New Journal of Glass and Ceramics, 2011, 1, 112-118
doi:10.4236/njgc.2011.13016 Published Online October 2011 (http://www.SciRP.org/journal/njgc)
Effect of AgI on Conduction Mechanism in
Silver-Vanadate Superionic Glasses
Poonam Sharma, D. K. Kanchan*, Meenakshi Pant, Manish S. Jayswal, Nirali Gondaliya
Solid Sate Ionics & Glass Research Laboratory, Department of Physics, Faculty of Science, The M.S. University of Baroda, Vado-
dara (Gujarat), India.
Received June 14th, 2011; revised July 27th, 2011; accepted August 9th, 2011.
ABSTRACT
A quaternary super-ionic glass system xAgI: (95-x) [Ag2O:2V2O5]: 5TeO2, where 40 ≤ x ≤ 65 in steps of 5, has been pre-
pared by melt quenching technique. The prepared glass samples are characterized by X-ray, FTIR and DSC studies. As
revealed by the FTIR spectra, the oxyanion network is not affected by the addition of AgI. The frequency dependence of
the electrical conductivity for various glass compositions at different temperatures has been analyzed in terms of Jon-
scher’s universal power law. The measurements reveal that the conductivity increases from σ = 7.62 × 10–7 S/cm to 1.15
× 10–4 S/cm with increasing AgI content. The temperature dependent conductivity obeys the Arrhenius relationship. The
impedance and modulus studies indicate the non-debye type of the frequency dispersion for all the glass samples.
Keywords: Conductivity, Glass Transition Temperature, Infrared Spectra, Impedance, Modulus
1. Introduction
AgI and Ag oxysalt based ion conducting materials at-
tracted much attention from last many years, because of
their high ionic conductivity at room temperature [1-4].
The glasses formed by AgI and Ag oxysalt complexes
are constituted by randomly oriented micro domains ma-
de by arrays of tetrahedral oxysalt complexes [5]. These
complexes are linked together and are surrounded by non-
mobile Ag+ ions which coordinate iodide polyhedra con-
taining mobile Ag+ ions. The conductivity maximum is
realized when the oxyanions are coordinated with the
largest number of iodide polyhedral which is compatible
with the vitreous state. In general, it is found that the
ionic conductivity increases with the AgI content in the
glass composition. Although AgI based glasses have
been studied widely, very limited studies have been re-
ported on silver-based vanado-tellurite glasses [6]. Hence,
we have used V2O5and TeO2 as two glass formers with a
very low amount of TeO2 salt (only 5 wt %) as it is dif-
ficult to obtain glasses with high V2O5 contents and small
amount of TeO2 is reported to induce superionic behavior
when it is doped with metal halide [7]. Montani et. al. [8]
had shown that addition of the Ag2O (network modifier)
to the electronic V2O5 and TeO2 glass results the block-
ing of the electronic paths which causes the electronic
conductivity to fall down. And increasing network modi-
fier concentration gives rise to more ionic transport due
to closeness of non-bridging oxygens.
The objective of present work is to investigate the in-
fluence of AgI salt content on conduction mechanism
and ionic relaxation behavior in Ag2O-V2O5 -TeO2 glass
system in framework of the modulus formalism i.e., the
conductivity relaxation mechanism. In order to view this
effect, we have prepared xAgI - (95-x)[Ag2O:2V2O5] -
5TeO2 glass system, where 40 ≤ x≤ 65 in steps of 5 in the
present paper.
2. Experimental
Analytical Reagent grade starting chemicals: AgI, Ag2O,
V2O5 and TeO2 were used to prepare the samples. All the
compositions were weighed according to their mol%,
crushed and then ground in an agate mortar and pestle for
2 hours by wet grinding method. The homogenous mix-
ture obtained was then kept in an alumina crucible in a
controlled electric muffle furnace at 673K. Subsequently,
the furnace was heated to 673K at a rate of 100K/h and
the melt was kept for 4 h at that temperature. After 4
hours, the melt was poured on a heavy thick copper plate
kept at room temperature and pressed by another similar
copper plate to quench it.
X-ray diffraction was carried by X-ray diffraction ana-
lyzer (Shimadzu) at 20 / min scan rate to confirm the amor-
phous nature of prepared glass samples. The glass transi-
tion temperature of the amorphous samples was measured

