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Engineering, Technology & Applied Science Research Vol. 13, No. 4, 2022, 11432-11436 11432  
 

www.etasr.com Najim: Synthesis and Electrical Behavior of Sodium Doped Monoclinic SrSiO3 

 

Synthesis and Electrical Behavior of Sodium 
Doped Monoclinic SrSiO3 

 

Mohd Najim 

Department of Electrical and Electronic Engineering, College of Engineering, University of Jeddah, 
Saudi Arabia 
mngalib@uj.edu.sa (corresponding author) 

Received: 5 April 2023 | Revised: 11 June 2023 | Accepted: 26 June 2023 

Licensed under a CC-BY 4.0 license | Copyright (c) by the authors | DOI: https://doi.org/10.48084/etasr.5893 

ABSTRACT 

The operating temperature of solid oxide fuel cells, oxygen division membranes, and oxygen sensors is 

determined by oxide-ion electrolytes. There is a strong incentive to reduce the operating temperature in 

solid oxide fuel cells, from 800°C to 500°C. The use of low-cost Na+ instead of K+ as dopant in monoclinic 

SrSiO3 offers a wider solid solution range (0.1<x< 0.5) in Sr1-xNaxSiO3-δ and obtains an oxide ion 

conductivity of 10
-2

 Scm
-1

 at 600°C, reducing the temperature of a smooth transition to full impairment of 

mobile oxide ions. For electrochemical characterization, the flat surfaces of the pellets were pasted with 

silver (Ag) paste and then sintered at 1200°C for 24 hours. The production of the Na2Si2O5 phase was 

observed for most compositions due to thermal treatment. Crystallization of Na2Si2O5 from glass was 

obtained in single-step calcination at 850°C after synthesis in an acetone medium, resulting in the highest 

conductivity. Although double calcination reduced conductivity, it improved thermal stability. Due to its 

low activation energy and lack of crystallization of other silicates, this material showed maximum 

conductivity after long-standing maturity at 600°C. Ethanol was used in place of acetone for powder 

assimilation and double calcination was also performed. 

Keywords-solid oxide fuel cell; electrolyte; conductivity; activation energy, SrSiO3 

I. INTRODUCTION  

Electrochemical energy conversion devices, such as Solid 
Oxide Fuel Cells (SOFCs), have been extensively studied as a 
potential technology for a wide range of applications, including 
large-scale stationary and portable power generators for both 
civilian and military applications [1]. The Yttria Stabilized 
Zirconia (YSZ) electrolyte used in conventional SOFCs has a 
suitable power density but also has the strong drawback of 
operating at high temperatures (~1000°C) [2]. On the other 
hand, high operating temperatures cause complicated 
difficulties for materials, such as the choice of materials and 
their chemical and physical compatibility with the restrictions 
of cell components for interconnects and seals, resulting in high 
cell manufacturing costs [2]. In this sense, the discovery of 
alternative electrolytes that can provide adequate performance 
in the so-called in-between temperature range of 500-700°C is 
one of the most crucial concerns for the widespread 
commercialization of SOFCs [3-4]. Several materials have 
been studied for intermediate temperature SOFCs, including 
doped ceria represented as oxide-ion conductors and LaGaO3 
and proton conductors signified by doped BaCeO3 [4]. In 
addition to these oxides, doped strontium silicate with the 
general formula Sr1-xAxMO3-δ (A = Na, K and M=Si/Ge) has 
attracted a lot of attention for its highest oxygen ion 
conductivity [5-7]. The main reason for the conductivity in Sr1-
XNaxSiO3 is that Na doping in SrSiO3 forms oxygen vacancies 
through which oxygen ion flows [8-9]. As evidenced by NMR 

spectroscopy, due to the steric pause of large Sr2+ and Na+ ions, 
conductivity was related to the development of the oxygen 
opportunity without changing the composition of SrSiO3 [8]. 
Oxygen ions, which normally promote conduction, are not 
present in rare-earth oxyapatites. Several studies challenged 
these conclusions by highlighting the crucial role that glassy 
phases play in the Na2O-SiO2 system [6-9]. Specifically, 
conduction in Sr1-xNaXSiO3 (SNS) due to Na

