Phase identification in electrodeposited Ag-Cd alloys by anodic linear sweep voltammetry and X-ray diffraction techniques

Article abstract of DOI:10.1016/j.electacta.2011.01.028

During electrodeposition of Ag-Cd alloy coatings phenomena of self-organization and formation of spatio-temporal structures can be observed. The difficulties in the determination of the local phase composition in the observed structures are mostly connected with the strong heterogeneity of the coatings consisting of several alloy phases. The results obtained with electrochemical techniques, such as anodic linear sweep voltammetry (ALSV) are compared with results obtained by X-ray analysis and SEM. In the proposed electrolyte for dissolution of Ag-Cd alloy coatings (12 M LiCl + 0.1 M HCl) the dissolution peaks of the pure metals, Ag and Cd, have a potential difference of about 700 mV. The peaks, corresponding to the alloy phases, are situated between the dissolution potentials of Ag and Cd, their height depending on the deposition current density, i.e. on the percentage content of the alloy. Different phases (Ag, Ag₃Cd, AgCd, AgCd₃ and pure Cd) are observed in the coatings deposited at different cathodic potentials. A good correlation between the XRD spectra of the Ag-Cd alloy coatings and the ALSV data obtained during their dissolution is established.

Full text of DOI:10.1016/j.electacta.2011.01.028

Electrochimica Acta 56 (2011) 4344–4350
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Phase identification in electrodeposited Ag–Cd alloys by anodic linear sweep
voltammetry and X-ray diffraction techniques
a,∗,1
, I. Krastev , B.M. Jovi c´ b,1, V.D. Jovi c´ b,1, G. Beck , U. La cˇ njevac , A. Zielonka
a
c
b
c
Ts. Dobrovolska
a
Institute of Physical Chemistry, Bulgarian Academy of Science, 1113 Sofia, Bulgaria
Institute for Multidisciplinary Research, 11030 Belgrade, P.O. Box 33, Serbia
Forschungsinstitut für Edelmetalle und Metallchemie, 73525 Schwäbisch Gmünd, Germany
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
During electrodeposition of Ag–Cd alloy coatings phenomena of self-organization and formation of
spatio-temporal structures can be observed. The difficulties in the determination of the local phase com-
position in the observed structures are mostly connected with the strong heterogeneity of the coatings
consisting of several alloy phases. The results obtained with electrochemical techniques, such as anodic
linear sweep voltammetry (ALSV) are compared with results obtained by X-ray analysis and SEM. In the
proposed electrolyte for dissolution of Ag–Cd alloy coatings (12 M LiCl + 0.1 M HCl) the dissolution peaks
of the pure metals, Ag and Cd, have a potential difference of about 700 mV. The peaks, corresponding to
the alloy phases, are situated between the dissolution potentials of Ag and Cd, their height depending on
the deposition current density, i.e. on the percentage content of the alloy. Different phases (Ag, Ag3Cd,
AgCd, AgCd3 and pure Cd) are observed in the coatings deposited at different cathodic potentials. A good
correlation between the XRD spectra of the Ag–Cd alloy coatings and the ALSV data obtained during their
dissolution is established.
Received 13 October 2010
Received in revised form 15 January 2011
Accepted 17 January 2011
Available online 21 January 2011
Keywords:
ALSV
Electrodeposition
Self-organization
Silver–cadmium alloys
XRD techniques
©
2011 Elsevier Ltd. All rights reserved.
1
. Introduction
and controlled experimental conditions, could be very effective for
their understanding.
Alloying of silver with other metals is stimulated by the
The experience gathered during electrodeposition of some silver
alloys shows that the appearance of self-organization phenomena
is closely connected with the phase heterogeneity of the obtained
coatings [5–8].
Silver–cadmium alloys have not achieved any practical impor-
tance, but they are of considerable scientific interest, mainly
because of the numerous phases formed and observed in this
system [16–22]. The phase composition of these alloys could be
analyzed by anodic linear sweep voltammetry (ALSV), which is
an appropriate electrochemical technique for fast and precise
phase analysis of thin alloy films deposited on the inert substrates
[23–27].
