Jan 1, 1986 - E. JABRY, G. BOISSIER, A. ROUSSET, R. CARNET* and A. LAGRANGE*. Laboratoire de Chimie des Matériaux Inorganiques,. Université.
PREPARATION OF SEMICONDUCTING CERAMICS (NTC THERMISTORS) BY CHEMICAL METHOD E. Jabry, G. Boissier, A. Rousset, R. Carnet, A. Lagrange
To cite this version: E. Jabry, G. Boissier, A. Rousset, R. Carnet, A. Lagrange. PREPARATION OF SEMICONDUCTING CERAMICS (NTC THERMISTORS) BY CHEMICAL METHOD. Journal de Physique Colloques, 1986, 47 (C1), pp.C1-843-C1-847. .
HAL Id: jpa-00225526 https://hal.archives-ouvertes.fr/jpa-00225526 Submitted on 1 Jan 1986
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destin´ee au d´epˆot et `a la diffusion de documents scientifiques de niveau recherche, publi´es ou non, ´emanant des ´etablissements d’enseignement et de recherche fran¸cais ou ´etrangers, des laboratoires publics ou priv´es.
JOURNAL DE PHYSIQUE Collogue CI, supplement au n"2. Tome 47, fevrier 1986
page cl-843
PREPARATION OF SEMICONDUCTING CERAMICS (NTC THERMISTORS) BY CHEMICAL METHOD
E. JABRY, G. BOISSIER, A. ROUSSET, R. CARNET* and A. LAGRANGE* Laboratoire de Chimie des Matériaux Inorganiques, Université Paul Sabatier, 118 Route de Narbonne, F-31062 Toulouse Cedex, France 'Société L.C.C.-CI.CE. , (Groupe Thomson-CSF), Avenue du Colonel Prat, St Rpollinnaire, F-21100 Dijon, France
Résumé - La décomposition en atmosphère contrôlée de précurseurs oxaliques mixtes (Mn, Ni )C„0 4 , 2H 2 0 permet de préparer directement et à basse température (600-700°C) des poudres de manganites de nickel Mn 3 Nix0.((kx0.50 i.e. f o r a l l t h e compounds concerning t h e N.T.C. t h e r m i s t o r s . For h i g h manganese contents
-
i t had been i m p o s s i b l e , whatever t h e o p e r a t i n g c o n d i t i o n s , t o end up w i t h monophasic a d m i t a non oxides. These r e s u l t s c o n f i r m t h o s e a o f SARKAR / 9 / and WALCH / l o / who m i s c i b i l i t y o f t h e o x i d e s Mn304 and NiO.
Fig. 1
The n i c k e l manganites p r e p a r e d i n t h i s way a t r e l a t i v e l y l o w t e m p e r a t u r e a r e c o n s t i t u t e d of v e r y weakly agglomerated p a r t i c l e s w i t h a r e g u l a r s i z e and shape ( s m a l l octahedra 4-5 u m ) ( P i g u r e n o 1 ) . T h e i r s u r f a c e a r e a e v o l v e s w i t h t h e h e a t t r e a t m e n t a n d can b e c o n t r o l l e d b e f o r e s i n t e r i n g . I11
-
PREPARATION AND CHARACTERISATION OF THE CERAMICS
1. P r e p a r a t i o n The powders f o r m e l y o b t a i n e d f r o m 600 t o 800°C,either t h e ones p e c i a1 l y t h e ones p r e p a r e d i n c o n t r o l l e d atmosphere, were p u t i n g a n i c b i n d e r had been added, a p p l y i n g a p r e s s u r e o f 4 kb The a d i a m e t e r 0 = 0.5 cm and t h i c k n e s s e = 0.1 cm, were s u b m i t t e d t r e a t m e n t s i n a i r w i t h d i f f e r e n t p r o f i l e s ( t a b l e 11).
.
p r e p a r e d i n a i r o r esa m a t r i x a f t e r an o r r e s u l t i n g discs, w i t h t o d i f f e r e n t heat
