8/11/2019 thermal expansion of sofc materials.pdf

1/11

Ionics 5 (1999) 129

T h e r m a l E x p a n s i o n o f S O F M a t e r ia l s

F. Ti e t z

Forschungszent rum J t i l ich , IWV 1, D-52425 J t i l ich , Germany

Abs t r ac t . A sho r t ove rv i ew i s g iven fo r t he t he rma l expans ion o f so l id o x ide fue l c e l l ma te r ia l s .

The therm ome chan ica l compat ib i l i ty of s ta te-of - the-ar t mater ia ls i s compared wi th a l te rna t ive , new

mater ia ls . With these a l te rna t ives a be t te r ad jus tment of the therm al expan s ion coeff ic ients of the

var ious fue l ce l l com pon ents i s poss ib le and fue l ce l ls based on the new ly developed mater ia ls a re

proposed.

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

Besides the e lec t r ica l and e lec t roca ta ly t ic proper t ies of

e lec t rochem ical conver ters , thermom echanica l proper t ies -

i .e . thermal expans ion coeff ic ient (TEC) , morphologica l

and geometr ica l s tab i l i ty in d i fferent a tmospheres , me-

chanica l toughn ess e tc . - a re impo r tant c r i te r ia for mate-

r ia l se lec t ion and appl ica t ion a t h igh tempera tures . In the

sol id oxide fue l ce l l (SOF C) severa l funct ional mater ia ls

(anode , e lec t ro ly te mem brane , ca thode , in terconnect , con-

tac t layers , sea l ing) have to b e jo ined . Therefore , a major

chal lenge in SOF C research i s to f ind mater ia ls wi th

s imi lar thermal expans ions to avoid mechanica l s t resses ,

especia l ly dur ing thermal cycl ing .Th e mater ia ls com binat io n used for J t il ich 's p lanar

anode-sup por ted SOFC des ign [1] fu l f i l s th is requi rement

qui te wel l . Only the e lec t ro ly te has 20 lowe r thermal

expans ion compared t o t he o the r ce l l componen t s . N ew

composi tes for anode subs t ra tes , based on Ni /A1203 or

Ni /TiO 2 cermets [2], and the use of advanced perovski tema te r i a ls f o r ca thodes w i th l ower TE C l ed t o improved

mem brane-e lec t rodes assembl ies (M EA). T he in ter-

connec t , howeve r, i s now a ma t t e r o f conce rn and i t s t her-

mal expans ion should be adjus ted to the ceramic com-

ponen t s . New in t e r connec t deve lopmen t s ba sed on t it ana-

tes [3] may g ive a reasonable so lu t ion for a fu ture SOFC

design.

2 . E x p e r i m e n t a l

Th e therma l expan s ion me asurem ents were car ried out

wi th Ne tz sch push - rod d i l a tome te r s 402E o r 402C. I f

gases o ther than a i r were appl ied , the m easurem ents w ere

perform ed unde r f lowing gas . Both d i la tometers w ere ca l i -

bra ted wi th a sapphi re s ingle crys ta l and a rod of N iCr20

a l loy. Cor r ec t i ons o f t he expans ion da ta we re m ade u s ing

an in terpola t ion rout ine wi th the two se ts of ca l ibra t ion

measurements .

Al l spec imens were e i ther prepared f rom powder pre-

cursors by uniaxia l o r i sos ta t ic press ing in to a rec tangular

shape (40 x 5 x 3-5 ram) and subsequent s in ter ing or by

cut t ing f rom larger compon ents , as in the case of sub-

s t ra te or in terconn ect spec imens . Th e te rmina l faces were

cu t and po l i shed t o g ive s amples 25 mm in l eng th .

3 . C u r r e n t l y U s e d M a t e r i a ls f o r A n o d e S u p p o r

t e d P l a n a r S O F C a t R e s e a r c h C e n t r e J i i l i c h

Since the ear ly 90s Research Cen t re J t il ich has m ade

t r emendous p rog re s s in t he deve lopmen t o f anode- suppor-

ted p lanar SOFC s as is docum ented in severa l s ta tus re-

por ts [1 ,4-7] . The main improvements in mater ia ls andcomponen t s deve lopmen t du r ing t he pas t f i ve yea r s have

been the in t roduct ion of com posi te e lec trodes resul t ing in

bet te r ce l l per form ance , the appl ica t ion of fe r r i t ic s tee l as

the in terconnect and hous ing mater ia l , and an opt imised

sea l ing g lass wi th h igh thermal expan s ion co eff ic ient and

high g lass t rans i t ion tempera ture . In Fig . 1 a schemat ic

cross sec t ion throug h an SO FC s tacking uni t inc luding

in terconnect p la tes i s shown and g ives an impre ss ion of

how many d i f fe r en t compo nen t s have t o be j o ined be fo rece l l opera t ion . The thermal expans ion of the ceramic

ma te r ia l s o f t he MEA i s g iven i n F ig. 2 t oge the r w i th the

8/11/2019 thermal expansion of sofc materials.pdf

2/11

130 Ionics 5 1999)

Fig. 1. Schematic cross section of a repeating unit of anSOFC stack FZJ design); the dimensions of the layers arenot true to scale,

TEC o f interconnect and sealant materials . In Table 1 the

l inear TEC s between room temperature and 800 ~ as

well as between room temperature and 1000 ~ are l isted

for the various materials shown in Fig. 2.

4 Al t e rna t i ve Componen t Ma te r i a l s f o r SOFC

wi th Improved The rmomechan ica l P rope r t i e s

Num erous develo pmen ts have been undertaken world-wide

to improve the electr ical and electrochemical propert ies of

the ME A c ompon ents by m eans of compos i t iona l or

microstructural optimisa t ions. In mo st cases where new

materials have been proposed, only minor at tention waspaid to the thermomechanical behaviour of s ingle or

jo ined components . However, the def lec t ion of SOFC

comp onents during sintering [12,13] due to different s in-

tering act ivi t ies or during thermal cycling due to thermal

expansion mismatches [8,14] is of great technological

impor tance and has to be min imised . Therefore a common

_-J

8/11/2019 thermal expansion of sofc materials.pdf

3/11

lon ics 5 (1999)

Table 2. Linear thermal expansion coeff icients between 30 ~ and 800 ~ as well as between 30 ~ and 1000 ~ forox ide ion conduc tors

131

Mater ia l A b b r e v i a t i o n a 3 0 - 8 0 0 ~/10-6 K-1

Zr0.85Y0.1501.93 8YS Z 10.5

Zr0.82Y0. 8Ot .9 t 10YSZ 10 .6

a 3 0 - 1 0 0 0 ~/10-6 K-1

Ref .

10 .9 [9 10]11 .0 [10]

Zr0.85Sc0.1501.93 8ScS Z 10.3 10.4 [15]

Zr0.80Sc0.19A10.02O1.90 10ScSZ 10.5 1 0.9 [ 10]

Ce0.8Gd0.2Ol.90 CGO 12.5 12.7 [ 10]

Ce0.9Sr0.101.90 CSO 12.8 13.1 [10]

La0 .gSr0 .2Ga0.9Mg0. iO 3 _ x LSG M-82 91 10 .4 10 .8 [8 ]

La0 . sSr0.2Ga0 .sMg0.203 .x LSG M-8 282 10 .5 11 .3 [ 16]

La0.9Sr0.1Ga0.8Mg0.203_ x LS GM -918 2 10.9 11.4 [8]

La0.9Sr0.1Ga0.75Mg0.2Co0.0503_x LS GM -91 82C o5 12.3 13.0 this wo rk

i n t e r c o n n e c t d u e t o t h e g r e a t t h i c k n e s s a n d r i g i d it y o f t h e

m e t a l l i c p l a t e . I n a n y c a s e , t h e c h o i c e o f m a t e r i a ls f o r t h e

e l e c t r o l y t e i s v e r y l i m i t e d a n d i s s u m m a r i s e d i n Ta b l e 2 .

