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

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Elschner b, A Dellicour c, d, e, D Chateigner c, B Vertruyen d, J-F

Vanderbemden d a Nexans SuperConductors GmbH, Hürth, Germany b

University of Caen Basse-Normandie, France d SUPRATECS, University of

1 The J c Dependence on Oxygen Doping in Polycrystalline Forms of Bi-2212 with Various Textures M O Rikel a, A Hobl a, J Ehrenberg a, J Bock a, S Elschner b, A Dellicour c, d, e, D Chateigner c, B Vertruyen d, J-F Fagnard d, P.Vanderbemden d a Nexans SuperConductors GmbH, Hürth, Germany b University 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 SuperConductors ASC 2012, Portland, October 9, /22 Sept 2002 / 1

2 Acknowledgments D C Larbalestier, F Kametani, J Jiang, A Polyanskii, E. Hellstrom (ASC, NHMFL, Tallahassee) H Miao, Y Huang, J Parrell, S Hong (OST, Carteret) C. Scheuerlein, A Ballarino, L Bottura (CERN, Geneva). 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) M Matras, V Moreau, (ENSCI, Limoges); E. Lugand (EPF, Paris) L Lutterotti (University of Trento ) ASC 2012, Portland, October 9, /22 Sept 2002 / 2

3 Melt Cast Processed Bulk 2212 Je(77 K; sf) ~ 1 ka/cm 2 12 kv/100 & 800 A FCLs ASC 2012, Portland, October 9, /22 Sept 2002 / 3

4 Optimization of Jc(T) in Bi2212 MCP Bulk How What SuperCurrent limits SuperCurrent flows?? ASC 2012, Portland, October 9, /22 Sept 2002 / 4

5 Bicrystal Jc vs Misorientation Angle Data for 2212 H. Hilgenkamp and J. Mannhart, Rev. Mod. Phys., Vol. 74, No. 2, 2002, pp ASC 2012, Portland, October 9, /22 Sept 2002 / 5

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

round wire can carry remarkably high Jc values (~10 5 A/cm 2 at 45 T and 4.

Almost no Local Texture J c (77 K, 0 T) ~ 5 ka/cm 2 J c (66 K = 0.

6 2212 Round Wires and Bulk: High Jc in the absence of Long-Range Texture Melt Cast Processed 2212 Despite absence of long-range texture powder-in-tube (PIT) Bi-2212 round wire can carry remarkably high Jc values (~10 5 A/cm 2 at 45 T and 4.2 K) Shen et al, Applied Physics Letters 95, (2009)]. Almost no Local Texture J c (77 K, 0 T) ~ 5 ka/cm 2 J c (66 K = 0.7T c ) ~ 15 ka/cm 2 ~ 20% of best J c (77 K = 0.7T c ) in Ag/Bi2223 ASC 2012, Portland, October 9, /22 Sept 2002 / 6

7 What is Unique in Bi2212 that SuperCurrent Flows across High-Angle GBs? Role of O overdoping Shen et al (2009); Rikel et al (2011) GB Bulk of the grain Special Nature of High-Angle GBs Kametani et al 2008, 2010 (2MC-07) ASC 2012, Portland, October 9, /22 Sept 2002 / 7

8 Role of O Overdoping The J c (77K, sf) dependence on O contents in Bi 2 Sr 2 CaCu 2 O 8+δ MCP bulk rods and tubes with only slight preferred orientation textured Ag sheathed round wires (19x85; 1.2 mm ; OST), textured Ag sheathed tapes Difference in texture => Difference in the dominant type of GBs => Difference in the optimum overdoping ASC 2012, Portland, October 9, /22 Sept 2002 / 8

9 100 Jc(77 K, sf) vs Oxygen Contents. Optimum overdoping 2000 T c, K 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 for tube for 8 mm rod for OST RW <J K, sf)>, A/cm 2 e (77 δ in Bi 2 Sr 2 CaCu 2 O 8+δ Rikel et al 2011 (EUCAS) ASC 2012, Portland, October 9, /22 Sept 2002 / 9

180 log(po2 [atm]) -1-2 -3-4 Delta = 0.192 Delta = 0.198 Delta = 0.

