[PPT] - Effect of cation composition on the doping state optimizing critical PowerPoint Presentation

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Effect of cation composition on the doping state optimizing critical current densities in Bi-2212 conductors

M O Rikel, L Koliotassis, J Ehrenberg, A Hobl, J Bock, A Ballarino, L Bottura, D. Richter, E Seiler, C Scheuerlein, H Miao, Y Huang, J Parrell, T Shen, P Li, L Cooley, J Jiang, F Kametani, E E Hellstrom, D C Larbalestier A Dellicour, D Chateigner, B Vertruyen

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1MOr3A-02 Acknowledgements

l S Elschner (University of Applied Science, Mannheim);

J-F Fagnard and P Vanderbemden (University of Liége) for fruitful discussions

l Z Abdoullaeva, S Krämer, R Deul, W Horst (NSC);

M Matras, V Moreau, A Camus, C Sillanfest (ENSCI, Limoges); E Lugand (EPF, Paris) for assistance in experiments

l EUCARD2 and IDS-FUNMAT Projects for financial support

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1MOr3A-02 Motivation

l Origin of Strong Compositional Effects on Jc(4.2 K, sf)

in Bi2212 Wires and Dip-Coated Tapes is unclear

l It is known that significant Overdoping is necessary for

ptimizing Ic in Bulk and Round Wire conductors

l Literature data suggest that optimum doping (highest

Tc) depends on cation composition of Bi2212

l Can the difference in the doping state explain

compositional effects on Ic in Bi2212 tapes and wires?

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1MOr3A-02 STRONG Effect of Cation Composition

n Wire and Tape Performance

l Microstructural studies of tapes and wires did not explain a factor of

four difference in Jc of best (Sr-rich, 521) and worst (Ca-rich; 524) compositions

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)

W521-524 2.14 : (2.86–x) : x :2.00 Sr/Ca = 2.25, 2.18, 1.75, 1.34

H. Miao et al 2006 Adv Cryo Eng. 52B, p. 673, (2006) [Proc. ICMC 2005]
M. Rikel et al 2006 J Phys: Conf Ser., 43 (2006) 51–54 [Proc. EUCAS 2005]

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1MOr3A-02 Microstructure of 521 vs 524. Dip coated tapes. 1

Amorphous

Grain Boundarie s

l Second phases

may explain ~10% difference in Ic (not a factor of 4 to 10)

l Amorphous

layers at GBs numerous in 524 limit current. But is this the whole story?

521 1000 A 7±3% 524 100-250 A 20±5% Property

Ic(4.2K, sf) Second Phases

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1MOr3A-02

10 20 30 40 50 60 70 80 90 100 110 30 40 50 60

Lin (Cps)

10 20 30 40 50 60 70 80 90 100 110 30 40 50 60

Microstructure of 521 vs 524. Dip coated tapes. 2

l Important

microstructure characteristics are much better in 524

l Why performance

f 524 is much

worse than that of 521 is still not clear Out-of- plane texture

521

Smaller

524

Twice Larger

Property

Grain Size Bi2201inter- growth defects 2 to 10% 0.1±0.2% 7.4(3)° 4.2(2)°

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1MOr3A-02

δ in Bi2Sr2CaCu2O8+δ

Overdoping Δδ Δδo is necessary for optimizing Ic. Tc & Ic(77 K, sf) vs δ in OST 521-like RW

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

Rikel et al ASC2012

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1MOr3A-02 OPTIMUM Doping Depends on Cation Composition

l Single Crystals grown using

Bi2+xSr2-xCa1Cu2O8+δ powder mixtures

l Annealed to vary O index l Smaller Sr/Ca requires more

verdoping

/* real compositions unknown =>exact effect to be quantified*/

Yamashita et al Physica C 470 (2010 s170

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1MOr3A-02 Hypothesis to Check

Plan of Studies:

l Use Bi2212 bulk and vintage (521 & 524) dip coated tapes and wires

f Bi2.00+zSr2.85-xCaxCu2.00O8+δ (x = 0.82; 0.90; 1.03; 1.22; z = 0.15,

0.08 & 0.00) compositions

l Vary O contents in the samples from δ = 0.175 to 0.252 l Justify Tc(δ) for various z & x l Study effect of δ on Jc(B) at various temperatures.

