Phase diagram and thermodynamic properties of the system As-Te-I

Article abstract of DOI:10.1016/j.jallcom.2010.09.198

The As-Te-I system has been investigated primarily by means of DTA, XRD analyses and EMF measurements with an arsenic electrode. The T-x diagram of the binary As-I system was accurately redefined and its phase diagram was constructed. A projection of the liquidus surface, an isothermal section at 300 K, and a series of polythermal sections of the phase diagram were constructed. The previously reported ternary compounds As₅Te₇I, As ₄Te₅I₂ and As₈Te₇I ₅ were confirmed to be equilibrium phases; the positions of phase areas with their participation were established. Areas of primary crystallization of phases, types and coordinates of the invariant equilibria on the T-x-y diagram were determined. From the X-ray powder diffraction (XRD) analysis, the crystallographic parameters of As₄Te₅I ₂ and As₈Te₇I₅ were determined. From the EMF measurements, the partial molar functions of arsenic (ΔG?,ΔH?,ΔS?) as well as standard integral thermodynamic functions of ternary compounds were calculated.

Full text of DOI:10.1016/j.jallcom.2010.09.198

Journal of Alloys and Compounds 509 (2011) 602–608
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Phase diagram and thermodynamic properties of the system As–Te–I
a
a
a,∗
b,∗∗
, I.R. Amiraslanovc
Z.S. Aliev , D.M. Babanly , M.B. Babanly , A.V. Shevelkov
a
Baku State University, General and Inorganic Chemistry Department, Baku, Azerbaijan
Moscow Lomonosov State University, Chemistry Department, Leninskie Gory 1-3, Moscow 119991, Russia
Institute of Physics, Azerbaijan National Academy of Science, Baku, Azerbaijan
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 July 2010
Received in revised form
The As–Te–I system has been investigated primarily by means of DTA, XRD analyses and EMF measure-
ments with an arsenic electrode. The T–x diagram of the binary As–I system was accurately redefined and
its phase diagram was constructed. A projection of the liquidus surface, an isothermal section at 300 K,
and a series of polythermal sections of the phase diagram were constructed. The previously reported
ternary compounds As5Te7I, As4Te5I2 and As8Te7I5 were confirmed to be equilibrium phases; the posi-
tions of phase areas with their participation were established. Areas of primary crystallization of phases,
types and coordinates of the invariant equilibria on the T–x–y diagram were determined. From the X-ray
powder diffraction (XRD) analysis, the crystallographic parameters of As4Te5I2 and As8Te7I5 were deter-
2
2 September 2010
Accepted 28 September 2010
Available online 8 October 2010
Keywords:
Phase diagrams
Arsenic
Thermodynamic properties
Electro-motive force
¯
¯
¯
mined. From the EMF measurements, the partial molar functions of arsenic (ꢀG, ꢀH, ꢀS) as well as
standard integral thermodynamic functions of ternary compounds were calculated.
© 2010 Elsevier B.V. All rights reserved.
1
. Introduction
For many years there has been an interest in the vast family
results. It was established that this section is quasi-binary and char-
acterized by monotectic and eutectic equilibriums. The eutectic
composition has the melting point of 553 K at 87.5 mol.% As Te5I .
4
2
of arsenic, antimony and bismuth chalcogen–halides. These com-
pounds exhibit properties that make them a good base for creating
various functional materials, including ferro- and piezoelectrics,
piezoelastics, thermoelectrics, and photoconductors [1–3]. The
preparative routes to these compounds, and especially to their large
crystals, are not always straightforward; in many cases they require
the knowledge of the respective phase diagrams.
