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Lattice structure and misfit between substrate/buffer/YBCO conductor

perovskiterocksaltfcc structurespinelfluoriteC-type REpyrochlore

Material Structure Tm/ oC a0 (300K) Lm

MisfitYBCO (%)

Misfit to Ni (%)

Misfit to NiO

(%)Ni fcc 1455 3.52 3.52 -9.38 0.00 -18.47

YSZ cubic / fluorite 2680 5.13 3.63 -6.06 3.03 -14.88

Gd2Zr2O7 cubic / pyrochlore 10.52 3.72 -3.49 5.38 -12.10

Y2O3 cubic / Mn 2O3 >2400 10.6 3.75 -2.67 6.13 -11.20

LaAlO3 rhombohedral / perovskite 2100 5.36 3.79 -1.58 7.12 -10.03

La2Zr2O7 cubic / pyrochlore 2300 10.8 3.81 -1.05 7.61 -9.45

Gd2O3 cubic / Mn 2O3 >2400 10.81 3.82 -0.79 7.85 -9.16

CaTiO3 orthorhombic / perovskite 5.38x5.44 3.82 -0.79 7.85 -9.16

CeO2 cubic / fluorite 2600 5.41 3.83 -0.52 8.09 -8.88

Eu2O3 cubic / Mn 2O3 >2300 10.87 3.84 -0.26 8.33 -8.59

LaNiO3 rhombohedral / perovskite 5.45 3.84 -0.26 8.33 -8.59YBCO orthorhombic 3.83x3.88 3.85 0.00 8.57 -8.31

Ca0.6Sr0.4TiO3 orthorhombic / perovskite 5.46x5.46 3.86 0.26 8.81 -8.03

NdGaO3 orthorhombic / perovskite 1670 5.43x5.5 3.86 0.26 8.81 -8.03

Sm2O3 cubic / Mn 2O3 >2300 10.93 3.86 0.26 8.81 -8.03

La2NiO4 tetragonal 3.86 3.86 0.26 8.81 -8.03

Sr2RuO4 tetragonal 3.87 3.87 0.52 9.04 -7.75LSMO rhombohedral / perovskite 5.49 3.88 0.77 9.28 -7.47NdBCO orthorhombic 3.87x3.92 3.89 1.03 9.51 -7.20

Pd fcc 1555 3.89 3.89 1.03 9.51 -7.20

Gd2CuO4 tetragonal 3.89 3.89 1.03 9.51 -7.20

SrTiO3 cubic / perovskite 2080 3.91 3.91 1.53 9.97 -6.65

LaMnO3 orthorhombic / perovskite 5.54x5.74 3.91 1.53 9.97 -6.65

Nd2O3 cubic / Mn 2O3 >2300 11.08 3.92 1.79 10.20 -6.38

SrRuO3 orthorhombic / perovskite 5.57x5.54 3.93 2.04 10.43 -6.11

Nd2CuO4 tetragonal 3.94 3.94 2.28 10.66 -5.84

BaTiO3 tetragonal / perovskite 3.99 3.99 3.51 11.78 -4.51Ag fcc 961 4.09 4.09 5.87 13.94 -1.96

SrZrO3 orthorhombic / perovskite 2800 5.79x5.82 4.10 6.10 14.15 -1.71

BaSnO3 cubic / perovskite 4.12 4.12 6.55 14.56 -1.21NiO cubic / rocksalt 1984 4.17 4.17 7.67 15.59 0.00

BaZrO3 cubic / perovskite 2690 4.19 4.19 8.11 15.99 0.48MgO cubic / rocksalt 3100 4.21 4.21 8.55 16.39 0.95TiN cubic / rocksalt 4.24 4.24 9.20 16.98 1.65

Conductive

buffer layers

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Twisted conductor

- the filaments must be transposed (or twisted) at least one time in the middle of the length provided that the magnetic field is exactly symmetric along both half lengths

-twisted decoupled filaments - ac loss reduction coefficient

- large circulating currents can exist among the filaments due to connections at the ends (in current leads)

-ac losses may increase by one order of magnitude or more in dependence on the distance between the filaments and the resistance at the end.

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3) multifilamentary tapes in a transverse magnetic field

- hysteresis losses in perpendicular magnetic field - about 2-3 orders ofmagnitude higher than in parallel field

Ho - amplitude of the applied magnetic field

w - tape width t - tape thickness

-for decoupled filaments - ac loss reduction directly proportional to the number of filaments (proved experimentaly)

Ho

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Initial design of multifilamentary CC for Supergenerator

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Multifilamentary YBa2Cu3O7 Coated Conductor

CC-20 filaments CC-1filament

1cm

Single filament < 500m

IRC in Superconductivity testing

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AC field AC current anisotropy at the IRC in Superconductivity

Magnet requirement for YBCO coated conductors in supergenerators is about 2T/400 Hz

QI/Q||~100 (high precision of angle required in parallel field - of the order of 0.1 degree)

Current AC magnet capability

In phase and out of phase measurements for transformers and generators

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Division to smaller filaments essential for Ha perp. to ab plane

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Transport critical current vs angle + Ca doping

102

103

104

105

106

107

0 2 4 6 8 10

grain2 deg4.5 deg7 deg15 deg20 deg24 deg

Cri

tica

l cu

rren

t de

nsit

y J

c (A

cm-2)

Magnetic field oH (Tesla) 102

103

104

105

106

107

0.0 10 20 30 40

BulkThin filmLPE

Cri

tica

l cu

rren

t J

c (A

cm-2)

