Phase diagram of the Sb-Se-I system and thermodynamic properties of SbSeI

Article abstract of DOI:10.1016/j.jallcom.2010.06.103

The Sb-Se-I system was investigated by using the DTA and XRD analyses and EMF measurements with an antimony electrode. The T-x diagram of the binary Sb-I system was accurately redefined. A number of polythermal sections and the projection of the liquidus surface were constructed. The fields of the primary crystallization, as well as the types and coordinates of non- and monovariant equilibria were determined. It is shown that the quasi-binary sections Sb ₂Se₃-SbI₃, Sb-SbSeI, SbI₃-Se, and SbSeI-Se triangulate the Sb-Se-I system, leading to five independent subsystems. A broad area of immiscibility, that overlaps a certain part of the antimony primary crystallization field, was found. From the EMF measurements, the partial molar functions of antimony (ΔG?,ΔH?,ΔS?) as well as standard integral thermodynamic functions of SbSeI were calculated. The latter were found to have the following values: ΔGf,2980=-80.121.81kJ/mol; ΔHf,2980=-77.31.8kJ/mol; S2980=155.29.5J/(molK).

Full text of DOI:10.1016/j.jallcom.2010.06.103

Journal of Alloys and Compounds 505 (2010) 450–455
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Phase diagram of the Sb–Se–I system and thermodynamic properties of SbSeI
Z.S. Alieva, S.S. Musaevaa, D.M. Babanlya, A.V. Shevelkovb, M.B. Babanlya,∗
a Baku State University, General and Inorganic Chemistry Department, Azerbaijan
b Moscow Lomonosov State University, Chemistry Department, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 April 2010
Received in revised form 8 June 2010
Accepted 13 June 2010
Available online 25 June 2010
The Sb–Se–I system was investigated by using the DTA and XRD analyses and EMF measurements with
an antimony electrode. The T–x diagram of the binary Sb–I system was accurately redefined. A number
of polythermal sections and the projection of the liquidus surface were constructed. The fields of the
primary crystallization, as well as the types and coordinates of non- and monovariant equilibria were
determined. It is shown that the quasi-binary sections Sb2Se3–SbI3, Sb–SbSeI, SbI3–Se, and SbSeI–Se
triangulate the Sb–Se–I system, leading to five independent subsystems. A broad area of immiscibil-
ity, that overlaps a certain part of the antimony primary crystallization field, was found. From the EMF
Keywords:
Antimony
Phase diagram
Electro-motive force
Thermodynamics
Phase equilibria
¯
¯
¯
measurements, the partial molar functions of antimony (ꢀG, ꢀH, ꢀS) as well as standard integral ther-
modynamic functions of SbSeI were calculated. The latter were found to have the following values:
ꢀGf0,298 = −80.12 1.81 kJ/mol; ꢀHf0,298 = −77.3 1.8 kJ/mol; S2098 = 155.2 9.5 J/(mol K).
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Selenium atoms can be partially replaced by sulfur atoms in the
SbSe double chains thus modifying the properties [5].
Chalcogen-halides of arsenic, antimony and bismuth are
regarded as potential functional materials. Quite a number of
their representatives display promising properties as low-gap
semiconductors, ferroelectrics, piezoelectric, thermoelectrics, pho-
toconductors, and piezoelastics. In particular, SbSI is known as a
compound combining properties of a ferroelectric and semiconduc-
tor. Several other compounds with the same structure type, though
having less pronounces functional properties, are useful as doping
agents in various attempts to enhance the functional properties in
terms of the Curie temperature and dielectric permittivity [1,3,6].
Most of the chalcogen-halides of arsenic, antimony and bismuth
have the 1:1:1 stoichiometry and belong to just three structure
types, one of which is known as the SbSI type [1,2]. SbSeI belongs
to the 1:1:1 compounds and crystallizes in the SbSI structure
type (Fig. 1), space group Pnma, with the unit cell parameters
a = 8.6862(9), b = 10.3927(9), c = 4.1452(3) Å [4]. In its crystal struc-
ture, antimony and selenium form double chains spreading along
the “c” direction of the unit cell. Within these chains, the Sb–Se
bonds range from 2.60 to 2.79 Å. Iodine atoms separate the chains,
with the Sb–I distances being 3.15 Å. Taking into account the
structural features and the values of the interatomic distances,
the semi-ionic description (SbSe)+I− is frequently applied to this
compound, similar to other phases of the SbSI structure type [1].