The monotectic temperature is achieved at 583 K, and the immis-
cibility area ranges from 2 to 70 mol.% As Te5I . The projection of
4
2
the liquidus surface of subsystem As–As Te –AsI consists of five
2
3
3
areas of the primary crystallization fields (As, As Te , AsI , As Te5I
2
3
3
4
2
and As Te7I5). The area of the primary crystallization of arsenic
8
occupies up to 95% of the As–As Te –AsI triangle area. There is a
2
3
3
wide immiscibility area in the subsystem. The comparative analy-
The ternary As–Te–I system was investigated along the poly-
thermal sections As Te –AsI , AsI –TeI , and in the composition
sis of the system As–As Te5I2 and the liquidus surface shows that
4
the borders of the immiscibility area in the subsystem are shown
incorrectly. Thus, according to [6], the immiscibility area on the
liquidus surface ranges from 21 to 95 mol.% As Te5I . Also, eutec-
2
3
3
3
4
area As–As Te –AsI [4–6]. The AsI –TeI4 system was reported to
2
3
3
3
be of a simple eutectic type [4]. The eutectic composition has the
4
2
melting point of 405 K at 5 mol.% TeI . According to the literature
tic and monotectic equilibriums of the system As–As Te5I2 are not
4
4
[
5], the section As Te –AsI includes the only compound As Te5I2
shown on the projection of the liquidus surface.
2
3
3
4
that melts congruently at 563 K, whereas the eutectic composi-
tions were found to be 23 and 92 mol.% AsI3 at the temperatures
Three phases are reported to exist in the system As–Te–I;
they are As Te5I , As Te7I5, and As5Te7I. All three compounds
4
2
8
5
53 and 403 K, respectively. In the system there are solid solubil-
possess different structures. The crystal structure of As5Te7I is
ity ranges on the base of both As Te3 and As Te5I . According to
well-explored [7,8]. It crystallizes monoclinically with the follow-
2
4
2
the literature [6], the composition area As–As Te –AsI of the sys-
ing lattice parameters: a = 14.5520 A˚ , b = 4.0335 A˚ , c = 13.8440 A˚ ,
2
3
3
◦
tem As–Te–I contains the ternary compounds As Te7I5. The phase
ˇ = 112 , z = 2, and the space group either Cm or C2/m, depend-
8
diagram of the system As–As Te5I2 was constructed from the DTA
ing on whether the Te/I joint occupancy of same crystallographic
positions allowed or not. In this structure, the As–Te–I slabs run
along the b axis in such a way that the As atoms inside the slab
are surrounded by six Te and/or I atoms while the As atoms at
the sides of the slab are three-coordinated. This structure forms
its own structure type, though some similarity to the crystal struc-
ture of Bi11Se9Cl12 can be noticed [9,10]. Less is known about the
4
∗
Corresponding author at: Z. Khalilov Str. 23, Baku, AZ 1148, Azerbaijan.
Corresponding author.
E-mail addresses: babanly mb@rambler.ru (M.B. Babanly),
∗
∗
shev@inorg.chem.msu.ru (A.V. Shevelkov).
0
925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2010.09.198

Z.S. Aliev et al. / Journal of Alloys and Compounds 509 (2011) 602–608
603
crystal structure of two other compounds. As Te5I2 is reported to
4
have the face-centered cubic structure with the unit cell parameter
of 5.7825 A˚ [6]. Arguably, it crystallizes with the defect zinc-blend
type. No crystallographic data are available for As Te7I5 save for
8
the XRD pattern [6].
In our previous report some results on the subsystem
As Te –AsI –Te [11] were presented. The phase diagrams of the
2
3
3
quasi-binary systems As Te –AsI and AsI3-–Te were constructed.
2
3
3
It was shown that below the solidus this subsystem consists of
three three-phase areas AsI –As Te5I –Te, As Te5I –As5Te7I–Te
3
4
2
4
2
and As Te –As5Te7I–Te.
2
3
In this work, we report the results of the complete investigation
of phase equilibriums in the As–Te–I system and of thermodynamic
properties of the three ternary compounds in this system, As5Te7I,
As Te5I , and As Te7I5. Similar reports on the investigation of the
4
2
8
Sb(Bi)–Te–I systems have been already presented in the literature
12–14].
[
2.
Experimental
As2Te3, AsI3, TeI4, TeI, TeI4, As5Te7I, As4Te5I2, and As8Te7I5 were synthesized
Fig. 1. Phase diagram of the As–I system.
−2
from elements of high purity grade in evacuated (∼10 Pa) sealed silica ampoules
according to the following schemes. As2Te3 was prepared by a one-step annealing
of the stoichiometric mixture of the elements at 700 K, which is above the melting
point of As2Te3 (654 K), followed by cooling with the furnace. For the preparation of
AsI3, TeI4, TeI, TeI4, As5Te7I, As4Te5I2, and As8Te7I5, 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 410–630 K, whereas
the temperature of the cold zone was about 400 K. After the main portion of iodine
reacted at about 470 K, the ampoules were relocated such that the products melted
at 550–630 K. The melts were stirred at these temperatures and then cooled with
the furnace.
