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X-RAY ABSORPTION STUDY OF FREE AND BOUND SULPHUR IN MoS2+x (0 ≤ x ≤ 1)
P. Belougne, B. Deroide, J. Esteva, R. Karnatak, J. Zanchetta
To cite this version:
P. Belougne, B. Deroide, J. Esteva, R. Karnatak, J. Zanchetta. X-RAY ABSORPTION STUDY OF FREE AND BOUND SULPHUR IN MoS2+x (0≤ x≤1). Journal de Physique Colloques, 1987, 48 (C9), pp.C9-1049-C9-1052. �10.1051/jphyscol:19879190�. �jpa-00227307�
JOURNAL DE PHYSIQUE
Colloque C9, supplgment au n 0 1 2 , Tome 48, dbcembre 1987
X-RAY ABSORPTION STUDY OF FREE AND BOUND SULPHUR IN MoS,+, ( 0 5 x 5 1 )
P. BELOUGNE*, B. D E R O I D E * , J.M. ESTEVA, R.C. KARNATAK and J
.
V. ZANCHETTA*Laboratoire d e Spectroscopie Atomique et Ionique and LURE, Universitt5 Paris-Sud, F-91405 Orsay Cedex, France
* ~ a b o r a t o i r e d e Chimie Physique USTL, Place Eugene Bataillon, F-34060 Montpellier Cedex, France
RESUME
Le spectre de photoabsorption X pres du seull
K
du soufre (XANES), presente des structures indiquant la presence de plusieurs degres de charge. Le spectre obtenu en retranchant la contribution de MoS2 du spectre de MoS3 est compare A celul du souf r e natif. Cette comparalson indique que le souf r e addi tlonnel dans MoS3 presente une coordination proche de celle du soufre natif et qu'il est probablement faiblement lie.ABSTRACT
The X-ray near K edge structure of S in MoS9 and MoS7 show features
-
indicating different charge states. The Moss-MoS2 difference spectrum i s compared to the K edge spectrum of native sulphur. From this comparison it i s concluded that the additional S atom In MoS3 has-similar coordination as in native sulphur and i s probably weakly bound
.
l NTRODUCT ION
The transition metal chalcogenides are generally used as catalysers In petroleochemistry. They are also employed i n photoconverslon of energy or as the electrode materials in the traditional accumulators. In the family of such compounds we were particularly interested i n the transport phenomena in MeS2+i (Me= Mo,W ;
O<x<l whose structure varies from amophous MeS3 to crystalline MeS2.These
comoounds are generally obtained by thermal d e ~ ~ m ~ ~ ~ i t i ~ n of ammonium thiornolybdate (NH4)MeS4 (1.2).
We recently studied the electrical conductivity of these componds as a f unctlon of the frequency and the temperature. This study(3~4) demonstrated that the electrlc conduction i n these compounds i s by a hopplng type of mechanism between the localized states.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879190
C9-1050 JOURNAL DE PHYSIQUE
Our electron paramagnetic resonance (EPR) s t ~ d i e s ( ~ ~ ~ ) showed the existence, i n MoS3 of the paramagnetic centers n o v and possibly the unbound sulphide radical. Although the XPS (X-ray photoelectron spectra), EXAFS (Extended X-ray Absorption Fine Structure) and X-ray RDF ( radial dtstribution function) s t u d ~ e s ( ~ - ~ ) were performed on these compounds, 1t seemed t o us approprlate t o look into the X-ray near edge structure t o elucidate further the state of sulphur bonding I n these compounds.
EXPERIMENTS
The S-K edges and Mo LI II edges were obtained from powder samples of MoS2
,
MoS3 and native sulphur by photoyield method using the synchrotron radiation from the ACO storage ring at ORSAY. A double crystal monochromator ( Ge ( 1 1 1)) was used to monochromatise the synchrotron radiation.RESULTS AND Dl SCUSSION
As an example the S-K edge and Mo Ll I I edge from MoS2 and MOS3 are given In Fig. 1. The Mo LllI edge practically remains unchanged i n both componds ( Fig. 2).
I
Figure IJU---J
nos2
PhotonEnergy
2450 2500 2550 2600
Figure 2
; ' -
\ - -
.
Nos3L
i
MoS2
PhotonEnergy
The S-K edge shows an appreciable change (Fig. 3) in i t s form and position on golng from MoS2 to MoS3. In case the additional S atom In MoS3 remains unbound then we would expect to observe f o r this compound a S-K edge formed of an edge from S in MoS2 like environment and elemntal S. So we f i r s t normalised the MoS,
L
and MoS3 spectra tn intensity at the Mo L l I l edge i n order t o take Into account the variation of the source intensity and the difference of the surface states of the two samples. We then plotted the MoS3-MoS2 difference and compared w i t h the K edge spectrum of native sulphur i n Fig. 4.
We see that there i s a good agreement i n the shape and position of the maln line of the difference spectrum and the native sulphur spectrum. However, we observe an additional weak structure A on the low energy side of the main line. On the higher energy side of this line some increase i n the absorption hight and appearance of a weak broad structure a t 2486 eV ts also noted.
C9-1052 JOURNAL DE PHYSIQUE
From these results we conclude that two type of S atoms w i t h different charge states are present i n MoS3. The similarity between the main line of MoS-(-MoS., "
-
difference spectrum and that of the native sulphur indicates that the additional S atom i n MoS3 has somewhat similar coordination as i n the native sulphur. The additional weaker features i n the difference spectrum indicate the presence of some additional p symmetry vacant states which may be the indication of a weak bonding.REFERENCES
I . P.Belougne, Thesis, Montpellier 1985 2. B.Deroide, Thesis, Montpellier 1986 3. P.Belougne et al, Phil Mag. B 52-3( 1986) 233 4. B.Deroide e t a1
