Correlation of Resistance and Thermogravimetric Measurements of

Chapter 26

Correlation of Resistance and Thermogravimetric Measurements of the Er Ba Cu O _ Superconductor to Sample Preparation Techniques 1

2

3

9

δ

Sung-Ik Lee, John P. Golben, Yi Song, Xiao-Dong Chen, R. D. McMichael, and J. R. Gaines

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: August 28, 1987 | doi: 10.1021/bk-1987-0351.ch026

Department of Physics, Ohio State University, Columbus, OH 43210

The resistance dependence and thermogravimetric analysis (TGA) of Er Ba Cu O has been measured in the temperature range 27 C to 920 C. The heat treat ments and oxygen flow rates simulated actual sintering and annealing processes used in sample preparation. Evidence of a phase transition in Er Ba Cu O near 680 C is discussed, as well as the implications of the maximum oxygen uptake near 400 C. The impact of sample preparation procedures on sample features is also discussed. 1

2

3

9-δ

1

Recently

there

has

superconductors. for

the

La-Ba-Cu-0

Y-Ba-Cu-O-F synthesis the a

of

specific this

time

content

of

erature

under

sample sion

of

and

the

two

include i n

used

i n

thermogravimetric formation

successes

a

insight

into

We w i l l

moment;

analysis w i l l

the

state

(TGA) d a t a

and

how

and

oxygen

room

and

temp

annealing of

specific

detailed

for

copper

reaction

method

resistance

and

i t

correlates

to

0097-6156/87/0351-0272$06.00/0 1987

discus oxide

the

follow.

©

and

the

reported.

importance a

i n

synthesis

been above

procedures

the range,

process,

dependence

with

the i n

temperature

these

the

A discussion of

reported

and

involved

sintering

start

solid

(2),

cooling

samples

simulated

oxide

been

differences have

resistance

common p r e p a r a t i o n

c o p r e c i p i t a t i o n method.

sample

or

provide

this

or

temperatures

Y-Ba^CuÔQ

copper

have

sintering of

procedures.

most

the

spite

and

i n

Key factors

annealing

the

9-δ

system

In

conditions

at

the

rate.

measured

results

interest

Y-Ba-Cu-O

superconducting

we h a v e

preparation

the

3

temperatures

respectively.

oxygen

Er^Ba^CuÔQ The

(1),

cooling

periods

superconductors the

of

slow

the

accelerated

transition

materials

similar

paper

process.

(3),

these

incorporation

procedures,

an

system

system

sufficiently

In

been Higher

2

A m e r i c a n Chemical Society

Nelson et al.; Chemistry of High-Temperature Superconductors ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

and the

26.

L E E ET AL.

