This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution
and sharing with colleagues.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies areencouraged to visit:
http://www.elsevier.com/authorsrights

Author's personal copy

Available online at www.sciencedirect.com

ScienceDirect
Journal of the European Ceramic Society 34 (2014) 373–379

Fabrication of apatite-type lanthanum silicate films and anode supported
solid oxide fuel cells using nano-sized printable paste
Hideki Yoshioka a,∗ , Hiroyuki Mieda b , Takahiro Funahashi b , Atsushi Mineshige b , Tetsuo Yazawa b ,Ryohei Mori ca Hyogo Prefectural Institute of Technology, Suma-ku, Kobe, Hyogo 654-0037, Japanb Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, Himeji, Hyogo 671-2201, Japanc Fuji-Pigment Co. Ltd., Kawanishi, Hyogo 666-0015, Japan

Received 14 May 2013; received in revised form 29 August 2013; accepted 30 August 2013
Available online 24 September 2013

Abstract
Apatite-type lanthanum silicate based films have attracted significant interests to use as an electrolyte of solid oxide fuel cells (SOFCs) working
at intermediate temperature. We have prepared Mg doped lanthanum silicate (MDLS) films on NiO–MDLS cermet substrates by spin coating
and sintering of nano-sized printable paste made by beads milling. Changes in crystal structure and microstructure of the paste films with thesintering temperature have been investigated to show that porous network structure with a grain growth evolves up to 1300 ◦ C, whereas densification
occurred above 1400 ◦ C. Anode supported SOFCs using the pasted MDLS films were successfully fabricated: an open circuit voltage of 0.91 V
and a maximum power density of 150 mW cm−2 measured at 800 ◦ C were obtained with the electrolyte film sintered at 1500 ◦ C.
© 2013 Elsevier Ltd. All rights reserved.
Keywords: Apatite-type ionic conductor; Lanthanum silicate; Solid oxide fuel cell; Nano-sized paste; Anode support

1. Introduction
Solid oxide fuel cells (SOFCs) have attracted great interest as
clean and high efficient electrical power sources. Reduction ofoperating temperature of SOFCs down to intermediate temperature (500–700 ◦ C) gives significant advantages such as wider
ranges of material selection, longer life and lower manufacturing costs.1,2 Development of solid electrolytes which exhibit
high ionic conductivity at reduced temperature is one of the key
issues for the commercialization of intermediate temperaturesolid oxide fuel cells (IT-SOFCs). However, ionic conductivityof a common SOFC solid electrolyte, yttria stabilized zirconia(YSZ) rapidly reduces as temperature decreases. Numbers of
research have been done searching for solid electrolyte materials which exhibit high ionic conductivity even at intermediate
temperature range such as doped ceria3 and doped lanthanum
gallate4 type solid electrolyte materials.

∗ Corresponding author at: 3-1-12, Yukihira-cho, Suma-ku, Kobe, Hyogo 654-

0037, Japan. Tel.: +81 78 731 4302; fax: +81 78 735 7845.
E-mail address: hide@hyogo-kg.jp (H. Yoshioka).
0955-2219/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jeurceramsoc.2013.08.041

Nakayama et al. have first demonstrated that apatite-typelanthanum silicate exhibits high ionic conductivity and highoxide-ion transport number even at intermediate temperature
range.5 Ionic conductivity of the lanthanum silicate was foundto be enhanced by introduction of excess oxide ions6 andcation doping into La or Si sites.7,8 Among them, Al doping
into the Si site of oxide-ion excess lanthanum silicate gives anmarked increase: these apatites showed ionic conductivity of
17–30 mS cm−1 at 700 ◦ C9–11 which were higher than YSZ.
We have reported that ionic conductivity of lanthanum silicate
can be also enhanced by doping Mg into the Si site12 andhas been attempted to be utilized for a solid electrolyte of
IT-SOFCs.13 Mg doped lanthanum silicate (MDLS) exhibitshigh ionic conductivity comparable to Sr and Mg doped
lanthanum gallate at temperatures less than 550 ◦ C.14 SOFCs
using doped lanthanum silicate ceramic electrolytes haveshown moderate power densities of 125–250 mW cm−1 at
800 ◦ C.14–16 However, fabrication of lanthanum silicate ceramics based SOFC for practical use is still difficult because of
the high sintering temperature of lanthanum silicate ceramics(>1600 ◦ C), which prevent us from preparing dense electrolyte
films with low manufacturing costs. To overcome this obstacle,