Angle (degrees)

30

40

50

60

70

80

90

100

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Y0.8Ca0.2Ba2Cu3O6+xYBa2Cu3O6+x

Cri

tical Te

mp

era

ture

Tc

(K)

Oxygen content, x

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Current percolation through the dislocations

I

Important factors:

• conductor aspect ratio • magnetic field angle • sample history • shunt layers, contactswidth

length

4Å

HREM of LAGB

[N.D. Browning et al, Micron 30, 425 (1999)]

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hInfluence of misoriented Ni grains on YBCO layer

CuO precipitates

NiO layer grown by surface oxidation epitaxy

CSTO grown by PLD via an amorphous route

YBCO grown by PLD

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0

0.05

0.1

0.15

0.2

0.25

1 10 100 1000 10000

Length (no. of grains)

Jc/J

c0

w=3

w=5

w=9

w=17

w=33

w=129

w=513

1 filament

5 filaments

11 filaments

Recommended division of the coated conductors to narrower tracks/filaments is a compromise between reduction of the current in the longer tracks and gain in reduction of AC losses.

w

l

Transport direction

2° 4° 6° 8°

The EBS maps above show regions misoriented by 2°, 4°, 6°, and 8° in a small area of the NiFe substrate.

Using a model with a 2D array of R rows and C columns of hexagonal grains (shown above left), a number of parameters may be assessed over a range of threshold angles.

Current percolation in In-plane and out of plane misoriented GB

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B.A.Glowacki

p=5

p=1

A New Grain Structure Model

MCS = 2 MCS = 25 MCS = 100

A Monte-Carlo grain growth model has been used to simulate more realistic grain structures. The grains are initially made up of single square pixels.

Each pixel has an energy based upon the number of neighbours which are in the same grain.

High energy pixels are consumed by neighboring grains.

As the simulation progresses, grain structures such as those below develop.

After N Monte-Carlo Steps (MCS) each pixel will, on average have been considered N times.

The average grain size in pixels (p) is related to MCS. The figures above shows grain structures for p=1 (simple square model) and p=5, both for samples 25 grains long and 10 grains wide.

2-D Grain growth modelling IBAD and RABIT

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Ic vs length and width of Coated Conductor

Ic (1/NL)1/NW

… a useful working approximation is

10 km1 cm

NL NW

Ic

102

104

106

108102

104

[Rutter and Goyal MRS 2003]

Nw=300 grains

Nw=100 grains

Nw=30 grains

Nw=10 grains

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Orientation of the GB in respect to the applied magnetic field is important

In plane critical current vs magnetic field measurements on YBCO thin films: (a) angular dependence of the critical current crossing low angle grain boundary at 8T. For the higher GB angle the minimum is wider and the absolute valuses are substantially lower; =90o represents Lorentz force-free configuration. Hexagons represent grains whereas black outlines of hexagons represent

grain boundaries; (b) schematic of the Jc vs (B,) in plain measurements.

Elongated hexagonal grains have the better percoative properties than the simple hexagonal ones. There is a difference in the response of hexagonal grains if all of them are aligned.

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Solution for the high magnetic field and low temperature magnet applications

NbTi + Nb3Sn + NbTi3(Sn,Ta) = 22.59T additional magnetic field generated by Bi-2212 coil = 1.46T ; total field > 24T

YBa3Cu2O7 B

I

High magnetic field superconducting electromagnet. (a) schematic cross section of the multi-section hybrid electromagnet. The materials used are NbTi + Nb3Sn + NbTi3(Sn,Ta) resulting in

22.59 Tesla and if additional magnetic field is generated by internal coil in the centre it would generate an additional field. The total magnetic field in such a hybrid configuration, currently exceeds 24 Tesla. (b) schematic outline of the favourable grain structure of the internal HTS coil

made from the YBa2Cu2O7 coated conductor.

(a) (b)

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B.A.Glowacki Presence of the magnetic material can have a detrimental and also beneficial influence on the reduction of AC losses and increase of Jc of superconductors. This problem is particularly important in case of the coated conductors and multifilamentary wires. The latest research on the multifilamentary conductors surrounded by magnetic material proved that losses can be reduced substantially according to eq.1 by coating individual filaments by magnetic material.

By comparing losses in a standard multifilamentary superconductor, Qst, to losses in a multifilamentary superconductor with the magnetic covers around individual filaments, Qcov, at the same reduced current i, one can obtain magnetic decoupling loss reduction coefficient, Kmd, (eq.1); where i=I/Ic Ic1=Ic/N, N number of filaments. The parameters k(i) and are to be determined from experiment and represent individual filament.

K md Q stQ cov

I c

2 F i Nk i a 2 I c 1

2 F i

N 2 I c 12

Nk i 2 I c12 N

k i 2 (eq.1)

3) multifilamentary tapes in a transverse magnetic field

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Minimisation of AC losses Magnetic decoupling

0

0.05

0.1

0.15

0.2

0.25

1 10 100 1000 10000

Length (no. of grains)

Jc/J

c0

w=3

w=5

w=9

w=17

w=33

w=129

w=5131 filament5 filaments11 filaments

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0 2 4 6 8 10 12

Ac loss

(Jm-1

)

Number of filaments

0.25mW/Am

0.45mW/Am

1.7 mW/Am !

Recommended division of the coated conductors to narrower tracks/filaments is a compromise between reduction of the current in the longer tracks and gain in reduction of AC losses.