Hiroaki Kumakura

National Institute for Materials Science(NIMS)

INTERNATIONAL WORKSHOP ON Construction of Low-Carbon Society Using

Superconducting and Cryogenics Technology, Mar. 7-9, Osaka

Outline

1. MgB2 wires(ALCA project)

2. BSCCO(Bi-2223 and Bi-2212) tapes

and wires

3. Summary

Bi-based high-Tc oxide and MgB2 tapes and wires

promising for CO2 emissions reduction

0

5

10

15

0 5 10 15 20 25 30 35 40

上部

臨界

磁界

, H

c2(T

)

温度, T(K)

Nb-Ti

Nb3Sn

無添加

10%SiC添加

H//c軸(薄膜)

H//ab面(薄膜)

Hc2 (

T)

10%-SiC-doped

MgB2 wire

H//c-axis

(MgB2 thin film)

MgB2 wire

w/o SiC doping

T (K)

(MgB2 thin film) H//a-b plane

Nb-Ti wire(4.2K operation)

MgB2 wire

(20K operation with

LH2 or cryocooler）

Bc2 of PIT processed MgB2 wire

High quality MgB2 single crystal

Zehetmayer M et al,

Phys. Rev. B 66(2002) 0525051-4

X. Zeng, et al., Nature Mater. 1(2002)35.

Examples of MgB2

wires and tapes

Mg+B+(SiC) powder

Metal tube

Heat treatment

Multi-filament

wire

Multi-filament

tape

Fabrication of MgB2 wire and tape

Powder-In-Tube(PIT) method

drawing

No grain orientation is required!

104

105

106

0 2 4 6 8 10 12

Jc (

A/c

m2)

Magnetic Field B(Tesla)

tape(PIT)

MgB2/-Al

2O

3 thin film

(PLD method) 4.2K

tape(PIT)20K

Nb3Sn

The density of MgB2： ~50%

Microstructure of PIT MgB2 wire

Shrinkage of volume

during heat treatment Mg+B MgB2

B: 2.34g/cm3

Mg: 1.7

MgB2: 2.6

Typical Jc-B curves of PIT processed MgB2 tape

One big problem of PIT is the low packing

density (large porosity) of MgB2 core.

Comparison of IMD and PIT

Metal Tube

B Powder Mg rod

Internal Mg diffusion(IMD) process

Mg+B Powder

PIT process PIT method

Packing density: ~50%

IMD method

Packing density: ~80%

Metal Tube

B+Mg(+SiC) powder

PIT method

B(+SiC) powder

Mg

diffusion

Mg diffusion method

Mono core wire

Cu-Ni Ta

200mm 200mm

200mm 200mm

Mg

B+SiC

7-filament wire

19-filament wire

Internal Mg Diffusion (IMD) Process

1.2 mm

Longitudinal cross sections of IMD processed MgB2 wires

(uniformity in longitudinal direction)

1000

104

105

7 8 9 10 11 12 13

En

gin

ee

rin

g J

c(J

e)

A/c

m2

Magnetic field H(T)

4.2K

PIT wire

IMD wire

104

105

0 2 4 6 8 10 12

Cri

tica

l cu

rren

t d

ensity J

c(A

/cm

2)

Magnetic field H(T)

IMD wire

PIT wire

IMD wire

PIT wire

4.2K

20K

Jc and Je comparisons of IMD and PIT

processed wires

Filament structure of IMD multi-filamentary wires

200μm

7-filaments

Ta

200μm

19-filaments

50μm

Ta Reacted Layer

The diffusion distance by

Mg liquid infiltration is

limited to <50μm !

The reduction of filament size is essential to complete the

reaction with short heat treatment time !

Single-filaments

-30 130

Measured magnetic field Bz (mT)

Lift-off: 200 mm

Jc_SiC (A/cm2)

0.0

5.0 x 105

1.0 x 106

1.5 x 106

2.0 x 106

1 2 3 4 5 6 7 8 9

Jc (A/cm2)

@10 K,0 T

x (mm)

-300 0 300

Measured magnetic field Bz (mT)

Bz |dBz0/dx,dy| superpose SEM

Locally low property Localized Mg2Si

J = 1 MA/cm2 per Bpeak = 80 mT

0.2 mm

1 mm

Local Ic distribution of SiC added IMD wire

(Analysis by scanning hole probe microscope)

LT-SHPM, Kiss Lab. Kyushu Univ.

(K. Togano et al.,

Supercond. Sci. Technol. 22 (2009) 015003)

About 3 times higher Jc is expected by the improvement of the homogeneity.

△: locally maximum Ic

estimated by the SHPM

Comparison of Jc values obtained by the resistive

method and SHPM

LT-SHPM, Kiss Lab. Kyushu Univ.