Author's personal copy374

H. Yoshioka et al. / Journal of the European Ceramic Society 34 (2014) 373–379

we have started the research to prepare thin films of lanthanum
silicates directly on the electrode substrates as electrodesupported-type SOFCs. There are some previous researches tomake lanthanum silicate films by sol–gel method,17 thermal
spraying,18–20 sputtering21,22 and tape casting.23 To the bestof our knowledge, none of these researches, however, havesucceeded in making highly conductive lanthanum silicate films
and in preparing electrode supported SOFCs. There is only
one paper published by our group reporting the fabrication ofanode supported SOFCs using thermal sprayed MDLS films on
NiO–MDLS cermet anodes.24 We have shown in this paper thatthe thermal sprayed MDLS films could be crystallized above
800 ◦ C to be an oxide-ion conductor. The SOFC thus obtained
showed a maximum power density of 80 mW cm−2 at 800 ◦ Cwith a common (La0.6 Sr0.4 )(Co0.8 Fe0.2 )O3-␦ (LSCF) cathodematerial.
The purpose of this study is to develop a more versatile andcost-effective procedure to make SOFCs having high power densities at intermediate temperature by using highly conductive
MDLS electrolyte films. We have successfully fabricated dense
electrolyte films from printable paste consisting of nano-sized
MDLS particles made by bead milling technique. This paper
reports fabrication of dense MDLS electrolyte films by spin
coating of the paste and application to anode supported SOFCs.
Optimization of the cell structure and the fabrication procedureincluding electrode microstructure control to increase power
density is under investigation and the results will be publishedelsewhere.
2. Experimental
2.1. Preparation of nano-sized MDLS paste
MDLS powder with a composition of La9.8 Si5.7 Mg0.3 O26.4
was prepared by a conventional solid state reaction of La2 O3 ,SiO2 and MgO powders at 1600 ◦ C, followed by grounding andsieving according to the particle sizes. Powders with particle
sizes less than 10 ␮m are used for fabrication of both MDLS
paste and anode substrates.
MDLS printable paste for spin coating was prepared bymixing the powder and polyoxyethylene sorbitan tristearate asa dispersant (Kao Corporation, Japan) in terpineol (Arakawa
Chemical Industries Co. Ltd., Japan) with zircon beads using astirring machine rotating for 30 min at 3500 rpm. The viscous
paste was made by combining 21 g of MDLS powder with 2 gof dispersant and 47 g of terpineol. Then 3 g of ethyl cellulose(Nisshin Kasei Co. Ltd., Japan, MW 20,000) was added to 45 gof sol slurry as a binder to increase viscosity and stirred foran additional 30 min at 2000 rpm to completely dissolve ethyl
cellulose.
Thermogravimetry (TG) and differential thermal analysis(DTA) were performed using a TG-DTA system (Thermoplus
EVO TG-8120, RIGAKU Corp., Japan) to evaluate the thermal
properties of the MDLS paste. Air flow rate and temperaturescanning rate were set to 300 ml min−1 and 20 ◦ C min−1 , respectively.

