Preparation conditions of Bi-based superconducting ceramics with high critical current density

PflYSICA

Physiea C 185-189 (1991) 2397-2398 North-Holland

PREPARATION CONDITIONS OF B I - B A S E D SUPERCONDUCTING CERAMICS WITH HIGH CRITICAL CURRENT DENSITY Hiroya

IMAO,Satoru

KISHIDA~,HeIzo

TOKUTAKA* a n d T o r u

M a t s u e C o l l e g e of T e c h n o l o g y , N i s h i i k u m a , M a t s u e t T o t t o r i Univ.,Koyama,Tottorl 6 8 0 , J a p a n

IKEUCHI ~

690,Japan

We investigated the effects of the pressures before sintering and of the sintering time on the critical current density {Jc} of the {BI,Pb}-(Sr,Ca)-Cu-O ceramics. The Jc of the samples increased with Increasin~ pressure before s~nterlng. The Jc of the sample prepared at a pressure of 1.56xi04 kg/cm Z was 1.57xi0 ° A/cm ~ (0T,77K}. This may be caused by the increase of the mass density and the decrease of the grain size. The Jc of the samples sintered for 305h was 25 times greater than that of those sDtered for 5h. This may be caused by the growth of a 110K-phase.

I. INTRODUCTION

in an atmosphere of Ar:02=12:1.

In order to apply superconducting oxides in

In addition, we

also investigated the effect of the sintering

the field of power electronics, it is important

time, which was changed from 5h to 305h at 850°C

to prepare samples with a high critical current

in an atmosphere of Ar:02=12:1.

density

(Jc).

superconductors

{Bi,Pb)-(Sr,Ca)-Cu-O

(Bi-based)

showed a critical

transition

temperature (Tc) of 110K. 1

However, the Jc of

3. RESULTS AND f)iSCOSSION Figure

the Bi-based superconducting ceramics are known

function

to be lower than those of other forms such as

increased

films,

when the

wires

and single

crystals.

In

s t u d y , we i n v e r t i g a t e d

the effects

sures before

and o f t h e s i n t e r i n g

sintering

this

of t h e p r e s time

on the Jc of the Bi-based ceramics.

Bi-based superconducting ceramics were prepared by a conventional method. 2

solid-state reaction

The materials with the

Bi:Pb:Sr:Ca:Cu=l.6:0.4:2:2:3 pressed at 136 kg/em 2.

composition of

were

mixed

and

They were calcined for

pressure

pressures

was t h e same.

changed from 136 TI~e Te of a l l

increased

remarkably with

sures

the

in

pressures

and

range were

over

mixed,

pressed

and s i n t : e r e d f o r

sintering

the effect

on Jc o f t h e

samples

ture

in

kg/cm 2.

the

range

of

136

at

room t e m p e r a -

kg/cm 2 to

They were r e - s i n t e r e d

1.56x104

f o r 5h a t

850°C

0921-4534/91/$03.50 © 1991 - Elsevier Sciience Publishers B.V.

increasing

the pres-

o f 136 kg/cm 2 t o approximately

1 . O x l O 4 kg/cm 2.

prepared

1.OxlO 4

saturated while

Jc

at in-

micro-

at

the

pressures

kg/em 2,

of the

of

136,

When t h e p r e s s u r e

changed from 138 k g / c e 2 to t.OxlO 4 k g / e ~ 2. between g r a i n s .

were g r o u n d a g a i n and p r e s s e d

o f t h e samples

scope (SLD~) i D a g e s o f t h e c r o s s s e c t i o n s

of the pressure before the products

kg/em 2 to

F i g u r e 2 shows t h e s c a n n i n g e l e c t r o n

In o r d e r

ceramics,

A/cm 2,

creased further.

samples becaNe

850°C i n an a t m o s p h e r e of A r : 0 2 = 1 2 : 1 . to investigate

89h a t

Jc

samples prepared

The mass d e n s i t i e s

!.Ox!O 4 and ! . 5 6 ~ ! 0 4 ground,

before slntering.

A/cm 2 t o 1 . 5 7 n 1 0 3

from 8 . 6 7

1.5Sx104 k~,:cm 2.

kg/cm 2,

2. SANPLE PREPARATIONS

1 shows t h e J c of t h e s a m p l e s as a of t h e

compact

by r e d u c i n g

T h i s r e s u l t was c o n s i s t e n t

t h a t of t h e mass d e n s i t y .

~be

~he c~'a~::ks ~th

The g r a i n s i z e in th~

sample p r e p a r e d a t a p r e s s u r e o f 1.5Sx104 kg/c~ 2 was a t h e n t h

ef

the

size

found

in

the

sampIe

p r e p a r e d a t 1.OxlO 4 kg/em 2. The Jc o f the f o r ~ e r

All fights reserved.

H. lmao et at / Preparation con&'tions of Bi.based superconducting ceramics

2398

A N

E 0

Ul tO CI

(b) 1.0xlff'

(a) 1.36x10z

tO L,

(kg/cm z)

/

0

rlOpm

L

I

,

!

102

PL

103

104

(c)

Pressure(kglcm z) FIGURE 1 Jc as a f u n c t i o n of p r e s s u r e b e f o r e s i n t e r ~ n g . The s a m p l e s ~ e r e p r e s s e d a t 136 k g / c m z t o 1.56x104 kg/cm z.

was h i g h e r t h a n t h a t of the l a t t e r .

In general,

t h e c o n t a c t a r e a of g r a i n s becomes l a r g e r as the grain

size

becomes

smaller.

i n c r e a s e of Jc of t h e

Therefore,

the

samples may be caused by

1.56x10 z'

FIGURE 2 SEM images of the cross section of the sample~ prepared at the pressures of (a}136, (b)l.OxlO q and {c)i.56x104 kg/cm 2.

4. CONCLUSIONS We investigated the effects of the pressures before sintering and the sintering time on the Jc of Bi-based ceramics.

The Jc of the samples

t h e i n c r e a s e of t h e c o n t a c t a r e a and t h e c u r r e n t

increased with the pressures before sintering.

pass.

This may be caused by the increase of the mass

We a l s o i n v e s t i g a t e d i n g time on Jc.

t h e e f f e c t of t h e s i n t e r -

densities and the decrease of the grain sizes.

The Jc of the sample s i n t e r e d

The Jc of the samples also increased with the

f o r 5h and 305h were 15.7 A/cm2 and 430 A/cm2,

slntering

respectively.

increase of a 11OK-phase.

tics

of t h e

The r e s u l t s samples,

of R-T c h a r a c t e r i s -

showed t h a t

the

diffraction

llOK-phase of

sintering time

the

patterns sample

indicated increased

the

that for

Therefore,

i n c r e a s e of Jc may be caused by t h e

of llOK-phase.

the

longer

and that the sample sintered for

305h showed a s i n g l e - p h a s e of llOK.

This may be caused by the

Tc a l s o

increased with the sintering time. The observed X-ray

time.

growth

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• ot_,o

;

t.~l:a.

2. S . g i s : ~ i d a , l { . T o k u t a k a , t~'.Futo, !v[.ChEhaya, K . N i s h i m o r i .!rod % . i ~ h i h a r a : Phys. s t a g . S o l . , ( a ) 1 2 4 (t991) Rl17.