Effect of AgI on Conduction Mechanism in Silver-Vanadate Superionic Glasses113
by Differential Scanning Calorimeter (DSC), TA Instru-
ments (Model MBSE-2910) at a heating rate of 10K/min.
Fourier Transform Infrared (FTIR) spectra were measured
in the range of 400 - 1100 cm–1 by a conventional KBr
pellet method using an FTIR spectrophotometer (Bruker
Model Vertex 70).
Electrical properties were measured by using an Im-
pedance / Gain Phase analyzer (Solartron 1260) in the 10
MHz to 10 Hz frequency range at temperatures from room
temperature to the glass transition temperature. The mea-
surements were made by two-probe method in which quen-
ched glass samples of about 1mm thickness and rectan-
gular in shape were coated with silver paint to serve as
electrodes. The samples were kept in contact with two
polished, cleaned and spring-loaded copper electrodes.
3. Result and Discussion
3.1. IR Spectra
The room temperature IR spectra in the region 400 -
1100 cm–1 for x = 45, 50 and 60 mol% are shown in Fig-
ure 1. The band observed at 497 cm–1 is assigned to υsym
stretching vibrations of V-O-V bridge of V2O7
–4 group.
The broad band in the range of 650 - 740 cm–1 may be due
to the stretching vibrations of the Te-Oax (axial), Te-Oeq
(equatorial) bonds in deformed TeO4 groups, stretching
vibrations of TeO3 of Te2O5 units and symmetric stretch-
ing vibrations of V-O-V bonds. The band at 966 cm–1 is
assigned to symmetric stretching vibrations of the VO2
groups of the VO4 polyhedra. A small kink observed at
1020 cm–1 corresponds to the vibrations of the non-brid-
ging V = O of the VO5 groups. We have observed no
change in the structure with increasing the AgI concen-
tration. Hence, from the IR spectra we have concluded
that the network structure of prepared glass samples is
formed of vanadate and tellurite oxides and it remains
Figure 1. IR spectra for x = 45, 50 and 60 mol%.
unaltered with AgI concentration. Similar results have
been observed by several workers [4,6].
3.2. Impedance Plot
Complex impedance data Z* is represented by its real, Z'
and imaginary, Z″ components through the relation:
*
Z
ZiZ



(1)
Figure 2 shows the complex impedance plot for all
glass compositions at 313 K and inset shows that of x =
45 mol% at various temperatures. Figure shows the de-
pressed semicircles which represent the presence of the
distribution of relaxation times within the bulk response
[9]. The high frequency semicircles are due to parallel
combination of bulk resistance Rb and bulk capacitance
Cb [10]. It is clear from the Figure 2 and its inset that by
increasing the AgI concentration and temperature, the
radius of the depressed semicircle decreases i.e., sample
resistance decreases which may be due to the enhance-
ment of the number of carrier ions and its mobility with
temperature. Semicircle fits are used to determine the
zero frequency impedance i.e., resistance and by using
the known geometrical dimensions of the glass sample,
the dc conductivity was determined.
3.3. Conductivity
The logarithmic dc conductivity σdc of various glass com-
positions at 303K is shown in Figure 3. It can be obser-
ved from figure that dc conductivity is increasing with
AgI content. It is also observed that for all glass compo-
sitions the dc conductivity shows an activated behavior
i.e., it increases with temperature. This behavior is char-
acteristic of a thermally stimulated process and is attrib-
uted to increase of charge carrier energy with rise of tem-
perature. It makes the hopping motion of charge carriers
easier through the free energy barriers in the glass matrix.
In addition to it, conductivity is also found to increase by
three orders of magnitude with AgI concentration varying
from 40 mol% to 65 mol%. When a plot is made between
dc conductivity versus activation energy for conduction,
a linear relationship is observed (inset of Figure 3); the
near linearity between the conductivity and the activation
energy suggests the conductivity enhancement is directly
related to the increasing the mobility of the charge carri-
ers. As it appears, due to the increasing AgI concentra-
tion i.e. more Ag+ ions, easy paths for the movement of
the charge carriers are created and hence an increase in
the conductivity is resulted with increase in AgI concen-
tration in the prepared glass matrix [7].
The frequency dependent conductivity of the present
glass samples has been measured in the frequency range
from 10 MHz to 10 Hz with the temperature range from
296K to 353K. The conductivity is determined from the

Effect of AgI on Conduction Mechanism in Silver-Vanadate Superionic Glasses
114
data of complex impedance values and calculated by using
the relation




