1. BSCCO 2212 Precursor Studies for EUCARD2 Origin of Hard Particles in Precursor Powder Cation Composition Effects on Tc and Jc vs O contents Mark Rikel Jürgen Ehrenberg, Lisa Koliotassis, Achim Hobl, Joachim Bock

2. Sept 2002 / 2 January 14, 2015 2 Acknowledgements Z Abdoulaeva, W Horst, S Krämer, C Jänke (NSC) C Scheuerlein, D Richter, E Seiler, A Ballarino, L Bottura (CERN) A Dellicour, B Vetruyen, P Vanderbemden, J-F Farnard (Uinversity of Lège); D Chateigner (ENSCI, Caen); S Elschner (FH Manheim) P Li, T Shen, L Cooley (FNAL) J Jiang, F Kametani, E Hellstrom, D Larbalestier (NHMFL) H Miao, Y Huang, J Parrell (OST)

3. Sept 2002 / 3 January 14, 2015 3 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c vs  o Conclusion o O distribution in melt-processed tapes and wires

4. Sept 2002 / 4 January 14, 2015 4 Hard Particles in wires Starting from precursor lot 78 (produced in 2010), various wire manufacturers reported in 2012 and 2013 presence of 1000±200 volume ppm hard Bi-2212 particles harmful for drawing wires ( the particles are not harmful when using swaging or groove rolling ) Based on the production protocol of lot 78 (a mixture of lots 77 and 74 where no hard particles were reported) two hypotheses were formulated that relate the origin of hard particles to  the breadth of particle size distribution in granular material (not confirmed when producing lot 82 in 2013)  effect of multiple compaction used to have a reasonable yield of granular material (checked when producing lot 87 in 2014)

5. Sept 2002 / 5 January 14, 2015 5 Hard particles observed using SEM(BSE) examination Polished sections of compacts studied as suggested by J. Jiang in the BSE mode denser particles are seen as having brighter contrast Particles of two types observed:  Very dense (no grain boundary structure seen) likely originate from melt-cast processed pieces  Less dense (grain boundary structure seen) likely originate from intermediate compaction and sintering

6. Sept 2002 / 6 January 14, 2015 6 Volume fraction of dense particles Multiple compaction may have only a positive effect on the presence of denser particles (not proven statistically) Compaction at steps 1 to 4 was done with the same load leading to the mass density of 3.7 g/cm 3 Compaction at step 5 is done with a factor of 4 larger load leading to the mass density of 4.3 g/cm 3. b

7. Sept 2002 / 7 January 14, 2015 7 Conclusion Multiple compaction is not the cause of denser particles in the granular precursor; these are present due to the bulk nature of processing (Melt Casting + Compacting to reach equilibrium) surviving Jet Milling Next Step  Checking which denser particles are harmful for drawing Necessary production and testing improvements:  Adjusting parameters of jet milling (higher rotation speeds) and compaction (higher loads)  Introducing wet sieving tests

8. Sept 2002 / 8 January 14, 2015 8 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation

9. Sept 2002 / 9 January 14, 2015 9 Effect of Cation Composition on Jc Why overall composition of Bi2212 has such a strong effect on performance of round wires and tapes ? 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]

10. Sept 2002 / 10 January 14, 2015 10 Data of Yamashita et al (2010) 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(  ) in round wires is at higher  than in the bulk may stem from the difference in T c (  ) 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 DOPING depends on composition /* exact effect to be studied*/

11. Studying Interplay between Cation-Composition and Oxygen Doping Effects using Melt Cast Processed Bulk Samples Why Bulk Samples? easy to produce compared to precursor//conductor Goals: double check effect of cation composition on optimum doping (maximum T c ) learn O doping optimizing J c (T, B) as function of cation composition choose new cation composition for optimizing J c (4.2 K, 5 T)

12. Sept 2002 / 12 January 14, 2015 12 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c vs  O distribution in melt-processed tapes and wires o Next Steps

