Phase equilibria and decomposition of solid solutions in the YbTe–SnTe–PbTe system

Article abstract of DOI:10.1134/S0020168517080015

Phase equilibria in the YbTe–SnTe–PbTe system have been studied using differential thermal analysis, X-ray diffraction, scanning electron microscopy, and emf measurements on YbTe concentration cells. We have mapped out a number of vertical sections, the 400-K isothermal section of the YbTe–SnTe–PbTe phase diagram, and projections of its liquidus and solidus surfaces. The results demonstrate that the system is characterized by the formation of a continuous series of high-temperature solid solutions with a cubic structure (NaCl type), which undergo decomposition below ~1050 K. At room temperature, the YbTe solubility in the Sn_1–xPb_xTe solid solution system is ~33–35 mol %, whereas the extent of the YbTe-based solid solution series does not exceed 3 mol %.

Full text of DOI:10.1134/S0020168517080015

ISSN 0020-1685, Inorganic Materials, 2017, Vol. 53, No. 8, pp. 797–803. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © Z.S. Aliev, G.I. Ibadova, S.Z. Imamaliyeva, Yu.A. Yusibov, M.B. Babanly, 2017, published in Neorganicheskie Materialy, 2017, Vol. 53, No. 8, pp. 810–816.
Phase Equilibria and Decomposition of Solid Solutions
in the YbTe–SnTe–PbTe System
Z. S. Aliev , G. I. Ibadova , S. Z. Imamaliyeva , Yu. A. Yusibov , and M. B. Babanly *
Institute of Catalysis and Inorganic Chemistry named after acad. M. Nagiyev, National Academy of Sciences,
a, b
c
a
d
a,
a
H. Javid ave. 113, Baku, AZ1143 Azerbaijan
Azerbaijan State Oil and Industry University, Azadliq ave. 20, Baku, AZ1010 Azerbaijan
b
c
Baku State University, Khalilov str. 23, Baku, AZ1143 Azerbaijan
Ganja State University, H. Aliyev ave. 187, Ganja, AZ2000 Azerbaijan
d
*
e-mail: babanly_mb@rambler.ru
Received July 4, 2016; in final form, January 30, 2017
Abstract⎯ Phase equilibria in the YbTe–SnTe–PbTe system have been studied using differential thermal
analysis, X-ray diffraction, scanning electron microscopy, and emf measurements on YbTe concentration
cells. We have mapped out a number of vertical sections, the 400-K isothermal section of the YbTe–SnTe–
PbTe phase diagram, and projections of its liquidus and solidus surfaces. The results demonstrate that the sys-
tem is characterized by the formation of a continuous series of high-temperature solid solutions with a cubic
structure (NaCl type), which undergo decomposition below ~1050 K. At room temperature, the YbTe solu-
bility in the Sn
Pb Te solid solution system is ~33–35 mol %, whereas the extent of the YbTe-based solid
x
1
– x
solution series does not exceed 3 mol %.
Keywords: tin and lead tellurides, ytterbium telluride, YbTe–SnTe–PbTe system, phase diagram, solid solu-
tions, spinodal decomposition
DOI: 10.1134/S0020168517080015
INTRODUCTION
would be expected to contain wide ranges of substitu-
tional solid solutions.
Lead and tin tellurides and related multicompo-
nent phases are promising materials for the develop-
ment of highly sensitive IR detectors [1] and thermo-
The purpose of this work was to study phase equi-
libria in the YbTe–SnTe–PbTe system and some prop-
erties of solid solutions in this system.
V
2
IV
electric generators [2–4]. In particular, A B Te ,
The constituent tellurides and constituent pseudo-
4
V
4
V
6
binary systems have been the subject of several studies.
