Vapor pressure and thermodynamic functions of TeI4 and its decomposition products

Article abstract of DOI:10.1134/S0020168507090191

Using a flow method, we have measured the vapor pressure of tellurium tetraiodide, an attractive reagent for chemical vapor deposition technology. The results, combined with earlier tensimetric data, have been used to evaluate the basic thermodynamic functions of TeI₄ and its thermolysis products.

Full text of DOI:10.1134/S0020168507090191

ISSN 0020-1685, Inorganic Materials, 2007, Vol. 43, No. 9, pp. 1018–1023. © Pleiades Publishing, Inc., 2007.
Original Russian Text © A.M. Kut’in, V.S. Polyakov, M.F. Churbanov, G.E. Snopatin, 2007, published in Neorganicheskie Materialy, 2007, Vol. 43, No. 9, pp. 1135–1140.
Vapor Pressure and Thermodynamic Functions of TeI4
and Its Decomposition Products
A. M. Kut’in, V. S. Polyakov, M. F. Churbanov, and G. E. Snopatin
Institute of Chemistry of High-Purity Substances, Russian Academy of Sciences,
ul. Tropinina 49, Nizhni Novgorod, 603950 Russia
e-mail: kutyin@ihps.nnov.ru
Received September 25, 2006
Abstract—Using a flow method, we have measured the vapor pressure of tellurium tetraiodide, an attractive
reagent for chemical vapor deposition technology. The results, combined with earlier tensimetric data, have
been used to evaluate the basic thermodynamic functions of TeI4 and its thermolysis products.
DOI: 10.1134/S0020168507090191
INTRODUCTION
temperatures, where the TeI4 vapor pressure is low.
Independent saturated vapor pressure (SVP) measure-
ments by a flow method provide more accurate results
at low pressures and make it possible to reveal the
inherent features of TeI4 transport by the flow of an
inert gas.
The objective of this work was to quantitatively
characterize TeI4 transport in flowing helium using
SVP measurements. The results were analyzed in con-
junction with literature data in order to determine tem-
perature-dependent thermodynamic functions of TeI4
vapor. We also attempted to calculate the compositions
of the condensed and gaseous products of TeI4 decom-
position and their enthalpies of formation and to obtain
a self-consistent set of thermodynamic functions for
major species by solving the inverse problem of chem-
ical and phase equilibria in the system.
Tellurium tetraiodide is of interest as a volatile pre-
cursor for the preparation of tellurium, its compounds,
and related high-purity materials. The ability to control
the vapor-phase transport of TeI4 to the reaction zone
and prepare the desired tellurium-containing material is
highly dependent on knowledge of the thermodynamic
functions of TeI4 and its conversion products in con-
densed and vapor phases. Such data are missing in ther-
modynamic databases (IVTANTERMO and NIST),
primarily because of the thermal lability of tellurium
halides, especially TeI4.
In physicochemical studies of TeI4 [1–7], consider-
able attention has been paid to static vapor pressure
measurements. Such measurements were performed
both at relatively low temperatures (low vapor pres-
sures) and at temperatures where tellurium tetraiodide
decomposes almost completely [4–7]. Analysis of
high-temperature data under arbitrary assumptions as
to the mechanism of decomposition through hypotheti-
cal reactions reduces to estimation of their equilibrium
constants. This approach does not include the total set
of linearly independent reactions and fails to properly
describe the general conditions of the heterophase equi-
librium between TeI4 and its decomposition products.
Accordingly, it gives no way of deducing a self-consis-
tent set of thermodynamic functions of tellurium
iodides. For this reason, the experimental data reported
by Ivashin and Petrov [4] and Oppermann et al. [5], on
the whole consistent, give no answer to the question of
what major gas-phase decomposition products are.
Ivashin and Petrov [4] conclude that the decomposition
products are I2 and Te, while according to Oppermann
et al. [5] these are I2 and TeI2.
EXPERIMENTAL
TeI4 was synthesized by reacting concentrated
hydriodic acid with aqueous orthotelluric acid, fol-
lowed by air drying and iodine extraction with CCl4.
The resultant TeI4 had the form of a microcrystalline
substance steel gray in color and contained no more
than 10 ppmw iodine impurity.
The experimental setup for measuring the TeI4
vapor pressure incorporated a quartz tube, which was
mounted in a thermostat and contained a quartz boat
with the sample, a carrier gas (high-purity helium)
delivery system, and a flowmeter. The temperature was
monitored with a Chromel–Alumel thermocouple.