Th e on ly m ate r ia l s wi th ~30_1000oc > 11 x 10 -6 K -1

w h i c h w o u l d b e s u i ta b l e f o r a n a d j u s t m e n t o f T E C s w i t h

t h o s e o f m e t a l l i c i n t e r c o n n e c t s a r e t h e c e r i a -b a s e d e l e c-

t r o l y t e s a n d c o b a l t - c o n t a i n i n g l a n t h a n u m g a l l a t e s . H o w -

e v e r, b o t h c l a s s e s e x h i b i t s i g n i f i c a n t d i s a d v a n t a g e s . T h e

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

f o r m a t i o n o f C e 3 + an d t h e r e l ea s e o f o x y g e n f r o m t h e

c r y s t a l l i n e l a t t ic e [ 8 , 1 7 , 1 8 ] a n d th e l a n t h a n u m g a l l a te s

s h o w s e v e r a l c h e m i c a l i n s t a b i l it i e s , e . g . G a e v a p o r a t i o n

d u r i n g s i n t e r i n g [ 1 9 , 2 0 ] , i n t e r a c t i o n w i t h N i O d u r i n g

s i n t e r i n g [ 2 1 , 2 2 ] o r d e g r a d a ti o n d u r i n g l o n g - t e r m e x p o -

s u r e i n r e d u c i n g e n v i r o n m e n t s ( g a l l i u m o x i d e d e p le t i o n )

[ 2 2 - 2 4 ] , w h i c h m a k e t h e m d u b i o u s c a n d i d a t e s f o r f u r t h e r

a p p l i c a t i o n i n S O F C s .

T h e r e f o r e , t h e m o s t u s e f u l e l e c t r o l y t e m a t e r i a l s a mt h e z i r c o n i a - b a s e d m a t e r i a ls , o f w h i c h t h e m a t e r i a ls w i t h

8 - 11 m o l % s c a n d ia o r 1 0 m o l % y t t r ia a r e t h e m o s t

r e l i a b l e b e c a u s e t h e y h a v e h i g h a n d n o t p e r t u rb a t e d i o n i c

c o n d u c t i v i t y e v e n a f te r l o n g p e r i o d s a t h i g h t e m p e r a t u r e

[ 1 5 , 2 5 , 2 6 ] . H e n c e , t h e t h e r m a l e x p a n s i o n o f t h e o t h e r

c e ll c o m p o n e n t s s h o u l d b e o ri e n t ed t o w a r d s t h e T E C s o f

t h e z i r c o n i a e l e c t r o l y t e s .4 2 Cathode Materials D u r i n g r e c e n t y e a r s a l o t o f

p e r o v s k i t e s ( A B O 3 ) w i t h l a n t h a n u m a n d s tr o n t i u m

c a t i o n s o n t h e A - s it e an d c o m b i n a t i o n s o f F e / M n [ 2 7-

2 9 ] , F e / C o [ 3 0 - 3 4 ] o r M n / C o [ 3 5 - 3 7 ] o n t h e B - s i te h a v e

b e e n in v e s t i g a te d b y m a n y r e se a rc h g r o u p s . T h e o u t c o m e

o f t h e s e i n v e s t i g a t i o n s i s t h a t th e i o n i c a n d e l e c t ro n i c

t r a n s p o r t p r o p e r ti e s a r e h i g h e s t f o r c o m p o s i t i o n s c o n -

t a i n in g a b o u t 5 0 % S r o n t h e A - s i t e a n d 5 0 - 1 0 0 % C o o n

t h e B - s i t e [ 3 3 - 3 5 ] . T h e s e c o m p o s i t i o n s a r e b e n e f i c i a l f o r

e l e c t r o c h e m i c a l p e r f o r m a n c e , b u t o n t h e c o n t r a r y d i s -

a d v a n t a g e o u s w i th r es p e c t to th e T E C s o f t h e s e m a t e ri a ls

[ 3 3 -3 5 ] an d t o i n te r a c ti o n s w i t h 8 Y S Z ( f o r m a t i o n o f

S r Z O 3 o r L a 2 Z r 2 0 7 ) . A s o l u t i o n f o r r e d u c i n g t h e T E C

a n d m a i n t a i n i n g g o o d c o n d u c t i v i ti e s i s t h e s u b s ti t u ti o n o f

7 ,./

O

14

12

10

8

6 -

4 -

2 -

O

m . - - : ~ . . ~ _ . . . . . . M . . . . . . . . m . . . . . . . . 90 u u . . . . D

t

O @

La Pr

LnSMCLnSM

i

N'd Sm

L a n t h a n i d e i o n

Eu Gd

Fig . 3 . L inear the rmal expans ion coeff i c ien t s be tweenroom tempera tu re and 800 ~ fo r va rious pe rovsk i te com -pos i t ions wi th the genera l fo rmula Ln l_x_ySrxMnl_zCozO3.The sym bols correspo nd to the ser ies with x = 0.3, y =0.05 , z = 0.2 (11); x = 0.3, y = 0.05, z = 0 (121); x = 0.2 , y =

0, z = 0.2 (O) [35,39,42];x = 0.2, y = 0 or 0.01, z = 0 (O )[35,39,42,46];x = 0.3, y = 0 or 0.01, z = 0 ( '~:) [40,41,46].

8/11/2019 thermal expansion of sofc materials.pdf

4/11

132 I o n i c s 5 ( 1 9 9 9 )

Tab le 3. Line ar thermal expansion coefficients between 30~ and 800~ as well as between 30~ and 1000 ~ ofperovskites for SOFC cathodes

Material Abbrev ia t ion ~30 800oc ~30 [Ref ./10-6 K-1 100ooc

1 0 - 6 K - I

La0.8 Sr0.2M nO 3-x LSM-82 13.1 * [35]

La0 .79Sr0 .2M nO3-x LSM-792 10 .8 11 .1 [46]

La0 .79Sr0 .2M nO3-x LSM -792 12 .4 [47]

La0 .69Sr0 .3M nO3-x LSM-693 11 .7 12 .0 [46]

La0 .69Sr0 .3M nO3-x LSM-693 - 12 .8 [47]

La0 .65Sr0 .3M nO3-x LSM-653 12 .0 12 .3 thi s work

La0.8 Sr0 .2M n0.8C o0.2 03-x LSMC-8282 14 .1 * [35]

L a 0 . 6 5 S r 0 . 3 M n 0 . 8 C o 0 . 2 0 3 - x L S M C - 6 5 3 8 2 11 . 6 11 . 7 th is w o r k

Pr0 .8Sr0 .2Mn O3-x PSM-82 9 .5 I0 .1 [39]

Pr0.7S r0.3M nO 3-x PSM-73 11.1 [40]

Pr0 .65Sr0 .3Mn O3-x PSM-653 1 1 .0 11 .6 thi s work

P r 0 . 8 S r 0 . 2 M n 0 . 8 C o 0 . 2 0 3 - x P S M - 8 2 8 2 9 . 6 1 0 . 3 [ 39 ]

Pr0 .8S r0 .2M n0.8C o0.20 3-x PSM-8282 10 .2 10 .9 thi s work

Pr0 .7S r0 .3M n0.8C o0.20 3-x PSMC-7382 10 .5 11 .1 thi s work

Nd0.7Sr0 .3MnO 3-x NSM-73 10 .8 [41]