Resistance and Thermogravimetric

Measurements

273


Sample P r e p a r a t i o n The s o l i d s t a t e r e a c t i o n method b e g i n s w i t h the o x i d e o r c a r bonate forms o f the i n d i v i d u a l c o n s t i t u e n t s i n s t o i c h i o m e t r i c r a t i o s . The mixed powder i s p u l v e r i z e d w i t h a m o r t a r and p e s t l e t o a u n i f o r m c o l o r , and "prebaked" t o 900 C f o r 9 h o u r s t o remove water and l i b e r a t e CO^. The p u l v e r i z i n g and p r e b a k i n g p r o c e d u r e s a r e r e p e a t e d a t l e a s t one more time. The a c t u a l importance o f the p r e b a k i n g p r o c e d u r e s i s as y e t u n c l e a r . Powder x - r a y d i f f r a c t i o n d a t a o f the p r e b a k e d powder demonstrates the p r e s e n c e o f the 1-2-3 phase. It is b e l i e v e d t h a t the s e r i e s o f p r e b a k i n g and p u l v e r i z i n g s t e p s a i d s i n homogenizing the sample and e x t e n d i n g the f o r m a t i o n o f the s o l i d solution. F o r 1-2-3 s u p e r c o n d u c t o r s , the samples a r e p r e s s e d t o 15000 p . s . i . , s i n t e r e d a t a temperature around 900 C f o r 12 h r s , and s l o w l y c o o l e d t o 500 C. A t t h i s temperature, an oxygen f l o w o f about 2 f t / h r i s m a i n t a i n e d f o r 12 h o u r s . The f u r n a c e i s t h e n s l o w l y c o o l e d t o room temperature. Many d i f f e r e n t v e r s i o n s o f t h i s method have been r e p o r t e d ; the main v a r i a b l e b e i n g the l e n g t h o f time u s e d f o r the v a r i o u s s t e p s . S u p e r c o n d u c t o r s have been s y n t h e s i z e d i n j u s t a few h o u r s (4) and c e r t a i n l y the c o n v e n i e n c e o f t h i s method i s one r e a s o n why i t i s p r e d o m i n a n t l y used. The c o p r e c i p i t a t i o n method s t a r t s w i t h the n i t r a t e forms o f the c o n s t i t u e n t s i n s o l u t i o n and t h e n p r e c i p i t a t e s them o u t i n c a r b o n a t e form t h r o u g h the a d d i t i o n o f Na^CO^. A t l e a s t one group has a l s o s u g g e s t e d t i t r a t i n g KOH i n t o the s o l u t i o n t o s u p p r e s s the f o r m a t i o n o f b i c a r b o n a t e s , t h e r e b y r e t a i n i n g the d e l i c a t e s t o i c h i o m e t r i c b a l ence. (5,6) The slow i n c o r p o r a t i o n o f Na^CO^ r e s u l t s i n a u n i f o r m b l u e p r e c i p i t a t e t h a t i s f r e e from clumping. A f t e r the two s o l u t i o n s have been mixed f o r about 45 minutes, the h e a t and the s t i r r e r a r e t u r n e d o f f and the p r e c i p i t a t e i s a l l o w e d t o s e t t l e f o r about two more h o u r s . The p r e c i p i t a t e i s t h e n d r i e d o v e r n i g h t a t a temperature o f about 140 C. The r e m a i n i n g s t e p s f o r the c o p r e c i p i t a t i o n method a r e the same as t h o s e u s e d f o r the s o l i d r e a c t i o n method. The advantage o f the c o p r e c i p i t a t i o n method i s t h a t the c o n s t i t u e n t s a r e mixed on an atomic s c a l e w h i c h h e l p s i n the f o r m a t i o n o f the d e s i r e d phase. The n i t r a t e v e r s i o n o f t h i s method a l s o tends t o p r e s e r v e the s t a r t i n g s t o i c h i o m e t r i c r a t i o t h r o u g h o u t the p r o c e s s . I n c o n t r a s t we have found t h a t our s o l i d s t a t e r e a c t e d samples o f t e n have o t h e r phases p r e s e n t as o b s e r v e d by x - r a y d i f f r a c t i o n . These o t h e r phases have appeared i n the x - r a y s p e c t r a p r e s e n t e d by o t h e r groups (4,7) and a r e l i k e l y the r e s u l t o f l o c a l i n h o m o g e n e i t i e s i n the sample m i x t u r e . The most common e x t r a phases o b s e r v e d a r e BaCuO^ and CuO. D i s c u s s i o n o f R e s i s t a n c e and TGA

Data

What a c t u a l l y o c c u r s d u r i n g t h e s e f i n a l p r e p a r a t i o n p r o c e d u r e s c a n be i n f e r r e d from r e s i s t a n c e measurements t a k e n on p e l l e t s w i t h i n the f u r n a c e . A DC t e c h n i q u e w i t h c u r r e n t r e v e r s a l was u s e d f o r these measurements. Four p l a t i n u m l e a d s were a t t a c h e d t o the p r e s s e d p e l l e t sample w i t h s i l v e r epoxy. The epoxy was c o v e r e d w i t h a l a y e r o f p r o t e c t i v e c e r a m i c p a s t e . (8) To compensate f o r i n d u c e d t h e r m a l emf's, an average o f the f o r w a r d and r e v e r s e d c u r r e n t d i r e c t i o n s was


274

CHEMISTRY OF HIGH-TEMPERATURE SUPERCONDUCTORS

used

for

small

each

measurement.

increments

so

as

The

to

temperature

obtain

thermal

changes

were

made

equilibrium at

i n

each

temp

erature . Figure

1

Er^Ba^CuÔQ I n i t i a l l y

the

with

the

temperture

observed

upon heating

present

360

along

the

The most

powder.

