Surfactant effect on the conductivity behavior of CsH2PO 4: Characterization by electrochemical impedance spectroscopy

Article abstract of DOI:10.1016/j.physb.2011.01.040

Cesium dihydrogen phosphate (CDP) nanoparticles were synthesized using the surfactants cetyltrimethyl ammonium bromide (CTAB), polyoxyethylenepolyoxypropylene (F-68) and (F-68:CTAB) with molar ratio 0.06. The samples conductivity such as CDP_CTAB, CDP_F-68 and CDP_{(F-68:CTAB)0.06} was studied by impedance spectroscopy in the frequency range 0.01 Hz to 1 MHz. The Nyquist plots were drawn at different temperatures of 210, 230 and 260 °C, which are defined below transition, phase transition and above transition, respectively. The measured conductivities obey the Arrhenius relation. The influence of surfactants on conductivity are more significant at higher temperature due to grain boundary. The conductivity of CDP_CTAB increased slightly with increasing temperature to 260 °C, whereas the conductivity of other samples decreased with increasing temperature over 230 °C. The results indicated that the conductivities increase in the order of CDP_CTAB>CDP _{(F-68:CTAB)0.06}>CDP_F-68. These are in accordance to the ion exchange capacities of the samples that the surfactant shows a direct influence on the samples proton mobility. It is found that the conductivity of CsH₂PO₄ is influenced by surfactant type.

Full text of DOI:10.1016/j.physb.2011.01.040

Physica B 406 (2011) 1689–1694
Contents lists available at ScienceDirect
Physica B
journal homepage: www.elsevier.com/locate/physb
Surfactant effect on the conductivity behavior of CsH2PO4:
Characterization by electrochemical impedance spectroscopy
S. Hosseini a,n, M. Homaiee b, A.B. Mohamad c, M.R. Malekbala a, A.A.H. Khadum c
a Department of Chemical and Environmental Engineering, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
b Department of Physics, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
c Institute of Fuel Cell, University Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Cesium dihydrogen phosphate (CDP) nanoparticles were synthesized using the surfactants cetyltri-
methyl ammonium bromide (CTAB), polyoxyethylene–polyoxypropylene (F-68) and (F-68:CTAB) with
molar ratio 0.06. The samples conductivity such as CDPCTAB, CDPF-68 and CDP(F-68:CTAB)0.06 was studied
by impedance spectroscopy in the frequency range 0.01 Hz to 1 MHz. The Nyquist plots were drawn at
different temperatures of 210, 230 and 260 1C, which are defined below transition, phase transition and
above transition, respectively. The measured conductivities obey the Arrhenius relation. The influence
of surfactants on conductivity are more significant at higher temperature due to grain boundary. The
conductivity of CDPCTAB increased slightly with increasing temperature to 260 1C, whereas the
conductivity of other samples decreased with increasing temperature over 230 1C. The results indicated
that the conductivities increase in the order of CDPCTAB4CDP(F-68:CTAB)0.064CDPF-68. These are in
accordance to the ion exchange capacities of the samples that the surfactant shows a direct influence on
the samples proton mobility. It is found that the conductivity of CsH2PO4 is influenced by
surfactant type.
Received 27 November 2009
Received in revised form
3 January 2011
Accepted 18 January 2011
Available online 1 February 2011
Keywords:
Cesium dihydrogen phosphate
Protonic conductivity
Surfactant
Impedance spectroscopy
& 2011 Elsevier B.V. All rights reserved.
1. Introduction
(P21/m to Pm-3m) corresponding to monoclinic and cubic phases,
respectively [5–8]. The three phases of CsH2PO4 can be presented
Recently, solid acid salts based on tetrahedral oxyanion groups
were of interest due to unusual proton conductivity at anhydrous
conditions. Above room temperature, many solid acids comprised
of hydrogen bonds undergo a phase transition and can be con-
sidered as protonic conductive. Protons as a charge carrier in solid
acids show different behavior due to small mass, size and without
any protector compared to other ions. Protons show a strong
tendency to form hydrogen bonds with neighboring atoms in a
lattice; so the proton migration depends on the atom dynamics of
surrounding [1–3]. Two types solid acid salts CsHSO4 and CsH2PO4
are widely investigated due to the existence of superprotonic
transition. Cesium dihydrogen phosphate, CsH2PO4, is made up of
the discrete PO4 tetrahedral connection by hydrogen bonds and
through the electrostatic interaction with the cesium cation.
