Oscillations and spatio-temporal structures during electrodeposition of AgCd alloys

Article abstract of DOI:10.1016/j.electacta.2012.06.100

During electrodeposition of cadmium both potentiostatic and galvanostatic oscillations are registered. Experiments under different hydrodynamic conditions show the possibility of formation/destruction of passive layers on the electrode surface, which besides the hydrogen evolution under limiting current density conditions could be an additional promoter of the oscillation behavior of the system. The duration of the observed galvanostatic potential oscillations decreases with increased current density, due to massive hydrogen evolution. XPS investigations confirm the existence of passive films at potentials corresponding to the onset of oscillations. Potential oscillations are observed again during electrodeposition Ag-Cd alloys at high current densities. They appear when the cadmium content in the deposits is more than 45 wt.% and they have possibly the same origin as the oscillations during cadmium electrodeposition. The period and regularity of the oscillations depend on the current density, respectively on the cadmium content. At high cadmium content during alloy deposition, the formation of periodical structures consisting of different phases of the alloy is registered. The cadmium content of the different morphological areas of the patterns is almost identical. The XRD spectra of the obtained structured coatings suggest the existence of two textured phases, with a very strong preferred orientations of the crystallites in the direction 〈1 0 1〉 for the pure cadmium phase.

Full text of DOI:10.1016/j.electacta.2012.06.100

Electrochimica Acta 79 (2012) 162–169
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Oscillations and spatio-temporal structures during electrodeposition of
AgCd alloys
Ts. Dobrovolskaa,∗, D.A. López-Saurib, L. Velevab, I. Krasteva
a Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
b Center for Investigation and Advanced Studies of IPN, Mérida, Yucatán 97310, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
During electrodeposition of cadmium both potentiostatic and galvanostatic oscillations are registered.
Experiments under different hydrodynamic conditions show the possibility of formation/destruction of
passive layers on the electrode surface, which besides the hydrogen evolution under limiting current
density conditions could be an additional promoter of the oscillation behavior of the system. The dura-
tion of the observed galvanostatic potential oscillations decreases with increased current density, due
to massive hydrogen evolution. XPS investigations confirm the existence of passive films at potentials
corresponding to the onset of oscillations. Potential oscillations are observed again during electrodepo-
sition Ag–Cd alloys at high current densities. They appear when the cadmium content in the deposits is
more than 45 wt.% and they have possibly the same origin as the oscillations during cadmium electrode-
position. The period and regularity of the oscillations depend on the current density, respectively on the
cadmium content.
Received 6 February 2012
Received in revised form 24 April 2012
Accepted 27 June 2012
Available online 5 July 2012
Keywords:
Oscillations
Self-organisation
Silver–cadmium alloys
Textured coatings
X-ray diffraction
At high cadmium content during alloy deposition, the formation of periodical structures consisting of
different phases of the alloy is registered. The cadmium content of the different morphological areas of
the patterns is almost identical. The XRD spectra of the obtained structured coatings suggest the existence
of two textured phases, with a very strong preferred orientations of the crystallites in the direction ꢀ1 0 1ꢁ
for the pure cadmium phase.
© 2012 Elsevier Ltd. All rights reserved.
1. Introduction
potential changes should be a result of a layer-by-layer deposi-
tion of both metals – silver and cadmium). The results from the
It was recently reported that during electrodeposition of
silver–cadmium alloys instabilities were observed, resulting in
periodical changes in the potential or current with time and for-
mation of periodical spatio-temporal structures onto the electrode
surface [1].
The interest in the investigation of this alloy system is based
also on the wide variety of phases observed in the electrodeposited
alloy coatings [2–6]. Recently the difficulties in determination
of the phase content of the different zones in electrodeposited
heterogeneous silver–cadmium alloy coatings were overcame by
comparative investigations by X-ray diffraction and anodic linear
sweep voltammetry (ALSV) [7].
Polukarov and Gorbunova supposed changes of the cathodic
potential corresponding to the changes of the phase composition
of the deposited silver–cadmium alloy [8]. They expected possible
potential oscillations during electrodeposition of the alloy, but
they were not able to register them (in this case the periodical
systematical investigations of some silver alloys [9–13], as well
as literature data [14–16] allow the conclusion, that potential or
current oscillations have not been registered in the pure silver
cyanide electrolyte under investigated electrolysis conditions.
