臺灣博碩士論文加值系統

在多晶銣鎢氧化物Rb0.23WOy(2.9＜y＜3.05)系統中，經由先前的研究得知氧含量對其正常態電阻及超導轉變溫度都有影響。由正常態的電阻率溫度對溫度關係圖中發現在氧含量3.0附近存在金屬-非金屬轉變，氧含量較少的樣品(y≦3.0)傳輸性質為金屬性，氧含量較多的樣品( y＞3.0)則為非金屬性，而且此轉變也會讓樣品電阻率大幅改變。藉由霍爾效應的量測可以發現在金屬-非金屬轉變時會伴隨傳導載子性質的改變(電子-電洞)，另外也說明氧含量較多的樣品其電阻率的增加是由於傳輸載子減少的關係。藉由X-ray的GSAS精算以及第一原理計算的結果，我們認為在氧含量較多的樣品中，多餘的氧是佔據銣的空缺位置，致使在傳輸性質中扮演重要角色的鎢氧八面體產生些微的扭曲。經由W L3-edge X光吸收光譜的測量，這個扭曲的現象會造成W-O鍵結變弱，使可移動的載子數量減少，這結果與霍爾量測相吻合。此外，鎢氧八面體的些微扭曲也會影響樣品中電子-聲子的交互作用，使超導性質出現改變。藉由氧含量的改變會使樣品有三個區域出現，分別為超導抑制區(Tc＜2 K)、較低區(Tc∼3 K)以及較高區(Tc＞3 K)。在氧含量對樣品超導態的影響這一部份，我們作了低溫比熱的量測，藉由比熱的數據可以發現當溫度低於超導轉變溫度時，樣品似乎並不是全部都變成超導態，可能存在著非超導性的電荷密度波。

Superconducting transition temperature Tc and normal-state resistivity as a function of oxygen content for hexagonal tungsten bronze Rb0.23WOy with 2.90 < y < 3.05 were obtained from transport measurements. It is remarkably interesting that Tc enhances about 50% and room-temperature resistivity increases about three orders of magnitude as oxygen content varies from 2.90 to 3.05. The low-temperature specific heat data indicate that the Einstein-like mode associated with Rb vibration has a dimensionality crossover from 3D to quasi-2D as oxygen content increases from 2.90 to 3.04﹐and show that the superconducting state is not condensed in some part of the sample.The Hall effect measurement indicate that the change of the transport charge occur in the vicinity of y = 3.00(electron-hole transition ) and the room-temperature resistivity increasing induced by the decreasing in transport charge. W L3-edge x-ray absorption spectra further show that W-O bond intensity gradually weakens as oxygen content increases, indicative of more oxygen disorder present in the oxygen-rich samples. The observed results strongly suggest that the local lattice distortion induced by oxygen disorder not only modulates Rb vibration, possibly coupled to electron-phonon interaction responsible for superconductivity, and also reduces the charge transfer between O 2p and W 5d orbital in the vicinity of y =3.00. This scenario can possibly account for significant increases of Tc and normal-state resistivity of Rb0.23WOy as
oxygen content slightly changes from 2.90 to 3.05.

致謝　………………………………………………………………　i
中文摘要　…………………………………………………………　iii
英文摘要　…………………………………………………………　iv
目錄　………………………………………………………………　vi
圖目錄　……………………………………………………………　ix
表目錄　…………………………………………………………　xiv
第一章　緒論 …………………………………………………　1
　 1-1　嵌入鹼金族元素的鎢氧化物回顧………………………　1
　　1-2 六角晶格銣鎢氧化物……………………………………　7
　　1-3 研究動機 ………………………………………………　12
1-3 論文架構 ………………………………………………　15
第二章　理論基礎　………………………………………………　16
　　2-1 BCS微觀理論……………………………………………　16　　
2-2 比熱基本理論…………………………………………… 20
　　　　2-2-1　比熱簡介　………………………………………　20
2-2-2　晶格比熱簡述　…………………………………　21
2-2-3　電子比熱簡述　…………………………………　23
　　2-3 電荷密度波(Charge Density Wave) ………………… 25
2-4 霍爾效應(Hall effect) ……………………………… 30
　　2-5 席貝克效應(Seebeck effect)……………………………… 34
　 2-6 X光吸收光譜簡介……………………………………… 36
　　　　2-6-1　吸收邊緣與E0值　………………………………　38
2-6-2　X光吸收近邊緣結構　…………………………　39
2-6-3　延伸X光吸收精細結構　………………………　40
2-7 局域密度近似(LDA+U) ………………………………… 44
第三章　樣品製備　………………………………………………　46
第四章　實驗裝置與測量系統　…………………………………　48
　　4-1　X-ray繞射儀　…………………………………………　48
4-1-1　X-ray基本原理簡介　……………………………　48
　　　　4-1-2　X-ray繞射儀實驗　………………………………　48
4-1-3　GSAS晶算法　…………………………………　49
4-2　高溫爐　…………………………………………………　51
　　4-3　低溫電阻量測系統　……………………………………　52
　　　　4-3-1　低溫電阻量測系統簡介　………………………　52
　　　　4-3-2　低溫電阻量測部分　……………………………　57
4-4　低溫比熱量測系統　……………………………………　60
　　　　4-4-1　比熱實驗原理　…………………………………　60
　　　　4-4-2　比熱儀器介紹　…………………………………　63
4-4-3　低溫He3系統降溫程序　………………………　68

