Chemistry of High-Temperature Superconductors - American

Chapter 20 High-Temperature Superconducting Oxide Synthesis and the Chemical Doping of the C u - O Planes J. M. Tarascon, P. Barboux, B. G. Bagley, L. H. Greene, W. R. McKinnon, and G. W. Hull

Downloaded by CORNELL UNIV on October 19, 2016 | http://pubs.acs.org Publication Date: August 28, 1987 | doi: 10.1021/bk-1987-0351.ch020

Bell Communications Research, 331 Newman Springs Road, Red Bank, NJ 07701-7020

Different synthesis techniques for the preparation of dense superconducting ceramics are discussed, and a sol-gel process is shown to be very promising. The effect of oxygen content, and the effect of substitution of Ni and Zn for copper, on the structural, transport and superconducting properties of the La-Sr-Cu-O and Y -Ba-Cu-O systems are presented. We find that substitution on the copper sites destroys T in the La-Sr-Cu-O system and decreases it in the Y-Ba-Cu-O system, and this effect is insensitive as to whether the 3d metal is magnetic (Ni) or diamagnetic (Zn). A detailed study of the YBa Cu O - system as a function of oxygen content (y) shows that superconductivity can be destroyed in these materials by the removal of oxygen and restored by reinjecting oxygen; either thermally at 500°C or at temperatures (80°C) compatible with device processing by means of a novel plasma oxidation process. Of scientific interest, the plasma process induces bulk superconductivity in the undoped La CuO . c

2

3

7 y

2

F o r the 23K

as

4

past decade the m a x i m u m s u p e r c o n d u c t i n g

obtained

with

a Nb Ge

alloy

3

(1).

critical temperature (T ) large

amount

of

synthesis, w h i c h resulted in a new family of superconducting compounds either

chalcogenides

Β3Ρ^_ Βί 0 χ

χ

discovery

3

(4)),

(Chevrel

the

Nb Ge T 3

of superconductivity

c

phases) of 2 3 K was

at 3 6 K i n t h e

(2)

or

never

oxides

exceeded.

La-Sr-Cu-O

materials containing

(LiTi 0 2

In late

system

i n a race

towards

new

high T

i n c r e a s e d to 4 0 K b y s e v e r a l g r o u p s

materials.

c

(6-8)

The

T

upper

c

(3.),

4

1986,

the

by B e d n o r z

and

M u l l e r (5.) h a s s t i m u l a t e d t h e f i e l d o f s u p e r c o n d u c t i v i t y , w i t h p h y s i c i s t s a n d now

was

c

D e s p i t e the

chemists

limit was

u s i n g the s a m e o x i d e s y s t e m

rapidly (with Sr

i n s t e a d o f B a ) a n d t h e n p u s h e d a b o v e l i q u i d n i t r o g e n t e m p e r a t u r e s b y W u e t a l . (9_) with a multiphase Y - B a - C u - O oxide.

S u p e r c o n d u c t i v i t y at 9 3 K w a s

independently

c o n f i r m e d b y other researchers ( 1 0 - 1 1 ) and the c o m p o u n d o f f o r m u l a Y B a C u 0 _ 2

w a s i d e n t i f i e d as t h e s u p e r c o n d u c t i n g p h a s e ( 1 2 ) a n d i t s c r y s t a l s t r u c t u r e , of a stack o f Y , C u 0 , B a O , C u O , B a O , C u 0 2

with

C u - O chains

exciting

time

the

running physics

chemistry because no major

along of

the

these

2

materials

was

established

received

problems were encountered

more

(12.).

During

attention

than

i n their preparation.

poorly understood

and i n this

0097-6156/87/0351-0198$06.00/0 1987

7

y

and Y planes p e r p e n d i c u l a r to the c-axis

b-axis,

materials science o f these oxides is, therefore,

©

3

consisting

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.

this their The paper

20.

T A R A S C O N ET

we

present

Superconducting Oxide Synthesis

AL.

different

novel

synthetic routes

to

199

obtain homogeneous

and

compact

ceramics. B a n d structure calculations performed

o n t h e s e o x i d e s b y L . F . M a t t h e i s et a l .

l e d to the c o n c l u s i o n that the C u 3 d - 0 2 p e l e c t r o n s g o v e r n

(14)

properties

of

these materials.

superconductivity substitutions.

i n these

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

further our understanding of

oxides

it was

important

to

the m e c h a n i s m

perform

several

of

chemical

W e recently r e p o r t e d that the s u b s t i t u t i o n of r a r e earths for L a i n the

L a - S r - C u - O system or for Y (15-16).