2.2. Preparation and characterization of MDLS paste ﬁlms
NiO and MDLS powders were mixed in 6:4 in weight ratio
and pressed into disks of 13 mm in diameter and 1.5 mm in thickness. They were sintered at 1400 ◦ C for 4 h to obtain cermet
anode substrates. MDLS pastes were spin-coated on the cermet
anode substrates with a spinning rate of 5000 rpm for 30 s. They
were dried at 180 ◦ C for 10 min and then heated at 500 ◦ C for
10 min to burn out organic component. After repeating this procedure for 4 times, the MDLS films on the anode substrates were
finally sintered for 4 h at various temperatures between 1000 and
1500 ◦ C.
Phases in the films were investigated by X-ray diffraction (XRD) method using a powder diffractometer (RAD-RU,
Rigaku Corp.) with Cu K␣ radiation of 40 kV–200 mA. Filmstructures were examined by a field-emission type scanningelectron microscope (SEM) (Sirion, FEI company) with anacceleration voltage of 5 or 10 kV.
2.3. Fabrication and evaluation of anode supported SOFCs
Anode supported single cells were obtained by screenprinting La0.6 Sr0.4 Co0.2 Fe0.8 O3 (LSCF) cathode paste to theelectrolyte film surfaces and heated at 1000 ◦ C. The cathodepaste was prepared by mixing LSCF powder in terpineol solvent.
Then, Pt paste electrodes of 8 mm in diameter were painted on
both LSCF and anode substrate faces and fired again at 1000 ◦ C
to ensure the electrical contact. This single cell was applied to
SOFC evaluation equipment and heated to 1000 ◦ C to complete
glass ceiling and set down to 800 ◦ C. Thus, oxygen was supplied to cathode side and H2 –Ar gas was supplied to anode side
to reduce NiO in the anode substrates. After open circuit voltages (OCV) became stable, current–voltage (I–V) characteristic
curves were measured using a galvanostat and an electrometer,
which then gave current–power densities (I–P) characteristic
curves. AC impedances at an open circuit state were measured
by a BAS ALS-760C impedance analyzer with frequencies ranging from 100 kHz to 10 mHz. I–V characteristic curves and AC
impedance measurements were performed at 800, 700 and then
600 ◦ C.
3. Results and discussion
3.1. Preparation of MDLS paste ﬁlms
Fig. 1 shows TG–DTA curves of the MDLS paste. The TG
curve revealed that approximately a half of organic solvent,terpineol, was evaporated until 250 ◦ C followed by a gradualdecomposition of dispersing chemical and resin observed up
to 450 ◦ C. Exothermic DTA peaks of 401 ◦ C and 422 ◦ C areascribed to decompositions of ethyl cellulose and dispersing
chemical, respectively. Thus, complete decomposition of dispersing chemical and resin would be expected when 500 ◦ C wasapplied after spin coating.
Fig. 2 shows pictures of (a) an anode substrate and (b) a film
surface after spin coating and heating at 500 ◦ C for 4 times.
Fig. 2(c)–(h) are film surfaces after heated at 1000–1500 ◦ C.

Author's personal copy

H. Yoshioka et al. / Journal of the European Ceramic Society 34 (2014) 373–379

600

401°C

400

-20
-40

-48%

200

422°C
-67%

0

-60
-80
0

DTA /µV

TG / %

0

-200
200

400

600

800

T / °C

Fig. 1. TG–DTA curves of MDLS paste.

Fig. 2. Photos of (a) an anode substrate, (b) MDLS paste spin-coated 4 times
on an anode substrate, films sintered at (c) 1000 ◦ C, (d) 1100 ◦ C, (e) 1200 ◦ C,(f) 1300 ◦ C, (g) 1400 ◦ C and (h) 1500 ◦ C.

A surface of (a) an anode substrate is deep green due to NiO
included in the cermet. Film surfaces of (b)–(d) are white due tolight scattering by fine particles in the pasted film. Film surfacesof (e)–(g) show a change in color from white to reddish brown.
This indicates that sintering and grain growth of the MDLS
paste proceeds gradually between 1200 ◦ C and 1400 ◦ C. Then adense transparent film with a smooth surface roughness is finallyobtained at 1500 ◦ C (h).

