高温超导变压器

高温超导变压器与常规变压器相比 ,具有体积小、重量轻、效率高、无火灾隐患、不污染环境和限制短路电流改善系统动态稳定性等诸多优点。阐述了欧洲、美国及日本等国家的高温超导变压器的研究现状、基本特点、优越性及研究中存在的技术问题等。并且讨论了高温超导变压器的设计原则和将来其投入电力系统运行时所需要进一步考虑的问题     

Non-vacuum laser deposition of buffer layers for coated conductors

A pulsed TEA-CO₂ laser in combination with the dynamic fluidized bed powder feeder was employed to deposit a thin CeO₂ buffer layer on the polycrystalline Ni-substrate in a non-vacuum environment. Use of the 30° powder jet inclination with respect to the laser beam axis along with the nano size precursor powder deposited a smooth layer on the entire surface of the substrate. Both EDS and X-ray diffractometry analyses were employed to confirm the stoichiometric nature of the deposited CeO₂ buffer layer.     

Electrochemical synthesis of Tl-based highT c single-phase superconductor thin films

Co-deposition of the Tl-based superconductors using electrodeposition technique was successfully carried out. Different processing parameters such as deposition potential, current density, deposition period etc were studied. The Tl-based alloyed thin films were deposited at a constant potential of −1·25V with respect to SCE electrode onto silver substrates and oxidized at 850°C in oxygen atmosphere. The samples thus prepared showed superconducting behaviour below 122·5 K and the critical current density was 1·5×10³A/cm². Electrochemical synthesis of Tl-based highT _c single-phase superconductor thin films is also reported.     

Studies on (Hg0.7Mo0.3)Sr2(Sr1?xLax)Cu2Oz with a Wide Range of Doping State

The single-phased series of Sr-bearing Hg-1212 superconducting cuprate,(Hg_0.7Mo_0.3)Sr₂(Sr_1–x La _x )Cu₂O _z has been prepared. X-ray diffraction showed that, the obtained samples belong to the 1212-structure with tetragonal space group P4/mmm, similar to that of (Hg, Mo)Sr₂(Ca, Y)Cu₂O_z, and stabilized in a wide compositional range of 0.25x0.75. Refinements of the structure are carried out in which the oxygen atoms at the (Hg, Mo) layer is shifted from high-symmetry position (0.5, 0.5, 0) to (x, x, 0). Magnetization and electrical resistivity measurements show that the as-prepared samples exhibit evidence for superconductivity and their superconducting properties were improved after O₂ annealing with T ^onset _c as high as 92 K.     

DC magnetization studies in Nb/Fe superconducting multilayers

The behavior of superconducting transition temperature T_C in superconducting/ferromagnetic (S/F) multilayers as a function of different layer thicknesses and for varying magnetic moment μ_B of the F layer atoms is studied. Multilayer structures consist of five bilayers of constant superconducting Nb layer thickness of 400 Å and Fe of 6 and 24 Å each. The analysis of the magnetization data revealed that for t_Fe=6 Å, the Fe layer is non-magnetic. The interpretation of the observed T_C behavior is attributed to the change of the interaction of the cooper pairs with this layer at the onset of ferromagnetism for t_Fe=6 Å. The hysteresis curve recorded under isothermal conditions at 4.5 K for [Nb (400 Å)/Fe (6 Å)]₅ multilayers shows the usual M–H hysteresis behavior which is typical of a hard type-II superconductor exhibiting an irreversibility field H_irr of 3.5 kOe with substantial pinning at lower field. In addition, [Nb(400 Å)/Fe(6 Å)]₅ multilayer displays anomalous behavior in the form of paramagnetic peak in the superconducting state just below the transition temperature T_C=6.25 K.     

A thermal reduction route to nanocrystalline transition metal carbides from waste polytetrafluoroethylene and metal oxides

Starting from waste polytetrafluoroethylene (PTFE), metal oxides (TiO₂, V₂O₅, Nb₂O₅, and MoO₃) and metal sodium, several nanocrystalline transition metal carbides (TiC, VC, NbC, and Mo₂C) have been prepared through a thermal reduction route in an autoclave at 600 °C. It is found that the obtained NbC nanocrystallines have a superconducting transition temperature at 11.6 K.     

Fundamental design and electrical characteristics of superconducting commutatorless motor

Since there are no iron cores in the rotor and stator windings of superconducting synchronous motors, some reactances are intrinsically smaller than those of conventional motors. Thus the low synchronous reactance would be expected to improve the torque-ampere ratio stability and the overload capacity in case of the variable-speed drive system of a load-commutated inverter due to the small armature reaction. Moreover, the low subtransient reactance may contribute to lessen the voltage stress during the shortened commutating period, especially in current source-type inverter (CSI) systems. In this paper, after presenting analytical formulas needed for a machine design, one design algorithm is described, citing one example of an experimental CSI-fed superconducting motor of 30 kVA which will be fabricated. Further, the distinguished features in its operation, as expected in the foregoing, are verified by the computer simulation study in comparison with a conventional machine in terms of a high specific power density, an extension of stable power limit, and so on.     

Ag-doping-induced coordination incompatibility and its effect on superconductivity in YBCO

A series of samples of YBa₂Cu_3-xAg_xO_7-y with 0≤x≤0.12 composition was studied to probe into the Ag substitution effect on oxygen stoichiometry, lattice parameters, and superconducting properties. With the samples prepared at a relatively lower sintering temperature, Ag could be doped in the grains rather than precipitate at grain boundaries. Thus, unlike in the case of YBCO + Ag composites or in doped systems annealed at high temperatures where Ag occupies mostly the grain boundary, the present system showed a drastic change inT _c, oxygen stoichiometry, and lattice parameters with Ag concentration, indicating the substitution of Ag at the Cu(l) sites in the grains. The stable 2-fold oxygen coordination of Ag substituting Cu(l)’s explains the observed variation of oxygen deficiency with Ag. A crystallochemical analysis has been made to reveal the crucial role of Ag-substitution-induced coordination incompatibility and charge state instability on carrier concentration andT _c.     

Interfacial Strain‐Induced Oxygen Disorder as the Cause of Enhanced Critical Current Density in Superconducting Thin Films

To understand the origin of the increase in critical current density of rare earth barium cuprate superconductor thin films with decreasing thickness, a series of sub‐300‐nm EuBa₂Cu₃O_7?δ thin films deposited on SrTiO₃ substrates are studied by X‐ray diffraction and electrical transport measurements. The out‐of‐plane crystallographic mosaic tilt and the out‐of‐plane microstrain both increase with decreasing film thickness. The calculated density of c‐axis threading dislocations matches the extent of the observed low‐field enhancement in critical current density for fields applied parallel to c. The in‐plane mosaic twist and in‐plane microstrain are both around twice the magnitude of the out‐of‐plane values, and both increase with decreasing film thickness. The results are consistent with the observed stronger field enhancement in critical current density for fields applied parallel to ab. The lattice parameter variation with thickness is not as expected from consideration of the biaxial strain with the substrate, indicative of in‐plane microstrain accommodation by oxygen disorder. Collectively, the results point to an enhancement of critical current by interfacial strain induced oxygen disorder which is greatest closest to the film‐substrate interface. The findings of this study have important implications for other thin functional oxide perovskite films and nanostructures where surface and interfacial strains dominate the properties.