1. Medium Effect on Permittivity of BaTiO3 by Solid State Reaction
  Hatice Z. AKBAS a*, Ferhat GUDERb, Zeki AYDINc, Selvin USTABASd
a* :Department of Physics, Faculty of Arts and Science, Mustafa Kemal University, Hatay
b :Jale Tezer Education Institutions, Ankara
c :Department of Chemistry, Faculty of Science and Arts, Mustafa Kemal University, Hatay
d :MARGEM, Mustafa Kemal University, Hatay

2. INTRODUCTION
Solid state reaction method is commonly used method for the preparation of BaTiO3 ceramics from a mixture of BaCO3 and TiO2 powders because it is easy, cheap and suitable for mass production, which is important for many industrial applications. The solid state reaction method could be summarized:
BaCO3 and TiO2 powders are mixed by shaker, ball milling etc. In this process, some liquid like acetone, alcohol, water can be added to the mixture to homogenize thoroughly.
BaCO3 and TiO2 powders do not react together at room temperature so the mixture is calcined about 1000 °C in order for the reaction.
After calcination, the powder are pressed into pellets and the pellets sintered to investigate (di)electric or ferroelectric properties.
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3. Homogenization conditions [Petrović, 2013],
Rate of solid state reaction and phases in the powders was very sensitive to the reactants and the synthesis conditions.
Homogenization conditions [Petrović, 2013],
Calcination conditions [Manzoor, 2007; Felgner, 2004] and
Sinterization conditions [Zhong, 1994] were already been studied.
Petrović, M. M. V. Et al., J Sol-Gel Sci Technol. 67, 267–272 (2013).
Manzoor, U. & Kim, D.K, J. Mater. Sci. Technol., 23 (5), (2007).
Felgner K.-H.et al., Materials Letters, 58 (12–13) 1943–1947, (2004)
Zhong, W. Et al., Ferroelectrics, 160, (1994)
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4. Relative volume fraction of the cubic and tetragonal phases in the powders prepared by hydro-thermal techniques was found that very sensitive to the synthesis condition [Moon, 2006].
Yoon et al.[2007] and Stawski et al. [2010] reported that particle sizes of powders prepared by hydro-thermal techniques increase with increasing water and crystal structure of particle change from tetragonal to cubic.
These studies showed that reaction medium was an important factor that controlled structural and morphological properties like rate of crystallization, phase and the crystallite size of the powders
Moon S.-M. et al., Journal of Electroceramics, 17 (2-4),  (2006)
Yoon S. et al., Journal of the American Ceramic Society, 90 (1), 311–314, (2007)
Stawski T. M. Et al., Journal of the American Ceramic Society, 93 (10) 3443–3448, (2010)
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5. AIM
Homogenization medium effect of BaTiO3 produced by solid state reaction method has not been investigated up to now.
In this study, BaTiO3 powders were produced in de-ionized water, methanol and acetone.
Influence of the homogenization medium on structural, morphological and dielectric properties of BaTiO3 ceramics by solid state reaction was investigated.
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6. EXPERIMENTAL
BaTiO3-based ceramics were prepared by solid-state process.
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7. Water, Methanol, Acetone
TiO2 powder
BaCO3 powder
Medium
with zirconia balls
STEP 1: Materials
BaCO3 and TiO2 powders used analytical grade with purity better than 99 %.
Powders were mixed inside polyethylene sample vials with 5 mm diameter zirconium balls in different medias (de-ionized water, methanol and acetone)
Shaker
Mixer
Compact
STEP 2: Homogenization
The vials are shaken simultaneously by Compact Mixer Shaker (Edmund Bühler, Germany ) at 200 rpm with motion orbital for 18 hours to homogenize and to de-agglomerate the powders
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8. Dried
STEP 3: Dried
All muddy mixtures were dried at 120 °C for about 1 hour at the same time.
BaCO3
TiO2
BaTiO3
STEP 4: Calcination
The powders were calcined at 1100 °C for 4 hours in alumina crucibles all together.
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9. The structure of powders were confirmed by X-ray diffraction (XRD).
