Showing papers by "G. Krabbes published in 2002"
TL;DR: In this paper, the magnetic properties of melt-processed YBCO doped with different content of Li, Ni and Pd impurities are reported, and the observed time dependence of the magnetization in doped materials can be described in the framework of collective pinning theory.
Abstract: Magnetic properties of melt-processed YBCO doped with different content of Li, Ni and Pd impurities are reported. The increase of critical currents of doped materials has been observed in intermediate magnetic fields. The normalized pinning force is scaled into a single curve for all measured isotherms (60–77 K) for the samples with higher impurities level. The analysis of magnetic relaxation measurements at a field of 1 T and in the temperature interval between 10 and 70 K reveals a logarithmic dependence of the effective activation energy vs. current density. The observed time dependence of the magnetization in doped materials can be described in the framework of collective pinning theory.
39 citations
TL;DR: In this article, the YBa2Cu3O7 based bulk material was prepared by the modified melt crystallization process from Y123 þ Y200 (þPt) precursor with 12 wt.% Ag forming silver precipitates in the as grown materials.
Abstract: The maximum field B0 ¼ 16 T was trapped at 24 K in the gap of a mini-magnet made of two cylindrical samples. B0 on top of a single cylinder was 12.5 T at 20 K and 9 T at 40 K. The YBa2Cu3O7 based bulk material was prepared by the modified melt crystallization process from Y123 þ Y200 (þPt) precursor with 12 wt.% Ag forming silver precipitates in the as grown materials. A bandage of stainless steel compensated the tensile stress during magnetization. The unfavorable influence of admixed Ag on the critical current density jc was compensated by doping with Zn ions. � 2002 Elsevier Science B.V. All rights reserved.
36 citations
TL;DR: In this article, the authors present new types of electric machines with the rotors containing bulk high-temperature superconductor (HTS) elements, including YBCO and Bi-Ag elements.
Abstract: We present new types of electric machines with the rotors containing bulk high-temperature superconductor (HTS)—YBCO and Bi–Ag—elements. We discuss different schematics of hysteresis, reluctance, 'trapped field' and composed synchronous HTS machines. The two-dimensional mathematical models describing the processes in such types of HTS machines were developed on the basis of the theoretical analysis of the electrodynamic and hysteresis processes in the single-domain and polycrystal YBCO ceramic samples and plate shape Bi–Ag elements. We give the test results of the series of hysteresis, reluctance, 'trapped field' and composed with permanent magnets HTS motors with an output power rating of 0.1–18 kW and current frequencies 50 Hz and 400 Hz. These results show that in the media of liquid nitrogen the specific output power per one unit weight of the HTS motor is four to seven times better than for conventional electric machines. A comparison of the theoretical and experimental characteristics of the developed HTS motors show that they are in good agreement. We discuss the test results for a liquid nitrogen cryogenic pump system with a hysteresis 500 W HTS motor. We describe several designs of new HTS motors operating in the media of liquid nitrogen with an output power 125 kW (and more) and a power factor of more than 0.8. We discuss future applications of new types of HTS motors for aerospace technology, on-land industry and transport systems.
36 citations
TL;DR: In this article, the design of a superconducting 150 kW reluctance motor with YBCO bulk material is presented. But the performance of the superconducted linear motor is not discussed.
Abstract: The test results of electrical reluctance motors with superconducting YBCO bulk material operating at 77 K are compared to conventional machines. The design of a superconducting 150 kW reluctance motor is presented. We discuss the demands on YBCO bulk material which are necessary for a high performance of superconducting motors. Furthermore, we present the conceptual design of a superconducting linear motor. In the end we discuss future applications for superconducting motors of medium power range.
33 citations
TL;DR: In this article, the authors compared the pinning forces and trapped magnetic fields obtained in bulk YBa2Cu3O7 (YBCO)-based material doped with Li.
Abstract: The pinning forces and trapped fields obtained in bulk YBa2Cu3O7 (YBCO)-based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K.
28 citations
TL;DR: In this paper, a simple coupling model of Mn+3/Mn+4 and Ru +3/Ru+4 ions in the high-spin state is proposed which explains the antiparallel alignment and the technological interesting increase of the Curie temperature.
Abstract: X-ray magnetic circular dichroism measurements in the hard and soft x-ray region have been performed at Mn K and L2,3 edges of the ruthenium (with x=0.05, 0.1 and 0.5) doped Ruddlesden–Popper-phase La1.2Sr1.8Mn2−xRuxO7. In combination with magnetometry, clear evidence of unexpected antiferromagnetic sublattice coupling between manganese and ruthenium was found. A simple coupling model of Mn+3/Mn+4 and Ru+3/Ru+4 ions in the high-spin state is proposed which explains the antiparallel alignment and the technological interesting increase of the Curie temperature.
26 citations
TL;DR: In this article, very high trapped fields (13.3 T at 33 K) were achieved in bulk YBa2Cu3O7−δ melt-textured monoliths, which were reinforced by steel tubes to compensate the tensile stress generated during activation.