Can the difference in the doping state explain compositional effects on Ic in Bi2212 tapes and wires?

First Results

l Tc and Jc vs δ for bulk samples of Sr- and Ca-rich compositions

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1MOr3A-02 Melt Cast Processed Bulk 2212

l Melt Casting ∅5 & ∅8 mm rods

f Bi2.00+zSr3.00-z-xCaxCu2.00O8+δ

cation compositions

. x = 0.82; 0.90; 1.03; 1.22; . z = 0.15, 0.08 & 0.00 & Bi1.95(3)Sr2.01(3)Ca0.92(3)Cu2.02(3)O8+δ + 0.1BaO +0.4SrSO4

. (NSC Bulk Standard)

l Heat Treatment to convert solidification microstructure to Bi2212

◗ far from equilibrium (Sr/Ca in Bi2212 phase from EDX larger than overall),

but

◗ well connected to show rather high self-field Jc(77 K)

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1MOr3A-02 Adjusting O Contents

The δ-pO2-T diagram of Schweizer et al (1993)

What is varied is not the O contents, but O activity. Real δ are likely dependent on the cation composition (TBD).

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) l Quench or cool down along the pO2-T cooling trajectory to suppress

O exchange

l For δ > 0.230, just annealing in air or O2 at 350 ≤ T ≤ 550°C l Anneal at high T for fast equilibration;

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1MOr3A-02 Justify Tc(δ) for various compositions

l Optimum δ and Tc depend on cation compostion

. (Sr/Ca in Bi2212 phase from EDX)

δopt = 0.177(3) δopt = 0.199(9) δopt = 0.221(5)

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1MOr3A-02 Tc and transport Jc(77 K, sf) Composition #147; Sr/Ca = 2.48(3)

δopt = 0.177(3) δo = 0.201(2) Δδ0 = 0.024(4)

Bi1.95)Sr2.01Ca0.92Cu2.02O8+δ

+ 0.1BaO +0.4SrSO4

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1MOr3A-02

100 200 300 400 500 600 700 65 70 75 80 85 90 95 100 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25 0.26

Self-Field Jc(, 77 K), A/cm2 Onset Tc, K δ

Tc Jc

Tc and transport Jc(77 K) Composition #83; Sr/Ca = 2.38(5) Bi2.15Sr2.85-xCaxCu2.00O8+δ x = 0.82

δopt = 0.199(9) δo = 0.219(4) Δδ Δδ0 = 0.020(9)

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5 10 15 20 25 30 35 65 70 75 80 85 90 95 100 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25 0.26

Self-Field Jc(, 77 K), A/cm2 Onset Tc, K δ

Tc Jc

Tc and transport Jc(77 K) Composition #524; Sr/Ca = 2.00(5) Bi2.15Sr2.85-xCaxCu2.00O8+δ x = 1.22

δopt = 0.221(6) δo = 0.236(4) Δδ Δδ0 = 0.015(7)

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1MOr3A-02 NSC Bulk Standard #147; Sr/Ca = 2.48(3) Magnetization Data at 4.2 to 77 K ΔM(H, T) data for ∅5 mm rods:

l Jc

ΔM(77 K) ≈ 1000 A/cm2 ≈

Jc

transport(77 K)

l δo is strongly T dependent

ΔM(77K, 0.05 T), emu/g ΔM(40K, 0.5 T) ΔM(4.2K, 3 T)

Δδ(4.2 K) = 0.061(5) Δδ(40 K) = 0.048(7) Δδ0 = 0.024(5)

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1MOr3A-02 Ic vs δ in OST 521-like RW Overdoping at 66 K

δ0 (77K)= 0.213(4) δ0 (66 K)= 0.219(3)

δ in Bi2Sr2CaCu2O8+δ Δδ0 = 0.024(7)

δopt (Tc)= 0.195(7)

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1MOr3A-02 T - δo(Jc) Map

l The difference in the doping state may explain the observed

compositional effects on Ic in Bi2212 tapes and wires

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