University of Wisconsin-Madison Applied Superconductivity Center Superconducting Materials Suitable...

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.


HgBa2Ca3Cu4Oy

Metallic low temperature superconductors

Oxide, high temperature superconductors

Transition TemperaturesTransition Temperatures

Onnes 1911


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


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


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


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.


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


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


I c. TI c. Tcc History History

HgBa2Ca3Cu4Oy

Metallic low temperature superconductors

Oxide, high temperature superconductors

MgBMgB22


I d. Low Temperature SuperconductorsI d. Low Temperature Superconductors

Type I

Type II

Bc

Bc2


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


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


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


I h. Vortex Imaging by Magneto OpticsI h. Vortex Imaging by Magneto Optics

Prof. Tom H. Johansen Department of Physics, University of Oslo

NbSe2


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


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)


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.


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


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


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


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)


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


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


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


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


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


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


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


II f. MgBII f. MgB22

Smaller B, larger Mg atoms


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


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!


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).

University of Wisconsin-Madison Applied Superconductivity Center Superconducting Materials Suitable...

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