　4-5　物理性質量測系統PPMS　……………………………　70
　　　　4-5-1　氣壓控制　………………………………………　70
　　　　4-5-2　液態氦容量測量　………………………………　71
4-5-3　磁場控制　……………………………………　73
4-6　振動樣品磁性量測儀　………………………………　76
4-6-1　操作原理　……………………………………　76
4-6-2　零件介紹　……………………………………　78
4-6-3　將樣品對到線圈對的中心　……………………　85
4-7霍爾量測(Hall Effect)　………………………………　87
第五章　結果與討論　…………………………………………　90
　　5-1　 Rb0.23WOy結構分析　…………………………………　90
　　5-2　 樣品之電性分析　……………………………………　101
　　5-3　 X光吸收光譜與第一原理計算　………………… 　108
　　5-4　 Rb0.23WOy超導特性　………………………………… 114
第六章　結論　……………………………………………………　120
參考文獻　…………………………………………………………　122


【圖1-1】 (a)NaxWO3超導臨界溫度對Na濃度之關係圖(b)KxWO3 、RbxWO3 、CsxWO3超導臨界溫度對K、Rb、Cs濃度之關係圖………………………………………………………　4
【圖1-2】不同鈉含量對費米能量附近佔據態的改變………………　5
【圖1-3】改變鉀以及銣含量，對KxWO3 、RbxWO3正常態電阻率異
常隆起溫度關係圖………………………………………5
【圖1-4】 (a) RbXWO3不同Rb濃度的電阻率對溫度之關係圖
(b)圖(a)中的TB對Rb濃度x之關係圖…………………　10
【圖1-5】RbXWO3超導臨界溫度對Rb濃度之關係圖……………　11
【圖1-6】RbXWOy在x = 0.19,0.23,0.27之超導臨界溫度對氧含量的關係圖………………………………………………………　13
【圖1-7】圖(a)為Brusetti所得結果，而圖(b)為我們變動氧含量所得的
結果…………………………………………………　14
【圖1-8】RbXWOy在x = 0.19,0.23,0.27之X-ray對氧含量的關係，可以發現x = 0.23時純相區域最寬………………………　14
【圖2-1】錫的超導態電子比熱與溫度關係………………………… 19
【圖2-2】99.9999%純銅聲子比熱圖………………………………　21
【圖2-3】 電荷密度波樣品測量I-V曲線圖………………………　26
【圖2-4】電子配對示意圖 ……………………………………… 26
【圖2-5】(a) 一維的線性金屬系統於正常的狀態(b)皮爾斯(Peierls)
皮爾斯(Peierls)預測之一維線性金屬系統基態。……　27
【圖2-6】一般金屬與電荷密度波在電荷分佈上的比較…………… 27
【圖2-7】典型的電荷密度波材料結構圖。 ………………………　29
【圖2-8】傳導電子受磁力作用示意圖……………………………　 30
【圖2-9】傳導電子受到磁力與電力影響示意圖………………… 31
【圖2-10】傳導電洞受到磁力與電力影響示意圖 ………………　33
【圖2-11】 Seebeck效應示意圖 ………………………………… 35
【圖2-12】光子能量與典型物質吸收截面關係圖…………………　37
【圖2-13】XANES與EXAFS分界圖………………………………　42
【圖2-14】光電子平均自由路徑與能量關係圖……………………　42
【圖2-15】單一散射與多重散射之圖像……………………………　43
【圖2-16】射出電子受鄰近原子的背向散射而產生干涉現象……　43

