Thermodynamic Evaluation of Chemical Transport of VSe2 and ZrSe2 with Сl2 and I2 as Transporting Agents

Article abstract of DOI:10.1134/S0036023620090120

Abstract: To study chemical transport and refine synthetic routes, single crystals of vanadium and zirconium diselenides were grown by the chemical transport reaction method using I₂ and Cl₂ as transporting agents. The thermodynamic parameters of chemical transport have been evaluated, and the mass transfer direction in a growth ampoule has been determined. The phase composition of the samples has been examined by X?ray powder diffraction. Analysis of X-ray powder diffraction patterns of samples from the low- and high-temperature zones of the growth ampoule has confirmed the predictions based on thermodynamic calculations. With both transporting agents, ZrSe₂ transport occurs from the cold to the hot zone of the ampoule, while the direction of VSe₂ transport depends on the nature of the transporting agent. With I₂ as a transporting agent, transport occurs from the hot to the cold zone of the ampoule, while with Cl₂, in the opposite mass transfer direction is observed. Microphotographs of the samples are consistent with thermodynamic and X?ray diffraction data. The results can be used to optimize the technology of producing layered transition metal dichalcogenides.

Full text of DOI:10.1134/S0036023620090120

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2020, Vol. 65, No. 9, pp. 1366–1372. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Neorganicheskoi Khimii, 2020, Vol. 65, No. 9, pp. 1222–1228.
THEORETICAL
INORGANIC CHEMISTRY
Thermodynamic Evaluation of Chemical Transport of VSe2
and ZrSe2 with Сl2 and I2 as Transporting Agents
K. S. Nikonova, *, A. S. Il’yasova, and M. N. Brekhovskikha
aKurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow 119991 Russia
*e-mail: NikonovK.S@yandex.ru
Received March 19, 2020; revised April 19, 2020; accepted April 30, 2020
Abstract—To study chemical transport and refine synthetic routes, single crystals of vanadium and zirconium
diselenides were grown by the chemical transport reaction method using I2 and Cl2 as transporting agents.
The thermodynamic parameters of chemical transport have been evaluated, and the mass transfer direction
in a growth ampoule has been determined. The phase composition of the samples has been examined by
X-ray powder diffraction. Analysis of X-ray powder diffraction patterns of samples from the low- and high-
temperature zones of the growth ampoule has confirmed the predictions based on thermodynamic calcula-
tions. With both transporting agents, ZrSe2 transport occurs from the cold to the hot zone of the ampoule,
while the direction of VSe2 transport depends on the nature of the transporting agent. With I2 as a transporting
agent, transport occurs from the hot to the cold zone of the ampoule, while with Cl2, in the opposite mass
transfer direction is observed. Microphotographs of the samples are consistent with thermodynamic and
X-ray diffraction data. The results can be used to optimize the technology of producing layered transition
metal dichalcogenides.
Keywords: TMDC, chemical transport reactions, vanadium diselenide, zirconium
DOI: 10.1134/S0036023620090120
Layered
transition
metal
dichalcogenides
Versions of molecular beam epitaxy are currently a
common method for producing nanoscale films of
various materials [12]. This method allows one to con-
trol the thickness and stoichiometry of the synthesized
layer with high accuracy, but is unsuitable for produc-
ing separate macroscopic single crystals. The main
method for producing large single crystals of VSe2 and
ZrSe2 is the chemical transport reaction (CTR)
method [13, 14]. This method is based on a reversible
reaction between a transported substance, in this case
VSe2 and ZrSe2, and a transporting agent to give a gas-
eous transported form (for example, VI4), the vapors
of which move along the temperature gradient until
the equilibrium is shifted in the opposite direction,
which leads to the formation of XSe2 crystals and the
release of the transporting agent [15].
A common choice of transporting agent when
using chemical transport reactions for the growth of
TMDC single crystals is crystalline I2. The use of
alternative transporting agents for the preparation of
single crystals of Mo, Ta, V, and Zr dichalcogenides
has been reported [16–18].
Unlike various ternary transition metal selenides,
the thermodynamic parameters of which have been
considered in detail [19], experimental data on the
thermodynamic characteristics of layered V and Zr
dichalcogenides are nearly absent in the literature.
(TMDCs) are a group of binary compounds with a
common characteristic structure and a very wide
range of physicochemical properties. Layered
TMDCs are distinguished by the variety of observed
physical effects, catalytic activity, and extensive possi-
bilities for obtaining nano- and intercalation materials
based on them [1–3]. These qualities enable the use of
TMDCs and materials based on them in rechargeable
batteries [4–6] and for creating catalysts [7] and
nanoscale electronic devices [8].
The structure of layered TMDCs consists of
repeating layers separated by van der Waals gaps so
that all covalent bonds in the structure lie within the
same layer. In turn, the layers are linked with one
another only through weak interatomic interactions.
Each triple block comprises three atomic layers: two
layers composed of chalcogen atoms and a layer of
transition metal atoms located between them. Crystals
of this structure belong to the structure type of CdI2.
The layered nature of TMDC crystals is responsible
for the ease with which these compounds form inter-
calation compounds [9] and for their propensity to
form thin films and 2D materials [10]. TMDC single
crystals can replace graphene as substrates when creat-
ing heterostructures described in [11].
1366

