釔鋁石榴石 (Y3Al5O12,YAG) 具有優異的光學性質和機械性能，近年來在工業上之應用已越發重要。前人的研究皆指出，YAG 的生成是藉由 Al 成分擴散進入 Y2O3 結構中而得，因此反應的情形會受到反應物的擴散速率和擴散距離所控制。本研究探討離子移動力對於 YAG 相轉換機制的影響，分別改變 Y 離子以及 Al 離子之移動力 (mobility)，並添加 NaCl 做為助熔劑以增加反應物的擴散速率，以觀察起使材料製備方式之改變對於 YAG 相轉換行為的影響。由實驗結果發現，即使讓 Y 離子有良好的移動力，YAG 的生成仍是以 Al 離子的擴散來進行，而 NaCl 的添加，可使 Al 為離子狀態之樣品其反應途徑由傳統固態反應法之途徑轉變為短時間內大量生成過渡相 hexagonal-YAP (YAH)，而後再快速轉換成 YAG。根據電子顯微鏡的觀察，Al 為離子狀態之起始材料添加 NaCl 後，Y2O3 晶粒會在反應初期受到 Al 離子的擴散侵入所崩解，使得 Y 離子和 Al 離子得以於原子尺度之混和情形達到 [Al3+]/[Y3+] = 1/1 之狀態，系統便可藉由成核成長的方式，在極短時間內形成大量YAH，此外根據初形成的 YAH 型態可發現其均為大小一致、長約 50 nm，寬約 20 nm 之為桿狀晶粒，顯示其生成機制應為成核成長作用控制。本研究再進一步製備 Y 離子和 Al 離子之來源皆為非晶質狀態之起始材料，於添加 NaCl 後進行熱處理，發現此起始材料可直接結晶出 YAG，不需經由其他中間相，且初生成之 YAG 晶粒具有相同的大小，於此系統中，Y 離子和 Al 離子在原子尺度之混和情形可達到 [Al3+]/[Y3+] = 3/5 之狀態，故此系統可直接結晶出 YAG。根據本研究結果可確認，YAG的生成不僅受到離子移動力影響，同時Y 離子和 Al 離子於原子尺度上的混合程度，也對反應途徑扮演決定性的角色。

Yttrium Aluminum garnet (YAG, Y3Al5O12) is a promising ceramic material which are largely used in optical applications. It is generally believed that the formation YAG phase via solid-state reaction is carried out by the diffusion of Al3+ ions into Y2O3 structure. Therefore, the formation of YAG under stoichiometric condition ([Y3+]/[Al3+] = 3/5) should depend on the ionic mobility of the used precursors. In the present work, the diffusional mobilities of Y3+ or Al3+ sources are modified by using different staring materials, either crystallized or amorphous precursors. In addition, NaCl is incorporated as a flux in order to further enhance the diffusion rate of the reactants. According to the experimental results, formation of YAG material is indeed carried out by the diffusion of Al3+ ions into Y2O3 structure even when the Y3+ ion exhibits a better mobility than Al3+ ions. For the samples prepared without NaCl, the phase transformation processes all follow the conventional pathway through firstly Y4Al2O9 (YAM), YAlO3 perovskite (YAP) and finally to stable YAG phase. However, the presence of NaCl flux gives a strong effect on the phase transformation behaviors for the sample prepared by using [Y2O3/ amorphous Al]. In this case YAM and YAP phases are never found in the system, nevertheless hexagonal-YAlO3 (YAH) is largely observed in a very short time of heat treatment that turns directly into YAG. According to TEM observations, the Y2O3 particles are apparently destroyed due to the accelerated diffusion of Al3+ ion into Y2O3 structure by the presence of NaCl flux and as a consequence generates the formation of YAH prior to YAM or YAP. Moreover, the as-formed YAH particles all exhibit similar sizes implying that they are formed by nucleation and growth controlled process. On the other hand, YAG phase is appeared directly without passing through intermediate phases if the precursors of Al and Y sources are both amorphous. According to the experimental results mentioned above, the phase transformation behaviors of YAG are found to dominate by the ionic mobility but also the atomic homogeneity of the using Y3+ ion or Al3+ sources.