To

i n the Y - B a - C u - O system has o n l y a m i n o r effect o n

T

c

I n this paper w e r e p o r t o n the c h e m i c a l d o p i n g of the C u - O planes w i t h

the replacement of magnetic (Ni)

or diamagnetic (Zn)

ions for C u i n b o t h the L a -

S r - C u - O a n d Y - B a - C u - O s y s t e m s , w h i c h i n t h e f o l l o w i n g w i l l b e d e n o t e d as 4 0 K a n d 9 0 K materials, respectively.

Independent

of the nature o f the 3 d m e t a l s u b s t i t u t i o n

s u p e r c o n d u c t i v i t y is r a p i d l y d e p r e s s e d .


These new H i g h T

c

o x i d e s b e l o n g to a l a r g e f a m i l y o f p e r o v s k i t e m a t e r i a l s w h i c h

h a v e b e e n s t u d i e d o v e r the years because o f t h e i r a b i l i t y to a b s o r b o r l o s e r e v e r s i b l y (i.e. for their n o n - s t o i c h i o m e t r y i n o x y g e n ) . of s u p e r c o n d u c t i v i t y that T Thus

it was

ambient)

of

affect

superconducting YBa Cu 0 _ 2

T

c

3

7

y

c

c a n be e x t r e m e l y s e n s i t i v e to p r o b l e m s o f

s p e c i a l interest to the

oxygen

study how

content

properties.

We

processing

in

have

these

conditions

materials

undertaken

a

and

detailed

system a n d r e p o r t h e r e i n that the changes i n o x y g e n

i n these materials are completely reversible.

T

stoichiometry. (temperature, thereby study

temperatures

(80°C)

content

and a highT

the

c o n t e n t (y)

and

is a m a x i m u m f o r the m a x i m u m

c

attractive

for

for

c

high-speed

using a novel plasma oxidation technique.

the

of

o x y g e n c o n t e n t (y = 0) w h e r e a s the c o m p o u n d is s e m i c o n d u c t i n g f o r y = l . that b o t h h i g h o x y g e n

oxygen

It i s w e l l k n o w n i n t h e f i e l d

these

oxides

can be

microelectronic

We

show

reached

device

at

processing

T h i s t e c h n i q u e is u s e d to p r o d u c e

bulk

s u p e r c o n d u c t i v i t y at 4 0 K i n L a C u 0 . 2

4

Synthesis a)

S o l i d state r e a c t i o n The 4 0 K doped materials L a !

8 5

Sr

0

1

reacting appropriate amounts of S r C 0 each 9 9 . 9 9 9 % .

The

5

3

mixed powders,

Cu _ M 0 _ 1

x

x

4

( M = Ni,Zn) were prepared

7

and the c o r r e s p o n d i n g metal o x i d e

by

powders,

pressed into pellets and placed into p l a t i n u m

c r u c i b l e s , w e r e r e a c t e d at 1 1 4 0 ° C u n d e r a n o x y g e n

a m b i e n t for 48 h o u r s a n d then

c o o l e d to 500°C b e f o r e b e i n g r e m o v e d f r o m the f u r n a c e .

After such a treatment

pellets w e r e w e l l sintered and the material was single phase.

the

W e o b s e r v e that l o w e r

r e a c t i o n temperatures result i n a s a m p l e c o n t a m i n a t e d by traces of u n r e a c t e d

La 0 2

3

( m o i s t u r e s e n s i t i v e ) , so that after s e v e r a l days the pellet disintegrates. The undoped and nickel doped Y B a C u 0 _ 2

way

3

7

to the 4 0 K m a t e r i a l s w i t h the difference

placed i n an a l u m i n a crucible and reacted T h e n the reacted p o w d e r s

phases w e r e prepared i n a similar

y

that, i n this case, loose p o w d e r s

at t e m p e r a t u r e s

of

950°C for

were g r o u n d , pressed into a pellet and reheated

same temperature for 48 h o u r s i n an o x y g e n ambient and then cooled s l o w l y 6 h o u r s ) to r o o m t e m p e r a t u r e . poorly

sintered.

A

carbonates,

a n d i n the

nitrate w i l l

be

denoted

similar

following A

at

the

(taking

T h e r e s u l t i n g m a t e r i a l s a r e s i n g l e p h a s e (as i n d i c a t e d

by powder x-ray diffraction using a Bragg-Brentano geometry w i t h C u K but

were

48 h o u r s .

synthesis the

was

samples

made

made

and B , respectively.

