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MOCVD and MOD of YBCO and Buffer Layers on Textured

Metal Tapes

Journal: IEEE Transactions on Applied Superconductivity; Special Issue from

the Applied Superconductivity Conference

Manuscript ID: 1MPH02.R1

Subject Area: Materials

Date Submitted by the

Author: 31-Oct-2008

Complete List of Authors: Stadel, Oliver; PerCoTech AG Muydinov, Ruslan; University of Braunschweig, Institut für Oberflächentechnik Bräuer, Günter; University of Braunschweig, Institut für Oberflächentechnik Rikel, Mark; Nexans SuperConductors Ehrenberg, Jürgen; Nexans SuperConductors Bock, Joachim; Nexans SuperConductors Kotzyba, Gunter; Forschungszentrum Karlsruhe, Institut für Technische Physik

Nast, Rainer; Forschungszentrum Karlsruhe, Institut für Technische Physik Goldacker, Wilfried; Forschungszentrum Karlsruhe, Institut für Technische Physik Samoylenkov, Sergej; Moscow State University, Chemistry Department Kaul, Andrej; Moscow State University, Chemistry Department

1MPH02.R1

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Abstract—Different layer architectures produced by only

MOD, only MOCVD and combinations of MOD buffers and

MOCVD YBCO are presented. RTR MOCVD-YBCO layers

obtained on MOD-CeO2/MOD-LZO/Ni5at%W tapes

demonstrate critical current densities up to 2 MA/cm2 at 77 K.

On single LZO (50-100 nm) buffered Ni5at%W tapes from

Nexans Superconductors and on RTR MOCVD buffer layers

critical current densities between 0.8 and 1.3 MA/cm are

obtained. RTR MOD-LZO layers often show delamination

during YBCO deposition. Preannealing treatment before YBCO

deposition allows to avoid this. Tapes up to 10 m are produced by

combination of MOD-LZO and RTR MOCVD-YBCO.

Index MOCVD, MOD, Coated Conductor, RABiTS

I. INTRODUCTION

hemical methods (Metal Organic Deposition: MOD and

Chemical Vapour Deposition: CVD) for superconducting

layers in Coated Conductors (CC) are rather established [1, 2,

3] whereas the buffer layers are usually produced by PVD

techniques (Physical Vapour Deposition). The buffer layer

architecture must enable epitaxial growth of YBCO with high

texture and prevent diffusion between the superconductor and

the metal substrate. Different numbers of buffer layers like 5

[1], 3 [3, 4] or 2 [5, 6] have been used for production.

Until now chemically produced buffer layers could not

fulfil the demands of high quality buffer layer architecture.

Although excellent MOD-YBCO was grown on MOD-

CeO2/MOD-LZO/PVD-Y2O3/Ni5at%W an all chemical buffer

layer approach did not allow the same quality as PVD-

techniques [7]. In this paper we will show the high potential of

MOD, CVD and their combination. Such total chemical

Manuscript received 15 August 2008. This work was supported in part by

BMBF within the WING program (project SupraNanoSol).

O. Stadel, is with PerCoTech AG, Bienroder Weg 53, 38108

Braunschweig, Germany (phone: +49-531-391-9424; fax: +49-531-391-9424; e-mail: o.stadel@percotech.de).

R. Yu. Muydinov and G. Bräuer are with Technical University

Braunschweig, Institut für Oberflächentechnik, Braunschweig, 38108 Braunschweig, Germany (e-mail: r.muydinov@tu-bs.de).

M. Rikel, J. Ehrenberg and J. Bock are with Nexans Superconductors

GmbH, Chemiepark Knappsack, 50351 Hürth, Germany (e-mail: mark.rikel@nexans.com).

G. Kotzyba, R. Nast and W. Goldacker are with the Forschungszentrum

Karlsruhe, Institut für Technische Physik, P.O.Box 3640, 76021 Karlsruhe, Germany (gunter.kotzyba@itp.fzk.de).

S. V. Samoylenkov and A. R. Kaul. are with Moscow State University,

Dept. of Chemistry, 119992, Mosсow V-234, Russia (e-mail:sam2@inbox.ru).

approach allows simple buffer layer architecture and promises

cost effective production of CC.

II. EXPERIMENTAL

A. Templates

The textured metal substrates are produced by

Forschungszentrum Karlsruhe (FZK), IFW Dresden and evico

GmbH. Only results on Ni4at%W and Ni5at%W alloyed tapes

will be presented in this paper. The experimental procedure

for production of these tapes is described elsewhere [8, 9]

B. MOCVD

A solution with Metal-(thd) precursors (thd =

Tetramethylheptanedionate) is used in the single source

evaporator. Buffer and YBCO are coated in two different

reactors in the same MOCVD system (Metal Organic CVD).

The buffer layer is deposited at sufficient low oxygen partial

pressure not to oxidize Ni. In the MOCVD YBCO process a

mixture of N2 and O2 is used. The reported layers are coated

on 10 mm wide textured Ni-W tapes with velocities of 4-

5 m/h. The length of the coated tapes is between 0.1 and 1 m.

