Plenarvorträge - DPG-Tagungen

Tiefe Temperaturen Montag
TT 8.11 Mo 14:30 Poster A
Finite size effects and JC simulations in high-JC coated conductors
— •J. Hänisch, L. Fernández, C. Cai, V.S. Sarma, L.
Schultz und B. Holzapfel — IFW Dresden, Helmholtzstr. 20, 01069
Dresden, Germany
The superconducting layer in coated conductors consists a network
of small angle grain boundaries. Due to the limitation of JC on grain
boundaries in high-TC superconductors, the current flow through this
network is of percolative nature and depends on misorientation angle
distribution, width and length of the tape and grain shape. The current
flow through grain boundary networks had been simulated widely with
purely statistical models on artificial networks. Recent investigations of
biaxially textured orthorhombic materials (as YBCO on coated conductors
is) showed a nonrandom distribution of misorientation angles in this
materials.
JC simulations using a fast and simple limiting-path algorithm were used
to investigate the influence of the grain boundary misorientation statistics
on JC in realistic networks. Input of the simulation program are
large EBSD (electron back scattering diffraction) maps and the misorientation
angle dependence of JC. We found a strong dependence of JC on
the bridge width for bridges smaller then 20 grains (in comparisson to
purely statistical models), whereas JC is not strongly varying for wider
bridges. In rotating the whole EBSD map, we could simulate the influence
of the grain aspect ratio on JC. In current direction elongated grains
show significantly higher JC values. Both these results are promissing for
the performance of coated conductors.
TT 8.12 Mo 14:30 Poster A
Coated Conductors by Inclined Substrate Deposition — •A.
Lümkemann 1 , J. Handke 1 , H. Kinder 1 , R. Nemetschek 2 , C.
Hoffmann 2 , G. Sigl 2 , and W. Prusseit 2 — 1 TU München, Physik
Department E10, 85748 Garching — 2 THEVA Dünnschicht GmbH,
Rote-Kreuz-Str. 8, 85727 Ismaning
Thermal evaporation is one of the most promising techniques for economic
industrial scale production of second generation HTS wire. The
in-plane alignment of the RBCO film necessary for high critical current
densities can be achieved by depositing biaxially textured buffer layers
by inclined substrate deposition (ISD).
The MgO buffer layer is grown at room temperature on electropolished
Hastelloy tape by ISD using electron beam evaporation at roughly
3nm/s and inclination angle of 25 ◦ with respect to the substrate normal.
This results in an in-plane alignment of 11 ◦ − 12 ◦ (FWHM). Meanwhile
33m long buffered Hastelloy tape has been fabricated using a 15 loop
tape winder. HTS deposition is currently performed on 20m long and
1cm wide tape. Average critical current densities over several meters of
tape are about 1.0MA/cm 2 at 77K, i.e. 100A/cm of transport current in
a 1µm DyBCO film.
We also present results on samples up to 20cm optained by HTSdeposition
in static mode which can be summarized as follows: Dy-
BCO on IBAD buffered tape exhibit critical current densities jc (77K)
>2.0MA/cm 2 whereas MgO-ISD-buffer sustain jc in the range of
1.6MA/cm 2 . Ni5%W-RABiTS tape can carry up to 0.8 - 1.2MA/cm 2 .
TT 8.13 Mo 14:30 Poster A
YBCO thin films prepared by a Fluorine-free sol-gel method
— •C. Apetrii 1 , I. v. Lampe 2 , M. Falter 1 , H. Schlörb 1 , B.
Holzapfel 1 , and L. Schultz 1 — 1 IFW Dresden, Helmholtzstr. 20,
01069 Dresden — 2 TU Berlin, Institut für Werkstoffwissenschaften und
-technologien, Englische Str. 20, 10587 Berlin
The chemical solution deposition procedure is a low cost method due
to non-vacuum approach for growing longer YBCO tapes. The polymer
metal precursor technique, a fluorine-free sol-gel method, leads to a stable
and non-aggressive precursor solution and also HF does not form during
the process. HF is difficult to remove in precursor films prepared by the
Trifluoracetates (TFA-method). Y, Ba, and Cu nitrates were chosen as
a starting substances for the preparation of the polymer metal precursor
to avoid the formation of BaCO3. The polymer metal precursor films
were produced by spin coating of a stoichiometric solution onto SrTiO3
single crystal substrate and then dried at 170 ◦ C. The heat treatment
was performed in a tube furnace with reaction temperature of 775 ◦ C. We
obtained epitaxially grown 240 nm thick YBCO films on single crystal
SrTiO3 with a resistively measured Tc of 89.9 K and ∆T of 2.0 K. The
temperature dependence of the critical current density was measured using
the standard 4 point geometry on 20 µm wide bridges and values of
10 5 A/cm 2 (at 77 K) were received.