IV
IV
IV
V
A B Te , and A B Te (A = Sn, Pb; B = Sb, Bi)
7
10
The binary compounds SnTe, PbTe, and YbTe melt
congruently at 1080, 1197, and 2000 K, respectively,
and have a cubic structure (NaCl type) with lattice
parameters a = 6.315, 6.4602, and 6.345 Å, respec-
tively [3, 10, 11].
ternary tetradymite-like phases offer high thermoelec-
tric performance [2–4] and, as shown recently [5–7],
are three-dimensional topological insulators that have
potential for use in spintronics and topological quan-
tum computers.
As shown earlier [12, 13], the SnTe–YbTe system
contains a continuous series of high-temperature solid
solutions. As the temperature is lowered, the solid
solutions decompose. The extent of the terminal solid
solutions is 35 (SnTe) and 5 mol % (YbTe). These data
differ significantly from what was reported by Aliev et
al. [14, 15]. According to their results, the system con-
tains a ternary compound with the composition
The incorporation of rare-earth elements into the
crystal lattice of these compounds is expected to
improve their properties and impart to them magnetic
properties [8, 9].
In searching for and developing scientific princi-
ples of the preparation of new nonstoichiometric
phases based on known compounds of practical inter-
est, it is reasonable to study phase equilibria in relevant
systems and the thermodynamic properties of inter-
mediate phases. Of particular interest for the fabrica-
tion of materials with tailored properties are multi-
YbSnTe , which melts congruently at 1335 K and has
2
an orthorhombic structure. The SnTe solubility in
YbTe was reported to reach 10 mol % [14].
Reaction of PbTe with YbTe, an isostructural com-
component systems containing compounds that are pound, was studied by Aliev et al. [15] and Erofeev
structural or formula analogs, because such systems et al. [16]. According to Erofeev et al. [16], in samples
797

7
98
ALIEV et al.
1
00
0
YbTe
5
0
9
0% YbTe
0% YbTe
8
60% YbTe
50% YbTe
40% YbTe
20% YbTe
10% YbTe
PbTe
10
20
30
40
50
60
70
2
θ, deg
Fig. 1. X-ray powder diffraction patterns of some PbTe–YbTe alloys quenched after annealing at 1100 K.
annealed between 770 and 800 K YbTe solubility in and held at this temperature for 5–6 h. Next, to best
PbTe reaches 33%. According to Aliev et al. [15], the equilibrate the samples, they were ground into pow-
YbTe–PbTe system contains a ternary compound of der, which was then thoroughly mixed and pressed
composition YbPbTe , which melts congruently at into pellets ~1 g in weight. The pellets were annealed
2
1
350 K and has an orthorhombic structure. The YbTe for 600 h at 1100 K (the samples containing more than
solubility in PbTe reaches 35 mol %.
70 mol % SnTe were annealed at 1050 K).
We prepared two groups of alloys. In the first
group, after annealing the samples were quenched by
dropping the ampules into cold water. In the second
group, the samples were slowly cooled to 400 K and
then held at this temperature for 100 h.
Ibadova et al. [13, 17] investigated the YbTe–
SnTe and YbTe–PbTe systems using emf measure-
ments. They demonstrated the formation of
extended (33–35 mol %) series of SnTe- and PbTe-
based solid solutions and studied their thermody-
namic properties.
The SnTe–PbTe system contains a continuous
series of cubic solid solutions (NaCl structure) and has
a type I phase diagram according to Roseboom’s clas-
sification [3].
The samples were characterized by differential
thermal analysis (DTA) Netzsch 404 F1 Pegasus sys-
tem), X-ray diffraction (Bruker D8 Advance powder
diffractometer), scanning electron microscopy (SEM)
(
Philips-XL30 FEG), and emf measurements in the
temperature range 300–400 K using concentration
cells of the type
EXPERIMENTAL
3+
(
–
)
YbTe
Yb in the alloy)(
In the cells of the type (1), the left-hand electrode
(
s
)
liquid electrolyte, Yb
(1)
The SnTe and PbTe compounds were synthesized
by melting high-purity elemental mixtures in evacu-
×
(
s + .
