Synthetic Metals, 34 (1989) 525 ~ 530
MAGNETfC BEHAVIOUR OF A STAGE-I NiCI 2 GRAPHITE INTERCALATION
M. EL HAFIDI*, G. CHOUTEAU** and R. YAZAMI*** *
Universit~ Hassan H, Casablanca
Service National des Champs Intenses, Scientifique,
National de la Recherche
associ~ ~ l'Universit~ Joseph Fourier, Grenoble) *** Laboratoire d'Ionique et drElectrochimie Ecole Nationale
BP 75, 38402 Grenoble C~dex
(U.A. CNRS 1213),
first-stage NiCI 2
GIC was prepared using very fine natural graphite
It is shown that three parameters are of importance in determining
: the specific area of the graphite,
competing with antiferromagnetic ones. The ordering temperature
interactions is found to
be 17,85 K by ac. susceptibility measurements. INTRODUCTION NiCI 2 sealed
first intercalated into graphite by Stumpp et al [i] using a
a wide temperature
and also the
Flandrois et al .
studies only stage-2 GIC was prepared and has been for a
while considered as the richest NiCI2-GIC. The presence of chlorine gas in the reactor was shown to play a key role in the activation of the reaction As
that the catalytic effect of
during the intercalation of NiCI 2 was enhanced by increasing both
and the graphite specific
surface area (<400 m~.g -I ). Under these conditions, stage-i
GIC was achieved.
stage-I and 2 or pure stage-2 or a
grain size are small stage-I
synthesis of rich
because their specific surface
. Endo et al also succeeded in the synthesis of highly
Natural or pyrolytic graphites give mixtures of
graphite fiber of iO00 A diameter 500°C and the
350 tort of p(Cl2)
© Elsevier Sequoia/Printed in Tile Netherlands
stage-i NiCI 2
as cathode material
paper we will briefly redescribe
in lithium batteries
stage-i GIC and show some of its structure characteristics properties
and the magnetic
on the stage-2 one
the aim of checking the effect of the graphite origin on the final
products under week
after the intercalation,
graphites were allowed to react
the same conditions i.e. iO atm of chlorine at 7OO°C, during one : I) fine powder (3 ~m) of high specific surface area (400 m2.g -1 ),
2) Natural graphite from Ceylan with granulometry
(7×7×.4 mm 3) provided by Union Carbide. The amount of anhydrous calculated to obtain the molar ratio C/Ni-3.5. After
water and methanol.
The structure Electron
The magnetic measurements coil.
in a dilute
The final compound was vacuum
The composition was determined by elemental ducting
NiCI 2 was removed by washing successively
NiCI 2 was
by X-Ray Diffraction
i Mev) for the finest powder. analysis of C, Ni and CI.
were performed at SNCI using a 13 T supercon-
RESULTS and DISCUSSION i. GIC characterization From
(Cu, K~) it was clearly shown that only FPHS graphite
the amount of stage-2 IOO with
increases with the grain Fig. i displays
parameter in the c-direction (interlayer spacing) Ic = 9.37 A. The broadening of the strongest 002 line at higher angles should be due to some stacking defects of the NiCI 2 domains. The chemical analysis of this compound leads to a rough formula C~. 9 NIC12.35 which implies a filling factor of 70 % close to that of stage-2 . The larger departure from stoiehiometry in this GIC (CI/Ni - 2.35) is directly related with the higher chlorine cointercalation when FPHS and high chlorine pressure were used. However, if the Flandrois's islandic model [2 - II] is applied, the calculation of the island size from the CI/Ni ratio would give 35 - 40 A. This was not observed in our sample by the HREM lattice image depicted in fig.2-a.
Fig. I X-ray diffraction (Cu, K) chart of stage-i NiCI2-GIC. The calculated lattice constant in the c-direction gives Ic=9.37 ~.
Fig. 2 a) High resolution electron microscopy lattice image NiCI2-GIC, some stacking defects show a random presence compound, b) 001 spots obtained by electron diffraction NiCI2-GIC.
NiCI 2 side.
of the as
determined NiCI 2 not
stage-i stage-2 stage-I
and shows the
stacking along the c-axis. The stage number is indicated on the left Some stage-2 domains remain in the GIC which is consistent with the
of of of
002 line in the XRD chart in fig.l. Taking the pristine
internal stages by XRD.
domains which exclude
Ic values were 9.2 and
would result from small size islands.
notice any discontinuities
some Ni z+ vacancies
Therefore we do
inside the NiCI 2 domains
(or islands) to explain the excess of chlorine. The in-plane crystal structure is determined from the electron diffractogram. NiCI 2 and graphite hexagonal superlattices are shifted by an angle of 30 degrees, which is in agreement with the XRD data [2 ° 12]. So the calculated lattice parameter a of NiCI 2 is found here equal to 3.50~_.O5 A.