THERMODYNAMIC EVALUATION OF CHEMICAL TRANSPORT
Table 1. Parameters of growth of VSe2 and ZrSe2 crystals
1367
Growth temperature, °С
Transporting agent, ×10–4 mol
System
Weighed sample, g
Time, h
Thot
Tcold
VSe2
VSe2
ZrSe2
ZrSe2
2.0
0.4
1.0
0.4
1.97 I2
1.32 Cl2
2.75 Cl2
1.77 I2
850
850
915
850
800
800
850
800
48
48
48
48
This study deals with chemical transport processes these systems can be described as follows: in the high-
in the MSe2/I2 and MSe2/Cl2 systems (M = V, Zr) in temperature zone of the furnace, a dichalcogenide
reacts with a transporting agent, i.e. with halogen
vapor, which leads to the formation of a gaseous tetra-
halide. In the low-temperature region of the furnace,
the halide reacts with selenium vapors to again form
the XSe2 dichalcogenide (X = V, Zr) and release the
transporting agent (Cl2 or I2).
Reactions (5)–(8) approximately describe the
course of the chemical transport in the МSe2/СI2 and
МSe2/I2 systems (М = Zr, V).
order to refine synthetic routes and conditions for
growing single crystals of these compounds by the
CTR method.
EXPERIMENTAL
Crystals of VSe2 and ZrSe2 were grown by the CTR
method using Сl2 and I2 as a transporting agent. VSe2
and ZrSe2 crystals were produced from elements by
annealing of a stoichiometric mixture of the starting
elements in an evacuated ampoule. Then, the crystals
together with the transporting agent source were
loaded into a quartz ampoule, which was evacuated to
a residual pressure of ~0.03 mbar and placed into a
tubular furnace with a temperature gradient. The
resulting crystals were characterized by X-ray diffrac-
tion on a Bruker D8 Advance diffractometer. Micro-
photographs of crystals were obtained using an MIM-7
microscope. The crystal growth conditions are pre-
sented in Table 1.
To avoid substance losses during evacuation and
sealing of the growth ampoule, crystalline I2 was intro-
duced into it as a thin-walled Pyrex capillary, which
was destroyed when the ampoule was heated to the
growth temperature, releasing iodine vapor into the
ampoule volume. Powders of VCl3 and ZrCl4 were
introduced into the ampoule in a dry box under a
nitrogen atmosphere. Upon heating in the growth
ampoule, the transition metal halides VCl3 and ZrCl4
decompose to Cl2 and VCl2 or ZrCl2, respectively.
(5)
(6)
(7)
(8)
ZrSe2(s) + 2Cl2(g) ↔ ZrCl4(g) + Se2(g)
ZrSe2(s) + 2l2(g) ↔ Zrl4(g) + Se2(g)
VSe2(s) + 2Cl2(g) ↔ VCl4(g) + Se2(g)
VSe2(s) + 2l2(g) ↔ Vl4(g) + Se2(g)
,
,
,
.
To get a more complete insight into the nature of
the processes occurring during the synthesis and
growth of ZrSe2 and VSe2 crystals by the CTR
method, we evaluated the thermodynamic parameters
of reactions (5)–(8) and the equilibrium constant in
the temperature range from 298 to 1400 K.
In calculation of ΔrG0 and Kp, it was assumed that
ΔfH of reactions in the range 298–1400 K is tempera-
ture independent. For VI4 and ZrI4, we used approxi-
0
mate values of the entropy of formation
extrapo-
S298
lated using the known values for related halides. The
need to introduce these assumptions is associated with
the lack of reliable experimental data on the thermo-
dynamic parameters of these substances in the litera-
ture [17–24]. The calculation results are presented in
Table 2.
Reactions (1)–(4) demonstrate the process of
decomposition of a compound, a source of a trans-
porting agent:
The temperature dependence of Кp is shown in Fig. 1.
According to our estimates, the behavior of the equi-
librium constant of reaction (8) with a change in tem-
perature differs from that for reactions (5)–(7). In the
range 300–1400 K, Кp decreases for reactions (5)–(7)
and increases for reaction (8). In all the four cases, the
rate of change in Кр decreases with increasing tem-
perature.
(1)
(2)
(3)
(4)
2VCl3 → VCl4 + VCl2,
2VCl4 → 2VCl3 + Cl2,
2ZrCl4 → 2ZrCl3 + Cl2,
2ZrCl3 → ZrCl4 + ZrCl2.
RESULTS AND DISCUSSION
On the basis of the data in [13, 15], we assume that,
in the general case, the chemical transport process in
The temperature dependence of the free Gibbs
energy of reaction ΔrG is shown in Fig. 2. Approximate
calculations show that ΔrG decreases with increasing
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 65 No. 9 2020