The

using

from

nitrates

the

powders

a

radiation), instead

carbonate

of

and

the

resulting from

the

above process contain crystals of reasonable size for some single crystal studies but not suitable for other physical measurements. L a r g e r crystals are o b t a i n e d either b y c h a n g i n g the a n n e a l i n g t e m p e r a t u r e c o o l i n g rate or by 400mg) reaction.

of

Rb

or

using Κ

an excess

carbonate

carbonate

is a d d e d

to

A f t e r r e a c t i o n at 8 9 0 ° C , f o l l o w e d

as f o l l o w s :

1.5g

of

A

and

small amount (up

to

the starting m i x t u r e p r i o r

to

b y s e v e r a l d a y s t r e a t m e n t at 9 6 0 ° C , t h e


CHEMISTRY OF H I G H - T E M P E R A T U R E

200 powders

are then

slowly

cooled.

I n the liquid

state

SUPERCONDUCTORS

(T>880°C)

the Κ

or R b

carbonates w e t the crucible a n dtend to creep u p the crucible w a l l leaving b e h i n d a sparkling black p o w d e r w i t h a few crystals o f about 1 m m size.

X - r a y diffraction of

the r e s u l t i n g p o w d e r indicates a single phase m a t e r i a l ( n o extra B r a g g peaks) lattice parameters (measured same

are s i m i l a r to those

of pure

YBa Cu 0 _ 2

by means of a S Q U I D magnometer)

preparation

heat

treatment,

3

7

and which

y

a 6 5 % M e i s s n e r effect.

the Meissner

effect

was always

whose

exhibits W i t h the

greater

for

materials m a d e w i t h the flux than w i t h o u t i t . W e thus believe that the p o t a s s i u m o r rubidium cleaner

carbonate

material.

fluxes

a c t as a g e t t e r

f o r impurities a n d thereby

Single crystals, isolated from

produce

this p r e p a r a t i o n s h o w

a

a resistive

s u p e r c o n d u c t i n g t r a n s i t i o n at 9 0 K . O n e disadvantage encountered i n preparing the Y B a C u 0 _ 2

3

7

ceramic by a solid

y

state r e a c t i o n at 950°C i s that t h e r e s u l t i n g m a t e r i a l i s p o o r l y s i n t e r e d .


to o v e r c o m e this p r o b l e m w e d e v e l o p e d

In a n attempt

a sol-gel (i.e. controlled precipitation a n d

g r o w t h ) p r o c e s s as w e d e s c r i b e n e x t . b)

S o l - G e l process The

gels

are obtained

b y a d d i n g , to a k n o w n

amount

a p p r o p r i a t e a m o u n t s o f y t t r i u m nitrate a n d c o p p e r acetate. pH

of

the solution

precipitation.

is constantly

adjusted

are then

amorphous

as t o

hydroxide,

provide

a

homogeneous

A f e w m i n u t e s after m i x i n g t h e s o l u t i o n s , c o l l o i d a l particles nucleate

and continue to g r o w until they f o r m gels

so

of barium

D u r i n g this process the

freeze-dried

powder,

a viscous blue g e l (after a f e w h o u r s ) .

a n d the resulting material

is then

fired

p r e p a r e d b y s o l i d state r e a c t i o n s .

i n a manner

The

,consisting of a very

s i m i l a r to that

fine

for the ceramics

A more detailed description o f the sol-gel

process

will be reported elsewhere (12). T h e c e r a m i c m a t e r i a l o b t a i n e d b y this m e t h o d (sample

C ) is c o m p a r e d to those

o b t a i n e d b y s o l i d state r e a c t i o n s u s i n g e i t h e r a c a r b o n a t e ( A ) o r n i t r a t e ( B ) as t h e source of b a r i u m .

