釔鐵柘榴石與雜質的添加對於以LHPG法生長晶纖之研究

毛之成(Tze-Chern Mao)

指導教授 ： 陳志臣

國立中央大學/工學院/機械工程學系/博士(2006年)

摘要

釔鐵柘榴石材料因具有磁光法拉第旋轉特性及於近紅外光範圍有優異的穿透性，故在磁光元件上被廣泛的應用著。然而，因YIG屬於非共熔材料且其浮熔區會有非穩態性的振盪，故欲生長高品質晶體相當不易。本文以雷射加熱提拉法對YIG的晶纖生長機制作為探討，發現當其熔區成分在含鐵量高過78 mole %時可直接提拉出YIG晶纖，但若低於此含量則熔區會藉由自我調適行為，以YFeO3相的凝固與氧化鐵的排入熔區，進行改變熔區的成分改變至超過78 mole %含鐵量之後，因此時的凝固相轉為YIG，而供料也為YIG，故可達到一平衡狀況，穩定生長YIG晶纖。另外，對於雷射加熱提拉法(Laser Heating Pedstal Growth, LHPG)的方法也可採用緻密化的熔媒晶種與二階段拉晶方式可生長出特定方向的晶纖，使其長出的晶纖於應用上更為的便利。
另外，隨著新型態的設計與發展，提升YIG的磁光法拉第旋轉量可藉由摻雜的方式達成，所以在本文中，CeO2被添加至YIG材料中，企圖生長優異的Ce：YIG晶纖。然而為了生長出此成分的高品質晶纖，影響浮熔區法生長的晶纖品質的最重要兩個因素：材料棒的製成與晶纖生長時的拉速，需被逐一檢視與探討。就以固態陶瓷燒結的實驗中發現，添加CeO2後的YIG陶瓷，其燒結溫度可視其添加量適度的降低燒結溫度即可完成高緻密的陶瓷，而陶瓷的成分、微結構與磁性表現則也會因不同的添加量而有不同程度的變化。對於Ce：YIG晶纖的生長，拉晶的速度則必須視添加量的增加而逐漸減緩，主要是因為受到組成過冷的影響所致，若生長速度未適度的調降，則生長出的晶纖會較未添加的晶纖容易生成胞狀組織，並且也因為熱張力對流的影響，溶質將聚集於生長介面的中心處，導致長出胞狀組織的晶纖，在中心部分之胞狀組織也會比周圍的部分發展的更為完整。

關鍵字

釔鐵柘榴石

並列摘要

Yttrium iron garnet (Y3Fe5O12, YIG) single crystal is widely used in magneto-optical applications in fiber-optical communication systems and magnetic field sensors, both because of its large Faraday rotation and because it is highly transparent in the near-infrared region.?However, growing YIG single-crystals is difficult because of the incongruent melting of the compound and the unsteady oscillatory molten zone. In this study, YIG single-crystal fibers were grown by LHPG method. Based on the experimental results show that YIG single-crystal fibers could be directly grown at the stable freezing interface when the melt had a composition of 78 ~ 87 mole % Fe2O3. When the seed’s Fe2O3 concentration was below 78 mole %, the YFeO3 would crystallize out until the composition of the melt increased along the liquidus curve until it needed a concentration of 78 mole % Fe2O3 or higher, whereupon YIG started to crystallize from the liquid. In addition, YIG single-crystal fibers with the desired crystallographic orientation could only be obtained using a two-pass method.
CeO2 was added into YIG materials to increase the quantitative Faraday rotation of YIG. With the floating zone method, there were two essential conditions for growing a single crystal fiber of YIG: the degree of sintering of the feed rod and the growth rate. From our study, it can be seen that Ce:YIG ceramic with the necessary densification could be fabricated using a lower sintering temperature than that required for pure YIG ceramic. Moreover, the greater the amount of CeO2 added, the slower the pulling rate needed to grow good quality single crystal fibers. When a faster pulling rate is used to grow Ce:YIG material, a more significant amount of foreign phase and cellular structures will form in the core region than in the peripheral region of the grown crystal fibers.

並列關鍵字

YIG

參考文獻

[1] X. W. Zhang, S. Y. Zhang and G. R. Han, “Growth and characterization of magneto-optical single-crystal ReYbBiIG with temperature-stabilized Faraday rotation”, J. Magn. Magn. Mater., Vol. 246, pp. 67-72 (2002).

[2] M. Kurimoto, S. Matsubayashi, K. Ando, T. Saito and T. Tsushima, “Temperature dependence of the Faraday effect in Rh4+-substituted magnetic garnets”, J. Appl. Physi., Vol. 83, pp. 4897-4901 (1998).

[3] K. Shinagawa, E. Tobita, T. Saito and T. Tsushima, “Faraday effect in(Pb2+, Th4+)-substituted magnetic garnets”, J. Magn. Magn. Mater., Vol. 171-181, pp. 251-252 (1998).

[4] M. N. Deeter, S. Milian, G. W. Day, G. Diercks and S. Samuelson, “Novel bulk iron garnets for magneto-optic magnetic field sensing”, IEEE Trans. Magn., Vol. 30, pp. 4464-4466 (1994).

[5] T. Sekijima, H. Kishimoto, T. Fujii, K. Wakino and M. Okata, “Magnetic, optical and microwave properties of rare-earth-substituted fiberous yttrium iron garnet single crystals grown by floating zone method”, Jpn. J. Appl. Phys., Vol. 38, pp.5874 (1999).