600

that

the

results

a

i n

the

planation tures.

the

t i v i t y

(comparable

resistance less

than

the

Er^Ba^CuÔ^ present the

i n

important discuss

to

the

Oxygen with

occupancy a

f u l l

atom

l i k e l y the

to

fact

cooled

result not

show

i n

for

et.

(12)

a l the

Τ

the

^

may

i n

hand,

that

a

TGA

data

2

above

liberation

taken ,

9

of

was

actual

shows

750 C0

the

C. 9

i n

f i r s t

on

a

Some

of

spite

to

well

as

This

ex

pic

and

high

the conduc

explain order

to

why

of

the

magnitude

reveal

that

the

grains

influence

be

on

inherently

materials.

is

are

is

We

w i l l

the

l i m i t s

oxygen

but

majority the the

weight

compounds,

set

while

a i r

i t

is

high

these the

previous

by

and

for

with

high

Murphy

the

oxygen

However

occupancy

relatively

due

range

easy

is

to

superconductivity

compounds. piece

weight

loss

Cu also

of

limited.

Τ

is

samples

results

this

the

evidenced i n

other

range

rather

by

deficiency

sintered

unsintered of

1-2-3

indirectly

TGA

correlated

oxygen

superconductors

a n d why i n

been

Full

the

The

why

have

For

occupancy

explain

of

temper

grains.

as

some

(9)

Cu v a l e n c e s ,

prebaked a

also

these

severe

observed

that

the

Y^Ba^CuÔ^

compounds

(10,11)

superconductors,

range

an

behavior,

set

these

also

quickly

state

Κ

is

prebaked

(SEM)

its

may

the

of

This

are

natural

90

C

unsintered

formed

believed

due

environment

may

500

the

As

about

insulators.

resistance).

This

the

resis

other

paths

are

behavior.

superconductors

achieved.

than

the

next.

unfavored

by

near

mentioned

i n

microscope

have

is

perovskite

the

to

boundaries.

retains

is

properties

superconducting

that

grain

than

which

insulator.

oxygen

of

the

SEM p h o t o g r a p h s

size

sample

other

occurs

resistance

We

with

conductive

sample

larger

Grain

is

dip

the

smaller

boundaries.

sample

sample.

i n

of

data

a

is

metal). i n

much

the

as

C

This

The

present

merging

sample

these

Er-Ba Cu^0 occurs

are

an

(zero

Er

C.

temperature

connections

the

dirty

present

samples

suggest

synthesize the

grain

130

indication

electron

i n

commonly in

scanning

cooled, a

by

more

for

general

curing

and pressed,

resistance

results

a high

constituent to

by

of

C

remains.

grain

superconducting

i n

many

values

grow

high

On t h e

that

do

prepared

of

grains

occupancy

valences.

an

room

pulverized

interaction

generally

oxygen

from

e l e c t r i c a l

and

the

800

920

curve.

the

considerably

C s t i l l

number

deficiencies

conducting

i n

to

however

800

formation of

to

the

is

to

is

samples.

oxygen

bump

trend

Er^Ba^CuÔ^

access

cooling

due

600

i n

near

phase

grains

our

oxygen

from

shown)

being

Y^Ba2Cu^0^ ^

^

slight

dip

superconducting

to

the

the

l i k e l y

bump

decreases

slight

to

comparison.

formation.

sizes

of

i t

for

grain

subsequently grain

very

extended

is

is

shown

sample

supported

After

i n

the

the

the

sample

The

of

large

number

is

absent

(not

after

increased,

reducing

is

C and

effect

contains is

A

resistive

However

pellet

C.

and

A

upon heating

but

500

upon heating,

between an

large,

to

gradual curve

general

l i k e l y

ature

a

cooling

previously

This

as

resistance

bump

but

curves

data

Y^Ba^CuÔ^

is

up

contacts.

well

i n i t i a l tive

i n both

epoxy

C as

for

resistance

of

s i l v e r

resistance

data

function is


shows

^,

loss

can be

prebaking

of upon

heating

attributed steps.


to

the

However


26.

LEE ET AL.


