Electronic properties of superconducting Pb-doped YBa2Cu3O7-y system

State C o m m u n i c a t i o n s , Vol. 68, No. 7, pp. 6 4 3 - 6 4 5 i 1988. ~Solld •s-~, P r i n t e d in Great Britain.

0 0 3 8 - 1 0 9 8 / 8 8 $3.00 + .00 P e r g a m o n Press ple

E l e c t r o n i c P r o p e r t i e s of S u p e r c o n d u c t i n g P b - d o p e d Y B a 2 C u 3 0 7 _ y system

Xia Jiansheng,

Cao Liezhao,

(Depa!r~ment of Physics,

Fang Minghu,

Zhang Qirui,

Zhang Han*, Qian Yitai*

* D e p a r t m e n t of Appl±ed Chemistry,

and T e c h n o l o g y of China,

Hefei,

(Received 19 September,

Anhui,

1988 by W. Y. Kuan)

The r e l a t i o n s h i p s b e t w e e n the granular structure, the s u p e r c o n d u c t i v i t y were s y s t e m a t i c a l l y

U n i v e r s i t y of Science

P.R. China)

normal state r~sistivity and

i n v e s t i g a t e d in Y B a 2 C u 3 _ x P b x O y

system.

We find that the normal state r e s i s t i v i t y and the critical current density are sensitive to the amount of lead.

Especially,

the critical current density of

the sample with x=0.1 is more twice higher than that of the sample with x=0 at liquid n i t r o g e n temperature.

The effects of the w e a k - l i n k

structure of sintered

bulk samples on the e l e c t r o n i c p r o p e r t i e s are d i s c u s s e d with the theories of M c m i l l a n and A m b e g a o k a r - B a r a t a f f .

i. I n t r o d u c t i o n

may be a e f f e c t i v e way to firm the intergrain

Since h i g h - T c s u p e r c o n d u c t i v i t y of Y-Ba-CuO system was d i s c o v e r e d / l / ,

c o u p l i n g and enhance the s u p e r c o n d u c t i v i t y of

it has been propos-

YBa2Cu307-y.

ed how to m a k e the new m a t e r i a l into practical application.

2. Experimental M e t h o d s

But, it is a m a t t e r of common

The samples with the nominal c o m p o s i t i o n

o b s e r v a t i o n that the c r i t i c a l current density

YBa2Cu3_xPbxOy(0~x'0.4)

were p r e p a r e d by usual

of sintered bulk samples is u n e x c e p t e d low

solid reaction method/7/.

though it has a higher Tc and Hc 2 due to their

tion p a t t e r n s were m a d e on Ligaku D / M A X - r A dif-

X-ray powder d i f f r a c -

typical g r a n u l a r s t r u c t u r e /2, 3, 4/. The int-

fractometer using monochromate high-intensity

ergrain w e a k - l i n k s t r u c t u r e is the m a i n obstac-

Cu(K~)

le for the p o t e n t i a l u s a g e of this material.

a m e t e r s of cell w e r e indexed by IBM-pc m i c r o c -

In

r a d i a t i o n at room temperature.

The par-

order to improve the e l e c t r i c p r o p e r t i e s of the

omputer.

1-2-3 phase compounds,

planks of 1 2 x O . 6 x 0 . 4 nun3. The r e s i s t i v i t y and

it must be done to

The e x p e r i m e n t a l

samples were cut into

strengthen the i n t e r g r a n u l a r c o u p l i n g between

the critical c u r r e n t d e n s i t y m e a s u r e m e n t s were

the grains.

p e r f o r m e d by the standard f o u r - p r o b e technique,

Some r e s e a r c h e r s have made use of

d o p i n g e f f e c t / 5 / and superfine powder m e t h o d

K e i t h l y 181 v o l t a m e t e r is used to m e a s u r e the

/6/ to e n h a n c e the s u p e r c o n d u c t i v i t y of the

v o l t a g e of samples. The ac m a g n e t i c suscep-

sintered bulk material.

t i b i l i t y m e a s u r e m e n t s were done e m p l o y i n g the

normal state

In this paper, the

resistivity,

ac m a g n e t i c suscep-

m u t u a l i n d u c t a n c e b r i d g e with a s e n s i t i v i t y

tibility and c r i t i c a l current d e n s i t y were

better than O.12~H. Both c a l i b r a t e d Ge thermom-

s y s t i m a t i c a l l y i n v e s t i g a t e d for the P b - d o p e d

eter and c o p p e r - c o n s t a n t a n

t h e r m o c o u p l e were

Y - B a - C u - O system. R e s u l t s show that the elec-

used to d e t e r m i n e the t e m p e r a t u r e d u r i n g the

tronic p r o p e r t i e s of the sintered samples are

measuring.