2. C h a r a c t e r i s a t i o n T a b l e I 1 g i v e s XRD a n a l y s i s and d e n s i t i e s .
Table I1
D i f f r a c t i o n a n a l y s i s r e v e a l e d t h e presence o f s p i n e l s t r u c t u r e and t h e absence o f any o t h e r c r y s t a l l i n e compounds (NiO + Mng04). The ceramics p r e p a r e d f r o m powders o b t a i n e d i n c o n t r o l l e d atmosphere have a h i g h e r d e n s i t y t h a n t h o s e t r e a t e d i n a i r atmosphere ( f i g u r e 2 ) . High d e n s i t i e s a r e o b t a i n e d f o r r e l a t i v e l y l o w s i n t e r i n g t e m p e r a t u r e (1160°C). The g r a i n s i z e i s about 2OPm. F i n a l l y , i t i s necessary t o p o i n t o u t t h a t t h e s i n t e r i n g of t h e powders Mn304 ana NiO heat t r e a t e d i n t h e same c o n d i t i o n s (1160°C) l e a d t o i n c o m p l e t e s o l i d e - s o l i d - r e a c t i o n s and t h a t t h e d e n s i t i e s remain low, about 4.2. g.cm-3. The f i g u r e s n o 3 and 4 a l l o w s us t o d e f i n e t h e d i f f e r e n c e s o f m i c r o s t r u c t u r e observed. F i g u r e n o 4 shows a more heterogeneous g r a i n s s i z e and an i m p o r t a n t p o r o s i t y .
30URNAL DE PHYSIQUE
c1-846
density
i g . ~ : Change o f 1 Fcontent
density w i t h the nickel
S i n t e r i n g a t 1160°C, 2 H , c o o l i n g a t 30°C/h
Y
s t a r t i n g powders o b t a i n e d a t 70 C i n c o n t r o i l e d atmosphere,7,5 10 ---- sPt as rctai ln g(Pa) p o l d e r s o b t a i n e d a t 800°C 4 H i n air. -.-ceramics o b t a i n e d b y convention_al method -(TT%Fring a t 1200°C, 2 H)
Fig. 4 IV
-
ELECTRICAL PROPERTIES OF THE N.T.C.
-10~m
THERMISTORS
To deteriiline t h e e l e c t r i c c h a r a c t e r i s t i c s , t h e samples were e l e c t r o d e d w i t h s i l v e r p r i n t and f i r e d a t 800°C. The r e s i s t i v i t y i s determined by r e s i s t a n c e measurements& RS (R = r e s i s t a n c e i n ohms, S = s u r f a c e 25 + U.05OC and u s i n g t h e r e l a t i o n s h i p 0 = "
i n cmL, e = t h i c k n e s s i n cm). A second measurement done a t 85 t i o n o f t h e t h e r m a l s e n s i t i v i t y c o e f f i c i e n t B /I/. The r e s u l t s o b t a i n e d a r e shown i n f i g u r e 5 . resistivity p .7000 (n.cm)
s t a r t i n g powders o b t a i n e d a t 700°C i n c o n t r o l l e d atmosphere, 7,5 l o 3 ( P a s c a l ) Pa.
1 '\,
- 5000 4000
1
'.\.
---
\. 'I
. 3000
a l l o w s deduc-
F i g . 5 : Change of r e s i s t i v i t y w i t h t h e n i c k e l content. S i n t e r i n g a t 1160°C, 2 H c o o l i n g at30°C/h
A
-60ao
+ 0.05OC
---
s t a r t i n g powders o b t a i n e d a t 800°C, 4 H i n a i r ceramics o b t a i n e d b y conventional met hod ( s i n t e r i n g a t 1200°C, 2 H)
For s i m i l a r s i n t e r i n o and composition, we can observe s e n s i b l e d i v e r g e n c e s o f r e s i s t i v i t y which can be a t t r i b u e d t o t h e d i f f e r e n c e s o f m i c r o s t r u c t u r e . Ceramics w i t h t h e h i g h e r d e n s i t i e s e x h i b i t l o w e r r e s i s t i v i t i e s . The minimum r e s i s t i v i t y (1030 a.cm) i s t h e l o w e s t o f a l l t h e ones we have f o u n d i n t h e b i b l i o g r a p h y concern i n g t h e n i c k e l manganites. It means t h a t t h e e l e c t r i c a l p r o p e r t i e s o f t h e s e compounds were n o t o p t i m i z e d and t h a t i t i s p r o b a b l y s t i l l p o s s i b l e t o o b t a i n i n f e r i o r v a l u e s by increasing the densification. The s i n t e r i n g t e m p e r a t u r e s above 1160°C d i d not a l l o w improvementinthe e l e c t r i c a l p e r formances f r o m t h e powders produced b y chemical methods. On t h e o t h e r hand, f o r t h e ceramics p r e p a r e d f r o m s o l i d - s o l i d r e a c t i o n s between Mng04 and NiO, t h e b e s t r e s u l t s a r e observed