After thermal equilibration, the boat was introduced
into the tube through the plug, the sample was heated to
the set temperature, and the system was flushed with
helium. Next, we began to measure the volume of the
Because of the thermal instability of TeI4 and the
presence of volatile dissolved I2, static measurements
give overestimated vapor pressures, especially at low carrier gas passed through the system. The amount of
1018

VAPOR PRESSURE AND THERMODYNAMIC FUNCTIONS OF TeI4
1019
log(p/Pa)
0.5
vaporized substance was determined from the weight
loss of the sample, which was weighed with an accu-
racy of 1 mg. Experiments were conducted at tempera-
tures from 420 to 470 K. The uncertainty in our temper-
ature measurements was within 1 K.
0
1
2
–0.5
The SVP measured in this manner is equal to the
partial pressure of the substance in the inert carrier gas
–1.0
–1.5
–2.0
–2.5
˙
extrapolated to zero flow rate, V
0. The measure-
ment results are most conveniently converted to the
sought pressure by combining the Clapeyron equation
and its form written for 1 mol of a gas under normal
conditions (p0 = 101325 Pa, V0 = 22.4141 l/mol, T0 =
273.15 K):
1.8
1.9
2.0
2.1
2.2
2.3
˜
0
103/T, K–1
TV
0 m
-------------
p(Pa) = p
,
(1)
M ˙
Vτ
Fig. 1. Measured SVP (data points), least squares fit (solid
line), and extrapolation results (dashed line); (1) this work,
(2) low-temperature data from Ivashin and Petrov [4].
where m (mg) is the mass of the vaporized substance, M
(g/mol) is its molar mass, τ (min) is the measurement
time, V (ml/min) is the volumetric flow rate, and T =
T/T0 is a dimensionless temperature.
˜
˙
The significant difference between the data obtained
by two experimental techniques (Fig. 1) suggests that,
in the case of thermolabile substances, determining the
SVP and assigning it to a particular species requires
theoretical analysis.
Additional measurements of the pressure as a func-
tion of carrier-gas flow rate in the range 20–50 ml/min
yielded the correlation equation
2
–3
–5
˙
˙
p0 = p/(1 – 1.25 × 10 V + 1.57 × 10 V ) ,
In the most general SVP determination, the molar
which indicates that, in the range of flow rates studied,
the pressure reduced to zero flow rate, p0, is on average
2% higher than the measured pressure, p. At the carrier-
gas flow rates in question (and, obviously, at slower
flow rates), helium is essentially saturated with TeI4
vapor.
Gibbs energies G of condensed and vapor phases are
assumed to be equal along the saturation line:
Gcond = H0cond(0) – RTϕc0ond = Gvapor
0
= Hvapor(0) – RTϕ0vapor + RT ln p.
˜
0
˜
The dimensionless pressure p = p/p (equivalent to
RESULTS AND DISCUSSION
pressure in atmospheres) can easily be expressed
through the temperature-dependent terms of the
reduced (divided by RT) molar Gibbs energy:
The measured TeI4 SVP (average over three or four
repeated measurements) is shown in Fig. 1 (open
squares) as a function of temperature. Using least
squares fitting, we obtained the equation
G(T)
RT
H0(0)
RT
g0(T) = ----------- = ------------- – ϕ0(T) .
4966
log(p/Pa) = – ----------- + 9.420.
T
We obtain
0
0
The flow method, commonly utilized to measure
low pressures, is believed to straightforwardly charac-
terize TeI4 vaporization and to be insensitive to subse-
quent TeI4 decomposition in the vapor phase. TeI4 ther-
molysis may, however, occur before and during vapor-
ization, leading to slightly underestimated vapor
pressures since the molar mass of TeI4, appearing in
Eq. (1), exceeds the average molar mass of (1 – y)TeI4 +
yI2 mixtures carried away by the flow of the carrier gas.
Clearly, static TeI4 vapor pressure measurements give
overestimated SVPs (Fig. 1, open triangles) because of
the higher volatility of I2 impurities and the possible
TeI4 decomposition in the vapor phase.
