1

Enhanced Ionic Conductivity of Scandia-Ceria-Stabilized-Zirconia (10Sc1CeSZ)

Electrolyte Synthesized by the Microwave-assisted Glycine Nitrate Process

Abdul Azim Jais1, Muhammed Ali S.A.1, Mustafa Anwar1,2, Mahendra Rao Somalu1,*,

Andanastuti Muchtar1,3, Wan Nor Roslam Wan Isahak3, Chou Yong Tan4, Ramesh

Singh4, Nigel P. Brandon5

1 Fuel Cell Institute, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor,

Malaysia.

2U.S-Pakistan Center for Advanced Studies in Energy, National University of Sciences

and Technology, Pakistan

3Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia,

43600 UKM Bangi, Malaysia

4Centre of Advanced Manufacturing & Material Processing (AMMP), Department of

Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala

Lumpur, Malaysia

5Department of Earth Science and Engineering, Imperial College London, South

Kensington Campus, London, SW7 2AZ, UK

*Corresponding author:

Email: mahen@ukm.edu.my

Tel: +603-89118522 and Fax: +603-89118530

Address: Fuel Cell Institute

Universiti Kebangsaan Malaysia,

43600 UKM Bangi, Selangor, Malaysia

1

2

Abstract

Scandia-stabilized-zirconia is a potential zirconia-based electrolyte for intermediate

temperature solid oxide fuel cells (IT-SOFCs). In this study, the properties of zirconia

co-doped with 10 mol% Sc and 1 mol% Ce (scandia-ceria-stabilized-zirconia,

10Sc1CeSZ) electrolyte synthesized by the microwave-assisted glycine nitrate process

(MW-GNP) were determined. The effects of microwave heating on the sintering

temperature, microstructure, densification and ionic conductivity of the 10Sc1CeSZ

electrolyte were evaluated. The phase identification, microstructure and specific surface

area of the prepared powder were investigated using X-ray diffraction, transmission

electron microscopy and the Brunauer-Emmett-Teller technique, respectively. Using

microwave heating, a single cubic-phase powder was produced with nanosized

crystallites (19.2 nm) and a high specific surface area (16 m2/g). It was found that the

relative density, porosity and total ionic conductivity of the 10Sc1CeSZ electrolyte are

remarkably influenced by the powder processing method and the sintering temperature.

The pellet sintered at 1400 °C exhibited a maximum ionic conductivity of 0.184 S/cm

at 800 °C. This is the highest conductivity value of a scandia-stabilized-zirconia based

electrolyte reported in the literature for this electrolyte type. The corresponding value

of the activation energy of electrical conductivity was found to be 0.94 eV in the

temperature range of 500-800 °C. Overall, the use of microwave heating has

successfully improved the properties of the 10Sc1CeSZ electrolyte for application in an

IT-SOFC.

Keywords: A. Microwave processing; A. Sintering; C. Ionic conductivity; E. Fuel cells

2

3

1. Introduction

Solid oxide fuel cells (SOFC) usually operate at very high temperatures ranging from

800 to 1000 °C [1]. Reduction of the operating temperature can be achieved by

developing new materials and adopting thin film techniques [2]. High ionic

conductivity, low thermal expansion, negligible electronic conduction and good

mechanical properties are the important factors to be considered in selecting the

electrolyte for intermediate temperature SOFCs (IT-SOFCs) [3]. Stabilized zirconia

such as yttria-stabilized-zirconia (YSZ) has been considered the most promising solid

electrolyte material for SOFC due to its high phase stability, high ionic conductivity and

low electronic conductivity in both the oxidizing and reducing environment of an SOFC

[4]. However, YSZ exhibits poor ionic conductivity at lower operating temperatures (<

700 °C). Therefore, wide attention has been focused on improving the ionic

conductivity of the YSZ electrolyte [5]. One approach is the use of scandium oxide

(Sc2O3) to stabilize ZrO2 to improve the conductivity at lower operating temperatures

[6,7]. The cubic fluorite-type phase of scandia-stabilized-zirconia (ScSZ) has been

reported to be an excellent electrolyte material for IT-SOFC. However, ScSZ exhibits a

phase transition from the highly conductive cubic phase to a low conductive

rhombohedral or tetragonal phase at the IT-SOFC operating condition [8]. In previous

studies, Al2O3 and the oxides of rare earth elements such as CeO2, Sm2O3, Yb2O3, and

Gd2O3 were used as dopants to mitigate the undesirable phase transition [9–12]. Several

authors have reported that the phase transition of ScSZ can be prevented by doping

ZrO2 with Sc2O3 and CeO2 [13,14]. According to previous reports, the 10 mol%Sc2O3–1

mol%CeO2–89 mol% ZrO2 composition (10Sc1CeSZ) enables the retention of the

3

4

highly conductive cubic phase at the IT-SOFC operating temperature [15,16].