Nd0.65Sr0 .3M nO3-x NSM-653 9 .3 9 .7 thi s work

N d 0 . 6 5 S r 0 . 3 M n 0 . 8 C o 0 . 2 0 3 - x N S M C - 6 5 3 8 2 1 0 . 4 1 0 . 8 th is w o r k

Gd0.8Sr0 .2Mn O3-x GSM-82 2 .3 3 .8 [42]

G d 0 . 8 S r 0 . 2 M n 0 . 8 C o 0 . 2 0 3 - x G S M C - 8 2 8 2 8 . 2 1 0 . 2 [ 42 ]

Gd0.65Sr0 .3M nO3-x GSM-653 9 .7 9 .9 thi s work

G d 0 . 6 5 S r 0 . 3 M n 0 . 8 C o 0 . 2 0 3 - x G S M C - 6 5 3 8 2 1 0 . 4 1 0 . 6 t hi s w o r k

La0.7Sr0 .3Co O3-x LSC-73 17 .5 19 .2 [8]

Pr0 .7Sr0 .3CoO 3-x PSC-73 18 .8 [43]

*: value for 200-800~ : value for 25-1100 ~

l a n t h a n u m b y o t h e r r a r e e a r th i o n s , w h i c h h a s b e e n r e -

p o r t e d in a s er i e s o f a rt ic l e s [ 3 2 , 38 - 4 5 ] . T h e T E C s o f t h epero vsk i tes decrease wi th decreas ing ion ic rad ius of the

lan thanide ion , wh ich i s sho wn in F ig . 3 and Tab le 3 .

S l i g h t v a r ia t i o n s o f S r o r C o c o n t e n t c a n b e c o m p e n s a t e d

b y i n tr o d u c i n g t h e p r o p e r l a n t h a n id e i o n . H o w e v e r, l a rg e

a m o u n t s o f S r an d / o r C o a l w a y s l e ad t o h i g h T E C s n o t

a p p l i c a b l e t o S O F C s [ 8 , 3 4 ,4 4 ] . A d e c re a se o f T E C w a s

o n l y o b s e r v e d f o r su b s t u t i o n s o f L a w i t h P r o r N d . O t h e r

lan thanides d id no t s ign i f ican t ly change the T EC. The

TE Cs of the series Lno.65Sro.3MnO3_ x a nd Lno.65Sro. 2

Mn0.8Co0.203_ x co inc ide w i th the resu l t s ob ta ined on

Ln0.TSr0.3MnO3. x [40,41,46 ] (Fig. 3) and demo nstrate

t h a t th e v a r i a ti o n o f S r c o n t e n t i s t h e d o m i n a t i n g p a r a -

m e t e r f o r t u n i n g t h e T E C o f t h e s e p e r o v s k i t e s . T h em e a s u r e d T E C s o f t h e g a d o li n iu m c o m p o u n d s s h o w e d t he

la rges t dev ia t ions f rom l i te ra ture da ta (F ig . 3 ) and i t i s

a s s u m e d t h a t t h e d a ta i n t h e p r e v io u s r e p o r t [ 42 ] w e r e n o t

proper ly cor rec ted for sample ho lder mater ia l o r ins t ru-

me nta l pecul ia r i t i es .4 3 A n o d e a n d S u b s t r a t e M a t e r ia l s U s u a l l y a n S O F C

with a th in e lec t ro ly te i s bu i l t up on one of the e lec t rodes

as the suppo r t ing un i t . In the case of the ca thode , the

T E C c a n b e a d j u s t e d m u c h m o r e e a s i l y t o th a t o f th e s o l i d

e lec t ro ly te used in the sys tem (cf . Tab les 2 and 3) . So fa r

an anod e s ubs t ra te had the d i sadv antage tha t the Ni (or the

8/11/2019 thermal expansion of sofc materials.pdf

5/11

Ionics 5 (1999)

Table 4. Linear thermal expansion coefficients between 30~ and 800~ as well as between 30 ~ and 100 0 ~ ofglasses for SO FC sealings

133

Material / Com pany ~30_800oc ~30_1000oc/10-6 K-1 /10-6 K-1

12.5M a c o r | G l a ss Wo r k

Photovee l / Sumi tomo Photon Ceramics10 .5

A 1 2 0 3 - M g O - S iO 2 - B 2 0 3 / F Z J 11 . 4 1 2 . 0

A1203-MgO-CaO-BaO-SiO2-B203 / FZJ 12.3 13.3

A1203-Nd203-BaO-SiO 2 / FZJ 13 .2 13 .5

Ref.

[51]

[51]

[6]

[6]

[6]

N i O i n t h e o x i d i s e d s t a t e ) h a s a h i g h e r T E C t h a n 8 Y S Z

a n d t h e r e fo r e a l s o t h e w i d e l y u s e d N i / 8 Y S Z c e r m e t[48 ,49] . Al te rna t ive cermets can be used i f the e lec t ro-

c h e m i c a l a n d m e c h a n i c a l f u n c t i o n s o f t h e s u b s t ra t e s a r e

separa ted and i f the subs t ra te se rves on ly as an e lec t ro-

n ica l ly conduct ive suppor t fo r the e lec t roca ta ly t ica l ly ac-

t i v e c o m p o n e n t s . C e r m e t s b a s e d o n N i a n d b i n a r y o r t e r-

nary ox ide s , e .g . Ni /Cr2 03 [50] , Ni /A I203 [2] , Ni /TiO2

[2], Ni /NiC r20 4 [50] or Ni /N iAI2 04 hav e been cons idered

for such fue l ce l l s . These cermets a l low an exac t ad jus t -

m e n t o f t h e T E C t o t h a t o f 8 Y S Z b e c a u s e th e m e n t i o n e d

o x i d e s h a v e a l o w e r T E C t h a n 8 Y S Z , w h i c h i s i nc re as ed

by the ad di t ion of Ni (or NiO) . Addi t iona l advantages of

s u c h s y s t e m s h a v e b e e n d e s c r i b e d e l s e w h e r e i n m o r e d e t a il

[2,11].

F o r t h e a n o d e f u n c t i o n a l l a y e r, h o w e v e r, a n e w m a t e -

r i a l w i th a n a p p r o p r i a t e T E C i s n o t i n s i g h t t o d a y a n d th e

c o n v e n t i o n a l N i / 8 Y S Z c e r m e t r e m a i n s a n e c es s a r y m a t e -

r ia l fo r the ca ta ly t ic ac t ive layer. The po ss ib i l i ty of sub-

s t it u ti n g m i x e d - c o n d u c t i n g c e r a m i c s i n s te a d o f 8 Y S Z h a s

t o b e e x p l o r e d i n t h e f u t u r e .

