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

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

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 2 Sept 2002 / 2 August 11, 2014

1MOr3A-02 Motivation l Origin of Strong Compositional Effects on J c (4.2 K, sf) in Bi2212 Wires and Dip-Coated Tapes is unclear l It is known that significant Overdoping is necessary for optimizing I c in Bulk and Round Wire conductors l Literature data suggest that optimum doping (highest T c ) depends on cation composition of Bi2212 l Can the difference in the doping state explain compositional effects on I c in Bi2212 tapes and wires? 3 Sept 2002 / 3 August 11, 2014

STRONG Effect of Cation Composition 1MOr3A-02 on Wire and Tape Performance 2000 (b) W521 W521-524 2.14 : (2.86– x ) : x :2.00 W522 Sr/Ca = 2.25, 2.18, 1.75, 1.34 1600 W523 2 1200 J e , A/mm W524 800 400 0 882 884 886 888 890 892 894 896 898 900 T max , °C H. Miao et al 2006 Adv Cryo En g. 52B , p. 673, (2006) [Proc. ICMC 2005] M. Rikel et al 2006 J Phys: Conf Ser., 43 (2006) 51–54 [Proc. EUCAS 2005] 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 4 Sept 2002 / 4 August 11, 2014

Microstructure of 521 vs 524. 1MOr3A-02 Dip coated tapes. 1 Property 524 521 100-250 A 1000 A Ic(4.2K, sf) l Second phases may explain ~10% 20 ± 5% 7 ± 3% difference in Ic (not Second a factor of 4 to 10) Phases l Amorphous Amorphous layers at GBs Grain numerous in 524 Boundarie limit current. s But is this the whole story? 5 Sept 2002 / 5 August 11, 2014

Microstructure of 521 vs 524. 1MOr3A-02 Dip coated tapes. 2 Property 521 524 Smaller Twice Larger l Important microstructure characteristics are Grain Size much better in 524 0.1 ± 0.2% 2 to 10% Bi2201inter- growth defects l Why performance of 524 is much worse than that of 110 110 4.2(2)° 7.4(3)° 100 100 Out-of- 521 is still not clear 90 90 80 80 70 70 Lin (Cps) plane 60 60 50 50 texture 40 40 30 30 20 20 10 10 0 0 30 40 50 60 30 40 50 60 6 Sept 2002 / 6 August 11, 2014

Overdoping Δδ Δδ o is necessary for optimizing I c . 1MOr3A-02 T c & I c (77 K, sf) vs δ in OST 521-like RW Δδ 0 = 0.018(7) δ opt = 0.195(7) δ 0 = 0.213(4) δ in Bi2Sr 2 CaCu 2 O 8+ δ Rikel et al ASC2012 7 Sept 2002 / 7 August 11, 2014

OPTIMUM Doping Depends on 1MOr3A-02 Cation Composition l Single Crystals grown using Bi 2+x Sr 2-x Ca 1 Cu 2 O 8+ δ powder mixtures l Annealed to vary O index l Smaller Sr/Ca requires more overdoping /* real compositions unknown =>exact effect to be quantified*/ Yamashita et al Physica C 470 (2010 s170 8 Sept 2002 / 8 August 11, 2014

1MOr3A-02 Hypothesis to Check Can the difference in the doping state explain compositional effects on I c in Bi2212 tapes and wires? Plan of Studies: l Use Bi2212 bulk and vintage (521 & 524) dip coated tapes and wires of Bi 2.00+ z Sr 2.85- x Ca x Cu 2.00 O 8+ 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 T c ( δ ) for various z & x l Study effect of δ on J c ( B ) at various temperatures. First Results l T c and J c vs δ for bulk samples of Sr- and Ca-rich compositions 9 Sept 2002 / 9 August 11, 2014

1MOr3A-02 Melt Cast Processed Bulk 2212 l Melt Casting ∅ 5 & ∅ 8 mm rods of Bi 2.00+z Sr 3.00-z-x Ca x Cu 2.00 O 8+ δ cation compositions . x = 0.82; 0.90; 1.03; 1.22; . z = 0.15, 0.08 & 0.00 & Bi 1.95(3) Sr 2.01(3) Ca 0.92(3) Cu 2.02(3) O 8+ δ + 0.1BaO +0.4SrSO 4 . (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 J c (77 K) 10 Sept 2002 / 10 August 11, 2014