528 2. M a g n e t i c m e a s u r e m e n t s Figure
the m a g n e t i z a t i o n
curve o b t a i n e d at 4.2 K in a m a x i m u m
f i e l d of Ii teslas. The f e r r o m a g n e t i c b e h a v i o u r the
m a g n e t i z a t i o n and
M = M s + Xh~ .H
: above 3 teslas where
s u p e r i m p o s e d p a r a m a g n e t i c susceptibi-
One finds M s = 8520 emu / mole c o r r e s p o n d i n g to an average m o m e n t of
1.53 lab per n i c k e l atom. On the other h a n d Xh f = .01076 emu / mole w h i c h is a
v e r y h i g h v a l u e w h e n c o m p a r e d w i t h the usual h i g h field s u s c e p t i b i l i t i e s
of t r a n s i t i o n metals.
413 J E al
i--I I-LIJ Z CO n-
2 T = 4.2
~ O.D IT]
3 H i g h f i e l d m a g n e t i z a t i o n at T - 4.2 K in emu/g.
low f i e l d
m o m e n t ~e~f The
static s u s c e p t i b i l i t y where
law, Xs t = X o + C/(T - 8)
c o r r e s p o n d s to the e f f e c t i v e
= 3.7 ~ , 0 = 41.5 K and Xo = Xh f .
than those of Ni z+
5.59 r e s p e c t i v e l y ) . On
we have r e p o r t e d the static s u s c e p t i b i l i t y in v e r y low fields .5
a r o u n d 20
field c o o l e d
K. The with
K. The zero f i e l d c o o l e d s u s c e p t i b i l i t y is one s h o w i n g
of a r e m a n e n t
m a x i m u m in X, t occurs at T N = 17.5 ± the
field. The ac. s u s c e p t i b i l i t y
f r e q u e n c y range iO Hz - 52 kHz exhibits a w e l l p r o n o u n c e d
at T - 17.85 K, independent of the f r e q u e n c y and in g o o d a g r e e m e n t
w i t h the static measurement.
Fig. 4 Static s u s c e p t i b i l i t y per gram. in two fields showing the m a x i m u m a r o u n d T - 17,5 ± 0.5 K and the r e m a n e n t m a g n e t i z a t i o n near 20 K.
0.5 mT and 2 mT appearance of the
low m a g n e t i c m o m e n t s and the h i g h Xh f c a n be i n t e r p r e t e d in two ways The c r y s t a l - f i e l d
O n l y the
s p l i t t i n g is lowest levels
Thus Xo a n d Xh f
d i f f e r e n t in the NiCI 2 GIC than in the are o b s e r v e d
at low t e m p e r a t u r e in the
are v a n V l e c k terms. T h e r e f o r e one s h o u l d observe an a
The NiCI 2
of the MCI 2 GICs, and
a m e t a l l i c character,
as it is the
thus the nickel m o m e n t is r e d u c e d w i t h respect
one b e c a u s e of the c o n t r i b u t i o n of the c o n d u c t i o n electrons.
X o (or Xhf)
u n u s u a l l y h i g h v a l u e of Xh~ , however, R e c e n t results of
the c o n d u c t i o n
case i) and case ii). The
favors case i).
(13) do not agree well w i t h ours. We think that the c o m p o u n d
p r o b a b l y consists
w h y the
authors find comparison with
in a m i x t u r e of stage-i and stage-2 and may an o r d e r i n g
(16), shows that, as expected,
do not a l l o w for a d i s t i n c t i o n
t e m p e r a t u r e T N = 22.5 K h i g h e r
the p r o p e r t i e s of stage-2 compounds
of the interlayer distance.
T N decreases w i t h the stage due to the For instance we find T N = 17.85 K for
the s t a g e - i and T~ - 16.5 K for the stage-2.
ACKNOWLEDGEMENTS One of us (YR) wishes to thank Dr. Audier (LTPCM, Grenoble) for his help in the HRME experiments and numerous discussions, Dr. Maire from Carbone Lorraine for providing FPHS graphite and Prof. P. Touzain (S2MC, Grenoble) and Prof. A. Hamwi (Clermont-Ferrand) for stimulating discussions concerning NiCI2-GICs. R. Tur has done the magnetic measurements. REFERENCES [i]   
   [I0] [ii]  
  
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