4 4 Glass Seal ing Mater ia ls During recent years cont i -

n u o u s a t t e m p t s h a v e b e e n u n d e r t a k e n t o o p t i m i s e t h et h e r m a l p r o p e r t i e s o f t h e s e a l in g m a t e r i a l . Wi t h r e ga r d to

t h e T E C , p r o g r e s s h a s b e e n a c h ie v e d b y i n c r ea s i n g th e

t h e r m a l e x p a n s i o n b u t m a i n t a i n i n g a h i g h g l a s s tr a n s it i o n

t e m p e r a t u r e a n d p r o p e r s o f t e n i n g t e m p e r a t u r e . T h e T E C s

o f s e a l i n g g l a s s e s w i t h t h e m o s t p r o m i s i n g p r o p e r t i e s t e s-

ted in var ious S OF C s tack tes t s in J i i l ich a re l i s ted in

Ta b l e 4 to g e t h e r w i t h s o m e c o m m e r c i a l e x a m p l e s g i v e n

in the l i t e ra ture . Because sea lan ts a re a very sens i t ive

i s s u e i n S O F C d e v e l o p m e n t , a n d i n m o s t c a s e s p r o p r ie -

ta ry, no de ta i led in format ion i s publ i shed [51 ,53] . A note-

w o r t h y i n v e s t i g a t io n o f c o m p l e x g l a s s e s in t h e S r O -

L a 2 0 3 - A 1 2 0 3 - B 2 0 3 - S i O 2 s y s t e m w a s c a rr ie d o u t b yK r u m p e l t e t a l. [ 5 4] . T h e g l a s s e s o r g l a s s - c e ra m i c s h a v e

h i g h T E C s r a n g i n g f r o m 8 - 1 3 x 1 0 -6 K - a n d s h o w s o f te -

n i n g t e m p e r a t u r es b e t w e e n 6 0 0 - 8 0 0 ~ A l t h o u g h th e

T E C s a r e a p p r o p r i a t e f o r S O F C a p p l i c a ti o n , t h e s o f t e n i n g

t e m p e r a t u re s a r e t o o l o w f o r t h e a c t u a l S O F C s y s t e m s

u n d e r d e v e l o p m e n t a n d h e n c e t h e y a r e n o t l is t e d i n Ta b l e

4 . H o w e v e r, i f o p e r a t i o n t e m p e r a t u r e s b e t w e e n 5 0 0 - 7 0 0

~ are envisag ed and rea l ised , such g lasses c ould be

a t t ra c t i v e f o r a s s e m b l i n g t h e S O F C s t a c k .

4 5 Interconnect Materials S i n c e t h e S O F C d e v e l o p -

m e n t t e n d s t o w a r d s lo w e r o p e r a t i n g t e m p e r a t u r e s , t h e

i n te r c o n n e c t m a t e r i a l s b a s e d o n l a n t h a n u m c h r o m i t e a re

subs t i tu ted by meta l l i c in te rconnec ts , e i ther by chro-

miu m-b ased a l loys [55] or by fe r r i t i c s tee l s [1 ,5 ,6] . The

C r- b a s e d a ll o y s c a n w i t h st a n d t e m p e r a t u r e s o f u p t o 1 0 0 0

~ b u t t h e y a r e r a t h e r e x p e n s i v e t o d a y a n d f o r m C r 2 0 3 o r

sp ine l sca les in contac t wi th perovski te mater ia l s [56-58] .

T h e r e le a s e o f C r s p e c i e s i n t o t h e c a th o d e c o m p a r t m e n t

[59] and sca le form at ion lead to de te r iora tion o f the

ca ta ly t ic ac t iv i ty of the ca thode [58] . Th erefore pro tec t ive

l a y er s a r e n e e d e d t o m i n i m i s e o x i d e s c a l e g r o w t h a n d t h edegrada t ion o f the ca tho de [60] . Ins tead , fe r r i ti c s tee l s have

a l i m i t i n g o p e r a t io n t e m p e r a t u r e o f a b o u t 8 0 0 ~ b u t

t h e y a r e c o m m e r c i a l l y a v a i l a b l e at a l o w p r i c e l e v e l. T h e y

a lso d iffe r s ign i f ican t ly in the i r the rma l ex pans io n

b e h a v i o u r as s h o w n i n Ta b l e 5 . T h e C r- b a s e d a l l o y h a s a

T E C c l o s e r to 8 Y S Z , w h e r e a s t h e f e r ri ti c s t ee l h a s T E C s

c o m p a r a b l e w i th t h o s e o f th e a n o d e s u b s t ra t e . A p a r t f r o m

fer r it i c s tee l s a l so N i -based a l loy s were cons idered [35] ,

b u t s h o w e d t o o l a rg e t h e r m a l e x p a n s i o n s . R e g a r d i n g a

T E C a d j u s te d t o 8 Y S Z , i t w i l l b e a d if f ic u l t t a s k to f in d

8/11/2019 thermal expansion of sofc materials.pdf

6/11

1 3 4 I o n i c s 5 ( 1 9 9 9 )

Tab le 5. Line ar therm al expansion coefficients (measured in air) between 30~ and 800~ as well asbetween 30 ~ and 100 0 ~ of interconnect materials for SOFC

Material o~30_800oc 0t30_ 000oc Ref./10-6 K-1 /10-6 K-1

Cr Fe5 Y2031 11.3 [55]

Cr Fe5 Y2031 11.3 12.0 [8]

X 10 CrA1 18 (1.4742) 12 .9 13.9 [8]

La0.9Sr0. ICrO3 10.7 [48]

La0.79Sr0.2CrO3 11.1 * [47]

La0.7Ca0.3Cr0.5Ti0.503 9.6 10.1 this work

La0.7Sr0.3Cr0.8Ti0.203 10 .4 10.7 this work

*: value for 350-1000~

an opt im ised fe rr i ti c a l loy, a l tho ugh f i r s t inves t iga t ion s

in th i s d i rec t ion showed som e perspec t ives for fu ture

m o d e l a l l o y s [ 6 1 ].

As in the case of the ca thodes , the in te rconnec t ma -

te r ia l s based on lan thanum chromi te a re s t i l l a t t rac t ive due

t o th e p o s s i b i l i ty o f s i m u l t a n e o u s s u b s t it u t io n s o n t h e A

a n d B s it e s o f th e p e r o v s k i t e a n d t h e r e b y t u n i n g t h e T E C

a n d o t h e r m a t e r i a l s p r o p e r t ie s . A l o t o f c o m p o s i t i o n s

h a v e b e e n i n v e s t i g a t e d i n th e p a s t a n d , a s a n e x a m p l e , o n eo f t h e m a t e r i al s m a t c h i n g t h e T E C o f 8 Y S Z i s

. ... L . . . . . . . . . . . . . . . . . . . . i - e / ~o c - -1 o o A 0 0 0 51 .0 8 - t . . . . . ~ '- '- , i . . . . . . . . ~ -~ . . . . . . . . ~ - - '

t A r / 4 Yo H 2 ~ - A r / 4 Yo H 2~ . ~ 1 0 0 /

l . . . . . . I I

-1 0 1 2 3 4 5 6 7 8T i m e / h

Fig. 4. Isoth erm al length chang es in oxid ising and re-ducing atmospheres for La0.7Ca0.3Cr0.5Ti0.503 (top) andLa0.7Sr0.3Cr0.8Ti0.203 (bottom ). Fo r the sa ke o f com pa-rison, the scaling o f the length changes is the same in b ot hgraphs. The time scale was set to zero for the first ch ang e

from air to A r/4 H 2

L a o . 9 S ro . lC r O 3 [ 4 8 ]. H o w e v e r, t h e m a i n p r o b l e m a s s o -

c i a t e d w i t h l a n t h a n u m c h r o m i t e s i s t h e v o l u m e e x p a n s i o n

in reduc ing a tmosphere [62 ,63] . In the pas t on ly the

mu l t ip le -doped in te rconnec t f rom D ornier had suff ic ien t

s h a p e s t a b i li t y f o r ad v a n ce d S O F C d e v e l o p m e n t [ 5 1] .