a t a s i n t e r i n g t e m p e r a t u r e o f 1300°C, w h ~ c ha l l o w s a minimum o f r e s i s t i v i t y a t 2200 a.cm o n l y . F i g u r e 2 shows t h e r e s i s t i v i t y versus n i c k e l c o n t e n t . F o r t h e ceramics o b t a i n e d b y c o n v e n t i o n a l method and s i n t e r e d a t 1200°C, i.e. i n c o n d i t i o n s r a t h e r c l o s e t o t h o s e p r e p a r e d b y chemical method, we observe h i g h values o f r e s i s t i v i t y as w e l l a s v e r y i r r e g u l a r v a r i a t i o n s w i t h t h e n i c k e l c o n t e n t , which shows l i t t l e coherence w i t h t h e model proposed. Such c h a r a c t e r i s t i c s can be e x p l a i n e d by c o n s i d e r i n g t h a t t h e subsc o n f i r m e d by t h e t i t u t i o n o f n i c k e l i n t h e s p i n e l l a t t i c e i s n o t c o n t r o l l e d as XRD s t u d i e s On t h e o t h e r hand, whatever t h e s i n t e r i n g temperature, t h e ceramics p r e p a r e d b y che mica1 method show a minimum of r e s i s t i v i t y . T h i s appears f o r a n i c k e l c o n t e n t o f x = 0.80 whereas t h e o r e t i c a l l y t h i s minimum was expected f o r x = 0.66. T h i s d i v e r gence can be t h e r e s u l t o f a d i s t r i b u t i o n s l i g h t l y d i f f e r e n t f r o m t h e one proposed i n i t i a l l y , t a k i n g i n t o account t h e presence o f Ni2+ i o n s i n t h e t e t r a h e d r a l s i t e s f o r example and i n t h e case o f t h e compound NiMn204 i t has a l r e a d y been D ~ O D O S /I1//14/. V
-
~ ~
CONCLUSION
The p r e p a r a t i o n b y chemical process a t r e l a t i v e l y l o w t e m p e r a t u r e o f p u r e p o w d e r s d n i c k e l manganites w i t h a c o n t r o l l e d morphology has a b e n i f i c i a l e f f e c t on t h e d e n s i t y o f N.T.C. ceramics. Besides l o w e r s i n t e r i n g temperature, c l e a r l y l o w e r r e s i s t i v i t e s can be o b t a i n e d and a b e t t e r c o r r e l a t i o n o f t h e e l e c t r i c a l p r o p e r t i e s w i t h t h e n i c k e l c o n t e n t can be &served I n c o n t r a s t t o t h e c o n v e n t i o n a l process based on t h e r e a c t i o n a t h i g h temp-erature o f m i x t u r e o f manganese and n i c k e l oxides, t h i s m e t h d allows us t o break away f r o m t h e problems o f p u r i t y b u t a l s o f r o m problems o f morphology o f r a w m a t e r i a l s , which t h r o u g h t h e m i c r o s t r u c t u r e l a r g e l y i n f l u e n c e s t h e e l e c t r i c a l p r o p e r t i e s . I n t h i s way u s i n g chemical process makes t h e ~ p t i m i s a t i ~ofn e l e c t r i c a l p r o p e r t i e s of n i c k e l based manganites e a s i e r . REFERENCES /1/ /2/ /3/ /4/ /5/ /6/ /7/ /8/ /9/
/lo/ /11/ /12/ /13/ /14/
Macklen, E.D., T h e r m i s t o r s E l e c t r o c h e m i c a l P u b l i c a t i o n (1979). Yan, F. ,Mat. Science and E n g i n e e r i n g 48 (1981) 53. B o i s s i e r , G., ThSse 3Sme c y c l e T o u l o u z (1984). Kingery, W. and Uhlmann, D.R., John W i l e y and Sons Inc. New York (1975). Haussonne, J.M., Rev. I n t . Hautes Temper. R e f r e a c t . 21 (1984) 95. V i l l e r s , G. and Buhl, R., C.R. Acad. S c i . P a r i s t 26U-(1965) 3406. B a f f i e r , N. and Huber, M. , J. Phys. Chem. S o l i W ( 1 9 7 2 ) 737. Boucher, B., Buhl, R. and P e r r i n , M., A c t a C r y s t . 825 (1969) 2326. Sarkar, S.K., Sharma, M.L., Bhaskar, H.L. and N a g p K K.C., J. o f Mat. Science 19 (1984) 545. G l c h , H., Siemens L e i t s c h u f t 47 n o 1 (1973) 65. Larson, E.G. A r n o t t , R.J. and mckham, D.G., J. Phys. Chem. S o l i d s 23 (7%2)1771. D u n i t z , J.D. and Orgel, L.E., J. Phys. Chem. S o l i d s 3 (1957) 20. Jabry, E., ThSse D o c t o r a t I.N.P. de Toulouse (1985). Brabers, V.A.M. and T e r h e l l , J.C.J.M., Phys. S t a t . S o l . ( a ) 69 (1982) 325.
