Some Recent Progress in Solid State Chemistry of ... - ACS Publications

5 Some Recent Progress in Solid State Chemistry

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of Electronic Materials R. A .

LAUDISE

B e l l Laboratories, M u r r a y Hill, NJ 07974 The

electronic

force

for

chemistry.

research

Recent

intercalation titanate

materials

much

community and

progress

compounds

microwave

in semiconductor (5) imperfections

a

driving

in solid

state

in five areas is described: for

dielectrics; silicon; in

provides

development

(4)

storage

batteries;

(3) the reactions amorphous

(2) of

(1) new

oxygen

dielectrics;

and

quartz.

" E l e c t r o n i c m a t e r i a l s are the b r i c k s a n d m o r t a r of s o l i d state -

L /

w h i c h i n t u r n are the sine q u a n o n of e l e c t r o n i c systems.

devices, Progress

i n t e l e c o m m u n i c a t i o n s , a u t o m a t a , c o m p u t e r s , a n d r e l a t e d fields is c r i t i cally

dependent

on

i m p r o v i n g the

properties

of

existing

electronic

m a t e r i a l s a n d d i s c o v e r i n g n e w m a t e r i a l s w i t h better p r o p e r t i e s .

Solid

state c h e m i s t r y p l a y s a c e n t r a l r o l e i n e l e c t r o n i c m a t e r i a l s r e s e a r c h a n d development.

M a n y of the goals of s o l i d state c h e m i s t r y are i d e n t i c a l

to those of e l e c t r o n i c m a t e r i a l s research. I n d e e d , often t h e g e n e r a l goals of s o l i d state c h e m i s t r y are best p u r s u e d b y u s i n g e l e c t r o n i c m a t e r i a l s as the v e h i c l e . F o r e x a m p l e , w e b e l i e v e s o m e i m p o r t a n t goals of s o l i d state c h e m i s t r y are the f o l l o w i n g : 1.

T o u n d e r s t a n d the c o n n e c t i o n b e t w e e n c h e m i c a l b o n d i n g a n d s t r u c t u r e i n solids a n d t h e i r p r o p e r t i e s . I n e l e c t r o n i c materials the f o u n d a t i o n s of u n d e r s t a n d i n g that the p h y s i cists h a v e b u i l t f o r e l e c t r o n i c p r o p e r t i e s o f t e n g i v e t h e s o l i d state c h e m i s t a s o l i d base f r o m w h i c h to b e g i n activities.

2.

T o u n d e r s t a n d the genesis of i m p e r f e c t i o n s i n solids, t h e i r equilibria, a n d their role i n determining properties. H e r e electronic properties often provide a u n i q u e probe that t h e s o l i d state c h e m i s t m a y e x p l o i t f o r d e t e r m i n i n g t h e n a t u r e a n d c o n c e n t r a t i o n of i m p e r f e c t i o n s . 0-8412-0472-l/80/33-186-095$05.00/l © 1980 American Chemical Society Holt et al.; Solid State Chemistry: A Contemporary Overview Advances in Chemistry; American Chemical Society: Washington, DC, 1980.

96

SOLID STATE

CHEMISTRY:

A CONTEMPORARY

OVERVIEW


T o i m p r o v e a n d u n d e r s t a n d p r e p a r a t i v e m e t h o d s so as to h a v e the p o w e r to p r e p a r e a v a r i e t y of solids. H e r e t h e goals of e l e c t r o n i c m a t e r i a l s a n d s o l i d state c h e m i s t r y are c o m p l e t e l y consistent, a n d t h e e c o n o m i c d r i v i n g forces f o r u s e f u l e l e c t r o n i c m a t e r i a l s often h a v e r e s u l t e d i n s u b t l e , difficult, a n d expensive p r e p a r a t i v e t e c h n i q u e s a n d e q u i p ment being routinely available. T o d i s c o v e r n e w solids w i t h i n t e r e s t i n g p r o p e r t i e s . H e r e e l e c t r o n i c m a t e r i a l s scientists w o u l d p r o b a b l y define " i n t e r e s t i n g " as " u l t i m a t e l y u s e f u l . " S e m a n t i c n u a n c e s aside, m o s t w o u l d agree that s o l i d state c h e m i s t r y a n d e l e c t r o n i c m a t e r i a l s are a g a i n i n resonance a n d t h a t " i n t e r e s t i n g " c a n c o v e r a great d e a l of t e r r i t o r y i n m o d e r n electronics. I n t h e r e m a i n d e r of this p a p e r w e w i l l g i v e b r i e f r e v i e w s of some r e c e n t s o l i d state c h e m i s t r y a c t i v i t i e s i n B e l l L a b o r a t o r i e s , w h i c h