R e c e n t l y M i t s u b i s h i s t a f f h a v e p r e s e n t ed a n i n t e re s t in g

a l te rna t ive based on Lal_xEAxCrl_yTiyO3 (EA = Mg , Ca ,

Sr, Ba) [3] . Here the Ti subs t i tu t ion supp resses the

swel l ing in reduc ing a tmosphere , as can a l so be seen in

Fig. 4 in the case of Lao.TCa0.3Cr0.sTi0.503 [64]. T he

l e n g th c h a n g e b e t w e e n o x i d i s i n g a n d r e d u c in g a t m o s p h e r e

i s no t on ly very smal l (0 .005 ) , i t i s nega t ive , too . This

p h e n o m e n o n h a s a l s o b e e n o b s e r v e d i n t i ta n i a - c o n ta i n i n g

z i rcona tes wi th f luor i te s t ruc ture [8] and seems to be typ i -

c a l o f t i ta n i u m - r i c h c o m p o u n d s . T h e T E C o f th i s m a t e r i a l

i s a b o u t 7 s m a l l e r t h a n t h a t o f 8 Y S Z a n d c a n b e t u n ed

by s l igh t ly v ary ing the ca t ion ra tios . O n the cont ra ry,

La0.7Sro.3Cro.sTio.203 exa ctly f i ts the TE C o f 8YS Z

( Ta b l e 5 ) b u t s h o w s t h e t y p i c a l e x p a n s i o n i n a t m o s p h e r e s

w i t h l o w p ( O 2 ) [ 6 2 ,6 3 ] , w h i c h p r e v e n t s t h e a p p l i c a t i o n o f

s u c h c o m p o u n d s a s i n t e r c o n n e c t in g m a t e r i a ls .

A genera l d i ffe rence in bo th m ater ia l s i s observed

dur ing a tmos pher ic cyc l ing : the Ti - r ich pero vski te (and

a lso the f luor i te [8] ) reaches the equi l ib r ium length wi th in

3 - 3 0 m i n u t e s , w h e r e a s t h e le n g t h c h a n g e o f t h e C r- r i c h

m a t e r i a l is c o m p o s e d o f a f a s t i n c r e as e a t t h e b e g i n n i n g

a n d a s u b s e q u e n t s l o w i n c r e a s e o v e r s e v e r a l h o u rs t o r e ac h

e q u i l ib r i u m . T h e r e a s o n s f o r t h e t w o c o n t r i b u t io n s a r e e x -

p la ined here by a (fas t ) e lec tron ic reduc t ion of the ca t ions

( the reduc t ion of (Cr,Ti ) 4+ to (Cr,Ti ) 3+) and a ( s low)

8/11/2019 thermal expansion of sofc materials.pdf

7/11

Ionic s 5 (1999) 135

Tab le 6. Materials and linear therm al exp ansion coefficien ts for a high-temperature plana r anod e-sup porte dSOFC operating at 1000~ selected from Tab les 2-5.

C om po ne nt M ate rial o~30_1000oC/10-6 K-1

inte rco nn ect (La,Ca)(Cr,Ti)O3 10.1

ca thode Pr0 .8Sr0 .2MnO3 10 .1

e lec t ro ly te 10YSZ 11 .0

anode 40 v/o Ni + 60 v/o 8YSZ 12.6

sub strate 50 v/o Ni + 50 v/o A120 3 [2] = 11

glass seal ing Dorn ier com posit ion [51] 10.0-1 0.5

di ffus ion-cont ro l led re lease of oxygen f rom the la t t i ce

[63] . The whole reac t ion can be wr i t ten in the Krrge r-

Vi n k n o t a t io n f o r t h e c h r o m i t e a s

X X .

0 0 + 2 C r c r = V O + 1 /2 0 2 ( g a s ) + 2 C r c r ( 1)

as the sum of the ind iv idua l reac t ions of the ions in the

crys ta l l ine la t t i ce

X

O O = g ; + 1 /2 0 2 ( g a s ) + 2 e ' ( 2 )

and

X

C r c r + 2 e = 2 C r c r ( 3 )

F o r t h e Ti - r ic h m a t e r i a l s i t is s u r p r i s in g t h a t n o v o l u m e

increase occurs as for the ch rom i tes , s ince the t r iva len tca t ions have a la rger ion ic rad ius than the te t rava len t

c a t i o n s . T h i s m e a n s t h a t t h e t it a n i u m i o n s r e m a i n i n t h e i r

o r i g i n a l v a l e n c e s t a t e , w h i c h i s i n a g r e e m e n t w i t h t h e l o w

a m o u n t o f o x y g e n r e l e a se d f r o m t h e l a t ti c e [ 8 ], b u t i t i s

surpr i s ing tha t the chro m ium ions a re no t reduced as in

the cas e of La0.7Sr0.3Cr0.8Ti0.203.To u n d e r s t a n d t h i s p h e n o m e n o n , i t is n e c e s sa r y to i n -

v e s t i g a t e t he e l e c t r o n i c s t a t e s a n d b i n d i n g e n e rg i e s o f b o t h

Ti a n d C r b y p h o t o e l e c t r o n s p e c t r o s c o p y. A l s o t h e e p a n -

s i o n b e h a v i o u r i n d e p e n d e n ce o f o x y g e n p a r ti a l p r e s su r e

has to be inves t iga ted in m ore de ta i l by d i la tom et ry and

X-ray d i ff rac t ion .

5 . P l a n a r A n o d e S u p p o r t e d S O F C s w i t h I m

p r o v e d T h e r m o m e c h a n i c a l P r o p e r t ie s a n d M a

t e r i a l s R e s e a r c h f o r T h e i r R e a l i s a t i o n

Based on the ma ter ia l s da ta l is ted in Ta bles 2-5 , a model

S O F C f o r h ig h a n d l o w o p e r a t i n g t e m p e r a t u r e s is p r o -

p o s e d i n Ta b l e 6 a n d 7 . I n b o t h c a s e s t h e T E C s o f t h e

c h o s e n m a t e r ia l s s h o u l d b e c l o s e t o t h e T E C o f t h e s o l i d

e l e c tr o l y te . A p a r t f r o m th e a d ju s te d T E C s , t h e c o m -

p o n e n t s o f t h e h i g h - te m p e r a t u r e S O F C ( H T - S O F C ) h a v e

t o h a v e b e t t e r c h e m i c a l s t a b i l i t y r a t h e r t h a n m a x i m i s e d

e lec t rochemica l per formance , because the e lec t rochemica l

reac t ions a re mu ch m ore acce le ra ted a t 1000 ~ than a t

7 5 0 ~ F o r t h e l o w - t e m p e r a t u r e S O F C ( L T- S O F C ) ,

h ighly ca ta ly t ica l ly reac t ive e lec trodes a re needed to ma in-

ta in suff ic ien t pow er ou tpu t , whereas d i ffus ive in te rac-t ions a t the in te r faces a re suppresse d due to the low opera-

t ing tempera ture .

W i th these genera l gu ide l ines in m ind , the proposed

H T- S O F C c o n t a i n s a l a n t h a n u m c h r o m i t e i n t e r c o n n e c t

(advantages : bes t chemica l s tab i l i ty, lowes t ra te of chro-

m ium evap ora t ion , suff ic ien t e lec tr ica l cond uct iv i ty ) , a

p r a s e o d y m i u m m a n g a n i t e c a th o d e ( a d v a n ta g e s : l o w e r c a-

t h o d ic o v e r p o t e n ti a l t h a n l a n t h a n u m m a n g a n i t e s [ 7 ,3 9 ,

6 5 , 6 6 ], l o w a m o u n t o f S r m i n i m i s e s r e a c t i o n s w i t h t h e

e l e c tr o l y te ) , a 1 0 Y S Z m e m b r a n e ( a d v a n ta g e s : g o o d l o n g -

8/11/2019 thermal expansion of sofc materials.pdf

8/11

1 3 6 I o n i c s 5 ( 1 9 9 9 )

Tab le 7. Materials and linear thermal exp ansion coefficien ts for a low-temperature planar anode-supp orted SOFC operating at 750~ selected from Tab les 2-5.