The phases observed in the silver–cadmium alloy system are
described in the monograph of Hansen and Anderko [28] in the
following way:
The solubility of Cd in Ag (␣-phase) reaches 42 at.%. In the com-
position range between 26 and 29 at.% Cd the high-temperature
main idea to improve its tarnish resistance [1,2]. Cadmium and
indium could be appropriate alloy metals to silver, because they
do not tarnish and are light coloured. In fact, the alloying of
silver with indium does not lead to an increase of its tarnish
resistance but pattern formation has been observed on the sur-
face of electrodeposited Ag–In alloys [3]. Later, the formation of
structures, which are typical results of reaction–diffusion mech-
anism have been observed and studied during electrodeposition
of silver with antimony [4,5], bismuth [6], tin [7] and indium
8,9]. Recently, the formation of spatio-temporal structures have
been discovered also in electrodeposited silver–cadmium coatings
10].
Self-organization phenomena are observed everywhere in
[
[
Nature – in the atmosphere, in geological structures, in sand dunes,
during propagation of fire, in the stripes onto the body of zebras and
panthers, in the spirals formed in the processes of heterogeneous
catalysis etc. [11–15]. The investigation of similar processes with
electrochemical methods, which are exact, due to the well defined
Ag Cd phase could be observed [29].
3
In the composition range between 42 and 60 at.% Cd, three
ꢀ
phases (␤, ␤ and ␨) are established in the vicinity of 50 at.% Cd
ꢀ
at different temperatures. The ␤- and ␤ -phases are characterized
by the b.c.c. lattices, and the ␨-phase by h.c.p. lattice. These phases
∗ Corresponding author. Tel.: +359 2 979 2595; fax: +359 2 873 49 68.
correspond to the AgCd compound. The existence of several phases
E-mail address: tsvetina@ipc.bas.bg (Ts. Dobrovolska).
ꢀ
(␥, ␥ , ␧ and ␩) is reported in the composition range between 60
1
ISE member.
0
013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.01.028

Ts. Dobrovolska et al. / Electrochimica Acta 56 (2011) 4344–4350
4345
and 100 at.% Cd. The first one (␥) is a hexagonal phase and the
ꢀ
second one (␥ ) possesses a b.c.c. lattice. They correspond to the
Ag5Cd compound. The pure hexagonal ␧-phase exists in the range
8
6
8–81.4 at.% Cd and corresponds to the Cd Ag compound. In the
3
composition range 81.4–96.9 at.% Cd ␧-phase exists together with
the ␩-phase, which is a solid solution of Ag in Cd. Pure ␩-phase is
◦
observed in the interval 96.9–100 at.% Cd (100 C).
In the present paper an attempt was made to determine the
phase composition of silver–cadmium coatings (deposited at dif-
ferent conditions) by ALSV technique and to compare the results
with those, obtained by XRD and SEM techniques.
2
. Experimental
The cadmium, silver and the alloy coatings were deposited from
cyanide electrolytes. Pure Cd from the solution containing 0.14 M
CdSO4. 8/3 H O + 0.56 M KCN, pure Ag from the solution containing
2
0
.032 M KAg(CN) + 0.56 M KCN and Ag–Cd alloys from the solu-
2
−1
Fig. 1. Polarization curves recorded at the sweep rate of 1 mV s for deposition of
.
tion containing 0.032 M KAg(CN) + 0.14 M CdSO4 8/3 H O + 0.56 M
2
2
pure Ag (dashed line), pure Cd (dotted line) and Ag–Cd alloy (solid line).
KCN. Chemical substances 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
3. Results and discussion
2
electrode (area 3 cm ), and the two counter electrodes were made
from platinum. An Ag/AgCl reference electrode was used. The ref-
erence electrode was placed in a separate compartment filled with
3.1. Polarization curves for Ag, Cd and Ag–Cd electrodeposition
3
M KCl solution. It was connected to the electrolyte cell by a
Fig. 1 shows polarization curves obtained with a sweep rate of
Haber–Luggin capillary through an electrolyte bridge containing
also 3 M KCl solution.
The experiments were carried out at room temperature by
means of a computerized potentiostat/galvanostat Reference 600
−1
1
mV s
in the electrolyte containing both metals separately or
together. The initial potential of the voltammetric scan is 0 mV.