2

2
ta ZZZ 
   (2)
The logarithmic conductivity as a function of frequen-
cy with different compositions at 323K is shown in Fig-
ure 4. The ac conductivity σac(ω) for all the samples ex-
hibit the same shape of the curve, with different con-
ductivity values depending on the glass composition. The
curve corresponds to bulk relaxation phenomenon, whereas
the plateau region is connected with the dc conductivity
(σdc) of the glasses. The low frequency dispersion de-
scribes electrode-electrolyte interfacial phenomenon or
space charge polarization [11].
As the frequency decreases, more and more charge
accumulation occurs at the electrode and the electrolyte
interface, which leads to a decrease in the number of
mobile ions and eventually to a drop in conductivity at
low frequency. In high frequency region, the mobility of
charge carriers, Ag+, is high (near to relaxation time) and
hence, the conductivity increases with frequency. Similar
behavior is reported for other silver based ionic conduc-
tors [10-13].
At higher frequencies, the ac conductivity has been
found to increase with frequency obeying Jonscher’s
Power Law [14] described by


s
dc
A



 (3)
where σdc is the dc conductivity of the sample, A is a
constant for a particular temperature, ω (= 2πf) is the
angular frequency of the applied field and ‘s’ is the
power law exponent in the range 0 < s < 1. The power
law exponent s is a measure of degree of interaction with
the environment. The value of s > 0 is due to energy
stored in the short range collective motion of ions and its
higher value implies that large energy is stored in such
collective motions. In present work, s is found to increase
with AgI content. The magnitude of s appears to be
Figure 2. Impedance plot for different co mpositions at 313K and inset shows impedance plot at different temperatures for x =
45 mol%.

Effect of AgI on Conduction Mechanism in Silver-Vanadate Superionic Glasses115
Figure 3. DC conductivity of AgI- Ag2O- V2O5- TeO2 glass series and inset show s plot of activation ene rgy vs. dc c onductivity
at 303K.
Figure 4. Frequency dependent conductivity for different
compositions at 303K.
associated with high degree of modifications. The hop-
ping frequency

p is calculated by using Almond and
West formula [15], frequency at which
 ′ (  ) = 2 
dc.
Since Ag+ ions are the mobile species in the present case,

p has been identified as the hopping rate of Ag+ ions.
Usually

p is a characteristic frequency associated with
the frequency of the dielectric loss peak and it is assumed
to be thermally activated. It increases with the increases
of temperature. It is, therefore, clear that the hopping rate
of silver ions in the present system is also a thermally
activated parameter. The mobile ion concentration factor
K' has been evaluated as
dc p
KT




(4)
where T is the temperature in Kelvin. The mobile ion
concentration factor K' is found to be independent of
temperature and is found to increase with AgI concentra-
tion. This shows that the increase in the mobile ion

Effect of AgI on Conduction Mechanism in Silver-Vanadate Superionic Glasses
116
concentration is attributed to the increase in the conduc-
tivity i.e; with the increase in the AgI content.
3.4. Modulus Formalism
Modulus spectroscopy highlights the bulk effects and it is
complementary to impedance spectroscopy which high-
lights electrode and grain-boundary effects. This forma-
lism is particularly suitable to detect phenomena as elec-
trode polarization and bulk property such as average re-
laxation time [16,17]. We have used the complex electric
modulus formalism to analyze the relaxation processes in
the present system as it discriminates against electrode
polarization and other interfacial effects. Electric modu-
lus can be represented by the following equation.
*
0
jC *
M
Z
 (5)
In an ideal solid electrolyte system, it can be repre-
sented by a single parallel RC element, where R and C
represent the resistance and capacitance, respectively and
is characterized by a single time constant as conductivity
relaxation time. In ideal system, the peak maximum of Z″
and M″ is found at the same frequency and the shape of
the peaks are identical with that predicted by Debye the-
ory [18]. With the appropriate scaling, the normalized-
modulus and impedance spectra of the Debye curves are
completely superposable and are given by the equation:

2
1
RC
ZR
RC


 

;

0
2
1
CRC
MCRC


 