The ternary Sb–Se–I system was investigated on the basis
of various polythermal sections, among which the quasi-binary
Sb2Se3–SbI3 section was the most studied [6–10]. According to Ref.
[3] this section includes the only compound SbSeI that melts con-
gruently at 721 K, whereas the eutectic compositions were found
to be 69 and 3 mol% Sb2S3 at temperatures 703 and 428 K, respec-
tively. Other authors [7,8] report slightly different data on the
melting points and eutectic compositions. The melting points vary
from one study to another, covering the range of 675–725 K; similar
disagreement can be found for the eutectic composition and tem-
perature. In particular, the degenerate eutectic (443 K) is reported
for the SbI3 side [9]. The SbI3–Se and SbSeI–Se quasi-binary sec-
tions are shown to be of eutectic type. The eutectic compositions
have melting point of 433 and 428, respectively, and have 62 and
74 mol% Se [10].
The data presented above already show that the data on the
phase equlibria in the Sb–Se–I system are far from being com-
plete and self-consistent. In this work, we report the results of the
complex investigation of phase equilibria in the Sb–Se–I system
and of thermodynamic properties of the only ternary compound
in this system, SbSeI. Similar reports on the investigation of the
Sb(Bi)–Te–I systems have been already presented in the literature
[11–14].
2. Experimental
∗
Corresponding author at: Z. Khalilov Str. 23, Baku, AZ 1148, Azerbaijan.
E-mail addresses: shev@inorg.chem.msu.ru (A.V. Shevelkov),
Sb2Se3, SbI3 and SbSeI were synthesized from the elements of high purity grade
in evacuated (∼10−2 Pa) silica ampoules according to the following schemes. Sb2S3
was prepared by a one-step annealing of the stoichiometric mixture of the elements
Babanly mb@rambler.ru (M.B. Babanly).
0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2010.06.103

Z.S. Aliev et al. / Journal of Alloys and Compounds 505 (2010) 450–455
451
Fig. 2. Phase diagram of the Sb–I system.
part of the Sb–Se–I system. That enabled us to build its T–x diagram
(Fig. 2), which shows substantial differences with that reported pre-
viously, especially in the Sb–SbI3 binary subsystem. According to
our data the monotectic temperature is 893 K, and the immiscibil-
ity area ranges from 5 to 70 at.% of I, which is very far from the data
reported in Ref. [15] (442 K and 28–74 at.%, respectively).
The combined analysis of all our experimental data and the
results found in the literature on the equilibria in the Sb–Se and
Se–I system enabled us to construct the self-consistent diagram of
the phase equilibria in the Sb–Se–I system.
Fig. 1. Projections of the crystal structure of SbSeI on [0 0 1] (top) and [1 0 0] (bot-
tom).
at 950 K, which is above the melting points of both Sb (900 K) and Sb2S3 (863 K),
followed by cooling with the furnace. For the preparation of SbI3 and SbSeI, the
specially designed method was used taking into account high volatility of iodine. The
synthesis was performed in the inclined three-zone furnace, with two hot zones kept
at 470 and 750 K, whereas the temperature of the cold zone was about 400 K. After
the main portion of iodine reacted at 470 K, the ampoule was relocated such that the
product melted at 750 K. The melt was stirred at this temperature and then cooled
with the furnace. The quality of the products was checked using differential thermal
analysis (DTA) using the NTR-72 pyrometer equipped with two chromel-alumel
thermocouples and X-ray powder diffraction (XRD) analysis (DRON-2, Cu-K␣).