)( )
–2
ated (~10 Pa) silica ampules at temperatures ~50–
1
00 K above their melting points, followed by slow was of the YbTe compound containing a slight excess
cooling. YbTe was also synthesized from an appropri- (0.01 at %) of tellurium, and the right-hand electrodes
ate elemental mixture, via ceramic processing route at were equilibrium alloys of the system under investiga-
1
300 K under vacuum. Given that ytterbium reacts tion. The procedures utilized to set up electrochemical
with silica at high temperatures, the YbTe compound cells and measure their emf were described in detail
and alloys of the system under study were synthesized elsewhere [18, 19].
in graphitized silica ampules. The resultant com-
X-ray powder diffraction patterns were indexed
using the Topas V3.0 program, supplied with the D8
Advance diffractometer.
pounds were identified by X-ray diffraction.
There is experimental evidence that the prepara-
tion of YbTe–SnTe–PbTe alloys from elemental mix-
tures leads to the formation of Yb–Sn and Yb—Pb
intermetallic phases in the initial stage of synthesis
RESULTS AND DISCUSSION
Given that there are discrepancies in previously
reported data for the YbTe–SnTe system [12–14], we
reexamined phase equilibria in the constituent
pseudobinary system YbTe–PbTe.
[
10]. Trace levels of such phases persist in the alloys
even after prolonged annealing. Because of this, the
alloys in question were prepared by reacting presyn-
thesized binary compounds under vacuum as follows:
First, thoroughly ground mixtures of SnTe, PbTe, and
Pseudobinary system YbTe–PbTe. Figure 1 shows
YbTe of various compositions were heated to ~1300 K X-ray powder diffraction patterns of a number of
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PHASE EQUILIBRIA AND DECOMPOSITION OF SOLID SOLUTIONS
Lattice parameters of solid solutions in the YbTe–SnTe–PbTe system
799
Lattice parameter, Å
slow cooling
Section
Composition
quenching from 1100 К
1
0 mol % PbTe
6.3591(5)
6.3696(5)
6.3936(5)
6.4067(6)
6.4150(6)
6.4381(5)
6.4502(6)
6.4233(4)
6.4245(5)
6.4236(4)
6.4230(6)
6.4243(5)
6.3492(5)
6.3486(5)
6.3495(6)
6.3504(5)
6.3497(5)
2
4
0
0
YbTe–PbTe
50
60
80
90
1
0 mol % Sn Pb Te
6.3511(7)
6.3556(6)
6.3642(7)
6.3723(8)
6.3805(6)
6.3846(5)
6.3889(6)
6.3755(5)
6.3751(6)
6.3748(5)
6.3753(5)
6.3476(6)
6.3470(6)
6.3467(5)
6.3471(5)
0.5
0.5
2
4
0
0
YbTe–Sn Pb Te
60
0.5
0.5
8
9
0
0
Sn Pb Te
0.5
0.5
Yb Sn Te
6.3331(6)
6.3462(7)
6.3603(7)
6.3730(8)
6.3852(7)
6.4105(6)
6.4366(6)
6.3270(6)
6.3435(6)
6.3622(6)
6.3764(7)
6.3471(7)
6.3475(6)
6.3469(6)
6.3476(7)
0.5
0.5
1
0 mol % PbTe
20
Yb Sn Te–PbTe
30
0.5
0.5
40
60
80
The lattice parameters of the slowly cooled YbTe, SnTe, and PbTe samples were 6.3462(3), 6.3160(2), and 6.4604(4) Å, respectively.
YbTe–PbTe alloys quenched after annealing at 1100 K. ternary compound YbPbTe reported by Aliev et al.
2
It is seen that the PbTe and YbTe compounds and [15] was not obtained in this study.
Pb
Yb Te intermediate alloys have qualitatively
1
–
x
x
The lattice parameter of the solid solutions evalu-
ated from their X-ray diffraction patterns varies con-
tinuously from 6.4604 (PbTe) to 6.3462 Å (YbTe), with
similar X-ray diffraction patterns, characteristic of
phases with a cubic lattice. The observed diffraction
angles vary with composition, which is characteristic a slight positive deviation from Vegard’s law (table,
of substitutional solid solutions. The orthorhombic Fig. 2).
