PHYSICOCHEMICAL STUDY
1663
Medvedeva said [2] that In2Te3 has three polymorphs:
T, K
α-In2Te3, β-In2Te3, and γ-In2Te3. However, Yatsenko [3]
mentioned only two In2Te3 phases: high-temperature
β-In2Te3 and low-temperature α-In2Te3. Figure 1 makes
2000
1800
1600
1200
1000
800
it clear that the α-In2Te3
β-In2Te3 phase transition
occurs at 785 K and has a eutectoid character. Primary
crystals of β-In2Te3-base solid solution are separated
from a cooled liquid in the In2Te3 crystallization region
(70–90 mol % In2Te3).
Addition of SmTe to indium sesquitelluride
depresses the polymorphic transition temperatures. The
L
L + SmTe
L + α
change in the α-In2Te3
β-In2Te3 transition tempera-
970
L + Sm In Te
3
2
5
ture is especially serious. Regions in which α + β solid
800
solutions coexist are insignificant (Fig. 1).
α
The extent of In2Te3-base solid solution is 10 mol %
SmTe + Sm In Te
5
3
2
Sm In Te + α
at 850 K and ~3 mol % SmTe at room temperature.
3
2
5
600
The SmTe–InTe phase diagram (Fig. 2) shows that
this a quasi-binary join and one incongruently melting
compound (Sm3In2Te5) is formed by the peritectic reac-
SmTe 20
40
60
mol %
80
InTe
tion L + SmTe
Sm3In2Te5 at 970 K.
Fig. 2. Phase diagram for the SmTe–InTe join.
The liquidus consists of the primary separation
curves of SmTe, Sm3In2Te5, and α InTe-base solid solu-
tions. The eutectic coordinates are 23 mol % SmTe and
800 K. The InTe-base solubility at room temperature is
9 mol % SmTe. In measuring microhardness of alloys
of the SmTe–InTe system, we obtained three sets of val-
ues corresponding to the dark SmTe phase (3250 MPa),
gray Sm3In2Te5 phase (1450 MPa), and light InTe phase
(400–450 MPa).
Figures 1 and 2 make it clear that the SmTe solubil-
ity in In2Te3 and InTe depends substantially on the
phase to which samarium telluride is added. The largest
homogeneity region exists along the SmTe–InTe join.
Indium is known to tend, under certain conditions, to
form octahedral structures; an InTe phase existing at
high pressures crystallizes in a NaCl-type structure, as
SmTe. This is responsible for the considerable solubil-
ity of SmTe in InTe. The dimensional factor is also
favorable: the relative difference between the Sm2+ and
In2+ ionic radii is 10%.
‡ = 8.56 Å, Ò = 7.24 Å) because In2+ has a smaller ion
radius than Sm2+ (~1.13 against 1.09 Å [7]). Addition of
SmTe to InTe leads to the formation of substitutional
solid solutions with vacancies in the cationic sublattice.
In summary, we have studied the Sm–In–Te system
along SmTe–In2Te3 and SmTe–InTe joins using physic-
ochemical methods and constructed phase diagrams of
these joins.
We have found ternary tellurides SmIn2Te4,
SmIn4Te7, and Sm3In2Te5 and indium telluride-base
incomplete solid solutions.
REFERENCES
1. M. E. Kost, A. L. Shilov, V. I. Mikheeva, et al., Com-
pounds of Rare Earths (Nauka, Moscow, 1983) [in Rus-
sian].
2. Z. S. Medvedeva, Chalcogenides of Group IIIB Ele-
ments of the Periodic System (Nauka, Moscow, 1968) [in
Russian].
Solubility along the SmTe–In2Te3 join is far lower
than along the SmTe–InTe join. This is likely because
of a dimensional factor. Along the SmTe–In2Te3 join,
there are stoichiometric vacancies in the cationic sub-
lattice, along with indium atoms; the crystal-chemical
radius of these vacancies (in In2Te3) is smaller than the
3. S. P. Yatsenko, Indium. Properties and Compounds
(Nauka, Moscow, 1987) [in Russian].
4. K. Schubert, E. Dorre, and E. Gunrel, Naturwiss. 41
(19), 448 (1954).
In2+ radius. As a result, the relative difference between
the Sm2+ ionic radius and the mean ionic radius of the
5. V. A. Petrusevich and V. M. Sergeeva, Fiz. Tverd. Tela 2
(11), 2881 (1960).
substituent complex (3Sm
for a neutral vacancy) increases.
2In + ‡0, where ‡0 stands
6. O. M. Aliev, T. Kh. Kurbanov, and P. G. Rustamov, Izv.
Akad. Nauk SSSR, Neorg. Mater. 12 (11), 1944 (1976).
The unit cell parameters of In1 – ıSmıí solid solu-
tions linearly increase with composition (for
In0.09Sm0.01íÂ, ‡ = 8.48 Å, Ò = 7.16 Å; for In0.91Sm0.09íÂ,
7. M.C. Day and J. Selbin, Theoretical Inorganic Chemis-
try (Reinhold, New York, 1969; Khimiya, Moscow,
1976).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 10 2009