Measurements

275

a l a r g e p o r t i o n o f the l o s s i s due t o the l i b e r a t i o n o f 0 from the Cu-0 bonds i n the sample. Though s i n t e r i n g a t a temperature as h i g h as p o s s i b l e w i t h o u t f o r m i n g an i n c o n g r u e n t l i q u i d phase i s i m p o r t a n t f o r the f o r m a t i o n o f l a r g e g r a i n s , the h i g h temperatures i n v o l v e d are c l e a r l y u n f a v o r a b l e t o the i n c o r p o r a t i o n o f oxygen i n t o the sample. T h e r e f o r e i t i s p a r t i c u l a r l y i m p o r t a n t t o s l o w l y c o o l the sample i n oxygen below t h i s temperature, o r t o i n c l u d e an oxygen a n n e a l i n g s t e p i n the p r e p a r a t i o n . The r o l e o f oxygen i n c o r p o r a t i o n a l o n g w i t h the TGA d a t a can p r o v i d e a q u a l i t a t i v e e x p l a n a t i o n f o r the o b s e r v e d r e s i s t i v e f e a t u r e s ( F i g u r e 2 ) . On h e a t i n g the sample i n a i r , a major uptake o f oxygen b e g i n s a t about 340 C and maximizes a t 410 C. The maximum uptake upon c o o l i n g i s a t around 360 C. T h i s oxygen i n h a l i n g c o r r e s p o n d s t o the s l i g h t r e s i t a n c e bump a t 360 C ( F i g u r e 1, i n s e t ) . One o f the p o s s i b l e l o c a t i o n s f o r the e x t r a oxygen i n c o r p o r a t e d would be on the Cu p l a n e s between the Ba l a y e r s o f a d j a c e n t u n i t c e l l s . In a recent n e u t r o n d i f f r a c t i o n s t u d y on Y^Ba^CuÔ^ (13) i t was c o n c l u d e d t h a t t h e r e were o r d e r e d oxygen v a c a n c i e s on t h e s e o u t e r p l a n e s such t h a t the r e m a i n i n g oxygen atoms formed " l i n e s " w i t h the Cu atoms. If a p o r t i o n o f the c o n d u c t i v i t y i n the sample were a s s o c i a t e d w i t h these l i n e s , t h e n the added i n c o r p o r a t i o n o f oxygen i n t o t h e s e p l a n e s might have a d i s r u p t i v e e f f e c t . The s l i g h t r e s i s t i v e bump c o u l d be the r e s u l t o f t h i s , o r any o t h e r oxygen i n c o r p o r a t i o n e f f e c t . The extended r e s i s t i v e bump between 600 C and 800 C c a n be interpreted similarly. I n t h i s case though, the r e s i s t i v e anomaly i s pronounced, b u t the TGA c u r v e s o n l y show a s l i g h t d e v i a t i o n near 680 C. The r e s i s t a n c e c u r v e f o r Y-Ba^CuÔQ - demonstrates a bump a t 750 C which c o r r e l a t e s w e l l w i t h tne r e p o r t e d t e t r a g o n a l t o o r t h o rhombic phase t r a n s i t i o n i n Y-Ba^CuÔ^ a t t h i s temperature (14,15). The c o r r e s p o n d i n g r e s i s t a n c e Bump f o r Ër-Ba^CuÔ^ ^ i n d i c a t e s t h a t t h i s type o f t r a n s i t i o n a l s o o c c u r s i n t h i s compound n e a r t h i s temperature. I t i s n o t a b l e t h a t the maximum oxygen uptake i n Er- B a ^ u ^ O p _ a t 410 C i s below the r e p o r t e d maximum uptake f o r Y É a C u 0 Q _ £ a t 500 C. (16) The temperature a t which an i n c o n g r u e n t phase i s formed i n Y^Ba^CuÔp ^ i s much h i g h e r t h a n the Er^Ba^CuÔp ^ compound. This f a c t ana the d i f f e r e n c e i n the g r a i n s s i z e s o f t h e s e two compounds c a n be e x p e c t e d t o a l t e r t h e i r r e s p e c t i v e oxygen a c c e s s and absorption. T h i s may e x p l a i n the d i f f e r e n c e s i n the r e s i s i t i v e b e h a v i o r upon c o o l i n g o f t h e s e compounds. From the c o r r e l a t i o n between the o b s e r v e d oxygen uptake and r e s i s t i v e f e a t u r e s f o r the compounds Er-Ba^CuÔp ^ and Y Ba^CuÔp we can u n d e r s t a n d why a q u i c k s o l i d s t a t e r e a c t i o n p r o c e d u r e would be successful. T h i s i s i n s p i t e o f " i m p u r i t y " phases b e i n g p r e s e n t i n the compounds. The q u i c k s i n t e r i n g t o 900+ C a l l o w s f o r the format i o n o f a c o n n e c t i n g p a t h o f g r a i n s , w h i l e c o o l i n g s l o w l y from 700 C ( e s p e c i a l l y i n the v i c i n i t y o f 500 C) i n the p r e s e n c e o f oxygen can p o s s i b l y s e r v e as a r e p l a c e m e n t f o r an a n n e a l i n g s t e p . I n seems p o s s i b l e t h a t o n l y a r e l a t i v e l y s h o r t l e n g t h o f time i s needed f o r the sample t r a n s i t i o n s t o o c c u r . However the extreme case o f "quenching" a sample from the oven o f t e n does n o t produce a superconductor. I n summary, we have shown t h a t the p r e v i o u s l y e m p i r i c a l sample p r e p a r a t i o n p r o c e d u r e s o f slow c o o l i n g and a n n e a l i n g i n oxygen seem 1