Most of the samples, having masses of 0.5 g, were pre-prepared from the
above mentioned binary and ternary compounds. After determining the solidus
temperatures, the sintering temperatures were adjusted to be 20–30 K below the
solidus. Subsequently, they were annealed for 800–1000 h at 500 K within the
As–As2Te3–As8Te7I5 field and at 380 K for the other fields.
the monotectic temperature (408 K), the immiscibility area ranges
from 25 to 69.5 at.% of I.
According to our data, the monotectic equilibrium is not
observed, whereas As2I4 decomposes by the peritectic reaction at
08 K. On the DTA curves of the As–AsI3 samples weak peaks at
95 K adjoining peaks at 408 K were observed. It is possible that
these peaks appear according to the solid state phase transition of
As I (Fig. 1). The eutectic composition between AsI and As I has
4
3
2
4
3
2 4
the melting point of 398 K at 70 at.% I.
The combined analysis of all our experimental data and the
results found in the literature on the equilibria in the As–Te and Te–I
system [16] enabled us to construct the self-consistent diagram of
the phase equilibria in the As–Te–I system.
X-ray powder diffraction and differential thermal analysis were used to analyze
the samples. The XRD analysis was performed on a Bruker D8 ADVANCE diffrac-
tometer with Cu-K␣ radiation. The lattice parameters were refined using the Topas
V3.0 software. For the DTA measurements, the NTR-72 pyrometer equipped with
two chromel–alumel thermocouples was used.
3
.1.2. The quasi-binary sections
For the electro-motive force (EMF) measurements, the following concentration
chains were used:
The section As2Te3–AsI3 is shown in Fig. 2. The compounds
As Te I and As Te I melt incongruently at 620 and 605 K, respec-
5
7
5 2
4
(−) As(solid)/glycerin + KI + AsI3/(As–Te–I)(solid)(+)
(1)
In the chains of type (1), “metallic” arsenic was the left (negative) electrode,
while equilibrium alloys of the As–Te–I system were exploited as right (positive)
electrodes. Saturated glycerin solution of KI with the addition of 0.1 mass% of AsI3
was used as the electrolyte. EMF was measured by the compensation method in
the temperature range of 300–400 K, with the accuracy of the temperature control
being 0.2 K. In each experiment the first reading was performed after approximately
3
0 h after the start of the experiment, and then 4–5 h after reaching the desired
temperature, which ensures the achievement of equilibrium.
3
3
3
. Results and discussion
.1. Phase relationship in the system As–Te–I
.1.1. The As–I phase diagram
Inspection of the DTA data for the As–As I –As I7I5 composi-
2
4
8
tional field showed that our results disagree with the As–I phase
diagram reported in the literature [15]. Consequently, we under-
took the complete study of this part of the As–Te–I system. That
enabled us to build its T–x diagram (Fig. 1), which shows substan-
tial differences from that reported previously [15], especially in the
As–AsI subsystem. According to Ref. 15, the As–I system is charac-
3
terized by monotectic and eutectic equilibriums. Two compounds
were reported to be present in this system, AsI3 that melts con-
gruently at 414 K and As2I4 forming by the syntactic reaction at
4
08 K, whereas the eutectic compositions were found to be 20, 70
and 86 at.% I at temperatures 393, 394 and 346 K, respectively. At
Fig. 2. T–x (bottom) and E–x (top) diagrams of the AsI3–As2Te3 system.

6
04
Z.S. Aliev et al. / Journal of Alloys and Compounds 509 (2011) 602–608
Fig. 3. Phase diagram of the As0.25I0.75–Te system.
tively. Solid solubility based on As Te is observed. At the peritectic
2
3
temperature this area ranges from 0 to 8 mol.% of AsI . We did
3
not observe appreciable solid solubility based on As Te5I . This
4
2
Fig. 4. Isothermal section at 300 K of the phase diagram of the system As–Te–I. The
EMF values (mV) of the concentration chains of type (1) in some phase areas are
indicated in parenthesis.