The alloys in the Sb–Se–I system for the investigation of the properties were
synthesized from the pre-prepared compounds Sb2Se3, SbI3 and SbSeI. A total load
for each sample was 0.5 g. After determining the solidus temperatures, the sintering
temperatures were adjusted to be 20–30 K below the solidus. Thus, the samples
were annealed for 800–1000 h at 670 K within the Sb–Sb2Se3–SbSeI field and at
420 K within the Sb–SbI3–SbSeI and SbI3–Sb2Se3–Se field.
3.1. The section Sb2Se3–SbI3
The DTA results for the selected alloys in this system showed the
coincidence with the results reported in the literature [7]. SbSeI
melts congruently at 725 K, its eutectic crystallizes at 58 mol.%
Sb2Se3 at 716 K, and the eutetic with SbI3 is degenerate (Fig. 3a). The
concentration dependence of EMF of the chains (1) is expressed by
two horizontal lines (Fig. 3b) such that the neglectible homogeniety
range is confirmed for SbSeI.
For the electro-motive force (EMF) measurements, the following concentration
chains were used:
3.2. The quasi-binary section Sb0.25 0.75
I
–Se
(−) Sb (solid)/glycerin + KI + SbI3/(Sb–Se–I) (solid) (+)
(1)
The quasi-binary section Sb0.25 0.75
I
–Se is of the simple eutectic
In the chains of type (1), metallic antimony was the left (negative) electrode,
while equilibrium alloys of the Sb–Se–I system were exploited as right (positive)
electrodes. The saturated glycerin solution of KI with the addition of 0.1 mass% of
SbI3 was used as the electrolyte. The details of the methods for the preparation of
electrolytes and electrodes were previously described in our papers devoted to the
thermodynamic study of the Sb(Bi)–Te–I systems [11–13]. EMF was measured by
the compensation method in the temperature range of 305–400 K, with the accuracy
of the temperature control being 0.2 K. In each experiment the first reading was
performed after approximately 30 h after the start of the experiment, and then the
data were read 4–5 h after reaching the desired temperature, which ensures the
achievement of equilibrium.
type. The eutectic composition lies at 20 at.% Se and 435 K, which
slightly disagrees from the data reported in Ref. [10].
3.3. The polythermal sections Sb–[Se0.5 0.5
I
] and [Sb0.5 0.5
I
]–Se
The polythermal sections Sb–[Se0.5 0.5
I
]
and [Sb0.5 0.5]–Se
I
(Figs. 4 and 5) that pass the stoichiometric composition of SbSeI are
the partially quasi-binary sections, in which one of the components
(expressed in square brackets) which is in fact of heterogeneous
compositions.
3. Results and discussion
Sb–SbSeI is the quasi-binary part of the Sb–[Se0.5I0.5] section. It
is characterized by the monotectic (m3mꢀ3, 865 K) and eutectic (e8,
The inspection of the DTA data for the Sb–SbI3–SbSeI composi-
tional field showed that our results disagree with those reported in
Ref. [15]. Consequently, we undertook the complete study of this
705 K) equilibria. In the compositional range SbSeI–[Se0.5I0.5] this
section intersects the SbI3–SbSeI–Se and SbI3–Se–I triangles, which
are the subsystems of the Sb–Se–I system. The comparative analy-

452
Z.S. Aliev et al. / Journal of Alloys and Compounds 505 (2010) 450–455
Fig. 3. T–x [7] (a) and E–x (b) diagrams of the SbI3–Sb2Se3 system. Our data are shown with black dots.
Fig. 4. Polythermal section Sb–[Se0.5I0.5] of the Sb–Se–I phase diagram.

Z.S. Aliev et al. / Journal of Alloys and Compounds 505 (2010) 450–455
453
Fig. 5. Polythermal section [Sb0.5I0.5]–Se of the Sb–Se–I phase diagram.
sis of Fig. 4 and Table 1 leads to the conclusion that the liquidus of
3.4. The polythermal section Sb0.4Se0.6–I
this area in composed of the primary crystallization curves of SbSeI
and Se. The horizontal line at 465 K corresponds to the join crystal-
lization of these two phases, while those at 432 and 325 K are the
temperatures of the ternary eutectics in the respective subsystems.
The SbSeI–Se part of the Sb0.5I0.5–Se section exhibits the eutec-
tic type of the T–x diagram. The eutectic contains approximately
98 at.% Sb and crystallizes at 492 K, which is far from the data pub-
lished in Ref. [10]. In the Sb0.5I0.5–SbSeI part this section crosses the
Sb–SbI3–SbSeI subsystem. The phase diagram explicitly shows the
existence of the immiscibility area between 0 and 25 at.% Sb.
