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    Title: 與BaFe2As2鐵基超導體有關之化合物的電子結構
    Electronic structures of compounds related to iron-based superconductor BaFe2As2
    Authors: 王瑞騰
    Contributors: 楊志開
    王瑞騰
    Keywords: 第一原理
    Date: 2011
    Issue Date: 2012-10-30 11:28:43 (UTC+8)
    Abstract: 探討近年來研究高溫超導材料的趨勢,除了傳統的銅氧化物超導體,鐵基超導(Iron-based superconductors)材料為探討的新方向,更高臨界溫度材料也不斷被發現。而鐵基超導始終尚未有一個完美的實際理論運作機制可以解釋,而不同材料的臨界溫度Tc在特定外加壓力或參雜時均會有增加的現象,故鐵基超導的研究領域實為廣闊。
    除了可利用實驗分析外,本論文利用第一原理計算軟體Vasp,亦可運用計算分析電子特性。研究分析內容分成三個部分︰
    第一部分探討基本的鐵基超導材料FeS、FeTe、FeSe的電子性質,如態密度、能帶結構及費米面。同結構的FeS、FeTe、FeSe有共通的特性,三種材料的態密度極為相似,其中Fe的d軌域貢獻在費米能量之上約在-2eV到2eV之間,而Se、Te及S的p軌域主要貢獻在費米能量之下,三種材料的費米面也極為相似。第一部分另探討√2×√2 AFMⅡ結構的FeSe,在0至120kB的外加壓力下晶格常數的趨勢變化,發現在70kB至80kB時,會有晶格常數Z軸長度小於X、Y長度的情況。
    第二部分探討在BaFe_2 As_2 晶格中,以參雜不同濃度的Ru以取代Fe, ( 即Ba(Fe1-xRux)2As2 ) 的電子性質。考慮不同Ru參雜濃度X = 0.125與0.25,及不同Fe及Ru的磁性方向排列,詳盡的探討Ru削弱Fe的實際運作,考慮是否因為電荷轉移而造成Fe磁性削弱的現象,並判斷哪一種參雜結構最為為穩定。
    第三部分探討在BaFe_2 As_2 晶格中,考慮同時以Ru取代Fe及以P取代As的參雜情況,( 即Ba(Fe1-xRux)2(As1-yPy)2 ),藉由不同Ru參雜濃度X = 0.125、0.25及Y = 0.125、0.25。Ru取代Fe及P取代As,以第一原理計算探討電子性質,可以發現與Fe連結的P,亦有削弱磁性的現象。
    In recent years, besides the traditional copper oxide superconductors, Iron-based superconductors and higher critical temperature materials have become a new trend in research of high Tc superconductors . As the traditional copper oxide superconductors are still lacking a perfect theorem to explain how they work, and the higher critical temperature materials in different outer pressures or in the situation of doping have the problem of Tc increase, the research of Iron-based superconductors is therefore considered to be more potential.
    Instead of experimental analysis, this thesis applies the first principle calculation software – Vasp to analyze the electron properties. The main discussions are broken down into three significant parts with conclusions as follows:
    Part I is the discussion on the electron properties of FeS, FeSe and FeTe, such as density of state, band structure and Fermi Surface, and the change of the lattice constant of FeSe.
    Part II is the discussion on the doping effect. I choose Ba(Fe1-xRux)2As2 , that is, we substitute Ru for Fe by different X. By considering different types of spin polarize and different places where Ru doped in Ba(Fe1-xRux)2As2 crystal. The doping of Ru shows a property of the suppression of the magnetic moment. Ru atoms like to remain nonmagnetic in this structure. We consider two circumstances, X = 0.125 and X = 0.25. By using the first principle calculation method, we are trying to figure out how the suppression works.
    Part III--- we consider Ba(Fe1-xRux)2(As1-yPy)2 . By replacing Ru and P at the same time, we find that the P substations also decrease the magnetic moment of the nearest iron atoms. We consider X = 0.125 and 0.25,Y = 0.125 and 0.25.
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    [17] R. G. Parr, and W. Yang,“Density-Functional Theory of Atoms and Molecules”,by Oxford University Press(1989).
    Description: 碩士
    國立政治大學
    應用物理研究所
    99755016
    100
    Source URI: http://thesis.lib.nccu.edu.tw/record/#G0099755016
    Data Type: thesis
    Appears in Collections:[應用物理研究所 ] 學位論文

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