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University of Wisconsin-MadisonUniversity of Wisconsin-MadisonApplied Superconductivity CenterApplied Superconductivity Center
Superconducting Superconducting Materials Suitable for Materials Suitable for
MagnetsMagnetsDavid C Larbalestier
Applied Superconductivity CenterDepartment of Materials Science and Engineering
Department of Physics
CERN January 14-18, 2002Note: Slight changes have been made to the final text which will differ from the video feed. Such changes are noted by highlighted text in this fashion wherever possible.
University of Wisconsin-MadisonUniversity of Wisconsin-MadisonApplied Superconductivity CenterApplied Superconductivity Center
HgBa2Ca3Cu4Oy
Metallic low temperature superconductors
Oxide, high temperature superconductors
Transition TemperaturesTransition Temperatures
Onnes 1911
University of Wisconsin-MadisonUniversity of Wisconsin-MadisonApplied Superconductivity CenterApplied Superconductivity Center
0
10
20
30
40
0 30 60 90 120Temperature (K)
Fie
ld (
T)
Helium
Nb-Ti
Nb3Sn
MgB2 film
MgB2 bulk
Hydrogen
Neon Nitrogen
BSCCO
YBCO
Cooling liquids
H-T Plane of SuperconductorsH-T Plane of Superconductors
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Critical CurrentDensity, A/mm²
100
1,000
10,000
100,000
0 5 10 15 20 25
Applied Field, T
YBCO75 K H||a-b
75 K H||c
Nb 3Al
Nb 3Sn
Nb-Ti
2212
2223
At 4.2 K UnlessOtherwise Stated
1.8 KNb-Ti-Ta
PbSnMo 6S 8
1.8 KNb-Ti
Nb 3Sn
2212
YBCO
Nb-Ti: Nb-Ti/Nb (21/6) 390 nm mult ilayer '95 (5°) , 50 µ V/cm - McCambridge et al. (Yale)Nb-Ti: Nb-Ti/Ti (19/5) 370 nm multilayer '95 ( 0°), 50 µ V/cm - N. Rizzo et al. LTSC'96 (Yale)Nb-Ti: APC strand Nb-47wt.%Ti with 24 vol.%Nb pins (24 nm nominal diam.) - Heussner et al. (UW-ASC)Nb-Ti: Aligned ribbbons, B|| ribbons, Cooley et al. (UW-ASC)Nb-Ti: Best Heat Treated UW Mono-Filament. (Li and Larbalestier, '87)Nb-Ti: Example of Best Industrial Scale Heat Treated Composites ~1990 (compilation)
Nb3Sn: Tape from (Nb,Ta) 6Sn5+Nb-4at.%Ta powder, [Core Jc, core ~25 % of non-Cu area] Tachikawa et al. (Tokai U.), ICMC-CEC '99
Nb3Sn: Internal Sn, ITER type low hysteresis loss design - (IGC - Gregory et al.) [Non-Cu Jc]Nb3Sn: Bronze route int. stab. -VAC-HP, non-(Cu+Ta) Jc, - Thoner et al., Erice '96.Nb3Sn: SMI-PIT, non-Cu Jc, 10 µV/m, 192 fil., 1 mm dia. (45.3 % Cu), - U-Twente data provided March 2000 by SMI
Nb3Al: Nb stabilized 2-stage JR process (Hitachi,TML-NRIM, IMR-TU), Fukoda et al. ICMC/ICEC '96
YBCO: /Ni/YSZ ~1 µm thick microbridge, H||c 4 K, - Foltyn et al. (LANL) '96YBCO: /Ni/YSZ ~1 µm thick microbridge, H||ab 75 K, - Foltyn et al. (LANL) '96YBCO: /Ni/YSZ ~1 µm thick microbridge, H||c 75 K, - Foltyn et al. (LANL) '96
Bi-2212: paste, B||tape, 4.2 K - Hasegawa et al. (Showa) IWS'95Bi-2212: stack, B||tape, 4.2 K - Hasegawa et al. (Showa) IWS'95Bi-2212: 19 filament tape B||tape face - Okada et al (Hitachi) '95Bi-2212: Round multifilament strand - 4.2 K - (IGC) Motowidlo et al. ISTEC/MRS '95Bi-2223: multi, B||tape, 4.2 K - Hasegawa et al. (Showa) IWS'95Bi 2223: Rolled 85 Fil., Tape, B||, - (AmSC) UW'6/96Bi 2223: Rolled 85 Fil. Tape, B , - (AmSC) , UW'6/96PbSnMo 6S8 (Chevrel Phase): Wire with 20%SC in 14 turn coil , - (Univ. Geneva/HFML&RIM - NL/U-Rennes), 97
Nb 3Al: Transformed rod-in-tube Nb3Al (Hitachi,TML-NRIM), Nb Stabilized - non-Nb Jc, APL, vol. 71(1), p.122, 1997
Nb-44wt.%Ti-15wt.%Ta: at 1.8K, monofil. optimized for high field, unpub. Lee, Naus and Larbalestier (UW-ASC'96)
Nb-Ti: Nb-47wt%Ti, 1.8K, Lee, Naus and Larbalestier (UW-ASC'96) ICMC-CEC1997.