˜
p = exp(gcond(T) – gvapor(T)),
(2)
which demonstrates that p is determined by the enthal-
pies of the condensed and vapor phases at absolute
zero, H0vapor (0) and H0cond (0), and by the dimensionless
Planck functions ϕ0vapor(T) and ϕc0ond(T). For condensed
substances, we used analytical forms common in ther-
modynamic databases [8, 9]:
ϕ0(T) = ϕ1 + ϕ2 lnx + ϕ3x–2 + ϕ4x–1 + ϕ5x
+ ϕ6x2 + ϕ7x3, x = T × 10–4.
INORGANIC MATERIALS Vol. 43 No. 9 2007

1020
p, Pa
KUT’IN et al.
termined quantity. It was found by least squares fitting
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
the present and earlier low-temperature SVP data to
Eq. (2). The fitting results (Figs. 1, 2) ensure a good
compromise between the two experimental techniques
and well represent the low-temperature data, both in
magnitude and in the slope of the logarithmic curve.
The method of thermodynamic functions ensures low-
and high-temperature SVP extrapolation for the distinct
compound TeI4. Note that the results of low-tempera-
ture static measurements by Oppermann et al. [5]
exceed ours and the SVP measured by Ivashin and
Petrov [4] (Fig. 2), which can well be accounted for by
the higher I2 content of the sample whose preparation
included saturation with iodine. “True” SVP values
were found in [5] using compensation calculations.
1
2
400
500
600
700
T, K
Fig. 2. Total pressure as a function of temperature in the sys-
tem tellurium tetraiodide–its thermal decomposition prod-
ucts: (1) data from [4], (2) data from [5]; the solid and
dashed lines at low temperatures represent the SVP results
for individual tellurium tetraiodide [Eq. (2)]; the solid lines
For convenience, the intricate analytical expression
for the temperature-dependent SVP [Eq. (2)] can be
approximated by a simpler formula in the temperature
range 420–570 K:
at high temperatures (almost complete TeI decomposition)
4
show the results of solving the inverse problem represented
by Eqs. (3'), (4'), (5'), (5''), and (6).
5838.2
log(p/Pa) = 11.425 – --------------- + 0.69911logT
T
– 4.27045 × 10–3T.
For the vapor phase, the classical ideal gas model in
the rigid rotator–harmonic oscillator approximation is
commonly accepted and is sufficient under the condi-
tions of this study.
The parametrization of the thermodynamic func-
tions of gaseous TeI4, completed by solving the inverse
problem, together with the available fitting parameters
To optimize the geometry and calculate the
moments of inertia and vibrational frequencies of gas-
eous tellurium iodides (TeI2, Te2I2, and TeI4), we used
the local-density-functional approximation. Compari-
son of the calculation results with available experimen-
tal data on the geometry and vibrational frequencies of
the species in question indicates that this approach is
2
for the solid state, except for the basis set of functions
(enthalpy H0 and entropy S0) and the SVP found using
Eq. (2) (see the table and Footnote 2) makes it possible
to straightforwardly calculate the temperature-depen-
dent enthalpy of sublimation from the difference
between the enthalpies of the vapor and condensed
1
accurate enough to calculate Planck functions.
phases: ∆sH = Hv0apor – Hc0ond . In the rigid rotator–har-
monic oscillator approximation, the enthalpy of the
At the same time, this method is not always capable
of accurately predicting the standard enthalpy of forma-
tion of molecules composed of heavy atoms (Te, I).
vapor phase is given by
With the parametrized thermodynamic functions of
solid TeI4 and the Planck functions derived in the rigid
rotator–harmonic oscillator approximation, the
enthalpy of formation of gaseous TeI4 is the only unde-
⎛
⎞
θi
5 + r
-----------
2
0
0
Hvapor = Hvapor(0) + R T
+
--------------------------------- ,
⎜
⎟
∑
exp(θi/T) – 1
⎝
⎠
i
where r is the number of rotational degrees of freedom
of the molecule, and the Einstein temperatures θi =
1
Results of quantum-chemical calculations (local-density-func-
tional approximation, MPW1PW91 potential, DGDZVP basis
set) of the moments of inertia (I, atomic units) and molecular
hcνi
–1
vibrational frequencies (ν , cm ) for evaluating Planck functions
----------
are expressed through molecular vibrational fre-
k
in the rigid rotator–harmonic oscillator approximation: {I } =
1–3
quencies νi (cm–1) using the Planck and Boltzmann
constants (h and k) and the speed of light in vacuum (Ò).