The deposition of Ag (dashed line) is characterized by the cathodic
shoulder, which is most likely indication of the diffusion limiting
current density (taking into account small concentration of Ag)
at a potential of about −0.82 V, with the deposition starting at
about–0.79 V. The increase of the current at potentials < −1.2 V dur-
ing the Ag deposition is connected with the reaction of hydrogen
evolution. The dotted line curve in Fig. 1 corresponds to cadmium
electrodeposition. The process of deposition commences at about
(
Gamry Instruments Inc.) using the software PHE 200, or PAR 263
A potentiostat/galvanostat using the software Soft Corr II.
The alloy coatings were deposited under potentiostatic, or gal-
vanostatic conditions at room temperature.
In order to determine the current efficiency for the deposition of
each metal, as well as their dissolution potentials, Ag and Cd were
deposited from cyanide electrolytes at different potentials (−1.0,
−
0.79 V and at potentials more negative than −1.6 V current oscil-
−
1.4, −1.6, −1.8 and −2.0 V) with a constant electrical charge of
lations with amplitude higher than 200 mV have been observed in
both scan directions. Probably, the oscillations start at a potential
determined by the onset of the massive hydrogen evolution during
the cadmium deposition.
−2
Q = 1.3 C cm using “potential controlled coulometry” technique
and then dissolved in the chloride electrolyte described below. The
thickness of the films, obtained at the potentiostatic and galvano-
static conditions is between 0.7 and 1 ␮m. The ALSV experiments
were carried out immediately after XRD investigations, the later
performed immediately after the deposition of each alloy sam-
ple. The cadmium, silver and alloy coatings were dissolved in the
tri-electrode cell for ALSV experiments with platinum counter elec-
trode and Ag/AgCl reference electrode in a solution containing 12 М
LiCl + 0.1 M HCl.
The phenomenon of potential oscillations under galvanostatic
conditions during electrocrystallization of cadmium from alkaline
cyanide solutions has been observed and reported by Kaneko et al.
30]. There are not any known reports about current oscillations in
this system under potentiostatic conditions.
In the case of Ag–Cd alloy deposition a shoulder represent-
ing diffusion-controlled deposition of Ag (solid line) appears at
about −0.51 V (for about 0.3 V more positive than the shoulder
of pure Ag deposition). At the same time deposition starts at
about −0.48 V. Hence, in the solution containing both metal ions
Ag starts to deposit at more positive potential. In order to find
out the reason for such behavior the analysis of Ag complexes
with cyanide has been performed. The results are presented in
Table 1. As can be seen, when pure Ag is present in the KCN solu-
[
All potentials are given vs. Ag/AgCl electrode.
The cadmium or silver distribution on the surface of the coatings
was examined by EDX-technique.
X-ray diffraction patterns for phase identification of the alloy
coatings deposited at a constant potential were recorded in the
angle interval 20–110 (2ꢀ), on a Philips PW 1050 diffractometer,
equipped with Cu-K␣ tube and scintillation detector.
The phase composition of the alloy coating deposited at a con-
stant current density was investigated by X-ray analysis in the 2ꢀ
range of 20 –85 with the D8 Discover diffractometer (Bruker axs)
in the Bragg-Brentano diffraction geometry. The measurements
were performed with Cu-K␣ radiation.
For qualitative phase analysis the Eva routine (Bruker axs) on
the basis of the powder diffraction file (PDF 2, Version Sep. 2004)
was used.
The surface morphology of the coatings was studied by optical
microscopy and scanning electron microscopy (SEM).
◦
2−
tion the dominant complex is [Ag(CN)3] , with the equilibrium
−
potential of −0.737 V. In the presence of Cd ions most of the CN
◦
◦
+
anions are consumed in Cd–CN complexes ([Cd(CN)] , [Cd(CN) ],
2
−
2−
[
Cd(CN)3] and [Cd(CN) ] ) and the dominant Ag–CN complex
4
−
becomes [Ag(CN) ] , with the equilibrium potential of −0.479 V
2
(
Table 1). Hence, from the presented analysis it is obvious that
the first shoulder on a solid curve in Fig. 1 for Ag–Cd alloy depo-
−
sition corresponds to the deposition of pure Ag from [Ag(CN)2]
complex [10] which is dominant in pure Cd–CN and Ag–Cd–CN
electrolytes.