Nb-Ti(Fe): 1.9 K, Full-scale multifilamentary billet for FNAL/LHC (OS-STG) ASC'98
Nb3Sn: Internal Sn High Jc design CRe1912, OI-STG, - Zhang et al. ASC'98 Paper MAA-06
Bi-2212: 3-layer tape (0.15-0.2 mm 4.0-4.8 mm) B||tape at 4.2 K face - Kitaguchi et al, ISS'98, 1 µV/cm
Nb3Sn: Internal Sn High Jc design ORe0038, OI-STG, - Zhang et al. ASC'98 Paper MAA-06
Nb3Al: 84 Fil. RHQT Nb/Al-Mg(0.6 µm), - Iijima et al. NRIM ASC'98 Paper MVC-04Nb3Al: 84 Fil. RHQT Nb/Al-Ge(1.5 µm), - Iijima et al. NRIM ASC'98 Paper MVC-04
Peter Lee UW: www.asc.wisc.edu
University of Wisconsin-MadisonUniversity of Wisconsin-MadisonApplied Superconductivity CenterApplied Superconductivity Center
Nb-Ti Nb3Sn
Coated conductor. (IBAD, RABiTS or ISD)
MgB2 powder inside Fe/Nb/Ni barrier inside Cu
Bi-2223
Generations of ConductorsGenerations of Conductors
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Outline of LecturesOutline of LecturesAs advertised in lecture 1 I. Basic Superconducting Parameters, mainly Critical Current Density II. Basic Materials Issues III. Niobium Titanium IV. Niobium Tin and Niobium Aluminum V. BSCCO VI. YBCO VII. Magnesium Diboride VIII. Summary Issues
As actually given:
I. Basic Materials suitable for magnets
II. Niobium Titanium
III. HTS conductors (mainly BSCCO) – key issues
IV. MgB2 conductors – key issues
V. Nb3Sn conductors – key issues.
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I a. “Zero Resistivity”I a. “Zero Resistivity”
Non-Superconducting Metals
– = o + aT for T > 0 K*
– = o Near T = 0 K
*Recall that (T) deviates from linearity near T = 0 K
Superconducting Metals
– = o + aT for T > Tc
– = for T < Tc
Superconductors are more resistive in the normal state than good conductors such as Cu
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I b. Perfect DiamagnetismI b. Perfect Diamagnetism
m = -1
Means:B = o(H + M)
B = o(H + m H)
B = 0
Normal Metal Superconductor
Flux is excluded from the Flux is excluded from the bulk by supercurrents bulk by supercurrents flowing at the surface to a flowing at the surface to a penetration depthpenetration depth ( () ) ~ 200-~ 200-500 nm500 nm
HM
M=-H
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I c. TI c. Tcc History History
HgBa2Ca3Cu4Oy
Metallic low temperature superconductors
Oxide, high temperature superconductors
MgBMgB22
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I d. Low Temperature SuperconductorsI d. Low Temperature Superconductors
Type I
Type II
Bc
Bc2
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I e. Type I and Type III e. Type I and Type II
Type I– Material Goes Normal
Everywhere at Hc
Type II– Material Goes Normal Locally at Hc1,
Everywhere at Hc2
HC2HC1 H
M
Complete flux exclusion up to Hc, then destruction of superconductivity by the field
Complete flux exclusion up to Hc1, then partial flux penetration as vortices
Current can now flow in bulk, not just surface
HC1
M
H
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I f. Vortex propertiesI f. Vortex properties
Two characteristic lengths– coherence length , the pairing
length of the superconducting pair– penetration depth , the length over
which the screening currents for the vortex flow
Vortices have defined properties in superconductors– normal core dia, ~2– each vortex contains a flux quantum
0 currents flow at Jd over dia of 2
– vortex separation a0 =1.08(0/B)0.5
Hc2 =22
h/2e = 2.07 x 10-15 Wb
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I g. Vortex Imaging by DecorationI g. Vortex Imaging by Decoration
Vortex state can be imaged in several waysMagnetic decorationSmall angle neutron
scatteringHall probesMagneto opticsScanning probe methods
First was by sputtering magnetic smoke on to a magnetized superconductor in the remanent stateLattice structure confirmed
and defects in lattice seen Trauble and Essmann 1967
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I h. Vortex Imaging by Magneto OpticsI h. Vortex Imaging by Magneto Optics
Prof. Tom H. Johansen Department of Physics, University of Oslo
NbSe2
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I j. Bean Model I j. Bean Model Bean (1962) and London (1963) introduced
the concept of the critical state in which the bulk currents of a type II superconductor flow either at +Jc, -Jc or zero.– Critical State is a static force balance between the