i m p r o v e d indeed by d o p i n g Pb. The normal state

3. R e s u l t s and D i s c u s s i o n s

r e s i s t i v i t y and the c r i t i c a l current d e n s i t y

X-ray p o w d e r d i f f r a c t i o n p a t t e r n s show that

are sensitive to the a m o u n t of lead. The Jc of

all samples are m u l t i - p h a s e materials.

sample Y B a 2 P b 0 . 1 C u 2 . 9 O y

phase is the s t a n d a r d YBa2Cu306.9,

is twice higher than

The main

and the

that of the single p h a s e YBa2Cu306. 9 at 77.4K

impure phase is the B a P b O 3, w h i c h increases in

and zero a p p l i e d field.

c o m p a n y with the a m o u n t of Pb. It is clearly

Therefore,

d o p i n g Pb 643

644

Pb-DOPED YBa2Cu307_y

pointed

out that lead forms

on the i n t e r f a c e is s u b s t i t u e d

the BaPbO 3 grown

or other e l e m e n t s

in

YBa2Cu307-y. The d e p e n d e n c e s

of normal

state r e s i s t i v i t y

of six samples

w i t h x f r o m 0 to

0.4 w e r e measured.

The results

features:

the t e m p e r a t u r e

firstly,

and the m a g n i t u d e

sensitively

Fig.l,

there

changes

of Pb are shown in minimum

increasing

earlier,

the Cu-O layer,

while

that the Tce of samples

or/and

so

even

semiconductor

and con-

layer of

or insulator,

to other

the

is a

one

so that its resisvalue;

then

the

boundary

the r e s i s t i v i t y

layer

increasing,

current

and the a m o u n t It is clear

and ~ ( x ) / ~ ( 0 )

and Jc(x)

density

of

that,

causes

especially,

to the lead,

related.

a higher

A

current

the ratio of Jc(0.1)

3.4 at 77.4K and

This result

Jc(x)/

b o t h Jc(x)/

are sensitive

resistivity

weak i n t e r g r a n u l a r

between

of Pb are also

and ~ (x) are d i r e c t l y

is about

of six samples

The r e l a t i o n s h i p s

77.4K)

shown in Fig.l.

Jc(0)

due to the

goes up again.

Jc(0)(at

Jc(0)

at

inter-

is of the s t r o n g e s t

samples,

is

the

with the x i n c r e a s i n g

is down to the lowest

to

zero a p p l i e d

can be well e x p l a i n e d links as well

by the

as the resis-

tivity. It is r e c o g n i z e d critical

current

resistivity and

which

Therefore,

weaker

in YBa2Cu307_y.

known that the i n t e r f a c e

coupling

layer

c o u p l i n g of grains b e c o m e s

field.

grains may be low Tc and n o n s u p e r c o n d u c t i n g materials

tivity

density,

by Pb,

the i n t e r c r y s t a l l i n e

layer

comparing

smaller

of 1-2-3

on both the t h i c k n e s s

of the b o u n d a r y

It is well

the

does not o b v i o u s l y

On the other hand,

c o u p l i n g depends

forms

BaPbO3,

for the sample with x=0.1,

crystalline

were measured.

associated

do not be d e s t r o i e d

first;

declines

68, No.

are very complicated.

conductor/8/.

The critical

only

that the C u - O c h a i n s

which are c l o s e l y

phase compounds,

ductance

properties

Pb, the i n t e r c r y s t a l l i n e

by the m e t a l l i c

resistivity

exists

of Pb(Fig.3).

with the high Tc s u p e r c o n d u c t i v i t y

change.

substitued

samples

the Pb d o e s not enter

the lattice of the 1-2-3 phase, BaPbO 3. It follows

in

of ~ ( x ) / ~ ( o )

the Tce of samples

slightly w i t h

As m e n t i o n e d

state resistiv-

the d e p e n d e n c e

is a r e s i s t i v i t y

secondly,

coefficient

w i t h the variations

on, the a m o u n t

at x=0.1;

show two obvious

of the normal

the a m o u n t of lead, (at 250K)

After d o p i n g

good electrical

on t e m p e r a t u r e

ity change

Vol.