375

SEM images of the film surfaces after heating at
1000–1500 ◦ C are shown in Fig. 3(a)–(f). Fig. 3(a) shows thatthe film heated at 1000 ◦ C has a small grain size (50–300 nm) of
MDLS particles which seems to be same as the particle size in thepaste. Grain growths of the nano-sized particles were observedwith formation of network above 1100 ◦ C. Below 1300 ◦ C, however, the films still include a lot of pores, showing porous
network structure. Both the grain sizes and pore sizes increased
simultaneously as the temperature increased from 1100 to 1200
and 1300 ◦ C. Contrarily, above 1400 ◦ C, pores are decreasing
rapidly until fully dense surface structure observed in the sample
heated at 1500 ◦ C. Microstructures of (e) and (f) reveals a melt
sintering process occurred in the pasted films above 1400 ◦ C.
Fig. 4(a)–(f) are corresponding fractured cross sections of
the films. In agreement with the surface SEM images, porous
network structure is gradually formed with grain growth of eachparticle below 1300 ◦ C, followed by densification of the film
occurred above 1400 ◦ C, resulting in the very dense microstructures of Fig. 4(f). In harmony with the densification, film
thickness of 20 ␮m observed in Fig. 4(a) decreased to 15 ␮m
in Fig. 4(f) after heated at 1500 ◦ C.
The above microstructure observation reveals that the sintering and densification of nano-sized particles in the MDLS paste
proceed above 1400 ◦ C, which is 200 ◦ C lower than the conventional solid state reaction. Lowering of the sintering temperature
is beneficial for preparing anode supported SOFCs which requiredense electrolyte layers on porous anode materials such as NiO
based cermets. The anode materials in general cannot be heatedat high temperatures to maintain porosity and avoid unwanted
reaction.
Fig. 5(a) shows X-ray diffraction (XRD) patterns of (i) the
anode substrate, (ii) the spin-coated film and the films sinteredat (iii) 1000 ◦ C, (iv) 1100 ◦ C, (v) 1200 ◦ C, (vi) 1300 ◦ C, (vii)
1400 ◦ C and (viii) 1500 ◦ C. XRD peaks of the anode substrate
are attributed to NiO and apatite-type phases, indicating thatno side reaction occurred during the anode fabrication process
at 1400 ◦ C. As for the paste films, only an apatite-type phase
was observed in all films up to 1500 ◦ C. A close observation,

Fig. 3. SEM images of the film surfaces sintered for 4 h at (a) 1000 ◦ C, (b) 1100 ◦ C, (c) 1200 ◦ C, (d) 1300 ◦ C, (e) 1400 ◦ C and (f) 1500 ◦ C. Micron bars show 2 ␮m.

Author's personal copy

376

H. Yoshioka et al. / Journal of the European Ceramic Society 34 (2014) 373–379

Fig. 4. SEM images of the fractured surfaces of the films sintered for 4 h at (a) 1000 ◦ C, (b) 1100 ◦ C, (c) 1200 ◦ C, (d) 1300 ◦ C, (e) 1400 ◦ C and (f) 1500 ◦ C. Micronbars show 5 ␮m.

Fig. 5(b) displays XRD patterns (2θ = 25–35◦ ) of the anodesubstrate and the films which demonstrate a change in peak
shapes and positions of the 2 1 1, 1 1 2 and 3 0 0 peaks. Obviously, peak positions of the films heated at 500–1300 ◦ C shift tothe higher angle side compared with a MDLS phase in the anodesubstrate. This implies lattice shrinkage due to compressive
stress induced in the paste milling process. On the other hand,in the films heated at 1400 and 1500 ◦ C, 2 1 1 and 3 0 0 peaks
restore the positions of the anode substrate revealing a release of
the stress during the densification process. Additionally, a clear

221310
302
113
222
312
321213
410
420
004

(a)

110
200
111
002
102
210
211
300112

however, reveals a change in the peak widths, the peak positions and the relative intensities with the sintering temperature.
Broad peaks of (ii) the spin-coated paste gradually change tosharp peaks observed in the films heated at high temperatures
because of grain growth and release of stress which has been
introduced in the milling process. In addition, relative intensitiesof the particular XRD peaks such as 0 0 2 and 0 0 4 apparently
increase with increasing sintering temperature compared withother peaks. This suggests a preference of orientation along
c-axis in the MDLS apatite phase with densification.