Otherwise, during cadmium electrodeposition from cyanide
electrolytes intensive potential changes with an amplitude of more
than 400–500 mV were observed by Vishomirskis [17] as well as by
Kaneko et al. [18].
Vishomirskis stated that in the case of cadmium deposition from
cyanide electrolytes the hydrogen evolution does not play the main
role originating the potential oscillations in time. The reason is the
formation/destruction of some passive film on the surface of the
electrode [17]. According this concept, during electrodeposition of
some metals from cyanide electrolytes, the passivation is a result of
the formation of a compound with general formula Mex(CN)y(OH)z
on the cathode.
Kaneko et al. [18] established that the potential oscillations
result from the decrease in the surface concentration of cadmium
ions during galvanostatic deposition almost nearly to zero, and as a
result the potential shifts rapidly to higher negative values reach-
ing the deposition potential of hydrogen. The evolved hydrogen
∗
Corresponding author.
E-mail address: tsvetina@ipc.bas.bg (Ts. Dobrovolska).
0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.electacta.2012.06.100

Ts. Dobrovolska et al. / Electrochimica Acta 79 (2012) 162–169
163
bubbles from the cathode surface provoke some agitation of the
electrolyte, facilitating in this way the mass transport process. As
a result, the surface concentration of cadmium ions increases and
the potential decreases again.
Current oscillations under potentiostatic conditions were
observed neither by Vishomirskis, nor by Kaneko et al.
Thus, the process of oscillatory behavior of Cd is discussed
from two different points of view in the galvanostatic case. Cur-
rent oscillations could be observed under potentiostatic conditions.
Obviously the oscillatory process is more complex and needs addi-
tional investigations.
The oscillations of potential and/or current, together with
spatio-temporal structure formation are observed in some other
silver alloy systems like Ag–Sb [19] and Ag–In [20]. Previous
experiments show that the oscillations, registered during elec-
trodeposition of silver–cadmium alloys and the observed pattern
onto the electrode are richer in variety of types, amplitudes and
periods [1].
The aim of this work is to answer the questions:
1. What is the nature of the oscillations, observed during electrode-
position of cadmium from cyanide electrolyte?
2. What is the connection between the oscillations during
alloy electrodeposition and the phase composition of the
silver–cadmium coatings with periodical spatio-temporal struc-
tures?
2. Experimental
The cadmium, silver and alloy coatings were deposited from
cyanide electrolytes. Pure cadmium was deposited from a solu-
tion containing mainly 0.15 M Cd as CdSO4·8/3H2O + 0.6 M KCN,
pure Ag from a solution containing 0.06 M Ag as KAg(CN)2 + 0.6 M
KCN and Ag–Cd alloys – from a solution containing 0.06 M Ag as
KAg(CN)2 + 0.15 M Cd as CdSO4·8/3H2O + 0.6 MKCN. Chemical sub-
stances of pro analisi purity and distilled water were used.
The experiments were performed in a 100 cm3 tri-electrode
glass cell at room temperature. The vertical working electrode
(area 2 cm2), the rotating disc electrode (Metrohm 628-10) (area
0.07 cm2) and the two counter electrodes were made from plat-
inum. An Ag/AgCl reference electrode (EAg/AgCl = −0.197 V vs NHE)
was used. The reference electrode was placed in a separate cell filled
with 3 M KCl solution. It was connected to the electrolyte cell by a
Haber–Luggin capillary through an electrolyte bridge containing
also 3 M KCl solution.
Fig. 1. Polarization curves recorded at the sweep rate of 25 mV s−1 for deposition of
pure Cd: curve a – stationary vertical electrode; curves b–e – rotating disk electrode,
with different rotation speeds.
equipped with Cu-K␣ tube and scintillation detector. The texture
of the coatings was investigated with the computer controlled four
circle X-ray texture goniometer Philips PW 1048.
