摘 要
RE-Ba-Cu-O(RE=Sm,Nd..)高溫超導體因其特殊的peak effect效應，隨著外加磁場增加、呈現出較YBCO材料較佳的臨界電流密度(Jc)，對於許多高磁場下的應用有著極大的發展潛力。
由於超導塊材所能擄獲的磁場強度正比於其Jc性質，而Jc性質與樣品中的釘扎中心種類及數量有關。因此在提升Jc的同時，瞭解釘扎機制與微結構間的關連性是相當重要的。
本實驗室目前已能利用MgO單晶為晶種，以冷接種方式進行熔融製程，成長直徑約2公分的Sm-Ba-Cu-O單晶粒超導塊材。為進一步提升Sm-Ba-Cu-O單晶粒超導塊材之超導性能，以提高其應用性，採用不同的方式以增加樣品中的有效釘扎中心數量：1. 於起始粉末中添加不同種類的添加物，包含m等級的Pd、Pt、CeO2；2. 奈米等級的Y2O3、Al2O3、SiO2、及利用溶膠-凝膠法合成之Sm2BaCuO5(Sm211)及Nd4Ba2Cu2O10(Nd422)相之奈米粉體；此外，為提高起始成分中的Ba/Cu比，以Sm210相取代起使粉末中的Sm211相。希望經由以上不同的添加方式，改變樣品中非超導相(Sm2BaCuO5)顆粒粒徑大小，並引入奈米級釘扎中心，以期對Jc性質有正面的助益，並由微觀結構分析討論可能的釘扎作用機制。
在添加m等級添加物方面的結果顯示，除Pd外，Pt及CeO2均可有效細化樣品中211顆粒，而使其Jc提高。但Pd會使211顆粒形狀轉變為矩形，而在211曲率較大處產生較高密度之缺陷。同時添加兩種不同添加物(Pd/Pt、Pd/CeO2、Pt/CeO2)可進一步細化211顆粒，增加有效釘扎中心數目，而進一步提高SmBCO (Sm-Ba-Cu-O)樣品之Jc。
在添加奈米級添加物方面，根據其與基地相的反應可分為三類：1. 不產生反應，維持顆粒狀，如Y2O3；2. 與基地相反應生成成分差異區，如Sm211及Nd422；3. 與基地相作用，導致樣品超導性質變差，如Al2O3及SiO2。
而奈米級Sm211的添加則在基地相中產生微小的成分差異區，此區域是於包晶反應過程中形成，並成為 pinning center，而使樣品於高磁場下之Jc提高，同時釘扎機制轉變為normal pinning 與 pinning同時作用。而添加奈米級Nd422的機制與奈米級Sm211相同，且因晶格扭曲的作用，對Jc的提升作用更加明顯。
在起始粉末的成分方面，將起始成分中之Sm211換為Sm210，確實可抑制Sm-Ba的固溶度，使樣品的Tc獲得改善。本研究同時在Sm210系統中添加Pd、Pt、Pd/Pt、Pt/CeO2等m等級添加物，以進一步提升其超導性質。結果與Sm211系統相同，均可經由細化211顆粒使樣品的超導性質改善。但在Sm210系統中添加奈米級Sm211的結果則不同於Sm211系統。
在釘扎機制分析結果方面，添加m等級添加物的樣品主要釘扎機制與未添加樣品相同，仍為由晶格缺陷及非超導相界所提供之normal pinning。而添加奈米級顆粒以及使用210為起使粉末的樣品則為 pinning，此部分樣品於高磁場下所提升的Jc特別明顯。
最後，本研究以R-T方式檢驗樣品於不同磁場下之電阻變化，發現釘扎機制為 pinning center的樣品，包含Sm210、添加奈米級Sm211以及添加奈米級Nd422之樣品中確實存在有另一較弱之超導相，而釘扎機制為normal pinning 的樣品，包含標準樣品（Sm123+Sm211，未添加）及添加Pt/CeO2之樣品則只有一個主要的超導相。此外，樣品中非超導相與超導相間的差異性及作用的磁場範圍會影響到樣品之Jc-H表現。
目前結果顯示，於Sm210系統中同時添加奈米級Sm211及Pt/CeO2可得到極佳之Jc (77K, 0T時為3.6104A/cm2；2T時為1.8104A/cm2)，此結果為目前SmBCO系統之最高值。

Abstract
REBCO high temperature superconductors have significant potential for high field engineering applications due to their inherent peak effect which exhibit high Jc values in a high magnetic field.
The magnitude of trapped field within bulk superconductors is proportional to the critical current density. In addition, Jc is related to both the type and number of pinning centers in the superconductor. Therefore, the key to enhancing Jc is an understanding of the relation between the pinning mechanism and microstructure.
In this study, bulk SmBCO was melt-processed in air using the cold seeding technique with MgO single crystal as the seed. In order to increase the number of pinning centers, m-sized additives, ex. Pd、Pt、CeO2, and nm-sized Y2O3、Al2O3、SiO2、Sm2BaCuO5 (“Sm211”) and Nd4Ba2Cu2O (“Nd422”) were used. Also, Sm210 was used to increase the Ba/Cu ratio of the precursor powders.
The results show that except for the Pd-doped samples, Jc of SmBCO with m-sized additives was enhanced by refining the 211-particles. Notably, for the Pd-doped samples, the shape of the 211-particles changed to rectangular, and thus induced a higher density of defects in the 123/211 interface. It was also found that Jc could be further enhanced by the combined addition of two types of additives.
As for the nm-sized additions, it was shown that the reactions between different nano-scale additives and the matrix can be classified into three types: one dose not react with the Sm123 (Sm1Ba2Cu3Oy) matrix (e.g. Y2O3), one becomes a compositional fluctuation region (e.g. Sm211 and Y2O3), and the other reacts with the matrix, which results in the suppression of superconductivity (e.g. Al2O3 and SiO2).
As for the effect of Sm210 addition, the results indicate that the substitution of Sm-Ba was suppressed and thus Tc was enhanced. In order to further enhance Jc for samples with Sm210 addition, different types of additives were also used. The results for the m-sized additives were similar to the Sm211 samples, in which 211-particles were refined. But the effect of nm-sized additives on Jc in the Sm210 and Sm211 samples was different.
In this study, scaling analysis found that the pinning mechanism for samples with m-sized additives were similar to the un-doped samples, in which defects and 123/211 interfaces contributed to pinning. As for samples with nm-sized addition, in which Jc is superior in high field regions, the dominant pinning becomes a combination of  pinning and normal pinning.
Finally, the current transport behavior for samples with different pinning mechanisms was examined. The poorer superconducting phase was found in samples with  pinning centers, ex. Sm210, nm211 doped samples. As for the control and Pt/CeO2 doped samples, there was only one type of superconducting phase. In addition, it was also found that the difference between the main superconducting phase and the poorer superconducting phase results in various Jc-H behaviors.
Notably, the Jc value for samples with Sm210/Pt/CeO2/nmSm211 addition was 3.6104 A/cm2 at 77K at 0T, and 1.8104 A/cm2 at 77K at 2T. The above results were the highest values for SmBCO samples grown in air.

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