The performance of the 10Sc1CeSZ electrolyte can be improved by optimizing

the powder characteristics, especially by adopting a suitable preparation technique.

Powder properties such as particle size, surface area and purity are influenced by

synthesis or preparation methods [17]. Thus, several powder synthesis methods have

been applied for the synthesis of 10Sc1CeSZ electrolyte materials, such as the glycine-

nitrate process [6,14], solid-state reaction [18], co-precipitation [19–21], the sol-gel

method [21,22], the modified Pechini method [23] and the solid-liquid method [24].

Each method has its own respective advantages and disadvantages. Every method

influences the final ionic conductivity depending on the powder properties and level of

impurities. Solution combustion synthesis is an effective and rapid method to produce

nanosized ceramic oxide powders at low calcination temperatures. This process

involves a self-sustained combustion of a homogenous solution containing metal

nitrates and fuels (urea, glycine, sucrose). The reaction temperature and reaction rate are

the important parameters that govern phase formation during combustion synthesis.

Microwave heating is a mature technique that has been widely used to replace the

conventional heating technique in combustion synthesis methods to produce nanosized

oxide powders within a shorter time [25–28]. Microwave energy generally provides

uniform heating and promotes faster reaction kinetics, which consequently increases the

reaction rate and homogeneity of the final product. In conventional heating, the heat is

slowly transferred through the walls of the vessel to the reactants. This is a relatively

slow and inefficient method for transferring energy into the reacting system. Owing to

its advantages, in recent years, researchers have employed the microwave heating

4

5

technique to produce materials for SOFC applications [25,29,30]. However, the solution

combustion synthesis of the 10Sc1CeSZ electrolyte using microwave heating has not

been previously reported, with the exception of a recent study that used the microwave-

assisted hydrothermal method [28] to synthesize the identical composition.

Based on these advantages, the present study aimed to investigate the effect of

the microwave-assisted glycine nitrate process (MW-GNP) on the phase formation,

microstructure, surface area and ionic conductivity of 10Sc1CeSZ. This study also

aimed to evaluate the influence of the sintering temperature on the microstructure,

density and electrochemical properties of 10Sc1CeSZ electrolytes. The grain size of the

pellets sintered at various temperatures ranging from 1300 °C to 1500 °C was observed

by field-emission scanning electron microscopy (FESEM). Electrochemical impedance

spectroscopy (EIS) was also applied to investigate the ionic conductivity of the

electrolytes from 400 °C to 800 °C.

2. Experimental Procedure

2.1 Synthesis of Materials

Zirconia co-doped with 10 mol% Sc and 1 mol% Ce (scandia-ceria-stabilized-zirconia,

10Sc1CeSZ) electrolyte was synthesized by the microwave-assisted glycine nitrate

process (MW-GNP). For the synthesis of 10Sc1CeSZ powder, the starting materials

were scandium oxide (Sc2O3, Aldrich), nitric acid (HNO3. Friendemann Schmidt),

zirconium (IV) oxynitrate hydrate (ZrO(NO3)2∙H2O, Acros Organics), cerium(III) nitrate

hexahydrate (Ce(NO3)3∙6H2O, Aldrich) and glycine (C2H5NO2, Genemark). The

5

6

stoichiometric amount of scandium oxide was first dissolved in a hot nitric acid solution

under stirring on the hot plate to form a clear solution of scandium nitrate. The

stoichiometric amount of zirconium (IV) oxynitrate hydrate and cerium (III) nitrate

hexahydrate were then dissolved in deionized water and mixed with the prepared

scandium nitrate solution. After that, glycine as a fuel was added to the resulting

solution with a glycine to nitrate ratio of 1:2. The solution was continuously stirred until

the solution become viscous. The viscous solution was introduced to the microwave

with a power of 80 %, and self-combustion occurred in the microwave oven (SHARP,

2450 MHz, 900 W). Finally, the ash was calcined at 700 °C for 2 h to obtain

10Sc1CeSZ oxide powder with the desired composition.

