The J c Dependence on Oxygen Doping in Polycrystalline Forms of - - PowerPoint PPT Presentation

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The Jc Dependence on Oxygen Doping in Polycrystalline Forms of Bi-2212 with Various Textures

M O Rikela, A Hobla, J Ehrenberga, J Bocka, S Elschnerb, A Dellicourc, d, e, D Chateignerc, B Vertruyend, J-F Fagnardd, P.Vanderbemdend

aNexans SuperConductors GmbH, Hürth, Germany bUniversity of Applied Science, Mannheim, Germany

c CRISMAT-ENSICAEN, University of Caen Basse-Normandie, France d SUPRATECS, University of Liege, Belgium e Internatinal Doctoral School on Functional Materials

Nexans ¡SuperC onductors

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Acknowledgments

l D C Larbalestier, F Kametani, J Jiang, A Polyanskii,

• E. Hellstrom (NHMFL, Tallahassee)

l H Miao, Y Huang, J Parrell, S Hong (OST, Carteret) l C. Scheuerlein, A Ballarino, L Bottura (CERN, Geneva). l S Krämer, J Schramm, C Janke, C Migge, R Deul,

Z Abdoulaeva, W Horst, A Klimt, S Hardenberg, J Schütz, D Kobersky, M Gross (NSC, Hürth)

l M Matras, V Moreau, (ENSCI, Limoges);

• E. Lugand (EPF, Paris)

l L Lutterotti (University of Trento )

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Melt Cast Processed Bi2212 Bulk

12 KV/100 & 800 A FCLs

Je(77 K; sf) ~ 1 kA/cm2

> 1 T Magnetic Screen @ 10 K

J-F Fagnard et al, Supercond. Sci. Technol. 23 (2010) 095012 (8 pp)

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How SuperCurrent flows? Optimization of Jc(T) in Bi2212 MCP Bulk What limits current ?

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Bicrystal Jc vs Misorientation Angle Data for 2212

• H. Hilgenkamp and J. Mannhart, Rev. Mod.

Phys., Vol. 74, No. 2, 2002, pp. 485-549.

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2212 Round Wires and Bulk: High Jc in the absence of Long-Range Texture

Despite absence of long-range texture powder-in-tube (PIT) Bi-2212 round wire can carry remarkably high Jc values (~105 A/cm2 at 45 T and 4.2 K) Shen et al, Applied Physics Letters 95, 152516 (2009)].

Jc(66 K = 0.7Tc ) ~ 15 kA/cm2 ~ 20%

• f best Jc (77 K = 0.7Tc) in Ag/Bi2223

Jc(77 K, 0 T) ~ 5 kA/cm2 Almost no Local Texture

2212

Melt Cast Processed

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What is Unique in Bi2212 that SuperCurrent Flows across High-Angle GBs ?

l Special Nature of

High-Angle GBs

Kametani et al 2008, 2010 (2MC-07)

l Role of O overdoping

Shen et al (2009); Rikel et al (2011)

Bulk of the grain GB Bulk of the grain GB

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Role of O Overdoping The Jc(77K, sf) dependence on O contents in Bi2Sr2CaCu2O8+δ

l MCP bulk rods and tubes with only slight preferred

• rientation

l textured Ag sheathed round wires (19x85; 1.2 mm ∅; OST), l textured Ag sheathed tapes

Difference in texture => Difference in the dominant type of GBs => Difference in the optimum overdoping

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Jc(77 K, sf) vs Oxygen Contents. Optimum overdoping

75 80 85 90 95 100 0.16 0.17 0.18 0.19 0.20 0.21 0.22 0.23 0.24 400 800 1200 1600 2000

Tc, K <Je(77 K, sf)>, A/cm2 δ in Bi2Sr2CaCu2O8+δ

Tc Data of Schweizer et al 1993 Tc of MCP-Bulk (21-T-36h ) Jc in 49.2/43 mm dia tube Jc 8 mm dia rods Jc 1.2 mm dia RW

Optimum δ 0.202 for tube 0.204 for 8 mm rod 0.212 for OST RW Rikel et al 2011 (EUCAS)

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• 5
• 4
• 3
• 2
• 1

3 4 5 6 7 8 9 Delta =0.180 Delta = 0.192 Delta = 0.198 Delta = 0.205

x = T/100, °C log(pO2 [atm])

Approach of Glowacki et al (2003) , Yamashita et al (2010)