4
346
Ts. Dobrovolska et al. / Electrochimica Acta 56 (2011) 4344–4350
Table 1
Concentration of different Ag complexes and their eqilibrium potentials.
Solution composition
Ag complexes
−
2−
3−
[
Ag(CN)2]
[Ag(CN)3]
21.7
[Ag(CN)4]
20.6
log(K/M 1), stability constant
−
21.2
−
0
.032 M KAg(CN)2 0.56 M KCN
Concentration (mole fraction (%)) 35.9
Eeq/V)
−0.737
61.2
2.6
(
−0.737
0
.032 M KAg(CN)2 0.14 M CdSO4 0.56 M KCN
(
(
Concentration (%)
Eeq/V)
98.1
−0.479
1.8
0.0009
E vs. Ag/AgCl.
This is confirmed also by the composition analysis (see section
.2).
The alloy deposition from this electrolyte is of a regular type
3
according to Brenner’s classification [1] and the cadmium content
in the coatings should increase with the increase in current density
−
1
Fig. 2. ALSV curves recorded at the sweep rate of 1 mV s for dissolution of Cd and
Ag deposited at different potentials (E). Cd dissolution: Solid line (E = −1.0 V), dashed
line (E = −2.0 V). Ag dissolution: dash-dot line (E = −1.0 V), dotted line (E = −2.0 V).
(
or increase of cathodic potential).
One of the conditions required for identification of the phase
structure of Ag–Cd alloys by ALSV technique is the presence of suf-
ficiently large difference between the dissolution potentials not
only of pure Ag and Cd metals, but also between the dissolu-
tion potentials of the alloy phases present in the deposit [26]. To
meet this requirement an appropriate electrolyte for the dissolu-
tion of the alloy coating is needed. The solution used in the present
investigations contained 12 М LiCl + 0.1 M HCl. The same electrolyte
was chosen and successfully applied during ALSV investigations of
Ag–Pd [25] and Ag–In alloys [27]. In this case the complete dissolu-
tion, without any passivation of the silver and palladium phases and
3
−
the formation of a strong Ag complex (probably AgCl
) with an
4
−6
instability constant of 1.2 × 10 were reported [25,27,31]. Accord-
ing to the literature data [32,33] in such high concentration of
chloride ions (12.1 M) the solubility of AgCl increases up to about
0
.05 M AgCl (at a given temperature) and in accordance with this
+
statement for small amount of dissolved Ag ions no precipitation
of AgCl should be expected. This is clearly demonstrated in the
reference [25], Fig. 3.
Fig. 3. Current density vs. time transients (j–t) recorded during deposition of Ag–Cd
−
2
alloys to a constant charge of 1.3 C cm at different potentials marked in the figure.
3
.2. The ALSV and XRD analysis of Ag, Cd and Ag–Cd alloys
result of the co-deposition of silver, since they are not registered
for deposition of pure Ag (Fig. 1, dashed line).
electrodeposited at a constant potential
The XRD patterns, obtained just after deposition of the coat-
ings (see Fig. 3) are presented in Fig. 4, while the ALSV curves
The ALSV curves of dissolution (v= 1 mV s−1) of pure Cd and
pure Ag coatings are shown in Fig. 2. Sufficiently large differ-
ence between the dissolution potentials of the pure metals of
about 0.75 V is registered. As was previously established, cad-
mium as the less noble constituent of the alloy is completely
dissolved at more negative potentials of about −0.75 V, while the
more noble silver has a dissolution peak at about 0.02 V [23–25].
Comparing the charge under the ALSV curves for Cd dissolution
−
2
with the total deposition charge of Qdep = 1.3 C cm it was found
that the current efficiency (ꢁ = Qdiss/Qdep) for cadmium deposi-
j
tion decreases with increasing potential from about 94% (−1.0 V)
to about 79% (−2.0 V), due to the increase of the contribution of
hydrogen evolution reaction to the whole process of electrodepo-
sition of cadmium at potentials more negative than −1.6 V. Similar
behavior is observed for pure Ag deposition with the current effi-
ciency of about 63% at a potential of −1.0 V and 37% at −2.0 V.
In the case of Ag–Cd alloy deposition current efficiency is also
found to decrease with increasing cathodic potential (from 63%
at −1.0 V to 54% at −2.0 V), as in the case of deposition of pure
metals.
