Phase equilibriums and thermodynamic properties of the system Bi-Te-I

Article abstract of DOI:10.1016/j.jallcom.2009.02.139

The system Bi-Te-I was studied by methods of differential thermal analysis and the X-ray diffraction, and also by measurements of electromotive forces (EMF) of concentration chains of type(-) Bi (s) | liquid electrolytic conductor, Bi³⁺ | (Bi-T

Full text of DOI:10.1016/j.jallcom.2009.02.139

Journal of Alloys and Compounds 481 (2009) 349–353
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Phase equilibriums and thermodynamic properties of the system Bi–Te–I
M.B. Babanlya, J.-C. Tedenacb,∗, Z.S. Aliyeva, D.V. Balitskyb
a Baku State University, Baku, AZ 1148, Z.Khalilov str, 23, BSU, Azerbaijan
b PMOF, ICGM UMR 5253 CNRS UM2, ENSCM, UM1, Place Eugene Bataillon, 34095 Montpellier, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The system Bi–Te–I was studied by methods of differential thermal analysis and the X-ray diffraction, and
also by measurements of electromotive forces (EMF) of concentration chains of type
Received 1 September 2008
Received in revised form 25 February 2009
Accepted 26 February 2009
Available online 13 March 2009
(−) Bi (s) | liquid electrolytic conductor, Bi3+ | (Bi–Te–I) (s) (+)
in the temperatures range of 300–400 K. The series of polythermal sections and isothermal section of
the phase diagram at 300 K, and a projection of the liquidus surface were constructed. Earlier indicated
ternary compounds BiTeI, Bi2TeI and Bi4TeI1.25 were confirmed, the position of phase areas and their
relationships was established. Areas of primary crystallization fields, types and coordinates of the non-
and mono-variant equilibriums were determined. The measurements of EMF have allowed calculation
of partial molar functions (ꢀG, ꢀH, ꢀS) of bismuth in alloys, standard thermodynamic functions of
formation and standard entropies of the indicated ternary compounds.
© 2009 Elsevier B.V. All rights reserved.
Keywords:
Phase equilibria
Thermodynamics
Chalcogenides
¯
¯
¯
1. Introduction
of two congruently melting ternary compounds Bi2Te3–I2 (693 K)
and Bi2Te3·3I2 (653 K). Single crystals of these compounds were
Chalcohalogenides of elements of arsenic subgroup relate to a
number of promising semiconductor materials. Many of these com-
pounds and phases on their basis have significant thermoelectric,
photoelectric and ferroelectric properties [1–4].
obtained by the Bridgman method [12].
The results of [11] and [12] are in contradiction, and as the two
cross-sections with eutectic character are not quasi-binary.
In [14] existence of two new lowest telluroiodides of bis-
muth Bi2TeI and Bi4TeI1.25 obtained by condensation from the gas
phase is reported. A single crystals of Bi2TeI obtained from a melt
have a monoclinic structure with lattice parameters: a = 7.586 Å,
b = 4.380 Å, c = 17.74 Å, ˇ = 98.20◦.
The ternary system Bi–Te–I was studied in a series of works
[5–13]. The greatest number of results [5–11] is devoted to the
study of phase equilibria in the quasi-binary system Bi2Te3–BiI3.
The results of [5–7] are very similar. Those publications shows that
the T-x diagram of this system relates to a dystectic type reaction
with formation of one intermediate compound BiTeI with a melt-
ing temperature of 828 5 K and it is characterized by a fine-bored
area of homogeneity. The results of the works [8,10] made by the
same authors concerning the melting temperature of BiTeI (743 K)
and some elements of the phase diagram Bi2Te3–BiI3 are a little bit
different to the data [5–7].
