二氧化鈰因其優越的穩定性和高氧離子導電度,為固態氧化物燃 料電池裡重要的電解質材料。在其導電性質上,因微結構而能夠區分 出晶粒導電度和晶界導電度,而在次微米尺度下之二氧化鈰其晶界導 電度因較低而成為主導整體電性關鍵,前人研究發現,利用共摻雜少 量鹼土族金屬如鎂、鈣和鍶等於釤或釓摻雜之二氧化鈰中,能藉由清 除材料內部之不純物,以有效促進其晶界導電度;此外,以往元素釤 摻雜二氧化鈰具有良好的離子導電性質,常做為固態氧化物燃料電池 重要的電解質材料,然而較貴之元素釤常成為業界成本之考量,因此 降低生產成本也成為現階段發展的核心。因此本研究將利用均勻製程 之噴霧熱解法製備不同鈣摻雜濃度之二氧化鈰系統,進而探討不同摻 雜濃度之元素鈣的在材料內部分佈情形對二氧化鈰導電性質之影響。 其中前驅物的量測分析,透過熱重分析量測不同前驅物的熱裂解溫度 以判定噴霧熱解法之運作溫度。在粉體的量測分析上,將利用 X 光繞 射儀鑑定(X-ray diffraction analysis, XRD)粉體的結晶結構,以及掃描 式電子顯微鏡(Scanning electron microscopy, SEM)觀察粉體形貌。在 電解質塊材的量測分析上,使用 XRD 觀察其結晶結構,以及透過金 相研磨技術並利用 SEM 觀察塊材內的微結構緻密程度,並以拉曼光 譜儀、背向散射電子影像與能量分散光譜儀進行二次相之鑑定,最後 以交流阻抗分析儀量測塊材之阻抗變化,並計算其離子導電度與並與 鈣摻雜濃度進行比較。本實驗發現,鈣摻雜能同時有效促進晶粒與晶 界導電度,由於晶界導電度的提升,其整體導電度在 10 mol% 鈣摻 雜濃度達到最高並可發現微結構中,晶界上具有許多元素鈣與不純物 產生之二次相。

Ceria-based materials have been attracted much attention due to their superior stability and high ionic conductivity. It is well known that ionic conductivity is controlled by grain and grain boundary conductivities. Recent studies have been demonstrated that for the ceria- based electrolytes, in general, ionic conductivity is dominated by the grain boundary conductivity. So far, many studies focused on increasing grain conductivity by adding rare earth elements of Sm, Gd and Y. However, rare experimental result has been reported for the enhancements of grain boundary conductivity.
In this study, Ca was chosen to increase the grain boundary conductivity, and then spray pyrolysis (SP) was used to synthesize pure CeO2 and Ca-doped CeO2 electrolytes. The characterizations were divided in three parts: the first part focused on precursor analysis. The decomposed temperatures of various precursors were measured by thermogravimeteric analysis. The second part was particle analysis, and the final part was bulk analysis. The crystalline structures of ceria bulks were characterized by X-ray diffractometer (XRD). The microstructures were observed by using scanning electron microscope (SEM), and raman spectroscopy and energy dispersive spectrometer were investigated to second phase identification. In addition, we also use th electrochemical impedance spectroscopy (EIS) to measure the ionic conductivities
It has been observed that 10 mol% Ca-doped ceria has the highest conductivities because the higher conductivity of grain boundary conductivity. The possible explanation is that Ca segregates on the grain boundaries to react with the lower conductive impurity of Si for forming the higher conductivity CaSiO3 phase, and then the ceria-based electrolytes with the higher ionic boundary conductivity have been achieved.

[1] U. Hennings, R. Reimert, Investigation of the structure and the redox behavior of gadolinium doped ceria to select a suitable composition for use as catalyst support in the steam reforming of natural gas, Applied Catalysis A: General, 325 (2007) 41-49.
[2] G. Chen, F. Zhu, X. Sun, S. Sun, R. Chen, Benign synthesis of ceria hollow nanocrystals by a template-free method, CrystEngComm, 13 (2011) 2904-2908.
[3] A. Trovarelli, Catalytic Properties of Ceria and CeO2-Containing Materials, Catalysis Reviews, 38 (1996) 439-520.
[4] H. Inaba, H. Tagawa, Ceria-based solid electrolytes, Solid State Ionics, 83 (1996) 1-16.
