Bulk Wires Research Articles

Magnetism in systems with various dimensionalities: A comparison between Fe and Co

A systematic ab initio study is performed for the spin and orbital moments and for the validity of the sum rules for x-ray magnetic circular dichroism for Fe systems with various dimensionality (bulk, Pt-supported monolayers and monatomic wires, free-standing monolayers and monatomic wires). Qualitatively, the results are similar to those for the respective Co systems, with the main difference that for the monatomic Fe wires the <Tz> term in the spin sum rule is much larger than for the Co wires. The spin and orbital moments induced in the Pt substrate are also discussed.

Current percolation and anisotropy in polycrystalline MgB(2).

The influence of anisotropy on the transport current in MgB(2) polycrystalline bulk samples and wires is discussed. A model for the critical current density is proposed, which is based on anisotropic London theory, grain boundary pinning, and percolation theory. The calculated currents agree convincingly with experimental data, and the fit parameters, especially the anisotropy, obtained from percolation theory agree with experiment or theoretical predictions.

Improvement of critical current density in MgB2 superconductors by Zr doping at ambient pressure

We present the superconducting properties and phase compositions of Mg1−xZrxB2 bulk samples fabricated by a solid-state reaction at ambient pressure. It is found that a small amount of Zr atoms may be introduced into the lattice of MgB2, while the majority of them forms ZrB2 phase. The Mg0.9Zr0.1B2 sample shows the highest JC of 2.1×106 A/cm2 in 0.56 T at 5 K and 1.83×106 A/cm2 in self-field at 20 K, higher irreversibility field and larger upper critical field in MgB2 bulk samples. The combination of good grain connection, the reduction of grain size and small ZrB2 particles in the sample may be responsible for the significant enhancement of JC in Zr-doped samples. This technique has a great potential to prepare high performance MgB2 bulk samples and wires on an industrial scale.

BiCaSrCuO superconductors: Powder synthesis, wire fabrication and hot extrusion experiments.

Abstract BiCaSrCuO and BiPbCaSrCuO powders were synthetized. Different research methods (SEM, EDS, XRF, XRD, DTA) were used to characterize the bulk specimen and wires. Resistance and current density were measured as a function of temperature. The ceramic products contained several phases. Lead containing specimen gave the best results and the synthesis was easily reproducible.

Tl2O3 vapor process of making Tl-Ba-Ca-Cu-O superconductors

A new process for making Tl-Ba-Ca-Cu-O superconductors which is based on reactions between solid precursor Ba-Ca-Cu-oxides and vapor Tl2O3 has been developed. The Tl2O3 vapor process allows Tl-Ba-Ca-Cu-O superconductors to be easily made in the forms of complex bulk components, wires and fibers, and thick and thin films, and minimizes problems caused by toxicity and volatility of Tl starting compounds.

Experiments on the dynamic destruction of superconductivity in niobium and niobium alloys

The dynamic behaviour of the superconductive-normal transition in bulk wires of niobium and niobium alloys has been investigated under two experimental conditions. Firstly the influence of the magnitude of dl/dt on the critical current was studied, secondly, a dynamic critical curve was measured using magnetic field pulses of large dH/dt. For most of the samples the dynamic critical curve was found to be much lower than the static one. Furthermore a pronounced decrease of the transition time with increasing external field was observed. This decrease of the transition time levels off at very high fields.