The MOCVD-system is described elsewhere [10]. Normally

the buffer layer quality is investigated by XRD and SEM and

then tested by deposition of a 350 nm thick YBCO film.

Additionally it was proven, that buffer and YBCO can be

deposited in one Reel to Reel coating process (RTR). The

metal tape passes only a single time the deposition zone. This

design avoids complicated moving mechanical parts in the

reactor like reverse rollers.

C. MOD

At FZK the precursors Ce(III) 2,4 pentanedionate hydrate,

La (III) 2,4 pentanedionate hydrate and Zr (IV) 2,4

pentanedionate hydrate are solved in propionic acid. The

precursor concentrations are 0.4 mol/l La3+

and Zr4+

for the

LZO-layer and about 0.25 mol/l Ce3+

for the CeO2 layer,

respectively. The ratio of La3+

and Zr4+

in the solution is

controlled by means of ICP OES (Inductively Coupled Plasma

Optical Emission Spectrometry). The tapes are dip coated at a

withdrawing velocity of 13 cm/min. The samples are dried at

200 °C in air and annealed under Ar/5% H2 at temperatures

between 1000 and 1100 °C for 30 min (LZO) and 15 min

(CeO2). Then the tapes are quenched to ambient temperature.

Up to 10 m long MOD-LZO-buffered Ni5at%W substrates

were produced at Nexans using their RTR-MOD system with

rigorous control of its quality [10]. The LZO crystallization

MOCVD and MOD of YBCO and buffer layers

on textured metal tapes

O. Stadel, R. Yu. Muydinov, G. Bräuer, M. Rikel, J. Ehrenberg, J. Bock, G. Kotzyba, R. Nast,

W. Goldacker, S. V. Samoylenkov, A. R. Kaul

C

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step was conducted either in continuous or static modes.

III. ALL RTR MOCVD

X-ray diffraction (XRD)) measurements show very good

YBCO in-plane and out-of-plane texture (5-8° and 1.5-4°,

respectively) on MOCVD buffered Ni alloyed tapes. The

excellent out-of-plane texture (much better than that of the Ni-

W substrate) was reported earlier [9]. Usually the YBCO film

had a preferential c-axis orientation sometimes with a small

part of a-axis orientation.

Fig. 1. Critical current density of all RTR MOCVD coated Ni-W-tape.

Figure 1 shows the Jc-measurements (Cryoscan, THEVA)

of a 19 cm long and 10 mm wide all RTR MOCVD Coated

Conductor sample. Only the results of the inner part of the

sample are displayed because of fringe effects. The j-V Graph

represents some typical curves with Jc = 0.8-1.2 MA/cm2. The

Jc-map of the tape shows a critical current density between 0.4

and 1.2 MA/cm2. The YBCO thickness is 350 nm. XRD-

measurements suggest that regions with lower Jc have worse

texture of the buffer layer.

IV. ALL MOD

A. Buffers

EBSD measurements show an excellent cube texture of

200 nm thick MOD-LZO layers (figure 2). The same high

texture without cracks (figure 3) can be detected for the MOD-

CeO2 buffer layer on top of the LZO buffer.

Fig. 2. EBSD (Electron Backscatter Diffraction) pictures of MOD-LZO on Ni4at%W (FZK): maps of the film texture and corresponding graphs of the

grains and grain boundaries.

Nexans MOD-LZO process is now in the stage of up

scaling to 50 m length. MOD process for (Ce,Gd)O2 (CGO)

buffer is under development on the lab scale.

Fig. 3. Scanning Electron Microscope (SEM) pictures of CeO2/LZO/Ni4at%W (FZK).

B. TFA-YBCO process

Nexans Superconductors is developing the standard TFA-

YBCO process with the final goal of making all CSD

YBCO/CGO/LZO/Ni-W conductors.

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Fig. 4. XRD pattern of all CSD sample MOD-TFA YBCO(200 nm)/CGO(30 nm)/LZO(50 nm)/Ni-W.

Figure 4 shows the XRD pattern of an all MOD tape sample

with rather good YBCO texture, moderate oxidation of Ni-W,

and only partly reacted CGO layer. This YBCO film exhibits a

low Jc < 0.1 MA/cm2.

The quality of MOD-CGO layer is considered as a major

issue. A good epitaxy of this layer was only possibly in thin

(≤30 nm) layers and only if the LZO layer is 100% epitaxial,

which is currently also achievable only in 50 nm thick layers.

We believe that the thin LZO layer that could not inhibit the

diffusional interaction between YBCO and the substrate is the

reason for low Jc.

C. Fluorine free YBCO process

Highly c-axis oriented and in plane textured YBCO films

are obtained on CeO2/LZO/Ni4at%W tapes. However the Jc of

the YBCO film is below 0.1 MA/cm2. This could be caused by

precipitation of BaCO3, which was detected by XRD Θ−2Θ

measurements. On single crystals this flourine free MOD-

YBCO process leads to critical current densities up to

2.8 MA/cm2. Further investigations are needed whether the

formation of BaCO3 on LZO buffered Ni-W tapes can be

avoided.

