Generation and Analysis of Magnetic Flux Pinning...

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1 Generation and Analysis of Magnetic Flux Pinning Sites in YBa 2 Cu 3 O 7-δ Thin Films Haiyan Wang Superconductivity Technology Center Materials Science & Technology Division Los Alamos National Laboratory

Transcript of Generation and Analysis of Magnetic Flux Pinning...

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Generation and Analysis of Magnetic Flux Pinning Sites in YBa2Cu3O7-δ

Thin Films

Haiyan WangSuperconductivity Technology Center

Materials Science & Technology DivisionLos Alamos National Laboratory

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OutlineI. High Temperature Superconductor Thin Films• Pulsed laser deposition and domain matching

epitaxy• Normal architecture of coated conductors;• Generation of magnetic flux pinning sites in YBCO

thin films.a. Nanoparticles generated on the buffer surface; b. Y2O3 nanoparticles doped in YBCO;c. BaZrO3 nanoparticles doped in YBCO.

II. Opportunities and Future Work

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Pulsed Laser Deposition

Heatedsubstrate

Plume of evaporant

Target

KrF excimer laser (248nm,pulse duration 25ns, 10Hz,deposition rate~2nm/s, a typical pulse~6J/cm2,

target-substrate distance 4-5cm);

Advantages: simple configuration, Reproduction of the target stoichiometry, low contamination,

In-situ control of the thin film properties.

Figure from Physical vapor Deposition of Thin Films, John E. Mahan (Wiley-interscience Publication)

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Domain matching epitaxy

Small lattice mismatchLattice matching epitaxy

Large lattice mismatchDomain matching epitaxy

af ≈ as maf ≈ nas

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Epitaxial TiN film on Si(100)Domain Matching Epitaxy

sf

sf

namanama

f+

−×= 2

Large lattice mismatch

4aTiN ≈ 3aSi

f=24.6%

sf

sf

aaaa

f+

−×= 2

Domain matching epitaxy

TiN af=0.4256nm, Si as=0.5430nm

f’=4.4%

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Domain epitaxy growth of TiN films on Si(100) TS=700oC

])110[2

( ab =Two set of extra half planes generated in TiN film form one 90o dislocation.

Wang et al. J. Mater. Res., 16, 2733, (2001).

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Normal architecture of YBa2Cu3O7-δ coated conductors

Ni alloy tape

IBAD MgObufferYBCO

Polished polycrystalline substrate

Ion Beam Assisted Deposition (IBAD) produces single-crystal-like MgO template.

PLD produce epitaxial buffer layer and YBCO film.

Tape is moving slowly .

Target rotation

For the growth of meter-long YBCO wires, the substrate is slowly moving during deposition.

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TEM and HRTEM show the microstructure of a typical coated conductor.

Ni Alloy

IBAD MgOBuffer

YBCO

Wang et al. J. Mater. Res., 19, 1869 (2004).

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sf

sf

namanama

f+

−×= 2

Large lattice mismatch

14aSrTiO3 ~ 13aMgO

f=7.38%

sf

sf

aaaa

f+

−×= 2

Domain matching epitaxy

STO af=3.905A, MgO as=4.21A

f’=0.02%~0%

Domain matching epitaxy between STO and MgO

Wang et al. J. Mater. Res., 19, 1869 (2004).

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Domain match epitaxy between STO and MgO: 14 to13 match

STO

MgO

14aSTOmatches13aMgO~0.02%

Fast Fourier Filtered Image

Wang et al. J. Mater. Res., 19, 1869 (2004).

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10 62J cE A /cm

Generators&

Transformers

Cables

10 4

10 5

10 3

2 64

77 K

0

Magnetic Energy Storage

Fault Current limiters

B / Tesla || to c

Motors

Current status,<1m

What in-field performance is needed for the future applications of YBCO coated conductors?

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Flux pinning in type II superconductors

Ideal type II superconductors (no extended defects)Force →dissipative flux movement →carrying transport current with losses.

2

0

1

oan

nB

=

Φ=

Ba 0

= Flux line arrangement containing high density dislocations in Pb-6.3 at.% In sample, B=35mT, T=1.2K.

Most type II superconductors have extended defects (dislocations, grain boundaries and precipitates) →pinning centers for flux lines

Lorentz force between flux and current. FL=Jtr x Φ0 . Need Fp>FL

nmaTB

cmGe

h

201

1007.22

270

=⇒=

⋅×≈≈Φ −

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Flux pinning measurements→ Field dependence and angular dependence

HAligned vortex

DefectJc

angle

Extended defects•Line defects and columnar defects•Planar defects (stacking faults and twin boundaries)

Jc ∝ length of vortex that is pinned.

