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    Title: 氮化鈮微米晶體的相與超導性研究
    Phase and superconductivity studies of micro-sized niobium nitride
    Authors: 李彥濬
    Li, Yen-Jun
    Contributors: 陳洋元
    Chen, Yang-Yuan
    李彥濬
    Li, Yen-Jun
    Keywords: 氮化鈮
    超導

    微米晶體
    Date: 2018
    Issue Date: 2018-08-06 18:13:33 (UTC+8)
    Abstract: 氮化鈮是一種低壓縮性與高硬度的材料,它擁有多種不同的相結構,包括立方晶系的δ- Cubic相、四方晶系的tetragonal相與六方晶系的δ’- hexagonal相和ε- hexagonal相。在我的研究中,探討每個相所存在的超導性質。其中,立方晶系δ-相的粉末樣品是從Alfa Aesar這間公司購得,藉由攝氏一千四百度的退火過程得到的產物。而此立方晶系δ-相的粉末樣品再藉由X光繞射分析儀的數據得知,晶格常數為4.385 Å。藉由電阻、磁化率的量測可以知道立方晶系δ-相的超導溫度為13.4K,這與文獻上描述超導溫度是晶格常數的方程式是一致的。另一批樣品是由Goodfellow這間公司所買來的粉末所製備,經由熱處理希望得到ε- hexagonal的純相。Zou et. al.他們這團隊在一篇文獻上描述到氮化鈮有兩個超導臨界溫度,分別為立方晶系δ-Cubic相的17.1K與六方晶系ε-hexagonal相的10.1K。為了要驗證ε- hexagonal是否擁有超導特性,我們從未經過熱處理的Goodfellow粉末中挑選出顆粒,進行拋光後,利用EBSD量測其結構,結果顯示ε-hexagonal結構。並對它進行電阻的量測,在電阻對溫度的關係中,呈現出的是金屬性的行為,並且在量測到最低溫2 K時,依然沒有出現超導的特徵。
    經過熱處理的Alfa Aesar粉末首先壓成塊狀,並且量測它的比熱行為。觀測到的超導轉變溫度Tc 13 K。根據BCS理論的計算,超導體電子比熱部分ΔC/γTc值是1.43,而我們的計算結果為0.82,結果指出並不是常規的超導性質。接著將樣品量測不同溫度底下的磁化率隨磁場變化,並計算出Hc1是185 Oe;不同磁場底下的電阻隨溫度變化,並計算出Hc2是19.22 T。最後從這批粉末中挑出塊才樣品,經過拋光後量測EBSD的結果為δ- cubic,經過電阻量測後,顯示出超導行為超導轉變溫度Tc 13 K,並且量測計算出Hc2是21.3 T,結果與壓成塊狀的C(T)以及R(T)一致。
    Niobium nitride is a low compressibility and high hardness material. It has many phases structures, including cubic δ-NbN, ε-hexagonal, δ’-hexagonal and tetragonal. In this work, we investigate the appearance of superconductivity of each NbN phase. Pure cubic δ-NbN specimens were prepared by annealing 1400 oC from NbN powder of Alfa Aesar. The lattice constant of this specimen was determined to be 4.385 Å by powder X-ray diffraction (XRD) measurement. Superconductivity of Cubic δ-NbN phase was revealed at 13.4 K by the measurements of resistivity magnetic susceptibility and heat capacity of pressed powders. It is consistent with previous reports that Tc is a function of lattice constant. Zou et. al. reported that two superconducting temperatures of 17.1 K and 10.1 K appear in the powder of Goodfellow, they claimed 17.1 K is of cubic phase and 10.1 K is of ε-hexagonal phase. We also observed two Tc from the powder of Goodfellow, based on X-ray and magnetic data the Tc =17.1 K is defined from cubic phase, but the phase of Tc =10.1 K is hardly fitted to the ε-hexagonal phase. In order to check whether ε-hexagonal phase have superconductivity or not, a sub-micron particles of single crystal was selected from the powder of Goodfellow, the ε-hexagonal phase of the particle is revealed by the measurements of EBSD (Electron Back Scattering Diffraction). The resistivity measurement of the sub-micro crystal shows no superconductivity as temperature down to 2 K.
    We also measured the specific heat of cubic NbN from pressed powder of Alfa Aesar. The superconductivity transition temperature Tc =11 K was observed. The electronic part of specific heat, ΔC/γTc is equal to 0.83 which is lower than BCS value, 1.43, indicating an unusual superconductivity. The critical field of superconductivity Hc1 obtained from the magnetic field dependent magnetization is 185 Oe. The Hc2 obtained from magneto resistivity data is 19.22 T. A sub-micron size δ-cubic crystal successfully selected from Alfa Aesar powder was confirmed by EBSD, Tc=13 K and Hc2 =21.3 T were obtained from resistivity measurements, the results are in consistent with that obtained from χ(T) and R(T) of the pressed powder specimen.
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    Description: 碩士
    國立政治大學
    應用物理研究所
    105755001
    Source URI: http://thesis.lib.nccu.edu.tw/record/#G0105755001
    Data Type: thesis
    DOI: 10.6814/THE.NCCU.AP.002.2018.B04
    Appears in Collections:[應用物理研究所 ] 學位論文

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