Effect of Cd Substitution for Bi on Superconductivity of the Bi-2201 Phase in the Bi—La—Ca—Cu—O System

A series of the Bi-2201 samples with the nominal composition of (Bi_2–x Cd _x )La_0.7Ca_1.3CuO _z has been synthesized and effect of Cd substitution for Bi on the superconductivity has been investigated. As a result, it is found that almost single phase samples are obtained for a considerable wide composition of 0.0 x 0.8, their crystal structures have a tetragonal or a pseudotetragonal symmetry in the whole composition range, and the sample unexpectedly changes from superconductor to semiconductor by little Cd-substitution of about 0.1. The semiconducting samples show a temperature dependence of the resistivity suggesting that the transport process is followed by a three-dimensional variable range hopping conduction.     

Comparative Analysis of the Fundamental Susceptibility in Bi-2212 Single Crystal

The temperature and field dependencies of the fundamental susceptibilities have been measured to study the vortex dynamics in Bi-2212 single crystal. The model incorporating both the concepts of collective creep and critical state has been used to explain amplitudes of the ac magnetic field and frequency with combination of dc magnetic field and temperature dependencies of the susceptibilities. The comparison performed between the results obtained from the measurements and the model calculations shows that a good agreement between them exists.      

Quench of the Superconductivity in the Yttrium-Doped Compounds Bi2Sr1.6 − xLa0.4YxCuO6 + δ of the Bi-2201 Phase

Journal of Superconductivity and Novel Magnetism - Effect of yttrium substitution on strontium sites in Bi2Sr1.6 – xYxLa0.4CuO6 + δ compounds (where x?=?0.0, 0.2, and 0.4) of...     

Substitution Effect of Sn for Cu in the Bi2Sr2CaCu2−xSnxO8+δ System

The Bi₂Sr₂CaCu₂O_8+δ system samples doped with Sn on Cu sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction and photoemission experiments have been performed. Suppression of superconductivity in the Sn-doped Bi₂Sr₂CaCu₂O_8+δ system has been observed. X-ray photoemission measurements show that Sn ion enters the lattice. Our results reveal that Sn ions are mostly in bivalent states.     

Substitution Effect of Pr for Ca in Bi2Sr2CaCu2O8+δ System

The Bi₂Sr₂CaCu₂O₈₊ system samples doped with Pr on Ca sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction, and photoemission experiments have been performed. Both X-ray diffraction and photoemission measurements show that Pr ion enters the lattice with a valence higher than 3⁺, which supports the hole-filling mechanism of the suppression of superconductivity.     

Effect of Grain Boundary on the Wettability and Interfacial Morphology in the Molten Bi／Cu System

The wetting behavior of molten Bi on polycrystalline Cu substrate and single crystal Cu substrate was studied by the sessile drop method in the temperature range from 673 to 873K. At low temperature the wetting behaviors of molten Bi on both types of Cu substrate were similar. However, at high temperature, the equilibrium contact angle of polycrystalline Cu substrate was lower than that of single crystal Cu substrate, because the preferred dissolution of grain boundaries leads to a smaller liquid/solid interracial energy for polycrystalline Cu substrate. The formation mechanism of arrow-shaped Cu grains at the Bi/single crystal Cu interface is also discussed.     

Substitution Effect of Sn for Cu in the Bi2Sr2CaCu2?xSnxO8+δ System

The Bi₂Sr₂CaCu₂O₈₊ system samples doped with Sn on Cu sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction and photoemission experiments have been performed. Suppression of superconductivity in the Sn-doped Bi₂Sr₂CaCu₂O₈₊ system has been observed. X-ray photoemission measurements show that Sn ion enters the lattice. Our results reveal that Sn ions are mostly in bivalent states.     

Experimental Presentation of Microwave Absorption due to Shaking of JV by AC Magnetic Field in Bi2212 and Bi2223

The Josephson Vortex dynamics in high anisotropy superconductors Bi2212 and Bi2223 induced by AC magnetic field collinear to DC magnetic field and parallel to the layers is studied via their interaction with microwave field. Experimental results as function of DC magnetic field, AC magnetic field and temperature are presented. The AC induced microwave dissipation is larger than dissipation without AC field. The results are explained by the theoretical interpretation reported recently due to shaking by the AC field that depins the JV (Shaltiel et al., Phys. Rev. B 77, 014508, 2008). Similar behavior in these two compounds as a function of the variables involved discloses that the shaking effect should be observed in any high anisotropy superconductors. It shows that the AC field interacting with JV has an active and not the usual passive modulating role of the DC field in EPR dissipation experiments. The technique can be used to investigate JV dynamics and JV phase diagram.     