211

(b)

112

300

(viii)(viii)

(vii)

(vii)

(vi)

(v)

Intensity

Intensity

(vi)

(v)

(iv)

(iv)

(iii)

(iii)

(ii)

(ii)
(i)

(i)
10

20

30

40
50
2θ/ °

60

70

30

31
2θ / °

32

Fig. 5. (a) XRD patterns of (i) the anode substrate, the spin-coated films heated for 4 h at (ii) 500 ◦ C, (iii) 1000 ◦ C, (iv) 1100 ◦ C, (v) 1200 ◦ C, (vi) 1300 ◦ C, (vii)
1400 ◦ C and (viii) 1500 ◦ C. Anode substrate consists of NiO (open triangle) and apatite phase (open circle). (b) Enlarged figure shows 2 1 1, 1 1 2 and 3 0 0 peaks.

Author's personal copy

H. Yoshioka et al. / Journal of the European Ceramic Society 34 (2014) 373–379

0.8

U/V

0.6

50

700°C

P / mW cm

100

-2

800°C

0.4

800°C
100

0.6
700°C

0.4
0.2

0.2
0

600°C
0

100

150

(b)

200
300
-2
I / mA cm

400

0
500

0

P / mW cm-2

0.8

1

150

(a)

U/V

1

377

50

600°C
0

100

200
300
-2
I / mA cm

400

0
500

Fig. 6. I–V and I–P characteristic curves of the SOFC-A and B at 800, 700 and 600 ◦ C.

Table 1
Materials and fabrication conditions of SOFC-A and B.
Component

Procedure

Anode substrate

NiO–MDLS cermet pressed and heated at
1400 ◦ C
MDLS spin-coated and heated at 1400 ◦ C(A) or 1500 ◦ C (B)LSCF screen-printed and heated at 1000 ◦ C

Electrolyte film
Cathode layer

cm-2

4

–Z'' /

Electrochemical properties were investigated on two SOFCs
having pasted MDLS electrolyte films which were spin-coatedon NiO–MDLS cermet disks and sintered for 4 h at 1400 ◦ C
and 1500 ◦ C. Materials and fabrication conditions are listed inTable 1. Screen-printed LSCF pastes fired at 1000 ◦ C were used
as a cathode. I–V and I–P characteristic curves of the SOFC-Aand B at 800, 700 and 600 ◦ C are shown in Fig. 6(a) and (b),respectively. Open circuit voltages (OCVs) of the SOFC-A were0.86–0.91 V, which were significantly lower than the theoreticalvalue (1.1 V). Since SOFCs using sintered ceramic electrolytesof MDLS showed OCVs being equal to the theoretical value,13,14
lower OCVs observed for SOFC-A are ascribed to a gas leakthrough pores and cracks in the thin electrolyte film. The SOFCB showed slightly higher OCVs of 0.91–0.96 V due to a denser
electrolyte film. The OCVs, however, are still low comparedto the theoretical value. Thus, there must be a small gas leakthrough the electrolyte film of the SOFC-B.
Maximum power densities of the SOFC-A were 112, 40 and
11 mW cm−2 at 800, 700 and 600 ◦ C, respectively. Densification of the electrolyte film brought about an enhancement on
power densities of the SOFC-B as 150, 51 and 14 mW cm−2
at 800, 700 and 600 ◦ C, respectively. AC impedances at 800,
700 and 600 ◦ C measured for the SOFC-A and B are shownin Fig. 7. Ohmic resistances and polarization resistances arelisted in Table 2 along with the OCVs and the maximum power

(a)