1368
NIKONOV et al.
Table 2. Approximate thermodynamic parameters of CTR
298
K (p
1188
K (p
1123
)
K (p
0
0
0
)
0
)
0
System
Δ
, kJ/mol Δ
, kJ/(mol K) Δ
, kJ/mol
Δ
, kJ/mol
Δ
, kJ/mol
rH298
rS298
rG298
rG1188
rG1123
ZrSe2/Cl2
ZrSe2/I2
VSe2/Cl2
VSe2/I2
1.17
1.04
1.15
0.10
–287.7
1.029
1.026
–
–
–
–
–
–414.3
–0.10
0.18
–382.31
–257.7
–41.4
–259.9
49.5
–95.59
–344.20
5.09
–
–
1.06
1.01
0.28
0.14
–606.6
–117.9
–
temperature for reactions (5), (7), and (8). For reac- cases of ZrSe2/Cl2, ZrSe2/I2, and VSe2/Cl2, crystal
tion (6), ΔrG increases and become positive at Т =
growth is observed in the high-temperature zone of
the ampoule and insignificant formation of small crys-
tals, in the low-temperature zone, which indicates the
coexistence of several transfer mechanisms in the
growth ampoule. In the case of ZrSe2, the accumula-
tion of impurity phases of various composition is
observed in the low-temperature zone of the ampoule.
In the case of VSe2/I2, the formation of numerous
large single crystals is observed in the low-temperature
°
3889.7 K. For reaction (8),
is slightly >0, but
ΔrG298
ΔrG decreases with increasing temperature.
The relationships between ΔrG, ΔrH, and ΔrS make
it possible to predict the behavior of the transport
reaction in each particular case according to the rules
deduced in [15]. These trends are presented in Table 3.
The observed experimental results coincide with
the predicted course of the transport process. In the zone.
Kp
1.16
(a)
1.14
1.12
1.10
1.08
1.06
1.04
1.0
ZrSe2/Cl2
ZrSe2/I2
1.00
0.98
1.16
(b)
1.14
1.12
1.10
1.08
1.06
1.04
1.0
VSe2/Cl2
VSe2/I2
1.00
0.98
250 350 450 550 650 750 850 950 10501150125013501450
T, K
Fig. 1. K vs Т for (a) ZrSe and (b) VSe .
p
2
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 65
No. 9
2020

THERMODYNAMIC EVALUATION OF CHEMICAL TRANSPORT
1369
T, K
250 350 450 550 650 750 850 950 10501150125013501450
0
(a)
ZrSe2/Cl2
ZrSe2/I2
–50
–100
–150
–200
–250
–300
–350
–400
–450
T, K
250 350 450 550 650 750 850 950 10501150125013501450
100
(b)
VSe2/Cl2
VSe2/I2
0
–100
–200
–300
–400
–500
–600
–700
Fig. 2. Temperature dependence of Δ G of transport of (a) ZrSe and (b) VSe .
r
2
2
The X-ray diffraction patterns of the samples are explained by the size of the crystals and the texture of
shown in Fig. 3. For vanadium diselenide, the use of
both transporting agents leads to the formation of pure
VSe2 in the high- and low-temperature zones, which
indicates the efficient operation of the transfer mech-
the resulting material.
In the case of ZrSe2, the X-ray diffraction pattern
demonstrates the formation of ZrSe2 and the lack of
anisms. The differences in peak intensities are noticeable impurities in the high-temperature zone,
Table 3. Evaluation of the possibility of the transport reaction and transfer direction
0
0
0
System
ZrSe2/Cl2
Possibility of the reaction Transport direction
Δ
Δ
Δ
rS298
rH298
rG298
<0
>0
>0
>0
<0
<0
<0
>0
<0
<0
<0
>0
Limited from above by Т
Possible
Тcold → Тhot
Тcold → Тhot
Тcold → Тhot
Тhot → Тcold
ZrSe2/I2
VSe2/Cl2
VSe2/I2
Possible
Limited from below by Т
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 65 No. 9 2020