Taking into account the inconsistency of data on different iso-
pleth sections available in the literature, and for the definition of
existence areas of known bismuth telluroiodides in a T-x-y dia-
gram we have launched the detailed study of phase equilibria in
the system Bi–Te–I for all compositions areas. Moreover possible
new ternary phases can be evidenced. In the previous reports some
results on the subsystems Bi2Te3–BiTeI–Te [14] and BiI3–BiTeI–Te
[15] and BiI3–TeI4–Te [16] were presented. It was shown, that the
first two subsystems relate to a type of systems with ternary eutec-
tic equilibrium. In subsystem BiI3–TeI4–Te four field of primary
crystallization (Te, BiI3, TeI4 and TeI) are shown. Some mono and
invariant equilibria including these phases are present (peritec-
tic as well as eutectic reactions). Below the solidus this subsystem
consists of two three-phase areas BiI3–TeI–Te and BiI3–TeI–TeI4.
In this work, the complete scheme of phase equilibria for the
whole system Bi–Te–I is presented, and the fundamental thermody-
namic functions of bismuth telluroiodides ꢀG2098 ꢀH2098, S2098, were
determined.
BiTeI crystallizes with formation of hexagonal structure of
¯
type CdI2 (space group P3ml), the lattice parameters: a = 4.31 Å,
c = 6.83 Å, z = 1, [1,5] and a = 4.3392 Å, c = 6.854 Å, z = 1 [8].
Isopleth sections BiI3–Te and BiTeI–Te are also quasi-binary
and relate to a simple eutectic type [11]. It is shown in [12]
that the section Bi2Te3–I2 is quasi-binary and shows existence
∗
Corresponding author.
E-mail addresses: Babanly mb@rambler.ru (M.B. Babanly),
tedenac@univ-montp2.fr (J.-C. Tedenac).
0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.02.139

350
M.B. Babanly et al. / Journal of Alloys and Compounds 481 (2009) 349–353
2. Experimental
The results of [14–16] primary determine the phase equilibria in the composi-
tions field Bi2Te3–BiI3–TeI4–Te of the system Bi–Te–I. Therefore, we have prepared
some alloys from the compositions areas Bi–Bi2Te3–BiI3 and BiI3–TeI4–I2. Firstly, the
compounds Bi2Te3, BiTe, Bi2Te, BiTeI, Bi2TeI, Bi4TeI1.25, BiI3, BiI, TeI4 and TeI were syn-
thesized by melting stoichiometric amount of the corresponding elements of a high
pure grade in quartz ampoules under vacuum (≈10−2 Pa). Bismuth tellurides were
synthesized by heating at ≈900 K followed by a slow cooling rate. Taking into account
the high pressure of iodine vapor, the synthesis of tellurium and bismuthiodides and
telluroiodides have been made in a tilted furnace under temperature gradient condi-
tions. The temperature of the top zone was 370 K, and the bottom at 20–30◦ higher
than melting temperature of the corresponding compounds. After the interaction
of the main part of iodine, the ampoule have been completely loaded in the lower
zone, the content was carefully mixed, heated and then slowly (≈2–3◦/min) cooled.
Thus, the congruently melting compounds BiI3, TeI4 and BiTeI have been obtained as
homogeneous phases. The incongruently melting phases BiTe, Bi2Te, BiI, TeI, Bi2TeI
and Bi4TeI1.25 have been annealed at temperatures 20–30◦ below of the correspond-
ing peritectics in the range 500–800 h in order to get a complete homogenization
of the alloys. Every 200 h of annealing the alloys have been grinded to a fine pow-
der and pressed to pellet. A completeness of the synthesis has been inspected by
methods of differential thermal analysis and X-ray analysis with follow comparison
to referred data [13,17].
The alloys from areas of compositions Bi–Bi2Te3–BiI3 and BiI3–TeI4–I2 have been
synthesized also by solid state diffusion technique under vacuum from initial phases
of given subsystems annealed firstly at mentioned conditions, and then at 400 K for
200 h.
The characterization has been made by using differential thermal analysis
(with use of pyrometer NTR-72, chromel/alumel probes) and X-ray analysis (X-ray
diffractometer DRON-2, Cu K␣-radiation), microhardness measurements (using a
microhardnesmeter PMT-3, loading 20 g) and by measurements of electromotive
forces (EMF). For the EMF measurements have been used chains of the follow type:
(−) Bi (s)/glycerine + KI + BiI3/(Bi–Te–I) (s) (+)
(1)
Fig. 1. Phase diagram (a), concentration relations of microhardnesses (b) and EMF
of chains of type (1) at 300 K (c) of the systems BiI3–Bi2Te3.
