由於有限能源逐漸的耗竭，開發新能源及節能減碳(例如: 燃料電池、生質酒精、太陽能及能源轉換等)，已經成為現今人類發展的重要趨勢，，熱電材料即為一受到期待的能源轉換方式的材料，熱電材料在溫差發電及熱電致冷方面都具有廣泛的應用，其中陶瓷熱電材料具有成本低廉、無毒、無污染等之優點，是深受期待的材料。陶瓷材料中之鈦酸鍶是功能性非常多元的材料，具有介電常數高、介電損耗低、熱穩定性好等之優點, 廣泛應用於電子、機械和陶瓷工業及光催化領域中。此外，鈦酸鍶也逐漸被發展至熱電領域的應用，但其有不易燒結成緻密塊材的缺點。
本研究旨在探討摻雜鑭之鈦酸鍶於強還原氣氛下(Ar-5%H2)之燒結行為及其塊材之熱電性質。研究結果顯示以有機物前導法製備之前驅物粉末，經600℃/9 h煆燒即可合成含鑭之SrTiO3粉體，其粉體大小約為10-30 nm，粉體經成形後於氣氛爐中1400℃ Ar-5%H2還原氣氛下燒結4小時所成之塊材，其相對密度皆高於92 %，摻雜鑭4 mol%之塊材 (Sr0.96La0.04TiO3)更高達99.2%，摻雜鑭量超過8 mol% 時會有第二相之形成。塊材之晶粒大小為1 ~ 4μm。
在塊材的熱電性質方面，摻雜鑭4 mol% 之鈦酸鍶塊材有最高的電傳導係數，在303k時其值為63.58 S/cm ; 而未摻雜鑭的塊材擁有最高的Seebeck係數值，於473k時其值為380.37μV/K ; 最大功率因子為摻雜鑭4 mol% 之鈦酸鍶塊材，於473k時其值為502.43 μW/mK2。
關鍵詞: 熱電材料，鈦酸鍶，PC法，高緻密塊材

Due to the limited resources exhaust gradually, development of new energy source、energy saving and carbon reduction, including fuel cell、reproductive alcohol、solar material, has become an important trend to our life. Thermoelectric materials is an expect way about the energy conversion. Thermoelectric materials and devices have widely used in the fields of energy conversion, sensors, and thermoelectric cooling. The ceramic thermoelectric materials are also well-known for no toxin and no pollution, is a highly anticipated material. SrTiO3 is a functional material it have lots of advantage for example : high dielectric constant、low dielectric loss and stable at high temperature, so it has widely used in electronic、mechanical、ceramic industry and photo catalytic fields. Recently it has been applied in the thermoelectric application, but difficult to sinter into dense bulk is a problem.
In this study, sintering behavior of La-doped SrTiO3 powders in reduction atmosphere (Ar-5%H2) and thermoelectric properties of dense bulk were investigated. Result shows that La-doped SrTiO3 powders were obtained from precursor by PC method and calcined at 600℃/9 h. The particle size of La-doped SrTiO3 is 10-30 nm . After CIP-ing, the powders were sintered at 1400℃/4h in Ar-5%H2 atmosphere. The bulks with relative density are higher than 92%, especially the Sr0.96La0.04TiO3 bulk with relative density of 99.2% were obtained. Second phase were found for the samples doping amounts of La larger than 8 mol%. The grain sizes of La-doped SrTiO3 bulks are 1 ~ 4 μm.
In terms of thermoelectric properties, the highest electrical conductivity of 63.58 S/cm at 303K was obtained in Sr0.96La0.04TiO3 sample. The specimen of SrTiO3 showed the best Seebeck coefficient of 380.37μV/K at 473K. And the maximum power factor of 502.43 μW/mK2 at 473K was obtained from the Sr0.96La0.04TiO3 sample.
Keywords: Thermoelectric materials, SrTiO3, PC method, High density bulks.

1.“京都議定書(Kyoto Protocol)” 奧地利、比利時、丹麥、芬蘭、法國、德國、希臘、愛爾蘭、義大利、盧森堡、荷蘭、葡萄牙、西班牙、瑞典、英國等、澳大利亞、保加利亞、加拿大、日本、立陶宛、摩納哥、紐西蘭、挪威、波蘭、瑞士。日本京都府京都市國立京都國際會館 (1997)。
2.H. J. Goldsmid, D. M. Rowe, and B. Raton, in CRC Handbook of Thermoelectrics, Chap. 3-4 (1995).
