The research paper published by IJSER journal is about Crystallographic Properties and Surface Analysis of Spin Coated YSZ Thin Films by Raman Spectroscopy, X-ray Diffraction and Scanning Electron Microscopy 1

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Crystallographic Properties and Surface Analysis of Spin Coated YSZ Thin Films by Raman Spectroscopy, X-ray Diffraction and Scanning Electron Microscopy

Shirley Tiong Palisoc, Simon Gerard Mendiola, Rose Ann Tegio, Michelle Natividad, Kevin Kaw, Stephen Tadios, Benjamin Tuason

Abstract— Yttria Stabilized Zirconia (YSZ) thin films (<10 μm) were fabricated by spin coating technique on steel (Fe/ Cr18/ Ni10). The concentration ratio of YSZ powder to solvent were varied accordingly. The effects of th ese variations were investigated and discussed. Using X-ray Diffraction and Raman Spectroscopy, the crystal structure of the samples were determined. The 8 -YSZ thin films have cubic fluorite structure. The X-ray diffraction patterns were in agreement with the samples’ Raman spectra. In the case of the 30YSZ: 70ethanol YSZ thin film on steel substrate, the Raman and XRD peaks shifted because of the stress -strain interaction between the steel and the YSZ thin film. Pores were evident on single coated substrates but were minimized using higher YSZ conc entrations.

Index TermsYttria Stabilized Zirconmia,YSZ, spin-coating, thin film

—————————— ——————————

1 INTRODUCTION

n order to answer the need for alternative sources of energy and to stop the effects of global warming, many researches and studies have risen, one of which is that on Solid Oxide Fuel Cells (SOFCs). A Solid Oxide Fuel Cell (SOFC) is an ener- gy-converting device or electrochemical power generation device, which can directly generate electricity from chemical energy.1-3) It can generate electricity at a high efficiency and in an environmentally friendly way. The commonly used materi- al for the electrolyte of SOFC is Yttria-stabilized zirconia (YSZ) because it can work at high temperatures in a highly efficient way. 4) Furthermore, YSZ is readily available and is a good ion
conductor.
Currently, conventional SOFCs operate at high tempera-
tures (800C -1000C).5) The high operating temperature is
necessary to obtain the maximum efficiency but as a conse-
quence, it can cause reactions and interdiffusion in the cell
especially in a long-term operation. As a result, it will reduce
cell performance and efficiency. 6)
In order to avoid the unnecessary reactions and complications,
the current demand for the development of SOFC is to de-

————————————————

Shirley Tiong Palisoc Ph.D. In Materials Science is a professor at the De- partment of Physics, De La Salle University – Manila, Philippines. E-mail: shirley.palisoc@dlsu.edu.ph

Simon Gerard Mendiola is a test engineer at Hitachi Philippines. E-mail:

sg_mendiola@yahoo.com

Rose Ann Tegio is a junior officer at PNB – Manila, Philippines.

Michelle Natividad Ph.D. in Physics is an assistant professor at the De-

partment of Physics, De La Salle University – Manila, Philippines. E-mail:

michelle.natividad@dlsu.edu.ph

Kevin Kaw is a senior student at De La Salle University – Manila, Philip-

pines. E-mail: kevinkaw08@yahoo.com

Stephen Tadios is a senior student at De La Salle University – Manila,

Philippines. E-mail: stephentadios@yahoo.com

Benjamin Tuason is a senior student at De La Salle University – Manila,

Philippines. E-Mail: benjamintuason@yahoo.com
crease the operational temperature to the range of 600C -
800C (Intermediate Temperature SOFC or IT-SOFC).5) To be
able to comply with the new operational temperature range
and improve its operational life, it is necessary to decrease the
electrolyte resistance and lower the overpotential of the elec-
trodes.2) The necessary adjustments can be done through de-
creasing the thickness of the electrolyte which should be less
than 1µm.
Numerous techniques can be used in order to make a thin
electrolyte. This includes chemical and physical deposition,
such as electrochemical vapor deposition or magnetron sput-
tering, and liquid precursor and powder processing tech-
niques such as spin coating, die pressing.4-7) The aforemen-
tioned techniques except for spin coating are very costly and
insurmountable to do because these techniques require a lot of
training and cost-inefficient. At the given time frame, the only
method that can be easily executed is the spin coating tech-
nique which is the least complicated and cost-effective.

2 METHODS

2.1. Preparation of the YSZ thin film
8-YSZ ((Y203)0.08 (ZrO2)0.92) thin films were fabricated using the spin coating technique. Commercially available 8-YSZ
powder (fuelcelmaterials, particle size: <1µm, purity: 99.9%)
was diluted in ethanol (Figure 8b) (Aced Laboratory, purity:
95%) in order to make a suspension. The suspension was then
homogenized using the ultrasonic stirrer for 3 hours. This ho-
mogenizing process was done in all sample concentrations, specifically, 10YSZ:90ethanol, 30YSZ:70ethanol and 50YSZ:50ethanol. (Note: the YSZ and ethanol ratio is expressed in weight percent)
The substrate underwent two coating stages. The first coating stage had a rotation speed of 700rpm for 6 seconds and the second cycle had a rotation speed of 2400-2500 rpm for 25-30 seconds.