1. H. S. Yoder, and M. L. Keith, “Complete substitution of aluminum for silicon: the system 3MnO．Al2O3．3SiO2-3Y2O3．5Al2O3,” American Mineralogist, 36, 519-533 (1951).
2. L. Dobrzycki, E. Bulska, D. A. Pawlak, Z. Frukacz, and K. Woźniak, “Structure of YAG crystals doped/substituted with erbium and ytterbium,” Inorg. Chem., 43, 7656-7664 (2004).
3. D. A. Pawlak, K. Woźniak, Z. Frukacz, T. L. Barr, D. Fiorentino, and S. Seal, “ESCA studies of yttrium aluminum garnets,” J. Phys. Chem., B 103, 1454-1461 (1999).
4. Y. N. Xu, and W. Y. Ching, “Electronic structure of yttrium aluminum garnet (Y3Al5O12),” Phys. Rev., B 59, 10530-10535 (1999).
5. T. Hahn, International tables for crystallography, Volume A, Space-group symmetry, 2nd revised Ed., D. Reidel Publishing Company, Holland, (1987).
6. R. C. Buchanan, “Ceramic materials for electronics：processing, properties, and application.,” Marcel Dekker, Inc. New York.
7. O. Fabrichnaya, H. J. Seifert, T. Ludwig, F. Aldinger, and A. Navrotsky, “The assessment of thermodynamic parameters in the Al2O3-Y2O3 system and phase relations in the Y-Al-O system”. Scand. J. Metall., 30, 175-183 (2001).
8. G. T. Adylov, G. V. Voronov, E. P. Mansurova, L. M. Sigalov, and E. M. Urazveva “Y2O3-Al2O3 system higher 1473K,” Russ. J. Inorg. Chem., 33, 1867-1869 (1988).
9. J. G. Li, T. Ikegami, J. H. Lee, T. Mori, and Y. Yajima, “Co-precipitation synthesis and sintering of yttrium aluminum garnet (YAG) powders: the effect of precipitant,” J. Euro. Ceram. Soc., 20, 2395-2405 (2000).
10. S. Ramanathan, M. B. Kakade, S. K. Roy, and K. K. Kutty, “Processing and characterization of combustion synthesized YAG powders,” Ceram. Int., 29, 477-484 (2003).
11. C. H. Lu, and W. T. Hsu, “Sol-gel pyrolysis and photoluminescent characteristic of europium-ion doped yttrium aluminum garnet nanophosphors,” J. Euro. Ceram. Soc., 24, 3723-3729 (2004).
12. M. Nyman, J. Caruso, and M. J. Hampden-Smith, “Comparison of solid-state and spray-pyrolysis synthesis of yttrium aluminate powders,” J. Am. Ceram. Soc., 80, 1231-1238 (1997).
13. S. F. Wang, K. Koteswara Rao, Y. C. Wu, Y. R. Wang, Y. F. Hsu, and C. Y. Huang, “Synthesis and characterization of Ce3+:YAG phosphors by heterogeneous precipitation using different alumina sources,” Int. J. Appl. Ceram. Tech., 6, 470-478 (2009).
14. A. E. Zhukovskaya, and V. I. Strakhov, “Influence of the molar ratio of Y2O3 to Al2O3 on the kinetics of synthesis of yttrium aluminates,” J. Appl. Chem. Ussr., 48, 1169-1171 (1975).
15. A. Y. Neiman, E. V. Tkachenko, L. A. Kvichko, and L. A. Kotok, “Conditions and macromechanism of the solid-phase synthesis of yttrium aluminates,” Russ. J. Inorg. Chem., 25, 2340-2345 (1980).