The polythermal section Sb0.4Se0.6–I that crosses three sub-
systems is shown in Fig. 6. It enables distinguishing primary
crystallization fields of Sb2Se3, SbSeI, SbI3, Se and I2. Also it helps
to precise the positions of the eutectic curves.
3.5. The liquidus surface of the Sb–Se–I system
The liquidus surface of the Sb–Se–I system (Fig. 7) consists of
six fields corresponding to primary crystallization of the elemental
components and compounds Sb2Se3, SbI3 and SbSeI. The system
exhibits the broad immiscibility region (m1m3m2mꢀ2m3ꢀ m1ꢀ ), which
lies within the field of primary crystallization of antimony and over-
laps some 90% of its area.
Table 1
Nonvariant equilibria in the Sb–Se–I system.
The quasi-binary sections (dashed lines in Fig. 7) triangulate
the Sb–Se–I triangle forming five independent subsystems. They
Point on Fig. 7
Equilibrium
Composition, at.%
Se
60
–
33.3
50
T, K
I
Table 2
D1
D2
D3
e1
e2∗
e3∗
e4
e5
e6
e7∗
e8
e9∗
e10
E1
E2∗
E3∗
E4
E5
L ↔ Sb2Se3
–
75
33.3
–
865
445
725
814
493
443
353
330
716
443
705
492
435
698
488
440
432
325
853
895
865
Monovariant equilibria in the Sb–Se–I system.
L ↔ SbI3
L ↔ SbSeI
Curve on Fig. 7
Equilibrium
Temperature range, K
L ↔ Sb + Sb2Se3
L ↔ Se + Sb2Se3
L ↔ SbI3 + Sb
>99
–
e1E1
e6E1
e6E2
e8E1
e8E3
e4E5
e5E5
e10E5
e7E4
L ↔ Sb + Sb2Se3
L ↔ Sb2Se3 + SbSeI
L ↔ Sb2Se3 + SbSeI
L ↔ Sb + SbSeI
L ↔ Sb + SbSeI
L ↔ SbI3 + I2
814–698
716–698
716–488
705–698
705–440
353–325
330–325
435–325
443–432
492–432
435–432
493–488
492–488
443–440
443–440
865–853
895–865
–
–
∼74
L ↔ I2 + SbI3
88
L ↔ Se + I2
50
38
50
28
L ↔ Sb2Se3 + SbSeI
L ↔ SbSeI + SbI3
L ↔ Sb + SbSeI
L ↔ SbSeI + Se
L ↔ SbI3 + Se
73
30
>99
20
30
L ↔ Se + I2
L ↔ SbI3 + Se
60
28
L ↔ SbSeI + SbI3
L ↔ SbSeI + Se
L ↔ SbI3 + Se
L ↔ Sb + Sb2Se3 + SbSeI
L ↔ Sb2Se3 + SbSeI + Se
L ↔ Sb + SbSeI + SbI3
L ↔ SbSeI + SbI3 + Se
L ↔ SbI3 + Se + I2
L1 ↔ L2 + Sb
32
e9E4
>98
*e10E4
*e2E2
*e9E2
*e3E3
*e7E3
m3m1(mꢀ mꢀ )
∼73
59
52
–
L ↔ Sb2Se3 + Se
L ↔ SbSeI + Se
L ↔ Sb + SbI3
19
46
16 (43)
m1(mꢀ )
L ↔ SbSeI + SbI3
L1 ↔ L2 + Sb
1
m2(mꢀ )
L1 ↔ L2 + Sb
–
5 (70)
5 (28)
2
3
1
m3(mꢀ )
L1 ↔ L2 + Sb
5 (28)
m2m3(mꢀ mꢀ )
L1 ↔ L2 + Sb
3
2
3

454
Z.S. Aliev et al. / Journal of Alloys and Compounds 505 (2010) 450–455
Fig. 6. Polythermal section Sb0.4Se0.6–I of the Sb–Se–I phase diagram.
are Sb–Sb2Se3–SbSeI (I), Sb–SbI3–SbSeI (II), SbSeI–SbI3–Se (III),
Sb2Se3–SbSeI–Se (IV), and SbI3–Se–I2 (V). The subsystems (I) and
(II) are characterized by monotectic and eutectic equilibria. The
other subsystems belong to the ternary eutectic type. The E2 and
E3 eutectics are degenerate at the SbI3 side.