we

b e l i e v e i l l u s t r a t e , to a c o n s i d e r a b l e degree, t h e f u l f i l l m e n t of m a n y of these goals a n d s h o w the s y n e r g y b e t w e e n

s o l i d state c h e m i s t r y a n d

e l e c t r o n i c m a t e r i a l s . E x a m p l e s c o u l d just as w e l l h a v e b e e n c h o s e n f r o m the w o r k o f m a n y other laboratories i n e l e c t r o n i c m a t e r i a l s . T h e subjects c o n s i d e r e d are these: i n t e r c a l a t i o n c o m p o u n d s

as storage b a t t e r y elec

trodes. ( H e r e w e s u b m i t t h a t the m o t i v a t i n g forces i n c l u d e t h e f u l f i l l m e n t of goals 1, 3, a n d 4 ) ; n e w titanate d i e l e c t r i c s ( g o a l s 1 a n d 4 ) ;

oxygen

precipitation i n dislocation-free S i (goal 2 ) ; n e w amorphous dielectrics ( g o a l s 1, 3, a n d 4 ) ; a n d i m p e r f e c t i o n s i n q u a r t z ( g o a l s 2 a n d 3 ) . O u r o v e r v i e w s of e a c h of t h e subjects w i l l , of necessity, b e c u r s o r y a n d w e r e c o m m e n d p e r u s a l of the o r i g i n a l papers f o r those w i s h i n g m o r e complete ( a n d rigorous) descriptions. Intercalation

Compounds

as Storage Battery

Electrodes

L a y e r e d c o m p o u n d s h a v e b e e n a v a i l a b l e since a n t i q u i t y , m i c a a n d g r a p h i t e b e i n g p r i m e examples. crystallographic

F o l l o w i n g the a v a i l a b i l i t y o f

structural information, it became

u n i q u e p r o p e r t i e s of s u c h c o m p o u n d s

X-ray

apparent that

the

( c l e a v a b i l i t y i n m i c a , slipperiness

i n g r a p h i t e ) w e r e c a u s e d b y a l a y e r e d c o n f i g u r a t i o n at the a t o m i c l e v e l , w i t h strong c h e m i c a l b o n d s w i t h i n the layers a n d w e a k b o n d s

between

t h e m . Interest i n solids w i t h i n t e r a c t i o n s i n less t h a n t h r e e d i m e n s i o n s , s u c h as l i n e a r c h a i n c o n d u c t o r s

and layered compounds,

is p r e s e n t l y

h i g h because t h e y often p r o v i d e tests of o u r u n d e r s t a n d i n g of the r e l a tionship between

b o n d i n g , structure, a n d properties.

O n e f a m i l y of

c o m p o u n d s of h i g h r e s e a r c h interest since the l a t e 1960s has b e e n the layered transition metal chalcogenides.

A s a n e x a m p l e , s t u d y of

these

c o m p o u n d s d i d m u c h to u n t a n g l e the connections b e t w e e n b o n d i n g a n d p r o p e r t i e s a n d s h o w e d t h a t t h e y w e r e the first m a t e r i a l s to e x h i b i t the p h e n o m e n o n of c h a r g e d e n s i t y w a v e s

(1,2).

Holt et al.; Solid State Chemistry: A Contemporary Overview Advances in Chemistry; American Chemical Society: Washington, DC, 1980.

5.

LAUDISE

Solid State Chemistry

of Electronic

Materials

97

A c h a r g e d e n s i t y w a v e ( C D W ) is a c o u p l e d p e r i o d i c d i s t o r t i o n b o t h of t h e c o n d u c t i o n e l e c t r o n d e n s i t y a n d t h e l a t t i c e , w i t h t h e w a v e l e n g t h of t h e d i s t o r t i o n d e t e r m i n e d b y t h e F e r m i surface.

S i n c e one- a n d t w o -

d i m e n s i o n a l solids h a v e F e r m i surfaces w i t h sections t h a t are p a r a l l e l or n e s t i n g , C D W o f t e n exist. I n t h r e e - d i m e n s i o n a l solids s u c h features m a y i n f r e q u e n t l y o c c u r b y a c c i d e n t , w h i l e i n solids of less t h a n three d i m e n sions t h e y w i l l b e l i k e l y to o c c u r .