3.H. Ohta, S. Kim, Y. Mune, T. Mizoguchi, K. Nomura, S. Ohta, T. Nomura, Y. Nakanishi, Y. Ikuhara, M. Hirano, H. Hosono, and K. Koumoto, “Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3”, Nature Mater. 6, 129 (2007).
4.T. C. Harman, P. J. Taylor, M. P. Walsh, and B. E. LaForge, “Quantum Dot Superlattice Thermoelectric Materials and Devices”, Science, 297, 2220 (2002).
5.C. H. Kuo, M. S. Jeng, J. R. Ku, S. K. Wu, Y. W. Chou, and C. S. Hwang, “Thermoelectric Properties of Fine-Grained PbTe Bulk Materials Fabricated by Cryomilling and Spark Plasma Sintering” , J. Electron. Mater, DOI: 10.1007/s11664-009-0677-7, online (2009).
6.R. Moos, A. Gnudi, K.H. Hrdtl, “Thermoelectric properties of non-doped and Y-doped SrTiO3 polycrystals synthesized by polymerized complex process and hot pressing”, J. Appl. Phys. 78 5042–5047 (1995).
7.S. Hashimoto, L. Kinderman, F.W. Poulsen, M. Mogensen, “Conductivity of SrTiO3 based oxides in the reducing atmosphere at high temperature”, J. Alloys. Compd. 397 245–249 (2005).
8.H. Obara, A. Yamamoto, C.H. Lee, K. Kobayashi, A. Matsumoto, R. Funahashi, “Thermoelectric Properties of Y-Doped Polycrystalline SrTiO3”, Jpn. J. Appl. Phys. 43 L540–L542 (2004).
9.P.K. Gallagher, F. Schrey, F.V. Dimarcello, “Preparation of semiconducting titanates by chemical methods”, J. Am. Ceram. Soc. 46 (8) 359–365 (1963).
10.D. Chen, X. Jiao, M. Zhang, “Hydrothermal synthesis of strontium titanate powders with nanometer size derived from different precursors”, J. Eur. Ceram. Soc. 20 1261–1265 (2000).
11.A. Kikuchi,N. Okinaka and T. Akiyama “A large thermoelectric figure of merit of La-doped SrTiO3 prepared by combustion synthesis with post-spark plasma sintering” Scripta materials 63 407-410 (2010)
12.Y. Mao, S. Banerjee, S. S. Wong, “Hydrothermal synthesis of perovskite nanotubes”, Chem. Commun. 408–409(2003).
13.W. D. Yang, K. M. Hung, “Optimization of the experimental conditions for the preparation of a thin strontium titanate film by hydrothermal process”, J. Mater. Sci., 37 1337 – 1342 (2002).
14.S. Zhang, J. Liu, Y. Han, B. Chen, X. Li, Mater. Sci. “Formation mechanisms of SrTiO3 nanoparticles under hydrothermal conditions”, Mat. Sci and Eng: B 110 11–17 (2004).
15.M. Kakihana, M. Yoshimura, H. Mazaki, H. Yasuoka, L. Borjesson, “Polymerized complex synthesis and intergranular coupling of Bi‐Pb‐Sr‐Ca‐Cu‐O superconductors characterized by complex magnetic susceptibility”, J. Appl. Phys.71 3904–3910 (1992).
16.P. Duran, F. Capel, J. Tartaj, C. Moure, “Low-temperature fully dense and electrical properties of doped-ZnO varistors by a polymerized complex method”, J. Eur. Ceram. Soc. 22 67–77 (2002).
17.M. Ito, T. Nagira, D. Furumoto, S. Katsuyama, H. Nagai, “Synthesis of NaxCo2O4 thermoelectric oxides by the polymerized complex method”, Scripta Mater. 48 403–408 (2003).
18.Hiroaki Muta , Ken Kurosaki, Shinsuke Yamanaka “Thermoelectric properties of reduced and La-doped single-crystalline SrTiO3” , J. Alloy. Compd. 392 306-309 (2005)
19.M. Nygren, “SPS Processing of Nano-Structured Ceramics”, J. Iron and Steel Research, International, 99-103 (2007).
20.T. Okuda, K. Nakanishi, S. Miyasaka, Y. Tokura, “Large thermoelectric response of metallic perovskites: Sr1-xLaxTiO3”, Phys. Rev. B 63 113104-1–113104-4 (2001).
21.S. Ohta, T. Nomura, H. Ohta, M. Hirano, H. Hosono, K. Koumoto, “High-temperature carrier transport and thermoelectric properties of heavily La- or Nb-doped SrTiO3 single crystals”, Appl. Phys. Lett 87 092108-1–092108-3 (2005).