The similar concentration circuits are widely used in practice in thermodynamic
study of ternary chalcogenides [18].
In such chains (1), the solid bismuth served as a left-hand electrode, and as right
electrodes—the equilibrium alloys of the system Bi–Te–I. The choice of composition
of the right electrode (1) is based on a general behaviour of the diagram described
in [18].
Glycerin solution saturated by KI with addition of BiI3 (0.1 mass.%) was used
as an electrolytic conductor. Procedures of the preparation of electrolytic conductor
and electrodes and assembly of an electrochemical cell were described in [18,19]. The
assembled electrochemical cell was placed in a vertical tube-type furnace. The values
of EMF of circuits of type (1) were measured in the temperature range 305–400 K by
a compensation method using a digital voltmeter V7-34A. The temperatures were
measured by a chromel/alumel thermocouple and by a mercury thermometer.
The first equilibrium values of EMF were measured in ∼30 h and following in
each 4–5 h after achieve of a stationary value of temperature.
The qualitative vicinity of diffraction patterns of bismuth, its tel-
lurides and telluroiodides rather complicates the determination of
phase areas in the subsystem Bi–BiI3–Bi2Te3 by X-ray diffraction. In
the same time, the EMF method allows to differentiate these areas
clearly. Fig. 2 shows the values of the EMF (mV) chains of the mode
(1) in certain phase areas of the system Bi–Te–I at 300 K. The mea-
surements are shown that under specified temperature in the range
of each of three-phase areas the EMF has a strict constant value
independent of general composition of alloys, but at transition from
3. Results and discussion
The analysis of summarized experimental results and data of
boundary binary systems Bi–Te, Bi–I and Te–I [18] and subsystem
Bi2Te3–BiI3–TeI3–Te [14–16] has allowed us to find a general phase
equilibria description in system Bi–Te–I (Figs. 1–6, Tables 1 and 2).
Fig. 1 shows the T-x phase diagram of the quasi-binary system
BiI3–Bi2Te3 constructed in [6,7] where our DTA data and results of a
microhardness and an EMF for the selected compositions points are
indicated. Thus, these data confirm the results of [6,7]. The phase
BiTeI is well determined in the H -x diagram with a microhard-
␮
ness value of ≈750 MPa (Fig. 1 b). The isothermal curve of E-x at
300 K consist of two horizontal straights with EMF values of 167
and 145 mV which step-wisely pass to each other at stoichiomet-
ric composition BiTeI that clearly fix a quality changing of phase
composition of alloys.
The diagram of solid-phase equilibriums (Fig. 2) confirms the
formation of ternary compounds BiTeI, Bi2TeI and Bi4TeI1.25. Fig. 2
shows that the critical influence on distribution of phase areas in
subsolidus. The phase BiI3 is the more thermodynamically stable
compound in the ternary. This compound is in interaction with tel-
lurium, tellurium iodides (TeI4 and TeI) and with all of the triple
compounds. The whole Bi–Te–I system consists, in solid state, on
17 three-phase and 8 two-phase areas.
Fig. 2. Isothermal section at 300 K of the phase diagram of the system Bi–Te–I.
The EMF values (mV) of concentration chains of type (1) in some phase areas are
indicated in parenthesis.

M.B. Babanly et al. / Journal of Alloys and Compounds 481 (2009) 349–353
351
Fig. 3. Projection of liquidus surface of the system BiI–Te–I. Areas of primary crystallization of phases: 1-BiI3; 2-I2; 3-TeI4; 4-TeI; 5-Te; 6-BiTeI; 7-Bi2Te3; 8-␥; 9-␤; 10-␤ꢀ;
11-Bi4TeI1.25; 12-Bi2TeI; 13-BiI; 14-Bi7I2; 15-Bi9I2; 16-Bi. Dot lines—quasi-binary sections and area of immiscibility.
one three-phase area to another a jump is observed. For example,
the jumps of the EMF at transition from BiI3–Bi4TeI1.25–Bi2TeI to
BiI3–Bi2TeI–BiTeI gives 73 mV (error of the measurement does not
exceed 0.2 mV).
