鐵基材料(鐵硒)之結構分析與超導性之研究

The Crystal Structures and Superconducting Behavior in Iron-Based (FeSe) Materials.

莊祿銘(Lu-Ming Jhuang)

中原大學/理學院/物理研究所/碩士(2011年)

https://doi.org/10.6840/cycu201101127

摘要

原本認為以磁性元素為主體的超導體是不存在的，但是已發現鐵在壓力為15-30 GPa時可形成超導體、其超導臨界溫度Tc約為2K左右，之後並發現了參雜砷(As)和硒(Se)的鐵基高溫超導體。因為高溫超導的傳輸機制還不完全清楚，所以希望藉由此類高溫超導材料來進一步瞭解高溫超導的物理機制，因此本論文主要是探討鐵基材料(FeSe)之超導特性與其結構之間的關係。
我們的鐵基材料(FeSe)是用固態燒結法所燒製而成的，可以得到Tetragonal FeSe相和一些副產物，在某些樣品中可得到在溫度為15K左右時電阻率有急遽下降的趨勢，其中A1樣品(成分含86%的Tetragonal FeSe相)之電阻率量測可觀察到其Tc約為7.5K，而在六個月後量測其電阻率的結果還是維持一樣。對所有樣品的磁化率作量測，只有A1樣品在Tc附近有出現磁性變化。
目前認為高溫超導體的傳輸機制主要與銅氧平面層有關、無法以電子-聲子散射之BCS理論描述，其電阻率在超過室溫時並不會飽和，因此一般高溫超導並無法使用基於電子-聲子散射理論的Bloch – Grüneisen公式來描述超導臨界溫度以上的電阻率變化。我們對樣品電阻率以 Bloch - Grüneisen公式擬合得出Debye temperature 和Debye frequency。此結果與銅氧化物高溫超導體有所不同。

關鍵字

傳輸性質 ； 硒化鐵 ； 鐵基超導體 ； 超導體

並列摘要

Superconductors with magnetic elements were not been considered to be existent initially, but irons was found the superconducting state under pressure of 15-30 GPa and the Tc is about 2K. After that, Iron-Based superconductors doped with arsenic(As) and selenium(Se) were found to be as High-Tc superconductors; Since the superconducting mechanism of the High-Tc superconductors has not been clear so far, we study the intrinsic property of Iron-Based materials for more understanding the mechanisms of High-Tc superconductivity.
The topic of this thesis focuses on investigating the relationship between the superconducting properties and the structure of the Iron-Based material. Iron-Based materials (FeSe) were fabricated by solid state reaction method. We obtained the Tetragonal FeSe phase with some impurities phase mixed by using this method. Some of the samples we made show rapidly dropping tendency around 15K in the resistivity measurement. Al sample with Tetragonal FeSe phase (86%) was observed a Tc around 7.5 K and the similar result of resistivity behavior have been observed in A1 sample even after 6 months. We have also measured the magnetic susceptibility for all sample and only Al sample indicates the transition behavior as approach the Tc.
At present, the superconducing mechanism of the High-Tc superconductors is dominated from the electron transport property of the copper oxide layer and cannot be described by the electron-phonon scattering mechanism of BCS theory. Because the resistivity behavior of the High-Tc superconductor does not saturate at room temperature, therefore High-Tc superconductors cannot be described by the Bloch-Grüneisen formula in the electron-phonon scattering theory. We fitted the Bloch-Grüneisen formula to the resistivity measurements of our samples to obtained the Debye temperature and Debye frequency. We found the resistivity behavior above Tc that can be described by Bloch-Grüneisen formula. This result is different from the High-Tc cuprate superconductor.

並列關鍵字

FeSe ； transport properties ； superconductor ； iron-based superconductor

參考文獻

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