Phase Formation and Transition Temperature Variation of TlSr2(Ca1−x R x )Cu2O7 (R = Dy, Ho and Tb) Superconductor

The TlSr₂(Ca_1−x R _x )Cu₂O₇ (Tl-1212) phase with R = Dy, Tb and Ho for x=0.1–0.6 has been studied by powder x-ray diffraction method and electrical resistance measurement. All the samples showed a metallic normal state behavior. No correlation between ionic radius and T _c onset is observed. The three series show the highest volume fraction (>97%) of Tl-1212 phase for x=0.5. The highest T _c onset does not correspond to the highest volume fraction. The above results are explained as due to the mixed valence state of Dy and Tb in the Tl-1212 phase.      

Melt-formed superconducting joints for Nb3Sn tape

Several new persistent-current superconducting magnet applications become possible for Nb₃Sn when joints can be fabricated that are superconducting over the full range of temperatures and fields accessible with Nb₃Sn. Melt forming has been found to be an effective way to form such a joint. Both tungsten inert gas welding and laser welding have been used successfully for this purpose. Methods for fabrication, microstructures, and performance of melt-formed Nb₃Sn superconducting joints are discussed in detail.     

Design study of a high‐temperature superconducting transformer

Many research and development projects on high‐temperature superconducting apparatus such as a transformer, fault current limiter, and cable are being actively pursued in the power field as a result of performance improvement of Bi silver sheath high‐temperature superconducting (HTS) wire. HTS transformers are considered to be among the most promising applications in view of efficiency improvement, the interface with cryogenic cable and normal temperature devices, incombustibility, overload capability, the function as a reactor, and the possibility of use as a fault current limiter. The necessary technical development items of an HTS transformer in order to achieve performance superior to conventional devices are examined. For this purpose, three‐phase 66‐kV 100‐MVA transformers were designed for the comparison of an HTS transformer and a conventional one with oil cooling. The desirable development items are an HTS wire current density of about 40 A/mm², an allowable winding strain of about 0.5%, a percent impedance of 7.5%, an air gap flux density of about 0.3 T, and AC losses of about 0.3 W/km‐A. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 25–31, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10087     

Local lattice instability and ionic transport in high-temperature superconductors

Ionic transport, a characteristic feature of superionic conductors, is analyzed microscopically for the RBa₂Cu₃O{7-Σ} (R = rare earth) high-temperature superconductors. The electronic correlation effects are considered to be responsible for the formation of a local double-well potential for apical oxygen, which in its turn results in a decrease of the activation energy for interstitial chain oxygen defects. The behavior of the double well upon reduction of the oxygen content is discussed and its possible manifestation in the low-frequency dynamical response is considered.     

遗传程序设计在含F铋系高温超导体制备中的应用

将遗传程序设计应用于含Ｆ铋系高温超导体制备条件的识别、预报。结果表明，该方法效果好，可用于材料设计等高层次知识处理领域。     

Stabilization of toroidal Abrikosov vortex in a nonuniform superconductor

The possibility of existence of stable closed Abrikosov vortices of small size in nonuniform type-II superconductors is shown. These compact magnetic structures localize in all three dimensions and interact weakly with the external magnetic environment. The closed vortex is stabilized near the cylindrical interface between two superconductors with different magnetic field penetration depths. The size of the closed vortices can be small enough compared with the penetration depth.     

A novel method for sensing rotational speed, linear displacement and current using superconducting BPSCCO magnetic sensor

For many decades, magnetic sensors have been of great assistance to mankind in variety of functions that include simple compass based navigational systems to devices that monitor the invisible biological activities. In industries magnetic sensors are in great demand for control and measurement of linear and rotary position sensing etc, because of its non destructive and contact less way of detection. Consequently, newer, smarter and cheaper materials are continuously being explored to suit the varied needs of technological requirements. In the present communication, the characteristics of a magnetic sensor, based on the non linear electromagnetic response of the weak links present in the polycrystalline BPSCCO superconductor are reported. The second harmonic response of sintered superconducting BPSCCO pellet in an alternating magnetic field at 40 kHz and 77 K being a strong linear function of low d.c. magnetic field has been utilized for the development of highly sensitive magnetic field sensors. The noise limited resolution of the sensor is found to be 3.16 ×10^-9 T/√Hz for H_a.c = 16 Oe and frequency 40 kHz. We further demonstrate that such HTSC based magnetic sensors are capable of sensing the rotational speed, small displacement and direct current with good resolution. The experimental methods and results obtained are discussed.     

Photoemission spectroscopy of high-T c superconductors: Proofs in favor of the impurity mechanism

A new interpretation of photoemission spectroscopy data is proposed. It is based on the impurity mechanism of high-temperature superconductivity proposed earlier. The band observed near the Fermi level in this interpretation is the impurity band, and the observed large “Fermi surface” is the surface of the mobility edge, different in different directions. Many other details are also explained naturally.