ꢀ
system is characterized by the monotectic (m m , 570 K) and
1
1
eutectic (degenerate, e7, 412 K) equilibriums in the As Te5I –AsI
4
2
3
subsystem. At the monotectic temperature, the immiscibility field
ranges from 45 to 80 mol.% of AsI . These results do not agree with
3
those reported elsewhere [5]. The isothermal curve of E–x at 300 K
Fig. 5. The XRD patterns of As4Te5I2 (a) and As8Te7I5 (b) compounds.

Z.S. Aliev et al. / Journal of Alloys and Compounds 509 (2011) 602–608
605
consists of three horizontal straights with the EMF values of 58,
3 and 107 mV, which step-wisely pass from one to another at
the stoichiometric compositions of As Te5I2 and As Te5I2 clearly
independent of the general composition of alloys, but at transition
from one three-phase area to another it is changed jump-like.
From the X-ray powder diffraction analysis, the lattice param-
eters of the As Te5I2 and As Te7I5 were determined. The XRD
7
4
4
fixing a quality changing of phase compositions of alloys (Fig. 2b).
4
8
In the 0–5 mol.% As Te3 the E–x curve changes continuously and
patterns of As Te5I and As Te7I5 are shown in Fig. 5. It is confirmed
2
4 2 8
this proves the existence of the solid solution based on As Te .
that As Te5I2 crystallizes in the face-centered cubic structure with
2
3
4
The section As0.25I0.75–Te0.2I0.8 is quasi-binary and relates to
the unit cell parameter a = 5.854(1) A˚ , which is in a good agree-
the simple eutectic type. The eutectic composition (e ) lies at 5 at.
ment with the literature data [6]. The XRD pattern of As Te7I5
9
8
%
TeI4 and 405 K, which is in agreement with that reported in Ref
was indexed in the trigonal unit cell with the lattice constants
a = 4.075(3) A˚ , c = 20.36(1) A˚ . No extra systematic conditions were
4
.
The section As0.25I0.75 (Fig. 3) is quasi-binary and character-
observed. The crystal structure of As Te7I5 requires further inves-
tigation, however, based on the lattice constants and symmetry it
is possible to propose a similarity with bismuth telluride-halides,
8
ꢀ
ized by the monotectic (m m , 630 K) and eutectic equilibriums
2
2
(
e , 410 K). The eutectic point is degenerated nearest of AsI . At the
8 3
monotectic temperature, the immiscibility field ranges from 13 to
which crystallize in trigonal space groups with the a parameter
slightly exceeding 4 A˚ [17].
7
0 at.% of Te.
3
3
.1.3. The isothermal section of the As–Te–I ternary system at
00 K
3.1.4. The liquidus surface of the As–Te–I system
The isothermal section of the As–Te–I ternary system at 300 K
The liquidus surface of the As–Te–I system (Fig. 6) consists
of eleven fields corresponding to primary crystallization of ele-
mentary components as well as binary and ternary compounds.
The fields of the primary crystallization of arsenic, tellurium and
TeI4 are very large and occupy up to 90% of the total area of the
As–Te–I triangle. The crystallization of ternary compounds from
liquid phase takes place in the narrow composition range along the
(
Fig. 4) was determined from the results of powder XRD and EMF
methods. There are twelve three-phase and two two-phase regions
␣ + As and ␣ + Te) in this system. The isothermal section con-
firms the formation of ternary compounds As5Te7I, As Te5I2 and
(
4
As Te7I5. Fig. 4 shows that AsI , being the more thermodynami-
8
3
cally stable compound of the system, has the critical influence on
the distribution of the phase areas in subsolidus. This compound
quasi-binary system As Te –AsI . Our results show that the phase
2
3
3
forms connod lines with tellurium, tellurium iodides (TeI and TeI),
C3 does not belong to any sections and its crystallization from sto-
ichiometric liquid is multistage. Firstly, arsenic crystallizes from
the liquid phase; secondly, arsenic and C2 jointly crystallize; and
thirdly, the phase C forms by the L + As + C ↔ C peritectic reaction
4
and also with ternary compounds As Te7I5 and As Te5I .
8
4
2
The EMF method allows to clearly differentiating these areas.