2.2 Powder and electrochemical characterization

The prepared 10Sc1CeSZ electrolyte powder was physically characterized. The thermal

decomposition behaviour of the uncalcined 10Sc1CeSZ was investigated via

thermogravimetry (PerkinElmer, STA 6000, USA) by ramping the sample from 30 °C

to 1000 °C with a heating rate of 10 °C/min. The phase characterization, theoretical

density, and crystallite size of the prepared powder were determined by X-ray

diffraction (XRD) using an X-ray diffractometer (Shimadzu XRD-6000, D8-Advance,

Bruker, Germany) with CuKα (λ = 0.15418 nm) radiation and 2θ ranging from 20° to

90°. Energy-dispersive spectroscopy (EDS) was conducted to determine the elemental

composition of the powders. The microstructure and particle size of the prepared

powders were also observed through transmission electron microscopy (TEM; Philips

CM12, OR, USA) at 80 kV. The specific surface areas of the calcined powders were

6

7

measured with a surface area analyser (Micromeritics, ASAP 2020, Georgia, USA) by

applying the Brunauer–Emmett–Teller technique with nitrogen gas as the adsorbate.

The 10Sc1CeSZ powder was then cold-pressed at 48 MPa into cylindrical

pellets with a 25 mm diameter and 1.3 mm thickness using a uniaxial die-press. The as-

prepared pellets were then sintered at 1300 °C, 1400 °C or 1500 °C for 5 h in air. Field

emission scanning electron microscopy (FESEM) (Zeiss Supra-55VP) was performed to

examine the microstructure, particle size, shape, and morphology of the sintered pellets.

The density of a pellet was determined by the Archimedes method using deionized

water at room temperature. The conductivities of the sintered pellets were measured

from 500 °C to 800 °C using impedance spectroscopy. Silver paste was applied to both

sides of the sintered samples and heated at 800 °C for 1 h. The effective working area of

the pellet was 1 cm2. The silver electrode area and thickness of the pellet were used to

determine the final conductivity. The measurement was conducted at 50 °C intervals

with a flow of compressed air at 100 ml/min. The test was performed in potentiostatic

mode using an Autolab PGSTAT302N coupled with a frequency response analyser

(Autolab 302, Eco Chemie, Netherlands) over the frequency range from 106 Hz to

0.1 Hz under a low-amplitude sinusoidal voltage of 10 mV. Data acquired from the

impedance testing were analysed using NOVA software (Version 1.11). AC-impedance

diagrams were plotted in Z’ (real) versus Z” (imaginary) to measure the conductivity of

the pellets sintered at different temperatures.

7

8

3. Result and Discussion

3.1 Thermogravimetry Analysis

TGA data for the 10Sc1CeSZ synthesized by the microwave-assisted glycine nitrate

process (MW-GNP) is presented in Fig. 1. The TGA was conducted to examine the

thermal behaviour of the 10Sc1CeSZ powder. Three stages of significant small weight

loss at temperatures of ~200 °C, 200-300 °C and 600 °C were observed. The first stage

of weight loss in the TGA occurred below 200 °C, indicating the desorption of water or

evaporation of moisture from the powder. The second stage of weight loss occurred in

the temperature range of 200 °C to 300 °C. This weight loss could be associated with

the decomposition of metal nitrates and unreacted glycine, where the decomposition of

glycine normally occurs at a temperature of approximately 240 °C [31]. The third stage

of weight loss occurred at 600 °C, demonstrating the decomposition of carbonaceous

residues and formation of the final product, 10Sc1CeSZ electrolyte powder.

Based on the TGA data, the microwave-assisted glycine nitrate process

produced high yields, as the thermal weight loss percentage was very small at only 4%.

The sol-gel synthesis method of ScSZ exhibited a higher weight loss percentage in the

TGA analysis, in the range of 23-60% [21,32]. Similarly, the precipitation method

produced a weight loss as high as 50% in the TGA analysis [21]. In addition, the weight

losses of 10Sc1CeSZ precursor powder synthesized using a polymeric precursor and the

modified Pechini method were approximately 50% and 80%, respectively, when the

precursors were analysed in the TGA [13,23]. Hence, the sample prepared using the

microwave-assisted glycine nitrate process exhibited significantly less weight loss

8

9

compared to those synthesized by conventional methods, which is probably due to the

formation of less organic substances during the combustion process assisted by

microwave energy.

