Ismaning, Germany
Ismaning, Germany

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Van Der Laan D.C.,University of Colorado at Boulder | Van Der Laan D.C.,U.S. National Institute of Standards and Technology | Abraimov D.,Florida State University | Polyanskii A.A.,Florida State University | And 4 more authors.
Superconductor Science and Technology | Year: 2011

Recent experiments have shown that reversible effects of strain on the critical current density and flux pinning strength in the high-temperature superconductor Bi 2Sr 2Ca 2Cu 3O x can be explained entirely by the pressure dependence of its critical temperature. Such a correlation is less simple for RE-Ba 2Cu 3O 7 - δ (RE = rareearth) superconductors, in part because the in-plane pressure dependence of its critical temperature is highly anisotropic. Here, we make a qualitative correlation between the uniaxial pressure dependence of the critical temperature and the reversible strain effect on the critical current of RE-Ba 2Cu 3O 7 - δ coated conductors by taking the crystallography and texture of the superconducting film into account. The strain sensitivity of the critical current is highest when strain is oriented along the [100] and [010] directions of the superconducting film, whereas the critical current becomes almost independent of strain when strain is oriented along the [110] direction. The results confirm the important role of the anisotropic pressure dependence of the critical temperature on the reversible strain behavior of RE-Ba 2Cu 3O 7 - δ. The reversible strain effect in RE-Ba 2Cu 3O 7 - δ is expected to decrease the performance of the conductor in many applications, such as high-field magnets, but the effect may be only minor in coated conductor cables, where strain is generally not aligned with the tape axis. © 2011 IOP Publishing Ltd.


Durrschnabel M.,University of Tübingen | Aabdin Z.,University of Tübingen | Grosse V.,THEVA Dunnschichttechnik GmbH | Bauer M.,THEVA Dunnschichttechnik GmbH | And 3 more authors.
Physics Procedia | Year: 2012

MgO buffer layers were grown by Inclined Substrate Deposition (ISD) for superconducting coated conductors. The surface structure, texture, and extended defects were analyzed for films with different MgO layer thicknesses. A rooftile structure was only observed for films with layer thicknesses exceeding 800 nm. MgO facet widths and amplitudes were determined for different MgO buffer layer thicknesses. At 800 nm the facets height was 18 nm and the facet width was 71 nm. The corresponding values measured for a 5 μm thick MgO film were 64 nm and 234 nm, respectively. For layers with layer thicknesses smaller than 200 nm the films were polycrystalline with a grain size of 20 nm. For larger layer thicknesses the ISD MgO film grew in the form of columns with diameter of 50 to 100 nm. The texture of the layers was analyzed by electron diffraction in the TEM. From radial intensity profiles obtained from electron diffraction patterns the background-corrected (002)/(111) intensity ratio was extracted. It was found that the (002)/(111) intensity ratio allows to quantify the degree of texture. ©2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.


Ochiai S.,Kyoto University | Okuda H.,Kyoto University | Arai T.,Kyoto University | Nagano S.,Kyoto University | And 3 more authors.
Cryogenics | Year: 2011

Transport current and n-value of DyBCO-coated conductor pulled in tension were measured experimentally and their relation to crack-induced current shunting was analyzed with the partial crack-current shunting model. The following features were revealed. The shunting current increases with increasing transport current and with increasing crack size. At low voltage where shunting current is low, the transport current of cracked sample normalized with respect to the transport current in non-cracked state is described with the modified ratio of non-cracked area to overall cross-sectional area of superconducting layer. At high voltage where the shunting current is high, the normalized transport current becomes higher than the modified ratio of non-cracked area. The increase in shunting current with transport current (and voltage) leads to a decrease in n-value at high current (voltage). This phenomenon is enhanced by crack extension. © 2011 Elsevier Ltd. All rights reserved.


Ochiai S.,Kyoto University | Okuda H.,Kyoto University | Arai T.,Kyoto University | Sugano M.,High Energy Accelerator Research Organization | And 2 more authors.
Materials Transactions | Year: 2013

The influence of the volume fraction (Vf) of copper, plated at room temperature over a DyBa2Cu3O7-δ- coated conductor, on the tensile strain tolerance and stress tolerance of critical current at 77K was studied over a wide range of copper Vf values. The copper plating exerts a tensile stress during cooling because copper has a higher coefficient of thermal expansion than the substrate conductor. Before application of tensile strain, the copper plated at room temperature yielded at 77K when the copper Vf was lower than a critical value, and was in an elastic state at 77K when the copper Vf was higher than the critical value. The strain tolerance of critical current increased with increasing copper Vf due to an increase in thermally induced compressive strain in the substrate tape. The stress tolerance of critical current decreased with increasing copper Vf because copper is softer than the substrate tape. These results, together with the trade-off between strain tolerance and stress tolerance (i.e., stress tolerance decreases with increasing strain tolerance), were analyzed by modeling. The results show that the restriction imposed by the trade-off, which limits the ability to simultaneously obtain a high strain tolerance and a high stress tolerance, can be relaxed by strengthening the copper. © 2012 The Japan Institute of Metals.


Ochiai S.,Kyoto University | Arai T.,Kyoto University | Toda A.,Kyoto University | Okuda H.,Kyoto University | And 3 more authors.
Journal of Applied Physics | Year: 2010

Influences of cracking of coating layer under applied tensile strain on V (voltage)-I (current) curve, critical current, and n -value of DyBa2 Cu3 O7-δ coated conductor were studied experimentally and analytically. The experimentally measured variations in V-I curve, critical current, and n -value with increasing applied strain and the correlation of n -value to critical current were described well by the partial crack-current shunting model of Fang Also, the variations in the ratio of shunting current to overall critical current and the ratio of voltage developed in the cracked region to overall voltage with extension of crack, and the variation in critical current with the ratio of noncracked area to overall cross-sectional area of superconducting layer were revealed. © 2010 American Institute of Physics.


