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Featured researches published by W. Bieger.


Physica C-superconductivity and Its Applications | 1995

Modified melt texturing process for YBCO based on the polythermic section YO1.5“Ba0.4Cu0.6O” in the YBaCuO phase diagram at 0.21 bar oxygen pressure

G. Krabbes; P. Schätzle; W. Bieger; U. Wiesner; G. Stöver; M. Wu; T. Strasser; A. Köhler; Doris Litzkendorf; K. Fischer; P. Görnert

Abstract Y 2 O 3 admixed to 123 significantly influences the mechanism of melt texturing of YBCO. Based on phase diagram considerations, it is shown that the process window for stable growth conditions can be considerably increased. Furthermore, a lower process temperature ( T a =960°C to 985°C) becomes possible. Samples have been grown by both directional solidification and zone melting techniques. The superconducting properties are determined by local and integral levitation force measurements.


Physica C-superconductivity and Its Applications | 1996

THE INFLUENCE OF INITIAL COMPOSITION AND OXYGEN PARTIAL PRESSURE ON THE PROPERTIES OF MELT-TEXTURED NDBACUO

W. Bieger; G. Krabbes; P. Schätzle; L. Zelenina; U. Wiesner; Peter Verges; J. Klosowski

Abstract The influence of several admixtures on the microstructure formation and the superconducting properties is explained on the base of phase-equilibrium considerations. Conditions are derived which permit the stabilization of Ba rich Nd-123 phase to occur which is a precondition for preparing textured NdBaCuO materials with Tc > 90 K and a sufficient high jc. A melt-textured bulk material with Tc = 91 K and jc(77 K, 0 T, B ∥c) = 21.8 kA/cm2 was produced at p(O2) ≈ 100 Pa using an initial mixture consisting of NdBa2Cu3O7−δ and Nd2BaO4.


Superconductor Science and Technology | 1996

Melt processing of (Nd, Y)BaCuO and (Sm, Y)BaCuO composites

P. Schätzle; W. Bieger; Ulrich Wiesner; Peter Verges; G. Krabbes

Solid solutions of and high-temperature superconducting materials were synthesized. The (Nd, Y)BaCuO composite samples melt textured in air atmosphere show high critical current densities of about . A double exchange of both and by (or by , respectively) was observed in these materials. The results indicate vacancies on barium sites to exist additionally as defects in the substituted 123 phase of the melt textured materials. The microstructure reveals (Nd, Y)-211 or (Sm, Y)-211 inclusions with different Nd,Y and Sm,Y contents, respectively.


Superconductor Science and Technology | 1999

Melt processing and high performance of binary (Nd, Sm)-Ba-Cu-O superconductors

Anming Hu; P. Schätzle; W. Bieger; Peter Verges; G. Fuchs; G. Krabbes

Binary (Nd, Sm)-Ba-Cu-O superconductors with Tc of 96 K and a high irreversibility field up to 8 T have been fabricated in air via a newly developed technique. The initial composition was controlled by using binary (Nd, Sm)2BaO4 as an addition. In comparison with both NdBaCuO and YBaCuO melt-textured superconductors, the present composition showed a remarkable enhancement of critical current densities in an intermediate field regime (1-3 T). Microstructural observations and compositional analysis showed that the distributions of Nd and Sm in the (Nd, Sm)-123 matrix were homogeneous while the atomic ratio between these two rare earth elements was inconsistent with that in the nominal composition. These new characteristics were thought to cohere with the different solubilities between Nd and Sm in the liquid phase. Finally, trapped magnetic field mapping showed a single-domain shape of the trapped field, which indicated the growth of a single grain in the samples.


Superconductor Science and Technology | 1998

Improved HTSC bulk materials : a thermodynamic approach to processing

G. Krabbes; W. Bieger; P. Schätzle; Ulrich Wiesner

Thermodynamic considerations, especially the study of the stability regions of the RE-123 phases and their primary crystallization fields, are a useful tool to find the optimum process conditions for YBaCuO and the more complicated NdBaCuO bulk materials. Trapped fields of 700 mT (77 K) or 5.5 T (30 K), levitation forces of 80 N and up to in YBaCuO and above in NdBaCuO have been achieved.