Table 1 summarizes the types and coordinates of non-
variant equilibria, including binary border systems, whereas
Table 2 compiles types and temperature intervals for monovariant
equilibria, with the asterisk marking the degenerate equilib-
ria.
Fig. 7. Projection of the liquidus surface of the Sb–Se–I system. Primary crystallization fields are shown: 1, Sb; 2, Sb2Se3; 3, SbSeI; 4, Se; 5, SbI3; 6, I2. Quasi-binary sections
are shown with dashed lines.

Z.S. Aliev et al. / Journal of Alloys and Compounds 505 (2010) 450–455
455
Table 3
¯
where ꢀZSb is the partial thermodynamic function of antimony;
Temperature dependencies of the EMF for the chains of type (1).
ꢀZS0bI is the standard thermodynamic function of formation of
3
Phase area
E, mV = a + bT 2SE()
SbI3. For the calculations according to (4) thermodynamic param-
eters of SbI3 were taken from the literature [19].
Standard entropy of the ternary compound was calculated using
the following equation:
ꢀ
ꢀ
ꢁ
ꢁ
1/2
+ 3, 7 × 10−5(T − 350, 96)2
+ 1, 4 × 10−4(T − 342, 68)2
0,54
26
SbI3 + SbSeI + Se E = 227, 15 + 0, 056
Sb2Se3 + SbSeI + SeE = 236, 70 − 0, 036
2
2
1/2
1,81
26
SS0bSeI = 0.667(ꢀSSb + SS0b) + 0.333SS0bI + SS0e
(5)
3
Table 4
For the calculations, the standard entropies (S2098) of antimony
and selenium were taken from the database [20] as 45,689 0.627
and 42,132 2092 J/mol K, respectively. The results of the calcula-
tions are presented in Table 5. In all cases the estimated standard
deviations were calculated by accumulation of errors. For com-
parison, Table 5 also contains thermodynamic data obtained from
the tensimetric measurements [7,20]. Also, our EMF measure-
ments for the alloys in the Sb2Se3–SbSeI–Se subsystem allowed
us calculating the standard integral thermodynamic functions
of Sb2Se3 (Table 5), which were found to be in a good agree-
ment with the literature data [14,18,19]. Such an agreement
additionally confirms that the data obtained in this research are
self-consistent.
Relative partial thermodynamic functions of antimony in the alloys of the Sb–Se–I
system at 298 K.
¯
¯
¯
Phase area
−ꢀGSb
−ꢀHSb
ꢀSSb
kJ/mol
J/(mol K)
SbI3 + SbSeI + Se
Sb2Se3 + SbSeI + Se
70.58 0.21 65.75 1.23
65.41 0.33 68.52 2.34
16.2 3.5
−10.4 6.9
Table 5
Standard integral thermodynamic functions of compounds in the Sb–Se–I system.
Compounds
−ꢀG2098
−ꢀH2098
S2098
kJ/mol
J/mol K
SbI3 [19]
Sb2Se3
99.2 5.0
100.4 2.8
215.5 1.7
4. Conclusions
130.8 0.7
137.0 4.7
208 14
132.4 8.0 [14]
134.0 6.0 [14]
127.7 1.0 [20]
212.1 4.2 [19]
As the principal conclusion, the application of various experi-
mental methods enabled us constructing the self-consistent phase
diagram of the Sb–Se–I system, which can be the base for growing
single crystals of SbSeI. The partial molar functions of antimony and
the standard integral thermodynamic functions of SbSeI have been
calculated form the reliable experimental data.
SbSeI
80.12 1.81
–
77.3 1.8
93 12 [20]
155.2 9.5
130 7 [20]
3.6. Thermodynamic functions
The EMF measurement results for the chains of type (1) not
only allowed confirming the correctness of all drawn solid-state
equilibria but also served as the basis for the calculation of the
thermodynamic functions for SbSeI.