magnetic driving force JxB and the pinning force exerted on vortices by the microstructure FP
|(Bx(xH))| = BJc(B)
– Solutions define the macroscopic current patterns and enable the Jc to be determined from magnetization measurements
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I k. Macroscopic Current Flow and I k. Macroscopic Current Flow and Flux PatternsFlux Patterns
After Peter Kes in Concise Encyclopedia on Magnetic and Superconducting Materials, Ed J. Evetts Pergamon 1991
MagnetizationTransport
Jc = f(H)
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I l. Magnetization and the Bean ModelI l. Magnetization and the Bean Model
m=MV=0.5(rxj)dV– where j=(1/m0)xB or m=MV=IixSi
Slab geometry is very simple– dB/dx = ±Jc(B)
Magneto optical image of current flow pattern in a BSCCO tape. The “roof” pattern defines the lines along which the current turns.
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I m. Flux Pinning TheoryI m. Flux Pinning Theory
Defects cause variation in G of FLL– up to 107A/cm2 at >30T
Vortex separation few for b>0.5
Dense interaction of FLL with defect array– unperturbed vortex array is a
FLL– defects perturb the FLL– defects seldom form a lattice
Experiment measures global summed pinning force Fp=JcxB, often >20GN/m3
Elementary interaction is fp, generally small, e.g.~ 10-14N for binding to a point defect
Predictive, quantitative theory of flux pinning is mostly lacking
3 step process– compute fp
– compute elastic/plastic interactions of defect(s) and FLL
– Sum interactions over all pins and vortices
2 main cases:– weak pinning, statistical
summation (Labusch, Larkin and Ovchinnikov)
– strong pinning with full summation
Useful materials try to fall into the second category
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I n. Defect-Fluxline InteractionsI n. Defect-Fluxline Interactions
Magnetic interactions on ~ Perturbations tocurrents by
interfaces and surfaces– no normal component of J
Strong in lowmaterials
Vortex core interactions on ~
Possibility for point defects, precipitates, dislocations to pin
Perturb local ||2 through density, elasticity or electron-phonon
Can also perturb electron mean free path and hence
F= d3r(A||2 +(B/2)||4 + C||2 + (h2/20) ,
A=N(0)(1-t), B= 0.1N(0)/(kBTc)2, C=0.552N(0)()
Core interactions dominate in useful materials
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I o. Summation and ScalingI o. Summation and Scaling
Strong pinning materials (Nb-Ti wires, irradiated HTS) often exhibit full summation– Fp=ndefectsfpdefect
Weak pinning requires statistical summation as already noted– many adjustable,
often non-verifiable parameters
Scaling of the global pinning force with H, T can often be seen:
Fp(B,T) = bp(1-b)q Nb-Ti often b(1-b), Nb3Sn b0.5(1-b)2, b=B/Bc2
HTS scaling functions complicated by thermal activation effects
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I p. The Irreversibility FieldI p. The Irreversibility Field
Simple H-T diagram for LTS: Suenaga, Ghosh, Xu, Welch PRL Suenaga, Ghosh, Xu, Welch PRL 6666, 1777 (1991), 1777 (1991)
Complex H-T diagram for HTS
Nishizaki and Kabayashi SuST 13, 1 (2000)Nishizaki and Kabayashi SuST 13, 1 (2000)
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I q. Summary of Current Density I q. Summary of Current Density IssuesIssues
Enormous Jc can be obtained in some systems– ~10% of depairing current density (~Hc/) in Nb-Ti
and for many HTS at low temperatures– HTS suffer from thermal activation and lack of
knowledge about what are the pins
Practical materials want full summation to get maximum Jc
To compute Fp a priori in arbitrary limit is so far
beyond us Useful materials tend to be made first and
optimized slowly as control of nanostructure at scale of 0.5-2 nm is not trivial
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II. Basic Materials IssuesII. Basic Materials IssuesCrystal Structures
– Nb-Ti: body centered cubic simple, ductile– Nb3Sn: cubic A15 Crystal structure with range of
off-stoichiometric compositions– Nb3Al is always off stoichiometry– BSCCO: complex layered phase(s) not found at
fixed stoichiometry of nominal phase– YBCO: layered phase of fixed cation