Fig. 1. TGA curve of the 10Sc1CeSZ powder synthesized by the microwave-

assisted glycine nitrate process

3.2 XRD Analysis

The phase of 10Sc1CeSZ powder synthesized by the microwave-assisted glycine nitrate

process was determined from the XRD pattern. Figure 2 shows the phase analysis data

of the 10Sc1CeSZ powder calcined at 700 °C. The 10Sc1CeSZ powder consisted of a

single phase with the cubic fluorite structure with a space group of Fm-3m. The

reference file for Zr0.82Sc0.18O1.91 (01-089-5483) was used for this verification. No other

phases were observed other than the cubic phase of 10Sc1CeSZ in the XRD pattern

taken at room temperature. The same observation was also reported in other studies

[15,16]. This suggests that in this study, a calcination temperature of 700 °C is sufficient

to obtain a highly crystalline and pure 10Sc1CeSZ electrolyte powder, as confirmed

from the TGA and XRD results.

For the cubic structure, the lattice parameter can be calculated using the

following equation:

a =d×√h2+ k2+ l2 (1)

9

10

whered= λ/2 sin θ , a is the lattice parameter, d is the plane-spacing for a given Miller

index (hkl), λ is the wavelength of X-ray used (0.154 nm), and θ is the Bragg diffraction

angle. The lattice parameter of 10Sc1CeSZ is 5.1089 Å and is in good agreement with

other reported values [6,15]. The crystallite size calculated from the (111) reflection was

found to be approximately 19.2 nm. This crystallite size was determined by the Debye-

Scherrer formula, as shown in Eq. 2:

D=0.9λ/β cos θ

(2)

where D is the crystallite size, λ is the wavelength of the X-ray radiation, β is the full

width at half maximum of intensity of the diffraction peak, and θ is the Bragg

diffraction angle of (111) peak. This result is also consistent with the crystallite size of

10Sc1CeSZ powder synthesized by the microwave-assisted hydrothermal method,

which was determined to be in the range of 10-30 nm [28]. The calculated theoretical

density (ρthd) of the prepared powder was found to be 5.89 g/cm3. This theoretical

density will be used to determine the relative density of the sintered electrolyte pellets.

Fig. 2. XRD pattern of 10Sc1CeSZ powder calcined at 700 °C

3.3 Microstructural Characterization of Powders

The TEM image of 10Sc1CeSZ powder calcined at 700 °C is shown in Fig. 3(a). It was

observed that the particles were strongly agglomerated and that the size of the particles

was approximately 20 nm. A similar particle size range was also reported for

10

11

10Sc1CeSZ powder prepared by the Pechini method and the microwave-assisted

hydrothermal method [13,28]. The observed particle size is consistent with the XRD

analysis results. The TEM analysis clearly indicated that in the agglomerates, the

particles were well-bonded together and exhibited neck formation at the contact points

[33]. These stronger agglomerated powders were ball-milled to form a fine nanosized

powder with a high specific surface area (16 m2/g). The surface area of the 10Sc1CeSZ

powders obtained in the present study was higher than that of commercially available

10Sc1CeSZ powders [34]. However, this surface area is considerably smaller than the

surface area of the powder synthesized by the microwave-assisted hydrothermal method

(120-190 m2/g) [28] because the powder synthesized by the latter method was washed

with distilled water and dried in a vacuum oven at 85 °C for 10 h rather than directly

calcined as in this study. The direct calcination at 700 °C led to particle agglomeration

and subsequently reduced the surface area of the synthesized powder. Fig. 3(b)

illustrates the EDS spectra of the 10Sc1CeSZ powder and the presence of Sc, Ce, Zr and

O peaks. Residual carbon and other impurities were not observed in the calcined

powder. This result indicated that the calcination temperature is sufficient to produce a

pure, single cubic phase 10Sc1CeSZ powder.

Fig. 3. (a) TEM Image and (b) Energy dispersive spectra of 10Sc1CeSZ powder

3.4 Electrochemical analysis

The effect of sintering temperature on the ionic conductivity of the 10Sc1CeSZ

electrolyte was evaluated by electrochemical impedance spectroscopy (EIS) using

Ag/10Sc1CeSZ/Ag symmetrical cells. Figs. 4 and 5 show typical Nyquist plots of the

11

12

electrolyte cells measured at 400 °C and 600 °C, respectively. The plot for each

operating temperatures was fit to the equivalent circuit of (Rb)(RgbCPEgb)(ReCPEe), in

which R represents the resistance and CPE corresponds to the constant phase element.