10 How we vary O contents? The δ-po 2 -T diagram of Schweizer et al (1993) 0 Approach of Glowacki et al (2003), Yamashita et al (2010) Delta =0.180 log(po2 [atm]) Delta = Delta = Delta = Anneal at high T for fast equilibration; x = T/100, C Cool down along the po 2 -T cooling trajectory to suppress O exchange Proof of consistency : Changes in δ measured for bulk using gravimetry give a good agreement with anticipations ASC 2012, Portland, October 9, /22 Sept 2002 / 10

11 How we quantify Texture? F Kametani et al SuST 2011 <FWHM> ~ 15 C Scheuerlein et al 2011 ASC 2012, Portland, October 9, /22 Sept 2002 / 11

1 0 0 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 ) 2 0 0 2 0 0 Texture in bulk Bi2212.

12 1 0 0 B i b u l k ( 5 ) x = 2,0 c h i = 0 ( K a 1, 8.6 K ) B i p o w d e r # ( K a K ) Texture in bulk Bi2212. Approach B i P O = I n t, % θ, d e g s , Normalized March-Dolase Function ( Ahkl / A ) = ( Ahkl / A200 ) P( ϕ) P( ϕ 200 RP hkl / 2 = ( PO cos ϕ + PO sin ϕ) ) P(ϕ) P( ϕ) dϕ /180 = 1 0 FWHM PO=2.25 ϕ hkl = ϕ = an angle between hkl and ϕ, ASC 2012, Portland, October 9, /22 Sept 2002 / 12

Texture in bulk Bi2212. Rough Estimates 1.8 1.

4 PO 00L 1.2 1.0 PO =1 => isotropic 2212 at outer & inner surfaces 0.8 0.

~ 15-20 FWHM ~ 50 R < PO >= 2 rpo( r) dr /( R r 2 r Sample <PO> <FWHM>,

13 Texture in bulk Bi2212. Rough Estimates Tube ( out: 50/in: 35 mm) Sample #1 Sample #2 1.4 PO 00L PO =1 => isotropic 2212 at outer & inner surfaces Distance from the surface, mm 8 mm rods R45, 3905 FWHM ~ FWHM ~ 50 R < PO >= 2 rpo( r) dr /( R r 2 r Sample <PO> <FWHM>, 49/43 mm 1.40(6) 60(5) 8 mm rod 1.71(4) 44(3) 5 mm rod 1.91(8) 37(3) 2 ) ASC 2012, Portland, October 9, /22 Sept 2002 / 13

14 Samples Studied. Texture Summary Bi2212 Bulk (Nexans) Fiber Texture MCP Tubes OD/ID = 49/43 mm MCP rods 8 and 5 mm diameter <FWHM> ~ 60 <FWHM> ~45-35 OST Bi2212 Round Wires melt processed at OST for optimizing Je(4.2K, 12 T) = 400 A/mm 2 in 1 m long barrel samples AzimuthalTexture <FWHM> ~ 15 Sample <PO> <FWHM>, 49/43 mm OD/ID 1.40(6) 60(5) mm rod 1.71(4) 44(3) mm RW 15(2) δ ASC 2012, Portland, October 9, /22 Sept 2002 / 14

15 Samples Summary. Cation Composition Bi2212 Bulk (Nexans) Cation composition MCP Tubes OD/ID = 49/43 mm MCP rods 8 and 5 mm diameter Sr/Ca = 2.35(8) to reach Tc ~ 94.5 K OST Bi2212 Round Wires melt processed at OST for optimizing Je(4.2K, 12 T) = 400 A/mm 2 in 1 m long barrel samples Bi 2.15 Sr 1.95 Ca 0.90 Cu 2.00 O 8+δ Sr/Ca = 2.18(3) MCP rods 8 mm diameter (precursor lot 79) Bi 2.15 Sr 1.95 Ca 0.90 Cu 2.00 O 8+δ Sr/Ca = 2.18(3) ASC 2012, Portland, October 9, /22 Sept 2002 / 15

16 Jc vs δ in Bi 2 Sr 2 CaCu 2 O 8+δ with Various Texture and Composition

17 δ 0 = (8) Refined Jc(δ) for Bulk δ 0 = 0.190(8) δ 0 = 0.203(2) <FWHM>, δ in Bi 2 Sr 2 CaCu 2 O 8+δ ASC 2012, Portland, October 9, /22 Sept 2002 / 17