6.46
6.42
6.38
6.34
6.46
~
6.424
1
2
3
~
6.349
YbTe
20
40
60
80
PbTe
mol %
Fig. 2. Composition dependences of lattice parameters for samples of the PbTe–YbTe system: (1) quenching from 1100 K, (2, 3)
annealing at 400 K.
INORGANIC MATERIALS Vol. 53 No. 8 2017

8
00
ALIEV et al.
(b)
3
0
0
2
10
2, 3
(a)
2000
L
1600
L + α
α
1200
1200
K
50 μm
(a)
800
α1 + α2
YbTe
20
40
60
mol %
80
PbTe
Fig. 3. (a) Phase diagram of the PbTe–YbTe system and (b)
composition dependence of the emf.
X-ray diffraction data for the 50 mol % PbTe alloy
quenched from 1000 K and the slowly cooled samples
containing 10–60 mol % PbTe demonstrate that
there are diffraction peaks of two cubic phases. This
suggests that the α-phase decomposes into two
mutually saturated solid solutions (α1 and α ).
2
50 μm
(
b)
According to the X-ray powder diffraction data for
the slowly cooled samples, the lattice parameters of
the α - and α -phases are essentially constant in the
Fig. 4. SEM images of the Pb Yb Te alloy: (a) quench-
ing after annealing at 1100 K and (b) annealing at 400 K.
0
.5 0.5
1
2
composition range 3–67 mol % PbTe (table, Fig. 2),
which allows us to evaluate the mutual solubility of the
constituent tellurides: 3 mol % YbTe and 33 mol % ples annealed at 400 K showed that the alloys in the
PbTe, respectively.
composition range 35–95 mol % YbTe were two-
phase. As an example, Fig. 4 shows SEM images of the
Pb Yb Te alloy.
Using the DTA data for the quenched alloys, we
mapped out a partial T–x phase diagram (T < 1400 K)
0.5
0.5
(
Fig. 3a), which is consistent with our X-ray diffrac-
Thus, the present experimental data lead us to con-
tion data. The system has a type I phase diagram clude that the high-temperature α-phase undergoes
according to Roseboom’s classification.
spinodal decomposition below ~1050 K. The assumed
decomposition curve is shown in Fig. 3a by a dashed
line.
According to emf measurements on concentration
cells of the type (1), their emf varies with composition
in the range 0–33 mol % YbTe and is constant at
YbTe–Sn Pb Te and Yb Sn Te–PbTe vertical
0
.5
0.5
0.5
0.5
higher YbTe concentrations (Fig. 3b). This confirms sections. The present experimental data demonstrate
the formation of PbTe-based solid solutions up to that the YbTe– Sn Pb Te section (Fig. 5) is charac-
0.5
0.5
3
3 mol % YbTe in the temperature range of our emf
terized by the formation of a continuous series of solid
solutions, which undergo spinodal decomposition.
measurements.
SEM examination confirmed that the quenched According to the X-ray diffraction data for the slowly
alloys were single-phase, whereas analysis of the sam- cooled samples, the lattice parameters of the α - and
1
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PHASE EQUILIBRIA AND DECOMPOSITION OF SOLID SOLUTIONS
801
(b)
(b)
6
.46
.42
6.387
6.387
~
6.375
6.38
6.36
6.34
6
1
2
3
1
2
3
~
6.347
6.38
.34
600
6
~
6.347
(
a)
(a)
L
1
2000
L
L + α
1
600
1200
800
1200
L + α
α
α
1200
1200
K
α1 + α2
800
α1 + α2
Yb Sn Te 20
40
60
mol %
80
PbTe
0
.5
0.5
YbTe
80
60
40
mol %
20 Sn Pb Te
0.5 0.5
Fig. 5. YbTe–Sn0 Pb Te vertical section: (a) phase dia-
Fig. 6. Yb Sn Te–PbTe vertical section: (a) phase dia-
.5
0.5
0.5 0.5
gram and (b) composition dependences of lattice parame-
gram and (b) composition dependences of lattice parame-
ters; (1–3) see Fig. 2.
ters; (1–3) see Fig. 2.