Fig. 2 shows the values of the EMF (mV) chains of the mode (1) in
certain phase areas of the system As–Te–I at 300 K. The measure-
ments show that under specified temperature, in the range of each
of three-phase areas, the EMF has a strict constant value which is
3
2
3
(Fig. 6, Table 1, point P ). The fields of the primary crystallization of
1
As I , AsI and elementary iodine are very narrow along the binary
2
4
3
system As–I.
Fig. 6. Projection of the liquidus surface of the As–Te–I system. Primary crystallization fields are shown: 1, As; 2, As5Te7I; 3, ␣; 4, Te; 5, As8Te7I5; 6, As4Te5I2; 7, TeI; 8, AsI3;
, TeI4; 10, I2; 11, As2I4.
9

6
06
Z.S. Aliev et al. / Journal of Alloys and Compounds 509 (2011) 602–608
Table 1
Nonvariant equilibria in the As–Te–I system.
Point on Fig. 6
Equilibrium
Composition (at.%)
Te
T (K)
I
D1
D2
D3
e1
L ↔ ␣
60
20
–
56
73
42
<1
–
–
80
75
654
553
414
653
636
456
386
346
398
412
410
405
344
400
408
395
458
408
605
620
580
600
615
610
600
405
400
405
570
630
L ↔ TeI4
L ↔ AsI3
L ↔ As ± ˛
–
–
e2
L ↔ Te ± ˛
e3
L ± TeI4 ± TeI
58
>99
86
∗
e
L ↔ I2 ± TeI4
4
e5
e6
L ↔ AsI3 ± I2
L ↔ As2I4 ± AsI3
–
71
∗
e
L ↔ AsI3 ± As4Te5I2
L ↔ AsI3 ± Te
<2
<2
2
<1
<2
<2
<1
46
–
40
47
36
39
45
48
41
<1
<1
<2
32(11)
70(13)
∼74
∼74
∼76
86
∼75
∼74
∼70
54
68
25
16
28
7
∗
e
8
∗
e
9
L ↔ AsI3 ± TeI4
∗
E
E
E
E
L ↔ AsI3 ± TeI4 ± I2
L ↔ AsI3 + TeI4 ± TeI
L ↔ AsI3 ± As4Te5I2 ± Te
L ↔ AsI3 ± As8Te7I5 ± As2I4
L ± Te ↔ TeI
1
∗
2
∗
3
∗
4
p1
p2
p3
p4
P1
P2
P3
P4
L ± As ↔ As2I4
L ± As5Te7I ↔ As4Te5I2
L + ␣ ↔ As5Te7I
L ± As ± As4Te5I2 ↔ As8Te7I5
L ± As5Te7I ↔ As4Te5I2 ± As
L ± ␣ ↔ As5Te7I ± As
L ± ␣ ↔ As5Te7I ± Te
L + As5Te7I ↔ As4Te5I2 ± As
L ± As ↔ As2I4 ± As8Te7I5
L ± As4Te5I2 ↔ AsI3 ± As8Te7Is
L ± Te ↔ AsI3 ± TeI
L1 ↔ L2 ± As4Te5I2
L1 ↔ L2 ± Te
24
16
18
26
P5
∗
P
P
P
∼67
∼71
∼74
6
∗
7
∗
8
ꢀ
m1(m )
34(61)
1
ꢀ
m2(m )
2
22.5(66)
38(57)
36(60)
33(63)
58(68)
62(68)
/
M1(M )
L1 ± As ↔ L2 ± As8Te7I5
L1 ± ↔ L2 ± As4Te5I2 + As8Te7I5
L1 ↔ L2 ± As4Te5I2 ± Te
L1 ↔ L2 ± Te ± TeI
27(12)
30(11)
35(11)
38(15)
31(16)
550
535
565
450
445
1
/
M2(M )
2
/
M3(M )
3
/
M4(M )
4
/
M5(M )
L1 ↔ L2 ± TeI ± TeI4
5
The interesting feature of the As–Te–I system is that there is
no immiscibility within the binary border systems. At the same
time, there is a wide immiscibility field inside of the ternary system.
section does not cross the immiscibility field. However, the mono-
tectic eqilibrium M1 and the three-phase field of L + L + As are
1
2
observed on the section. The bottom border of the immiscibility
field is shown conditionally (dashed line). This section crosses three
heterogeneous fields As + As I + C , As + C + C and C + Te in the
This field occupies about 60% of the quasi-binary section AsI –Te
3
and expands to the both sides, penetrating into the fields of pri-
mary crystallization of TeI, TeI , C1 and C . Subsequently, some
2
4
3
2
3
2
subsolidus region.