The high frequency arc relates to the grain bulk resistance represented by Rb in the

equivalent circuit model. The medium frequency arc relates to the grain boundary

resistance (Rgb) and a CPEgb in the equivalent circuit model. The low frequency regime

demonstrates the electrode resistance (Re) and a CPEe. As shown in Fig. 4, two different

arcs can be clearly distinguished in the investigated frequency range representing Rgb

and Re for all of the sintered pellets. However, at high operating temperatures, the arc

corresponding to the contribution of Rgb disappears, as shown in Fig. 5 for the pellet at

600 °C. As the operating temperature increases from 400 °C to 600 °C, the relaxation

frequency of the grain-boundary conduction process increases and the arcs shift towards

the low frequency region. Therefore, not all arcs are observed at all operating

temperatures, with only one semi-circle appearing at 600 °C (Fig. 5), which represents

the electrode resistance. The total resistance of the electrolyte is given by Eq. 3:

Fig. 4. EIS plot measured at 400 °C for the 10Sc1CeSZ electrolyte pellets sintered

at different temperatures

Fig. 5. EIS plot measured at 600 °C for the 10Sc1CeSZ electrolyte pellets sintered

at different temperatures

R t = R b + Rgb (3)

12

13

At 600 °C and above, the combined sum of Rb and Rgb was determined by the

high frequency intercepts on the real axis. Figs. 4 and 5 show that the electrolyte pellet

sintered at 1400 °C exhibited a lower resistance ( Rb + Rgb ¿ than the pellets sintered at

1300 °C and 1500 °C. Rb and Rgb values were used to determine the total ionic

conductivity of the pellets sintered at different temperatures. The ionic conductivity (σ)

for each sample was calculated using the following equation:

σ= 1 /(R b+ Rgb ) × Lp/Ap (4)

where Lp and Ap represent the thickness and the cross-sectional area of the pellet,

respectively. Arrhenius’ law was used to represent the relation between the conductivity

and temperature (Fig. 6), and the activation energies were calculated from the slopes of

the Arrhenius plot. The Arrhenius relationship is given by the following equation:

σT=A exp( -Ea /kT ) (5)

where A is the pre-exponential factor, Ea represents the activation energy (eV), k

is the Boltzmann’s constant (8.617 х 10-5 eV/K), and T is the absolute temperature (K).

Fig. 6. The ionic conductivity of the 10Sc1CeSZ electrolyte sintered at various

temperatures

The Arrhenius plot (Fig. 6) shows that for all sintering temperatures, the ionic

conductivity increases with rising temperature and that the pellet sintered at 1400 °C

13

14

exhibits the highest values of ionic conductivity, followed by the pellets sintered at

1500 °C and 1300 °C for 5 h, respectively. The highest conductivity shown by the pellet

sintered at 1400 °C for 5 h was due to its microstructure and improved density. The

cross-sectional images of the pellets sintered at different temperatures are shown in Fig.

7. The figure clearly shows that the porosity of the pellets decreases with the increase in

sintering temperature from 1300 °C to 1400 °C. However, the pore size in the pellets

sintered at 1500 °C appeared to be larger than the pore sizes of the pellets sintered at

lower temperatures. The grain size of the electrolyte pellets consistently increases with

the sintering temperature. The results were further verified by measuring the relative

densities of the sintered pellets. The relative densities were found to be 80%, 90% and

88% for the pellets sintered at 1300 °C, 1400 °C and 1500 °C, respectively. These

values are comparable with the values reported in the literature [35]. The sample

sintered at 1500 °C was over-sintered, which resulted in increased porosity and non-

uniform grain growth. This is probably the reason for the lower ionic conductivity of the

pellet sintered at 1500 °C compared to that of the pellet sintered at 1400 °C. Based on

this study, the optimum sintering temperature for the 10Sc1CeSZ pellet was 1400 °C for

maximum conductivity. In future work, the current-voltage (I-V) characterization of Ni-

10Sc1CeSC/10Sc1CeSZ/LSCF cells will be evaluated as a function of temperature for

both hydrogen and methane fuels.

Fig. 7. Cross-sectional views of pellets sintered at (a) 1300 °C, (b) 1400 °C, and (c)

1500 °C for 5 h

14

15

In this study, the highest ionic conductivity obtained at 800 °C was 0.184 S/cm

for the 10Sc1CeSZ electrolyte sintered at 1400 °C for 5 h. This conductivity is higher

than the conductivities of 10Sc1CeSZ electrolytes prepared by any other method,

including the microwave-assisted hydrothermal method, as listed in Table 1. This fact

strongly suggests that the efficiency of microwave energy in assisting the glycine nitrate

process for the preparation of the 10Sc1CeSZ electrolyte improved the electrolyte

properties. Therefore, it can be said that the microwave-assisted GNP is a facile route to

synthesize electrode or electrolyte materials for SOFC applications.