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10. Sintered at 1300 °C for 2 hours
Pressed at 235 MPa by computer-controlled press machine into disc shaped pellets
Sintered at 1300 °C for 2 hours
to get dense ceramic
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11. Raman Spectroscopy was used to verify sintered BaTiO3 pellets.
SEM images were used to analyze the morphology of sintered pellets.
The complex impedance measurements of samples were carried out using dielectric spectrometer.
Complex permittivity and resistivity of ceramics were studied in a wide frequency range of μHz- 20 MHz at room temperature.
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12. RESULTS AND DISCUSSION
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13. X-ray diffraction patterns of BaTiO3 powders were calcined at 1100 °C for 4 h.
The predominant XRD peaks of;
BaTiO3: 2 =22°, 32°, 38° , 45°, 55° and 65° at ICSD card number:
BaCO3 :2=10°-30° [Antao, 2007]
TiO2 : 2 =28°, 36°, 42° and 55° [Thamaphat, 2008]
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14. Raman spectra of BaTiO3 pellets were sintered at 1300 °C for 2 h.
Raman active modes of BaTiO3 pellets are 715 cm-1, 512 cm-1, 305 cm-1, 261 cm-1, 162 cm-1 and 118 cm-1. Around 310 cm-1 peak is a peak for tetragonal BaTiO3 [Qi, 2011].
There are no sign of Raman peaks for BaCO3 (1059 cm-1 and 694 cm-1) [Pasierb, 2001] and TiO2 (143 cm-1) [Choi, 2005].
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15. Scanning electron microscopy (SEM) images of sintered samples
X 200
X 1000
X 2000
d) Methanol
e) Methanol
f) Methanol
g) Acetone
h) Acetone
i) Acetone
a) Distilled water
b) Distilled water
c) Distilled water
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16. Reel part of complex permittivity of sintered pellets
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17. Imaginary part of complex permittivity of sintered pellets
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18. Resistivity of sintered pellets
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19. CONCLUSION
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20. DIELECTRIC POLARIZATION MECHANISMS
Dipolar and space charge polarizations contribute to dielectric constant dominantly at lower frequency.
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21. CONDUCTION AND FAILURE MECHANISMS IN BaTiO3 (Rawal)
The intrinsic type imperfections :
various electronic disorders,
dislocations,
grain boundaries ….
This cause a sudden current which results in an immediate breakdown
The extrinsic type imperfections:
porosity,
cracks,
local contamination
This generate a leakage current which leads to (self) heating
Rawal, B. S., & Chan, N. H. InProceedings of the 34th Electronic Components Conference, New Orleans, (1984,).
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22. CONDUCTION AND FAILURE EFFECT IN MEDIUM
Ba and Ti could be hydrolyzed [Stawski, 2010] different proportion in different mediums.
Ion incorporation in the lattice could be different for samples homogenized in water (H2O), methanol (CH4O) and acetone (C3H6O). It could be changed structural properties of synthesized BaTiO3 [Yoon, ].
Disproportionation of the medium solution:
H2O+H2OH3O++OH- Water
CH2OH+CH2OH  CH3OH-+CH2O- Methanol
C3H6O  None Acetone
The hydroxyl ions in BaTiO3 [Yoon, 2007; Stawski, 2010] and structural properties of samples homogenized in water, methanol and acetone can be changed dielectric properties of the ceramics.
Yoon S. et al., Journal of the American Ceramic Society, 90 (1), 311–314, (2007)
Stawski T. M. et al., Journal of the American Ceramic Society, 93 (10) 3443–3448, (2010)
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23. CONCLUSION
Using water in the homogenization process keeps the grains together while the acetone separated them.
There is a clear correlation between particle size and homogenization medium.
The pellets homogenized in different medium have different grain sizes, and cavities between grain walls.
The complex permittivity and complex AC conductivity of samples by solid state reaction processes strongly depends on grain sizes [Zhong, 1994], and cavities between grain walls.
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24. THANK YOU FOR YOUR ATTENTION ANY QUESTION
Acknowledgement The authors thank to Scientific Research Projects Coordination Unit for project founding by grant no: 326, Mustafa Kemal University, Hatay.
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25. St. Pierre Church is in city of Hatay (Antakya or Anṭiokia), TURKEY.
It is considered the world's first cave church.
UNESCO submitted it one of the World Heritage at 2011
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