T h e F e r m i surface delineates t h e

d i s t r i b u t i o n of m o m e n t u m of electrons i n the c o n d u c t i o n b a n d a n d h e n c e


is r e l a t e d to nonisotropic surfaces.

the d i s t r i b u t i o n of bond

A t the

b o n d s i n the s o l i d .

d i s t r i b u t i o n thus possess onset t e m p e r a t u r e of

the

Solids w i t h

quite asymmetric

a

Fermi

C D W its w a v e l e n g t h is

i n c o m m e n s u r a t e w i t h t h e l a t t i c e s p a c i n g , so t h a t w h i l e , for e x a m p l e , M

+

ions m o v e t o w a r d regions of h i g h n e g a t i v e c h a r g e , n o s u p e r l a t t i c e occurs. A t a l o w e r t e m p e r a t u r e the C D W w a v e l e n g t h c a n o f t e n b e a m u l t i p l e of l a t t i c e s p a c i n g , p r o d u c i n g a s u p e r l a t t i c e s t r u c t u r e . S o m e of t h e p h a s e changes t h o u g h t to l i m i t e l e c t r i c a l storage c a p a c i t y as m o r e l i t h i u m s are i n t e r c a l a t e d into t r a n s i t i o n m e t a l c h a l c o g e n i d e s are b e l i e v e d to b e asso c i a t e d w i t h C D W - l i k e b e h a v i o r . A l l o y i n g of F e , for e x a m p l e , w h i c h w a s p r e v i o u s l y s h o w n to i n h i b i t C D W s , has b e e n u s e d to e x t e n d the c a p a c i t y of p r a c t i c a l electrodes. I t is p o s s i b l e to i n t r o d u c e atoms ( i n t e r c a l a t e ) b e t w e e n the layers of m a n y - l a y e r e d m a t e r i a l s , e s p e c i a l l y w h e n the b o n d i n g b e t w e e n layers is as w e a k as v a n d e r W a a l s forces.

F o r instance, i n V S , L i m a y 2

be

i n t r o d u c e d b e t w e e n the layers ( F i g u r e 1) w i t h o u t s u b s t a n t i a l l y p e r t u r b i n g the s t r u c t u r e . Research on intercalation compounds conducted

f o r e n e r g y storage has b e e n

by M u r p h y , DiSalvo, Trumbore, Broadhead and their col

leagues

(3,4,5,6)

leagues

(7,8)

at B e l l L a b o r a t o r i e s a n d b y W h i t t i n g h a m a n d c o l

at E x x o n . W e w i l l r e v i e w h e r e some of t h e r e c e n t B e l l

L a b o r a t o r i e s a c t i v i t i e s . I t b e c a m e a p p a r e n t to D . W . M u r p h y a n d F . J . D i S a l v o (3,4)

a n d t h e i r colleagues

(5,6)

that L i - i n t e r c a l a t e d c h a l c o

genides m i g h t b e a t t r a c t i v e as b a t t e r y m a t e r i a l s f o r s e v e r a l reasons: 1.

T h e structure was little p e r t u r b e d by intercalation, sug g e s t i n g t h a t a n electrode c o u l d s u r v i v e m a n y c h a r g e d i s c h a r g e cycles w i t h o u t d e t e r i o r a t i o n .

2.

T h e r e d u c t i o n p o t e n t i a l of the L i ° / L i c o u p l e is h i g h , i n d i c a t i n g a b a t t e r y w i t h a h i g h v o l t a g e m i g h t b e possible.

3.

T h e a t o m i c w e i g h t of L i is l o w , i n d i c a t i n g t h a t a b a t t e r y i n w h i c h e a c h g r a m of L i d i s c h a r g e d c o u l d p r o d u c e m a n y c o u l o m b s m i g h t be p o s s i b l e . S u c h a b a t t e r y w o u l d h a v e a v e r y f a v o r a b l e c h a r g e storage d e n s i t y p e r k i l o g r a m of electrode, t h a t i s , m a n y w a t t hours p e r k i l o g r a m of elec t r o d e c o u l d b e stored.

*» +


98

SOLID STATE

CHEMISTRY:

A CONTEMPORARY

OVERVIEW

TYPICAL INTERCALATION STRUCTURE


Li VS

O

S.Se.etc.

£

M

0

ALKALI

2

0 •-Q

_ Figure

1.

Schematic

0

of Li intercalation in transition metal nides

dichalcoge-

MX

Li

2

Li

+

CL0 " 4

IN PROPYLENE CARBONATE

DISCHARGE L i — » - L i + e" +

Li + VS +e--*»LlVS +

Figure 2.

2

2

Cell configuration for intercalation electrode storage battery


5.

Solid State Chemistry

LAUDISE

of Electronic

Materials

99

I n v e s t i g a t i o n o f a v a r i e t y of p o s s i b l e m a t e r i a l s f o r electrodes r e q u i r e d that n e w synthetic techniques for layered chalcogenides be devised. These have been

discussed i n the l i t e r a t u r e a n d w i l l n o t b e r e v i e w e d

(9,10,11).