V. MOD BUFFERS AND MOCVD YBCO

A. MOCVD-YBCO on MOD double buffer layers

3-5 cm long tape pieces, which are coated twice with MOD-

LZO (to 200 nm final thickness) and then with MOD-CeO2

(50 nm), are used for RTR CVD-deposition of YBCO

(350 nm). The inductive Jc of several samples is between 1-

2.1 MA/cm2.

B. MOCVD-YBCO on MOD LZO/Ni-W

1) RTR MOD Stationary Annealed Single Buffer Layers

MOD-LZO tapes with a length up to 10 m are provided by

Nexans Superconductors to PerCoTech for RTR-YBCO. The

LZO is produced by single RTR dip coating and followed by

stationary crystallization heat treatment. Up to 90% epitaxial

LZO layer (see [11]) over the whole length was obtained.

The results of MOCVD-YBCO on MOD-LZO/Ni-W were

presented earlier by our group [12, 12] and then by the group

from Grenoble [13]. The reported inductively measured

maximum Jc were 1.1 MA/cm2 on a 150 mm long [13] and

max. 0.8 MA/cm2 [15] on a 15 mm long sample. Both Ni-W

samples were buffered only with 80-100 nm thick MOD-LZO.

The measured end-to-end direct currents were 58 A for 10 cm

long and 21 A for 4.4 m long tapes [13].

The reduction of the MOD-LZO thickness to 50 nm still

enable the growth of MOCVD-YBCO, but the critical current

density is slightly lower. Figure 5 shows the Jc-map of 350 nm

thick YBCO on 50 nm thick LZO buffered Ni-W. The

maximum Jc is 0.88 MA/cm2.

Fig. 5. Critical current density of YBCO on single buffered 50 nm thick-LZO.

The XRD measurement in figure 6 show the textured LZO,

the preferential c-axis and partly a-axis oriented YBCO and

low Ni-oxidation. In comparison to the TFA-MOD process

higher local deposition rate at similar deposition temperature

allows a shorter exposure time of few minutes.

Fig. 6. XRD Θ−2Θ-measurement of RTR MOCVD-YBCO(350 nm)/MOD-LZO(50 nm)/Ni5at%W.

2) RTR MOD Continuously Processed Single Buffer

Layers

Nexans SuperConductors produced 10 m long 80-150 nm

thick MOD-LZO buffered on Niat%5W tapes in a continuous

RTR process. At PerCoTech these tapes were coated with

RTR MOCVD-YBCO (Fig. 7).

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Fig. 7. 10 m long RTR MOCVD-YBCO/MOD-LZO/Ni5at%W tape.

Although the same high quality (>80% epitaxy) LZO buffer

layer was produced in both stationary and continuously

processed LZO/Ni5at%W substrates, deposition of CVD

YBCO on the latter was accompanied by a severe

delamination (Fig. 8) with peeling off between either LZO and

the oxidized Ni5at%W (major mode) and sometimes along the

YBCO /LZO interface.

Fig. 8. Delamination after YBCO deposition on RTR-LZO.

The mechanism of delamination is not clear. It is obviously

related to particular processing conditions, but not to the

conductor architecture. It is known that carbon dissolved in

the metal substrate can lead to delamination after buffer layer

or YBCO deposition [15]. Internal stresses and/or defects in

the buffer layer may play a role.

Fig. 9. CVD-YBCO/RTR MOD-LZO/Ni5at%W and its Jc-map (two scales).

MOD-LZO/NiW was preannealed before YBCO deposition, which suppresses

delamination.

Whatever the reason, we found that preannealing the RTR

LZO/Ni5at%W substrates before CVD YBCO deposition may

suppress delamination. This is demonstrated on short samples

(Fig. 9); Jc up to 1.25 MA/cm2 was achieved. Experiments on

long lengths are under way.

VI. CONCLUSION

MOD and MOCVD buffers on Ni-W enable the YBCO

deposition with critical current densities of 1-2 MA/cm2. Only

low critical current densities are obtained for all MOD of CC.

The end-to-end current of 0.1 m and 4.4 m long

YBCO(700 nm)/LZO(100 nm)/Ni5at%W tape is 58 A and

21 A, respectively. 10 m long Ni5at%W tapes are coated by

all chemical RTR methods.

The combination of MOCVD-YBCO and MOD-LZO

demonstrated the worldwide simplest layer architecture and

promises the cost effective production of CC.

ACKNOWLEDGMENT

We acknowledge R. Semerad (THEVA) and our colleagues:

H. Keune, J. Schmidt (PerCoTech AG), G. Wahl (Technical

University Braunschweig), A. Will, A. Jung

(Forschungszentrum Karlsruhe), A. Blednov, G. Dosovitsky

and O. Gorbenko (Moscow State University) for their help.

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