1MOr3A-02 Adjusting O Contents The δ - p O 2 - T diagram of Approach of Glowacki et al (2003) , Schweizer et al (1993) Yamashita et al (2010) 0 Delta =0.180 Delta = 0.192 log(pO2 [atm]) -1 Delta = 0.198 Delta = 0.205 -2 -3 -4 -5 3 4 5 6 7 8 9 x = T/100, °C l Anneal at high T for fast equilibration; l Quench or cool down along the p O 2 - T cooling trajectory to suppress O exchange l For δ > 0.230, just annealing in air or O 2 at 350 ≤ T ≤ 550°C What is varied is not the O contents, but O activity . Real δ are likely dependent on the cation composition (TBD). 11 Sept 2002 / 11 August 11, 2014

1MOr3A-02 Justify T c ( δ ) for various compositions δ opt = 0.177(3) δ opt = 0.199(9) δ opt = 0.221(5) l Optimum δ and Tc depend on cation compostion . (Sr/Ca in Bi2212 phase from EDX) 12 Sept 2002 / 12 August 11, 2014

T c and transport J c (77 K, sf) 1MOr3A-02 Composition #147; Sr/Ca = 2.48(3) Bi 1.95) Sr 2.01 Ca 0.92 Cu 2.02 O 8+ δ Δδ 0 = 0.024(4 ) + 0.1BaO +0.4SrSO 4 δ o = 0.201(2) δ opt = 0.177(3) 13 Sept 2002 / 13 August 11, 2014

T c and transport J c (77 K) 1MOr3A-02 Composition #83; Sr/Ca = 2.38(5) Bi 2.15 Sr 2.85-x Ca x Cu 2.00 O 8+ δ x = 0.82 100 700 Δδ Δδ 0 = 0.020(9 ) Tc Jc 95 600 Self-Field J c (, 77 K), A/cm 2 90 500 Onset Tc, K 85 400 80 300 δ o = 0.219(4) 75 200 δ opt = 0.199(9) 70 100 65 0 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25 0.26 δ 14 Sept 2002 / 14 August 11, 2014

T c and transport J c (77 K) 1MOr3A-02 Composition #524; Sr/Ca = 2.00(5) Bi 2.15 Sr 2.85-x Ca x Cu 2.00 O 8+ δ x = 1.22 100 35 Tc Δδ Δδ 0 = 0.015(7) 95 30 Jc Self-Field J c (, 77 K), A/cm 2 90 25 Onset Tc, K 85 20 80 15 75 δ o = 0.236(4) 10 δ opt = 0.221(6) 70 5 65 0 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25 0.26 δ 15 Sept 2002 / 15 August 11, 2014

NSC Bulk Standard #147; Sr/Ca = 2.48(3) 1MOr3A-02 Magnetization Data at 4.2 to 77 K Δ M(77K, 0.05 T), emu/g Δ M ( H , T ) data for ∅ 5 mm rods: l J c Δ M ( 77 K) ≈ 1000 A/cm 2 ≈ J c transport (77 K) l δ o is strongly T dependent Δδ 0 = 0.024(5) Δ M(40K, 0.5 T) Δ M(4.2K, 3 T) Δδ (4.2 K) = 0.061(5) Δδ (40 K) = 0.048(7) 16 Sept 2002 / 16 August 11, 2014

I c vs δ in OST 521-like RW 1MOr3A-02 Overdoping at 66 K Δδ 0 = 0.024(7) δ 0 (66 K)= 0.219(3) δ opt (Tc)= 0.195(7) δ 0 (77K)= 0.213(4) δ in Bi 2 Sr 2 CaCu 2 O 8+ δ 17 Sept 2002 / 17 August 11, 2014

1MOr3A-02 T - δ o ( J c ) Map l The difference in the doping state may explain the observed compositional effects on I c in Bi2212 tapes and wires 18 Sept 2002 / 18 August 11, 2014

1MOr3A-02 Conclusion l Optimum doping of Bi2212 strongly depends on cation composition. Reducing Sr/Ca ratio in the Bi2212 phase shifts optimum doping to higher O index δ /* to be quantified using equilibrium samples */. l Optimizing J c needs overdoping Δδ = δ max_Jc - δ max_Tc that increases from 0.024(3) at 77 K to 0.061(6) at 4.2 K /* to be double checked for all compositions and different conductors */ l Including O doping level in the parameter space for conductor optimization is the MUST . It should help correlating performance and microstructure 19 Sept 2002 / 19 August 11, 2014