[5] C.-Y. Chen, C.-L. Liu, Doped ceria powders prepared by spray pyrolysis for gas sensing applications, Ceramics International, 37 (2011) 2353-2358.
[6] I. Radev, K. Koutzarov, E. Lefterova, G. Tsotridis, Influence of failure modes on PEFC stack and single cell performance and durability, International Journal of Hydrogen Energy, 38 (2013) 7133-7139.
[7] Air Products in AFC project to use surplus industrial hydrogen, Fuel Cells Bulletin, 2013 (2013) 6.
[8] S. Ganguly, S. Das, K. Kargupta, D. Bannerjee, Optimization of Performance of Phosphoric Acid Fuel Cell (PAFC) Stack using Reduced Order Model with Integrated Space Marching and Electrolyte Concentration Inferencing, in: A.K. Iftekhar, S. Rajagopalan (Eds.) Computer Aided Chemical Engineering, Elsevier2012, pp. 1010-1014.
[9] S. Kim, J.Y. Jung, H.H. Song, S.J. Song, K.Y. Ahn, S.M. Lee, Y.D. Lee, S. Kang, Optimization of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine hybrid system for distributed power generation, International Journal of Hydrogen Energy, 39 (2014) 1826-1840.
[10] N. Kim, B.-H. Kim, D. Lee, Effect of co-dopant addition on properties of gadolinia-doped ceria electrolyte, Journal of Power Sources, 90 (2000) 139-143.
[11] S.P.S. Badwal, K. Foger, Solid oxide electrolyte fuel cell review, Ceramics International, 22 (1996) 257-265.
[12] M. Dokiya, SOFC system and technology, Solid State Ionics, 152–153 (2002) 383-392.
[13] U.S.D.o. Energy, Fuel Cell Handbook by EG&G Technical Service Inc., (2004).
[14] N.Q. Minh, Ceramic Fuel Cells, Journal of the American Ceramic Society, 76 (1993) 563-588.
[15] S.C. Singhal, Advances in solid oxide fuel cell technology, Solid State Ionics, 135 (2000) 305-313.
[16] Y. Teraoka, T. Nobunaga, K. Okamoto, N. Miura, N. Yamazoe, Influence of constituent metal cations in substituted LaCoO3 on mixed conductivity and oxygen permeability, Solid State Ionics, 48 (1991) 207-212.
[17] T. Ishihara, H. Matsuda, Y. Takita, Doped LaGaO3 Perovskite Type Oxide as a New Oxide Ionic Conductor, Journal of the American Chemical Society, 116 (1994) 3801-3803.
[18] N. Ramadass, ABO3-type oxides—Their structure and properties—A bird's eye view, Materials Science and Engineering, 36 (1978) 231-239.
[19] C.-W. Huang, Electrical properties and microstructure of cerium oxide electrolytes produced by two-step sintering, (2013).
[20] E.D. Wachsman, G.R. Ball, N. Jiang, D.A. Stevenson, Structural and defect studies in solid oxide electrolytes, Solid State Ionics, 52 (1992) 213-218.
[21] R. Chockalingam, V.R.W. Amarakoon, H. Giesche, Alumina/cerium oxide nano-composite electrolyte for solid oxide fuel cell applications, Journal of the European Ceramic Society, 28 (2008) 959-963.
[22] B.C.H. Steele, Oxygen ion conductors and their technological applications, Materials Science and Engineering: B, 13 (1992) 79-87.
[23] B. Park, H. Lee, K. Park, H. Kim, H. Jeong, Pad roughness variation and its effect on material removal profile in ceria-based CMP slurry, Journal of Materials Processing Technology, 203 (2008) 287-292.
[24] A. Bumajdad, J. Eastoe, A. Mathew, Cerium oxide nanoparticles prepared in self-assembled systems, Advances in Colloid and Interface Science, 147–148 (2009) 56-66.
[25] C. Peng, Y. Wang, K. Jiang, B.Q. Bin, H.W. Liang, J. Feng, J. Meng, Study on the structure change and oxygen vacation shift for Ce1−xSmxO2−y solid solution, Journal of Alloys and Compounds, 349 (2003) 273-278.
[26] C. Ying-Yu, R. Schmid, Y.A. Chang, Calculation of the equilibrium phase diagrams and the spinodally decomposed structures of the Fe瑖Cu瑖Ni system, Acta Metallurgica, 33 (1985) 1369-1380.