its e l e c t r o n i c

of the 1-2-3 phase rather than

for copper

SYSTEM

boundaries

that the b e h a v i o u r

density

reveals directly

and the normal

the features in sintered

Zhao et al /i0/ r e p o r t e d

of the state

of grain bulk

samples/9/.

that the w e a k - l i n k

of

L2

grains

show the c h a r a c t e r i s t i c

of the S - N - I - N - S

I

3~ 05

o

08

O,J

~6

0.4

2

06

S

S

05

04 x

q

I

O2

×

-9

-3

1'-02 o

I OI

I

I

02

I

05

05

04

Ol

X

0 084 Fig.l

the d e p e n d e n c e

of

Jc(x)/Jc(0)(at

77.4K)

lead. ~(0) state

and Jc(0)

resistivity

cal c u r r e n t

P(x)/j~(0)(at

092

0 96

T/Tc

on the amount of express

the normal

(250K) and the criti-

density(77.4K)

O 7 _ y respectively.

088

250K)

of YBa2Cu 3

Fig.2 the r e l a t i o n critical

between

density

the reducing

and the temperature.

a: for YBa2Cu307_y;

b: for sample with

x=0.1;

curve.

c: AB theory

7

Vol.

68, No. 7

Pb-DOPED

YBa2Cu3OT_y

92

12

Jc(T)

m u s t use the A B ( A m b e g a o k a r - B a r a t o f f )

theory/12/ I

~

9O

--

to express

Curve b r e p r e s e n t s x=0.1.

Q8

645

SYSTEM

o6

86~

-

Namely

X 04

-- 84

w i t h the AB theory except n e a r Tc.

the c o n n e c t i n g

changed

d N is n e a r l y

same in both cases,

be l o n g e r 0

I

I

I

I

0 I

0.2

Q5

04

8o 0.5

than that of u n l e a d e d

current

sample will

the v o l u m e

fration

zero t e m p e r a t u r e

w i t h the a m o u n t

of lead..~(0):

susceptibility

for all six samples.

and the p r o p e r t i e s

described

by M c m i l l a n

metal

free path.

of s u p e r c o n d u c t i n g

phase

theory/ll/,

can be

the d i s t i n g -

is d 2 j c ( T ) / d T 2 > 0

monotonously

copper

with the i n c r e a s i n g

for the larger

to form the YBa2Cu307_y.

pointed

out that the effect

between

grains

the v o l u m e

x there

fraction

It is

of b o u n d a r y

on Jc is greater

of

is no

layer

t h a n that of

of s u p e r c o n d u c t i n g

phase,

the sample w i t h x=0.1 has the highest

layer and 1 is the e l e c t r o n

current

d e n s i t y but not the largest

Our e x p e r i m e n t a l

tion.

x=O,

where

0.i)

d N is the thickness

results

on two

are shown in Fig.2.

Curve a is well a g r e e m e n t the t e m p e r a t u r e junction

vs the

It shows that

because

and dN~l,

samples(with

of Jc(T)

of this theory

fraction

Obviously,

enough junction,

The~(x)

ac

lead.

of n o r m a l

were well

of YBa2Cu307_y. decrease

feature

susceptibility

of Pb are shown in Fig.3.

the v o l u l m e

T~Tc

and higher

varing amount

magnetic

resistivity

so that

of s u p e r c o n d u c t i n g measured

phase and the

one,

density.

A.C. m a g n e t i c

S-N-S

If the

then the el-

free path in P b - d o p e d

the f o r m e r has a lower

X .--.-,~

within

has

Pb.

-- 8 2

02

mean

w a y of i n t e r g r a i n

f r o m dN~l to dN'l by d o p i n g

ectron mean

when

seen that curve b is

-- 88

8

uishing

the result of sample w i t h

It can be c l e a r l y

in a g r e e m e n t

Fig.3

as the curve c in Fig.2.

current

w i t h above formula

of 77K-91K.

and w h e n dN
But,

Perhaps,

the w a y of

of

eriments

composition

fractakes

( Y B a 2 C u 3 0 7 _ y ) l _ x P b x , the critical

density

for a suitable

for a

the b e h a v i o u r

if the nominal

volume

will

enhance

amount

to higher

value

of Pb. the further

exp-

are undertaken.

Reference

/i/.

M. K. Wu, Lett.

/2/.

J.R.Ashburn,

et al.,

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J. R. Clem,

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