【圖4-1】Gsas軟體圖 ……………………………………………　50
【圖4-2】溫度計接線示意圖 ……………………………………　52
【圖4-3】樣品量測桿示意圖 ……………………………………　54
【圖4-4】樣品裝置處示意圖　……………………………………　54
【圖4-5】液氦儲存桶內部構造示意圖　…………………………　55
【圖4-6】電阻量測系統線路概要配置圖　………………………　56
【圖4-7】樣品接上白金線示意圖 ………………………………　58
【圖4-8】等效電路圖　……………………………………………　59
【圖4-9】Sample holder示意圖　…………………………………　60
【圖4-10】熱流模型圖　……………………………………………　61
【圖4-11】比熱測試棒示意圖　……………………………………　64
【圖4-12】比熱量測系統線路簡圖　………………………………　65
【圖4-13】PPMS壓力控制閥門管路示意圖　……………………　70
【圖4-14】Sample Tube外觀示意圖　……………………………　72
【圖4-15】液態氦容量測量示意圖　………………………………　73
【圖4-16】PPMS磁場模式示意圖　………………………………　75
【圖4-17】VSM訊號傳遞示意圖　………………………………　77
【圖4-18】Coilset Puck外觀示意圖………………………………　78
【圖4-19】Coilset Puck內部構造圖 ……………………………　79
【圖4-20】Sample Tube外觀示意圖　 ……………………………　80
【圖4-21】VSM裝置到PPMS示意圖 …………………………　 81
【圖4-22】Linear Motor Transport外觀示意圖……………………　82
【圖4-23】Linear Motor Transport內部構造圖 …………………　82
【圖4-24】Sample Rod示意圖 ……………………………………　83
【圖4-25】Sample holder示意圖　…………………………………　84
【圖4-26】VSM touchdown模式示意圖　…………………………　86
【圖4-27】電性、霍爾效應基座圖　………………………………　87
【圖4-28】Hall effect接點示意圖　………………………………　88

【圖5-1】Rb0.27WO3之結構圖 …………………………………… 90
【圖5-2】室溫Rb0.27WO3之X-ray繞射圖 ……………………… 91
【圖5-3】Rb0.23WOy在y = 2.8∼3.07時X-ray對氧含量的關係 … 93
【圖5-4】Rb0.23WOy不同氧含量的GSAS擬合以及各項參數 … 94
【圖5-5】Rb0.23WOy在改變氧含量時a軸與c軸的改變 ……… 95
【圖5-6】WO6八面體示意圖 ……………………………………… 96
【圖5-7】隨氧含量改變W-O1、W-O2長度之改變 …………… 98
【圖5-8】 隨氧含量改變Rb-O1、Rb-O2長度之改變 ……………　98
【圖5-9】隨氧含量改變Rb-Rb長度、O2-W-O2夾角之改變 ……　99
【圖5-10】RbxWOy，鎢氧八面體的扭曲方式 ……………………　100
【圖5-11】計算Rb0.25WO3.0在不同能量時的態密度分佈 ………　103
【圖5-12】W-5dxz/yz與O-2p軌域交互作用　……………………　104
【圖5-13】Rb0.19WOy和Rb0.27WOy改變氧含量時電性之變化 …　104
【圖5-14】Rb0.23WOy改變氧含量時電性之變化…………………　105
【圖5-15】Rb0.23WOy改變氧含量時，載子濃度隨溫度的變化 …　106
【圖5-16】氧多與氧少樣品之seebeck coefficient ………………　107
【圖5-17】X光吸收光譜(a) O K-edge(b) O Kα-emission ………　110
【圖5-18】利用第一原理計算(a)Rb0.25WO3.0(b)Rb0.25WO3.083態密度分
佈 ………………………………………………… 111
【圖5-19】分別針對 (a)Rb0.25WO2.917及 (b) Rb0.25WO3.083分別計算其能帶結構 ………………………………………　112
【圖5-20】X光吸收光譜Rb K-edge …………………………… 113【圖5-21】W L3-edge延伸X 光吸收精細結構傅立葉轉換……… 113
【圖5-22】氧含量對Rb0.23WOy樣品超導轉折溫度的影響 …… 116
【圖5-23】零場下Rb0.23WO2.90的比熱量測……………………… 117
【圖5-24】零場下Rb0.23WO3.0的比熱量測………………………… 118
【圖5-25】零場下Rb0.23WO3.02的比熱量測 …………………… 119


【表1-1】各種鎢氧化物之結構與超導臨度…………………………　6
【表4-1】溫度計誤差值 …………………………………………　53
【表4-2】低溫比熱儀器列表　……………………………………　67
【表5-1】改變銣含量對各離子間鍵長鍵角的影響 ………………　99

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