Superprotonic phase transition at high temperature is distinguish-
able by rapid proton transfer in hydrogen bond and the liberation
of oxyanion (PO4) at 504 K; accordingly, the observed conductivity
with the devoted space group as follows:
Ferroelectric-Paraelectric-Superprotonic
ðmonoclinicÞ-ðmonoclinicÞ-Cubic
Haile et al. examined the conductivity of CsH2PO4 in the
temperature range of 170–255 1C using PH O¼0.4 atm. The results
2
showed that the conductivity rises from 8.5 ꢁ 10ꢀ6 at 223 1C to
1.8 ꢁ 10ꢀ2 at 233 1C, which is in well agreement with that of
Baranov et al. [9,10]. Park et al. [11] reported that the complex
dielectric constant of CsH2PO4 is in the temperature range of 30 to
270 1C and concluded that the high temperature transformation
produced an onset of thermal decomposition CDP into CsH2P2O7
and CsPO3 at 230 1C. Taninouchi et al. [12] studied behavior of
CsH2PO4 above 260 1C under highly humidified condition. They
suggested CDP molecules dehydrate to CsPO3 through a stable
liquid phase with the conductivity 5 ꢁ 10ꢀ2
O
cmꢀ1 at 283 1C and
PH2O¼0.3 atm. The nanoparticles of CDP were synthesized using
self-assembly method by surfactants with reduction in particles
size. Surfactants are usually amphiphilic organic compounds
including two hydrophobic and hydrophilic groups. A variety of
surfactant molecules are widely used to synthesize nanoparti-
cles [13,14]. The aim of the present work was to investigate
surfactants effect on the amount of CsH2PO4 conductivity using
impedance spectroscopy. A comparative study was carried out
of current samples is very low (E10ꢀ5
perature. However, the protonic conductivity increased two or
three times (E10ꢀ2 cmꢀ1) with increase in temperature to
O
cmꢀ1) at room tem-
O
230 1C [4–6]. A transition from low to high symmetry does exist
n Corresponding author. Fax: +603 89216024.
E-mail addresses: Soraya@eng.ukm.my, hosse_so@yahoo.com (S. Hosseini).
0921-4526/$ - see front matter & 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2011.01.040

1690
S. Hosseini et al. / Physica B 406 (2011) 1689–1694
between three types of samples, namely CDPF-68, CDP(F-68:CTAB)0.06
and CDPCTAB
ranging 2.31 to 601 at room temperature. Lattice parameters of the
identified phases were determined by using the Rietveld refinement
method. Thermal behavior of the samples on heating was studied by
thermal gravimetric analysis (TGA) and differential scan calorimetry
(DSC). TGA and DSC runs were carried out under nitrogen from 30 to
600 1C at heating rate ranging 5 1C minꢀ1. Small fragments of the
samples (ꢂ20 mg) were encapsulated in alumina pans for testing.
The temperatures of detected events by DSC were further used for
planning temperature ranges of the proton conductivity measure-
ments, phase transition and weight loss during dehydration
process [15].
The proton conductivity was measured by impedance spectro-
scopy technique using a Solarton 200 over the frequency range of
0.01 Hz–1 MHz and applying different voltage in the range of
10–2500 mV. The impedance scans were carried out in the tempera-
ture range between 30 and 260 1C. Both faces of the pellets were
polished and painted with the paste Pt/C (50 wt%) as Pt electrode. The
prepared pellet was placed between two bronze holders inside a
quartz cell. A silver wire was attached both edge of the holders and
connected to impedance analyzer. The sample temperature was
controlled by a thermocouple that connected to the bronze holders.
Gaseous mixture Ar/H2O (0.9/0.1 vol%) was flowed through the glass
tube at 15 mL minꢀ1 under atmospheric pressure and temperature
30 1C. The samples were heated during the conductivity measure-
ment in a furnace with the temperature interval 20 1C. The data was
recorded using the commercial software package, ZView2 in order to
measure the amount of proton conductivity.
