Influence of ionic mobility on the YAG transformation and investigation of the formation mechanism of hexagonal-YAP and YAG

• Main Authors: Meng-JungLi, 李孟蓉
• Other Authors: Yu-Chun Wu
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/62130031230533882009

碩士 === 國立成功大學 === 資源工程學系碩博士班 === 98 === 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.