Table 1. Comparison of the conductivity and activation energy of the 10Sc1CeSZ

electrolyte prepared by various methods

4. Conclusion

Zirconia stabilized with 10 mol% scandia and 1 mol% ceria (10Sc1CeSZ) has been

successfully prepared using the microwave-assisted glycine nitrate process. Very fine

nanosized powders with a particle size and surface area of 20 nm and 16 m2/g,

respectively, were obtained in this study. The obtained powders were single cubic phase

with a small crystallite size (19.2 nm). The optimum sintering temperature of 1400 °C

was highlighted for the 10Sc1CeSZ electrolyte pellets due to the higher ionic

conductivity, lower activation energy and higher relative density compared with those

sintered at 1300 °C and 1400 °C. A maximum value of the ionic conductivity of 0.184

S/cm at 800 °C was obtained for pellets sintered at 1400 °C, and this value is higher

than any other reported values for this type of electrolyte. The results indicated that

15

16

powder preparation via the glycine nitrate process assisted by microwave heating

greatly influenced the densification, microstructure and ionic conductivity of the

electrolyte.

5. Acknowledgement

The authors gratefully acknowledge the financial support given by the Universiti

Kebangsaan Malaysia (UKM) and the Ministry of Education Malaysia via the research

sponsorships of DIP-2016-005 and FRGS/2/2013/TK06/UKM/02/9. The authors also

would like to thank the Center for Research and Instrumentation Management (CRIM)

for excellent testing equipment.

References

[1] S. (Rob) Hui, J. Roller, S. Yick, X. Zhang, C. Decès-Petit, Y. Xie, R. Maric, D.

Ghosh, A brief review of the ionic conductivity enhancement for selected oxide

electrolytes, J. Power Sources. 172 (2007) 493–502.

[2] T. Ishihara, J. Tabuchi, S. Ishikawa, J. Yan, M. Enoki, H. Matsumoto, Recent

progress in LaGaO3 based solid electrolyte for intermediate temperature SOFCs,

Solid State Ionics. 177 (2006) 1949–1953.

[3] N. Jaiswal, S. Upadhyay, D. Kumar, O. Parkash, Ionic conductivity investigation

in lanthanum (La) and strontium (Sr) co-doped ceria system 41953, J. Power

Sources. 222 (2013) 230–236.

[4] S.A. Muhammed Ali, R.E. Rosli, A. Muchtar, A.B. Sulong, M.R. Somalu, E.H.

16

17

Majlan, Effect of sintering temperature on surface morphology and electrical

properties of samarium-doped ceria carbonate for solid oxide fuel cells, Ceram.

Int. 41 (2015) 1323–1332.

[5] V. Esposito, C. Gadea, J. Hjelm, D. Marani, Q. Hu, K. Agersted, S. Ramousse,

S.H. Jensen, Fabrication of thin yttria-stabilized-zirconia dense electrolyte layers

by inkjet printing for high performing solid oxide fuel cells, J. Power Sources.

273 (2015) 89–95.

[6] Z. Lei, Q. Zhu, S. Zhang, Nanocrystalline scandia-doped zirconia (ScSZ)

powders prepared by a glycine-nitrate solution combustion route, J. Eur. Ceram.

Soc. 26 (2006) 397–401.

[7] G.Y. Cho, Y.H. Lee, S.W. Hong, J. Bae, J. An, Y.B. Kim, S.W. Cha, High-

performance thin film solid oxide fuel cells with scandia-stabilized zirconia

(ScSZ) thin film electrolyte, 2015.

[8] S. Kazlauskas, A. Kežionis, E. Kazakevičius, A.F. Orliukas, Charge carrier

relaxation and phase transition in scandium stabilized zirconia ceramics,

Electrochim. Acta. 134 (2014) 176–181.

[9] C. Varanasi, C. Juneja, C. Chen, B. Kumar, Electrical conductivity enhancement

in heterogeneously doped scandia-stabilized zirconia, J. Power Sources. 147

(2005) 128–135.

[10] W. Preis, J. Waldhäusl, A. Egger, W. Sitte, E. De Carvalho, J.T.S. Irvine,

Electrical properties of bulk and grain boundaries of scandia-stabilized zirconia

co-doped with yttria and ceria, Solid State Ionics. 192 (2011) 148–152.

[11] C.X. Guo, J.X. Wang, C.R. He, W.G. Wang, Effect of alumina on the properties

of ceria and scandia co-doped zirconia for electrolyte-supported SOFC, Ceram.

17

18

Int. 39 (2013) 9575–9582.

