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Present a study which investigated the intermediate phases produced in the growth of Bi[sub2]Sr[sub2]Ca[sub2]Cu[sub3]O[sub10+δ]. Details of the experimental techniques used; Factors which dominate the initial X-ray spectrum of the starting pellet.

Examines several aspects of decomposition of BiPb(2223) under a variety of conditions. X-ray data for the starting powder illustrating the identification of all of the major peaks as BiPb peaks; Discussion on the decomposition of BiPb(2223).

Presents information on a study which investigated crystallization of a bismuth compound as a function of the partial pressure oxygen using in situ high temperature x-ray measurements, in order to determine the phases that form and the kinetics of growth. Methods; Results; Discussion.

Studies the strain tolerance of doctor blade tapes of a high-temperature superconductor to determine the suitability of these materials for magnet conductors. Method of the study; Results and discussion; Conclusion.

Discusses a study which examined strain tolerance of Bi[sub2]Sr[sub2]Ca[sub1]Cu[sub2]O[sub8-8]/Ag composites at fields up to 20 T and bending strains up to 2.6% in order to determine the factors that control the critical current density. Idea in using silver to provide regions of plastic flow; Conductors that are easy to fabricate; Role of grain boundaries and silver barriers in the weak-link problem.

Presents a study that utilized transport currents in a cross strip superconducting-normal metal-superconducting (SNS) Josephson junction to bias the current-voltage characteristics of the junction. Features of SNS junctions; Approximation of the current-voltage characteristics of SNS junctions.

Thermodynamic critical fields, H[sub c], have been measured for the La[sub 2-x]Sr[sub x]CuO[sub 4] family of superconductors in order to determine the changes in free energy of the system as the number of carriers is reduced. Magnetization vs. magnetic field curves are thermodynamically reversible over large portions of the H-T plane, so the free energy is well defined in these regions. Magnetization vs. field data are then fit to theoretical models to determine the thermodynamic critical fields. As the Sr concentration is changed from x = 0.10 to 0.23, the values of H[sub c](T = 0) goes through a maximum at optimum doping in a manner similar to the T[sub c] vs x curve. The ratio of H[sub c](T = O)/T[sub c] also peaks in the region of x somewhat larger than optimum doping. As the value of x increases from underdoped to optimum doping, the cross-over temperature in the M[sub sc] vs. T curve, T[sup *], approaches the transition temperature. In the overdoped regime there is no crossing in these M[sub sc] vs. T curves. [ABSTRACT FROM AUTHOR]

Measurements of 10 GHz microwave surface resistance, R[sub s], of dense MgB[sub 2] wire and pellet are reported. Significant improvements are observed in the wire with reduction of porosity. The data lie substantially above the theoretical estimates for a pure Bardeen-Cooper-Schrieffer s-wave superconductor. However, the R[sub s] (20 K) of the wire is an order of magnitude lower than that of polycrystal YBa[sub 2]Cu[sub 3]O[sub 6.95] and matches with single-crystal YBa[sub 2]Cu[sub 3]O[sub 6.95]. The results show promise for the use of MgB[sub 2] in microwave applications. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A pressure cell has been designed to study the magnetostrictive properties of a material as a function of both pressure and magnetic field. For changes in length on the order of 2000 ppm, it is necessary to have a substantial compliance in the pressure cell to retain a constant stress over the length of travel. [ABSTRACT FROM AUTHOR]

The conversion of long slender filaments of Bi-based high-temperature superconductors from the amorphous to the crystalline phase has been studied in order to determine the suitability of these fibers for use in a multifilamentary magnet conductor. For very fine filaments, coarsening may be a problem, so special emphasis was placed on the optimum values of time and temperature used for recrystallization. Amorphous fibers approximately 1 μm in diameter can be crystallized to form granular filaments about 0.2 μm thick (in the c direction) and 3 to 4 μm wide. The c axis generally grows perpendicular to the long axis of the fiber. [ABSTRACT FROM AUTHOR]

Procedures have been developed for the preparation of long slender fibers of Bi-Sr-Ca-Cu-O using a gas jet to shape and freeze the material. The fibers emerge in amorphous form and are converted to the Bi[sub 2]Sr[sub 2]Ca[sub 1]Ca[sub 2]O[sub x] phase by subsequent heat treatment. Magnetization and scanning electron microscopy studies show the material to be a very fine grained bulk superconductor with intragranular critical currents of 7 × l0[sup 6] A/cm² at 5 K and 1.8 T. [ABSTRACT FROM AUTHOR]

A study of the motion of quantized vortices in cylindrical superconducting thin films was undertaken to determine the feasibility of constructing a magnetic shield in which the trapped transverse magnetic flux could be systematically swept out. The idea is to induce vortex-antivortex annihilation along one side of the cylinder under the influence of the Lorentz force using a transport current parallel to the axis of the cylinder. It is found that for a granular aluminum film approximately 1500 Å thick, there is a narrow temperature window near the critical temperature in which the vortices and antivortices can indeed be swept to one side and the internal field significantly reduced. [ABSTRACT FROM AUTHOR]

The upper critical field, H(c2), of Mg(B1-xCx)(2) has been measured in order to probe the maximum magnetic field range for superconductivity that can be attained by C doping. Carbon doped MgB2 filaments were prepared, and for carbon levels below 4% the transition temperatures are depressed by about 1 K/% C and H(c2)(T=0) rises by about 5 T/% C. This means that 3.8% C substitution will depress T(c) from 39.2 to 36.2 K and raise H(c2)(T=0) from 16.0 to 32.5 T. These rises in H(c2) are accompanied by a rise in resistivity at 40 K from about 0.5 to about 10 microOmega cm.

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB2 superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, Hc2, with magnetization data giving dHc2/dT = 0.44 T/K at the transition temperature of Tc = 40.2 K. Close to the transition temperature, magnetization curves are thermodynamically reversible, but at low temperatures the trapped flux can be on the order of 1 T. The value of dHc/dT at Tc is estimated to be about 12 mT/K, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter kappa approximately 26. Estimates of the critical supercurrent density, Jc, using hysteresis loops and the Bean model, give critical current densities on the order of 10(5) A/cm2. Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like Nb3Sn.

MgB2 becomes superconducting just below 40 K. Whereas porous polycrystalline samples of MgB2 can be synthesized from boron powders, in this Letter we demonstrate that dense wires of MgB2 can be prepared by exposing boron filaments to Mg vapor. The resulting wires have a diameter of 160 microm, are better than 80% dense, and manifest the full chi = -1/4pi shielding in the superconducting state. Temperature-dependent resistivity measurements indicate that MgB2 is a highly conducting metal in the normal state with rho(40 K) = 0.38 microOmega cm. By using this value, an electronic mean-free path, l approximately 600 A can be estimated, indicating that MgB2 wires are well within the clean limit. Tc, Hc2(T), and Jc data indicate that MgB2 manifests comparable or better superconducting properties in dense wire form than it manifests as a sintered pellet.