Durrschnabel M.,University of Tübingen | Aabdin Z.,University of Tübingen | Bauer M.,THEVA Dunnschichttechnik GmbH | Semerad R.,THEVA Dunnschichttechnik GmbH | And 2 more authors.
Superconductor Science and Technology | Year: 2012

DyBa 2Cu 3O 7-x (DyBCO) films with MgO buffer layers were grown on Hastelloy substrates by inclined substrate deposition (ISD). An almost linear increase of the critical current with the DyBCO film thickness was observed. A maximum critical current of 1018 A cm -1 was measured for a DyBCO film with 5.9 μm thickness, yielding a critical current density of 1.7 MA cm -2 at 77K and self-field. Transmission electron microscopy (TEM) yielded highly biaxially textured DyBCO films at all thicknesses and, thus, no significant decrease of the critical current density occurs with the film thickness. ISD yields a non-zero component of the growth direction parallel to the DyBCO (a, b)-plane since the DyBCO grows on a faceted MgO surface and avoids a-axis growth. Therefore, the ISD technology offers a unique possibility to overcome thickness limitations in coated conductor technology. © 2012 IOP Publishing Ltd.


Van Der Laan D.C.,University of Colorado at Boulder | Van Der Laan D.C.,U.S. National Institute of Standards and Technology | Douglas J.F.,Intel Corporation | Goodrich L.F.,U.S. National Institute of Standards and Technology | And 2 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2012

The uniaxial pressure dependence of the critical temperature causes a reversible effect of strain on the critical current density and the flux pinning strength in many high-temperature superconductors. Recent experiments on patterned coated conductor bridges have shown that the anisotropic nature of the pressure dependence of the critical temperature of rare earth (RE)-Ba 2Cu 3O 7-δ (REBCO) has a major impact on the performance of coated conductors under strain. The strain effect on the critical current density is most prominent when the strain is along the [100] and [010] directions of the superconducting film, whereas it almost completely disappears when the strain is along [110]. In this paper, we investigate the correlation between the uniaxial-pressure dependence of the critical temperature and the reversible strain effect on flux pinning in REBCO coated conductors. We show that axial strain has a large effect on the irreversibility field and the pinning force in coated conductors when the [100] and [010] directions of the superconducting film are aligned along the conductor axis. The magnitude of the strain effect in these conductors largely depends on the angle at which the magnetic field is applied. On the other hand, the critical temperature is not expected to change with the axial strain in coated conductors when the [110] direction is aligned along the conductor axis. Indeed, the irreversibility field and the magnetic field dependence of the pinning force of these conductors are almost independent of the axial strain for all angles at which the magnetic field is applied. The minor strain dependence of the critical current measured in these conductors could be caused by the average in-plane grain misalignment of between 6° and 8 °, which causes a slight variation in the strain alignment with the axes of the superconducting film. The results confirm that the reversible strain effect in REBCO coated conductors is largely determined by the uniaxial pressure dependence of the critical temperature. © 2006 IEEE.


Ochiai S.,Kyoto University | Okuda H.,Kyoto University | Sugano M.,High Energy Accelerator Research Organization | Osamura K.,Research Institute for Applied science | Prusseit W.,THEVA Dunnschichttechnik GmbH
IEEE Transactions on Applied Superconductivity | Year: 2012

This paper was carried out to reveal the influence of plated copper onto the substrate tape constituting of DyBa 2Cu 3O 7-δ, MgO, Ag, and Hastelloy C-276 on the stress-strain behavior, and tensile strain and stress tolerance of critical current at 77 K. From the analysis of the stress-strain relation of the copper-plated tape at 77 K, it was shown that the copper plated at room temperature is yielded in tension at 77 K due to the higher coefficient of the thermal expansion of copper than that of the substrate tape. The plated copper gave compressive strain to the substrate tape and, hence, the superconducting layer at 77 K, due to which the strain tolerance of critical current was improved. The observed improvement of the strain tolerance with increasing volume fraction of plated copper was quantitatively described from the viewpoint of the stress balance at 77 K between the substrate tape and yielded copper. The tolerant strain increased, but the tolerant stress decreased with increasing copper volume fraction. Such a tradeoff correlation between the tolerant strain and stress was well described by modeling analysis. © 2006 IEEE.


Patent
Theva Dunnschichttechnik Gmbh | Date: 2011-06-15

The invention relates to a high temperature superconducting tape conductor having a flexible metal substrate that comprises at least one intermediate layer disposed on the flexible metal substrate and comprising terraces on the side opposite the flexible metal substrate, wherein a mean width of the terraces is less than 1 m and a mean height of the terraces is more than 20 nm, and that comprises at least one high temperature superconducting layer disposed on the intermediate layer, which is disposed on the at least one intermediate layer and comprises a layer thickness of more than 3 m. The ampacity of the high temperature superconducting tape conductor relative to the conductor width is more than 600 A/cm at 77 K.


Grosse V.,Institute For Festkorperphysik | Grosse V.,THEVA Dunnschichttechnik GmbH | Schmidl F.,Institute For Festkorperphysik | Seidel P.,Institute For Festkorperphysik
Applied Physics Letters | Year: 2012

We report on the study of the low temperature electronic transport in strontium titanate thin films having a thickness of 25-30 nm. I-V characteristics measured below 4.2 K show unique structures which are evidence for the occurrence of a Coulomb blockade. Simulations of the measured characteristics suggest that this behavior is closely related to the formation of nanoscopic metallic islands within an insulating matrix which arrange in a network connected via tunneling currents. © 2012 American Institute of Physics.

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