.
2. Experimental
2.1. Preparations nanoparticles using surfactants
Nanoparticles CsH2PO4 were synthesized by cationic and non-
ionic surfactants. Cetyltrimethylammoniumbromide (99 wt %, Sigma
Chemical Company) as cationic, polyoxyethylene–polyoxypropylene
(Pluronic F-68 SIGMA) as non-ionic and the mixture of both
(F-68:CTAB) with mole ratio 0.06 were used as templating agent.
The surfactants solution was separately prepared using ethanol and
appropriate amount of the surfactant as shown in Fig. 1. The initial
aqueous solutions were prepared dissolving appropriate amounts of
Cs2CO3 (99.99 wt%, Aldrich) in distilled water. The aqueous solution
was added into the surfactant solution at room temperature and
stirred for 1 h. Orthophosphoric acid H3PO4 (85 wt%, Aldrich) solution
was added dropwise to the above solution (surfactant and aqueous
solution). The increase in turbidity was observed during the crystals
production (the existence of ethanol in surfactant solution). While
stirring the solution, methanol was added to the mixture. The white
mass was slowly precipitated and continued to stir for 2 h. The
mixture was filtered by vacuum pump at room temperature and the
white mass was dried at 130 1C for 24 h. The prepared precipitates
were activated at 220 1C for 8 h under nitrogen gas in order to
remove the rest of the surfactants completely. Powders were pressed
uniaxially in a stainless steel die under a pressure of 100 kg cmꢀ2 in
order to prepare pellets (thickness 2 mm, diameter 10 mm).
The ion exchange capacity (IEC) of the samples was measured via
titration using NaOH. 1 gram of each sample was separately allowed
to stir in 50 ml of saturated NaCl solution for 24 h to replace all H+
ions with Na+. Then the solution was titrated with NaOH (0.1 N) to
determine the amount of H+ in the solution.
2.2. Characterization methods
The measurement conditions and the experiments setup were
selected equally for all samples. X-ray powder diffraction (XRD)
measurements were performed by diffract meter (D & Advance)
3. Results and discussion
X-ray diffraction measurements were performed by a (A&
Advance) diffractometer under the acceleration voltage of 40 kV
and current of 40 mA. The XRD patterns of three samples CDPF-68,
and CuK radiation with wavelength (
l
¼0.15408 nm). All peaks
a
1
were obtained with scanning speed of 21 in a standard 2 setup
y
Fig. 1. Flow chart of the preparation method of CsH2PO4 using surfactants.

S. Hosseini et al. / Physica B 406 (2011) 1689–1694
1691
CDP(F-68:CTAB)0.06 and CDPCTAB were compared and shown in Fig. 2.
All XRD patterns clearly displayed the characteristic peaks of the
solvents and surfactant concentration. The effect of ethanol
solution on crystal morphology was to suppress crystal growth
by extracting the water from solution and adsorbing in different
crystal surface and on particular sites of the crystallite which
changes the expanded capacity of every plane.
Moreover, the diffraction peaks based on the presence of
CsH2P2O7 and CsPO3 were not observed for all cases that were
confirmed by the EDX results. The alkyl chain length of surfactants
can be detected at lower angles whereas no peaks were seen due to
the surfactant existence [18]. The lattice parameters are summar-
ized in Table 1 and compared to the literature. Good agreement
samples supported at 2
y¼24.51, 301, 34.51 and 48.51. The diffrac-
tion peaks of samples CDPF-68 and CDPCTAB show monoclinic
phase whereas CDP(F-68:CTAB)0.06 shows orthorhombic phase. Also,
the orthorhombic phase of CsH2PO4 was reported by some
researchers [16]. All of the obtained peaks are compared to the
data that were defined as the reference in the Eva software library
JCPDS File Card (no. 084-0122) [17].
Differences were observed in the Miller indices of the peaks
and directly effective on the morphology of particles. Growth and
morphology of crystals depends on the Miller indices planes
which can be influenced by parameters such as amount of
was observed between the monoclinic lattice parameters of CDPF-68
,
CDPCTAB and the reported values [17]. The elements analysis
(ICP-AES) demonstrated the value 1.0270.03 for the mole ratio
cesium/phosphorus (Cs/P) represents good compatible to the mole
ratio on CsH2PO4 formula.