3. Results and discussion
3.1. Electrodeposition of cadmium
The experiments were carried out at room temperature by
means of a computerized potentiostat/galvanostat Reference 600
(Gamry Instruments Inc.) using the software PHE 200. The polar-
Fig. 1 shows parts of the linear cathodic polarization curves,
registered in the electrolyte for deposition of cadmium on two dif-
ferent types of electrodes – on a stationary vertical electrode under
natural convection conditions and on the rotating disc electrode
(RDE) under definite mass transport conditions corresponding to
the different rotating speeds: 0, 1000, 2000 and 3000 rpm. The ini-
tial potential of the voltammetric scan was 0 mV vs. Ag/AgCl. The
registered curves are presented in the window −0.4 V to −2.4 V for
better visualization of the obtained results.
Curve a in Fig. 1 is the polarization curve on the stationary ver-
tical electrode. It is characterized by the wave at about −1.4 V. The
current density level of the wave could be assumed as a limiting
current density for the cadmium reduction process. At potentials
more negative than −1.8 V oscillations of the current appear. It was
suggested that the oscillations start at a potential determined by
the onset of the hydrogen evolution during the cadmium deposi-
tion [7], which corresponds to the mechanism proposed by Kaneko
et al. [18].
ization curves are recorded at the sweep rate of 25 mV s−1
.
The coatings were deposited under potentiostatic, or galvanos-
tatic conditions at room temperature.
For the XPS analysis (ESCALAB MkII (VG Scientific)) of the sur-
face composition of the coatings, the cadmium electrodeposition
was performed onto copper substrate 2 cm × 1 cm. Symmetrical
Gaussian–Lorentzian curve fitting after Shirley-type subtraction of
the background was performed [21].
The surface morphology of the coatings was studied by scanning
electron microscopy (SEM).
For the investigation of the phase composition and texture of the
coatings the deposition was performed onto copper substrate with
an area of 3.2 cm2. The cadmium or silver distribution on the surface
of the coatings was determined by energy dispersive analysis (EDX).
X-ray diffraction patterns for phase identification of the potentio-
statically deposited cadmium and alloy coatings were recorded in
the interval 20–120◦ (2ꢀ) with a Philips PW 1050 diffractometer,
Curve b in Fig. 1 shows the polarization curve registered on the
rotating disc electrode (RDE) without rotation at 0 rpm. In this case

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Ts. Dobrovolska et al. / Electrochimica Acta 79 (2012) 162–169
Fig. 3. Chronoamperometric curves, obtained at different potentials in the elec-
trolyte for deposition of cadmium.
disappear (curves b and c) in spite of the hydrogen evolution at
high cathodic potentials. This fact allows the conclusion, that the
observed instability is more complicated than in the case reported
by Kaneko et al. in the presence of 1.6 M free cyanide ions in the
electrolyte [18].
Fig. 2. Polarization curves on RDE at different concentrations of cyanide ions in the
electrolyte for deposition of pure cadmium: (a) 0.6 M; (b) 0.9 M; (c) 1.2 M. Sweep
rate of 25 mV s−1
.
Possibly the suggested formation of passive films on the elec-
trode surface is the reason for the observed current oscillations in
potentiostatic regime. Similar oscillations were not observed by
Kaneko et al. as well as by Vishomirskis, because both of them per-
formed experiments with high concentration of free cyanide ions
in the electrolyte.
Fig. 3 shows the current density oscillations in the chronoam-
perometric curves, registered on the vertical electrode at different
applied potentials. The investigated potentials were chosen on the
basis of the linear polarization curves – from −0.8 V to −2.0 V with
a step of 0.2 V. Coulometric technique with set potential was used,
i.e. the deposition was performed with the charge of 2 C cm−2. After
applying the respective potential and after a short transition time
the reduction of cadmium starts.
the natural convection is embarrassed and the free removal of the
hydrogen bubbles is hindered. A peak, connected with the cadmium
reduction is observed at the potential of about −1.25 V and current
oscillations are not observed.