6021, 9589, 10725, {ν1–9 } = 29.9, 45.1, 56.9, 68.2, 69.6, 118.3,
177.5, 191.7, 195.5 for TeI ; {I } = 914, 4055, 4968, {ν1–3 } =
4
1–3
61.4, 204.9, 205.9 for TeI . Calculated and measured (in paren-
2
2
theses) frequencies of TeCl (similar in symmetry to TeI ):
Fitting parameters of the thermodynamic functions of TeI (s) in
2
2
4
the temperature range 300–750 K: H0(0) ⁄ (104R) = –0.862008;
{ν1–3 } = 120.8 (125), 355.6, 374.1 (377). I : ν = 214.0 (214.5).
2
–10
Te I : {I } = 2318, 8656, 9682; {ν1–6 } = 29.2, 58.3, 69.7,
{ϕ } = 72.8460, 14.1494, 6.0494 × 10 , 0.045541, 70.8358, –
2 2
1–3
1–7
190.7, 192.4, 202.2.
42.5740, 955.446.
INORGANIC MATERIALS Vol. 43 No. 9 2007

VAPOR PRESSURE AND THERMODYNAMIC FUNCTIONS OF TeI4
1021
Temperature-dependent “total” enthalpy (kJ/mol) (with allowance made for the level it is measured from), entropy
(J/(mol K)), vapor pressure (Pa), and enthalpy of sublimation (kJ/mol) of TeI4
H0*
S0
p
∆sH**
H0***
TeI4 (g)
S0
H0***
TeI2 (g)
S0
T, K
TeI4 (s)
298.15
400
–35.146
–18.819
–10.259
–1.3069
8.0657
17.891
28.205
39.046
345.08 7.4565 × 10–9
392.09 6.6503 × 10–4
412.24 2.5632 × 10–2
106.52
101.04
97.827
94.236
90.233
85.783
71.371
82.217
87.568
92.930
98.299
103.67
109.05
114.44
540.34
571.63
584.23
595.53
605.77
615.12
623.73
631.71
97.432
103.26
106.13
109.01
111.90
114.79
117.69
120.58
384.63
401.43
408.20
414.27
419.78
424.81
429.44
433.73
450
500
431.10
448.96
431.10
482.56
498.62
0.43428
550
4.6418
600
33.562
650
180.36
700
757.66
Note: The thermodynamic functions of Te I are not given since the enthalpy of its formation found by solving the inverse problem cannot
2 2
be assigned to a meaningful quantity because of the insignificant Te I concentration in the system.
2 2
0
0
* To calculate the enthalpy H of solid TeI , we used the standard enthalpy of formation ∆ H (298.15 K) = –35.15 kJ/mol found
4
f
from the enthalpy of solution in KOH [12].
** Note the marked difference between the enthalpies of sublimation of TeI reported in the literature: ∆ H (298.15 K) = 131.4 kJ/mol
0
4
s
0
[5] and ∆ H = 65.7 kJ/mol (average over the temperature range 450–510 K) [6].
s
0
*** The standard enthalpies of formation of gaseous TeI and TeI , found by solving the inverse problem, are ∆ H (298.15 K) =
4
2
f
71.37 and 99.63 kJ/mol, respectively.
In the representation commonly accepted in data- curve and, concurrently, calculating the chemical com-
bases, the enthalpy of condensed TeI4 has the form
positions of the condensed and vapor phases.
The conditional extremum problem of minimizing
the Gibbs energy at fixed external parameters, T and p,
is known [10, 11] to reduce to nonlinear balance equa-
tions for phases f,
H0cond = H0cond(0) + R × 104
× (ϕ2x – 2ϕ3x–1 – ϕ4 + ϕ5x2 + 2ϕ6x3 + 3ϕ7x4).
The calculated temperature-dependent enthalpy of
sublimation is given in the table (see Footnote 2).
nfi = nf ,
∑
(3)
i
Comparison of the extrapolated SVP values (Fig. 2,
dashed curve) with the data obtained by static measure-
ments indicates that, in the temperature range of signif-
icant TeI4 disproportionation (490–520 K), the total
pressure exceeds the TeI4 contribution. The higher tem-
perature behavior (data points below the dashed curve)
reflects a combination of hetero- and homophase TeI4
decomposition processes and a transition to the unsat-
urated vapor region. Finally, the high-temperature por-
tions of the three curves, differing in the specific vol-
ume of the system, Vb, in three experiments (see
below), represent the chemical and phase equilibria of
the gaseous and condensed products of TeI4 decompo-
sition.
f = 1(condensed phase), 2(vapor phase),
and independent components j,
nfiaij = bj, j = 1(Te), 2(I).