Physica C-superconductivity and Its Applications | 1999

On the superconductivity and phase stability of (Nd0.33Sm0.67)1+xBa2-xCu3O7-δ

Anming Hu; G. Krabbes; P. Schätzle; W. Bieger

Abstract A series of solid solution powders with the compositions of (Nd 0.33 Sm 0.67 ) 1+ x Ba 2− x Cu 3 O 7− δ ( x =0, 0.05, 0.1, 0.2, 0.3) were synthesized in air and the superconductivity and phase stability were investigated. Single-phase powders were obtained and the maximum solid solubility limit x was revealed as 0.2 by quenching from 1040°C for x =0, 0.05, 0.1 and 1030°C for x =0.2 and 0.3 to room temperature in air. The unusual two-kink superconducting transitions were reported and discussed in the framework of phase separation. The post-annealing in Ar displayed a dramatic suppression of solid solubility limits. The precipitate due to the decomposition in Ar treatments may act as additional pinning centers. These results demonstrated that Ar isothermal treatments can act as a key measure to process light rare-earth 123 superconductors with desired properties for applications.


Physica C-superconductivity and Its Applications | 2002

Very high values of Jc obtained in NdBa2Cu3Ox by use of the U/n process

Roy Weinstein; Ravi Sawh; Drew Parks; Masato Murakami; Tadashi Mochida; N. Chikumoto; G. Krabbes; W. Bieger

Abstract The U/n process has been used to introduce quasi-columnar pinning centers into Nd123, textured in 1% O 2 , 99% Ar. The process involves adding 235 U to precursor powders of the superconductor, texturing, and irradiating with thermal neutrons. The two resulting ions, from each nuclear fission, cause aligned discontinuous electronic damage of length ∼5.4 μm, which acts as a pinning center. Best results for J c require U deposits spaced by s ⩽5.4 μm. This has been achieved by deposits containing two foreign elements, U and Zr, and three native elements. The deposits of UZrNdBaO and Nd422 refined by the Zr, act as additional non-aligned pinning centers. The U/n process increases J c by a factor R J ⩾10, to values of J c ∼274 kA/cm 2 at T =77 K, B =666 G.


Physica C-superconductivity and Its Applications | 2000

Composition-controlled melt processing of Nd1+xBa2−xCu3O7−δ-based bulk material in air

P. Schätzle; G Ebbing; W. Bieger; G. Krabbes

Abstract Nd1+xBa2−xCu3O7−δ (Nd-123) superconductors were melt-processed in air atmosphere starting from an initial precursor consisting of Nd2O3, BaCuO2 and CuO, or Nd-123 and BaCuO2, respectively, to stabilise the process to proceed in equilibrium with compositions along the tie line Nd-123–Nd-422, both with its stoichiometric compositions. The Nd:Ba ratio was stabilised close to 1:2 and high Tc values up to 96 K were achieved. As a result, Jc values of 30 kA/cm2 (0 T) and an expressed peak effect of 10 kA/cm2 arises at an applied external magnetic field of 2 T at 77 K.


Journal of Low Temperature Physics | 1996

Melt texturing and properties control of Nd1+yBa2-yCu3Ox bulk materials

W. Bieger; U. Wiesner; G. Krabbes; P. Schätzle; A. Bauer; Peter Verges; L. Zelenina

Melt textured NdBaCuO samples with Tc = 94 K and jc(0 T, 77 K) = 46 kA/cm2 have been prepared on an isothermal route. The thermodynamic background of this procedure which aims at the production of a Ba rich Nd-123 is pointed out.


Archive | 1996

Melt Texturing of YBCO with Excess of Yttrium Oxide

Peter Görnert; Pavel Diko; W. Gawalek; Tobias Habisreuther; Anke Köhler; Doris Litzkendorf; Thorsten Strasser; M. Wu; G. Krabbes; W. Bieger; P. Schätzle; Gudrun Stöver; U. Wiesner

To prepare large diameter YBa2Cu3O7-x (YBCO or Y123) bulk materials for cryomagnetic applications mostly melt texturing is carried out with an excess of Y2BaCuO5 (Y211). Using Y2O3 instead of Y211 a different behaviour of melt processing occurs. Lower process temperatures of 940°C ≤ T ≤ 1020°C become possible compared with about 1020°C for Y211 admixtures. Polarized light microscopy reveals the influence of 211 particles on the microstructural features. The macroscopically and microscopically compositional inhomogeneities influence the field trapping properties. Applications of melt textured YBCO materials for hysteresis motors and linear transport systems are illustrated.

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P. Schätzle

Russian Academy of Sciences

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Peter Verges

Russian Academy of Sciences

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U. Wiesner

Russian Academy of Sciences

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Doris Litzkendorf

Leibniz Institute of Photonic Technology

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H. Lütgemeier

Forschungszentrum Jülich

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A. Bauer

Russian Academy of Sciences

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L. Zelenina

Russian Academy of Sciences

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