C o m p o n e n t M a t e r i a l o~3 _8 oC/10-6 K-1

in te rconnec t (La,Ca)(Cr,Ti)O 3 or

modified ferritic steel orCr-based al loyPr0 .65Sr0 .3MnO3

9 . 6

11 .3ca thode 11 .0

e lec t ro ly te 10YSZ 10 .6

anode 40 v/o Ni + 60 v/o 8YSZ 12.5

substrate 40 v/o Ni + 60 v/o T it 2 [2] 11.0

Photovee l o r [modi f iedMgO-A1203-SiO2-B203

glass seal ing 10.511 .4

t e r m s t a b i l i t y o f i o n i c c o n d u c t i v i t y, c o m m e r c i a l l y a v a i l-

a b l e , m o r e r e a d i l y a v a il a b l e t h a n S c S Z ) , a N i / 8 Y S Z c er-

m et as the anode func t iona l l ayer on a Ni /A120 3 (50:50

v/o) subs t ra te (advantages : good h igh- tempera ture s tab i -

l i ty, ad jus ted TE C [2], low-co s t raw m ater ia l s ) and f ina l ly

a g lass -ceram ic sea l ing , p re fe rab ly based on the Dorn ie r

c o m p o s i t i o n [ 51 ] d u e t o g o o d e x p e ri e n c e in S O F C

a s s e m b l i e s i n t h e p a s t [ 5 1 , 6 7 ]. T h e m o s t c r it i c a l p o i n t i nth i s ma ter ia l s se lec t ion i s the anod e wi th a 15 h igher

T E C c o m p a r e d t o t h e o t h e r c e l l c o m p o n e n t s . H e r e a

s u b s t i t u ti o n o f t h e Y S Z b y a d i ff e re n t m i x e d c o n d u c t i n g

mater ia l should be cons idered .

F o r t h e LT- S O F C t h e m a t e r i a l s a r e e a s i l y s e le c te d f o r

t h e M E A , i .e . a s u b - s t o i c h i o m e t r i c p r a s e o d y m i u m m a n -

g a n i t e w i t h h ig h e r S r c o n t e n t f o r i m p r o v e d e l e c t ro c h e m i -

c a l p e r f o r m a n c e , a 1 0 Y S Z e l e c t r o l y t e a n d a N i / 8 Y S Z

a n o d e a s m e n t i o n e d a b o v e a n d a N i / Ti O 2 s u b s t r a te w i t h

h i g h e l e c tr i c al c o n d u c t i v i t y a n d g a s p e r m e a b i l i t y a s w e l l

as low s in te r ing tempera ture [2 ,11] . Whereas the reduced

T E C g i v e s m o r e d e g r e e s o f fr e e d o m i n t h e c a s e o f s e a l a n t

d e v e l o p m e n t f o r a s s e m b l i n g t e m p e r a t u r e s in t h e r a n g e o f

800-9 00 ~ the in te rcon nec t ma ter ia l i s the mos t c r i t ica l

p o i n t o f c o n c e r n . I n p r i n c i p l e b o t h a c e r a m i c o r a m e t a ll i c

b i p o l a r p l a t e c a n b e c o n s i d e r e d , b u t b o t h m a t e r ia l s h a v e t o

b e o p t i m i s e d . O n t h e o n e h a n d , t h e l a n t h a n u m c h r o m i t e

has low e lec t r ica l cond uct iv i ty a t low tempera tu res , espe-

c i a l ly in a t m o s p h e r e s w i t h l o w o x y g e n p a r ti a l p r es s u r e s.

T h i s h a s t o b e i m p r o v e d s i g n i f ic a n t l y b e s id e s t h e c h a l l en -

g i n g t h e r m o m e c h a n i c a l p r o p e r t i e s . O n t h e o t h e r h a n d ,

there i s no fe r r i ti c s tee l ava i lab le w i th TE C = 10-12 x

10 -6 K - I and mu ch effor t i s needed to ach ieve such low

t h e r m a l e x p a n s i o n s b y m u l t i - e l e m e n t a l l o y i n g . A r a th e r

exp ens iv e and in te rmedia te so lu t ion to th i s mater ia l

p r o b l e m i s t h e C r-b a s e d a ll o y. H e r e t h e C r e v a p o r a t i o n

and pro tec t ion layers have to be re -eva lua ted wi th respec t

to the s ign i f ican t ly lowered opera t ing tempera tures in

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

6 C o n c l u s i o n sDue to the res t r ic ted choice of e lec t ro ly te mater ia l s the

o t h e r S O F C c o m p o n e n t s s h o u l d f o l lo w t h e T E C o f t h e

m e m b r a n e m a t e r ia l ( Y S Z o r S c S Z ) . B a s e d o n t h e t h e r m a l

expa ns ion da ta ava i lab le , two se t s o f ma ter ia l s were

s e le c te d t o d e s i g n a h ig h - a n d l o w - t e m p e r a t u r e S O F C .

W h e r e a s m a t e r i a l s fo r th e M E A s c a n b e c l e ar l y i d e n ti fi e d,

the in te rconnec t and sea lan t ma ter ia l s a re s t i l l a m at te r o f

d e v e l o p m e n t a n d o p t im i s a t i o n . A l s o n e w a n o d e m a t e r i a ls

b a s e d o n c e r m e t s c o n t a i n i n g N i a n d m i x e d -c o n d u c t i n g

c e r a m i c s a r e n e e d e d f o r T E C a d j u s tm e n t .

7 A c k n o w l e d g e m e n t s

T h e a u t h o r t h a n k s a l l m e m b e r s o f t h e s o l id o x i d e f u e l c e ll

p r o j e c t t e a m a t J ii li c h w h o s u p p l i e d h i m w i t h s a m p l e s

a n d m a t e r ia l s d a t a . F i n a n c ia l s u u p p o r t f r o m t h e E u r o p e a n

C o m m i s s i o n u n d e r t h e c o n tr a c t n r. E R B F M R X - C T 9 7 -

0130 i s g ra te fu l ly acknowledged .

8/11/2019 thermal expansion of sofc materials.pdf

9/11

Ionics 5 (1999) 137

8 R e f e r e n c e s

[1] H .P . Buc hkrem er, U. Diek ma nn, L. G. J . de Haart ,

H. Kabs , U. St imming, D. St6ver, in : Proc . 5 th

Int . Sym p. Sol id Oxide Fuel C el ls (SOFC -V), eds .

U. St im min g, S . C. Singhal , H. Tagawa, W .

Lehner t , The Elec t rochemical Socie ty, Pennington,

NJ, 1997, p. 160.

[2] F. Tietz, F. J . Dias, A. Nao um idis, in: Proc. 3rd

Eur. SOFC Forum, Nantes , ed . Ph. Stevenson,

1998, Vol. 1, p. 17 1.

[3] T. Nishi , N. Hisa tome, H. Yamamoto, N.

Murakam i , in : P roc . 9 th CIM TE C - Wor ld Ce ramicCong ress and Forum on New Mater ia ls , ed. P.

Vincen zini , Techna Publ ishers S . r. l. , Faenza , I ta ly,Vol . 24: Innovat ive Mater ia ls in Advanced Energy

Te chn olog ies (1999), p. 41.[4] H. P. Buchkremer, U. Diekm ann, D. St6ver, in :

Proc . 2nd Eur. SO FC Foru m, Oslo , ed . : B. Thor-

s tensen, European Sol id Oxide Fuel Cel l Forum,

Ob errohrdo rf, Switze rland (1996), V ol. 1, p. 221.