4
2
peritectic and eutectic curves pass through this area and transform
quadriphase monotectic equilibria (M , M , M , M and M5) (Fig. 6).
1
2
3
4
The types and coordinates of nonvariant equilibriums are listed
in Table 1. Herein, also presented are the invariant equilibriums of
binary border systems and quasi-binary sections of the ternary sys-
tem As–Te–I; degenerate equilibria are marked with the asterisks.
Apparently, our results disagree with the As–As Te –AsI phase
2
3
3
diagram presented in Ref. [6]. Mainly, immiscibility area in a wide
composition range was not observed in this subsystem. The sec-
tion As–As Te5I is not quasi-binary and is not characterized by
4
2
monotectic and eutectic equilibria. In the wide composition range,
the liquidus curve belongs to elementary arsenic, which is different
from reported in the literature [6] (Fig. 6).
3.1.5. The non-quasi-binary polythermal sections
Figs. 7–10 present some polythermal sections of the phase
diagram As–Te–I, clearly representing the processes of the crys-
tallization in the system and also helps to determine the positions
of the eutectic, monotectic and peritectic curves.
The section As0.667Te0.333–Te (Fig. 7) passes the stoichiometric
composition of C . Primary crystallization of As (0–42 at.% Te) and
2
Te (50–100 at.% Te) occurs in the wide composition range, while
C1 and ␣-phase crystallize in a narrow range. The peritectic equi-
libriums P , P , P , P5 and P are reflected on this section. The
Fig. 7. Polythermal section As0.667I0.333–Te of the As–Te–I phase diagram.
1
2
4
6

Z.S. Aliev et al. / Journal of Alloys and Compounds 509 (2011) 602–608
607
Table 2
Temperature dependencies of the EMF for the chains of type (1).
ꢀ
ꢁ
1/2
2
S
2
E
2
b
Phase area on Fig. 4E = a + bT ± t
+ S (T − T)
n
ꢂ
ꢃ
1/2
0
.24
+ 2.4 × 10−5(T − 360.4)2
C1 + C2 + Te
E = 66.80 + 0.021T ± 2
E = 103.63 + 0.012T ± 2
2
5
ꢂ
ꢃ
1/2
0
.21
+ 2.2 × 10−5(T − 361.1)2
+ 3.5 × 10−5(T − 358.1)2
AsI3 + C2 + Te
AsI3 + C2 + C3
2
5
ꢂ
ꢃ
1/2
0.36
E = 81.20 − 0.011T ± 2
2
5
The section As–Te0.583–I0.417 (Fig. 8) passes the stoichiometric
composition of C3 (40 at. % As) and the immiscibility fields. This
section clearly features some nonvariant equilibria (P , M , M and
1
2
3
M ) and the curves that connect them. A schematic description
4
of some degenerate non- and monovariant equilibriums and the
phase areas around the m1 are given in Fig. 8 as blow-ups.
The section As–Te0.2I0.8 (Fig. 9) crosses six heterogeneous fields
in the subsolidus. In the composition area of 12–18 at.% Te, this
section is characterized by more complex reaction scheme. A
schematic description of some degenerate non- and monovariant
equilibriums and phase areas around the m1 are given in Fig. 9 as
blow-ups.
Fig. 8. Polythermal section As–Te0.583–I0.417 of the As–Te–I phase diagram.
The section As0.4Te0.6–I that crosses three subsystems is shown
in Fig. 10 and indicates practically all equilibrium processes in
the area As Te –AsI –I–Te. This section crosses the quasi-binary
2
3
3
sections AsI –Te and AsI –TeI at 53 and 78 at. % Te (e8 and e ),
3
3
4
9
respectively, and is characterized by the immiscibility area (L + L )
1
2
in the region of 29–67.5 at. % Te. Below the solidus, it crosses six
heterogeneous fields. Also it helps to precise the positions of the
eutectic, monotectic and peritectic curves.