(4)
∑∑
f
i
The number of moles of species i in phase f (nfi) can
be expressed through the chemical potentials λj of the
independent components (elemental Te and I):
⎛
⎜
⎝
⎞
n = n exp
a λ – g (T, p) ,
(5)
⎟
fi
f
ij
j
fi
∑
⎠
j
where
The high-temperature data can be processed using
general methods of thermodynamic analysis of chemi-
cal and phase equilibria. The hypothesis that chemical
and phase equilibria are reached at the level of all the
possible chemical transformations is qualitatively
explained by the lifting of kinetic limitations at temper-
atures above 620 K in the thermolabile system under
investigation. This hypothesis can be checked and vali-
H0fi(0)
g (T, p) = -------------- – ϕ0 (T) +
⎧
˜
ln p, vapor
⎨
⎩
fi
fi
RT
0, condensate
is the reduced Gibbs energy of component (chemical
species) i in phase f ; nf is the number of moles of phase
f, and aij is a coefficient which determines the number
dated by formulating and solving the relevant inverse of atoms j per formula unit of chemical species (com-
problem of quantitatively processing the tensimetric ponent) i. The composition of the system in terms of
INORGANIC MATERIALS Vol. 43 No. 9 2007

1022
KUT’IN et al.
independent components is expressed as the numbers only condensed phase present in addition to the neces-
of moles of Te (b1) and I (b2).
sary vapor phase is a Te(s) solution, with a residual
amount of TeI4 and, possibly, TeI2.
The exhaustive thermodynamic characteristic of
each species i in phase f provided by the set of gfi(T, p)
functions, and the overall composition of the system
{bj} constitute the input data set for the so-called direct
problem at fixed p and T which determines the chemical
and phase compositions {nfi} (5) satisfying the balance
equations (3) and (4). In calculations with fixed volume where the mole fraction of species i in the vapor phase
and temperature, the volume and pressure are given by can be obtained from Eq. (5):
the equation of state
The phase balance equations (3) can then be written
in a clearer form, using mole fractions:
yi0
(
yi = 1),
xi = 1,
(3')
˜
p =
∑ ∑
∑
yi0
˜
p
⎛
⎜
⎝
⎞
0
i
˜
˜
˜
pVb = nvaporRT, pV = nvapor
T
˜
----
y = exp
a λ – g – ln p =
,
⎟
i
ij
j
∑
(6)
⎠
0
i
˜
˜
˜
(p = p/p , V = Vb/V0, T = T/T0).
(5')
⎛
⎜
⎝
⎞
y0 = exp
a λ – g0 .
For a system containing condensed and vapor
phases of variable composition, it is convenient to
relate the specific volume Vb = V/b to a constant elemen-
⎟
i
ij
j
i
∑
⎠
j
tal composition, b =
bj . The number of moles of the
The expression for the mole fraction of species i in
the condensed phase can also be obtained from Eq. (5):
∑
vapor phase, nvapor = nvapor/b, is then a relative, dimen-
sionless quantity, expressed in mol/mol-at. Since pres-
⎛
⎜
⎝
⎞
˜
sure appears in dimensionless form ( p ) in all expres-
x = exp
a λ – g (T) .
(5'')
⎟
i
ij
j
i
∑
⎠
sions of chemical thermodynamics, Eq. (6) also gives
the dimensionless form of the equation of state.
j
With the above designations and the equations of
state (6), the balance equations (4) take the form
The specifics and complexity of the inverse problem
are associated with the necessity to concurrently solve
several copies of system (3)–(5) (for each data point).
In addition to the “internal” variables λTe and λI, there
are general parameters to be determined in each point.