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The research paper published by IJSER journal is about Crystallographic Properties and Surface Analysis of Spin Coated YSZ Thin Films by Raman Spectroscopy, X-ray Diffraction and Scanning Electron Microscopy 2

ISSN 2229-5518

The coated substrate was baked in a furnace at 300C for 3 minutes to remove excess moisture. Then the coated substrate was sintered in a furnace at about 650C for 4 hours with a heating and cooling rate of 2C/min.

(111)

2.2. Characterization of YSZ thin films
The morphology and cross-section of the sintered samples
were studied under the scanning electron microscope (SEM)
(JEOL- 5310). Crystal structure and phase change identifica-
tion of the pre-sintered and sintered samples were studied
through x-ray diffraction (with Scan range: 27o-83o, Step size:

(200)

Peak o2f2S0te)el

(

(311)

222)

(

400)

(

0.02 o, Time per step: 0.5s with Cu-Kα radiation, λ=1.541Å as the parameters). Crystallite size was measured and estimated. The pre-sintered and sintered samples were also characterized by Raman spectroscopic technique using Raman Systems R-
3000 (785nm and laser power ~290mW)

3 RESULTS

3.1. XRD results
Figures 1 to 3 show the same diffraction angles for pre-
sintered and sintered samples. This shows that the YSZ is very ideal to be used as a primary electrolyte material since there were no evident phase changes (i.e. appearance of new peaks or doubling of peaks) seen in the pre-sintered and sintered

samples. If there was phase change this would greatly affect the performance of the electrolyte because the crystal structure of the electrolyte would be constantly subjected to phase change while operating.

Peak of Steel

400)

Fig.3 XRD results of 50YSZ:50Ethanol weight percent ratio on silicon (Si) sub- strate for pre-sintered (red) and sintered (blue) samples.

All diffraction patterns for both Figures (2 & 3) have simi- lar location (in 2θ) of peaks approximately at 30o (111), 35o (200), 50o (220), 59o (311), 63o (222) and 74o (400). Notice also that some peaks in Figure 1-3 (but more prominent in Figure 1 and 2) shifted by a fraction. This shifting can be attributed to the stress and strain at the interface with the steel substrate on the YSZ.
Comparing the intensity of diffraction peaks of Figure 1 to
Figure 3, it is evident that the peaks of the sintered samples
are higher. This increase of intensity means that larger crystals
are present. Since the intensity increases, the width of the peak
narrows.
3.2 Raman results
Raman spectroscopy was used in order to confirm the
results of the XRD. Since this technique is much more sensitive
it would confirm that there are other phases (i.e. tetragonal or
monoclinic) of YSZ existing in the film. According to the re-
sults, the Raman peaks of all samples were consistent all throughout. The first set of peaks ranging from 370/cm to
750/cm were obtained, which showed a good fit with the re-

(111)

(200)

220)

(

(

(311)

222)

(

sults of A. Gosh et. al. 9)
But since the Raman results obtained in this research has a
wider scan range, a second set of peaks appeared at range of
1200/cm to 1550/cm. Both sets of peaks are attributed to YSZ
and not to any impurity that may be present. As can be seen

Fig.1 XRD results of 10YSZ:90Ethanol weight percent ratio on silicon (Si) sub- strate for pre-sintered (red) and sintered (blue) samples.

(111)

Peak of Steel

from Fig. 4 to 6, the peaks in the pre sintered and sintered samples have the similar peak position (wavenumber cm-1). The peaks in the sintered samples are higher and more de- fined. This affirms the XRD results where sintering alleviates the level of crystallization. Furthermore, as the intensity of the Raman peak increased, the width of the peak decreased as well. This is additional evidence that the YSZ crystal size be-

(200)

220)

(

400) (31212)2) (

(

came larger (better quality).
Figures 4 to 6 indicate that the type of substrate is not a
factor in the position of the Raman peaks. There was little or
no shift in the Raman peaks as the substrate was changed.

Fig.2 XRD results of 30YSZ:70Ethanol weight percent ratio on silicon (Si) sub- strate for pre-sintered (red) and sintered (blue) samples.

3.3 SEM results
Surface Analysis
Figure 7 shows the SEM micrographs of sintered steel
(Fe/Cr 18/ Ni 10). In Figure 7(a) it can be observed that there are no uneven heavy depositions seen.