13. Sept 2002 / 13 January 14, 2015 13 Intended Melt Cast Compositions 4 similar to 521 to 524 studied in 2004-2006 + 147 (empirically optimized at NSC since 1990’s) 4 more with smaller Bi contents to double check correlations 83 85 148 86 148

14. Sept 2002 / 14 January 14, 2015 14 Samples not at Equilibrium EDX and XRD were used to assess the composition of Bi2212 phase L % Bi, Sr 2212 CaO T, °C 524: Melt Cast State ~885°C ~745°C MCP Bulk Precursor

15. Sept 2002 / 15 January 14, 2015 15 Nonequilibrium Bi2212 phase. I 008 /I 0010 = 0.75 instead of ~1.0  = 7.2(8)% Bi2201 intergrowths from XRD line shifts & broadening 2 , °

16. Sept 2002 / 16 January 14, 2015 16 Composition of Bi2212 phase from EDX corrected based on XRD Sr/Ca ratio varied from ~1.9 to ~2.8 instead of from ~1.3 to ~2.5 Studying T c vs  and I c vs  still valuable, but vintage tapes and wires with smaller Sr/Ca should also be studied i = Bi, Sr, Ca, Cu

17. Sept 2002 / 17 January 14, 2015 17 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c vs  O distribution in melt-processed tapes and wires o Next Steps

18. Sept 2002 / 18 January 14, 2015 18 Adjusting O Contents The  -pO 2 -T diagram of Schweizer et al (1993) What is varied is not the O contents, but O activity. Real  are likely dependent on the cation composition (TBD). Quench or cool down along the pO 2 -T cooling trajectory to suppress O exchange For  > 0.230, just annealing in air or O 2 at 350  T  550°C Anneal at high T for fast equilibration; 0 -3 -2 -4 -5 log(pO2 [atm]) 300500400700600800900 T (°C) Approach of Glowacki et al (2003), Yamashita et al (2010) 10 -5 10 -4 10 -3 10 -2 0.11 pO 2 (atm) Oxygen index  0.26 0.16 0.24 0.22 0.20 0.18 0.14 0.12

19. Sept 2002 / 19 January 14, 2015 19 Attaining Equilibrium. Case of  = 0.256(2). Annealing at 300°C Equilibration time depends on geometry and texture The texture depends on composition and cooling rates Using the  RT /  77K resistance ratio in case when T c (  )  77 K 10 -5 10 -4 10 -3 10 -2 0.11 pO 2 (atm) Oxygen index  0.26 0.16 0.24 0.22 0.20 0.18 0.14 0.12

20. Sept 2002 / 20 January 14, 2015 20 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c vs  O distribution in melt-processed tapes and wires o Next Steps

21. Sept 2002 / 21 January 14, 2015 21 T c decreases and  opt increases for decreasing Sr/Ca Optimum  and T c depend on cation compostion (Goal 1 accomplished)  opt = 0.177(3) TcTc  opt = 0.199(9) TcTc  opt = 0.221(5) TcTc Ca^

22. Sept 2002 / 22 January 14, 2015 22 The effect of cation composition on Tc(  ) can be very strong Optimum O doping  opt (maximum T c ) versus assessed Sr/Ca ratio in the Bi2212 phase of MCP bulk samples of composition 147, 83 and 524 (filled circles). Also plotted (open rectangles) are similar data of Yamashita et al (2010) for single crystals grown from Bi 2+x Sr 2-x CaCu 2 O 8+  powders (Sr/Ca ratio taken for overall composition: Sr/Ca = 2–x). Note that the absolute values of  as well as the overall Sr/Ca ratios in samples of Yamashita et al could differ from the reported ones.