16. V. B. Glushkova, V. A. Krzhizhanovskaya, O. N. Egorova, Y. P. Udalov, and L. P. Kachalova, “Interaction of yttrium and aluminum oxide,” Inorg. Mater., 19, 95-99 (1983).
17. C. K. Ullal, K. R. Balasubramaniam, A. S. Gandhi, and V. Jayaram, “Non-equilibrium phase synthesis in Al2O3-Y2O3 by spray pyrolysis of nitrate precursors,” Acta Mater., 49, 2691-2699 (2001).
18. K. J. D. MacKenzie, and T. Kemmitt, “Evolution of crystalline aluminates from hybridgel-derived precursors studied by XRD and multinuclear solid-state MAS NMR. II.Yttrium-aluminium garnet, Y3Al5O12,” Thermochim. Acta, 325, 13-18 (1999).
19. Y. Iida, A. Towata, T. Tsugoshi, and M. Furukawa, “In situ Raman monitoring of low temperature synthesis of YAG from different starting materials,” Vibra. Spectro., 19, 399-405 (1999).
20. O. Yamaguchi, K. Matui, and K. Shimizu “Formation of YAlO3 with garnet structure,” Ceram. Int., 11, 107-108 (1985).
21. C. D. Veitch, “Synthesis of polycrystalline yttrium iron garnet and yttrium aluminum garnet from organic precursors,” J. Mater. Sci., 26, 6527-6532 (1991).
22. N. J. Hess, G. D. Maupin, L. A. Chick, D. S. Sunberg, D. E. McCreedy, and T. R. Armstrong, “Synthesis and crystallization of yttrium-aluminium garnet and related compounds,” J. Mater. Sci., 29, 1873-1878 (1994).
23. R. S. Hay, “Phase transformation and microstructure evolution in sol-gel derived yttrium-aluminum garnet films,” J. Mater. Res., 8, 578-604 (1993).
24. T. I. Mah, T. A. Parthasarathy, and R. J. Kerans “Processsing, microstructure, and strength of alumina-YAG eutectic polycrystals,” J. Am. Ceram. Soc., 83, 2088-2090 (2000).
25. G. Gowda “Synthesis of yttrium aluminates by the sol-gel process,” J. Mater. Sci. Lett., 5, 1029-1032 (1986).
26. T. Tachiwaki, M. Yoshinaka, K. Hirota, T. Ikegami, and O. Yamaguchi “Novel synthesis of Y3Al5O12 (YAG) leading to transparent ceramics,” Solid State Comm., 119, 603-606 (2001).
27. M. K. Cinibulk “Synthesis of yttrium aluminum garnet from a mixed-metal citrate precursor,” J. Am. Ceram. Soc., 83, 1276-1278 (2000).
28. P. Apte, H. Burke, and H. Pickup “Synthesis of yttrium aluminum garnet by reverse strike precipitation,” J. Mater. Res., 7, 706-711 (1992).
29. M. B. Kakade, S. Ramanathan, and P. V. Ravindran “Yttrium aluminum garnet powders by nitrate decomposition and nitrate-urea solution combustion reactions-a comparative study,” J. Alloys Compd., 350, 123-129 (2003).
30. H. Wang, L. Gao, and K. Niihara, “Synthesis of nanoscaled yttrium aluminum garnet powder by the co-precipitation method,” Mater. Sci. Eng., A 288, 1-4 (2000).
31. D. R. Messier and G. E. Gazza “Synthesis of MgAl2O4 and Y3Al5O12 by thermal decomposition of hydrated nitrate mixtures,” Am. Ceram. Soc. Bull., 51, 692-697 (1972).
32. R. W. Balluffi, S. M. Allen, W. C. Carter, “Kinetics of materials,” John Wiley-Interscience, Hoboken, N. J. (2005).
33. A. Putnis, Introduction to mineral science, Cambrige University Press, (1992).
34. C. H. Bamford, and C. F. H. Tipper, Reaction in the solid-state, comprehensive chemical kinetics, Vol. 22, Else. Sci. Pub. Co., New York, (1980).