The rotation of the electrode causes a definite hydrodynamic
flow resulting in a constant thickness of the diffusion layer over
the entire surface of the electrode. This ensures the removal of
the hydrogen bubbles with a constant speed corresponding to the
rotation speed of the electrode, so that the pulsating hydrogen evo-
lution should be in part or whole eliminated. At 1000 rpm in the
potential interval between −1.6 V and −1.8 V current oscillations
are registered (Fig. 1, curve c). By increasing the rotating speed
the onset of the oscillations moves to more negative potentials. At
2000 rpm the oscillations start at −1.7 V and continue almost to the
potential of −1.9 V (Fig. 1, curve d). At the higher rotation speed of
3000 rpm the oscillations start at −1.75 V and continue to −1.95 V
(Fig. 1, curve e).
Up to the applied potential of −1.4 V (the first presented curve
in Fig. 3 there are not any oscillations registered on the verti-
cal stationary electrode). At more negative potentials (−1.6 V) the
oscillations start with very small amplitude, about 1–3 mA cm−2
.
From these experiments it could be concluded that depending
on the improved mass transport conditions (by using rotating disc
electrode) in spite of the partial removal of the hydrogen bubbles
by the tangential hydrodynamic flow, current oscillations could be
registered at linear polarization experiment in different potential
regions (at low rotation speed between −1.6 and −1.8 V and at high
rotation speed – at potentials more negative than −1.7 V).
The existence of oscillations with different origin in the one
and the same system (for example during reduction of hydrogen
peroxide onto platinum electrode) due to formation/destruction of
passive films in the potential region just before hydrogen evolu-
tion or due only to the hydrogen evolution were claimed by other
authors [22,23].
In the investigated system the formation of passive films
leading to oscillation according to the mechanism proposed by
Vishomirskis [17] could be possible because of the absence of free
complex forming agent. The minimal molar ratio of cadmium to
cyanide ions in the electrolyte should be 1:4 which ensures the
formation of soluble cyanide complexes of cadmium.
The change of the applied potential to −1.8 V results in an increase
in the amplitude of the observed oscillations in the range between 2
and 10 mA cm−2 and at the potential of −2 V the amplitude reaches
50 mA cm−2
.
The observed behavior of the chronoamperometric curves does
not elucidate the reason of the oscillations – it could be some
changes in the active surface of the working electrode due to its
blocking by passive layers or hydrogen bubbles.
Fig. 4 shows the chronopotentiometric curves, on stationary
vertical electrode obtained at different current densities, chosen
according to the linear polarization curves: at current densities up
to 15 mA cm−2 which are smaller than the limiting current den-
sity the oscillations do not appear (curve a). The increase of the
applied current to 20 mA cm−2 leads to the appearance of potential
oscillations with amplitude of about 600–800 mV. The period of the
oscillations is 19–23 s. At the higher current density (25 mA cm−2
)
the amplitude of the oscillations increases to more than 1.2 V and
the period decreases to 10–12 s. When potentials between −1.2
and −1.5 V are reached the oscillations appear. In this case, pulsat-
ing evolution (not massive) of hydrogen bubbles from the cathode
surface could be observed by naked eyes. At increased current den-
sities the oscillations stop as earlier, as higher current density is
applied, possibly due to the massive hydrogen evolution.
The possibility of formation of passive films is confirmed by the
results presented in Fig. 2. In absence of free cyanide current oscil-
lations can be registered on the rotating disc electrode (curve a).
In the presence of free cyanide (0.3 M or more) the oscillations

Ts. Dobrovolska et al. / Electrochimica Acta 79 (2012) 162–169
165
Fig. 5. (a) SEM image of the sample, deposited at −1.2 V in the electrolyte for cad-
mium deposition. (b) SEM image of the sample, deposited at −1.8 V in the electrolyte
for cadmium deposition. (c) Comparison between distributions of the elements on
the surface of both samples, determined by EDX (dashed line – at −1.2 V; solid line
– at −1.8 V).
Fig. 4. Chronopotentiometric curves, obtained at different current densities in
the cadmium electrolyte: (a) 15 mA cm−2; (b) 20 mA cm−2; (c) 25 mA cm−2; (d)
3 mA cm−2; (e) 40 mA cm−2; (f) 50 mA cm−2; (g) 60 mA cm−2
.