Fig. 3 shows current transients (j vs. t), obtained during the depo-
sition of alloys. The oscillations are not registered, possibly as a
Fig. 4. XRD spectra of the alloy coatings deposited at different potentials (marked
in the figure).

Ts. Dobrovolska et al. / Electrochimica Acta 56 (2011) 4344–4350
4347
−
1
Fig. 5. ALSV curves recorded at the sweep rate of 1 mV s for dissolution of alloys
deposited under conditions presented in Fig. 3. Deposition potentials are marked in
the figure.
Fig. 6. Surface morphology (SEM) of the alloy coating deposited at a potential
E = −1.0 V.
for dissolution of Ag–Cd coatings deposited at different cathodic
potentials (−1.0, −1.4, −1.6, −1.8, and −2.0 V) are presented in
Fig. 5.
to some previously reported results obtained by ALSV technique
the peaks in between should be attributed to different alloy phases
[26]. These could be the registered AgCd3 (B) and AgCd (C) phases,
the latter with negligible amount according to the XRD spectra, as
well as to the ALSV results.
In the coatings deposited at −1.0 V two peaks, one correspond-
ing to pure Ag and two corresponding to the Ag Cd phase could
3
be detected on the diffractogram. The Ag Cd phase is, according
The heterogeneity of this coating is well visible – its morphol-
ogy is presented in Fig. 7a. In the rough areas of the coating the
cadmium content is about 40 at.% (Fig. 7b), while in the smooth
areas it reaches 58 at.% (Fig. 7c).
3
to the phase diagram [29], high-temperature phase of the Ag–Cd
system which was not detected in previous investigations of elec-
trodeposited Ag–Cd alloys [16–18,22]. A well defined peak D on
the ALSV for alloy deposited at −1.0 V (Fig. 5) is the indication of
The deposition at higher cathodic potentials, −1.6 or −1.8 V,
leads to the appearance of some periodic structured areas on the
surface (Fig. 8a and b), the reflections of pure cadmium disappear
(Fig. 4), which could be connected with the changes in the current
efficiency and the enhanced formation of Ag–Cd alloy phases.
The corresponding ALSV curves (Fig. 5) show that the peak of
pure cadmium (A) becomes smaller and practically disappears in
the alloys deposited at the most negative potential (−2.0 V), while
the next one (B), corresponding to the dissolution of cadmium-rich
phase, grows. It could be seen that the peak of AgCd3 phase disso-
lution (B) appears at more positive potentials for alloys deposited
at −1.8 V and −2.0 V, indicating that its amount in the deposit
increases. There is a certain difference between the X-ray and ALSV
analysis for these two alloys. According to the ALSV results the
amount of the AgCd phase increases (peak C becomes more pro-
nounced, Fig. 5), while this phase disappears on the diffractograms
(Fig. 4). Such a behavior could be the consequence of high intensity
of AgCd3 peaks on the diffractograms, masking the peaks corre-
sponding to the AgCd phase.
At the most negative potential of −2.0 V preferentially the phase
AgCd3 is formed and mainly the corresponding reflections of this
phase are registered on the XRD spectra. This is in agreement with
the ALSV results, where the peak of AgCd3 phase dominates over
all other peaks.
The morphology of a coating deposited at a potential of −2.0 V
is shown in Fig. 8c. The surface is smooth and shiny, indicating the
presence of mainly one phase in the deposit (AgCd3).
the presence of Ag Cd phase, while the peak E corresponds to the
3
dissolution of reprecipitated Ag [26], which is in accordance with
the diffractograms shown in Fig. 4. As can be seen in Fig. 5 this
peak practically disappears on the ALSVs of dissolution of alloys
with higher content of Cd (ALSVs recorded for alloys deposited at
−1.4, −1.6, −1.8 and −2.0 V), transforming into hardly visible shoul-
der, which is in agreement with the diffractograms presented in
Fig. 4. Such behavior is not unexpected, since it is quite possible
that its amount becomes lower with the increase of Cd content in
the alloy and its detection by the X-ray technique is not possible,
while on the ALSVs its presence could be hardly detected, although
not as well defined peak, but as a shoulder. It is interesting that this
phase is well defined on the ALSV of sample deposited at a con-
stant current density (Fig. 9), indicating that the conditions of alloy
deposition (potentiostatic or galvanostatic) produce alloys with dif-
ferent phases as well as with different amounts of the same phases
in the deposit.