Variation of Oxygen Contents

The δ-pO2-T diagram of Schweizer et al (1993) l Anneal at high T for fast equilibration; l Proof of consistency :

Changes in δ measured for bulk using gravimetry give a good agreement with anticipations

l Cool down along the pO2-T cooling trajectory to suppress O exchange

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Texture in Bi2212. Multifilamentary Wires

C Scheuerlein et al 2011

F Kametani et al SuST 2011

<FWHM> ~ 15°

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2 5 3 0 3 5 2 0 4 0 6 0 8 0 1 0 0

0 0 8 1 1 1 1 1 3 0 1 7 1 1 5 1 0 8 0 0 1 0 1 1 7 2 0 0 2 0 2 0 0 1 2 1 1 9 2 0 0 , 1 0 0 9 0 0 1 1 0 0 1 3

I n t , % 2 θ , d e g s

B i 2 2 1 2 b u l k 1 3 4 - 8 ( 5 ) x = 2 ,0 c h i = 0 ( K a 1 , 8 .6 K ) B i 2 2 1 2 p o w d e r # 4 3 1 1 4 7 3 2 0 1 ( K a 1 2 . 5 K )

B i2 2 1 2 P O = 1 . 7 9 2

2 0 0

Texture in bulk Bi2212. Approach

) ( ) / ( ) / (

200 200 hkl RP hkl hkl

P A A A A ϕ × =

2 / 3 2 1 2 2

) sin cos ( ) (

− −

+ = ϕ ϕ ϕ PO PO P

1 2 3 4 5 20 40 60 80 100 120 140 160 180

ϕ, ° P(⎠ ⎠ )

Normalized March-Dolase Function

ϕhkl = ϕ = an angle between hkl and 001

FWHM PO=2.25

∫

=

180

1 180 / ) ( ϕ ϕ d P

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Texture in bulk Bi2212. Rough Estimates

0.6 0.8 1.0 1.2 1.4 1.6 1.8 1 2 3 4 5 6 7 8

Depth, mm PO Sample #1 Sample #2

Distance from the surface, mm PO00L Tube 136-12 (∅ out: 50/in: 35 mm)

PO =1 => isotropic 2212 at

• uter & inner

surfaces

FWHM ~ 50°

) /( ) ( 2

2 2

r R dr r PO r PO

R r

− >= <

∫

8 mm rods R45, 3905

FWHM ~ 15-20°

Sample < PO > < FWH M> , ¡° 49/43 ¡mm ¡ 1.40(6) 60(5) 8 ¡mm ¡rod 1.71(4) 44(3) 5 ¡mm ¡rod 1.91(8) 37(3)

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Samples Studied . Texture Summary

l Bi2212 Bulk (Nexans)

◗

MCP Tubes OD/ID = 49/43 mm

◗

MCP rods

n

8 and 5 mm diameter l OST Bi2212 Round Wires

melt processed at OST for optimizing Je(4.2K, 12 T) = 400 A/mm2 in 1 m long barrel samples

l Fiber Texture

◗

<FWHM> ~ 60°

◗

<FWHM> ~45-35°

l AzimuthalTexture

◗

<FWHM> ~ 15°

Optimum δ 0.202 for tube 0.204 for 8 mm rod 0.212 for OST RW

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Samples Summary. Caton Composition

l Bi2212 Bulk (Nexans)

◗

MCP Tubes OD/ID = 49/43 mm

◗

MCP rods 8 and 5 mm diameter

l OST Bi2212 Round Wires

melt processed at OST for optimizing Je(4.2K, 12 T) = 400 A/mm2 in 1 m long barrel samples

l Cation composition

◗

Sr/Ca = 2.35(8) to reach Tc ~ 94.5 K

l Bi2.15Sr1.95Ca0.90Cu2.00O8+δ

◗

Sr/Ca = 2.18(3)

l Bi2.15Sr1.95Ca0.90Cu2.00O8+δ

◗

Sr/Ca = 2.18(3)

l MCP rods 8 mm diameter

(precursor lot 79)

Jc vs δ in Bi2Sr2CaCu2O8+δ

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Refined Jc(δ) for Bulk

δ0 = 0.203(2) δ0 = 0.190(8) Δδ0 = 0.013 (8)

<FWHM>, ° 60 44 37

δ in Bi2Sr2CaCu2O8+δ

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Tc & Ic vs δ in OST RW

δ0 = 0.213(4) δ0 = 0.195(7) Δδ0 = 0.018(8)