The XRD data can give the particles size using calculation by the
Debye–Scherrer equation. The estimated data using the XRD results
represented nanosize scale of particles with well agreement to BET
method. According to the TEM analysis and the normal size
distribution plots, the smallest size of particles is generated by
surfactant F-68 as shown in Table 2. It is usual the TEM analysis to
yield average particle sizes is biased toward smaller sizes, since the
method of sample preparation often uses a TEM grid which selects
(filters) only the smallest particles deposited from solution, then
two methods of particle size measurement was performed by XRD
and BET measurement. The comparison between these techniques
is listed in Table 2. The obtained particle sizes from the XRD were in
the range of 10 nm, which are in good agreement with those
calculated from the BET analysis.
In order to investigate the resistance during changing applied
voltage, two pellets were pressed at different die pressures of
191 and 64 MPa. Both pellets were tested by voltages 10, 500,
1000 and 2500 mV at room temperature, as shown in Fig. 3. The
resistance of pellet-191 was constant during the voltage changes,
while the resistance of pellet-64 changes with the applied voltage,
indicating discrepancy on real resistance (Z0 axis). The bulk
resistance is defined as resistance of material along the signal
path and is found to be constant. Contact resistance is a variable
resistance due to constriction resistance, and is dependent upon
the applied force via contact. Constriction resistance occurs as the
electrical current must squeeze through the asperities (contact
points) to cross the interface. Indeed, the optimum pressure can be
applied for reduction of the resistance variation minimum. The
grain boundary and bulk conductivity and the influence of
surfactants on conductivity were investigated by impedance
spectroscopy. According to the thermal behaviors of CDP, the
impedance spectra were measured below phase transition 210 1C,
at phase transition 230 1C and above phase transition 260 1C for all
samples, as shown in Fig. 4. The impedance spectrum sample
CDPCTAB was individually formed at three parts at 210 1C, which
can be considered at low, medium and high frequencies. The
lowest frequency region (linear diffusion spike) is attributed to the
sample-electrode connection or effect of surface layer; the second
semicircle at medium frequency represents to grain boundaries
and the highest frequency arc corresponds to the bulk response
Fig. 2. X-ray diffraction patterns of the CDP powder using surfactant, namely
CDPF-68, CDP(F-68:CTAB)0.06 and CDPCTAB
.
Table 1
Structural parameters of the CDP samples at room temperature.
Parameters
CDP [17]
CDPF-68
CDP(F-68:CTAB)0.06
CDPCTAB
a
b
7.912
6.386
4.88
7.997
4.872
7.907
6.383
6.368
6.386
c
4.88
15.049
4.88
107.73
2
107.73
4
90.22
107.71
2
b
z
4
Space group
P21/m
C2/c
B21/m
P21/m
GOF
R
1.105
1.127
1.165
4.3570.01%
7.9470.03%
6.0870.02%
5.3270.02%
9.2270.05%
7.5470.03%
5.1570.03%
8.3470.04%
6.1770.01%
Rwp
Rexp
Table 2
Average particle size, ion exchange capacity and density of CDP nanoparticles.
Samples
TEM
XRD (nm)
BET
Ion exchange capacity
(mmol gꢀ1
Density (g cmꢀ3
)
)
CDPCTAB
3.770.488
10.370.45
6.8570.87
11.2370.54
11.3570.48
8.7170.69
10.8170.45
1.0970.02
0.7570.03
0.8970.02
3.5370.13
3.4270.2
3.3770.18
CDPF-68
2.6670.89
3.570.56
CDP(F-68:CTAB)0.06

1692
S. Hosseini et al. / Physica B 406 (2011) 1689–1694
Fig. 3. Variation of resistence for two pellets (64 and 191 MPa).
Table 4
Values of equivalent circuit parameters at 210 1C of CDPCTAB
.