The morphology of the coating deposited at −1.0 V is pre-
sented in Fig. 6. The morphology of this coating is typical to those,
described during the investigations of Jayakrishnan [22], where
the gradual increase in crystalline size with increase in cadmium
content is observed.
At more negative potential (−1.4 V) the coating becomes very
heterogeneous (see Fig. 7a) and reflections of Cd, AgCd , AgCd and
3
Ag phases were registered on the XRD spectra, which should corre-
spond to the separate peaks on the ALSV curves. The heterogeneity
of the coating could be the consequence of two factors: the alloy
composition and the influence of simultaneous hydrogen evolu-
tion, since the natural convection must be significantly disturbed
by the hydrogen evolution at this potential [8].
Comparing the results of XRD and ALSV phase analysis of alloys
deposited at a constant potentials it could be stated that satisfactory
agreement has been obtained.
The ALSV curve of the alloy coating deposited at a potential of
1.4 V is characterized by the presence of three additional peaks, A,
3.3. The ALSV and XRD analysis of Ag–Cd alloys electrodeposited
at a constant current density
−
B and C (Fig. 5). The most negative peak A (at about −0.68 V) could
be ascribed to the peak of pure cadmium (see Fig. 2), which is also
well defined on the diffractogram presented in Fig. 4. According
The deposition under galvanostatic conditions, which is used
in the practice, offers the possibility for a stronger heterogeneity

4
348
Ts. Dobrovolska et al. / Electrochimica Acta 56 (2011) 4344–4350
Fig. 7. (a) Surface morphology (SEM) of the alloy coating deposited at E = −1.4 V. (b)
Fig. 8. Surface morphology (SEM) of alloy coatings deposited at different (more
negative) potentials: (a) E = −1.6 V; (b) E = −1.8 V; (c) E = −2.0 V.
and (c) different areas of the same coating at higher magnification.
of the coatings and possibly for better differentiation of the sepa-
rate phases of the alloy. The observed heterogeneity is impressive
due to the formed spatio-temporal structures [10]. In Fig. 9 are
presented ALSV of Ag–Cd alloy dissolution deposited at a constant
current density of −2.5 mA cm and corresponding E–t response
for deposition (in the inset). The oscillations of the potential (Fig. 9
inset) are most probably due to the formation of spatio-temporal
structures, which are also connected with the hydrogen evolution
reaction [10,30]. The oscillations of potential or current density dur-
ing the Ag–Cd alloy deposition will be the subject of our future
investigations.
As can be seen all peaks corresponding to dissolution of certain
phases (A, B, C, D and E) are much better defined in comparison
with those for alloys deposited at a constant potential, indicating
that during galvanostatic deposition better separation of the ALSV
peaks could be obtained, most probably as a consequence of more
pronounced heterogeneity of the alloy.
−2

Ts. Dobrovolska et al. / Electrochimica Acta 56 (2011) 4344–4350
4349
−
1
Fig. 9. ALSV curve recorded at the sweep rate of 1 mV s
of the alloy coat-
−
2
ing deposited at a constant current density j = −2.5 mA cm . Corresponding E–t
response for alloy deposition is shown in the inset.
In order to find the exact correlation between the ALSV peaks
and the phases in the coating deposited under galvanostatic condi-
−2
tions (2.5 mA cm ) in the first step only the phase corresponding
to the first peak A was dissolved (arrow 1 in Fig. 9). In the sep-
arate runs the potential was swept to the arrows 2–4 marked in
the figure. During the second sweep, starting from the same poten-
tial (−0.80 V), the phases corresponding to the first (A) and to the
second (B) peaks were dissolved; in the third sweep – the phases
corresponding to the A, B and C peaks were dissolved, while prac-
tically whole deposit was dissolved at the potential marked with
the arrow 4.
The parallel XRD investigations of the as-deposited layer and
of the layer after electrochemical treatments (ALSV) are depicted
in Fig. 10. Fig. 11 shows cut-outs of the patterns in the 2ꢀ range
◦
◦
between 36 and 41 .