2
0

800°C

700°C

600°C

-2
cm-2

3.2. Electrochemical properties of the anode supported
SOFC

densities. The AC impedance results evidently show that higher
power densities at 800 and 700 ◦ C of the SOFC-B are ascribedto lower ohmic resistance, while the higher power density at
600 ◦ C is due to both lower ohmic resistance and polarization
resistance.
Fig. 8 shows SEM images of the fractured cross sections of
the SOFC-A and B after the fuel cell tests. Thickness of thefilms was 20 and 15 ␮m for SOFC-A and B, respectively. The
porous cermet anode has two types of grains, MDLS particles
with 5–10 ␮m diameter and aggregates of very small Ni particles, with a triple phase boundary spreading into the anode.
The porous cathode consists of LSCF particles with a diameter
about 1 ␮m. An electrolyte film of the SOFC-A is fairly dense but
includes significant pores and cracks inside. The SOFC-B has
a much denser microstructure which can explain higher power
densities, OCVs and lower ohmic resistances. Some pores andcracks, however, would be found in the pasted film of the SOFCB considering the measured OCVs (0.91–0.96 V) although nopores and cracks can be seen in this view of the SEM image.
There are few papers reporting electrochemical propertiesof anode supported fuel cells based on apatite-type lanthanum
silicate electrolyte films. We have reported fuel cell properties of the SOFC having a plasma sprayed electrolyte filmwith 100 ␮m thickness and LSCF cathode which showed OCVsof 0.90–0.97 V and maximum power densities of 80, 45 and2–Z'' /

separation of 2 1 1 and 1 1 2 peaks is found to be characteristicof the pasted films heated above 1000 ◦ C. At present, however,a relationship between the film microstructures and transport
properties was not clear and remains to be further studied inorder to prepare high performance pasted electrolyte films.

0
-2
0

700°C
800°C

(b)

600°c

4

8
Z' /

cm-2

12

16

Fig. 7. AC impedance plots of (a) SOFC-A and (b) SOFC-B at 800, 700 and
600 ◦ C.

Author's personal copy

378

H. Yoshioka et al. / Journal of the European Ceramic Society 34 (2014) 373–379

Table 2
Fuel cell properties and area specific resistances of the SOFCs prepared.
SampleA
B
RE

Max. power density (mW cm−2 )OCV (V)

800 ◦ C700 ◦ C600 ◦ C

800 ◦ C700 ◦ C

112
150
146

40
51
78

11
14
41

0.86
0.91
0.87

0.90
0.95
0.90

Ohmic resistance ( cm2 )Polarization resistance ( cm2 )600 ◦ C

800 ◦ C700 ◦ C600 ◦ C

800 ◦ C700 ◦ C600 ◦ C

0.91
0.96
0.93

1.9
1.7
1.8

3.2
2.7
2.6

4.6
3.5
3.8

0.3
0.4
0.1

1.4
1.3
0.5

9.6
7.3
1.8

Fig. 8. SEM images of the fractured cross sections of (a) SOFC-A and (b) SOFC-B after the fuel cell tests. Micron bars show 10 ␮m.

22 mW cm−2 at 800, 700 and 600 ◦ C, respectively.24 Recently,
maximum power densities have increased to 146, 78 and
41 mW cm−2 at 800, 700 and 600 ◦ C, respectively, with changing composition of NiO:MDLS in the anode substrate from 5:5
to 6:4. They are also listed in Table 2 as RE along with the
impedance results. While the OCVs of the SOFC-A are similar
with those of the plasma sprayed SOFC-RE, the OCVs of the
SOFC-B are slightly higher than SOFC-RE though the pasted
electrolyte films are much thinner than the plasma sprayed ones.
This indicates that the pasted electrolyte film sintered at 1500 ◦ C
has dense structure with a smaller amount of pores and cracks
running across the electrolyte film.
As for the power density, a maximum power density of the
SOFC-A at 800 ◦ C is lower than SOFC-RE, whereas that of
the SOFC-B is slightly higher than RE. With decreasing temperature to 700 and 600 ◦ C, however, power densities of thepasted electrolyte SOFC-A and B, decrease significantly compared with the SOFC-RE. The lower power densities at 700 and
600 ◦ C are clearly attributed to higher polarization resistanceof the pasted SOFCs as observed in Table 2. Note that, evenat 800 ◦ C, polarization resistance of SOFC-A and B are muchhigher than SOFC-RE.
Higher polarization resistance indicates lower electrode
performance which includes electrode surface reaction andgas diffusion processes.25 In the anode supported SOFC
using the MDLS paste, the electrolyte film with the anodesubstrate must be sintered above densification temperatureof 1400 ◦ C. Such high sintering temperature often induces
unwanted electrolyte–electrode interface reaction and sinteringof fine particles in the anode substrate, which leads to reducing
electrode performance.
Power densities of 112 and 150 mW cm−2 of the pasted electrolyte SOFCs at 800 ◦ C seem to be low, considering thicknessof the electrolyte, compared with the plasma sprayed SOFCRE, or sintered ceramic electrolyte supported SOFCs.14–16 As