In order to answer the question what happens at the most pos-
itive potential of the oscillations, and what – at the most negative
one, following experiments were performed: Two samples were
deposited in the investigated cadmium electrolyte at the potentials
of −1.2 V and −1.8 V (the most positive and most negative poten-
tials in the oscillation curve (for instance, corresponding to Fig. 3c
– 25 mA cm−2)) for 300 s.
suggests presence of some passive film on the surface of the
electrode. To clarify the nature of the formed film the sample with
the coating, obtained at −1.2 V was investigated by X-ray photo-
electron spectroscopy – а technique, which could perform not only
quantitative and qualitative analysis of the present elements, but
also their chemical state [21].
The appearance of the coatings was different – the deposited
one at −1.2 V was dark gray and the other, deposited at −1.8 V was
silvery white with the metallic color of cadmium.
Fig. 6 shows the XPS spectra of the ascertained in the coatings
elements – cadmium (Fig. 6a), oxygen (Fig. 6b) and carbon (Fig. 6c).
As typically for the d-elements the cadmium peak is split [21].
The morphology of these coatings is shown in Fig. 5. The com-
position of the deposit, obtained at −1.2 V contains about 85 wt.%
of Cd, 8 wt.% of O and 6.9 wt.% of C, and of the deposit obtained at
−1.8 V – about 96 wt.% of Cd, 3.3 wt.% of O, and absence of carbon.
The sponge-like morphology of the coating, obtained at −1.2 V
is shown in Fig. 5a. In contrary, the coating, deposited at −1.8 V
has morphology with well-defined crystals of cadmium onto the
almost whole surface (Fig. 5b).
The maximum of the peak at the 401 eV (N1s) belongs to the C N
bond, the peak with maximum at the 404.8 eV indicate the exis-
tence of Cd(OH)2 (Fig. 6a). Almost all oxygen is bonded in the
hydroxide group – the peak with a maximum at 531 eV in the oxy-
gen spectrum (Fig. 6b, peak 1) corresponds to hydroxide bonds and
the peak at 533 eV (Fig. 6b, peak 2) could be assigned to the compli-
cated structure of N
O Cd compounds. Two peaks are registered
in the carbon spectrum (Fig. 6c) – the first big one (peak 1) at 285 eV
corresponds to carbon–hydrogen bonds, the second one (peak 2) at
287 eV (resulting from the de-convolution of the spectra) refers to
the carbon–nitrogen bonds (typical bonds in the cyanide group) and
The comparison between the spectra of above mentioned
samples is presented in Fig. 4c. The different content of the carbon
and oxygen together with optical and morphological differences

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Ts. Dobrovolska et al. / Electrochimica Acta 79 (2012) 162–169
Fig. 6. XPS spectra, obtained in the coating, deposited at −1.2 V (SEM image of the sample is shown at Fig. 5a). a – cadmium; b – oxygen; c – carbon. Dotted line – experimental
results, solid lines – deconvolution.
potential of −1.3 V with a current density of 15 mA cm−2, which
the third one (peak 3), with a maximum about 289 eV corresponds
to complicated structures of C with N, O and H [21].
could be assigned to the maximum rate of the reaction of co-
deposition of Cd. The next increase in the current density, which
could be connected with the massive hydrogen evolution. The
electrode processes during deposition of both metals – silver and
cadmium from cyanide complexes were discussed in a previous
paper [7]. The galvanostatic chronoamperometric curves, obtained
Therefore it could be stated, that at the most positive potential of
the oscillations some passive film of cadmium hydroxide and cad-
mium cyanide is formed. Most probably, the passive film is a result
of formation of some insoluble cadmium compounds due to some
alkalization at the electrode/electrolyte interface and insufficient
amount of complex forming cyanide ions. This film needs time to
be formed in sufficient amount to be able to block the active sur-
face (Fig. 4b–d). When the active surface is blocked, the potential
increases rapidly to a level enough high to destroy the film and to
start the hydrogen evolution. This could be the explanation why at
higher current densities, which ensure a potential, more negative
than the region of “passivity” the oscillations stop, independently
of the visible massive hydrogen evolution under galvanostatic con-
ditions.