[5] L. G. J . de Haart , Th. H auber, K. M ayer, U.

S t imming , i n : P roc . 2nd Eur. SO FC Forum, Os lo ,

ed . : B. Thors tensen, European Sol id Oxide Fuel Cel l

Foru m , Ob errohrdo rf, Sw itzerlan d (1996), Vol. 1, p.

229.[6] H .P . Buch krem er, U. Diek ma nn, L. G. J . de Haart ,

H. Kabs , H. Nabie lek , D. St6ver, I . C. Vinke, J .

Aus t ra las ian Ceram . Soc. 34 , 136 (1998) .

[7] D. St6ver, U. Diekm ann, U. Flesch, H. Kabs , W . J .

Quadakkers , F. Tie tz , I . C. V inke, Proc . 6 th In t .

Sym p. Sol id Oxide Fue l Cel ls (SOFC-VI) , eds . S .

C. Singhal , M . D okiya , The Elec t rochemical So-

c ie ty, Pennington , NJ , 1999, p . 812.[8] F. Tie tz , in : Proc . 9 th CIM TE C - World Ceramic

Cong ress and Foru m on Ne w Mater ia ls , ed . P. Vin-

cenzini , Techna Publ ishers S . r. l. , Faenza , I ta ly,

Vol . 24: Innovat ive Mater ia ls in Advanced EnergyTe chn olog ies (1999), p. 61.

[9] R. M aenn er, E. Ivers-Tiff~e, W . W ersing, W.

Klein l ien , Proc . 2nd Eur. Ceram. Soc. Conf . (Euro-

Ceram ics I I ), eds .: G. Ziegler, H. Hausner, D eutsche

Kera misch e Ge sel lschaf t (1991) , p . 2085.

[10] F. Tie tz , G. Stochniol , A. Naoumidis , Proc . 5 thEur. Conf. on Advanced Materials, Processes and

App l ica t ions (Eurom at 97) , eds .: L . A. J . L . Sar-

ton , H. B. Zeedi jk , Nether lands Socie ty for Mate-

rials Science (1997), Vol. 2, p. 271.

[11] F. Tietz, F. J . Dias, B. Dub iel , H . J . Pen kalla,

Mater. Sci . Eng. B, in print .

[12] R. W . Steinbrech, A. Caro n, G. BlaB, F. J . D ias,

Proc . 5 th In t . Symp. Sol id Oxide Fuel Cel ls

(SOFC -V), eds. U. St im min g, S . C . Singha l , H.

Tagawa, W. Lehner t , The Elec t rochemical Socie ty,

Pe nnin gton, NJ, 1997, p. 727.

[13] R. VaBen, R. W . Steinbrech, F. Tietz, D . S t6ver,

in : Proc . 3rd Eur. S OF C Foru m, N antes , ed . Ph.

Stevenson, 1998, Vol. 1, p. 557.

[14] F. Meschke, R. W. Ste inbrech, to be publ ished in :

Proc . 6 th In t . Sym p. Sol id Oxide Fuel Cel ls(SOFC-VI) , Hawai i , Nov. 1999, eds . S . C. Singhal ,

M. Dokyia , The Elec t rochemical Socie ty, Penning-ton, NJ, 1999, p. 1047.

[15] Y. Mizutani , M. Tam ura , M. Kaw ai , O. Yama-mo to, Sol id Sta te Ionics 72 , 271 (1994) .

[16] I . Yasuda, M. Hishin um a, in : Proc . 64th Ann.

Meet ing Elec t rochem. Soc. Japan, Extended Ab-s t racts , Yoko ham a, March 1997, The E lec t rochemi-

cal Soc ie ty of Japan, p . 63 .

[17] M. Mogensen, Th. Lindegaard , U. R. Hansen, G.

Mogensen, J . Elec t rochem. Soc. 141, 2122 (1994) .

[18] I . Yasuda, M. Hishinuma, in : Proc . Fal l Meet ing

Ceram ics Soc. Japan, K anazaw a, Oct . 1996, p . 233.

[19] J. W. Stevenson, T. R. Armstrong, L. R. Pederson,

J . Li , C. A. Lewinsohn, S . Baskaran, Sol id Sta te

Ionics 113-115, 571 (1998) .[20] A. Ahm ad-Khanlou, F. Tie tz , D. St6ver, in : Proc .

12th Int . Conf. Solid State Ionics (SSI-12), Exten-

ded Abstracts, Ha lkidiki , Greece, Jun e 1999, Inter-nat ional Socie ty for Sol id Sta te Ionics , p . 230.

[21] P. H uang, A. Hork y, A. Pet ric , J. Am . Ceram . Soc.82, 2402 (1999).

[22] A. A hmad -Khanlou, J . K oepke, F. T ie tz , to be

published.

[23] K. Yamaj i , T. Hor i ta , M. Ishikawa, N. Sakai , H.Yok okaw a, Sol id Sta te Ionics 108, 415 (1998) .

[24] K. Hua ng, R. T ichy, J . B. Gooden ough, J . A m.

Ceram. Soc. 81, 2581 (1998).

[25] O. Yam am oto, Y. Arat i , Y. Takeda, N. Im anishi ,Y. Mizutani , M. Kawai , Y. Nakamura , Sol id Sta te

Ionics 79, 137 (1995).

[26] Ch. Haering, A. Roosen, H. Schichl, M. Schn611er,

i n : P roc . 9 th CIMTEC - Wor ld Ce ramic Congres s

and Foru m on N ew Mater ia ls , ed . P. Vincenzini ,Techna Publ ishers S . r. l. , Faenza , I ta ly, Vol . 24:

8/11/2019 thermal expansion of sofc materials.pdf

10/11

138 Ionics 5 1999)

Innovative Materials in Advanced Energy Techno-logies 1999), p. 89.

[27] B. Schmid, L. O. Jerdal, R. Tunold, in: Proc. 2ndEur. SOFC Forum, Oslo, e d. : B. Thorstensen,European Solid Oxide Fuel Cell Forum, Ober-rohrdorf, Switzerland 1996), Vol. 1, p. 443.

[28] A. Naoumidis, F. Tietz, G. Stochniol, A. Gupta,Th. Hauber, in: Proc. 2nd Eur. SOFC Forum, Oslo,ed.: B. Thorstensen, European Solid Oxide Fuel CellForum, Oberrohrdorf, Switzerland 1996), Vol. 2, p.727.

[29] L. Kindermann, D. Das, R. Bahadur, R. Weir3, H.Nickel, K. Hilpert, J. Am. Ceram. Soc. 80, 9091997).

[30] Y. Teraoka, T. Nobunaga, K. Okamoto, N. Miura,

N. Yamazoe, Solid State Ionics 48, 207 1991).[31] S. Sekido, H. Tachibana, Y. Yamamura, T. Kam-

bara, Solid State Ionics 37, 253 1990).[32] I. C. Fullarton, J. A. Kilner, B. C. H. Steele, P. H.

Middleton, in: Proc. 1st Symp. Ionic and MixedConducting Ceramics, eds. T. A. Ramanarayanan,W. L. Worrell, H. L. Tuller, The Electrochem.Soc., Pennington, NJ USA), p. 9 1994).

[33] L.-W. Tai, M. M. Nasrallah, H. U. Anderson, D.M. Sparlin, S. R. Sehlin, Solid State Ionics 76,1995) 259 and 273.

[34] A. Petric, P. Huang, F. Tietz, in: Proc. 12th Int.Conf. Solid State Ionics SSI-12) , Extended Ab-stracts, Halkidiki, Greece, June 1999, InternationalSociety for Solid State Ionics, p. 292.