mentioned above, we consider that the low power densities aremainly due to electrode microstructure and electrolyte–electrodeinterface reaction which were not sufficiently controlled. Relating to this, however, Jo et al. have claimed that lanthanum silicate
electrolyte should be sintered above 1600 ◦ C to have high ionic
conductivity.26 According to their theory, the MDLS electrolyte
films of the SOFC-A and B sintered at 1400 and 1500 ◦ C, respectively, should have low ionic conductivity and power densities.
It is not favorable, however, to raise sintering temperature of theanode supported SOFCs up to 1600 ◦ C, which may results in theserious electrolyte–electrode interface reaction and degradationin the electrode microstructure. At present, we consider 1500 ◦ C
is the best sintering temperature to fabricate dense MDLS electrolyte films from the nano-sized paste. Our next target is torealize high power density by optimizing cell structure including
insertion of buffer layer16 and electrode microstructure.
4. Conclusions
We have successfully fabricated apatite-type MDLS films
and anode supported SOFCs using nano-sized MDLS printable
paste. After development of porous network structure with grain
growth up to 1300 ◦ C, densification of the paste films occurred
above 1400 ◦ C which is 200 ◦ C lower than the conventional solidstate reactions. Anode supported SOFC using the MDLS pasted
film sintered at 1500 ◦ C exhibited an OCV of 0.91 V and a maximum power density of 150 mW cm−2 at 800 ◦ C which is similar
with the SOFC with a thermal sprayed MDLS electrolyte film.
Acknowledgment
This work was supported by Adaptable and Seamless Technology Transfer Program through target-driven R&D, fromJapan Science and Technology Agency (JST), Japan.

Author's personal copy

H. Yoshioka et al. / Journal of the European Ceramic Society 34 (2014) 373–379

References
1. Molenda J, Świerczek K, Zaj˛ac W. Functional materials for the IT-SOFC. J
Power Sources 2007;173:657–70.
2. Brett DJL, Atkinson A, Brandon NP, Skinner SJ. Intermediate temperaturesolid oxide fuel cells. Chem Soc Rev 2008;37:1568–78.
3. Steele BCH. Appraisal of Ce1−y Gdy O2−y/2 electrolytes for IT-SOFC operation at 500 ◦ C. Solid State Ionics 2000;129:95–110.
4. Ishihara T, Matsuda H, Takita Y. Doped LaGaO3 perovskite type oxide as a
new oxide ion conductor. J Am Chem Soc 1994;116:3801–3.
5. Nakayama S, Kageyama T, Aono H, Sadaoka Y. Ionic conductivity of lanthanoid silicates, Ln10 (SiO4 )6 O3 (Ln = La, Nd, Sm, Gd, Dy, Y, Ho, Er andYb). J Mater Chem 1995;5:1801–5.
6. Tao S, Irvine JTS. Preparation and characterisation of apatite-type lanthanum silicate by a sol–gel process. Mater Res Bull 2001;36:1245–58.
7. Abram EJ, Sinclair DC, West AR. A novel enhancement of ionic conductivity in the cation-deficient apatite La9.33 (SiO4 )6 O2 . J Mater Chem
2001;11:1978–9.
8. 8.Kendrick E, Islam MS, Slater PR. Developing apatites for solid oxide fuelcells: insight into structural, transport and doping properties. J Mater Chem
2007;17:3104–11.
9. Marques FMB, Kharton VV, Naumovich EN, Shaula AL, Kovalevsky AV,
Yaremchenko AA. Oxygen ion conductors for fuel cells and membranes:
selected developments. Solid State Ionics 2006;177:1697–703.
10. Guillot S, Beaudet-Savignat S, Lambert S, Roussel P, Vannier RN. Effectof the dopant nature on the conductivity of oxygen overstoichiometric
oxyapatites with controlled microstructures. Solid State Ionics 2011;185:
18–26.
11. Gasparyan H, Neophytides S, Niakolas D, Stathopoulos V, Kharlamova T, Sadykov V, et al. Synthesis and characterization of doped
apatite-type lanthanum silicates for SOFC applications. Solid State Ionics
2011;192:158–62.
12. Yoshioka H. High oxide ion conductivity in Mg-doped La10 Si6 O27 withapatite-type structure. Chem Lett 2004;33:392–3.
13. Yoshioka H, Tanase S. Magnesium doped lanthanum silicate with apatitetype structure as an electrolyte for intermediate temperature solid oxide fuelcells. Solid State Ionics 2005;176:2395–8.
14. Yoshioka H, Nojiri Y, Tanase S. Ionic conductivity and fuel cell properties
of apatite-type lanthanum silicates doped with Mg and containing excess
oxide ions. Solid State Ionics 2008;179:2165–9.