3.2. Electrodeposition of silver–cadmium alloy
Fig. 7 presents the polarization curve, obtained in the Ag–Cd
alloy electrolyte. A shoulder representing the diffusion-controlled
deposition of Ag appears at −0.55 V and the limiting current den-
sity for the silver deposition in this electrolyte could be determined
as 7 mA cm−2. The co-deposition of Cd starts at the potentials,
more negative than −1.0 V and the next shoulder appears at the
Fig. 8. Chronopotentiometric curves, obtained at different current densities in the
alloy electrolyte onto vertical platinum electrode.
Fig. 7. Linear polarization curve for an electrolyte for silver–cadmium alloy depo-
sition, scan rate 25 mV s−1
.

Ts. Dobrovolska et al. / Electrochimica Acta 79 (2012) 162–169
167
during deposition of silver–cadmium alloys from the investigated
electrolyte are shown in Fig. 8.
At a current density of 10 mA cm−2 the obtained coatings have
an average content of about 15–17 wt.% of Cd. Potential oscillations
were not registered. The coatings are silver-white.
At an increased current density of 15 mA cm−2 the coating
contains about 48–50 wt.% of Cd. The surface is bright and pro-
nounced oscillations are observed. The increase of the current
density leads to an increase in the content of Cd as follows: at
20 mA cm−2 – 80 wt.%, at 30 mA cm2 – 87 wt.%, and at 40 mA cm−2
–
almost 96 wt.% of Cd. At higher cadmium content the morphology
of the coatings become smoother. The potential oscillations start
when the cadmium content of the deposit becomes sufficiently
high (more than 45 wt.%). They are possibly connected with the
decreased hydrogen overvoltage on the cadmium-rich alloy sub-
strate and the formation of passive films which most probably have
the same nature as those observed during pure cadmium electrode-
position. The contribution of the different possible reasons cannot
be distinguished because of the formation of different alloy phases
during deposition.
Fig. 9. Cross section of a silver–cadmium deposit, obtained in the electrolyte for
silver–cadmium alloy deposition, 20 mA cm−2, 30 min.
At the beginning of the process preferentially silver as
more positive metal in the system [7,24] is deposited and the
Fig. 10. Scanning electron microscopy images of the coatings obtained at different potentials: (a) −1.2 V; (b) −1.5 V; (c) and (d) different areas of the sample of Fig. 10b; (e)
part of the area shown in Fig. 10c under higher magnification.

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Ts. Dobrovolska et al. / Electrochimica Acta 79 (2012) 162–169
Fig. 12. Cut-outs (2ꢀ interval between 30◦ and 80◦; intensity interval between 0
and 1000 counts) of the X-ray patterns presented in Fig. 11 (ꢀ), overlaid by the XRD
pattern of pure cadmium coatings (O), obtained at −1.5 V.
Fig. 11. XRD spectra of the potentiostatic deposited coatings: (a) −1.2 V, (b) −1.5 V
and (c) −1.8 V.
oscillations are irregular possibly due to its influence. With
increased deposition time they become more regular and repro-
ducible and their period increases. With increased cadmium
content the oscillations become again more regular, similar to
the case of pure cadmium. Layered structures from different alloy
phases could not be observed in the cross section of the electrode-
posited silver–cadmium coatings by optical microscopy (Fig. 9).
Spatio-temporal structure formation was observed during
electrodeposition of silver–cadmium alloys. Alloy coatings were
deposited at 3 different potentials: at −1.2 V; −1.5 V and −1.8 V
(potentials of just before the most positive, middle and most neg-
ative part of the oscillation curve obtained at 15 mA cm−2) (Fig. 8).
The obtained coatings were compact, dark-gray and bright.
Fig. 10a shows the morphology of the coating, obtained at the
most positive potential of the oscillations (−1.2 V) during elec-
trodeposition of Ag–Cd alloy in the investigated electrolyte. The
deposit contains about 65 wt.% of Cd. Spots and details from not
very well formed targets are visible on the electrode surface.