δ in Bi2Sr2CaCu2O8+δ

vs 0.013 (8) in bulk

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Ic in Rods and Wire. The same Composition Bi2.15Sr1.95Ca0.90Cu2.00O8+δ

δ0 = 0.213(4) δ0 = 0.215(3)

δ in Bi2Sr2CaCu2O8+δ

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Conclusion

l Overdoping Bi2212 is necessary to optimize Ic

lower application temperatures need larger overdoping

l The level of overdoping for maximum Jc is within the error

independent of the material texture (FWHM from 15 to 60°) Δδ0 = 0.018(8) in RW vs 0.013(8) in Bi2212 bulk

δ0 = 0.213(4) in RW vs 0.215(5) in Bi2212 bulk

l The O contents optimum for Ic is strongly dependent on

cation composition: δ0 = 0.203(2) for Sr/Ca = 2.35(8)

δ0 = 0.214(3) for Sr/Ca = 2.18(3)

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Practical Consequences

l Optimizing O doping, we improved performance of Bi2212

bulk at 77 K by 20 to 50%

Ic(77K,sf) ~ 600 A in 8 mm rods; 6.3 kA in 49/43 mm (OD/ID) tubes

l Optimization of Bi2212 bulk for applications at lower T

should include optimization of cation composition and O doping

Magnetic screens / Trapped-field magnets for 3-5 T at 10-20 K could be possible

l Optimizing O doping should be a part of compositional

studies for OPIT round wires:

Thank you

for your attention

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Overdoping at 66 K

δ0 = 0.213(4) δ0 = 0.218(3) in agreement with data of Matsumoto et al (2004) on Bi2212 OPIT wire

δ in Bi2Sr2CaCu2O8+δ

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OST-Nexans Data 2004-2006

400 800 1200 1600 2000 882 884 886 888 890 892 894 896 898 900

T max, °C J e, A/mm

2

W521 W522 W523 W524

(b)

Why overall composition of Bi2212 has such a strong effect on performance of round wires and tapes ?

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Data of Yamashita et al (2010)

Yamashita et al (2010) studied single crystals grown from powders of Bi2+xSr2-xCa1Cu2 cation compositions and annealed to have various O contents. They found that the crystals with smaller Sr/Ca ratio have maximum Tc at stronger

• verdoping levels. Though the real compositions were not measured, the Sr/Ca ratio in the 2212 phase should scale with

that in the overall composition (Rikel et al 2006). Thus, our observation that maximum of Jc(δ) in round wires is at higher δ than in the bulk may stem from the difference in Tc(δ) for bulk (Sr/Ca = 2.45±0.02) and round wire (Sr/Ca = 2.20±0.03). We should first measure Tc of the wires. Anticipated, from Bi and Sr ionic radii measured. MR comment:

• Bi contents in 2212 phase should be

almost constant (2.10-2.15)

• what is really changed is Sr/Ca ratio.

This is reflected in the fall of lattice parameter

Optimum O contens depends on composition

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δ ~ 0.20 Tc = 94 K δ ~ 0.20 Tc = 94 K Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x)

δ(x)

λ

δ(x)

λ

δ(x)

λ

δ ~ 0.20 Tc = 94 K δ ~ 0.20 Tc = 94 K Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x)

δ(x)

λ

δ(x)

λ

δ(x)

λ

c0

Importance for O Uniformity in Bulk Annealing in air at ~830°C gives uniform O distribution in Bi2Sr2CaCu2O8+δ with δ ~ 0.192 Usual cooling in constant pO2 leads to overdoping of the surface layer of thickness λ. Because of the preferred

• rientation in MCP bulk,

λ = λab||grad cO ~ 100λc| grad cO ~ 1 mm !!

δ ~ 0.20 Tc = 94 K δ ~ 0.20 Tc = 94 K Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x)

δ(x)

λ

δ(x)

λ

δ(x)

λ

δ ~ 0.20 Tc = 94 K δ ~ 0.20 Tc = 94 K Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x) Tc(x) Jc0(x)

δ(x)

λ

δ(x)

λ

δ(x)

λ

c0

0.19 94 K

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Improving Performance Diameter mm 21%O2 δ = 0.203 Tube 49/43 900 1420 5 200-250 290-310 8 470-520 570-630 15 1000 1200 Cooling Ic(77 K, sf), A Jc(77 K, sf), A/cm2 Sample Rods Proper Cooling gives 20 to 50% better Perfromance