Liquidus surface (Fig. 3) consists of 16 areas of the primary
crystallization fields; five of them (areas of the primary crystal-
lization of Bi, I2, BiI, Bi7I2 and Bi9I2) are degenerated. These areas
are connected by different curves and points indicating the mono-
and invariant eutectic and peritectic equilibria (Tables 1 and 2). In
Table 1, it is also presented invariant equilibria of border binary
systems and quasi-binary sections of the ternary system Bi–Te–I.
The quasi-binary sections divide the system Bi–Te–I on five inde-
pendent subsystems: BiI3–TeI4–I (I), BiI3–TeI4–Te (II), BiI3–BiTeI–Te
(III), Bi2Te3–BiTeI–Te (IV) and Bi–Bi2Te3–BiI3 (V).
The liquidus of the subsystem (I) consist on surfaces of the pri-
mary crystallization fields of BiI3, TeI4 and I2. The last area and the
corresponding eutectic point E4 are degenerated on the melting
temperature.
The subsystems (III) and (IV) are also related to the invariant
Fig. 4. Polythermal section Bi2Te3–I2.
eutectic reactions E1 and E2 type.
Fig. 6. Polythermal section BiI–Te.
Fig. 5. Polythermal section Bi–TeI.

352
M.B. Babanly et al. / Journal of Alloys and Compounds 481 (2009) 349–353
Table 1
Table 2
Nonvariant equilibriums in Bi–Te–I system.
Monovariant equilibriums in system Bi–Te–I.
No.
Point in Fig. 3
Equilibrium
Composition, at.%
T, K
Curves in Fig. 3
Equilibrium
Temperature ranges, K
Bi
Te
e1E1
L ⇔ Bi2Te3 + Te
L ⇔ BiTeI + Te
L ⇔ BiTeI + Bi2Te3
L ⇔ Bilj + Te
680–670
e8E1; e8E2
e9E1; e9P3
e10 E2; e10 P1
enE3; enE4
e5*E4*
e6*E4*
p7P1
e7E3
P0E3
e4E2; e4P2
P2M (MꢀP7)
p8P2; p8P4
p1P3
P3P4
P4P5
p2P5
P5P6
p9P6; p9P7
p3P8
P6P8
P8E5*
e2*E5*
675–670; 675–645
823–670; 823–800
650–645; 650–455
523–448; 523–383
386–383
386–383
458–455
451–448
455–448
678–645; 678–675
675–665
750–675; 750–730
821–800
800–730
730–683
693–683
683–670
688–670; 688–665
585–570
670–570
665–535
539–535
540–535; 539–535
542–538
568–560
560–538
573–570
570–560
603–600
1
2
3
4
5
6
7
8
9
D1
D2
D3
D4
e1
e2*
e3
e4*
e5*
e6*
e7
LD1 ⇔ Bi2Te3
–
60
–
20
33.3
90
–
–
–
–
–
42
77
36
20
14
–
77
20
39.5
–
–
–
37
18
8
858
680
553
828
686
539
542
678
386
386
451
675
823
650
523
540
670
645
448
383
535
538
821
693
585
568
573
603
458
750
688
455
675
800
730
683
670
665
570
560
570
600
623
670
LD2 ⇔ BiI3