Parameters
Values
Rf
(
O)
80
R1
C1
R (
(
O
F)
)
150
(m
0.001
150
O
)
A (nF)
B (
0.0003
109
O
)
t
n
(s)
3.98
0.1
m
0.48
Here n and m are the constant and j2¼ ꢀ1,
t
¼L2/D (
t is the
diffusion time constant, L is the diffusion layer thickness and D is
the diffusion coefficient). In the present case, the values of
equivalent circuit parameters at 210 1C (calculated using fitting
the experimental data) were listed at Table 4. The degree of
frequency dispersion leading to CPE behavior is indicated using
parameter n, varying in the range 0–1. The frequency dispersion
has been commonly attributed to the deviation from the ideal
capacitive behavior due to irregularities, surface inhomogeneities,
roughness factors and adsorption effects [20].
Fig. 4. Complex impedance plots of CDPCTAB
.
Table 3
Impedance and admittance of different electrical elements.
Element
Description
Impedance
L
Inductor
Resistor
Capacitor
Warburg
joL
R
R
An ideal capacitor corresponds to n¼1 while n¼0.5 can be
considered as CPE in a Warburg component [21]. In the present
case, the value n¼0.85 showed a high capacitance and low
diffusion of hydrogen ion (H+) at low temperature 30 1C, while
the value n¼0.1 indicated low capacitance and high diffusion of
hydrogen ion due to superprotonic phase transition at 230 1C.
At higher temperatures, the semicircles in the high frequency
region, corresponding to bulk and grain boundaries, were not
observable because the ionic conduction process was too fast to
observe with the present impedance analyzer. One ‘spike’ like
response was observed at low frequency corresponding to the
charge build-up at the electrodes. The resistance (the radius of
arcs) disappeared with increasing temperature due to the fast
proton conduction process that it observed at high temperature
with the present impedance analyzer. In Fig. 4, the results indicate
that the bulk and grain boundary properties dominate the overall
electrical conductivity at below phase transition, while at higher
temperatures the difference in bulk and grain boundary conduc-
tivities becomes insignificant. Fig. 5 shows a typical impedance
response (Cole-Cole plot) of CDPF-68 sample. Two depressed
semicircles can be separated throughout the entire frequency
range. As seen in Fig. 5, the first high frequency semicircle could
be assigned to the grain boundary response and the second
semicircle of low frequency is a typical response of electrode
process at temperature 210 1C.
C
1/j
o
c
pffiffiffiffiffiffi
W
Zo=
j
o
)
a
Q
CPE
Zo/(j
o
(ionic conduction of bulk). The impedance spectra were simulated
by the equivalent circuit consisting of elements that are connected
in the form of series and parallel as shown in Fig. 4. The equivalent
circuit model was designed to represent the complex geometrical
and physical description of the conduction processes within the
pellet. The fitting of impedance data with an equivalent circuit
was required in order to simulate impedance. Various electrical
elements were applied to symbolize different processes and
complicated systems due to analyze the physical and chemical
structural. Elements that are used in the equivalent circuits are
listed in Table 3. Here R, C, L, W and Q are resistor, capacitor,
inductor, Warburg element and constant phase element (CPE),
respectively. It is possible to express the impedance as a complex
function including constant phase element (CPE) and infinite
length Warburg components and given as follows [18,19]:
1
Zð
o
o
Þ ¼
ð1Þ
ð2Þ
n
ðj
oAÞ
n
Zð
Þ ¼ Btanh½ðjotÞꢃ =ðjot m
Þ

S. Hosseini et al. / Physica B 406 (2011) 1689–1694
1693
Fig. 6. Complex impedance plots of CDP(F-68:CTAB)0.06
.
Fig. 5. Complex impedance plots of CDPF-68
.
In order to determine the resistive and capacitive elements, a
series of the RC elements was fitted to the experimental data,
indicating the grain boundary and the bulk response. At tempera-
ture 230 1C, the second arc was distorted into a straight line (nearly
to 451 to the real axis). The straight line resulted from diffusion
impedance indicates the Warburg impedance law for semi-infinite
diffusion. The diffusion region is not limited due to high conductivity
at phase transition. The complex plane representation of the
impedance data was comprised of a high frequency semicircle and
a low frequency linear diffusion spike, as shown in Fig. 5. The finite
Warburg impedance appears using different style and a bending of
the impedance curve towards the real axis appears at very low
frequencies at around 260 1C. The finite diffusion blocked ion
transfer at the end of the diffusion layer (arisen decomposition
products or insulation); therefore, the result produced a distorted
semicircle in the Nyquist plot. The similar behaviors were obtained
for CDP(F-68:CTAB)0.06 at temperatures 210, 230 and 260 1C.
the bulk, the grain boundaries and electrode surface could not be
separated.