In the problem in hand, these are enthalpies of forma-
tion of the possible TeI4 conversion products, which
appear in gfi. In contrast to the general problem (3)–(6),
this problem is simplified by its phase determinacy. In
the high-temperature region under consideration, the
˜
V
y0i aij + ncond xiaij = bj, j = 1(Te), 2(I). (4')
---
∑
∑
˜
T
i
i
Eliminating ncond from the last two equations and
supplementing the result with the second equation in
(3'), we obtain a system of two equations in two vari-
ables, λ1 and λ2. The total quadratic residual of these
equations for each data point and the deviations of the
calculated pressures (first equation in (3')) from exper-
imental data can be used to determine, along with the
set of internal variables, the missing parameters of ther-
modynamic functions and, more importantly, to con-
currently calculate the composition of the major prod-
ucts of TeI4 decomposition. Note that the volume of the
measuring cell, Vb, unspecified in [4, 5], was included
in the set of fitting parameters for each of the three
experiments. The dimensionless volume (see the sec-
logyi, logxi
1
*Te
0
I2
–1
–2
–3
–4
–5
–6
–7
–8
TeI2
TeI2
TeI4
˜
ond equation in (6)) was determined to be V = 2.02,
*TeI4
2.17, and 4.11.
The calculation results for high-temperature vapor
pressure data (Fig. 2) were used to determine the com-
position of TeI4 decomposition products; Fig. 3 corre-
sponds to the bottom curve in Fig. 2.
Te2I2
600
640
680
720
760
T, K
The set of thermodynamic functions derived here
opens up the possibility of detailed macrokinetic mod-
eling of TeI4 transport and conversion in chemical
vapor deposition processes.
Fig. 3. Temperature-dependent compositions (mole frac-
tions) of gaseous (y , open points) and condensed (x , filled
i
i
points) TeI thermolysis products.
4
INORGANIC MATERIALS Vol. 43 No. 9 2007

VAPOR PRESSURE AND THERMODYNAMIC FUNCTIONS OF TeI4
1023
rium(IV) Chloride, Bromide, and Iodide, J. Chem. Soc.
A, 1966, no. 10, pp. 1479–1480.
3. Ivashin, S.A., Petrov, E.S., and Samsonova, T.I., Physic-
ochemical Study of the Te–I System, Izv. Sib. Otd. Akad.
Nauk SSSR, Ser. Khim. Nauk, 1969, vol. 6, no. 14,
pp. 51–54.
4. Ivashin, S.A. and Petrov, E.S., Thermal Stability of Tel-
lurium Tetrahalides: TeCl4, TeBr4, and TeI4, Izv. Sib.
Otd. Akad. Nauk SSSR, Ser. Khim., 1971, vol. 2, no. 4,
pp. 28–33.
5. Oppermann, H., Stöver, G., and Wolf, E., Die Sublima-
tion und thermische Zerzetzung von TeI4 und die Exis-
tenz von TeI2 in der Gasphase, Z. Anorg. Allg. Chem.,
1976, vol. 419, pp. 200–212.
CONCLUSIONS
Using vapor pressure measurements (flow method,
temperatures from 420 to 480 K) and earlier low-tem-
perature data, we determined the temperature-depen-
dent SVP of tellurium tetraiodide, expressed through its
thermodynamic functions in solid and vapor phases,
with the possibility of extrapolating it to low and high
temperatures.
The high-temperature vapor pressure data obtained
by solving the inverse problem of two-phase chemical
equilibrium were used to determine the composition of
TeI4 decomposition products. The condensed phase
was found to consist of solid tellurium and trace
amounts of TeI4 dissolved in it. The vapor phase con-
sists predominantly of I2, with a minor amount of TeI2.
6. Kuliev, A.A., Kulieva, S.A., and Gadzhiev, S.M., Te–I
System, Izv. Akad. Nauk SSSR, Neorg. Mater., 1972,
vol. 8, no. 5, pp. 825–827.
Using the local-density-functional approach in the
rigid rotator–harmonic oscillator approximation, we
parametrized the thermodynamic functions of the gas-
eous species of interest. Their consistent enthalpies of
formation were determined by solving the inverse prob-
lem of heterophase equilibrium.
7. Safonov, V.V., Lemeshko, O.V., Chernykh, S.M., and
Kortunov, B.G., Stability of TeI4 and Me2TeI6 Studied by
Vapor Pressure Measurements and Thermogravimetry,
Zh. Neorg. Khim., 1974, vol. 19, no. 6, pp. 1454–1456.
8. Bank dannykh termodinamicheskikh velichin IVTAN-
TERMO. Elektronnaya versiya dlya WINDOWS (IVTAN-
TERMO Thermodynamic Database: Electronic Version
for Windows), Moscow: TERMOTsENTR Ross. Akad.
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ACKNOWLEDGMENTS
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Database, no. 69, June 2005 Release.
This work was supported by the Russian Foundation
for Basic Research, grant no. 05-08-33671a.
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