The analysis showed the linearity of the EMF dependencies upon
temperature for various alloys belonging to the heterogeneous
subsystems SbI3–SbSeI–Se and Sb2Se3–SbSeI–Se. Accordingly, the
linear least-square treatment of the data was performed [16] and
the results were expressed according to the literature recommen-
dations [17] as
References
[1] E.I. Gerzanich, V.M. Fridkin, Ferroelectric materials of type AVBVICVII. M.: Nauka,
1982, p. 114.
[2] A.V. Shevelkov, E.V. Dikarev, R.V. Shpanchenko, B.A. Popovkin, J. Solid State
Chem. 114 (1995) 379–395.
ˇ
[3] A. Audzijonis, R. Sereika, R. Zaltauskas, Solid State Commun. 147 (2008) 88–89.
[4] G.P. Voutsas, P.J. Rentzeperis, Z. Kristallogr. 161 (1982) 111–118.
[5] J. Petzelt, Czech. J. Phys. B 23 (1973) 484–487.
[6] D.P. Belotskiy, V.F. Lapshin, R.F. Boychuk, N.P. Novalkovskiy, Inorg. Mater. 8
(1972) 572–574.
[7] V.A. Dolgikh, B.A. Popovkin, I.N. Odin, A.V. Novoselova, Inorg. Mater. 9 (1973)
919–922.
[8] Yu.I. Rodionov, V.V. Klokman, K.G. Myakishev, Russ. J. Inorg. Chem. 17 (1973)
919–922.
[9] J. Fenner, A. Rabenau, G. Trageser, Adv. Inorg. Radiochem. 23 (1980) 329–
416.
ꢂ
ꢃ
1/2
SE2
n
E = a + bT
t
+ Sb2(T − T)2
(2)
where n is the number of pairs of E and T values; SE and Sb are the
error variances of the EMF readings and b coefficient, respectively;
T is the mean absolute temperature; t is the Student’s test. At the
confidence level of 95% and n ≥ 20, the Student’s test is t ≤ 2 [16].
Using this model (Table 3) and common thermodynamic functions
the partial molar functions of antimony at 298 K were calculated,
and the values are shown in Table 4.
According to the phase diagram of the Sb–Se–I system, the par-
tial molar functions of antimony in the SbI3–SbSeI–Se subsystem
are the thermodynamic functions of the following potential-
forming reaction [14]:
[10] G.I. Chervenyuk, F.V. Niyger, D.P. Belotskiy, N.P. Novalkovskiy, Inorg. Mater. 13
(1977) 989–991.
[11] M.B. Babanly, Z.S. Aliyev, Yu.M. Shikhiyev, Intern. Conf. High Mat. Tech. 2007,
Proceedings of Conference, Kiev, p. 95.
[12] Z.S. Aliyev, M.B. Babanly, Inorg. Mater. 44 (2008) 1203–1207.
[13] M.B. Babanly, J.C. Tedenac, Z.S. Aliev, D.M. Balitsky, J. Alloys Compd. 481 (2009)
349–353.
[14] M.B. Babanly, Yu.A. Yusibov, V.T. Abishov, EMF method for thermodynamics of
the composite semiconductor compounds. BSU, Baku, 1992, 327 pp.
[15] R.F. Rolsten, Iodide Metals and Metal Iodides, John Wiley and Sons, New York,
1961.
[16] K. Doerffel, Statistik in der analytischen Chemie, Grundstoffindustrie, Leipzig,
1990.
[17] A.N. Kornilov, L.B. Stepina, V.A. Sokolov, J. Phys. Chem. 46 (1972) 2975–
2979.
Sb(solid) + 0.5SbI3(solid) + 1.5Se(solid) = 1.5SbSeI(solid)
(3)
[18] O. Kubaschewski, C.B. Alcock, P.J. Spencer, Materials Thermochemistry, Perga-
mon Press, Oxford, 1993.
Using this equation, the integral thermodynamic functions of for-
mation of SbSeI can be calculated as:
[19] V.S. Yungman (Ed.), Database of Thermal Constants of Substances. Digital Ver-
sion, 2006. http://www.chem.msu.su/cgi-bin/tkv.
[20] V.B. Lazarev, J.H. Greenberg, B.A. Popovkin, Curr. Topics Mater. Sci. 1 (1978)
659–695.
ꢀZSbSeI = 0.667ꢀZSb + 0.333ꢀZ0
(4)
0
¯
SbI
3