23. Sept 2002 / 23 January 14, 2015 23 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c vs  O distribution in melt-processed tapes and wires o Next Steps

24. Sept 2002 / 24 January 14, 2015 24 T c and transport J c (77 K) Composition #147; Sr/Ca = 2.48(3)  0 = 0.024(4 ) Bi 1.95 Sr 2.01 Ca 0.92 Cu 2.02 O 8+  + 0.1BaO +0.4SrSO 4  opt = 0.177(3) TcTc  o = 0.201(2) JcJc

25. Sept 2002 / 25 January 14, 2015 25 Transport self-field Ic(77 K) and RT resistivity vs . Sr/Ca = 2.43(14) For NSC standard composition, the I c (77K, sf) results are very reproducible within one batch, though RT resistivity is less reproducible 5 mm rods  o = 0.201(2)

26. Sept 2002 / 26 January 14, 2015 26 Transport self-field Ic(77 K) and RT resistivity vs . Other compositions For other compositions, the Ic reproducibility is worse

27. Sept 2002 / 27 January 14, 2015 27 Large scatter in the first series The reasons to be understood  

28. Sept 2002 / 28 January 14, 2015 28 Optimum  opt and Sr/Ca ratio O contents  opt optimum for I c depends on the Sr/Ca ratio No possibility to model the situation with NSC standard (147) suggests there are other factors contributing to the effect

29. Sept 2002 / 29 January 14, 2015 29 Excellent correlation between  opt (I c ) and I c,max (77 K, sf) Initially considered as indication that variation in connectivity may need different optimum doping levels Evidence is obtained that the major contribution comes from changes in cation composition (to be double checked)

30. Sept 2002 / 30 January 14, 2015 30 I c,max (77 K, sf) vs  opt & T c,max vs  o Ca^

31. Sept 2002 / 31 January 14, 2015 31 I c,max (77 K, sf) vs  opt & T c,max vs  o Both correlations are likely of the same (compositional) origin To be checked by more T c vs  measurements

32. Sept 2002 / 32 January 14, 2015 32 Similar Tc Behavior in Co doped Bi-2212 J L Tallon et al (2000) Is Ca to Sr substitution similar to Co doping?

33. Sept 2002 / 33 January 14, 2015 33 I c,max (77 K, sf) vs  opt & T c,max vs  o Necessity to overdope Bi-2212 for optimizing J c is likely related to the necessity of maximizing the condensation energy, which is roughly N(  )  (T,  ), where N(  ) is the density of states at the Fermi level and  (T,  ) is the energy gap

34. Sept 2002 / 34 January 14, 2015 34 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c vs  O distribution in melt-processed tapes and wires o Next Steps

35. Sept 2002 / 35 January 14, 2015 35 NSC Bulk Standard #147 Magnetization Data at 4.2 to 77 K  M(H, T) data for  5 mm rods: J c  M( 77 K)  1000 A/cm 2  J c transport (77 K)  o is strongly T dependent  increases with decreasing T  M(40K, 0.5 T)  (40 K) = 0.048(7) JcJc TcTc  M(4.2K, 3 T)  (4.2 K) = 0.061(5) JcJc TcTc  M(77K, 0.05 T), emu/g  0 = 0.024(5) JcJc TcTc

36. Sept 2002 / 36 January 14, 2015 36 NSC Bulk Standard #147 Jc at 4.2 K  M(H, T) data for  5 mm rods: J c  M (4.2 K, 3T)  6.10 4 A/cm 2 is only a factor of 5 smaller than in RW with Je(4.2K, 3T) ~3.10 5 A/cm 2  M(4.2K, 3 T)  (4.2 K) = 0.061(5) JcJc TcTc

37. Sept 2002 / 37 January 14, 2015 37 Bulk samples #83 and #524. Sr/Ca =2.37(16) and 2.03(8) No optimum is reached at 4.2 K   = 0.256 samples to be measured  Measurements at 40 K

38. Sept 2002 / 38 January 14, 2015 38  in Bi 2 Sr 2 CaCu 2 O 8+  Rikel et al ASC2012 I c vs  in OST 521-like RW Overdoping at 77 and 66 K  0 (66 K) = 0.024(7)  0 (J c ) (77K) = 0.213(4) JcJc JcJc  opt (T c )= 0.195(7) TcTc

39. Sept 2002 / 39 January 14, 2015 39 Temperature dependence of overdoping likely reflects changes in the condensation energy proportional to N(  )  (T,  ) Overdoping [T -  o ] Map.