α -solid solutions are constant in the α + α two- under study is a pseudoternary section of the quater-
2
1
2
phase region (Fig. 5b). This indicates that, even nary system Yb–Sn–Pb–Te and is characterized by
though the vertical section under consideration is not unlimited mutual solubility of its constituent compo-
pseudobinary, the tie lines in the α + α region lie in nents in both liquid and solid states. The liquidus sur-
1
2
face is formed by a single primary crystallization field:
that of the α-phase. We detected no primary crystalli-
zation fields of any other phases, in particular no field
of YbSnTe or YbPbTe , in contrast to what was
its T–x plane.
A somewhat different picture was obtained in the
Yb Sn Te –PbTe section (Fig. 6). Analysis of the X-
0.5
0.5
2
2
ray powder diffraction patterns of the slowly cooled
samples indicates that the high-temperature α-phase
undergoes decomposition in the alloys containing less
than 32 mol % PbTe. In this process, the lattice parame-
ter of the α -phase remains constant (~6.347 Å),
whereas that of the α -phase varies with composition.
Together with the data in Fig. 5, this indicates that, at
room temperature, the tie lines in the α + α two-
phase region have the form of rays issuing from the
YbTe corner of the composition triangle.
reported by Aliev et al. [14, 15].
CONCLUSIONS
2
The pseudoternary system YbTe–SnTe–PbTe is
characterized by unlimited mutual solubility of its
constituent components in both liquid and solid states.
The high-temperature (≥1100 K) solid solutions (α-
phase) have a cubic structure (NaCl type). The com-
position dependences of their lattice parameters have
1
1
2
Subsolidus phase equilibrium diagram. Using the a small positive deviation from Vegard’s law along
present X-ray diffraction and SEM data for the slowly YbTe–Sn Pb Te ray cuts, including the pseudobi-
1
– x
x
cooled samples, we constructed the 400-K subsolidus
phase equilibrium diagram of the YbTe–SnTe–PbTe
system (Fig. 7). It is seen that the system is character-
ized by the formation of a wide continuous series of
nary systems YbTe–SnTe and YbTe–PbTe, and are
essentially linear along the SnTe–PbTe constituent
binary system. At temperatures below ~1050 K, the α-
phase undergoes spinodal decomposition into two
solid solutions (α -phase) along the SnTe–PbTe con-
1
mutually saturated phases: α (solid solutions along
1
stituent binary system, which is connected by tie lines
the SnTe–PbTe constituent binary system) and α2
(YbTe-based solid solutions). In this study, we
to the YbTe-based α -phase.
2
Liquidus and solidus surfaces. The phase equilib- obtained neither YbSnTe nor YbPbTe , in contrast to
2 2
rium diagram in Fig. 8 demonstrates that the system what was previously reported in the literature.
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8
02
ALIEV et al.
YbTe
α2
80
60
α1 + α2
40
20
α1
SnTe
20
40
60
80
PbTe
mol %
Fig. 7. 400-K subsolidus phase equilibrium diagram of the YbTe–SnTe–PbTe system.
YbTe
1800
80
60
40
1
200
20
SnTe
20
40
60
80
PbTe
mol %
Fig. 8. Projections of the liquidus (solid lines) and solidus (dashed lines) surfaces in the YbTe–SnTe–PbTe system.
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803
3
+
3+
3+
ACKNOWLEDGMENTS
Eu , Gd , Tb ) nanomaterials and investigation of
their optical properties, Z. Anorg. Chem., 2011, vol. 637,
pp. 87–93.
This research was supported by the Science Foun-
dation, State Oil Company of Azerbaijan Republic
1
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(
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