The impedance spectrum of two samples CDPF-68 and
CDP(F-68:CTAB)0.06 show large arc of grain boundaries, indicating the
grain boundaries are highly covered by a phase of poor electrical
conductivity or impurities CsH2P2O7 and CsPO3 due to dehydration
of CsH2PO4 particles at temperature above 230 1C. As it is seen, the
minimum value of weight loss during dehydration process occurred
in CDPCTAB, that was reported by TGA analysis [15].
The present complex impedance measurements of CDP using
different surfactants revealed that the surfactants played an
important role in the enhancement of conductivity. Although a
detailed mechanism is not clarified by surfactants, it is observed
that the effect of hydrophobic and hydrophilic moieties of surfac-
tants on the molecular organization and grain boundaries act as
the additional source of defects, resulting in the enhancement of
the ionic conductivity. It is known that many crystals of solid acids
indicated electrical properties due to the introduction of defects by
cationic substitution in the host framework. Proton intrabond and
interbond transfer in hydrogen bonds of some solid acids is the
mechanism for the dynamic behavior of proton conductivity that
is associated with thermally-activated of created intrinsic defects.
The proton defects in the networks can be considered of two types
D and L indicating doubly occuped and unoccupied bonds (with-
out hydrogen), respectively. The proton conduction is known via
the Grotthuss mechanism. Several researchers suggested ionic
conduction models due to a surface interaction at ionic conductor
following mechanisms such as space charge model [25–27],
defect-induced order–disorder phase transition (or defect-induced
sublattice melting) [28–30] and formation of a structurally dis-
ordered phase [31,32]. The defect-induced order–disorder phase
transition model was proposed by Ishii and Kawamura [28]. The
model is based on the ion-hopping conduction of an ionic
conductor. The defects existing in the interface region induced
an order–disorder phase transition for the ionic transfer that leads
to the enhancement of the ionic conductivity. The order–disorder
phase transition is influenced by the defects to enhance the ionic
Fig.
6
shows
a
complex plane (Nyquist diagram) of
CDP(F-68:CTAB)0.06. Throughout the entire frequency range at 210 1C,
two depressed semicircles were obtained due to grain boundary
response in the first high frequency semicircle and the second low-
frequency semicircle was assigned to the response of electrode
process. The second depressed semicircle was reformed to spike
(nearly 451 to the real axis) at 230 1C. At temperature above phase
transition, the spike corresponding to the process of electrode
polarization was turned to a semicircle. The impedance spectra
can be modeled with the equivalent circuit including combination of
two R7C (parallel) circuits. It is noticeable that the different
behaviors of impedance were resulted in three samples. On the
other hand, the synthesized samples using surfactants CTAB or
(F-68:CTAB)0.06 showed more conductivity in compared to the
synthesized sample using F-68. In the three samples, well agree-
ment was found between theoretical and experimental results for
the whole frequency range with an average error of 4%.
The resistance and capacitance of the bulk and grain boundary
could be different and depend on the sample preparation condi-
tion. The grain boundary resistance depends on bulk conductivity
due to detour around grain boundaries [22–24]. For all the
samples, the resistance of grain boundary is more than the
bulk resistance. It may be concluded that the grain boundaries
was affected mainly due to the surfactants with the different
templating. The significant differences were noticed in the Nyquist
plots of three samples. The CDPCTAB response shows three arcs
response whereas two arcs responses were observed for the
samples CDPF-68 and CDP(F-68:CTAB)0.06, and polarization effects of
conductivity below the superionic phase transition. In CDPCTAB
,
CDP and CDPF-68 samples, the conductivity is influ-
(F-68:CTAB)0.06
enced by dominance of interfacial phenomena. Indeed, the proton
diffusion and dc conductivity depend strongly on parameters such
as grains, porosity, individual phase, particle size and morphology.