+ ion movement in 
the amorphous phase was observed by solid-state NMR 
spectroscopy investigations [10-11], and X-Ray Diffraction 
(XRD) analysis revealed constrained doping of Na in SrSiO3 
[12-13]. Conductivity appeared to be significantly affected by 
the crystallization of Na2Si2O5 after some processing at 
approximately 650°C [12-13]. Some studies described how the 
amalgamation process and processing situations affect the 
structure and conducting qualities of alkali-doped SrSiO3 and 
SrGeO3 [14]. In large amounts, most of the materials 
investigated were made by a traditional solid-state method that 
involved mixing silica with acetone Na and Sr carbonates [12-
14]. Spark Plasma Sintered (SPS) powders generated using the 
solid-state method create single-phase materials with tiny 
grains and strong ionic conductivity [15]. This study 
demonstrated that processing, in particular precursor reaction 
conditions and thermal properties, must have a major impact on 
phase composition and, subsequently, electrical properties. So, 
this study used a solid-state reaction to create Sr1-xNaxSiO3 (x = 
0.0 and 0.45). 



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II. EXPERIMENTAL PART 

The solid-state reaction method approach was used to 
create powders of Sr1-xNaxSiO3 (x=0.0 and 0.45), indicated as 
SNS. Wet ball milling with zirconia balls combined 
stoichiometric quantities of Sr and Na carbonates and 
nanometric SiO2 in ceramic jars. To investigate the effects of 
solvent on Na inclusion and glassy phase development, three 
dissimilar dispersion media with growing polarity, acetone 
C3H6O, ethanol C2H6O, and distilled water H2O, were used. 
Slurries were stored at 4°C after 24 hours of milling to acquire 
the final reaction result, and then the dry particles were sieved 
and heated to high temperatures in the air. The final product 
was produced by:  

�1 � �����	
 �
�

 ��
�	
 � ��	
 →

                    ����� ��� ��	
��/
 � �1 �
�

� �	
 (1) 

The composition with the highest conductivity for only x = 
0.0 and x = 0.45 [2] was made with ethanol and water. 
Additionally, all compositions were "aged" in the air for 24 
hours at 1200°C to further confirm their stability and to permit 
the crystallization or devitrification of any glassy phase. The 
powders obtained were compacted into pellets for conductivity 
testing that were generally 0.2 cm thick and 1 cm in diameter. 
Powder XRD with a Philips X'pert diffractometer (Cu Kα-
radiation = 1.5418 Å) with Bragg Brentano reflection geometry 
seemed to verify its chemical phase purity. SEM was used to 
study the microstructures (shape and surfaces) of the powder 
and pellets at an accelerating voltage of 20 kV (JEOL, JSM-
5610). The composition and apparent regularity of the 
compounds were confirmed by Energy-Dispersive X-ray 
(EDX) spectroscopy using a probe connected to the SEM. The 
samples were heated at a rate of 2°C/min while subjected to 
Thermo-Gravimetric Analysis (TGA) in an air atmosphere 
(airflow: 20 cm3/min). Oxide ion conductivity was measured in 
an ambient atmosphere using a Solartron impedance analyzer 
(model 1287) with two probes at frequencies between 1 Hz and 
10 MHz and an AC amplitude of 10 mV. Two Pt-blocking 
electrodes were produced by coating Pt paste (from Heraeus) 
over the two faces of the pellets and firing them for an hour at 
800 °C. All measurements were taken at temperatures ranging 
from 300 to 800°C. To estimate the intercept to the real Z′ axis 
of a low-frequency semicircle, conductivity was calculated by 
extrapolating the difference between the source and the 
extrapolation of the intercept to the real Z′ axis. 

III. RESULTS AND DISCUSSION 

Figure 1 shows the XRD patterns of SrSiO3 and 
Sr0.55Na0.45SiO3 at ambient temperature. Both materials are 
monoclinic with a single-phase structure [16]. A high 
temperature (~1100C) is needed for the parent SrSiO3 to 
eliminate impurities such as Sr2SiO4 and SiO2 and produce the 
single phase. The presence of voids is indicated by the broad 
flat top at 2~ (12-17) for SrSiO3. However, for 
Sr0.55Na0.45SiO3, these flat tops become peaks. Peak splitting is 
observed for Sr0.55Na0.45SiO3 at higher 2>40, due to a 
disorder imposed on the parent SrSiO3 [16]. The disorder in Na 
doping into SrSiO3 may be due to stress and vacancy 
formation. In Sr0.55Na0.45SiO3, the monoclinic phase formation 

is controlled by both the SiO2 layers and the amorphous SiO2 
matrix, as opposed to SrSiO3 where only the SiO2 layers 
regulate the monoclinic phase growth [16]. EDX was used to 
examine the formulations of the Sr1-xAxSiO3-δ (A = Na). Figure 
2 shows SEM micrographs and Figure 3 shows the EDX 
profile of Sr0.55Na0.45SiO3-δ. 