35. T. Ozawa, “Kinetic analysis of derivative curve in thermal analysis,” J. Thermal Anal., 2, 301 (1970).
36. H. G. Wang, H. Herman, and X. Liu, “Activation energy for crystal growth using isothermal and continuous heating processes,” J. Mater. Sci., 25, 2339-2343 (1990).
37. J. R. Lo, and T. Y. Tseng, “Phase development and activation energy of the Y2O3-Al2O3 system by a modified sol-gel progress,” Mater. Chem. Phys., 56, 56-62 (1998).
38. D. Y. Chen, E. H. Jordan, and M. Gell, “Sol-gel combustion synthesis of nanocrystalline YAG powder from metal-organic precursors,” J. Am. Ceram. Soc., 91, 2579-2762 (2008).
39. J. G. Hou, R. V. Kumar, Y. F. Ou, and Dalibor Krsmanovi, “Crystallization kinetics and densification of YAG nanoparticles from various chelating agents,” Mater. Res. Bull., 44, 1786-1791 (2009).
40. 劉文貴，(Na0.5K0.5)NbO3 - SrZrO3 系統之合成、分析、及介電性質，國立成功大學資源工程研究所碩士論文，民國 94 年。
41. 歐建志，(Ba(1-x)Srx)5Nb4O15 陶瓷材料的結構與微波介電性質，國立成功大學資源工程研究所碩士論文，民國 94 年。
42. 黃恩萍，角閃石類礦物之拉曼光譜研究，國立成功大學地球科學研究所碩士論文，民國 92 年。
43. H. S. Yoo, H. S. Jang, W. B. Im, J. H. Kang, and D. Y. Jeon, “Synthesis and size control of monodisperse spherical Y2O3:Eu3+ phosphor and its photo- luminescence properties,” J. Mater. Res., 22, 2017-2024 (2007).
44. K. Ohno, and T. Abe, “Bright green phosphor Y3Al5-yGaxO12:Tb for projection CRT,” J Electrochem. Soc., 134, 2072-2076 (1987).
45. M. Gervais, S. L. Floch, N. Gauthier, D. Massiot, and J. P. Coutures, “Crystallization of Y3Al5O12 garnet from deep undercooled melt effect of the Al-Ga substitution,” Mater.Sci. Eng., B45, 108-113 (1997).
46. A. S. Gandhi, and C. G. Levi, “Phase selection in precursor-derived yttrium aluminum garnet and related Al2O3-Y2O3 compositions,” J. Mater. Res., 20, 1017-1025 (2005).
47. X. Li, J. G. Li, Z. Xiu, D. Huo, and X. Sun, “Transparent Nd:YAG ceramics fabricated using nanosized -alumina and yttria powders,” J. Am. Ceram. Soc., 92, 241–244 (2009).
48. J. G. Li, X. Li, X. Sun, T. Ikegami, T. Ishigaki, “Uniform Colloidal Spheres for (Y1-xGdx)2O3 (x= 0–1):Formation Mechanism,Compositional Impacts,and Physico chemical Properties of the Oxides,” Chem.Mater., 20, 2274–2281 (2008).
49. A. Pillonnet, C. Garapon, C. Champeaux, C. Bovier, H. Jaffrezic, and J. Mugnier, “Fluorescence of Cr3+ doped alumina optical waveguides prepared by pulsed laser deposition and sol-gel method,” J. Lumin., 87-89, 1087-1089 (2000).
50. M. S. Tsai, W. C. Fu, W. C. Wu, C. H. Chen, and C. H. Yang, “Effect of the aluminum source on the formation of yttrium aluminum garnet (YAG) powder via solid state reaction,” J. Alloys Compd., 455, 461-464 (2008).