75
80
33.3
–
–
–
–
–
–
58
11.5
30
60
78.5
–
10.5
59
58.5
–
–
–
–
–
–
–
–
–
54
22
15
55.5
60
15.5
17
12
13
6
LD3 ⇔ TeI4
L ⇔ BiI3 + TeI4
L ⇔ BiI3 + I2
LD4 ⇔ BiTeI
L ⇔ Bi2Te3 + Te
L ⇔ TeI4 + I
L ⇔ BI + ␤ꢀ
L + Te ⇔ TeI
L ⇔ Bi + Bi9I2
L ⇔ TeI4 − TeI
L ⇔ BiI3 + TeI
L ⇔ BiTel + BiI3
L ⇔ BiI3 + I2
L ⇔ BiI3 + BiTeI
L1(L2) − Bil3 ⇔ Bi2Tel
L + BiTeI ⇔ Bi2TeI
L − Bi2Te3 ⇔ ␥
L + BiTeI ⇔ ␥
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
L ⇔ TeI4 + I2
L ⇔ TeI4 + TeI
e8
e9
e10
e11
L ⇔ BiTeI + Te
L ⇔ BiTeI + Bi2Te3
L ⇔ BiI3 + Te
L + ␥ ⇔ Bi2TeI
L + ␥ ⇔ ␤
L ⇔ BiI3 + TeI4
e12
E1
E2
E3
*
L ⇔ Bi + Bi4TeI1.25
L ⇔ Bi2Te3 + BiTeI + Te
L ⇔ BiTeI + Te + BiI3
L ⇔ BiI3 + TeI + TeI4
L ⇔ BiI3 + TeI4 + I2
L ⇔ Bi + ␤ꢀ + Bi4TeI1.25
L ⇔ Bi + Bi9I2 + Bi4TeI1.25
L + Bi2Te3 ⇔ ␥
L + ␤ ⇔ Bi2TeI
L + Bi2TeI ⇔ Bi4TeI1.25
L + ␤ ⇔ ␤ꢀ
L + ␤ ⇔ Bi4TeI1.25
L + ␤ꢀ ⇔ Bi4TeI1.25
L ⇔ Bi + ␤ꢀ
E4*
E5*
E6*
p1
p2
p3
p4*
p5*
p6*
p7
p8
p9
P1
P2
P3
P4
P5
P6
P7
P8
P9*
e
12 * E5*; e12 * E6*
L ⇔ Bi − Bi4Tel1.25
L ⇔ Bi − Bi9I2
e3*E6*
P4*E9*
L − ␥ ⇔ ␤
L − Bi7I2 ⇔ Bi9I2
L ⇔ Bi9I2+Bi4TeI125
L + BiI ⇔ Bi7I2
L + Bi7I2 ⇔ Bi4TeI1.25
L + BiI3 ⇔ BiI
L + ␤ ⇔ ␤ꢀ
P9*E6*
L + Bi7I2 ⇔ Bi9I2
L + BiI ⇔ Bi7L
–
–
–
*
p5 P10
*
P10 *P9*
L + BiI3 ⇔ B1I
p6*P11
P11 *P10
P7P11
*
*
L + Te ⇔ TeI
46
22
13
42
3
31
24
18
15
3
6
–
–
–
–
2(3)
L + BiIoBi4TeI1.25
L − Bil ⇔ Bi4Te1.25
600–570
665–600
L + BiTeI ⇔ Bi9TeI
L + Bi2TeI ⇔ Bi4TeI1.25
L + Te ⇔ TeI − BiI3
L + BiTeI ⇔ BiI3 + Bi2TeI
L + Bi2Te3 ⇔ ␥ + BiTeI
L − BiTeI ⇔ ␥ − Bi2TeI
L + ␥ ⇔ ␤ + Bi2TeI
L + Bi2TeI ⇔ ␤ + Bi4TeI1.25
L + Bi2TeI ⇔ Bi4TeI1.25 + BiI3
L + ␤ ⇔ ␤ꢀ + Bi4TeI1.25
L − Bi7I2 ⇔ BiTel1.25 + Bi9I2
L − Bil ⇔ BiTel1.25 + Bi7I2
L + Bil3 ⇔ Bi4Tel1.25 + Bi7I2
L ⇔ L2 + BiI3
*
The liquidus consists of curves of the primary crystallization
field of Bi2Te3, BiTeI, Te, BiI3 and I2. The liquidus of tellurium
occupies wide area of compositions, and the liquidus of the I2
is degenerated. It is well indicated on this section that the ther-
mal effects are representative of mono-variant processes of the
phases crystallization (isotherm ≈800 K, curves e8E1, e8E2, e10P1,
P1E3, e11 E3, etc.), and of an invariant peritectic as well as an eutec-
tic equilibriums P1, E1, E2, E3, E4 (horizontal lines at 455, 670, 645,
448 and 384 K) (Fig. 3, Tables 1 and 2).