At the higher potentials of −1.5 V and −1.8 V the whole surface
of the coatings is covered by periodical spatio-temporal structures
in different scales (Fig. 10b–d). Because of the similarities in appear-
ance and morphology between the samples obtained at −1.5 V and
−1.8 V the morphology of the latter is not presented.
EDX analysis show, that in the both different morphological
areas of the spatio-temporal structures the content of cadmium
is almost the same – about 79 wt.% (Fig. 10e).
The XRD spectra of the samples, deposited at −1.2 V, −1.5 V
and −1.8 V are presented in Fig. 11. In spite of the believed mul-
tiphase heterogeneity of the coatings, only reflections with a very
strong preferred orientation of the crystallites of the hexagonal
Fig. 13. 3D pole figures in direction ꢀ1 0 1ꢁ of the Ag1.05Cd3.95-phase in the alloy
coatings, shown in Figs. 10 and 11 deposited at: (a) −1.2 V, (b) −1.5 V and (c) −1.8 V.

Ts. Dobrovolska et al. / Electrochimica Acta 79 (2012) 162–169
169
Ag1.05Cd3.95 phase (PDF 065-7991) are presented in all three spec-
tra. The intensities of the reflexes in the three spectra are different.
In the spectrum of the coating, deposited at −1.2 V the highest
intensity is registered of the reflex corresponding to the ꢀ1 0 1ꢁ ori-
entation, which reaches about 30 000 counts (a.u.). In the next two
samples the highest reflex intensity corresponds to the ꢀ1 0 0ꢁ ori-
entation and reaches 12 000 counts for the coatings, deposited at
−1.5 V and 5000 counts for the coatings, deposited at −1.8 V.
The question which needs to be answered at this stage is: are
the observed structures formed only by the phase Ag1.05Cd3.95 or by
two phases – the phase Ag1.05Cd3.95 and the pure Cd phase, which
peaks are possibly overlapped?
Fig. 12 presents the cut-outs ((2ꢀ)- in the same 2ꢀ interval but
with the upper limit of intensity counts (a.u.) of 1000) of the X-
ray spectra presented in Fig. 11, overlaid by the spectrum of the
cadmium coating, deposited at −1.5 V (dashed curve). The com-
parison between the spectra of pure cadmium coatings and each
spectrum of the alloy coatings shows, that only one cadmium peak
could appear on the same position as a peak of the ꢀ1 0 1ꢁ-peak of
the Ag1.05Cd3.95 phase (ꢀ1 0 1ꢁ). It could be presumed that the pure
cadmium phase has a very strong preferred orientation along the
axis ꢀ1 0 1ꢁ (PDF 03-065-3363) and due to the same type of crystal
lattices (hcp) of both phases the coincidence of the corresponding
maxima would be possible.
Texture investigations were performed along the ꢀ1 0 1ꢁ-reflexes
of the Ag1.05Cd3.95 phase in the three samples, deposited at −1.2 V,
−1.5 V and −1.8 V (see Figs. 11 and 12). The 3D pole figures are
presented in Fig. 13a–c. The split peak in the pole figures of the
coatings, deposited at −1.5 V and −1.8 V at higher cadmium content
in the coatings is visible (Fig. 13b and c). On this basis it could be
assumed, that in the case of potentiostatic deposition, when the
spatio-temporal structures cover the entire electrode surface they
are formed by crystallites of the Ag1.05Cd 3.95 phase and the highly
oriented along the ꢀ1 0 1ꢁ-axis pure Cd-phase.
Potential oscillations are observed again during electrodeposi-
tion of Ag–Cd alloys at high current densities. They appear when
the cadmium content in the deposits is more than 45 wt.% and they
have possibly the same origin as the oscillations during cadmium
electrodeposition. The period and regularity of the oscillations
depend on the current density, respectively on the cadmium con-
tent.
At high cadmium content during alloy deposition, the formation
of periodical structures consisting of different phases of the alloy
is registered. The cadmium content of the different morphological
areas of the patterns is almost identical. The XRD spectra of the
obtained structured coatings suggest the existence of two textured
phases, with very strong preferred orientations of the crystallites in
the direction ꢀ1 0 1ꢁ of Ag1.05 Cd 3.95 and the pure cadmium phase.
