由於近來網際網路的發達，促使具有寬頻特性的光纖通訊蓬勃發展，而其被動元件如光隔離器、光連結器和光纖耦合器等市場需求也日益增加，釔鐵柘榴石因具有磁性及磁光法拉第效應的特性，常使用在光隔離器上，阻止光在傳輸過程中，因反射干擾原光源，造成不穩定，或衰減入射光振幅，影響光纖傳輸品質。因此，釔鐵柘榴石晶體的生長相當具有研究價值。本實驗使用雷射加熱提拉法(LHPG, laser heated pedestal growth method)對釔鐵柘榴石(YIG, Y3Fe5O12)進行晶體生長實驗，此長晶法為浮區式(floating zone)長晶法的一種，主要是藉由表面張力支撐熔區，一般材料在熔區形成時，為一穩定的熔區，然而YIG在熔區形成的瞬間，熔區即開始產生上下振盪的情形，此種現象稱為非穩態振盪性熱張力對流，振盪性的熔區會導致晶體不易生長，因此欲長出YIG單晶，則須對其熔區流場加以研究，探討流場振盪的原因，並找出抑制其振盪的方法。然而欲觀察熔液振盪性熱張力對流的現象並不容易，因此分析振盪性熱張力對流所導致的熔區上下振盪對晶體生長界面型態(morphology)的影響，對於振盪性熱張力對流的探討有很大的助益；其它如長晶參數對晶體結構與組成分佈的關係，及使用不同配比之陶瓷棒生長YIG，探討非化學計量組成對長晶熔區液體物性的影響，及對固液界面之影響，皆對了解YIG晶體的生長機制有很大的幫助。另外，由於YIG為鐵磁性材料，因此本論文也針對不同長晶參數下所獲得的晶體進形磁性檢測，依據不同組成磁化值亦不同的原理分析材料組成與長晶參數的關係。 The growth of the yttrium iron garnet (YIG, Y3Fe5O12) crystals have been studied widely because of its magneto-optical properties, such as Faraday rotation applied to isolators. But due to its incongruent peritectic reaction and unsteady oscillatory molten zone, it is difficult to grow by float zone method. In this study, the laser heated pedestal growth (LHPG) was applied to growing stoichiometric YIG single crystal fibers. The effect of growth parameters on microstructures and compositions of YIG crystal fibers were investigated. In order to realize a virtual mechanism for growing stoichiometric YIG crystals using the LHPG method, various ratio off-stoichiometric YIG ceramics were used as feed and seed, and were grown at different conditions. In additions, the effect of the oscillatory thermocapillary convection on the morphology of growth interface is discussed. The magnetic properties of YIG crystals were measured in order to analyze the relationship between compositions and growth parameters. Finally, the crack analysis is helpful to obtain the maximum axial temperature gradient, under which the crack will be avoided. Through this study, we could obtain the high-quality YIG single crystal fibers by well controlling the growth parameters.