3
–
–
–
P10
P11
*
*
m(mꢀ)
M(Mꢀ)
59(5)
56.5 (9)
L ⇔ L2 + BiI3 + Bi2TeI
The section BiI–Te (Fig. 5) is a partial quasi-binary. In the area of
the compositions BiTeI–Te this section is characterized by an eutec-
tic type reaction (e8) and in the area of the compositions BiI–BiTeI
the section BiI–Te cross the three-phase areas and is characterized
by the peritectics (P8, P11 ) monotectic (M) equilibria.
The section Bi–TeI (Fig. 6) is also partial quasi-binary, it is prac-
tically quasi-binary in the area of the compositions Bi–BiTeI. The
T-x diagram (Fig. 6) shows clearly marked isotherm at 723 and
688 K according to peritectic reactions (p8, p9) of formation of the
intermediate phases based on the ternary compositions Bi2TeI and
The subsystem (II) is characterized by a peritectic (P1) and by
eutectic (E3) reactions. Under the solidus three-phase areas exist:
BiI3–TeI–Te and BiI3–TeI4–TeI. The initial crystallization of TeI from
melt takes place in very narrow composition range.
The subsystem (V) is characterized by more complicate reaction
scheme. It is characterized by formation of two ternary compounds
(Bi2TeI and Bi4TeI1.25) decomposing by peritectic reactions corre-
sponding to the invariant points p8 and p9 in the section TeI–Bi,
and to points P2, P4 and P11 from which last three points degener-
ated at Bi corner of the concentration triangle. Eutectics E5 and E6
are also degenerated.
Bi4TeI1.25
.
The stability of equilibria this section in composition area
Bi–BiTeI is proved using X-ray diffraction, micro-structural, micro-
hardness analysis and EMF.
The area of immiscibility mmꢀ of the boundary binary system Bi–I
to penetrated into a ternary system and forms a wide area of mixing
of two liquid phases (surface mMkMꢀmꢀ). The curve of peritectic
issued from point P2 go through this area and result the isotherm
(MMꢀ) associated to monotectic equilibrium.
On Figs. 4–6 it is presented some isopleth sections showing the
processes of the equilibrium crystallization in the system.
The section Bi2Te3–I2 (Fig. 4) is presented as a non quasi-binary
contrarily to data [11]. This section traverses four (I–IV) of the five
independent subsystems and indicates practically all processes of
the crystallization occurred there.
In the composition area BiTeI–TeI this section goes through the
subsystems (II) and (III) and reflected the invariants (E2, P1) and the
monovariant equilibria.
Thermodynamic properties of telluroiodides of bismuth. The
results of the EMF measurements of chains of type (1) also have
allowed calculating thermodynamic properties of telluroiodides of
bismuth (Tables 4 and 5).
For analysis, we had used values of the EMF for three-phase
areas BiI3–I–Te, BiI3–I–II and BiI3–II–III which are responsible in
potential-forming reactions with involving of the ternary com-
pounds [18,19].

M.B. Babanly et al. / Journal of Alloys and Compounds 481 (2009) 349–353
353
Table 3
Table 5
Temperature dependences of EMF of chains type (1) in some phase areas of the
system Bi–Te–I (T = 305–400 K).
Standard integral thermodynamic functions of telluroiodides and triiodide of
bismuth.