[12] C.N. Shyam Kumar, R. Bauri, Enhancing the phase stability and ionic

conductivity of scandia stabilized zirconia by rare earth co-doping, J. Phys.

Chem. Solids. 75 (2014) 642–650.

[13] H. Tu, X. Liu, Q. Yu, Synthesis and characterization of scandia ceria stabilized

zirconia powders prepared by polymeric precursor method for integration into

anode-supported solid oxide fuel cells, J. Power Sources. 196 (2011) 3109–3113.

[14] H.P. Dasari, J.S. Ahn, K. Ahn, S.-Y. Park, J. Hong, H. Kim, K.J. Yoon, J.-W.

Son, H.-W. Lee, J.-H. Lee, Synthesis, sintering and conductivity behavior of

ceria-doped Scandia-stabilized zirconia, Solid State Ionics. 263 (2014) 103–109.

[15] M.R. Somalu, V. Yufit, D. Cumming, E. Lorente, N.P. Brandon, Fabrication and

characterization of Ni/ScSZ cermet anodes for IT-SOFCs, Int. J. Hydrogen

Energy. 36 (2011) 5557–5566.

[16] J. Tan, Y. Su, H. Tang, T. Hu, Q. Yu, R. Tursun, X. Zhang, Effect of calcined

parameters on microstructure and electrical conductivity of 10Sc1CeSZ, J. Alloys

Compd. 686 (2016) 394–398.

[17] R.A. Richardson, J.W. Cotton, R. Mark Ormerod, Influence of synthesis route on

the properties of doped lanthanum cobaltite and its performance as an

electrochemical reactor for the partial oxidation of natural gas., Dalton Trans.

(2004) 3110–3115.

[18] S. Omar, W. Bin Najib, W. Chen, N. Bonanos, Electrical Conductivity of 10 mol

% Sc2O3-1 mol% M2O3-ZrO2 Ceramics, J. Am. Ceram. Soc. 95 (2012) 1965–1972.

[19] M. Liu, C. He, J. Wang, W.G. Wang, Z. Wang, Materials for Intermediate-

Temperature Solid Oxide Fuel Cell, J. Alloys Compd. 502 (2010) 319–323.

18

19

[20] J. Grzonka, V. Vereshchak, O. Shevchenko, O. Vasylyev, K.J. Kurzydłowski,

Characterization of Sc2O3&CeO2-Stabilized ZrO2 Powders Via Co-Precipitation

or Hydrothermal Synthesis, Microsc. Microanal. 19 (2013) 29–32.

[21] J. Raharjo, S.A. Muhammed Ali, O.P. Arjasa, A. Bakri, Damisih, E.L. Dewi, A.

Muchtar, M.R. Somalu, Synthesis and characterization of uniform-sized cubic

ytterbium scandium co-doped zirconium oxide (1Yb10ScSZ) nanoparticles by

using basic amino acid as organic precursor, Int. J. Hydrogen Energy. (2016) 1–

10.

[22] H.A. Abbas, C. Argirusis, M. Kilo, H.D. Wiemhöfer, F.F. Hammad, Z.M.

Hanafi, Preparation and conductivity of ternary scandia-stabilised zirconia, Solid

State Ionics. 184 (2011) 6–9.

[23] M.R. Loghman-Estarki, M. Hajizadeh-Oghaz, H. Edris, R.S. Razavi,

Comparative studies on synthesis of nanocrystalline Sc2O3-Y2O3 doped zirconia

(SYDZ) and YSZ solid solution via modified and classic Pechini method,

CrystEngComm. 15 (2013) 5898–5909.

[24] M. Liu, C.R. He, W.G. Wang, J.X. Wang, Synthesis and characterization of

10Sc1CeSZ powders prepared by a solid-liquid method for electrolyte-supported

solid oxide fuel cells, Ceram. Int. 40 (2014) 5441–5446.

[25] S.P.S. Shaikh, M.R. Somalu, A. Muchtar, Nanostructured Cu-CGO anodes

fabricated using a microwave-assisted glycine–nitrate process, J. Phys. Chem.

Solids. 98 (2016) 91–99.

[26] A. Manikandan, L.J. Kennedy, M. Bououdina, J.J. Vijaya, Synthesis, optical and

magnetic properties of pure and Co-doped ZnFe2O4 nanoparticles by microwave

combustion method, J. Magn. Magn. Mater. 349 (2014) 249–258.

19

20

[27] L.C. Nehru, C. Sanjeeviraja, Rapid synthesis of nanocrystalline SnO2 by a

microwave-assisted combustion method, J. Adv. Ceram. 3 (2014) 171–176.