M i c r o g r a p h s f o r t h e t h r e e s a m p l e s a r e s h o w n i n F i g u r e 1.

that s a m p l e C is h o m o g e n e o u s

w i t h a particle size o f about 1 m i c r o n whereas

100 a n d 2 0 m i c r o n particle sizes a r e o b s e r v e d Resistivity

measurements

standard four-probe with

a Si-diode

observed

for samples

set o f s a m p l e s ,

A

and Β

were

respectively.

performed

m e t h o d w i t h silver paint contacts i n a n exchange

thermometer.

for sample

respectively.

o n the same A

C whereas

T

of 9 1 K with

c

samples

exhibit widths

using a

gas cryostat

a transition width

Β and A

Note about

o f 0 . 5 K is

of 2 and I K

T h e M e i s s n e r effect w a s o b s e r v e d to b e 3 5 , 6 5 a n d 5 0 % f o r s a m p l e s

A , Β and C respectively. From

this study

homogeneous

w e conclude

a n d dense

ceramics

that the sol-gel with

technique

the sharpest

produces

the most

superconducting transitions.

A l s o , the use o f b a r i u m nitrate instead of of b a r i u m carbonate o r the flux (with

R b C 0

3

or K C 0 )

allows

3

a more

complete

reaction giving

method

rise to a better

M e i s s n e r effect a n d sharper transitions. Results and Discussion a)

Substitution for copper Nickel

(IS.)

and zinc

with

studied.

doped

the materials

8

5

Sr

0

1

5

Cu _ M 0 _

single

1

x

phase

x

4

over

y

compounds the range

were

investigated

of stoichiometry

(x)

T h e x-ray p o w d e r diffraction patterns are completely i n d e x e d o n a basis o f

a tetragonal unit cell. for

La!

being

the nickel

substituted decreases. elongated

T h e c r y s t a l d a t a a r e s u m m a r i z e d i n t a b l e I as a f u n c t i o n o f χ

and zinc

element,

doped

4 0 k materials.

the " a " lattice

parameter

F o r the L a - S r - C u - O phase along the c axis.

and its variation w i t h x .

Note

increases

the C u 0

6

that, while

octahedron

independent

of the

the " c " parameter is distorted,

being

T h e c/a r a t i o c a n b e u s e d t o c h a r a c t e r i z e t h i s d i s t o r t i o n

T a b l e I s h o w s t h a t , f o r b o t h N i a n d Z n s u b s t i t u t i o n s , c/a


T A R A S C O N ET

AL.

Superconducting Oxide Synthesis

201


20.

F i g u r e 1. (A),

Scanning electron microscopy pictures of

nitrate (B) and by sol-gel process

samples made

from

carbonate

(C).


202

C H E M I S T R Y OF H I G H - T E M P E R A T U R E

decreases w i t h increasing χ (i.e. the octahedron becomes way. d

1 0

less distorted)

T h i s indicates that the J a h n - T e l l e r d i s t o r t i o n is r e m o v e d

and

N i for copper. (Zn

) or d

2 +

(Ni

8

This 2 +

is expected

since

there

is n o J a h n - T e l l e r 9

T h e v a r i a t i o n o f the unit cell v o l u m e is

w h i c h is s m a l l e r than that o f Z n

2

+

(Cu

also s h o w n i n T a b l e

a n d decreases

f r o m size considerations, since the ionic radius o f N i

i n a similar

by substituting Z n

) ions whereas it is a m a x i m u m f o r d ions

i n c r e a s e s as a f u n c t i o n o f χ w h e n M = Z n

SUPERCONDUCTORS

2

2 +

effect

I.

The volume

when M = N i

as e x p e c t e d

is s m a l l e r than that o f

+

for

).

Cu

2

+

either i n an octahedral (0.83 Ό C

3.8 6

a a

3.84

—

3.82

υ 3.8

(b) 182 11. 180 11.75

178

C3 11.7

DO c

> Β

Η

176

3

11.65

174 11.6 172 11.55

0.2

0.4

y inY B a

2

C u

0.6

3

0

7

0.8

y

F i g u r e 3. V a r i a t i o n o f t h e o r t h o r h o m b i c l a t t i c e p a r a m e n t e r s function of y for the Y B a C u 0 _ 2

3

7

y

a, b, c and V

series.

a) T h e u n i t c e l l l e n g t h s a a n d b a r e s h o w n . b) T h e u n i t c e l l l e n g t h c a n d u n i t c e l l v o l u m e V a r e s h o w n .


as a


206

CHEMISTRY OF HIGH-TEMPERATURE SUPERCONDUCTORS

20

40

60

80

100

Temperature ( K ) Figure 4. Effect YBa Cu 0 _ . 2

3

7

of

oxygen

content

on

the

superconducting

properties

of

y

a) T e m p e r a t u r e

dependent

magnetization

for the Y B a C u 0 _ 2

3

7

y

series

(0

Chemistry of High-Temperature Superconductors - American

Recommend Documents