ꢀ
ꢁ
1/2
2
E
Compound
−ꢀG2098
−ꢀH2098
S2098
J/mol K
S
Phase area on Fig. 2
E = a + bT
t
+ Sb2(T − T)2
n
kJ/mol
ꢂ
ꢃ
ꢃ
1/2
BiI3 [23]
BiTeI
Bi2TeI
148.8 8.0
81.8 2.7
107.7 3.0
130.1 4.0
150.6 6.0
82.6 2.5 77 9 [3]
110.7 4.2
224.7 6.3
161.6 3.6 176 11 [3]
211.3 9.1
+ 1.4 × 10−4(−342.4)2
1.84
BiI3 + BiTeI + Te
E = 168.1 − 0.004
E = 97.06 − 0.025
E = 12.4 + 0.020
2
26
ꢂ
1/2
+ 6.7 × 10−4(−346.6)2
7.26
26
BiI3 + Bi2TeI + BiTeI
BiI3 + Bi4TeI1.25 + Bi2TeI
2
Bi4TeI1.25
130.0 6.8
350.1 16.6
ꢂ
ꢃ
1/2
2.68
26
2
+ 3 × 10−4(−354.5)2
(ꢀZ0- ꢀG2098 and ꢀH2098 —values for the correspond-
ing compound, ꢀZBi − ꢀGBi, ꢀHBi). The standard entropies
of telluroiodides of bismuth are calculated using relations
(9)–(11):
Table 4
Relative partial thermodynamic functions of bismuth in alloys of the system Bi–Te–I
at 298 K.
¯
¯
¯
Phase area from Fig. 2
−ꢀGBi
−ꢀHBi
ꢀSBi
SB0iTeI = 0.667(ꢀSBi + SB0i) + 0.333SB0iI + ST0e
(9)
(10)
(11)
3
kJ/mol
J/mol K
SB0i
= ꢀSBi + SB0i + SB0iTeI
BiI3 + BiTeI + Te
BiI3 + Bi2TeI + BiTeI
BiI3 + Bi4TeI1.25 + Bi2TeI
48.31 0.11
25.94 0.26
5.32 0.20
48.66 0.78
28.1 1.7
3.6 1.2
−1.2 2.3
−7.2 5.0
5.9 3.3
TeI
TeI
2
4
SB0i
= 1.917(ꢀSBi + SB0i) + SB0i TeI + 0.083SB0iI
1,25
2
3
The corresponding thermodynamic data of BiI3 (Table 5), Te
The analysis of the temperature dependences of the EMF of the
alloys in the indicated heterogeneous areas has shown that they
are practically linear. It is confirmed by these data that the com-
positions of coexisted phases in the given heterogeneous areas in
the studied temperature range are constant, and it gives a base
for estimations of the partial entropy and enthalpy from values of
the temperature coefficients of the EMF [18,19]. The EMF results
had been analyzed by an approximation of the linear temperature
function using the method of least squares [20]. Thus, according to
recommendations [21], it is expressed as linear equation:
(S0 = 49.5 0.3 J/(K mol)) and Bi (S0 = 56.9 0.5 J/(K mol)) [22,23]
had been used for calculations in relations (6)–(11).
The results of calculations are presented in Table 5. The accuracy
has been determined by a method of errors accumulation. In Table 5,
it is also shown some data of the work [3] obtained by an indirect
way from the measurements of the saturated vapor pressure of BiTeI
which agree with our data in the range of errors.
References
ꢄ
ꢅ
[1] E.I. Gerzanich, V.M. Fridkin, Nauka (1982) p. 114.
[2] J. Fenner, A. Rabenau, G. Trageser, Adv. Inorg. and Radiochemistry, v. 23, Acad.
Press, New York, 1980, pp. 329–416.
1/2
SE2
n
E = a + bT
t
+ Sb2(T − T)2
(2)
[3] B.A. Popovkin, Physico-chemical fundamentals of the control synthesis of
sulpho-iodide of antimony and other chalcogeno- (oxo)-halogenides of anti-
mony and bismuth, Doctoral thesis, M.: MSU, 1983, p. 349.
[4] V.V. Sobolev, E.V. Pesterev, V.V. Sobolev, Inorg. Mater. 40 (2) (2004) 172–173.
[5] J. Horak, H. Rodot, C.r. Akad. Sci. Paris Serie B 267 (6) (1968) 363–366.
[6] N.R. Valitova, V.A. Aleshin, B.A. Popovkin, A.V. Novoselova, Inorg. Mater. 12 (2)
(1976) 225–228.