In the as-deposited layer the following reflections were identi-
fied: all reflections of the hexagonal Ag1.05Cd3.95 phase with very
high intensity of the (0 0 2) orientation, the (1 0 0) reflex of hexag-
onal Cd, the (1 1 0) reflex of cubic AgCd and all reflections of the
Pt substrate (Figs. 10 and 11). Therefore the main phase is the
Ag1.05Cd3.95 phase. This phase shows a preferred ꢁ0 0 1ꢂ orienta-
tion. The fractions of ꢁ1 1 0ꢂ orientated AgCd and ꢁ1 0 0ꢂ orientated
Cd are much smaller. It should be stated here that Ag Cd phase,
3
well defined on the ALSV (peak D) has not been detected by the
◦
◦
Fig. 11. Cut-outs (between 2ꢀ = 36 and 2ꢀ = 41 ) of the X-ray patterns presented in
Fig. 10.
X-ray technique. At the present stage of investigations the authors
cannot offer reasonable explanation for such behavior, but this phe-
nomenon will be the subject of our more detailed investigations of
the system Ag–Cd.
After dissolving the phase corresponding to peak A by the ALSV
a new XRD spectrum is recorded. In the second diffractogram the
peak of pure Cd disappears (Fig. 11, curve 2), but the other phases
Ag1.05Cd3.95 and AgCd are still registered. Instead of AgCd3 phase
(PDF 028-0199), detected in samples deposited at a constant poten-
tial, phase Ag1.05Cd3.95 (PDF 065-7991) has been detected in the
sample deposited at a constant current density (they have the same
space group P63/mmc).
After the next dissolution step, in the potential range between
−
0.8 and −0.3 V (arrow 2 in Fig. 9) the phase corresponding to
the potential of the next peak B, was not totally dissolved. About
the half of the intensity of the Ag1.05Cd3.95 reflections remained,
thus, about the half of this phase has been dissolved in this
step.
Fig. 10. XRD spectra at different stages of dissolution of the coating deposited at a
constant current density (Fig. 9).

4
350
Ts. Dobrovolska et al. / Electrochimica Acta 56 (2011) 4344–4350
After the next dissolution step in the potential range between
Acknowledgements
−
0.8 and −0.1 V (arrow 3 in Fig. 9) the XRD measurement shows
the absence of any Cd containing phases, only the characteristic
peaks of Ag and Pt are registered (Figs. 10 and 11, curve 4). Accord-
ingly, the whole amount of cadmium is dissolved and only silver
remained in the deposit. In the last step this silver is dissolved
The authors express their gratitude to Deutsche Forschungsge-
meinschaft (DFG) (Project 436 BUL 113/97/0-4), as well as to the
Ministry of Science and Technological Development of the Republic
of Serbia, for financial support of this work.
(
nearly completely) and only the peak of the platinum substrate
has been detected.
References
Considering the ALSV curves shown in Figs. 5 and 9 and the
results of the X-ray analysis presented in Figs. 4, 10 and 11 following
statements could be made:
[
[
1] A. Brenner, Electrodeposition of Alloys. Principles and Practice, vol. 2, Academic
Press, New York, London, 1963, p. 658.
2] K.M. Gorbunova, Yu. Polukarov, Electroosazhdenie metallov i splavov, Itogi
nauki, Moskva, 1966, p. 59.
•
•
the peak A corresponds to the pure Cd-phase;
the peak B corresponds to the Ag1.05Cd3.95 phase in sample
deposited at a constant current density;
the same peak corresponds to the AgCd3 phase in samples
deposited at a constant potential;
[3] E. Raub, A. Schall, Z. Metallkd 30 (1938) 149.
[
[
4] I. Kristev, M. Nikolova, J. Appl. Electrochem. 16 (1986) 875.
5] I. Krastev, M.T.M. Koper, Physica A 213 (1995) 199.
[6] I. Krastev, T. Valkova, A. Zielonka, J. Appl. Electrochem. 33 (2003) 1199.
[7] A. Hrussanova, I. Krastev, J. Appl. Electrochem. 39 (2009) 989.
•
[
8] Ts. Dobrovolska, L. Veleva, I. Krastev, A. Zielonka, J. Electrochem. Soc. 152 (2005)
C137.