3.2. Thermodynamic functions of arsenic telluroiodides
The EMF measurement results for the chains of type (1) allowed
confirming the correctness of all drawn solid-state equilibria and
also served as the basis for the calculation of the thermodynamic
functions for As5Te7I, As Te5I2 and As Te7I5.
4
8
The analysis showed the linearity of the EMF dependences upon
temperature for various alloys belonging to the heterogeneous
fields C + C + Te, AsI + C + Te and AsI + C + C . Accordingly, the
1
2
3
2
3
2
3
linear least-square treatment of the data was performed [18] and
the results were expressed according to the literature recommen-
dations [19] as
ꢄ
ꢅ
1/2
2
S
2
E
2
Fig. 9. Polythermal section As–Te0.2I0.8 of the As–Te–I phase diagram.
E = a + bT ± t
+ S (T − T)
(2)
b
n
where n is the number of pairs of E and T values; SE and Sb are the
error variances of the EMF readings and the b coefficient, respec-
tively; T is the mean absolute temperature; t is Student’s test. At
the confidence level of 95% and n ≥ 20, Student’s test is t ≤ 2 [18].
Using this model (Table 2) and common thermodynamic functions
the partial molar functions of arsenic at 298 K were calculated, and
the values are shown in Table 3.
According to the phase diagram of the As–Te–I system, the par-
tial molar functions of arsenic in the C + C + Te, AsI + C + Te and
1
2
3
2
AsI + C + C subsystems are the thermodynamic functions of the
3
2
3
Table 3
Relative partial thermodynamic functions of arsenic in the alloys of the As–Te–I
system at 298 K.
Phase area on Fig. 4 −ꢀGAs (kJ mol−1) −ꢀHAs (kJ mol−1
)
ꢀSAs (J K mol
−1
−1
)
C1 + C2 + Te
AsI3 + C2 + Te
AsI3 + C2 + C3
21.15 ± 0.19
31.03 ± 0.18
22.55 ± 0.23
19.34 ± 1.2
30.00 ± 0.96
23.50 ± 1.23
6.08 ± 2.87
3.47 ± 2.73
−3.18 ± 3.42
Fig. 10. Polythermal section As0.4Te0.6––I of the As–Te–I phase diagram.

6
08
Z.S. Aliev et al. / Journal of Alloys and Compounds 509 (2011) 602–608
Table 4
Standard integral thermodynamic functions of the compounds in the As–Te–I system.
0
−1
0
−1
S0(298 K) (J K−1 mol−1
)
Compounds
−ꢀfG (298 K) (kJ mol
)
−ꢀfH (298 K) (kJ mol
)
AsI3
65.8 ± 3.2 [21,22]
137.1 ± 1.4
64.9 ± 3.9 [21,22]
129.7 ± 5.9
213.1 ± 5.1 [21,22]
609.4 ± 16.4
As5Te7I
As4Te5I2
As8Te7I5
147.3 ± 2,7
143.3 ± 5.8
523.1 ± 13.6
292.1 ± 6.5
287.4 ± 13.1
942.5 ± 28.5
following potential forming reactions [20]:
For the calculations, the standard entropies of arsenic and
tellurium were taken from the database [22] as 36.6 ± 2.2 and
As(solid) + 0.167As Te5I (solid) + 1.5Te(solid)
4
2
−1
−1
4
9.5 ± 0.3 J K mol , respectively. The results of the calculations
=
0.333As5Te7I(solid)
(3)
are presented in Table 4. In all cases the estimated standard devia-
tions were calculated by accumulation of errors.
As(solid) + 0.2AsI (solid) + 1.5Te(solid) = 0.3As Te5I (solid) (4)
3
4
2
References
As(solid) + 0.44AsI (solid) + 0.84As Te5I (solid)
3
4
2
1] E.I. Gerzanich, V.M. Fridkin, Ferroelectric Materials of Type A BVICVII, Nauka,
V
[
=
0.6As Te7I5(solid)
(5)
Moscow, 1982.
8
[
2] A. Audzijonis, R. Sereika, R. Zˇ altauskas, Solid State Commun. 147 (2008) 88–89.
Using these equations, the integral thermodynamic functions of
formation of SbSeI can be calculated as:
[3] A.V. Shevelkov, Russ. Chem. Rev. 77 (2008) 1–19.
