Superconducting properties in hexagonal rubidium tungsten bronze RbxWO3+δ

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Title:	Superconducting properties in hexagonal rubidium tungsten bronze RbxWO3+δ
Other Titles:	銣鎢氧化物超導性質之研究
Authors:	丁立中;Ting, Li-chung
Contributors:	淡江大學物理學系博士班錢凡之;Chien, F. Z.
Keywords:	銣鎢氧化物;六角晶格;超導電性;金屬非金屬轉變;各向異性;Rubidium Tungsten Bronze;Hexagonal;superconductivity;Metal-Nonmetal Transition;Anisotropy
Date:	2007
Issue Date:	2010-01-11 02:15:45 (UTC+8)
Abstract:	在多晶材料銣鎢氧化物RbxWOy（0.19 < x < 0.33，2.9 < y < 3.05）系統中，隨著銣、氧含量的不同，其超導臨界溫度亦隨之變化。依其Tc-x,y相圖，可以界定出超導抑制區（Tc < 2 K）、Tc較低區（Tc ~ 3 K）以及Tc較高區（Tc > 3 K），而超導抑制區會隨著銣含量的增加而朝向氧多的方向位移。Tc較高區的超導上臨界場比Tc較低區大了一個數量級，而Tc較高區的超導渦旋維度為準二維、Tc較低區的超導渦旋維度為各向異性之三維。此外，銣鎢氧化物存在氧含量相依之金屬—非金屬轉變，當樣品氧含量小於3.00時，其傳輸性質呈現金屬性，而氧含量大於3.00時，則為非金屬性。此金屬—非金屬轉變與樣品之銣含量無關，因此應與其超導機制無密切關係。最後，不同氧含量的Rb0.23WOy單晶樣品已被成功製備出，而單晶樣品在氧氣中的退火處理可以驗證銣鎢氧化物氧含量與超導性質之間的定性關係。 The superconducting critical temperature Tc dependence of both rubidium and oxygen concentrations were identified for hexagonal rubidium tungsten bronze RbxWOy. Three regions corresponding to Tc < 2 K (superconductivity suppressed region), Tc ~ 3 K (lower Tc region) and Tc > 3 K (higher Tc region) were identified in Tc–x,y phase diagram for RbxWOy. The boundaries of the superconductivity suppressed regions shift toward high oxygen concentration as rubidium concentration increases. Two entirely different properties of superconductivity were observed for polycrystalline Rb0.23WOy with y = 2.90 and 3.02. The upper critical field Hc2 of higher Tc region samples is consistently one order of magnitude larger than that of lower Tc region samples. The vortex dimensionality of lower Tc region samples is anisotropic 3D and that of higher Tc region samples is quasi 2D in Tc-x,y phase diagram for RbxWOy. On the other hand, the oxygen concentration dependenct metal-nonmetal transition was observed in RbxWOy with y = 3.00, and it should be not intimately related with superconductivity in RbxWOy. Finally, the single crystalline Rb0.23WOy samples were made by normal freezing melt growth technique, and the qualitative effect of various oxygen concentrations in superconductivity for rubidium tungsten bronze was confirmed by single crystal annealing in pure oxygen.
Appears in Collections:	[Graduate Institute & Department of Physics] Thesis

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