[28] H. Ao, X. Liu, H. Zhang, J. Zhou, X. Huang, Z. Feng, H. Xu, Preparation of

scandia stabilized zirconia powder using microwave-hydrothermal method, J.

Rare Earths. 33 (2015) 746–751.

[29] R.B. Nuernberg, M.R. Morelli, Synthesis of BSCF perovskites using a

microwave-assisted combustion method, Ceram. Int. 42 (2016) 4204–4211.

[30] H. Sun, Y. Zhang, H. Gong, Q. Li, Y. Bu, T. Li, Anode-supported SOFCs based

on Sm0.2Ce0.8O2-δ electrolyte thin-films fabricated by co-pressing using microwave

combustion synthesized powders, Ceram. Int. 42 (2016) 4285–4289.

[31] P. Seeharaj, P. Charoonsuk, P. Kim-Lohsoontorn, N. Vittayakorn, BaZr 0.3Ti 0.7O

3 Nanoparticles Synthesized by Glycine-Nitrate Autocombustion, Ferroelectrics.

456 (2013) 55–62.

[32] B.Ş. Vasile, E. Andronescu, D. Florea, Ghiţulică, Cristina, Structural

investigations of scandia - doped zirconia nanopowders obtained by sol-gel

method, UPB Sci. Bull. Ser. B. 72 (2010).

[33] R.K. Lenka, T. Mahata, P.K. Sinha, B.P. Sharma, Combustion synthesis, powder

characteristics, and shrinkage behavior of a gadolinia-ceria system, J. Am.

Ceram. Soc. 89 (2006) 3871–3873.

[34] R.L. Grosso, M. Bertolete, I.F. Machado, R. Muccillo, E.N.S. Muccillo, Ionic

conductivity and phase stability of spark plasma sintered scandia and ceria-

stabilized zirconia, Solid State Ionics. 230 (2013) 48–51.

[35] A. Kumar, A. Jaiswal, M. Sanbui, S. Omar, Scandia stabilized zirconia-ceria

solid electrolyte (xSc1CeSZ, 5<x<11) for IT-SOFCs: Structure and conductivity

20

21

studies, Scr. Mater. 121 (2016) 10–13.

[36] D. Lee, I. Lee, Y. Jeon, R. Song, Characterization of scandia stabilized zirconia

prepared by glycine nitrate process and its performance as the electrolyte for IT-

SOFC, Solid State Ionics. 176 (2005) 1021–1025.

21

22

List of Figures

Fig. 1. TGA curve of the 10Sc1CeSZ powder synthesized by the microwave-assisted

glycine nitrate process

Fig. 2. XRD pattern of 10Sc1CeSZ powder calcined at 700 °C

Fig. 3. (a) TEM Image and (b) Energy dispersive spectra of 10Sc1CeSZ powder

Fig. 4. EIS plot measured at 400 °C for the 10Sc1CeSZ electrolyte pellets sintered at

different temperatures

Fig. 5. EIS plot measured at 600 °C for the 10Sc1CeSZ electrolyte pellets sintered at

different temperatures

Fig. 6. The ionic conductivity of the 10Sc1CeSZ electrolyte sintered at various

temperatures

Fig. 7. Cross-sectional views of pellets sintered at (a) 1300 °C, (b) 1400 °C, and (c)

1500 °C for 5 h

List of Tables

Table 1. Comparison of the conductivity and activation energy of the 10Sc1CeSZ

electrolyte prepared by various methods

22

23

23

24

24

25

25

26

26

27

27

28

28

29

29

30

Table 1 Conductivity and activation energy of the 10Sc1CeSZ electrolyte prepared

by different preparation methods

MethodsSintering

condition

Conductivity σ,

(S/cm) at 800/600

°C

Activation

Energy (eV)Reference

Microwave 1400 °C/5h 0.184/0.0330.93

(500-800 °C)This study

Solid state reaction 1550 °C/6h -/0.0127 1.09 (600 °C) [12]

Co-precipitation 1580 °C/10h 0.040/- - [13]

Sol-gel with

ethylene glycol and

citric acid

1500 °C/5h -/0.01141.22

(400-650 °C)[14]

solid-liquid method 1500 °C /5h 0.14/- - [15]

Hydrothermal

method1400 °C /2h 0.131/-

1.01

(600-800 °C[21]

Commercial powder 1500 °C/6h -/0.0188 1.023 (600 °C) [24]

Glycine-nitrate

process1600 °C/6h 0.159/- - [25]

30