1370
NIKONOV et al.
I
(a)
а
а
а
а
а
1
2
3
4
15
20
25
30
(b)
35
40
45
а
b
d
b
c
d
а
а
c
а
c
e
4
3
2
1
12
16
20
24
28
32
2θ, deg
36
40
44
48
52
Fig. 3. X-ray diffraction patterns of (a) VSe samples formed in the high-temperature zone of an ampoule with (1) Сl and (2) I
2
2
2
2
and in the low-temperature zone with (3) Cl and (4) I (a—characteristic peaks of VSe , PDF 01-074-1411); and (b) ZrSe sam-
2
2
2
ples formed in the high-temperature zone of an ampoule with (1) Сl and (2) I and in the low-temperature zone of an ampoule
2
2
with (3) I and (4) Cl (а—ZrSe (PDF 03-065-3376), b—ZrSe (PDF 00-036-1338), c—ZrCl (PDF 01-072-1904), d—Zr Se
2
2
2
3
2
4
3
(PDF 00-015-0221), e—Se (PDF 00-027-0603)).
while ZrSe3 and other impurities are accumulated in
the low-temperature zone, which confirms the
hypothesis that chemical transport occurs towards the
hotter zone.
CONCLUSIONS
The chemical transport of layered dichalcogenides
VSe2 and ZrSe2 with the participation of I2 and Cl2 as
a transporting agent is considered.
The CTR method with I2 and Cl2 as transporting
agents afforded samples of VSe2 and ZrSe2.
A thermodynamic evaluation of the direction and
possibility of the process at different temperatures pre-
dicts that the transport should proceed from the low-
temperature zone to the high-temperature zone of the
ampoule in the case of VSe2/Cl2 and in the case of
The micrographs of the samples from the high- and
low-temperature zones of the growth ampoule clearly
show a layered structure of the synthesized crystals
(Figs. 4d and 4f). The presence of characteristic angles
of 120° demonstrates the crystals have a hexagonal
structure. In Fig. 4g, a crystal of ZrSe3, which is the
major impurity phase in this sample, can be seen.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 65
No. 9
2020