[
[
4] B.G. Korshunov, V.V. Safonov, Halogenide systems, Metallurgy, Moscow, 1984.
5] A.P. Chernov, S.A. Dembovskii, L.A. Chubirka, Inorg. Mater. 6 (1970) 468–470.
0
0
[6] A.P. Chernov, S.A. Dembovskii, N.P. Luzhnaya, Russ. J. Inorg. Chem. 20 (1975)
208–1212.
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[8] R. Kniep, H.D. Reski, Z. Naturforsch. B37 (1982) 151–156.
ꢀf Z (As5Te7I) = 3ꢀZ + 0.5ꢀ Z (As Te5I )
(6)
(7)
As
f
4
2
1
[
0
0
ꢀf Z (As Te5I ) = 3.333ꢀZ + 0.667ꢀ Z (AsI )
4
2
As
f
3
[
9] U. Eggenweiler, E. Keller, V. Kramer, U. Petasch, H. Oppermann, Z. Kristallogr.
214 (1999) 264–270.
0
0
ꢀf Z (As Te7I5) = 1.667ꢀZ + 0.733ꢀ Z (AsI )
8
As
f
3
[
10] V.A. Trifonov, A.V. Shevelkov, E.V. Dikarev, B.A. Popovkin, Russ. J. Inorg. Chem.
2 (1997) 1237–1241.
[11] Z.S. Aliev, M.B. Babanly, Chem. Prob. 4 (2010) 256–259.
4
0
+
0
1.4ꢀ Z (As Te5I ),
(8)
f
4
2
[
12] M.B. Babanly, Z.S. Aliyev, Yu.M. Shikhiyev, Intern. Conf. High Mater. Technol.
Proceedings of Conference, Kiev, 2007.
0
0
where ꢀfZ are ꢀ G and ꢀ H values for the corresponding com-
f
f
[
[
13] Z.S. Aliyev, M.B. Babanly, Inorg. Mater. 44 (2008) 1203–1207.
14] M.B. Babanly, J.C. Tedenac, Z.S. Aliev, D.M. Balitsky, J. Alloys Compd. 481 (2009)
349–353.
pound, and ꢀZAs is ꢀGAs, ꢀHAs. For the calculations according to
Eqs. (6)–(8), the thermodynamic parameters of AsI3 were taken
from the literature [21,22] (Table 4).
The standard entropy of the ternary compounds was calculated
using the following equations:
[15] R.F. Rolsten, Iodide Metals and Metal Iodides, John Wiley and Sons, New York,
961.
1
[
[
[
16] T.B. Massalski, Binary Alloy Phase Diagrams, Second ed., v.3, ASM Inter Mat.
Park, Ohio, 1990, pp. 2242–2244.
17] A.V. Shevelkov, E.V. Dikarev, R.V. Shpanchenko, B.A. Popovkin, J. Solid State
Chem. 114 (1995) 379–395.
0
0
0
0
S (As5Te7I) = 3ꢀS(As) + 3S (As) + 0.5S (As Te5I ) + 4.5S (Te)
4
2
18] K. Doerffel, Statistik in der analytischen Chemie, Grundstoffindustrie, Leipzig,
(9)
1990.
[
[
19] A.N. Kornilov, L.B. Stepina, V.A. Sokolov, J. Phys. Chem. 46 (1972) 2975–2979.
20] M.B. Babanly, Yu.A. Yusibov, V.T. Abishov, EMF method for thermodynamics of
the composite semiconductor compounds, BSU pbl., Baku, 1992.
0
0
0
S (As Te5I ) = 3.333ꢀS(As) + 3.333S (As) + 0.667S (AsI )
4
2
3
0
[21] O. Kubaschewski, C.B. Alcock, P.J. Spencer, Materials Thermochemistry, Perga-
mon Press, Oxford, 1993.
[
+
4.5S (Te)
(10)
(11)
22] V.S. Yungman (Ed.), Data base of thermal constants of substances. Digital ver-
sion, 2006, http://www.chem.msu.su/cgi-bin/tkv.
0
0
0
S (As Te7I5) = 1.667ꢀS(As) + 1.667S (As) + 0.733S (AsI )
8
3
0
+
1.4S (As Te5I )
4 2