 

 
Fig. 1.  XRD pattern of SrSiO3 (with structure) and Sr55Na0.45SiO3-δ. 

 
Fig. 2.  FE-SEM image of Sr0.55Na0.45SiO3−δ. 

 
Fig. 3.  EDX plot of Sr0.55Na0.45SiO3−δ. 



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www.etasr.com Najim: Synthesis and Electrical Behavior of Sodium Doped Monoclinic SrSiO3 

 

The SEM analysis demonstrated the dense structure of the 
grains that ranged in size from 5 to 10 μm. On the other hand, 
the grains were in good contact due to the well-sintered pellets. 
The EDX analysis, shown in Figure 3, confirms the 
composition and superficial homogeneity (on the surface, not 
deep) of the material. The Archimedean principle produced 
pellets with a density of 97% of the theoretical density of the 
substance in water. It is difficult to estimate the oxide ion 
conductivity of the undoped sample, as SrSiO3 is an electrical 
insulator within the measured temperature range and the 
conductivity is not due to the doped SrSiO3 but due to the Na-
rich phase (Na2Si2O5). Figure 4 shows the complex impedance 
spectra of Sr0.55Na0.45SiO3-δ at various temperatures. The bulk 
and grain boundary response was reflected in an apparent 
semicircle at high frequencies, while the electrode response 
was reflected in an apparent semicircular with a spike at low 
frequencies [17-18]. Total conductivity and not individual 
responses can be measured from bulk and grain boundaries if 
there are no clearly defined high-frequency semicircles [19]. 
Due to the high density of the pellet, the lack of a semicircle at 
high frequencies suggests that the contribution of the relative 
grain boundary to the resistance is almost minimal at high 
temperatures, as shown in Figure 4 [20-21]. The intercept of 
the low-frequency semicircle or the spike on the real (Z′) axis 
is used to represent the bulk crystal conductivity in the 
spectrum in the non-appearance of a high-frequency semicircle 
[22]. The investigated system Sr1-xNaxSiO3-δ, for x = 0.45, 
achieved conductivity σ ≥ 10-2 Scm-1 at a lower temperature 
than Sr1-xKxSi1-yGeyO3-δ by shifting a smooth variation in 
activation energy centered at 550°C in Sr0.8K0.2Si0.5Ge0.5O3-δ to 
a slightly lower temperature [22]. 

The potential for protonic conduction was expected in the 
investigated electrolytes due to the existence of absorbed water 
or hydroxide content, which was revealed by TGA 
measurement [16]. Figure 5 shows the TGA plots of 
Sr0.55Na0.45SiO3-δ. Sr0.55Na0.45SiO3-δ had a negligible weight 
decrease at 400°C, possibly due to the vaporization of the 
adsorbed water. 

 

 
Fig. 4.  Impedance plot of Sr0.55Na0.45SiO3-δ at 500 (with electrical circuit) 
and 700°C. 

The lack of weight loss at high temperatures (~ 400°C) due 
to the loss of lattice oxygen may be responsible for the 
improved electrical conductivity. Ions from absorbed water 
strongly approve the absence of any protonic conductivity at 
400°C in the sample. However, it was unclear whether oxygen 
vacancies existed in the lattice or whether the sample 
Sr0.55Na0.45SiO3-δ produced oxygen interstitials since there was 

little or no water adsorption. Glass transition and glass melting 
features are absent in SrSiO3 and glassy phase formation in Na-
doped SrSiO3. When it formed, other phases such as Sr2SiO4 
and SiO2 were always present, proving that it is impossible to 
create pure oxygen-stoichiometric SrSiO3 in a single 
monoclinic phase [23]. The overall conductivity of the system 
can be calculated as the sum of Na+ conduction in the glassy 
phases in the strontium sodium silicate. It is impossible to say 
whether the Sr0.55Na0.45SiO3-δ or glass contributes more to 
conduction in the sample. Separation of two contributions is 
not possible in impedance diagrams because only one 
semicircle is present, and an additional investigation using 
different methods would be necessary to clarify this 
characteristic. Table I shows the conductivity and activation 
energy of similar studies [23-25]. 