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The research paper published by IJSER journal is about Crystallographic Properties and Surface Analysis of Spin Coated YSZ Thin Films by Raman Spectroscopy, X-ray Diffraction and Scanning Electron Microscopy 3

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(a)

(b)

(a)

(b)

Fig.6 Raman results of 50:50 YSZ ratio on steel substrate (a) before sin- tering and (b) after sintering.

Fig.4 Raman results of 10:90 YSZ ratio on steel substrate (a) before sin- tering and (b) after sintering.

(a)

(b)

Fig.5 Raman results of 30:70 YSZ ratio on steel substrate (a) before sin- tering and (b) after sintering.

In Fig. 8, in terms of accumulation of material, relatively it is almost the same with the previous figure. The only differ- ence between 30:70 YSZ films and 10:90 YSZ films is the amount of accumulation where the 30:70 YSZ film has fewer accumulation. This is because in this batch of samples, there is more YSZ in the suspension thus, making the suspension more viscous. Due to this increase of YSZ material, 30:70 YSZ films are denser compared to the 10:90 YSZ films because there is sufficient YSZ available that can cover the pores.
In Figure 9, there are no evident accumulations on the
substrate. This absence of accumulation can be attributed to
the density of the deposited suspension. Due to abundance of YSZ material, the 50:50 YSZ film (Figure 9(b)) became very dense and the pores are smaller compared from the other film concentration. In Figure 9(b), very few pores (pinhole like) are
present.
Cross-sectional Analysis
Figure 10(a) shows a cross sectional view of a spin coated
10:90 YSZ. It shows that making a thin film through spin coat-
ing (≤1µm) is very possible in this concentration. But there are
complications when using the 10:90 YSZ concentrations. First-
ly, the film that will be created using this type of concentration
is very prone to accumulation.
As shown in Figure 10(b), this is the cross sectional micro-
graph of a spin coated 30:70 YSZ. When using a 30:70 YSZ
concentration, it is still possible to achieve a thin film (≤1µm)
through spin coating. Furthermore, the micrograph of Figure
16-17 shows that the film is almost uniform in every section of
the film. This goes to show that spin coating technique is very
ideal in order to produce an even thin film.
Figure 10(c) shows, the cross sectional micrographs of a
spin coated 50:50 YSZ. When using a 50:50 YSZ concentration,
it would be very difficult to achieve a thin film (≤1µm)

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through spin coating because 50:50 concentration is very vis- cous. Longer spin time should be considered in order to pro- duce thinner 50:50 YSZ film.

(a) (b)

Fig. 7 SEM micrograph of sintered 10:90 YSZ ratio, spin coated on steel

(a) x1,000 and (b) x3,500.


(a) (b)

Fig. 8 SEM micrograph of sintered 30:70 YSZ ratio, spin coated on steel

(a) x1,000 and (b) x3,500


(a) (b)

Fig.9 SEM micrograph of sintered 50:50 YSZ ratio, spin coated on steel

(a) x1,000 and (b) x3,500.



(a) (b) (c)

4 DISSCUSSION

X-ray Diffraction
The XRD patterns revealed a cubic fluorite structure. X-ray
diffraction techniques identified that the YSZ material is very
stable since in every case or parameter imposed (YSZ to etha-
nol concentration) in the material the diffraction pattern is
more likely the same. Furthermore, XRD results also showed
that sintering increases the intensity of the diffraction peaks.
This increase in intensity means that larger crystals are present
[6].
Raman Spectroscopy
Raman spectroscopy results further confirmed the results of
the XRD that the samples have cubic fluorite structure and
that the YSZ thin film did not undergo any phase change. The
only changes that occurred are the increase in intensity and
narrowing of the Raman peaks. This means that larger crystals
were present that made the scattering more concentrated.
Scanning Electron Microscope
The surface micrographs show that the problem of accumula-
tion of materials that causes uneven distribution of the film
can be resolved by using a higher concentration of YSZ or by
using a substrate that is very smooth and even. By using a higher concentration of YSZ in a suspension, pore density can also be minimized. But as a consequence of using higher con- centration of YSZ, it is expected that the film that will be fabri-
cated will be thicker.

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[8] W. Tennyson. X-ray Diffraction-The basics Followed by a Few Examples of

Data Analysis. (2007) Retrieved from http://www.nhn.ou.edu/~bumm/NanoLab/ppt/X- ray_Diffraction_files/frame.htm December 14, 2010

[9] A. Gosh, A. Suri, M. Pandey, S. Thomas, T. Rama Mohan, & B. T. Rao: Ma- terials Letters. 60 (2006) 1170-1173.

Fig.10 SEM micrographs of (a) sintered 10:90 YSZ ratio, spin coated on steel at 2500rpm for 30 seconds, (b) sintered 30:70 YSZ ratio, spin coated on steel at 2500rpm for 30 seconds, and (c) sintered 50:50 YSZ ratio, spin coated on steel at 2500rpm for 30 seconds (cross-section view).

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