22.PENG-PENG SHANG,BO-PING ZHANG,YONG LIU,JING-FENG LI and HONG-MIN ZHU“Preparation and Thermoelectric Properties of La-Doped SrTiO3 Ceramics” Journal of electronic materials 926-934 (2011)
23.H. Muta, K. Kurosaki, S. Yamanaka. “Thermoelectric properties of reduced and La-doped single-crystalline SrTiO3”, J. Alloys Compd. 392 306–309 (2003).
24.Hong Chao Wang, Chun Lei Wang, Wen Bin Su, Jian Liu, Yi Sun, Hua Peng, and Liang Mo Mei “ Doping Effect of La and Dy on the Thermoelectric Properties of SrTiO3” J. Am. Ceram. Soc., 94 [3] 838–842 (2011).
25.Mikio Ito and Naoki Hasegawa “ Thermoelectric properties and desification behavior of SrTiO3/TiB2 composites” Material Science Forum Vols. 706-709, 1909-1914 (2012).
26.G.H. Zheng, Z.H. Yuan, Z.X. Dai, H.Q. Wang, H.B. Li, Y.Q. Ma, G. Li “Improvement of the Thermoelectric Properties of (Sr0.9La0.1)3Ti2O7
by Ag Addition” J. Low Temp. Phys., 173, 80-87 (2013).
27.S. B. Riffat, and X. Ma, “Thermo-electrics: A review of present and potential applications Applied Thermal Engineering”, Applied Thermal Engineering 23, 913–935 (2003).
28.F. Stabler, “Automotive applications for high efficiency thermoelectrics”. San Diego, CA., 2002, DARPA/DOE High Efficient Thermoelectric Workshop.
29.杨水彬,邹桂梅,黄晓敏,博和青, “钛酸锶合成方法研究进展” 絕緣材料 (2004).
30.G. S. Nolas, and H. J. Goldsmid, “A comparison of projected thermoelectric and thermionic refrigerators”, J. Appl. Phys., 4066~4070 (1999).
31.M. P. Pechini, “Barium Titanium Citrate, Barium Titanate and Processes for Producing Same”, U.S. Pat., No. 3 231 328, Jan. 25, (1969)
32.J. W. Liu, Z. Zeng, Q. Q. Zheng, H. Q. Lin, “Effective Transfer Integrals for the Jahn-Teller Distortion in LaMnO3”, Physical Review B 60 , 12968-12973 (1999).
33.高弘任，檸檬酸法製備鋁酸鍶鈣螢光粉體及其光性質研究，國立成功大學材料科學及工程學系，碩士論文，民國九十七年二月。
34.D. Hennings, W. Mayr, “ Theraml Decomposition of (BaTi) Citrates into Barium Titanate”, J. Solid State Chem., 26, 329-338 (1978).
35.G. A. Hutchins, G. H. Maher, S. D. Ross, “ Control of the Ba：Ti Ratio of BaTiO3 at a Value of Exactly 1 via Conversion to BaO．TiO2．3C6H8O7．6H2O” , Am. Ceram. Soc. Bull., 66 (4), 681-684 (1987)
36.M. S. G. Baythoun and F. R. Sale, “ Production of Strontium - substituted Lanthanum Manganite Perovskite Powder by the Amorphous Citrate Process”, J. Mater. Sci., 17, 2757-2769 (1982).
37.P. A. Lessing, “ Mixed-Cation Oxide Powders via Polymeric Precursors”, Am. Ceram. Soc. Bull., 68 (5), 1002-1007 (1989).
38.M. Kakihana, M. M. Milanova et al., “ Polymerized Complex Route to Synthesis of Pure Y2Ti2O7 at 750°C Using Yttrium-Titanium Mixed-Metal Citric Acid Complex”, J. Am. Ceram. Soc., 79 (6), 1673-1676 (1996).
39.S. G. Cho, P. F. Johnson and R.A. Condrate, “ Thermal decomposition of (Sr, Ti) organic precursor during the Pechini process”, J. Mater. Sci., 25, 4738-4744 (1990).
40.L. G. Shcherbako, L. G. Mamsurova, and G. E. Sukhanova Russ “Lanthanide Titanates”, Chemical Reviews, 48 (3), 228-242 (1979).
41.Http://baike.baidu.com/view/913556.htm, online.
42.Q. X. Fu, S. B. Mi, E. Wessel, F. Tietz, J. Eu. “Influence of sintering conditions on microstructure and electrical conductivity of yttrium-substituted SrTiO3”, J. ECS., 28, 811-820 (2008).