2

3


276

CHEMISTRY OF HIGH-TEMPERATURE

SUPERCONDUCTORS

1500 100 -

ο ΕΓ.ΒαΧυ,Ο 80 (SOI

60 -

-C

40 -

~ 1000

ΟΟΟΟΟΟοο"

rr

100

20 -

ω ο c σ

0 200

ο

rf> 4>

250

300

350

ω ο c σ

400

T(C) ω


Φ

rr

500

0

50

ο

200

400

600

800

Ο

1000

T(°C) F i g u r e 1. The r e s i s t a n c e above room t e m p e r a t u r e f o r n o m i n a l c o m p o s i t i o n s o f E r Ba^Cu^ÛQ ^ ( t r i a n g l e s ) and Y^Ba^CuÔ ( s q u a r e s ) upon h e a t i n g . The i n s e t enhances the r e g i o n berwee C

l

B a

2

C u

3°9-5

100.0

99.8

h

99.6 CD 99.4

99.2 100

200

300

400

500

600

700

800

900

T e m p e r a t u r e (C) F i g u r e 2. The TGA c u r v e s f o r a p r e v i o u s l y s i n t e r e d Er^Ba^CuÔQ sample upon warming i n a i r ( t o p ) and c o o l i n g i n oxygen (bottom). The s l i g h t d i p n e a r 680 C and the maximum oxygen u p t a k e n e a r 400 C c o r r e l a t e w i t h r e s i s t i v e f e a t u r e s .


26.

L E E ET AL.


Measurements

277

t o be a c t u a l l y i m p o r t a n t towards i n s u r i n g t h a t t h e p r o p e r sample t r a n s i t i o n s take p l a c e . I n E r BaûÔg , a t e t r a g o n a l to ortho rhombic phase t r a n s i t i o n n e a r 680 C i s i m p l i e d when compared t o the c o r r e s p o n d i n g d a t a on t h e Y B a C u O compound. The maximum oxygen uptake o f E r B a C u 0 ^ near 400 C a l s o c o r r e l a t e s w e l l t o the r e p o r t e d uptake temperature f o r Y-BaûÔg . S i n c e oxygen d e f i c i e n c i e s and p o s i t i o n s i n t h e u n i t c e l l seem t o be i n t r i c a t e l y r e l a t e d t o t h e s u p e r c o n d u c t i n g mechanism, t h e sample p r e p a r a t i o n p r o c e d u r e s h o u l d be s t r u c t u r e d t o maximize t h e oxygen i n t e r a c t i o n w i t h t h e sample. $

1

1

2

3

2

3

p

9

$


Acknowledgments We w i s h t o thank Roy S. Tucker and Sang Young Lee f o r h e l p i n sample p r e p a r a t i o n , M a r g a r i t a R o h k l i n f o r h e r work on t h e SEM, and M. S. Wong f o r h e l p w i t h t h e TGA. The f i n a n c i a l s u p p o r t o f t h e N a t i o n a l S c i e n c e F o u n d a t i o n t h r o u g h a g r a n t DMR 83-16989 t o t h e Ohio S t a t e U n i v e r s i t y M a t e r i a l s R e s e a r c h L a b o r a t o r y and g r a n t DMR 84-05403 i s g r a t e f u l l y acknowledged.