Larger angle →shorter pinned segments →lower Jc

Maximum pinning

Always H⊥J (maximum Lorentz force)

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Flux pinning → directional pinning by correlated defects → angular dependence

H

H

Aligned vortex

Staircase vortex

Defect

Defect

Jc

angle

Extended defects•Line defects and columnar defects•Planar defects (stacking faults and twin boundaries)

Jc ∝ length of vortex that is pinned.

Larger angle →shorter pinned segments →lower Jc

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Flux pinning → directional pinning by correlated defects → angular dependence

H

H

H

Aligned vortex

Staircase vortex

Unpinned vortex

Defect

Defect

Defect

Jc

angle

Extended defects•Line defects and columnar defects•Planar defects (stacking faults and twin boundaries)

Jc ∝ length of vortex that is pinned.

Larger angle →shorter pinned segments →lower Jc

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Possible practical ways to increase pinning

More line defects– Miscut substrates– Lower growth temperatures (smaller island sizes)– Heteroepitaxial nanoparticles

Point defects (and associated strain)– cation or anion vacancies– RE-Ba cross substitution

Volume defects (and associated strain)– Second phase particles– Interlayers of non-superconducting material– Substrate surface roughening

Lorentz force between flux and current. FL=Jtr x Φ0 . Need Fp>FL

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Three simple and effective approaches to enhance pinning demonstrated

Method 1. Introduction of buffer roughness-epitaxial STO nanoparticles grown on the YBCO deposition surface

-more low angle grain boundaries // c;

Method 2. Introduction of heteroepitaxial second phases Y-rich YBCO films—self-assembled Y2O3 nanoparticles;

Method 3. Introduction of heteroepitaxial second phases Nanoparticles (BaZrO3) grown in the YBCO film.

-Increase c-axis dislocation density.Materials selection for second phase:a) Can grow heteroepitaxially with YBCOb) Lattice mismatch producing strain leading to misfit dislocationsc) High melting temperature phase, yielding slow growth kinetics andhence small particlesd) Chemical compatibility with YBCO

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Method 1-Introduction of buffer roughnessSTO nanoparticles can be generated at lower temperature.

670oC, STO

760oC, STO

820oC, STO

SEM

Wang et al. J. Mater. Res., 19, 1869 (2004).

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STO nanoparticles (outgrowth) at interface generated low angle boundaries in YBCO.

Wang et al. J. Mater. Res., 19, 1869 (2004).

STO at 820oCSmooth interface

STO at 700oCNanoparticleat interface

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STO at 820oCSmooth interface

STO at 700oCLattice distortions

Wang et al. J. Mater. Res., 19, 1869 (2004).

STO nanoparticles (outgrowth) at interface generated local lattice distortions in YBCO.

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STO nanoparticles enhance in-field performance at high field.

0 1 2 3 4 5 6 7

0.01

0.1

1

TSTO=700oCSTO nanoparticles

Jc [M

A cm

-2]

H [T]

TSTO=820oC

smooth surface

H//c T=75.5K

0.01 0.1 1

0.01

0.1

1

α=0.44

J c/Jcsf

µ0H[T]

α=0.55

Wang et al. to be published in App. Phys. Lett.

α value is temperature independent, architecture dependent and repetitive.Smaller α value, better field dependence.

α−∝ HJc

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The angular dependence of Jc shows a larger c-axis peak.

Wang et al. to be published in App. Phys. Lett.

The angular effect isconsistent with the presenceof low angle boundaries //c(introduced by tilted a-bplanes induced by buffersurface roughness)

0 1 2 3 4 5 6 7

0.01

0.1

1

TSTO=700oCSTO nanoparticles

Jc [M

A c

m-2

]

H [T]

TSTO=820oC

smooth surface

H//c T=75.5K

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Method 2. Introduction of heteroepitaxial second phasesSelf-assembled epitaxial Y2O3 nanoparticles in YBCO

Wang et al. submitted to Appl. Phys. Lett.

Y2O3

YBCOCeramic target of Y-rich YBCO fabricated and ablated

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Y2O3 nanoparticles enhance in-field performance at low field.

0 1 2 3 4 5 6 71E-3

0.01

0.1

1

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.1

1

YBCO YBCO with10mol% Y2O3

J c (MA

/cm

2 )

B (T)

J c (MA

/cm

2 )

B (T)

Wang et al. submitted to Appl. Phys. Lett.

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Method 3. Introduction of heteroepitaxial second phasesEpitaxial BaZrO3 nano-particles in YBCO films

Nature Materials, 3, 439-443, (2004)

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HRTEM and FFT shows the presence of BaZrO3 nano-particles.