 

 
Fig. 5.  TGA plot of Sr0.55Na0.45SiO3−δ. 

TABLE I.  COMPARATIVE STUDY OF CONDUCTIVITY 
AND ACTIVATION ENERGY 

Sample σ Scm
-1 

at 700C Activation energy (Ea) in eV 

SrSiO3 1.5 × 10
-3 0.35 

Sr0.6Na0.4SiO3 (1.4-6.3) × 10
-3 (0.16-0.49) 

La0.9Ba0.1InO3 3.0 × 10
-3 0.88 

La0.9Ca0.1InO3 1.6 × 10
-3 0.81 

 
Figures 6 and 7 show the variation of conductivity with 

temperature, indicating its dependence. Conductivity increases 
as temperature rises, showing that the movement of oxygen ion 
vacancies is speeding up [26-28]. The following equation was 
used to determine conductivity: 

� = �
��

       (2) 

where t is thickness, A is the area, and R is the resistance of the 
pellet. 

As can be observed, the experimental data and the recorded 
temperatures are nicely matched by a straight line [27-29], 
implying that the Arrhenius formula can be used to express 
conductivity: 

� =  (��/�) �� (−!�/"#�)   (3) 

where Ea is the activation energy, kB is Boltzmann's constant, 
and σ0 is the pre-exponential factor. 

Comparing the results of this study with [30], the observed 
conductivity is lower in this study. The same disparity was 
found in [31-33]. Sr0.55Na0.45SiO3 has an activation energy of 



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www.etasr.com Najim: Synthesis and Electrical Behavior of Sodium Doped Monoclinic SrSiO3 

 

0.39 eV and its conductivity at 700C is higher (1.73×10-2 Scm-
1) than that of other solid electrolytes such as 
La0.9Sr0.1In0.8Mg0.2O3 (10

-3 Scm-1), La0.9K0.1Ga0.9Mg0.1O3 
(7.65×10-3 Scm-1), and La0.9Ca0.1InO3 (1.6×10

-3 Scm-1) [34-38]. 
Finally, it can be concluded that Sr0.55Na0.45SiO3 is a low-cost, 
rare-earth-free composite system, with a Na-rich amorphous 
phase (Na2Si2O5) in the grain and Na-SrSiO3 along the grain 
borders. 

 

 
Fig. 6.  Arrhenius plot for Sr55Na0.45SiO3-δ conductivity. 

 
Fig. 7.  Conductivity variation of Sr0.55Na0.45SiO3-δ with temperature. 

IV. CONCLUSION 

In this study, SrSiO3 and Sr0.55Na0.45SiO3 were produced 
using solid-state processes. SrSiO3 acts as an insulator over the 
temperature range studied, and Sr0.55Na0.45SiO3 has strong ionic 
conductivity. XRD and SEM studies revealed that there are two 
phases in Sr0.55Na0.45SiO3: intragrain SrSiO3 and intergrain 
Na2Si2O5. TGA indicated that glass transition and glass melting 
features were absent in SrSiO3 and glassy phase formation in 
Na-doped SrSiO3. FE-SEM confirmed the presence of 
Na2Si2O5, which is the main cause of the improved electric 
characteristics of Sr0.55Na0.45SiO3. The electrical conductivity of 
this system was caused by the movement of charge carriers 
with grain boundaries. Therefore, this study concludes that 
Sr0.55Na0.45SiO3 could be used as a suitable electrolyte material 
for IT-SOFCs. 

ACKNOWLEDGMENT  

This work was funded by the Deanship of Scientific 
Research (DSR), University of Jeddah, Saudi Arabia, under 
Grant No. UJ-21-DR-126. The author acknowledges the 

University for technical and financial support and the Indian 
Institute of Technology, Kanpur, India, for providing 
experimental facilities. 

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