[27] S. Hui, J. Roller, S. Yick, X. Zhang, C. Deces-Petit, Y. Xie, R. Maric, D. Ghosh, A brief review of the ionic conductivity enhancement for selected oxide electrolytes, Journal of Power Sources, 172 (2007) 493-502.
[28] H. Li, C. Xia, M. Zhu, Z. Zhou, G. Meng, Reactive Ce0.8Sm0.2O1.9 powder synthesized by carbonate coprecipitation: Sintering and electrical characteristics, Acta Materialia, 54 (2006) 721-727.
[29] D.A. Andersson, S.I. Simak, N.V. Skorodumova, I.A. Abrikosov, B. Johansson, Optimization of ionic conductivity in doped ceria, Proceedings of the National Academy of Sciences of the United States of America, 103 (2006) 3518-3521.
[30] H. Yahiro, Y. Eguchi, K. Eguchi, H. Arai, Oxygen ion conductivity of the ceria-samarium oxide system with fluorite structure, J Appl Electrochem, 18 (1988) 527-531.
[31] H. Inaba, H. Tagawa, Ceria-based solid electrolytes - Review, Solid State Ionics, 83 (1996) 1-16.
[32] G.B. Balazs, R.S. Glass, ac impedance studies of rare earth oxide doped ceria, Solid State Ionics, 76 (1995) 155-162.
[33] F.T. M. C. Steil, Densification of Yttria-Stabilized Zirconia, J. Electrochem. Soc., (1997).
[34] M.N. Rahaman, Sintering of ceramics, Taylor & Francis Group2007.
[35] R.M. German, Sintering theory and practice, John Wiley & Sons1996.
[36] S.J.L. Kang, Sintering densification, grain growth & microstructure, Elsevier2005.
[37] S.Y. D. Wolf, Materials interfaces: atomic-level structure and properties, Chapman & Hall1992.
[38] M. Kronberg, F. Wilson, Secondary recrystallization in copper, AIME TRANS, 185 (1949) 501-514.
[39] Y.-J. You, Investigation of Sr/Ti ratio on microstructure and electrical properties of SrTiO3, (2012).
[40] M. Aoki, Y.-M. Chiang, I. Kosacki, L.J.-R. Lee, H. Tuller, Y. Liu, Solute Segregation and Grain-Boundary Impedance in High-Purity Stabilized Zirconia, Journal of the American Ceramic Society, 79 (1996) 1169-1180.
[41] Z.-P. Li, T. Mori, G.J. Auchterlonie, J. Zou, J. Drennan, Direct evidence of dopant segregation in Gd-doped ceria, Applied Physics Letters, 98 (2011) 093104-093104-093103.
[42] T. Sugiura, S. Itoh, T. Ooi, T. Yoshida, K. Kuroda, H. Minoura, Evolution of a skeleton structured TiO2 surface consisting of grain boundaries, Journal of Electroanalytical Chemistry, 473 (1999) 204-208.
[43] C. Tian, S.-W. Chan, Ionic conductivities, sintering temperatures and microstructures of bulk ceramic CeO2 doped with Y2O3, Solid State Ionics, 134 (2000) 89-102.
[44] J. Maier, Ionic conduction in space charge regions, Progress in Solid State Chemistry, 23 (1995) 171-263.
[45] J. Maier, Defect chemistry and ionic conductivity in thin films, Solid State Ionics, 23 (1987) 59-67.
[46] T.S. Zhang, J. Ma, Y.Z. Chen, L.H. Luo, L.B. Kong, S.H. Chan, Different conduction behaviors of grain boundaries in SiO2-containing 8YSZ and CGO20 electrolytes, Solid State Ionics, 177 (2006) 1227-1235.
[47] B. Li, X. Wei, W. Pan, Improved electrical conductivity of Ce0.9Gd0.1O1.95 and Ce0.9Sm0.1O1.95 by co-doping, International Journal of Hydrogen Energy, 35 (2010) 3018-3022.
[48] R.A. Montalvo-Lozano, S.M. Montemayor, K.P. Padmasree, A.F. Fuentes, Effect of Ca2+ or Mg2+ additions on the electrical properties of yttria doped ceria electrolyte system, Journal of Alloys and Compounds, 525 (2012) 184-190.