Nature Materials, 3, 439-443, (2004)

20 40 60 80 1000

20

40

60

80

100

120

140

160

Par

ticle

Num

ber

Particle Size (nm)

1µmx1µm area

39

165

77

124 21 1 1 1 1

Fast Fourier Transform indicates FCC,a ~4.27Å

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Comparison of YBCO+BaZrO3 and YBCO shows a 1.5~5× increase in Jc.

Nature Materials, 3, 439-443, (2004)

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Angular dependence shows a huge c-aixspeak indicating extra c-axis pinning.

Nature Materials, 3, 439-443, (2004)

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Summary

• By pulsed laser deposition, high quality YBCO thin films can be grown on Ni substrates using domain matching epitaxy.

• We have discovered three methods to introduce nanoparticles (c-axis defects in YBCO).

• Nanoparticles significantly improve the in-field performance of YBCO thin films.

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Opportunities and future workSuperconductors

Explore fundamental physics of nanoparticle enhanced pinning mechanism in YBCO thin films (modeling and simulation)Precisely control the size and distribution of nanoparticles in YBCO thin films.

Nitride materials for electronic and optical devicesElectrical properties of nanocrystalline TiN;Cu diffusion mechanism in epitaxial and polycrystalline TaN;Electrical property and Cu diffusion in epitaxial TiN/TaNsuperlattice.GaN LED devices

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Nanocrystalline TiN films grown on Si(100)Ts=25oC

AverageGrain size size=8nm

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Nanocrystalline TiN films grown on Si(100)Ts=200oC

Average grain size ~ 20nm, with high angle grain boundaries.

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Nanocrystalline TiN Films Electrical Properties

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

40

60

80

100

120

140

160 25oC

200oC400oC500oC

600oCRes

istiv

ity(x

10-6

Ohm

cm

)

1/d(nm-1)

ratio of atoms on the grainboundary to that in the bulk;

grain boundary width;

grain size.

Resistivity increasing is mainly controlled by grain boundaryscattering.

dδ3=Ω

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Epitaxial and polycrystalline TaN

Single crystal cubic TaNwith TiN buffer layer

Hexagonal Polycrystalline TaN

Latticematching

Domain matching

Si a=5.43ATiN a=4.24ATaN a=4.33A

Cubic: metastable

phase;Hexagonal:

Stable phase.

Wang et al. Appl. Phys. Lett., 80, 2323 (2002).

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Single crystal cubic TaN on Si(100) and Si(111) using TiN buffer layer--TEM & STEM

Low Mag TEM and STEM HRTEM

Wang et al. Appl. Phys. Lett., 80, 2323 (2002).

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Cu diffusion into single crystal cubic TaNand polycrystalline TaN after 700oC, 30min

Single crystal TaN Polycrystalline TaN

Wang et al. Appl. Phys. Lett., 81, 1453 (2002).

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Cu diffusion characteristics in single crystal cubic TaN

1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14 1.16 1.18 1.20-41

-40

-39

-38

-37

-36

-35

-34

-33574 oC604636670707

Cu diffusion coefficient in single crystalline TaN

Activation energy Q0=3.27±0.1eV

600oC

650oC

700oC

lnD

(cm

2 /s)

1000/T(K)

12]/)1.027.3(exp[)5.9160( −±−±= scmTkeVD B

eVQTaNgb 6.127.35.0 ≈×=

eVQTiNgb 29.0=

TaN has a denser interstitial structure (more closely packed than TiN)

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TaN/TiN Superlattice as advanced Cu diffusion barrier

Low mag and SAD

Wang et al. Appl. Phys. Lett., 83, 3072 (2003)

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STEM of TaN/TiN Superlattice

Z-contrast intensity profile

STEM (Z-contrast)

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Electrical Property of TiN/TaN SL

0 50 100 150 200 250 300200

220

240

260

280

300

320

340

360

ρ (µΩ

-cm

)

T(K)0 50 100 150 200 250 300

70

80

90

100

110

120

130

Res

istiv

ity (µ

Ω-c

m)

T(K)

•TaN/TiN SL RT resistivity is ~130 µΩ-cm with a small temperature coefficient of resistivity of 0.002 K-1.•RT resistivity of TaN/TiN SL is lower than TaN itself.•semiconductor (TaN only) to metallic behavior.

TaN/TiN SLTaN only

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Growth defects in GaNsuperlattice LED devices

Threading dislocations terminate near the pits.

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Colossal magnetoresistance materials (CMR)

The influence of defects (misfit dislocations) on the performance of Colossal Magnetoresistance (CMR) materials. (Nd0.67Sr0.33MnO3 on LaAlO3)

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Acknowledgements

Drs. Quanxi Jia, Stephen Foltyn(Los Alamos National Laboratory)

Profs. Jagdish Narayan,Carl Koch, Mike Rigsbee, Hans Conrad.(North Carolina State University)