379

15. Mineshige A, Nakao T, Ohnishi Y, Sakamoto R, Daiko Y, Kobune M, et al.
Ionic and electronic conductivities and fuel cell performance of oxygen
excess type lanthanum silicates. J Electrochem Soc 2010;157:81465–70.
16. Marrero-López D, Martín-Sedeño MC, Peña-Martínez J, Ruiz-Morales JC,
Núñez P, Aranda MAG, et al. Evaluation of apatite silicates as solid oxide
fuel cell electrolytes. J Power Sources 2010;195:2496–506.
17. Masubuchi Y, Higuchi M, Takeda T, Kikkawa S. Preparation of apatitetype La9.33 (SiO4 )6 O2 oxide ion conductor by alcoxide-hydrolysis. J Alloys
Compd 2006:408–12, 641–4.
18. Dru S, Meillot E, Wittmann-Teneze K, Benoit R, Saboungi ML. Plasma
spraying of lanthanum silicate electrolytes for intermediate temperaturesolid oxide fuel cells (ITSOFCs). Surf Coat Technol 2010;205:1060–4.
19. Wang WZ, Sun F, Guo XP, Liao HL, Elkedim O, Liang JC. Effect of substrate surface temperature on the microstructure and ionic conductivity oflanthanum silicate coatings deposited by plasma spraying. Surf Coat Technol
2011;205:3665–70.
20. Sun F, Zhang N, Li J, Liao H. Preparation of dense silicate electrolyte coatingwith low pressure plasma spraying and very low pressure plasma spraying for intermediate-temperature solid oxide fuel cells. J Power Sources
2013;223:36–41.
21. Brois P, Mazataud C, Fourcade S, Mauvy F, Grenier JC, Billard A. Synthesis and characterization of apatite structure sputter deposited coatings
dedicated to intermediate temperature solid oxide fuel cells. J Electrochem
Soc 2011;158:81479–84.
22. Vieira MM, Oliveira JC, Shaula AL, Cavaleiro A, Trindade B. Lanthanum
silicate thin films for SOFC electrolytes synthesized by magnetron sputteringand subsequent annealing. Surf Coat Technol 2012;206:3316–22.
23. Santacruz I, Porras-Vázquez JM, Losilla ER, Aranda MAG. Preparation ofaluminium lanthanum oxyapatite tapes, La10 AlSi5 O26.5 , by tape casting andreaction sintering. J Eur Ceram Soc 2011;31:1573–80.
24. Yoshioka H, Mitsui T, Mineshige A, Yazawa T. Fabrication of anode supported SOFC using plasma-sprayed films of the apatite-type lanthanum
silicate as an electrolyte. Solid State Ionics 2010;181:1707–12.
25. Leonide A, Sonn V, Weber A, Ivers-Tiffée E. Evaluation and modeling of
the cell resistance in anode-supported solid oxide fuel cells. J Electrochem
Soc 2008;155:B36–41.
26. Jo SH, Muralidharan P, Kim DK. Raman and 29 Si NMR spectroscopic
characterization of lanthanum silicate electrolytes: emphasis on sintering temperature to enhance the oxide-ion conductivity. Electrochim Acta
2009;54:7495–501.