•
•
the peak C corresponds to the AgCd phase;
[
9] Ts. Dobrovolska, I. Krastev, A. Zielonka, Russ. J. Electrochem. 44 (2008) 676.
the peak D corresponds to the Ag Cd phase in samples deposited
[10] Ts. Dobrovolska, I. Krastev, A. Zielonka, ECS Trans. 25 (2010) 1.
11] I.R. Epstein, Physica D 51 (1991) 152.
3
[
[
[
[
[
[
[
at a constant potential;
the peak E corresponds to the pure Ag.
12] A.M. Turing, Philos. Trans. R. Soc. London, Ser. B 237 (1952) 37.
13] I. Prigogine, Science 201 (1978) 777.
14] M.C. Cross, P.C. Hohenberg, Rev. Mod. Phys. 65 (1993) 851.
15] A.S. Mikhailov, G. Ertl, Chem. Phys. Chem. 10 (2009) 86.
16] C.W. Stillwell, J. Am. Chem. Soc. 53 (1931) 2416.
17] C.W. Stillwell, L.E. Stout, J. Am. Chem. Soc. 54 (1932) 2583.
•
Considering the phase diagram of the alloy system Ag–Cd [28]
it appears that each phase exists in a very broad atomic percent-
age range. The potential interval of each phase registered by ALSV
technique depends on the percentage range of its existence. Taking
into account that the distribution of Cd in the coating is non-
homogeneous, one can expect the change of the position of some
peaks on the ALSV.
[18] C.W. Stillwell, H.I. Feinberg, J. Am. Chem. Soc. 55 (1933) 1864.
[
[
19] I. Nambissan, A.J. Allmand, Trans. Faraday Soc. 47 (1951) 303.
20] L.N. Rastorguev, I.D. Kudryavtseva, E.A. Kislitsyn, S.A. Barinov, V.M. Momotova,
Sov. Electrochem. 11 (1975) 1696.
[21] L.W. Flott, Met. Finish. 83 (1985) 11.
22] S. Jayakrishnan, Trans. Inst. Met. Finish. 78 (2000) 124.
[
[
23] V.D. Jovic, R.M. Zejnilovic, A.R. Despic, J.S. Stevanovic, J. Appl. Electrochem. 18
(
1988) 511.
[24] V.D. Jovic, S. Spaic, A.R. Despic, S. Stevanovic, M. Pristavec, Mater. Sci. Technol.
(1991) 1021.
4
. Conclusions
7
[
[
25] V.D. Jovic, B.M. Jovic, A.R. Despic, J. Electroanal. Chem. 357 (1993) 357.
26] A.R. Despic, V.D. Jovic, in: R.E. White, J.O.M. Bockris, B.E. Conway (Eds.), Modern
Aspects of Electrochemistry, vol.27, Plenum Press, 1995, p. 143.
Different phases (Ag, Ag Cd, AgCd, AgCd3 and pure Cd) are
3
observed in the coatings deposited at different cathodic potentials.
A good correlation between the XRD spectra of the Ag–Cd alloy
coatings and the ALSV data obtained during their dissolution is
established.
[27] Ts. Dobrovolska, V.D. Jovic, B.M. Jovic, I. Krastev, J. Electroanal. Chem. 611 (2007)
32.
28] M. Hansen, K. Anderko, Constitution of Binary Alloys, McGraw-Hill, New York,
958, p.26.
2
[
1
In the case of Ag–Cd alloy deposited at a constant current density
instead of the AgCd3 phase, Ag1.05Cd3.95 phase has been detected
by the X-ray analysis at the position of the ALSV peak B, while the
[29] Landolt-Bornstein, Database Numerical Data and Functional Relationships in
Science and Technology, Springer, 1991, p. 1, IV-5A.
[30] N. Kaneko, H. Nezu, N. Shinohara, J. Electroanal. Chem. 252 (1988) 371.
31] Spravochnik Himika, second ed., Himia, Moskva, 1965, pp. 119-167.(Russ.).
[
Ag Cd phase, characterized by well defined peak D on the ALSV,
was not detected on the corresponding diffractogam.
[32] U. Cohen, K.R. Walton, R. Sard, J. Electrochem. Soc. 131 (1984) 2489.
33] U. Cohen, F.B. Koch, R. Sard, J. Electrochem. Soc. 130 (1983) 1987.
3
[