40. Sept 2002 / 40 January 14, 2015 40 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c (4.2 K) vs  O distribution in melt-processed tapes and wires o

41. Sept 2002 / 41 January 14, 2015 41 Ic(4.2K) in OST wire with 521 composition. Sr/Ca = 2.18(3) To be double checked. If confirmed: Not only the composition, but other factors play a role (e.g., texture, i.e., dominant type of GBs)  opt = 0.237(5) Jianyi Jiang & Yavuz Oz (2014) MCP bulk #83 & #524

42. Sept 2002 / 42 January 14, 2015 42 Ic(4.2K) in OST Tapes 521 & 524 compositions. Sr/Ca = 2.18(3) & 1.35 Larger scatter than in bulk and wires => no definite conclusions For 521,  opt = 0.235(10) as in wire For 524,  opt > 0.256 Pei Li & Tengming Chen (2015) Ic(4.2K, sf); 521 Ic(4.2K, sf); 524 

43. Sept 2002 / 43 January 14, 2015 43 Conclusion It is confirmed that cation composition affects optimum O contents that maximizes T c, and the effect seems to be very strong  Further work [T c vs  ] is necessary to better define the dependence I c optimization needs significant overdoping, which is temperature dependent.  Further work [M(H, T) vs  is necessary to Oxygen contents  opt optimizing I c in MCP bulk seem to differ from that for PMP wires (to be double checked) suggesting that not only composition, but other factors (e.g., texture) may affect  opt

44. Sept 2002 / 44 January 14, 2015 44 Outline Origin of Hard Particles Compositional Effects in Bi 2+z Sr 3-z-x Ca x Cu 2 O 8+  o Motivation o Melt Cast Processed Bulk Samples Cation Composition and Microstructure Adjusting O contents and attaining equilibrium Physical Properties T c versus  I c (77 K,sf) vs   Correlation between  opt and I c,max  M(H, T) versus  (results from CERN and University of Caen)  Correlation between overdoping  and temperature o Wires and Tapes First results on J c (4.2 K) vs  O distribution in melt-processed tapes and wires o

45. Sept 2002 / 45 January 14, 2015 45 Lattice Parameter c vs . Early Results Tapes processed with bulk samples

46. Sept 2002 / 46 January 14, 2015 46 Lattice Parameter c vs Sr/Ca.  = 0.242(3) Results of Rikel et al (2010) for dip coated tapes of 521-524, 45 and 32 compositions melt processed in 100% O 2 via screening heat treatment, for which c is found to be independent of T max

47. Sept 2002 / 47 January 14, 2015 47 Lattice Parameter c vs . Current Status The observed scatter is likely due to o slight difference in cooling conditions that affect the ~1 µm thick outer layers strongly contributing to XRD patterns => control pO2 down to T = 350°C, otherwise quench (Q) o variations in Sr/Ca ratio in the Bi2212 phase.  = (–0.395 ± 0.038)´(c – 30.8117) + (0.2420 ± 0.0005) for T521 (x = 0.90)  = (–0.433 ± 0.051)´(c – 30.7397) + (0.2200 ± 0.0009) for T524 (x = 1.22)

48. Sept 2002 / 48 January 14, 2015 48 XRD studies of Oxygenation and Deoxygenation Kinetics  = 0.180 to 0.252 transformation when annealing dip coated tapes in 100%O 2 at 350°C t = 0, 1, 2, …., 93 h

49. Sept 2002 / 49 January 14, 2015 49 Dip Coated Tapes with 10 µm thick Bi2212 Oxygenation Kinetics in 100%O 2 at 350°C.  from the average lattice parameter (to be double checked using more adequate models) Similar studies on deoxygenation and oxygenation at 300°C ongoing. Activation energy for O diffusion will be deduced

50. Sept 2002 / 50 January 14, 2015 50 O distribution in wires Based on the lattice parameters, O doping level in just melt processed tapes is  = 0.240(3). O distribution in just melt processed wires is not uniform across the filaments as cooling The 1 to 2 µm layers next to Ag interface are more overdoped. Variation in Sr/Ca ratio in the melt processed wires (heat treatment dependent) should contribute to variation in J c