Abstract: We report on very high trapped fields (13.3 T at 33 K) achieved in bulk YBa2Cu3O7−δ melt-textured monoliths, which were reinforced by steel tubes to compensate the tensile stress generated during activation. The flux pinning properties were improved by neutron irradiation. The resulting increase of the critical current density shifts the maximum attainable trapped fields to higher temperatures (by about 10 K).
20 citations
TL;DR: In this paper, high pressure (HP)-synthesized MgB 2 superconductive material has been shown to have a critical current density of 68 kA/cm 2 in the 1 T field and of 160kA/ cm 2 in zero field, its field of irreversibility at 20 K being 5.7 T.
Abstract: The high-pressure (HP) synthesis seems to be very promising for manufacturing of the bulk MgB 2 superconductive material. The positive influence of tantalum in the form of a foil that covered the sample and as an addition of Ta powder in the starting mixture of B and Mg on critical current density in the magnetic field and on the field of irreversibility of MgB 2 has been observed during MgB 2 synthesis. At 20 K HP-synthesized MgB 2 has a critical current density of 68 kA/cm 2 in the 1 T field and of 160 kA/cm 2 in the zero field, its field of irreversibility at 20 K being 5.7 T. Vickers microhardness of the samples is 12.79±1.14 GPa at a 4.96-N load, fracture toughness is 4.1 MN/m 3/2 at the 147.2-N load (while at the 4.96-N load there are no cracks from the corners of the indent). The density of HP-synthesized MgB 2 samples is 95–97% the theoretical one.
19 citations
TL;DR: In this paper, the phase equilibria in (RE)BaCuO-Ag systems, the influence of Ag on the processing of BaCuO/Ag composites and the resulting properties were investigated.
Abstract: We have investigated the phase equilibria in (RE)BaCuO–Ag systems, the influence of Ag on the processing of (RE)BaCuO/Ag composites and the resulting properties. YBCO/Ag composites have been grown by the modified melt crystallization process with YBa2Cu3O7, Y2O3, Pt and Ag2O in the precursor. The improved strength of the YBCO/Ag composites compared with the conventional YBCO bulk material permitted us to magnetize these materials to achieve trapped fields up to 16 T (at 24 K) in the gap of a mini-magnet. The investigation of the microstructure revealed a remarkable increase of the spacing between micro-cracks especially of those perpendicular to a–b planes when 12 wt% Ag was added. In the case of SmBaCuO/Ag composites Ag has a strong influence on processing and causes interactions between RE123 seeds and the sample. We report on the growth of single-grain SmBaCuO/Ag composites in air and we discuss the influence of post-annealing on increasing Tc and jc.
16 citations
TL;DR: In this article, magnetic properties of bulk melt-processed YBa2Cu3O7−δ based material (YBCO), doped with Ca and Cd, were investigated.
Abstract: We report studies of magnetic properties of bulk melt-processed YBa2Cu3O7−δ based material (YBCO), doped with Ca and Cd. The superconducting parameters such as critical temperature, irreversibility field and critical current are found to be strongly dependent both on Ca content and oxygen variation in the (Y,Ca)BCO samples. In contrast, no pronounced change of superconducting properties of Cd doped YBCO has been observed in the wide range of Cd substitution before and after annealing. No scaling of the normalized pinning forces at different temperatures has been found for a Cd content varying between 0.1 and 1 wt.% as well. It is suggested that only a small amount of Cd is incorporated into the YBa2Cu3O7−δ phase.
16 citations
TL;DR: In this paper, single crystal growth of spin-ladder compound La 2 Cu 2 O 5 (4-leg) and spinladder-like compound CaCu 2 O 3 (2-leg), using self-flux method using a modified slow cooling technique, was reported.
Abstract: We report single crystal growth of the spin-ladder compound La 2 Cu 2 O 5 (4-leg) and spin-ladder-like compound CaCu 2 O 3 (2-leg). Crystal growth of La 2 Cu 2 O 5 has been carried out by the self-flux method using a modified slow cooling technique. Single crystals of CaCu 2 O 3 have been grown by the travelling solvent floating zone method under oxygen pressure (∼5 bar). An optimum solvent for growth of CaCu 2 O 3 was found to be Ca 0.8 Sr 0.2 Cu 2 O 3 . The grown crystals were characterized for their purity and structure by using optical polarized microscope, energy dispersive X-ray spectroscopy, and X-ray diffraction methods.
TL;DR: The morphological and compositional changes of the Pt-based phase in melt-grown Y-Ba-Cu-O samples grown on the Al2O3 substrate were studied in this article.
Abstract: The morphological and compositional changes of the Pt-based phase in melt-grown Y-Ba-Cu-O samples grown on the Al2O3 substrate were studied. It was shown that Al dissoluted in the melt is effectively consumed by the Pt-based phase, by replacing Cu with Al until it becomes fully converted to the Pt, Al-based phase. Al substitution changes irregular shape of Pt-based particles into Pt, Al-based crystals with well-developed habits. Ag addition hinders Al diffusion into the Y-Ba-Cu-O sample during melt processing.