Literature Cited 1. 2.

J.G.Bednorz and K.A.Muller, Z. Phys. Β 1986, 64, 189. M.Κ. Wu, J.R.Ashburn, C.J.Torng, P.H.Hor, R.L.Meng, L.Gao, Z.J.Huang, Y.Q.Wang, and C.W.Chu, Phys. Rev. Lett. 1987, 58, 908. 3. S.R. Ovshinsky, R.T. Young, D.D. Allred, G. DeMaggio, and G.A. Van der Leeden, Phys. Rev. Lett. 1987, 58, 2579. 4. M. Hirabayashi, H. Ihara, N. Terada, K. Senzaki, K. Hayashi, S. Waki, K. Murata, M. Tokumoto, and Y. Kimura, Jap. J. Appl. Phys. 1987, 26, 1454. 5. Hau H. Wang, K. Douglas Carlson, Urs Geiser, Robert J. Thorn, Huey-Chuen I. Kao, Mark A. Beno, Marilyn R. Monaghan, Thomas J. Allen, Roger B. Proksch, Dan L. Stupka, Jack M. Williams, Brian K. Flandermeyer, and Roger B. Poeppel, (submitted to Inorg. Chem. [Commun.]). 6. Aravinda M. Kini, Urs Geiser, Huey-Chuen I. Kao, K. Douglas Carlson, Hau H. Wang, Marilyn R. Monaghan, and Jack M. Williams, (submitted to Inorg. Chem. [Commun.]). 7. Ε. Takayama-Muromachi, Y. Uchida, Y. Matsui, and K. Kato, Jap. J. Appl. Phys. 1987, 26, 1476. 8. We use Acme E-Solder 3022 with hardener #18 available from Acme Chemicals & Insulation Company; a Division of Allied Products Corp.; New Haven Conn. 06505, and Alumina Cement available from L.H. Marshall Co.; 270 W. Lane Ave; Columbus Ohio 43201. We emphasize that no particular endorsement of products is implied. 9. Francis S. Galasso, Structure, Properties, and Preparation of Perovskite-Type Compounds (Pergamon Press, New York, 1969). 10. Sung-Ik Lee, John P. Golben, Sang Young Lee, Xiao-Dong Chen, Yi Song, Tae W. Noh, R.D. McMichael, Yue Cao, Joe Testa, Fulin Zuo, J.R. Gaines, A.J. Epstein, D.L. Cox, J.C. Garland, T.R. Lemberger, R. Sooryakumar, Bruce R. Patton, and Rodney T. Tettenhorst, Extended Abstract Materials Research Society, 1987.


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Sung-Ik Lee, John P. Golben, Sang Young Lee, Xiao-Dong Chen, Yi Song, Tae W. Noh, R.D. McMichael, J.R. Gaines, D.L. Cox, and Bruce R. Patton, Phys. Rev. Β 1987 (to be published). D.W. Murphy, S. Sunshine, R.B. van Dover, R.J. Cava, B. Batlogg, S.M. Zahurak, and L.F. Schneemeyer, Phys. Rev. Lett. 1987, 58, 1888. J.E. Greedan, A. O'Reilly and C.V. Stager, (submitted to Phys. Rev. Lett.). Ivan K. Schuller, D.G. Ηinks, M.A. Beno, D.W. Capone II, L. Soderholm, J.-P. Locquet, Y. Bruynseraede, C.U. Segre, and K. Zhang, (submitted to Sol. State Comm.). P. Strobel, J.J. Capponi, C. Chaillout, M. Marezio, and J.L. Tholence, Nature 327, 306 (1987). J.M. Tarascon, W.R. McKinnon, L.H. Greene, G.W. Hull and E.M. Vogel (submitted to Phys. Rev. Lett.).

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RECEIVED July 6, 1987


Correlation of Resistance and Thermogravimetric Measurements of

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