The Arrhenius plots of conductivity for the three samples were
shown in Fig. 7. The Arrhenius plots of conductivity shows a
different linear trend with large deviations at temperatures above

1694
S. Hosseini et al. / Physica B 406 (2011) 1689–1694
without CTAB showed more conductivity on the particles using
CTAB [35]. The surfactant CTAB can be considered as the increasing
proton mobility between particles.
0
-1
-2
-3
-4
-5
-6
-7
CDP (F-68:CTAB)0.06
CDP (F-68)
CDP (CTAB)
260
260
230
230
4. Conclusion
The impedance spectra indicate the charge-transfer controlled
processes in the high frequency range and diffusion-controlled
processes in the low-frequency region. While the charge-transfer
behavior was characterized by a semicircle, the diffusion behavior is
typified by a linear spike in the complex plane impedance diagrams
at phase transition temperature. The protonic conductivity show
the sequential as CDPCTAB4CDP(F-68:CTAB)0.064CTABF-68 and the
210
180
180
150
150
210
values 1.89 ꢁ 10ꢀ2, 2.83ꢁ 10ꢀ2 and 3.04 ꢁ 10ꢀ3
O
cmꢀ1 at tem-
perature 230 1C. Ion exchange capacity indicated the values from
1.09, 0.89 and 0.75 mmol gꢀ1 for this sequential, respectively. CTAB
as a cationic surfactant enhances proton mobility of the particles.
1.8
1.9
2
2.1
1000/T (K)
2.2
2.3
2.4
Acknowledgments
Fig. 7. Temperature dependencies of the conductivity for three samples.
The authors will appreciate the financial support of the IRPA-02-
02-02-0006 PR0023/11-08. This work was conducted at the Institute
of Fuel Cell University Kebangsaan Malaysia, Selangor, Malaysia.
phase transition. It was observed that the conductivity increased
with the increasing two to three orders of magnitude at tempera-
ture 230 1C in all samples.
The different synthetic methods or conditions may produce
the same material with different morphologies (relative density,
particle size) consequently changing electrical properties. The sample
CDPCTAB demonstrated a higher conductivity in the whole tempera-
ture range under investigation and showed a much better perfor-
mance beyond 210 1C. This clearly shows a significant considerable
influence of surface morphology particles on conductivity due to
cationic surfactant. For samples CDPF-68 and CDP(F-68:CTAB)0.06, con-
ductivity undergoes a sharp decrease above 230 1C from 2.8ꢁ 10ꢀ3
to 3.5 ꢁ 10ꢀ3 S cmꢀ1 due to the dehydration process.
References
[1] K.D. Kreuer, Chem. Mater. 8 (1996) 610.
[2] K.D. Kreuer, Solid State Ion. 97 (1997) 1.
[3] K.D. Kreuer, Solid State Ion. 136 (2000) 149.
[4] J. Otomo, N. Minagawa, C. Wen, K. Eguchi, H. Takahashi, Solid State Ion. 156
(2003) 357.
[5] D.A. Boysen, S.M. Hiale, H. Liu, R.A. Secco, Chem. Mater. 15 (2003) 727.
[6] W. Bronowska, J. Chem. Phys. 114 (2001) 611.
[7] A.I. Baranov, V.P. Khiznichenko, L.A. Shuvalov, Ferroelectrics 100 (1989) 135.
[8] J.D. Kim, T.M., T.K., I.H., Solid State Ion. 179 (2008) 1178.
[9] S.M. Haile, C. Chisholm, K. Sasaki, D.A. Boysen, T. Uda, Faraday Discuss. 134
(2007) 17.
[10] A.I. Baranov, V.P. Khiznichenko, V.A. Sandler, L.A. Shuvalov, Ferroelectrics
81 (1988) 183.
[11] J.H. Park, Phys. Rev. B 69 (2004) 054104.
[12] Y.K. Taninouchi, T. Uda, Y. Awakura, Solid State Ion. 178 (2008) 1648.
[13] D.F. Evans, D.J. Mitchell, B.W. Ninham, J. Phys. Chem. 90 (1986) 2817.
[14] P.S. Goyal, V.K. Aswal, J. Kohlbrecher, P. Bahadur, Chem. Phys. Lett. 349
(2001) 458.
[15] S. Hosseini, A.B. Mohamad, A.H. Kadhum, W.R.Wan Daud, J. Therm. Anal.
