6 shows that, in this section, there are also pound SnBi Te4 do not exceed 1 and 4 mol %, respecꢀ
2
monovariant equilibria along the e1E1
curves (Table 2).
,
e4E2, and P1P4 tively. Numerous inꢀ and monovariant equilibria in
this section can be identified using Fig. 6 and Tables 1
and 2.
Section Tl SnTe –Bi Te (Fig. 3) below the solidus
4
3
2
3
The liquidus surface of system A (Fig. 6) consists of
intersects a number of twoꢀ and three phase regions:
six fields corresponding to the primary crystallization
γ
1
+
δ,
γ
1
+
γ
2
+
δ,
γ
1
+
γ
2, 2, and 2. The
β
+ +
γ
γ
β
+
γ
1
of
γ
1,
δ,
γ' ,
β
, SnBi Te7, and SnBi Te4. These fields are
thermal events at 750 K characterize the polymorphic
2
4 2
transition γ2 ↔ γ' . The liquidus comprises the primary
separated by 11 eutectic and peritectic curves and six
invariant equilibrium points.
The coordinates of the invariant points and their
corresponding equilibria are presented in Table 1, and
the temperature ranges of monovariant equilibria are
given in Table 2.
We confirmed the data [20] on a deviation of the
dystectic maximum of the γ'2 phase from the stoichioꢀ
metric composition TlBiTe2 toward BiTe. Therefore, the
2
crystallization curves of the
In regions below the liquidus, there are monovariant
equilibria e1E1 e4E1 e4E2, and e3E2 (Table 2; Fig. 6)
δ
ꢀ
,
γ
1ꢀ, γ'2
ꢀ
, and
β
phases.
,
,
and fourꢀphase eutectic equilibria E2 and E3 (Table 1).
Section SnBi Te –TlBiTe (Fig. 4) presents the
4
7
2
invariant peritectic (P4
,
P5), eutectic E2 (Table 1), and
eutectoid (γ'2 ↔β
+ γ2) equilibria and P1P4, P4P5, P5E2,
and e3E monovariant equilibria (Table 2). Below the
solidus, this section intersects the phase regions of
*
2
point
D
3
(Fig. 6) is actually somewhat (by 3–4 mol %)
deviated from the true dystectic point, and the γ'2
phase of this composition crystallizes within a narrow
temperature range, rather than at a constant temperaꢀ
ture (Table 1).
SnBi Te +
β
+
γ
1,
β
+
γ
1,
β
+
γ
1+
γ
2,
β
+
γ
2, and 2.
γ
4
7
Section Tl Te–SnBi Te (Fig. 5) is characterized by
2
4
7
a complex pattern of phase equilibria and shows most
of the inꢀ and monovariant equilibria in system A. In
Isothermal section of the phase diagram of system A
the composition range >65 mol % Tl Te, the first phase (Fig. 7) is constructed based on the results of studying
2
to crystallize from melt is the
δ
phase, and in the range the alloys quenched after annealing at 800 K with the
4
–65 mol % Tl Te, this is the
γ
phase. The primary consideration of the corresponding isotherm in Fig. 6.
2
1
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

PHASE EQUILIBRIA
1987
The directions of the tie lines in the L + 1
γ
, L + γ'2, and 10. Physical and Chemical Properties of Semiconductor.
Handbook, Ed. by A. V. Novoselova and V. B. Lazarev
Nauka, Moscow, 1976) [in Russian].
L + twoꢀphase regions allow one to choose the comꢀ
δ
(
positions of alloys for growing single crystals of the
corresponding solid solutions of given compositions
by directional solidification.
1
1. M. M. Asadov, M. B. Babanly, and A. A. Kuliev, Izv.
Akad. Nauk SSSR, Neorg. Mater. 13 (8), 1407 (1977).
1
2. N. Kh. Abrikosov and L. E. Shelimova, Semiconducting
Materials Based on IV–VI Compound (Nauka, Moscow,
1975) [in Russian].
REFERENCES
1
3. R. Cerny, J. Joubert, Y. Filinchuk, and Y. Feutelais,
1
. A. V. Shevel’kov, Usp. Khim. 77 (1), 3 (2008).
Acta. Crystallogr., Sect. C 58 (5), 163 (2002).
2. L. Shelimova, O. G. Karpinskii, and V. S. Zemskov,
Perspektivn. Mater., No. 5, 23 (2000).
1
4. Gotuk Ali Alarik, M. B. Babanly, and A. A. Kuliev,
Uch. Zap. MV SSO Azerb. SSR., Ser Khim. Nauk,
No. 3, 30 (1978).
3
4
5
6
7
8
. A. F. Ioffe, Semiconductor Thermoelements (Akad.
Nauk SSSR, Moscow, 1960) [in Russian].
1
1
1
1
5. Gotuk Ali Alarik, M. B. Babanly, and A. A. Kuliev, Izv.
. O. G. Karpinskii, L. E. Shelimova, M. A. Kretova,
Akad. Nauk SSSR, Neorg. Mater. 15 (8), 1356 (1979).
et al., Neorg. Mater. 39 (3), 305 (2003).
6. S. Bradtmöller and P. Böttcher, Z. Anorg. Allg. Chem.
. B. Wolfing, C. Kloc, J. Teubner, and E. Bucher, Phys.
619, 1155 (1993).
Rev. Lett. 36 (19), 4350 (2001).
. Sh. Yamanaka, A. Kosuka, and K. Korosaki, J. Alloy
Compd. 352, 275 (2003).
7. M. B. Babanly, A. Akhmad’yar, and A. A. Kuliev,
Zh. Neorg. Khim. 30 (9), 2356 (1985).
8. W. Gawel, E. Zaleska, and J. Terpilowski, J. Therm.
. G. B. Dashdieva, D. M. Babanly, and F. N. Guseinov,
Khim. Problemy (Baku), No. 4, 704 (2006).
Anal. 35, 59 (1989).
19. T. Doert and P. Böttcher, Z. Kristallogr. 209, 95 (1994).
. F. N. Guseinov, G. B. Dashdieva, and M. B. Babanly, 20. A. Pradel, J. C. Tedenac, G. Brun, and M. Maurin,
AzTU Elmi Yasyarlyari. Fund. Elmlyar 7(25) (1), 31
J. Solid Stat. Chem (1), 99 (1982).
2008).
5
(
2
1. L. E. Shelimova, V. N. Tomashik, and V. I. Grytsiv,
Phase Diagrams in Materials Science of Semiconductors.
Handbook (Nauka, Moscow, 1991) [in Russian].
9. M. B. Babanly, G. B. Dashdieva, and F. N. Guseinov,
Neorg. Mater. 44 (10), 1187 (2008).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011