TT 8.14 Mo 14:30 Poster A
Preparation of perovskite buffer layers on surface oxidized
Ni tapes for coated conductor applications — •R. Hühne 1 , B.
Holzapfel 1 , A. Kursumovic 2 , B. A. Glowacki 2 , J. E. Evetts 2 ,
A. Cavallaro 3 , F. Sandiumenge 3 , A. Pomar 3 , T. Puig 3 , and X.
Obradors 3 — 1 IFW Dresden, Germany — 2 Department of Materials
Science, University of Cambridge, UK — 3 Institut de Ciencia de Materials
de Barcelona, Spain
The preparation of cube textured NiO buffer layers on biaxially textured
Ni tapes (RABiTS) using surface oxidation epitaxy (SOE) offers a
cheap and scalable route for the production of long-length YBCO coated
conductors. A second buffer layer is necessary to ensure epitaxial growth
of the YBCO as well as to prevent Ni contamination of the superconducting
layer. Therefore, different perovskite buffer were grown on SOE-NiO
using pulsed laser deposition (PLD) and metal-organic decomposition
(MOD). Ca0.6Sr0.4TiO3, BaZrO3 and SrZrO3 buffers were successfully deposited
on NiO showing a high quality epitaxial growth with an in-plane
orientation similar to the underlying NiO. The subsequent deposition of
YBCO on top of these buffers using different methods resulted in epitaxial
layers with a Tc0 above 83 K and jc up to 1 MA/cm −2 . Microstructural
investigations showed that in all cases the roughness and the surface topography
of the buffer layers is mainly determined by the quality of the
NiO layer.
TT 8.15 Mo 14:30 Poster A
Ca- und Ag-dotierte YBCO-Filme aus Polymer-Metall-
Precursoren auf STO und Ni-YSZ-Substrat — •Frank
Zygalsky und Irene von Lampe — TU-Berlin, Inst. f. Werkstoffwissenschaften
u. -technologien, Englische Str. 20, 10587 Berlin
Die thermische Zersetzung von durch Spincoating erzeugten Polymer-
Metall-Precursorschichten stellt ein verfahrenstechnisch unkompliziertes
Schichtdepositionsverfahren zur epitaktischen Abscheidung von hochtemperatursupraleitenden
Phasen dar. Ziel der Forschungsarbeit ist die
Weiterentwicklung dieses kostengünstigen Nicht-Vakuum-Verfahrens hinsichtlich
Epitaxiequalität und kritischer Stromdichte der erzeugten
HTSL-Schichten. Dabei wird die Schichtabscheidung sowohl auf einkristallinen
STO-Substraten als auch auf technisch relevanten biaxial texturierten
Ni-Metallbändern mit YSZ-Pufferschicht betrachtet, sowie der
Einfluß von Ca- und Ag-Dotierungen auf die supraleitenden Eigenschaften
untersucht.
TT 8.16 Mo 14:30 Poster A
Superstructure on hightemperature superconductors (N=1,2,3)
affirmed with STM — •Torsten Stemmler, Hendrik
Glowatzki, and Recardo Manzke — Humboldt-Universität,
Institut für Physik
We present new pictures on HTCs from STM.
TT 8.17 Mo 14:30 Poster A
Oxygen superstructures throughout the phase diagram
of (Y,Ca)Ba2Cu3O6+x — •Joerg Strempfer 1 , Ioannis
Zegkinoglou 1 , Uta Ruett 1 , Martin von Zimmermann 2 ,
Christian Bernhard 1 , Chengtian Lin 1 , Thomas Wolf 3 ,
and Bernhard Keimer 1 — 1 Max-Planck-Institut fuer Festkoerperforschung,
Heisenbergstr. 1, 70569 Stuttgart — 2 Hamburger
Synchrotronstrahlungslabor HASYLAB at DESY, Notkestr. 85, 22603
Hamburg — 3 Forschungszentrum Karlsruhe, ITP, 76021 Karlsruhe
Short-range lattice superstructures have been studied with high-energy
x-ray diffuse scattering in underdoped, optimally doped, and overdoped
(Y, Ca)Ba2Cu3O6+x. A new four-unit-cell superstructure was observed
in compounds with x=0.92. The great similarity of the diffuse
scattering pattern of the YBa2Cu3O6.92 compound with the one of
Y0.8Ca0.2Ba2Cu3O6.95, which has approximately the same oxygen-content
but different charge carrier concentration due to the Ca- substitution,
clearly indicates that the origin of these superstructures lies in shortrange
oxygen vacancy ordering rather than in electronic instabilities in
the CuO2 layers. This is further supported by the absolute absence of
any significant diffuse scattering in YBa2Cu4O8, a compound that contains
no oxygen vacancies. The persistence of the diffuse reflections up
to temperatures well above room temperature is also not in favour of the
stripe-related scenario for their origin.