Calorim. 99 (2010) 197.
[16] L.N. Rashkovich, KDP-Family Single Crystals, IOP Publishing, 1991, p. 202.
[17 ] H. Matsunaga, K. Itoh, E. Nakamura, J. Phys. Soc. Jpn. 48 (1980) 2011.
[18] S.B. Yoon, J.Y. Kim, J.H. Kim, Y.J. Park, K.R. Yoon, S.K. Park, J.S. Yu, J. Mater.
Chem. 17 (2007) 1758.
[19] W.H. Mulder, J.H. Sluyters, T. Pajkossy, I. Nyikos, J. Electroanal. Chem. 285
(1990) 103.
The decreased conductivity at high temperature was attribu-
ted to the decomposition of CsH2PO4 to CsH2P2O7 and CsPO3.
Nevertheless, conductivity of hybrids was greatly improved
although a decrease was also observed at higher temperature.
Therefore, it can be realized that type surfactant may play a vital
role in the conduction of protons and can significantly improve
the conductivity at high temperatures.
Proton conductivities of the particles are consistent with their
ion exchange capacity (IEC) values that are well represented by
Arrhenius equation. All measurements were performed by titrat-
ing the number of available exchange sites to proton at room
temperature. The IEC value of samples and their density are listed
in Table 2. Since the linear relationship between proton conduc-
tivity and IEC value was observed by [33,34]
[20] T. Jacobsen, K. West, Electrochim. Acta 40 (1995) 255.
[21] A.M. Fekry, Electrochim. Acta 54 (2009) 3480.
[22] U. Retter, A. Widmann, K. Siegler, H. Kahlert, J. Electroanal. Chem. 546 (2003)
87.
s
¼ Znem
ð3Þ
[23] J. Fleig, Solid State Ion. 131 (2000) 117.
Conductivity (s) is represented as the product of the carrier
[24] J. Fleig, J. Maier., J. Am. Ceram. Soc. 82 (1999) 3485.
[25] J. Maier, J. Phys. Chem. Solids 46 (3) (1985) 309.
[26] S. Jiang, J.B. Wagner Jr., J. Phys. Chem. Solids 56 (8) (1995) 1101.
[27] T. Jow, J.B. Wagner Jr., J. Electrochem. Soc. 126 (1979) 1963.
[28] T. Ishii, J. Kawamura, J. Phys. Soc. Jpn. 67 (10) (1998) 3517.
[29] N. Hainovsky, J. Maier, Solid State Ion. 76 (1995) 199.
[30] N. Hainovsky, J. Maier, Phys. Rev. B 51 (22) (1995) 15789.
[31] N.F. Uvarov, P. Vanek, J. Mater. Synth. Process 8 (5–6) (2000) 319.
[32] N.F. Uvarov, B.B. Bokhonov, A.A. Politov, P. Vanek, J. Petzelt, J. Mater. Synth.
Process 5–6 (2000) 327.
[33] Y. Iwai, T. Yamanishi, K. Isobe, M. Nishi, T. Yagi, M. Tamadab, Fusion Eng. Des.
81 (2006) 815.
[34] Ch. Zhao, H. Lin, K. Shao, X. Li, H. Ni, Z. Wang, J. Power Sour. 162 (2006) 1003.
[35] Y. Daiko, K. Katagiri, K. Ogura, M. Sakai, A. Matsuda, Solid State Ion. 178
(2007) 601.
number (n) and mobility (m) of charge carriers per unit volume, Z is
the valence (Z¼1 for proton) and e is the electrical charge.
Conductivities can be plotted as a function of the product of n and
e and the mobility is directly equal to the slope (Eq. (3)). Further-
more, the IEC values for CDPCTAB, CDP(F-68+CTAB)0.06 and CDPF-68 were
found to be 1.09, 0.89 and 0.75 mmol gꢀ1, respectively. As seen, The
IEC values declined by decreasing the conductivities. The IEC values
suggested that the amount of CTAB increased the proton conductiv-
ity. The resulted impedance shows the sequence of conductivity
CDPCTAB4CDP(F-68+CTAB)0.064CDPF-68. A comparison of proton con-
ductivity between the PhSiO3/2–MeSiO3/2 particles using CTAB and