43.PENG-PENG SHANG, BO-PING ZHANG, YONG LIU, JING-FENG Li and HONG-MIN ZHU “Effect of sintering temperature on thermoelectric properties of La-doped SrTiO3 ceramics prepared by sol-gel process and spark plasma sintering”. Solid State Science , 1341-1346 (2010).
44.R. Richman, Prospects for efficient thermoelectric materials in the near term. San Diego, CA, DARPA/DOE High Efficient Thermoelectric. (2002).
45.TE Technology Inc. Frequently asked questions on thermoelectrics. [Online]. http://www.tetech.com/techinfo/#faqs. (2005).
46.N. F. Fedorov, O. V. Mel'nikova, V. A. Saltykova, and M. V. Chistyakova, Zh. Neorg. Khim Russ. J. Inorg. Chem. 24 649-651 (1979)
47.H. Ohta, “Thermoelectrics based on strontium titanate”, Mater. Today. 10, 44-49, (2007).
48.J. P. Coutures, P. Odier, and C. Proust, “Barium titanate formation by orangic resins formed with mixed citrates”, J. Mater. Sci. 27, 1849 -1856 (1992).
49.Syh-Yuh Chang, Shen-Li Fu , Chung-Chuang Wei, “ Sintering of SrTiO3 with Li2O3 addition” , Ceramic International 15 , 231-236 (1989).
50.Kuo-Shung Liu, Nan Li, “ Enhanced densification of SrTiO3 perovskite ceramics” , Applications of Ferroelectrics, 261-264 (1991).
51.S.G. CHO, P.F. Johnson, “ Evolution of the microstructure of undoped and Nb-doped SrTiO3” J. Mater. Sci. 29 , 4866-4874 (1994).
52.Feng Gao, Hailei Zhao, Xue Li, Yunfei Cheng, Xiong Zhou, Fenge Cui, “ Preparation and electrical properties of yttrium-doped strontium titanate with B-site deficiency” J. Power Sources 185 , 26-31 (2008).
53.Lui ´s Amaral, Ana M.R. Senos, Paula M. Vila rinho, “ Sintering kinetic studies in nonstoichiometric strontium titanate ceramics” Material Research Bulletin 44, 263-270 (2009).
54.Chandy N. George, J.K. Thomas, R. Jose, H. Padma Kumar, M.K. Suresh, V. Ratheesh Kumar, P.R. Shobana Wariar, J. Koshy, “ Synthesis and characterization of nanocrystalline strontium titanate through a modified combustion method and its sintering and dielectric properties” J. Alloys. Compd. 486, 711-715 (2009).
55.Karel Maca, Vaclav Pouchly, Zhijian Shen, “ Two-step sintering and spark plasma sintering of Al2O3, ZrO2 and SrTiO3 ceramics” Intergrated Ferroelectrics 99, 114-124 (2010).
56.Okuta. T, Nakanishi. K, Miyasaka. S, Tokura. Y, “ Large thermoelectric response of metallic perovskites : Sr1-xLaxTiO3 (0<=x<=0.1) ” Physical Review B 63, 114103 (2001).
57.H. Muta, K. Kurosaki, S. Yamanaka, “ Thermoelectric properties of rare earth doped SrTiO3” J. Alloys. Compd. 350, 292-295 (2003).
58.Lihua Zhang, Tsuyoshi Tosho, Noriyuki Okinaka, Tomohiro Akiyama, “ Thermoelectric properties of combustion-synthesized Lanthanum-doped strontium titanate” Mater. Transactions 48, 1079-1083 (2007).
59.Ning Wang, Hongcai He, Xiao Li, Li Han, Chunqiu Zhang, “ Enhanced thermoelectric properties of Nb-doped SrTiO3 polycrystalline ceramic by titanate nanotube addition” J. Alloys. Compd. 506 293-296 (2010).
60.S. Havelia, K.R. Balasubramaniam, S. Spurgeon, F. Cormack, P.A. Salvador, “ Growth of La2Ti2O7 and LaTiO3 thin film using pulsed laser deposition” J. Crystal Growth 310, 1985-1990 (2008).
61.http://www.chemguide.co.uk/atoms/properties/atradius.html.
62.http://zh.wikipedia.org/zh-tw/%E9%92%9B%E9%85%B8%E9%94%B6.
63.Lihua Zhang, Tsuyoshi Tosho, Noriyuki Okinaka, Tomohiro Akiyama, “ Thermoelectric properties of combustion synthesis and spark plasma sintered Sr1-xRxTiO3 (R = Y, La, Sm, Gd, Dy, 0 < x ≤ 1) ” Mater. Transactions, 48, 2088-2093 (2007)