Comparison of C24H12 and SiC addition

(IMD processed MgB2 wires)

7 8 9 10 11 1210

3

104

105

IMD wires, = 0.6 mmJc (

A/c

m2)

B (T)

undoped

SiC-added

C24-added

Jc = 1.02 x 10

5 A/cm

2 4.2 KJc = 1.1x105A/cm2

7 8 9 10 11 1210

2

103

104

Je = 1.13 x 10

4 A/cm

2

IMD wires, = 0.6 mm

B (T)

Je (

A/c

m2)

undoped

SiC-added

C24-added

4.2 KJe = 1.3x104A/cm2

Coronene(C24H12)

Decomposition temperature:

~600oC

TEM image

104

105

106

0 2 4 6 8 10 12

Critica

l cu

rre

nt

de

nsity, J

c(A

/cm

2)

Magnetic field, H(T)

4.2K

20K

PIT wire

IMD wire

PLD thin filmNb

3SnNb-Ti

PIT wire

IMD wire

PLD thin film

Present status of MgB2 wires

eirr d(Ic/Ic0)/de

IMD 0.67% 0.143

PIT 0.54% 0.213

IMD-MgB2 wire shows larger

eirr and smaller strain

sensitivity

0.67%

0.54%

slope=0.21

slope=0.14

a

a’

b

b’

c

c’

d

d’

e

e’ a

a’

b

b’

c

c’

Stress effect of PIT and IMD mono-filamentary MgB2

wires(at 10 T, 4.2 K)

Voids at the center of IMD wires

seem to have no negative effect

on strain sensitivity of Jc.

Superconducting joint of IMD processed MgB2 wire

Fe sheath

C24H12 added MgB2 wire Mg

core

B layer

Pressing

(one end)

Metal tube

Pressing

Heat treatment

(under the same

condition as the

wire)

Fe or SS tube

Examples of joints

1

10

100

0 2 4 6 8 10 12Magnetic field B(T)

Critica

l curr

en

t I c

(A)

Fe tube

Wire

S.S. tube

4.2K

Ic-B curves of superconducting joints(IMD MgB2 wire)

Crystal structure of Bi-based oxide superconductors

Bi2Sr2CaCu2O8+d

(Bi-2212) Bi2Sr2Ca2Cu3O10+d

(Bi-2223)

Bi-2212 (n = 1) Bi-2223 (n = 2)

N.S.C

S.C.

N.S.C.

S.C.

N.S.C.

Tc ~ 90K

Tc~110K

Bi

Cu

Sr

Ca

O

a-axis

b

c

Bi-based oxide wire and tape fabrication by a powder-in-tube(PIT) method

Powder Bi2O3, SrCO3, CaCO3, CuO

Metal tube(Ag)

Heat treatment

Multi-filamentary wire

(Bi-2223)

Multi-filamentary tape

drawing

Grain orientation of Bi-oxide is essential

to obtain large current transfer.

結晶粒の配向化が必須

Microstructure of Bi-2212 tape

Slow cooling from melting state

Conventional Sintering

C-axis grain orientation is obtained by the

Slow cooling from partially melting state.

Heat treatment schedule of Bi-2212 tape

• Various wire configurations to fit different application requirements- cable (0.8-

1.0 mm) and insert coil (1.0-1.5 mm)

0.8 mm 0.8 mm 1.2 mm 1.5 mm 1.0 mm

Wire configuration (filament number in

sub x number of sub bundle)

Fill factor (%) Optimized wire

diameter (mm)

19 x 36 24.0 0.8

37 x 18 24.8 0.8

55x18 24.9 1

85 x 18 25.2 1.2

121 x 18 25.4 1.5

Bi-2212 wire configurations for different operating current

demands

Examples of Bi-2212 wires

100

200

300

400

500

600

700

800

4 6 8 10 12 14 16

JE (

A/m

m2)

Magnetic Field (T)

As-drawn wire, closed ends

CIP at 100 ksi, closed ends

CIPed wire + OP HT, closed ends

1.2 mm 85 x18

1m barrel sample

Over Pressure Heat Treatment (10 bar HT by ASC/FSU)

1 bar HT, As-drawn

1 bar HT, CIP

Core densification by over pressure HT

10 bar HT

• Highly reproducible Bi-2212 wires with good Je performance

• Maximum length of Bi-2212 wire: ~1000m

4.2K

Fabrication of Bi-2223 tapes by Powder-In-Tube(PIT) method

Powder

Metal tube(Ag)

Heat treatment

Multi-filamentary wire

(Bi-2223)

Multi-filamentary tape

drawing

Formation of Bi-2223 phase Bi-2212+Ca2PbO4+Ca2CuO3+? Bi-2223

Cross section of typical Bi-2223 tape

C-axis grain oriented microstructure of

Bi-based superconducting tapes

Bi-2212 tape

Grain orientation by the slow

solidification from melting state.

Bi-2223 tape:

Grain orientation is obtained by the

combination of cold rolling and

heat treatment. (Y. Yamada, et al.)

km-class Bi2223/Ag tape

Je~20,000A/cm2

(77K, self-field)

(4.2mmwx0.22mmt)

Cross section of typical Bi-2223 tape

(4.2mmwx0.22mmt)

Recent progress of Bi-2223/Ag tape conductors