THERMODYNAMIC EVALUATION OF CHEMICAL TRANSPORT
1371
(a)
(c)
(b)
(e)
(f)
40 μm
(d)
(g)
(h)
Fig. 4. Microphotographs of the substance removed from the high-temperature (hot) and low-temperature (cold) zones of growth
ampoules. VSe /Cl : (а) cold, (b) hot; VSe /I : (c) cold, (d) hot: ZrSe /Cl : (e) cold, (f) hot; ZrSe /I : (g) cold, (h) hot. All
2
2
2
2
2
2
2
2
images were obtained at the same magnification.
4. Y. Y. Lee, G. O. Park, Y. S. Choi, et al., RSC Adv. 6,
14253 (2016).
ZrSe2, regardless of the nature of the transporting
agent. In the case of VSe2/I2, the transport should pro-
ceed in the direction of the low-temperature zone.
Studies of the phase composition of the samples from
the high- and low-temperature zones of growth
ampoules confirm this assumption. The thermody-
namic parameters of chemical transport processes
have been evaluated, but taking into account the
assumptions made in the calculations, the values of
these quantities should be considered approximate
https://doi.org/10.1039/C5RA19799F
5. Y. Onuki, R. Inada, S. Tanuma, S. Yamanaka, et al.,
Solid State Ionics 8, 141 (1983).
https://doi.org/10.1016/0167-2738(83)90075-9
6. A. H. Thompson, J. C. Scanlon, and C. R. Symon, Sol-
id State Ionics 1, 47 (1980).
https://doi.org/10.1016/0167-2738(80)90021-1
7. H. Li, X. Jia, Q. Zhang, and X. Wang, Chem 7, 1510
(2018).
https://doi.org/10.1016/j.chempr.2018.03.012
FUNDING
8. T. Roy, M. Tosun, J. S. Kang, et al., ACS Nano 8, 6259
(2014).
The studies were carried out as part of a State task in the
field of basic research of the Institute of General and Inor-
ganic Chemistry, RAS, with the use of equipment of the
Shared Facility Center at the IGIC, RAS.
https://doi.org/10.1021/nn501723y
9. J. Rouxel, Physica B+C 99, 3 (1980).
https://doi.org/10.1016/0378-4363(80)90203-X
10. Zh. Zhang, P. Yang, M. Hong, et al., Nanotechnology
30, 182002 (2019).
CONFLICT OF INTEREST
https://doi.org/10.1088/1361-6528/aaff19
11. E. Yu. Buslaeva, S. V. Kraevskii, Yu. A. Groshkova,
et al., Russ. J. Inorg. Chem. 65, 5 (2020).
The authors declare no conflict of interest.
https://doi.org/10.1134/S0036023620010040
REFERENCES
12. A. V. Kochura, S. F. Marenkin, et al., Russ. J. Inorg.
Chem. 63, 1087 (2018).
1. Q. H. Wang, K. Kalantar-Zadeh, A. Kis, et al., Nat.
Nanotech. 7, 699 (2012).
https://doi.org/10.1134/S0036023618090139
13. O. Tsukio, N. Hideaki, N. Mitsuoki, and I. Motohiko,
J. Less-Common Met. 77, 185 (1981).
https://doi.org/10.1038/nnano.2012.193
2. S. Das, J. A. Robinson, M. Dubey, et al., Annu. Rev.
Mater. Res. 45, 1 (2015).
https://doi.org/10.1016/0022-5088(81)90169-7
14. M. J. Mleczko, C. Zhang, H. R. Lee, et al., Sci. Adv. 3,
e1700481 (2017).
https://doi.org/10.1146/annurev-matsci-070214-021034
3. C. N. R. Rao, H. S. S. Ramakrishna Matte, and
U. Maitra, Angew. Chem., Int. Ed. Engl. 9, 13162
(2013).
https://doi.org/10.1126/sciadv.1700481
15. H. Schefer, Chemical Transport Reactions (Academic
https://doi.org/10.1002/anie.201301548
Press, New York, 1964; Mir, Moscow,1964).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 65 No. 9 2020

1372
NIKONOV et al.
16. A. Ubaldini, J. Jacimovic, N. Ubrig, and E. Giannini, 21. K. C. Mills, Thermodynamic Data for Inorganic Sulphi-
Cryst. Growth Des. 13, 4453 (2013).
https://doi.org/10.1021/cg400953e
des, Selenides and Tellurides (Butterworths, London,
1974).
22. Thermal Constants of Substances, Ed. by V. P. Glushko
(VINITI, Moscow, 1965–1982), Iss. 1–10, [in Rus-
sian].
17. K. S. Nikonov, M. N. Brekhovskikh, A. V. Egorysheva,
et al., Inorg. Mater. 53, 1126 (2017).
https://doi.org/10.1134/S0020168517110061
23. F. K. McTaggart and A. D. Wadsley, Aust. J. Chem. 11,
18. K. S. Nikonov, M. N. Brekhovskikh, T. K. Menshchi-
kova, and V. A. Fedorov, Inorg. Mater. 55, 898 (2019).
https://doi.org/10.1134/S0020168519090097
445 (1958).
https://doi.org/10.1071/CH9580445
24. J. G. Hooley, Preparation and Crystal Growth of Materi-
als with Layered Structures, Ed. by R. M. A. Lieth
(Springer, Dordrecht, 1977).
19. M. B. Babanly, L. F. Mashadiyeva, D. M. Babanly,
et al., Russ. J. Inorg. Chem. 64, 1649 (2019).
https://doi.org/10.1134/S0036023619130035
https://doi.org/10.1007/978-94-017-2750-1
20. A. V. Blinder, A. S. Bolgar, and Zh. A. Trofimova,
Powder Metall. Met. Ceram. 32, 234 (1993).
https://doi.org/10.1007/BF00559756
Translated by G. Kirakosyan
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 65
No. 9
2020