[49] Y.H. Cho, P.-S. Cho, G. Auchterlonie, D.K. Kim, J.-H. Lee, D.-Y. Kim, H.-M. Park, J. Drennan, Enhancement of grain-boundary conduction in gadolinia-doped ceria by the scavenging of highly resistive siliceous phase, Acta Materialia, 55 (2007) 4807-4815.
[50] D.K. Kim, P.-S. Cho, J.-H. Lee, D.-Y. Kim, H.-M. Park, G. Auchterlonie, J. Drennan, Mitigation of Highly Resistive Grain-Boundary Phase in Gadolinia-Doped Ceria by the Addition of SrO, Electrochemical and Solid-State Letters, 10 (2007) B91-B95.
[51] Z. Zhan, T.-L. Wen, H. Tu, Z.-Y. Lu AC Impedance Investigation of Samarium-Doped Ceria, Journal of The Electrochemical Society, 148 (2001) A427-A432.
[52] L.L. Hench, J.K. West, The sol-gel process, Chemical Reviews, 90 (1990) 33-72.
[53] G.L. Messing, S.-C. Zhang, G.V. Jayanthi, Ceramic Powder Synthesis by Spray Pyrolysis, Journal of the American Ceramic Society, 76 (1993) 2707-2726.
[54] T. Masui, K. Fujiwara, K.-i. Machida, G.-y. Adachi, T. Sakata, H. Mori, Characterization of Cerium(IV) Oxide Ultrafine Particles Prepared Using Reversed Micelles, Chemistry of Materials, 9 (1997) 2197-2204.
[55] M. Hirano, T. Miwa, M. Inagaki, Effect of the Presence of Ammonium Peroxodisulfate on the Direct Precipitation of Ceria and Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions, Journal of the American Ceramic Society, 84 (2001) 1728-1732.
[56] K. Kaneko, K. Inoke, B. Freitag, A.B. Hungria, P.A. Midgley, T.W. Hansen, J. Zhang, S. Ohara, T. Adschiri, Structural and Morphological Characterization of Cerium Oxide Nanocrystals Prepared by Hydrothermal Synthesis, Nano Letters, 7 (2007) 421-425.
[57] C.Y. Chen, T.K. Tseng, C.Y. Tsay, C.K. Lin, Formation of irregular nanocrystalline CeO 2 particles from acetate-based precursor via spray pyrolysis, Journal of Materials Engineering and Performance, 17 (2008) 20-24.
[58] S.-J. Shih, Y.-Y. Wu, C.-Y. Chen, C.-Y. Yu, Controlled Morphological Structure of Ceria Nanoparticles Prepared by Spray Pyrolysis, Procedia Engineering, 36 (2012) 186-194.
[59] T.C. Pluym, Q.H. Powell, A.S. Gurav, T.L. Ward, T.T. Kodas, L.M. Wang, H.D. Glicksman, Solid silver particle production by spray pyrolysis, Journal of Aerosol Science, 24 (1993) 383-392.
[60] T.C. Pluym, T.T. Kodas, L.-M. Wang, H.D. Glicksman, Silver-palladium alloy particle production by spray pyrolysis, Journal of Materials Research, 10 (1995) 1661-1673.
[61] P.S. Patil, Versatility of chemical spray pyrolysis technique, Materials Chemistry and Physics, 59 (1999) 185-198.
[62] C. Naşcu, I. Pop, V. Ionescu, E. Indrea, I. Bratu, Spray pyrolysis deposition of CuS thin films, Materials Letters, 32 (1997) 73-77.
[63] J. Fleig, J. Maier, A finite element study on the grain boundary impedance of different microstructures, Journal of The Electrochemical Society, 145 (1998) 2081-2089.
[64] J.R. Macdonald, E. Barsoukov, Impedance spectroscopy: theory, experiment, and applications, History, 1 (2005) 8.
[65] S.-Y. Yang, S.-G. Kim, Characterization of silver and silver/nickel composite particles prepared by spray pyrolysis, Powder Technology, 146 (2004) 185-192.
[66] C.Y. Chen, T.K. Tseng, S.C. Tsai, C.K. Lin, H.M. Lin, Effect of precursor characteristics on zirconia and ceria particle morphology in spray pyrolysis, Ceramics International, 34 (2008) 409-416.
[67] J.P. Huang, Study on Morphology and Conductivity for Sm-doped Ceria by Spray Pyrolysis, National Taiwan University of Science and Technology, 2012.