Search

In this study, the superconducting properties of MgB 2 bulk samples fabricated at different conditions were investigated. Ex situ MgB 2 samples were further mixed with Mg and B at different amounts and sintered at different times and temperatures. Using Raman spectroscopy, the bearing of electron-phonon (e-ph) coupling (EPC) has been investigated. The dependence of temperature on magnetization, M(T), along with the dependence of magnetic field on magnetization, M(H), were evaluated to analyze the superconducting characteristics. Using the McMillan formular, which is modified by Allen–Dynes, and the frequency of phonon located in the mid peak centre ω 2 (E 2g), the contribution of EPC, whose value is closely proportional to the variation of critical temperature was reckoned. The lowest EPC value was determined by Raman spectrum analysis to be 1.094 for the MgB 2 sample added with 0.5 Mg and sintered at 1000 °C for 1 h. In addition, the sample showed the lowest critical temperature along with the highest critical current density. The small bundle field (B sb) as well as the large bundle field (B lb) were obtained using the collective pinning theory, demonstrating the expansion of the small also the large bundle regimes under suitable sample fabrication conditions. Based on the dependence of temperature on normalized critical current density (j) and normalized small bundle field (B sb), δT c pinning is the predominant flux pinning mechanism across totally MgB 2 bulk samples. The model of Dew–Hughes confirmed that the addition of Mg along with B creates surface pinning in the matrix by analyzing the pinning properties. [ABSTRACT FROM AUTHOR]

The impact of adding SnO 2 nanoparticles on the enhancements of critical current density (J c) of the Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+ δ superconductors was studied. Polycrystalline superconductors with stoichiometry of (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+ δ) 1− x (SnO 2) x where was x was ranged from 0.000, 0.002, 0.004, 0.006, 0.008 to 0.010 were made through traditional solid state reaction technique. X-ray diffraction data revealed that all fabricated samples consisted of Bi-2223 and Bi-2212 superconducting phases. The volume fraction of the Bi-2223 phase decreased with SnO 2 addition. Analyses of textural structure using scanning electron microscopy data evidenced a clear decrease in grain orientation and porosity with increased doping levels. SnO 2 presence in connection to Bi-2223 deceleration reduced the critical temperature. Values of J c deduced from the magnetization hysteresis loops measured at different temperatures of 35 K, 45 K, 55 K, 65 K were found to enhance for the SnO 2 added samples. In the x = 0.002 samples, the field dependent J c achieved its maximum values. In order to have a deeper understanding in the improvements of flux pinning properties, small and large bundle fields were determined by using the collective pinning theory. The obtained values indicate the expansion of the two corresponding regimes with appropriate. By analyzing the dependence of normalized J c versus normalized critical temperature, the dominant flux pinning mechanisms in all samples were consistent with δl pinning. Besides, the addition of SnO 2 nanoparticles was likely to produce pinning centers in form of core point as evidenced by using the Dew–Hughes model. [ABSTRACT FROM AUTHOR]

TiO 2 doping content affects the critical temperature (T c) and the variations of local structure on Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ. The (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ) 1-x (TiO 2) x samples were fabricated with the solid-state reaction process, where x = 0, 0.002, 0.004, 0.006, 0.008, and 0.01. The T c values of the samples were obtained by measuring resistivity versus temperature, indicating that T c gradually decreased with increasing doping content (x). To explain the obtained degradation of T c , carrier properties, role of interlayer coupling, and local structure were systematically investigated using Azlamozov–Larkin theory and its Lawrence–Doniach modification for strong anisotropic superconductors. The calculation of excess conductivity at the mean field region showed that the c-axis coherence length (ξ c) and the effective inter-layering spacing (d) increased with increasing doping content. X-ray diffraction patterns also showed that the bond distances increased with increasing TiO 2 content. The copper valence (V) and carrier concentration (p) of the samples were determined by analyzing the Cu L 2,3 -edge X-ray absorption near edge structure spectra. The values of V and p showed the same trend of decreasing with increasing x. A close correlation between the changes in local structure parameters and degradation of T c of (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ) 1-x (TiO 2) x was then probably concluded. [ABSTRACT FROM AUTHOR]

The effects of adding TiO 2 nanoparticles on the flux pinning properties of the Bi–Pb–Sr–Ca–Cu–O (BPSCCO) system were investigated. Polycrystalline samples of (Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O 10+δ) 1-x (TiO 2) x , where x = 0.000, 0.002, 0.004, 0.006, 0.008, and 0.010, were fabricated by the conventional solid-state reaction method. The X-ray diffraction (XRD) results showed that all samples consisted of Bi-2223 and Bi-2212 phases. The Bi-2223 volume fraction decreased with the addition of TiO 2. Scanning electron microscopy (SEM) examination presented a degradation in texture structure with increasing misoriented grain and porosity with high doping contents. The critical temperature was decreased by TiO 2 appearance in relation to Bi-2223 deceleration. Critical current density dependence on the magnetic field J c (B) was enhanced with x = 0.002, 0.004 and reached maximal values on the x = 0.002 sample. In the collective pinning theory framework, the small bundle field (B sb) and the large bundle field (B lb) were estimated, revealing the extension of the small and large bundle regimes with proper amounts of dopant. The temperature-dependent normalized critical current density (j) indicated that δl pinning is the dominant flux pinning mechanism in all samples. The Dew-Hughes model analyzed the pinning center properties and confirmed that TiO 2 nanoparticles create normal core point pinning centers in the matrix. [ABSTRACT FROM AUTHOR]