臺灣博碩士論文加值系統

K2Fe4Se5具有鐵空缺，可以藉由不同的降溫方式，使得鐵空缺在呈現有序排列或者是無序排列。由於在K2Fe4Se5的系統中，鐵空缺的有序排列或無序排列會影響到其物理性質，藉由鐵空缺的排列來影響K2Fe4Se5的熱電性質。
在磁性的實驗結果中，750OC、800OC和850OC的磁化率差異最大。且從磁化率可以發現這三個樣品均有超導相的存在，只是比例的不同，這也是導致K2Fe4Se5的西貝克係數並不太大的原因。從X射線繞射圖形中可以得知利用淬火降溫的方式，可以使得鐵空缺呈現無序排列；利用自然降溫的方式，可以使得鐵空缺呈現有序排列。根據熱傳導率和電阻率的實驗結果，顯示了鐵空缺的無序排列可以降低熱傳導，也可以使得電阻率下降。
這意味著K2Fe4Se5可以透過鐵空缺的無序排列，降低熱傳導率和提升導電性，這樣可以有效地提升熱電優值係數10倍。如果能提升K2Fe4Se5的西貝克係數，K2Fe4Se5將會成為一個很好的熱電材料。

There exists iron vacancies in the K2Fe4Se5 compound, and the iron vacancy can be either in an ordering or disordering states depending on the processing conditions. In this study, we have three sets of samples, which were synthesized at temperature 750OC, 800OC and 850OC, respectively. Those samples prepared after directly quenching from high temperature exhibit different temperature dependent susceptibility. However, all three samples show superconducting characteristics in the susceptibility data with an onset temperature close to ~30K. Due to the presence of minor superconducting phase, these three K2Fe4Se5 samples have relatively low Seebeck coefficient.
The XRD pattern data can provide information regarding the order or disorder of the iron vacancy, which can be controlled by two different cooling methods. Quenching the sample directly from high temperature leads to the sample showing iron vacancy disorder. While cools the sample slowly to room temperature will lead to the ordered iron vacancies.
Detailed measurements on the thermal conductivity and resistivity show that the disorder of iron vacancy disorder will lead to the reduction in thermal conductivity and resistivity decrease. Even with the reduction in Seebeck coefficient we still observed the thermoelectric figure of merit of K2Fe4Se5 can be enhanced by about 10 times in the sample with iron vacancy disordered. If one can maintain the high Seebeck coefficient in disordered K2Fe4Se5, further enhancement in its Figure of Merit can then be achieved.

目錄
致謝--------------------------------------------------------------I
摘要------------------------------------------------------------III
Abstract---------------------------------------------------------V
目錄------------------------------------------------------------VII
圖目錄---------------------------------------------------------XIII
表目錄----------------------------------------------------------XXI
第一章 緒論------------------------------------------------------1
1-1 研究背景------------------------------------------------------1
1-2 研究動機------------------------------------------------------4
1-3 研究方向------------------------------------------------------5
第二章 基礎理論---------------------------------------------------7
2-1 熱傳導(Thermal Conductance)-----------------------------------7
2-1-1 電子對熱傳導的影響-------------------------------------------9
2-1-2 聲子對熱傳導的影響------------------------------------------10
2-2 熱電勢(Thermoelectric Power)---------------------------------14
2-2-1 西貝克效應(Seebeck Effect)---------------------------------14
2-2-2 西貝克係數(Seebeck Coefficient)----------------------------15
2-3 電阻率(Resistivity)------------------------------------------19
2-4 X光射線繞射(X-Ray Diffraction)-------------------------------21
2-5 磁性(Magnetic)-----------------------------------------------23
2-5-1 順磁性(paramagnetism)--------------------------------------24
2-5-2 逆磁性(Diamagnetism)---------------------------------------25
2-5-3 鐵磁性(Ferromagnetism)-------------------------------------26
2-5-4 反鐵磁性(Anti-ferromagnetism)------------------------------27
2-5-5 亞鐵磁性(Ferrimagnetism)-----------------------------------29
第三章 實驗方法--------------------------------------------------31
3-1 樣品製備-----------------------------------------------------31
3-1-1 製作樣品---------------------------------------------------31
3-1-2 製作量測樣品-----------------------------------------------33
3-2 量測系統-----------------------------------------------------37
3-2-1 樣品準備---------------------------------------------------37
3-2-2 TTO-熱傳導-------------------------------------------------39
3-2-3 TTO-西貝克係數---------------------------------------------40
3-2-4 TTO-電阻率-------------------------------------------------40
3-2-5 熱電優質係數-----------------------------------------------40
第四章 實驗結果與分析--------------------------------------------41
4-2 X射線繞射(X-Ray Diffraction)---------------------------------46
4-3 熱傳導率(Thermal conductivity)-------------------------------48
4-4 電阻率(Resistivity)------------------------------------------52
4-5 西貝克係數(Seebeck Coefficient)------------------------------55
4-6 熱電優值係數(Thermoelectric figure of merit)-----------------60
第五章 結論-----------------------------------------------------65
參考文獻---------------------------------------------------------67

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