Microstructure effects on Jc-B properties in YBCO thin films

mu

Physiea C 185-189 (1991) 2215-2216 North-Holland

Microstructure Effects on Jc-B Properties in YBCO Thin Films

H. Fuke, H. Yoshino, K

Yamazaki, T. D. Thanh, K. Ando and Y.

Advanced Research Laboratory, Research and Development Komukai-Toshiba-cho, Saiwai-ku, Kawasakl, 210 JAPAN: • Super-GM, 5-14-10, Nishi Temma, Osaka, 530 JAPAN.

Kobayashi *

Center, Toshiba Corporation.

l,

We h a v e i n v e s t i g a t e d t h e r e l a t i o n s h i p between microstructure a n d p i n n i n g forces. The boundaries between grains a-axis oriented and c-axis oriented are clarified to be effective as a pinning center.

I. INTRODUCTION

mm-long bridges,

The large critical for

the

high

important Jc>lO 6 YBCO

Tc

for

oxide

power

A/ca 2

at

77

films. W h e n

parallel

to

current

superconductors

applications. K, 0

T

was

a magnetic

the

ab-plane

obtained

field of

are

u p t o 27 T 1.

in

is applied

YBCO

crystal,

However,

when

the m a g n e t i c field is applied p e r p e n d i c u l a r the

ab-plane

(H 3_ ab-plane),

Jc

steeply with increasing magnetic work.

we

investigated

effects on Jc-B in

YBCO

thin

properties

the

properties films,

to

microstructure

and

$zV/cm c r i t e r i o n .

3. RESULTS AND DISCUSSION Three kinds

of

Y B C O films, which have

different microstructures, varying their

were fabricated

c h e m i c a l compositions; (a) h i g h l y

c-axis oriented

film. (b) c-axis oriented

in which a-axis

oriented

studded

(see

by

Fig.l). and

slab-like

film.

grains are

(c) c-axis

oriented

film. which contains continuous a-axis oriented l~rains.

H 3_ ab-plane

improve

for HJ.ab-plane

to

decreases

field. In this

for

The c r i t i c a l c u r r e n t (Ic) is defined as the 1

Recently,

reported at 77 l{ in a high

Jc>lO 4 A/cm 2 was magnetic field,

densities (Jc's)

using ion m i l l i n g technique.

the

Jc-B

to clarify

the

pinning mechanism. n

2. EXPERIMENTAL The YBCO thin films were p r e p a r e d ionized

cluster

Details

on

beam (ICB) d e p o s i t i o n

the

ICB

described in ref.2. (100) o r i e n t a t i o n The s u b s t r a t e during

The

critical films

were used

were

as

the

The d e p o s i t i o n

film

thickness

properties

resistivity

current

method.

method are

t e m p e r a t u r e was k e p t

Superconducting four-probe

deposition

SrTtO 3 s i n g l e c r y s t a l s

deposition.

nm/mln.

by t h e

were

substrate. at

660 °C

rate

was 4

2000

into

measurements, 0.5

am-wide

Fig.1 T h e m i c r o g r a p h o f c - a x i s o r i e n t e d film. m which a - a x i s oriented s l a b - l i k e g r a i n s are studded.

A. and

angular

For

d e p e n d e n c e o f Jc a r e shown m Fig.2.

When the

the

magnetic f i e l d

measured b y

measurements.

density

patterned

was

with

and

Magnetic

2

0921-4534/91/$03.50 © 1991 - Elsevier Science Publishers B.V. All rights reserved.

held

dependence

ts a p p l i e d p e r p e n d i c u l a r to the

H. Fuke et aZ

2216

/

Microstructure effects on Jc-B properties in YBCO thi~lfilms

substrate (H±ab-plane). in the case of samples

ordered,

(a)

oriented grains and c-axis oriented grains are

and

(c).

Jc

decreases

steep ly

with

sample

(b) the

decrease

in Jc

boundaries

The pinninR

is small.

force

Moreover Jc(H=IT) in samples (a) and (c) have a

difference in energy

minimum

through

value

for

H I ab-plane.

However,

between

a-axis

considered as the effective pinning centers.

increasing magnetic field. However, in the case of

the

in

the

originates

from

the

pet,alty of the fluxoids

difference

in coherence

length.

sample (b). Jc(H=IT) has a peak. These results

The critical current density in sample (b) for

show

H _Lab-plane was approximately i06 A/cm 2 at ~7

the

that

pinning

force

for

fluxoid

perpendicular to the ab-plane in sample (b) is

K, I T,

stronger than the ones in samples (a) and (c).

force.

No

than

marked

differences

could

be

observed

the three samples by TEM. except

in

that

axis oriented ~rains distribution. We consider

is

result.

pinning

a-axis

oriented

centers

for

grains

8ct

H [ ab-plane.

as the

Since

of

in eood

have

Io' T=77K

(a)

agreement

with

kinds

YBCO thin films, which

oriented

--0=0

--e =90

grains are studded, applied

of

grains

v

film, in which

field was

boundaries

experimental

For cori~nted

the decrease in Jc in the small

between

and

a-axis

for HJ_ab-plane.

studded

c-axls

a-axis

oriented

The

oriented

grains

are

clarified to be effective as a pinning[ center.

10`+

According

to

this

pinning

properties for H±ab-plane

mechanism,

Jc-B

could be explained

qualitatively.

Io" 0

O.%(T) 1.0

This

R&D

I+0 - - o ~

,

Q8

,

~--

~-,=°~m:= •

<> <)

÷

g <>+ <> s 0.6 0,4

the

by varyinE their chemical compositiorL axis


•-~

it

different microstructures, were prepared

E ,P, ¢.)

result,

4. SUMMARY Several

Io"

experimental

the

inside of the a-axis oriented grains is well-

--1 1•%

the

turned out that the shape of the Jc-B curve

for the a-

that

the

derived from the calculated pinning Though this value is one order larger

.,.

(b)

0

" '

+.,.

Magnetic field dependence of J c

90

1~5

8

T=?7K.H=I

Fig.2 dependence

Project

of Agency

under of

Industrial

MITI, being

for

the

of

Electric Moonlight

Science

consigned

and Industrial Technology

part

by

and New

Development

180

T

1. K. Watanabe, S. Awaji, N. Kobayashi, H. Yamane, T. Hirai, Y.Muto and T. Yamashita; Proc. Int, Simposium on Superconductivity (ISS'90), Sendai, 1990. 2.

and

Technology

a

REFERENCES

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45

Apparatuses

as

Organization (NEDO).

<>J+ I

'

performed

Superconducting

Energy

(a) ,+%<>° ;+++:+0+°0°°000°°°°°°°°°?+01+++

0.2

was

Power

Technology,

<¢ +0

.,.<>

work

angular

H. Yoshino, M. Yamazaki, T. D. Thanh and K. Ando; Proc. Int. Simposium on Superconductivity (ISS'89), Tsukuba, 1989.