[7] A. Tomokiyo, T. Okada, S. Kawanos, Jpn. J. Appl. Phys. 16 (6) (1977) 291–298.
[8] A.V. Shevelkov, E.V. Dikarev, R.V. Shpanchenko, B.A. Popovkin, J. Solid State
Chem. 114 (1995) 379–395.
[9] D.P. Belotskiy, I.N. Antipov, V.F. Nadtochiy, S.M. Dodik, Inorg. Mater. 5 (10) (1969)
1163.
[10] D.P. Belotskiy, C.M. Dodik, I.N. Antipov, Z.I. Nefedov, Ukr. Chem. J. 36 (9) (1970)
897–900.
[11] L.T. Evdokimenko, M.I. Tsypin, Inorg. Mater. 7 (8) (1971) 1317–1320.
[12] D.P. Belotskiy, C.M. Dodik, O.A. Demkiv, Inorg. Mater. 38 (8) (1972)766–768.
[13] S.V. Savilov, V.N. Khrustalev, A.N. Kuznetsov, B.A. Popovkin, M.Ju. Antipin, Ser.
Chem. (1) (2005) 86–91.
[14] Z.S. Aliev, M.B. Babanly, News Baku Univ., Nat. Sci. ser. (4) (2006) 35–38.
[15] Z.S. Aliev, M.B. Babanly, Chem. Probl. (4) (2006) 691–693.
[16] Z.S. Aliev, M.B. Babanly, Chem. J. (2) (2007) 83–85.
where n—number of pairs of values E and T; SE and Sb—dispersion of
individual measurements of the EMF and the factor b, accordingly;
T —average absolute temperature; t—Student’s criteria. Remark: the
Student’s criteria is less than 2 (t ≤ 2) at the confidence level of 95%
and at the number of runs more than 20 (n ≥ 20).
The composed equations of the mode (2) are presented in
Table 3. The partial molar functions of bismuth in the indicated
three-phase areas (Table 2) had been calculated from these equa-
tions using the known thermodynamic relations (Table 4).
According to [18,19] and Fig. 2, these partial molar values are
related to the follow potential-formation reactions:
Bi + 0.5BiI3 + 1.5Te = 1.5BiTeI
Bi + BiTeI = Bi2TeI
(3)
(4)
(5)
Bi + 0.522Bi2TeI + 0.043BiI3 = 0.522Bi4TeI1.25
[17] T.B. Massalski, Binary Alloy Phase Diagrams, v. 3, second ed., ASM Inter. Mat.
Park, Ohio, 1990, 2242 p.
[18] M.B. Babanly, Yu.A. Yusibov, V.T. Abishov, EMF method for thermodynamics of
the composite semiconductor compounds, BSU, Baku, 1992, 327 p.
[19] M.B. Babanly, A.A. Kuliyev, Mathematical Problems of Chemical Thermodynam-
ics, Novosibirsk, Nauka, 1985, pp. 192–201.
According to equations of the reactions (3)–(4), the standard
thermodynamic functions of telluroiodides of bismuth are calcu-
lated in relations (6)–(8):
ꢀZB0iTeI = 0.667ꢀZBi + 0.333 ꢀZ0
(6)
(7)
(8)
[20] K. Derffel, Stat. Anal. Chem. M. Mir (1994), 268 p.
BiI
3
[21] A.N. Kornilov, L.B. Stepina, V.A. Sokolov, J. Phys. Chem. 46 (11) (1972) 2975–2979.
[22] O. Kubaschewski, C.B. Alcock, P.J. Spencer, Materials Thermochemistry, Perga-
mon Press, Oxford, 1993, 350 p.
[23] Data Base of Thermal Constants of Substances, Digital version, in: V.S. Yungman
(Ed.), 2006, http://www.chem.msu.su/cgi-bin/tkv.
ꢀZB0i
= ꢀZBi + ꢀZ0
TeI
TeI
BiTeI
2
4
ꢀZB0i
= 1.917ꢀZBi + ꢀZ0 TeI + 0.083 ꢀZB0iI
Bi
1.25
2
3