(6)
The term, ωRC /[1+(ωRC)2 ] in imaginary part of im-
pedance, Z″ and imaginary part of modulus, M″ is re-
sponsible for debye-like peak shapes. To understand the
non-debye behavior of the prepared glass samples, Z″
and M″ at 303K have been plotted in Figure 5 for x = 60
mol% glass sample. It is observed from figure that the
Z″max and M″max do not occur at the same frequency
which indicate a wide distribution of relaxation times. At
low frequencies, Z″ shows large rise due to electrode
02468
0.0
-2.0x106
-4.0x106
-6.0x106
-8.0x106
Z"
M"
log f
Z"
0.000
0.005
0.010
0.015
0.020
M"
Figure 5. The impedance and modulus spectrum for x =
40mol% at 303K.
polarization and at high frequency broadened modulus
spectra indicates the distribution of relaxation times [19].
The real and imaginary part of modulus spectra for x =
45 mol% at different temperatures is presented in Figure
6 (a) and Figure 6 (b) respectively. Other glasses also
showed almost similar M′ and M″ temperature depend-
ence behavior. From M′ graph, it shows that whatever be
the temperature, the value of M′(
 ) reaches a constant
value at higher frequencies. At low frequencies, M′ and
M″ approaches to zero indicating that the electrode po-
larization phenomenon make a negligible contribution to
M* and may be ignored when the electric data has been
analyzed in this form [20]. The observed long tail at low
frequencies is due to the large capacitance associated
with the electrodes.
The M″(
 ) spectrum relative to a given temperature
shows an asymmetrical peak approximately centered in
the dispersion region of M′(  ). The asymmetrical peaks
obtained suggest that the material can be interpreted by
an equivalent circuit composed of a single parallel RC
element [18]. The left part of the peak corresponds to
234567
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
296K
303K
313K
323K
333K
343K
353K
log M'
log f (Hz)
(a)
(a)
1234567
0.000
0.006
0.012
0.018
296K
303K
313K
323K
333K
343K
353K
M"
log f (Hz)
(b)
(b)
Figure 6. Frequenc y dependence of (a) re al part, M′ and (b)
imaginary part of modulus, M″ at different temperatures
for x = 45mol%.

Effect of AgI on Conduction Mechanism in Silver-Vanadate Superionic Glasses117
long range mobility and the right part of the peak is at-
tributed to ions spatially confined in narrow potential
wells. The frequency range where the peak occurs indi-
cates the transition between long and short range mobil-
ity and is defined by the condition

c

c = 1 [21] where

c
is the most probable relaxation time of ions. The M″ (  )
peak height is found to be nearly same at different tem-
peratures and it is observed to shift to a higher frequency
with increasing temperature. The peak in M″ variation
corresponds to the relaxation frequency and the corre-
sponding relaxation time is systematically shifted to higher
frequencies as the temperature increases.
Figure 7 shows the normalized plot of M″ / M″max ver-
sus log f / fmax of the modulus for the glassy system for x =
50 mol% at different temperatures. The approximate over-
lap of the modulus curves for all temperatures indicates
the dynamical processes occurring at different frequent-
cies are independent of temperature. Such results were
also observed for other glass compositions. It is found
that the normalized plot for different compositions do not
merge on a single master curve which implies that the
conductivity relaxation depends on the glass composition.
This has usually been regarded as an indication of a dis-
tribution of relaxation times in the conduction process
[20].The observed broad peak can be assigned to the sum-
mation of relaxations occurring in the bulk materials. The
full width at half height obtained is greater than the De-
bye type of relaxation with single time constant is attrib-
uted to the presence of strong ion-ion interaction. The
observed normalized plot is non-symmetric in agreement
with the non-exponential behavior of the electrical func-
tion described by Kohlrausch-William-Watts (KWW)
exponential function [22]
 
exptt



 ;

(7)

10  
where  and  are the conductivity relaxation time and
Kohlrausch exponent respectively. The value of the Kohl-
rausch parameter
 for most practical solid electrolyte is
Figure 7. Normalized plot of M″ at different temperatures
for x = 50mol%.
smaller than one. The calculated values of  lies in the
range of 0.6 - 0.9 that is in agreement with the values
reported [23].
4. Conclusions
The ionic conduction of the prepared glasses is a cones-
quence of the presence of glass modifier (Ag2O) and the
dopant (AgI). IR spectra show that the network structure
of prepared glass samples is formed of vanadate and tel-
lurite oxides and remains unaltered with AgI concentra-
tion. The conductivity is found to obey the universal
power law. The ionic conductivity as well as power law
exponent is found to increase with AgI concentration.
The modulus plot shows non-debye behavior and is
asymmetric with respect to the peak maxima. The peaks
are considerably broader on both sides of the maxima.
The broadened modulus spectrum indicates the distribu-
tion of relaxation times in the conduction process. It is
inferred from the normalized plot of the prepared glass
samples that the conductivity relaxation is independent of
temperature but composition dependent.
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