ELECTROCHEMICAL DEPOSITION OF TELLURIUM
solutions is higher than that in acetonitrile solutions.
1329
Furthermore, the solvents specified strongly differ in
viscosity: 2.003, 0.796, and 0.328 cP for DMSO,
DMF, and AN, respectively [9], which is also an im-
portant factor of electrode polarization.
The increase in the cathode currents with temper-
ature does not exceed 25% per 10 (Fig. 1). This
indicates that the cathodic deposition of tellurium
occurs under the diffusion control. As the concentra-
tion of TeCl4 increases from 0.01 to 0.1 M, the cath-
ode currents grow virtually proportionally.
In deposition of compact tellurium from DMSO,
DMF, and AN solutions, comparatively solid and
uniform coatings (Fig. 2) are formed. At low cathode
potentials, crystallites with distinct configuration
(Fig. 2a) are formed. As the potential (current den-
sity) increases in the DMSO medium, there occurs
a kind of flattening and branching of the crystallites
(Fig. 2b), which is manifested in that the coating
becomes smoother and more lustrous. The tendency
toward smoothing of the surface of a tellurium coat-
ing with increasing cathode potential (current density)
is also observed in DMF solutions. However, this
is mostly due to a decrease in the size of the crystal-
lites and to an increase in their packing density
(Fig. 2c). In AN, no smooth films are deposited
(Fig. 2d). In this case, as the cathode potential in-
creases, the crystallites decrease in size and coarsely
crystalline dark gray coatings turn into finely crys-
talline black velvety crystals.
Fig. 3. Anodic polarization curves obtained on tellurium
in 0.005 M TeCl solutions in (1) DMSO, (2) DMF, and
4
(3) AN at 40 C.
(Fig. 2f), as indicated by electron-microscopic studies
in the COMPO. According to the energy-dispersion
X-ray microanalysis, this phase contains chlorine.
Thus, the anodic dissolution of tellurium in DMF
occurs via formation of a solvated salt film. A similar
pattern is observed in acetonitrile solutions. However,
the film formation in DMF does not passivate the an-
ode, as can be seen from the shape of the polarization
curve (Fig. 3, curve 2), whereas in AN, tellurium is
passivated (Fig. 3, curve 3).
CONCLUSIONS
(1) In dimethyl sulfoxide and dimethylformamide
solutions of TeCl4, the cathodic deposition of tel-
lurium occurs with an appreciable polarization.
As demonstrated by the results of the study, the na-
ture of a substrate chemically indifferent toward tel-
lurium affects the morphology of a cathodic deposit
only slightly. For example, the microscopic structure
of the tellurium coating and the shape and sizes of
crystallites on titanium and graphite samples differ
only slightly in identical solvents at close cathode
current densities (potentials).
(2) Smooth films are formed on a graphite sub-
strate in dimethylformamide, and smooth and lustrous
coatings, in dimethyl sulfoxide. In acetonitrile, tel-
lurium is deposited in the form of velvety coat-
ings.
(3) In dimethyl sulfoxide solutions of TeCl4, there
occurs uniform electrochemical dissolution of tel-
lurium, without accumulation of anodic products on
the surface. This makes it possible to use soluble
anodes in deposition of tellurium films in dimethyl
sulfoxide.
The anodic dissolution of tellurium in DMSO and
DMF solutions, as well as the cathodic deposition,
occurs with polarization (Fig. 3, curves 1 and 2). At
potentials of 0.3 1.5 V, the anode currents depend vir-
tually linearly on potentials, which points to an un-
hindered dissolution of tellurium.
Comparison of the initial surface tellurium with
that after the anodic dissolution in DMSO solutions of
TeCl4 (Fig. 2e) shows that crystallites are etched-out
in electrolysis. In this case, the surface becomes cor-
rugated, but single-phase. In DMF solutions, a new
phase appears in electrolysis on the tellurium surface
REFERENCES
1. Baeshov, A., Zhurinov, M.Zh., and Zhdanov, S.I.,
Elektrokhimiya selena, tellura i poloniya (Electro-
chemistry of Selenium, Tellurium, and Polonium),
Alma-Ata: Nauka, 1989.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 8 2007