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The electronic structures of five polycrystalline YNi2−xCoxB2C (x=0, 0.05, 0.1, 0.15, and 0.2) borocarbide superconductors were studied by photoemission and photoabsorption spectroscopies and theoretical calculations. The valence-band (VB) photoemission spectrum is compared with the theoretical total and partial density-of-states (DOS) curves. The VB satellite is peaked at a binding energy (EB) of 6 eV. The Ni K-edge x-ray absorption near edge spectra (XANES) are compared with the calculated XANES spectra for these intermetallic compounds. Extended x-ray absorption fine structure (EXAFS) spectra at the Ni and Co K edges are analyzed to yield the structural parameters. The decrease of the superconducting transition temperatures (Tc) with addition of Co dopant in these compounds is due to a decrease of the total DOS at the Fermi level (EF).
A novel rapid densification technique for fabrication of bulk shape YBa2Cu307–xsuperconductor is presented. The Ceracon process is a one‐step, quasi‐isostatic consolidation route utilizing conventional P/M equipment and set‐up. The Ceracon technology has enabled successful fabrication of bulk, shapes such as discs, cylinders, hollow cylinders and spheres along with significant increases in the density up to 95‐98% of the theorertical. The superconducting volume fraction is preserved due to short hold times at the operating temperatures and avoidance of high processing temperatures. Results based on densities, microstructure, susceptibility measurements, X‐ray diffraction patterns and TGA measurements are discussed.
The time-dependent magnetic relaxation was measured in a full field penetrated YBa2Cu3O7-δ detwinned crystal for long times up to 5×105 sec. The relaxation data exhibit a power-law time dependence over a wide range of temperatures and magnetic fields indicative of flux creep with logarithmic dependence of the effective creep activation barrier U(J). A theoretical model is employed to analyze the data and to determine the activation energy.
Several sandwich panels with Ti-6AI-4V facesheets and syntactic metal foam (i.e., alumina microballoons (mb) in aluminum matrix) core were produced by a single step casting press. Optical microscopy and scanning acoustic microscopy techniques were used to examine the integrity of Ti/Al and mb/Al matrix interfaces. Mechanical property tests including compression, tension, flexure, and impact tests were performed to determine the characteristics of as-cast Ti//(alumina)mb/Al//Ti laminates. Presented in this paper are the specific details of design, processing, and mechanical behavior of the as-cast laminates.
The electronic structures of six polycrystalline borocarbide superconductors YPd5-xRhxB3C0.4 (x=0, 0.05, 0.1, 0.15, 0.2, and 0.25) were studied by photoemission and photoabsorption spectroscopies and theoretical calculations. The valence-band (VB) photoemission spectrum is compared with the theoretical total and partial density-of-states (DOS) curves. The Pd L3-edge x-ray absorption near edge spectra (XANES) are compared with the calculated XANES spectra for these intermetallic compounds. The decrease of the superconducting transition temperatures (Tc) with addition of Rh dopant in these compounds is due to a decrease of the total DOS at the Fermi level (EF).