A s a r e s u l t of these studies, several c o m p o u n d s w e r e c h a r a c

here

t e r i z e d a n d t h e i r o p t i m i z a t i o n f o r electrode m a t e r i a l s has p r o c e e d e d a c o n s i d e r a b l e distance. A t y p i c a l c e l l c o n f i g u r a t i o n t h a t r e s u l t e d f r o m these studies is s h o w n i n F i g u r e 2, a r o o m t e m p e r a t u r e c e l l u s i n g L i C 1 0


as t h e electrolyte.

4

i n propylene carbonate

T h e t h e o r e t i c a l storage d e n s i t y o f a v a r i e t y o f elec

trodes i s s u m m a r i z e d (3,4) i n F i g u r e 3. A s c a n b e seen, g r e a t e r - t h a n - a f a c t o r - o f - t w o i m p r o v e m e n t over P b a c i d a n d N i - C d batteries is possible. Cells have been c y c l e d many times. development

M u c h s o l i d state c h e m i s t r y a n d

r e m a i n s t o b e d o n e , b u t the c o n t r i b u t i o n s o f s o l i d state

c h e m i s t r y are a l r e a d y a p p a r e n t .

m WATT-H0UH3/KG

CB1 U/TISi

400

U/VSt

510

U/Vi-x«iS, (M = Ft£r)

Figure 3. New

Titanate

510-560

WCt

240

K AGS OATTERY

247

Power storage density for battery electrodes

Dielectrics

A n i m p o r t a n t field i n s o l i d state c h e m i s t r y o f e l e c t r o n i c m a t e r i a l s is m o l e c u l a r e n g i n e e r i n g . O b v i o u s l y , r e a l m a t e r i a l s are d e v e l o p e d t h r o u g h a l a r g e a m o u n t o f e m p i r i c i s m . H o w e v e r , as m u c h as p o s s i b l e , m o d e r n researchers a t t e m p t t o d e s i g n u s e f u l materials f r o m first p r i n c i p l e s — t o m a k e use o f o u r b a s i c a t o m i c a n d m o l e c u l a r k n o w l e d g e to devise m a t e r i a l s w i t h o p t i m u m e n g i n e e r i n g p r o p e r t i e s f o r r e a l devices, t h a t is, to m o l e c u l a r l y engineer m a t e r i a l s .

S o l i d state c h e m i s t r y , w h i c h addresses t h e

basic p r o p e r t i e s o f m a t e r i a l s a n d attempts t o u n d e r s t a n d t h e c o n n e c t i o n between b o n d i n g a n d structure a n d properties, provides perhaps a u n i q u e viewpoint t o w a r d engineering real materials. A n example of materials that have been engineered to have u n i q u e useful properties

a r e t h e t i t a n i u m - r i c h b a r i u m titanates, w h i c h

have

b e e n d e s i g n e d t o h a v e a h i g h d i e l e c t r i c constant, a u n i q u e l o w d i e l e c t r i c


100

SOLID S T A T E

CHEMISTRY:

A CONTEMPORARY

OVERVIEW

loss, a n d a t e m p e r a t u r e s t a b i l i t y at m i c r o w a v e f r e q u e n c i e s so t h a t t h e y c a n r e p l a c e l a r g e , expensive m e t a l l i c resonant c a v i t i e s .

In microwave

c i r c u i t r y i t is i m p o r t a n t to c o n t r o l p r e c i s e l y the c a r r i e r f r e q u e n c i e s .

This

is a c c o m p l i s h e d b y the use of c a r e f u l l y s i z e d a i r - f i l l e d m e t a l c a v i t i e s or b y the use of d i m e n s i o n a l l y c o n t r o l l e d c e r a m i c d i e l e c t r i c s . I n e a c h case the d i m e n s i o n s a n d t h e d i e l e c t r i c constant fix the resonant f r e q u e n c y of the d e v i c e a n d thus set the f r e q u e n c y t h a t is p a s s e d or s t o p p e d .

Since

c e r a m i c s h a v e a h i g h e r d i e l e c t r i c constant t h a n a i r , s m a l l e r devices

are


p o s s i b l e . H o w e v e r , for p r a c t i c a l devices t h e loss a n d t e m p e r a t u r e s t a b i l i t y f o r a c e r a m i c - b a s e d system m u s t b e c o m p a r a b l e w i t h t h a t f o r a m e t a l c a v i t y system. F o r a c o p p e r c a v i t y at 4 G H z , t y p i c a l specifications are loss t a n

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