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.

Chapter 1  Interduction...................................1
1.1 Background of Tungsten Bronzes........................1
1.2 Overview of Alkali Tungsten Bronzes...................4
1.3Resistivity Anomaly and Superconducting Properties for Rubidium Tungsten Bronze and Motivation...................7
Chapter 2  Theoretical Background........................18
2.1 Fundamental of Superconductivity.....................18
2.2 Anisotropy in Superconductivity......................20
Chapter 3  Experimental Details..........................22
3.1 Samples Synthesis....................................22
3.2 X-ray Diffraction Analysis...........................23
3.3 Transport Properties.................................24
3.4 Magnetic Properties Measurements.....................25
Chapter 4  Results and Discussion........................26
4.1 Polycrystalline Samples Investigated for HTB Rubidium Tungsten Bronze..........................................26
4.2 The Structure Properties in RbxWOy...................27
4.3 Metal-Nonmetal (MN) Transition in RbxWOy.............30
4.4 Superconductivity in RbxWOy..........................32
4.5 Magnetic Measurements and Various Thermodynamic Parameters in Rb0.23WOy..................................34
4.6 Structure and Superconducting Properties of Single Crystalline Rb0.23WOy....................................37
4.7 Detailed Discussion and Speculation of Superconductivity Properties for HTB RbxWOy..............40
Chapter 5  Conclusion....................................66
References...............................................68
List of Figures and Tables

Fig. 1.1	Various types of ITB structures. The solid squares are WO6 octahedras with the c-axis directed out of the paper.	12
Fig. 1.2	TTB structures with the c-axis directed out of the paper. (a) TTB II type. (b) TTB I type.	12
Fig. 1.3	(a) Superconducting critical temperature Tc versus Na concentration in TTB NaxWO3. (b) Photoemission spectra hυ = 60 eV of the valence-band region for NaxWO3 as a function of x.	13
Fig. 1.4	The structure of HTB Rb0.27WO3. (a) Framework by WO6 octahedras. (b) Hexagonal tunnels along c direction.	14
Fig. 1.5	The high-temperature resistivity anomaly occurs for RbxWO3. (a) Resistivity as a function of temperature for various x values. (b) Variation of the temperature TB as a function of x.	15
Fig. 1.6	(a) The neutron diffraction pattern taken at about 10 K for Rb0.27WO3. (b) The intensity of the (1 0 3/2) superlattice peak versus temperature for Rb0.27WO3.	16
Fig. 1.7	The superconducting transition Tc as a function of the rubidium content x in RbxWO3.	17
Fig. 1.8	The time dependence of the relative mass increase of Rb0.19WO3 powder under 1 atm O2 at different temperatures. The inset shows the x dependence of the relative mass increase after 930 minutes at 470oC.	17
Fig. 4.1	XRD pattern with (hkl) of Rb0.27WO3.	42
Fig. 4.2	XRD pattern of polycrystalline Rb0.19WOy.	43
Fig. 4.3	XRD pattern of polycrystalline Rb0.23WOy.	44
Fig. 4.4	XRD pattern of polycrystalline Rb0.27WOy.	45
Fig. 4.5	XRD Rietveld refinement pattern for Rb0.23WO3.00.	46
Fig. 4.6	The lattice parameter a and c versus oxygen concentration y in polycrystalline Rb0.19WOy.	47
Fig. 4.7	The lattice parameter a and c versus oxygen concentration y in polycrystalline Rb0.23WOy.	48
Fig. 4.8	The lattice parameter a and c versus oxygen concentration y in polycrystalline Rb0.27WOy.	49
Fig. 4.9	The room temperature resistivity ρRT of polycrystalline RbxWOy versus oxygen concentration y with x = 0.19, 0.23, 0.27 and 2.80 < y < 3.08.	50
Fig. 4.10	Resistivity as a function of temperature for Rb0.19WOy with y = 3.00, 3.02 and for Rb0.23WOy with y = 2.85, 3.04.	51
Fig. 4.11	Schematic band diagram for semiconducting (a) and (b), and metallic (c) NaxWO3.	52
Fig. 4.12	Photoemission spectra at hυ = 110 eV of conduction band with the Fermi level aligned for single crystalline Rb0.23WO2.95 and Rb0.23WO3.00.	52
Fig. 4.13	The ZFC magnetic susceptibility curves in a field of 10 G and the normalized resistivity as a function of temperature for polycrystalline Rb0.23WOy with y = 2.82, 2.85, 3.03 and 3.04.	53
Fig. 4.14	The superconducting critical temperature Tc versus oxygen concentration in polycrystalline RbxWOy with x = 0.19, 0.23, 0.27 and 2.80 < y < 3.08.	54
Fig. 4.15	The schematic diagram of the superconducting critical temperature Tc versus rubidium and oxygen concentration in RbxWOy. The inset shows the section with oxygen concentration y = 3.00.	55
Fig. 4.16	The temperature dependence of the upper critical field for polycrystalline Rb0.23WO2.90 and Rb0.23WO3.02. The insets display resistivity versus temperature at different field.	56
Fig. 4.17	Low-field M-H curves at superconducting state for polycrystalline Rb0.23WO2.90 and Rb0.23WO3.02.	57
Fig. 4.18	The irreversibility lines for polycrystalline Rb0.23WO2.90 and Rb0.23WO3.02. The insets show a log-log plot of Hirr versus 1-T/Tc.	58
Fig. 4.19	Magnetization as a function of temperature at various magnetic fields for polycrystalline Rb0.23WO2.90 and Rb0.23WO3.02. The insets show 3D and 2D scaling of the magnetization around Tc(H).	59
Fig. 4.20	The Laue patterns for single crystalline Rb0.23WO2.90 samples along (a) a-direction (b) c-direction.	60
Fig. 4.21	The Laue patterns for single crystalline Rb0.23WO3.00 samples along (a) a-direction (b) c-direction.	61
Fig. 4.22	Laue patterns for single crystalline Rb0.23WO2.90 samples after annealing in pure oxygen along c-direction and its following computer fitting pattern.	62
Fig. 4.23	The ZFC magnetic susceptibility curves for single crystalline Rb0.23WO3 after different annealing conditions.	63
Fig. 4.24	The lattice parameter c and the F.W.H.M. of (001) peak versus annealing times for single crystalline Rb0.23WO3.00. The 1st to 11th and 16th to 19th means annealing in pure oxygen. On the contrary, the 12th to 15th means annealing in vacuum.	64
Fig. 4.25	The mass variation versus annealing times for single crystalline Rb0.23WO2.90 and Rb0.23WO3.00.	65



Table 1.1	The structure and superconductivity of tungsten bronze MxWO3.	11
Table 4.1	XRD Rietveld refinement details for Rb0.23WO3.00.	46

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