References
[1] Ts. Dobrovolska, I. Krastev, A. Zielonka, ECS Transactions 25 (2010) 1.
[2] C.W. Stillwell, Journal of the American Chemical Society 53 (1931) 2416.
[3] C.W. Stillwell, L.E. Stout, Journal of the American Chemical Society 54 (1932)
2583.
[4] C.W. Stillwell, H.I. Feinberg, Journal of the American Chemical Society 55 (1933)
1864.
[5] L.N. Rastorguev, I.D. Kudryavtseva, E.A. Kislitsyn, S.A. Barinov, V.M. Momotova,
Soviet Electrochemistry 11 (1975) 1696.
[6] S. Jayakrishnan, Transactions of the Institute of Metal Finishing 78 (2000) 124.
[7] Ts. Dobrovolska, I. Krastev, B.M. Jovic, V.D. Jovic, G. Beck, U. Lacnjevac, A.
Zielonka, Electrochimica Acta 56 (2011) 4344.
[8] Yu. Polukarov, K.M. Gorbunova, Zh Physicheskoj khimii 31 (1957) 2281.
[9] I. Kristev, M. Nikolova, Journal of Applied Electrochemistry 16 (1986) 875.
[10] I. Krastev, T. Valkova, A. Zielonka, Journal of Applied Electrochemistry 33 (2003)
1199.
[11] Ts. Dobrovolska, L. Veleva, I. Krastev, A. Zielonka, Journal of The Electrochemical
Society 152 (2005) C137.
[12] Ts. Dobrovolska, I. Krastev, A. Zielonka, Russian Journal of Electrochemistry 44
(2008) 676.
[13] A. Hrussanova, I. Krastev, Journal of Applied Electrochemistry 39 (2009) 989.
[14] N.A. Shumilova, G.V. Zhutaeva, Silver, in: J.A. Bard (Ed.), Encyclopedia of Elec-
trochemisrty of the Elements, Marcel Dekker Inc., New York/Basel, 1973, p.
1.
4. Conclusions
[15] R.Y. Bek, N.A. Rogozhnikov, Journal of Electroanalytical Chemistry 447 (1998)
109.
[16] G. Baltrunas, Electrochimica Acta 48 (2003) 3659.
[17] R.M. Vishomirskis, Kinetika Electroosazhdenia Metallov iz Kompleksnih Elek-
trolitov, Nauka, Moskva, 1969.
[18] N. Kaneko, H. Nezu, N. Shinohara, Journal of Electroanalytical Chemistry 252
(1988) 371.
[19] I. Krastev, M.E. Baumgartner, C. Raub, Metalloberfläche 46 (1992) 115.
[20] T. Dobrovolska, P. Zabinski, R. Kowalik, I. Krastev, A. Zielonka, Archives of Met-
allurgy and Materials 56 (2011) 645.
[21] J.F. Moulder, W.F. Sticke, P.E. Sobol, K.D. Bombel, in: J. Castain (Ed.), Hand-
book of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corporation, Physical
Electron Division Minnesota, USA, 1992.
[22] T.G.J. Van Venrooij, M.T.M. Koper, Electrochimica Acta 40 (1995) 1689.
[23] Y. Mukouyama, S. Nakanishi, H. Konishi, Y. Nakato, Journal of Electroanalytical
Chemistry 473 (1999) 156.
[24] A. Brenner, Electrodeposition of Alloys. Principles and Practice 2, Academic
Press, New York, London, 1963.
During electrodeposition of cadmium both potentiostatic and
galvanostatic oscillations are registered. Potentiostatic oscillations
were observed for the first time. Experiments with different
electrodes under different hydrodynamic conditions show the pos-
sibility of formation/destruction of passive layers on the electrode
surface, which besides the hydrogen evolution under limiting cur-
rent density conditions could be an additional promoter of the
oscillation behavior of the system. The duration of the observed
potential oscillations decreases with increased current density, due
to massive hydrogen evolution. XPS investigations confirm the
existence of passive films at potentials corresponding to the onset
oscillations.