Design of the Cryogen-Free Cryogenic System for the CUORE Experiment

We present here the final design of the cryogenic system where the CUORE detector will be installed in 2010. It is a large cryogen-free cryostat cooled by pulse tubes and by a high-power dilution refrigerator. To avoid radioactive background, about 15000 kg of lead will be cooled to below 1 K and only few construction materials are acceptable. The detector assembly will have a total mass of about 1500 kg and must be cooled to less than 10 mK in a vibration-free environment. We discuss the adopted technical solutions, the results of the preliminary thermal analysis of the system, and its expected performance.      

The Effect of AgNO<Subscript>3</Subscript> Addition on the Formation and Superconducting Properties of the Bi2223 Phase

Superconducting samples with nominal composition Bi_1.66Pb_0.34Sr₂Ca₂Cu₂O _x –Ag are prepared by the solid-state reaction method. The samples are characterized by X-ray diffraction and DC electrical resistivity. According to X-ray diffraction patterns of specimens, the highest amount of Bi-(2223) phase along with the minimum amount of Bi-(2212) phase and minimum effect on the crystal structure was accessible in the sample with 10 wt. % of AgNO₃ content. The standard four-probe technique is applied to measure the DC electrical resistivity in the temperature range from 77 to 250 K and the influence of different Ag contents on the normal phase resistance, transition width and critical temperature T _c has been investigated comparatively.     

The Influence of the Interface on the Magnetic State in Two-Layer Films of the Fe–Bi System

Technical Physics Letters - Results of the experimental investigation of two-layer films in the Fe–Bi system are presented. It is found that the order of sequential deposition of the magnetic...     

Equal-Channel Multi-Angle Pressing Effect on the Properties of NbTi Alloy

An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) combined with hydrostatic extrusion, drawing and thermal treatment is revealed. The ECMAP method allows to increase the billet accumulated deformation with preserving its initial dimensions. The formed highly dispersed and homogeneous nanocrystalline structure with a more uniform distribution of α-phase precipitations as a result of ECMAP treatment improves the functional properties of the alloy. In the field of 5 T, the critical current density in wire samples produced with application of the ECMAP method is enhanced approximately by a factor of 2 in comparison with the values obtained for the samples produced without the ECMAP treatment.     

Effect of Interfacial Roughness Configuration on the Exchange-Bias Field in NiO Based Spin Valves

Two series of NiO-Co-Cu-Co based spin valves with the same nominal structure were grown by the magneton sputtering technique with different deposition parameters. Texture, surface and interfacial microstructures and the magnetic properties have been investigated in detail. X-ray diffraction, grazing incident X-ray reflectivity and transverse X-ray diffuse scattering were combined to analyze the microstructure of the multilayers. The results show that the texture of the multilayers is not a prerequisite factor for an exchange-bias (EB) field in NiO/Co/Cu/Co spin valves. And the EB effect is also independent of the average roughness at the interfaces. Large correlation lengths and two dimensions of the roughness at the interface are more advantageous for the EB effect.     

Stable and Metastable Phase Equilibria in the Bi2O3–BiPO4 System

The stable and metastable phase equilibria in the Bi₂O₃–P₂O₅ system were studied in the range 0–50 mol % P₂O₅ by differential thermal analysis and x-ray diffraction. The results were used to construct the corresponding phase diagrams. In the equilibrium state, the system contains one sillenite phase with Bi₂O₃ : P₂O₅ = 12 : 1 and four other bismuth phosphates (2 : 1, 3 : 1, 5 : 1, and 1 : 1). In a metastable state, resulting from solidification of metastable melts, there exist * solid solutions (0–25 mol % P₂O₅) based on the high-temperature form of Bi₂O₃. At lower temperatures, the * phase transforms eutectoidally into the metastable phase, which has the same structural basis as the high-temperature solid solutions. At room temperature, the phase exists in a narrow composition range around 15 mol % P₂O₅. At lower P₂O₅ contents, the * phase decomposes at 868 K by a monotectoid reaction to form a mixture of the metastable and phases. The phases 3Bi₂O₃ · P₂O₅ () and 2Bi₂O₃ · P₂O₅ (), melting incongruently at 1193 and 1223 K, respectively, appear in both the equilibrium and metastable phase diagrams.     

Role of Coexistence of Superconductivity and Paramagnetism in Magnetostriction of High-T c Superconductors

Total magnetostriction in the superconducting state for high T _c superconductors has been separated into critical state and paramagnetic components in terms of a H(x) dependent magnetic flux density. We show that the paramagnetic part is χ(2+χ)〈H(x)²〉, where χ is paramagnetic susceptibility. We have reproduced successfully ΔL/L−H _a curves measured by de la Fuente et al. (Phys. C 244:214, [1995]), in which they clearly observed coexistence of superconductivity and paramagnetism, employing the concepts presented in this work.