[35] E. Ivers-Tiff6e, W. Wersing, M. Schie[31, H. Grei-ner, Ber. Bunsenges. Phys. Chem. 94, 978 1990).

[36] J. A. M. Roosmalen, E. H. P. Cordfunke, SolidState Ionics 52, 303 1992).

[37] G. Stochniol, A. Gupta, A. Naoumidis, D. St6ver,in: Proc. 5th Int. Symp. Solid Oxide Fuel Cells

SOFC-V), eds. U. Stimming, S. C. Singhal, H.Tagawa, W. Lehnert, The Electrochemical Society,Pennington, NJ, 1997, p. 888,

[38] T. L. Wen, N. Sammes, O. Yamamoto, in: Proc.4th Int. Symp. Solid Oxide Fuel Cells SOFC-IV),eds. M. Dokiya, O. Yamamoto, H. Tagawa, S. C.Singhal, The Electrochemical Society, Pennington,NJ, 1995, p. 463.

[39] R. Chiba, T. Ishi i, in: Proc. 4th Int. Symp. SolidOxide Fuel Cells SOFC-IV), eds. M. Dokiya, O.Yamamoto, H. Tagawa, S. C. Singhal, The Elec-

trochemical Society, Pennington, NJ, 1995, p. 482.[40] G. Ch. Kostogloudis, N. Vasilakos, Ch. Ftikos, J.

Eur. Ceram. Soc. 17, 1523 1997).[41] G. Ch. Kostogloudis, Ch. Ftikos, J. Eur. Ceram.

Soc. 19, 497 1999).[42] M. B. Phillipps, N. M. Sammes, O. Yamamoto,

Solid State Ionics 123, 131 1999).[43] G. Ch. Kostogloudis, N. Vasilakos, Ch. Ft ikos,

Solid State Ionics 106, 207 1998).[44] H. Y. Tu, Y. Takeda, N. Imanishi, O. Yamamoto,

Solid State Ionics 117, 277 1999).

[45] G. Ch. Kostogloudis, P. Fertis, Ch. Ftikos, SolidState Ionics 118, 241 1999).

[46] Hammouche, E. Siebert, A. Hammou, Mater. Res.Bull. 24, 367 1989).

[47] H. U. Anderson, Solid State Ionics 52, 33 1992).[48] N. Q. Minh, J. Am. Ceram. Soc. 76, 563 1993).[49] M. Moil, T. Yamamoto, H. Itoh, in: Proc. 5th Int.

Symp. Solid Oxide Fuel Cells SOFC-V), eds. U.Stimming, S. C. Singhal, H. Tagawa, W. Lehnert,The Electrochemical Society, Pennington, NJ,1997, p. 869.

[50] A. Hartley, G. Lindsay, in: Proc. 2nd Eur. SOFCForum, Oslo, ed.: B. Thorstensen, European SolidOxide Fuel Cell Forum, Oberrohrdorf, Switzerland1996), Vol. 2, p. 557.

[51] T. Yamamoto, H. Itoh, M. Mori, N. Mori, T. Abe,in: Proc. 4th Int. Syrup. Solid Oxide Fuel CellsSOFC-IV), eds . M. Dokiya, O. Yamamoto, H.

Tagawa, S. C. Singhal, The Electrochemical So-ciety, Pennington, NJ, 1995, p. 245.

[52] D. Stolten, E. Monreal, W. Sch~ifer, in: Proc. 1stEur. SOFC Forum, Lucerne, ed.: U. Bossel, Euro-pean Solid Oxide Fuel Cell Forum, Oberrohrdorf,Switzerland 1994), Vol. 1, p. 517.

[53] C. Gtinther, G. Hofer, W. Kleinlein, in: Proc. 5th

Int. Symp. Solid Oxide Fuel Cells SOFC-V), eds.U. Stimming, S. C. Singhal, H. Tagawa, W. Leh-nert, The Electrochemical Society, Pennington, NJ,1997, p. 746.

[54] K. L. Ley, M. Krumpelt, R. Kumar, J. H. Meiser,I. Bloom, J. Mater. Res. 11, 1489 1996).

[55] W. K6ck, H.-P. Martinz, H. Greiner, M. Janousek,in: Proc. 4th Int. Symp. Solid Oxide Fuel CellsSOFC-IV), eds . M. Dokiya, O. Yamamoto, H.

Tagawa, S. C. Singhal, The Electrochemical Socie-ty, Pennington, NJ, 1995, p. 841.

8/11/2019 thermal expansion of sofc materials.pdf

11/11

Ionics 5 1999) 139

[56] H. Schmidt, B. Brfickner, K. Fischer, in: Proc. 4thInt. Symp. Solid Oxide Fuel Cells SOFC-IV),eds. M. Dokiya, O. Yamamoto, H. Tagawa, S. C.Singhal, The Electrochemical Society, Pennington,NJ, 1995, p. 869.

[57] W.J. Quadakkers, H. Greiner, M. H~nsel, A.Pattanaik, A. S. Khanna, W. Mall6ner, Solid StateIonics 91, 55 1996).

[58] S.P.S. Badwal, R. Deller, K. Foger, Y. Ram-prakash, J. P. Zhang, Solid State Ionics 99, 2971997).

[59] D.H. Peck, M. Miller, H. Nickel, D. Das, K.Hilpert, in: Proc. 4 th Int. Symp. Solid Oxide FuelCells SOFC-IV), eds. M. Dokiya, O. Yamamoto,H. Tagawa, S. C. Singhal, The Electrochemical

Society, Pennington, NJ, 1995, p. 858.[60] R. Ruckd~ischel, R. Henne, G. Schiller, H. Greiner,

in: Proc. 5th Int. Symp. Solid Oxide Fuel CellsSOFC-V), eds. U. Stimming, S. C. Singhal, H.

Tagawa, W. Lehnert, The Electrochemical Society,

Pennington, NJ, 1997, p. 1273.[61] Th. Malkow, U. v. d. Crone, A. M. Laptev, T.

Koppitz, U. Breuer, W. J. Quadakkers, in: Proc. 5thInt. Symp. Solid Oxide Fuel Cells SOFC-V), eds.U. Stimming, S.C. Singhal, H. Tagawa, W.

Lehnert, The Electrochemical Society, Pennington,NJ, 1997, p. 1244.

[62] T.A. Armstrong, J. W. Stevenson, L. R. Pederson,P.E. Raney, J. Electrochem. Soc. 143, 2919 1996)

[63] P. H. Larsen, P. V. Hendriksen, M. Mogensen, J.Thermal Analysis 49, 1263 1997).

[64] G. Pudmich, B.A. Boukamp, M. Gonzalez, W.Jungen, F. Tietz, in: Proc. 12 th Int. Conf . SolidState Ionics SSI-12), Extended Abstracts, Halkidiki,Greece, June 1999 , International Society for SolidState Ionics, p. 186.

[65] T. Ishihara, T. Kudo, H. Matsuda, Y. Takita, J .Electrochem. Soc. 142, 1519 1995).

[66] V. N. Tikhonovich, V. V. Kharton, E. N.Naumovich, A. A. Savitsky, Solid State Ionics

106, 197 1998).[67] E.K. Erdl e, in: Proc. 1st Eur. SOFC Forum,

Lucerne, ed .: U. Bossel, European Solid Oxide FuelCell Forum, Oberrohrdorf, Switzerland 1994), Vol.2, p. 937.

Ma nuscr ip t presented a t the 6 th Euroconference on S ol idState lonics Cetraro Calabria I taly Sept. 12-19 1999.

Pa per rec. Sept. 1 19 99 ; acc. Oct. 3 1999.