stoichiometry but variable O content– MgB2: Mg cages B
Only Nb-Ti is ductile!Essential Phase Diagram Information
– well known for LTS, poorly known for HTS
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400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
90
Composition, Weight Percent Niobium
Liquid
Liquid +
Nb-47 weight % Ti
Ms
Composition, AtomicPercent Niobium
Tem
pera
ture
, °C
0 20 30 40 50 60 70 80 10010
0 20 30 40 50 60 70 80 10010
Key features:•Very high melting points•Large separation liquidus and solidus leads to segregation on cooling•Nb is bcc at all T, while Ti is bcc at high T and hcp at low T•Nb-Ti alloys want to become 2 phase hcp and bcc at low T but cannot transform by diffusion•The lattice acquires a soft phonon that has very important consequences:
•E declines on cooling•p increases on cooling
•The martensitic phase transformation is only incipient for Nb47wt.%Ti but the resistivity is greatly increased and Hc2 increased too
II a. Nb-Ti Phase DiagramII a. Nb-Ti Phase Diagram
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II b. Nb-Sn Phase Relations II b. Nb-Sn Phase Relations
TTCC
CC
C: Cubic A15, higher HC: Cubic A15, higher Hc2c2 phase, T: Tetragonal A15 phase phase, T: Tetragonal A15 phase
TTCC
Broad composition range 18-25at.%Sn, LT shear transformation to a small tetragonality, lowering Tc and Hc2
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II c. NbII c. Nb33Sn StructureSn Structure
Cubic structure with 3 orthogonal chains in which the Nb atoms are more closely spaced than in pure Nb:
high N(0).
Departures from stoichiometry must be accommodated by vacancies or anti-site disorder
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II d. The BSCCO FamilyII d. The BSCCO Family
Tc ~30K ~70-95K ~105-110K
CuO2
CuO2
CuO2
CuO2
Ca
Ca
Bi-O double layer
Bi-O double layer
Sr
Sr
~ 200-300 may be ~ 50
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II e. YBCOII e. YBCO
YBCO (YBa2Cu3O7-x) possesses the first crystal structure with Tc > 77K
It has defined cation stoichiometry 1:2:3, but O content is variable from 6-7– Tc > 90K demands x<0.05
YBCO is often thought of as being archetypal but in fact the Cu-O chain layers are very unusual– Make charge reservoir layer
metallic– Most HTS are 2D, but YBCO is
anisotropic 3D with electron mass anisotropy = (mc/ma)0.5 of ~7
Cu-O chain layer
CuO2 layer
CuO2 layer
CuO2 layer
CuO2 layer
Y
Y
Ba
Ba
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II f. MgBII f. MgB22
Smaller B, larger Mg atoms
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Mg
B CuO2
CuO2
CuO2
CuO2
Ca
Ca
Bi-O double layer
Bi-O double layer
Sr
Sr
Cu-O chain layer
CuO2 layer
CuO2 layer
CuO2 layer
CuO2 layer
Y
Y
Ba
Ba
a. b
cd e
II g. Higher Tc II g. Higher Tc – greater – greater complexitycomplexity
9 K 18-23 K
39 K
92-95 K 110 K
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II h. Summary Materials IssuesII h. Summary Materials IssuesHigher Tc means greater crystal complexity
– body centered cubic Nb-Ti with random site occupation, ductile
phonon anomalies
– Nb3Sn ordered A15 phase, brittle other intermetallics often distort phase field
– YBCO is anisotropic 3D, low carrier density, cation stoichiometric, brittle
metallic charge reservoir layer
– BSCCO has 3 layered phases none of which exist at cation stoichiometry, micaceous with self-aligning tendencies
strongly anisotropic, 2D (but depends on doping state) poorly understood phase relations
Materials quality at scale of is always an issue!
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Global UW ReferencesGlobal UW References
L. D. Cooley, P. J. Lee, and D. C. Larbalestier, "Conductor Processing of Low-Tc Materials: The Alloy Nb-Ti," to appear as Chapter 3.3 of “The Handbook on Superconducting Materials," Edited by David Cardwell and David Ginley, Institute of Physics UK to appear March 2002.
L. D. Cooley, C. B. Eom, E. E. Hellstrom, and D. C. Larbalestier, “Potential application of magnesium diboride for accelerator magnet applications”, Proceedings of the 2001 Particle Accelerator Conference to appear.
David Larbalestier, Alex Gurevich, Matthew Feldmann and Anatoly Polyanskii, “High Transition Temperature Superconducting Materials For Electric Power Applications”, Nature 414, 368-377, (2001).