18 Tc & Ic vs δ in OST RW δ 0 = 0.018(8) vs (8) in bulk δ 0 = 0.195(7) δ 0 = 0.213(4) δ in Bi 2 Sr 2 CaCu 2 O 8+δ ASC 2012, Portland, October 9, /22 Sept 2002 / 18

19 Overdoping at 66 K δ 0 (66 K)= 0.219(3) δ 0 (77K)= 0.213(4) δ in Bi 2 Sr 2 CaCu 2 O 8+δ in agreement with data of Matsumoto et al (2004) on Bi2212 OPIT wire ASC 2012, Portland, October 9, /22 Sept 2002 / 19

20 Ic in Rods and Wire. The same Composition Bi 2.15 Sr 1.95 Ca 0.90 Cu 2.00 O 8+δ δ 0 = 0.215(3) δ 0 = 0.213(4) δ in Bi 2 Sr 2 CaCu 2 O 8+δ ASC 2012, Portland, October 9, /22 Sept 2002 / 20

21 Conclusion Overdoping Bi2212 is necessary to optimize Ic lower application temperatures need larger overdoping The level of overdoping for maximum Jc is within the error independent of the material texture (FWHM from 15 to 60 ) δ 0 = 0.018(8) in RW vs 0.013(8) in Bi2212 bulk δ 0 = 0.213(4) in RW vs 0.215(5) in Bi2212 bulk The O contents optimum for Ic is strongly dependent on cation composition: δ 0 = 0.203(2) for Sr/Ca = 2.35(8) δ 0 = 0.214(3) for Sr/Ca = 2.18(3) ASC 2012, Portland, October 9, /22 Sept 2002 / 21

22 Practical Consequences Optimizing O doping, we improved performance of Bi2212 bulk at 77 K by 20 to 50% Ic(77K,sf) ~ 300 A in 5 mm rods; 600 A in 8 mm rods; 6.3 ka in 49/43 mm (OD/ID) tubes 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 K could be possible Optimizing O doping should be a part of compositional studies for OPIT round wires: ASC 2012, Portland, October 9, /22 Sept 2002 / 22

23 Thank you for your attention

24 OST-Nexans Data (b) W521 W522 J e, A /m m W523 W T max, C Why overall composition of Bi2212 has such a strong effect on performance of round wires and tapes? ASC 2012, Portland, October 9, /22 Sept 2002 / 24

25 Data of Yamashita et al (2010) Anticipated, from Bi and Sr ionic radii measured. MR comment: Bi contents in 2212 phase should be almost constant ( ) what is really changed is Sr/Ca ratio. This is reflected in the fall of lattice parameter Optimum O contens depends on composition Yamashita et al (2010) studied single crystals grown from powders of B i2+x Sr 2-x Ca 1 Cu 2 cation compositions and annealed to have various O contents. They found that the crystals with smaller Sr/Ca ratio have maximum Tc at stronger overdoping 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 T c (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. ASC 2012, Portland, October 9, /22 Sept 2002 / 25

26 Importance for O Uniformity in Bulk Annealing in air at ~830 C gives uniform O distribution in Bi 2 Sr 2 CaCu 2 O 8+δ with δ ~ δ(x) δ ~ T c = 94 K c0 T c (x) J c0 (x) λ Usual cooling in constant po 2 leads to overdoping of the surface layer of thickness λ. Because of the preferred orientation in MCP bulk, λ = λ ab grad co ~ 100λ c grad co ~ 1 mm!! ASC 2012, Portland, October 9, /22 Sept 2002 / 26

27 Improving Performance Sample Diameter Cooling mm 21%O2 δ = Jc(77 K, sf), A/cm 2 Tube 49/ Ic(77 K, sf), A Rods Proper Cooling gives 20 to 50% better Perfromance ASC 2012, Portland, October 9, /22 Sept 2002 / 27

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

The J c Dependence on Oxygen Doping in Polycrystalline Forms of Bi-2212 with Various Textures M O Rikel a, A Hobl a, J Ehrenberg a, J Bock a, S Elschner b, A Dellicour c, d, e, D Chateigner c, B Vertruyen