EXAFS STUDIES OF DISORDER IN CRYSTALLINE LAMELLAR COMPOUNDS OF THE MPS3 FAMILLY

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EXAFS STUDIES OF DISORDER IN CRYSTALLINE LAMELLAR COMPOUNDS OF THE MPS3 FAMILLY

Y. Mathey, H. Mercier, A. Michalowicz

To cite this version:

Y. Mathey, H. Mercier, A. Michalowicz. EXAFS STUDIES OF DISORDER IN CRYSTALLINE

LAMELLAR COMPOUNDS OF THE MPS3 FAMILLY. Journal de Physique Colloques, 1986, 47

(C8), pp.C8-875-C8-878. �10.1051/jphyscol:19868169�. �jpa-00226073�

EXAFS STUDIES OF DISORDER IN CRYSTALLINE LAMELLAR COMPOUNDS OF THE MPS, FAMILLY

Y. MATHEY, H. MERCIER and A. MICHALOWICZ*

Laboratoire SET, CNRS - U A 420, Universite Paris-Sud, F-91405 Orsay Cedex, France

" L U R E (CNRS, CEA and MEN), F-91405 Orsay France and

Laboratoire d e Physicochimie Structurale, Universite Paris XII, F-94000 Creteil, France

R e s d

Quelques composes de la famille MPS3 partiellement substitues ont BtB etudies conjointement par EXAFS et par diffraction des rayons X et par leurs proprietes magnetiques dans le cas de la serie NixCdl-PS3.0n a pu ainsi caracteriser le plus completement possible l'ordre local de llesp&ce substitube repartie au hasard dans la matrice hdte.

Abstract

Some partially substituted MPS3 familly compounds were studied both by EXAFS and X-ray diffraction used in conjunction and also by their magnetic properties in the case of the Ni,Cdl-,PSg series.It was then possible to characterize the local stucture of the diluted ion randomly distributed in the host matrix.

On account to their attractive topochemical,optical electric and magnetic properties layered systems of the MPS3 family have been the subject of intense investigations in the recent period.

EXAFS appears to play an invaluable role in the study of disorder problems in such compounds

It has been used first to detect local distortions induced by intercalation process [11 and to correlate these distortions to the magnetic properties of such compounds [2].EXAFS was also particularly useful1 to characterize the partially substituted NixMnl-xPS3 phase obtained by a "soft chemistry

method [3l,in aqueous solution.Another way to obtain such partially sustituted MPS3 derivatives is to synthetise them directly from the elements at high temperature

(700 K).Following this route two classes of compounds will by presented

I) Cu0.26 Mn0.87PS3 [41 where the irreductible apparent mismach between EXAFS and single crystal X ray diffraction determinations of the Cu-S distance (respectively 2.22 and 2.07 A) was analysed in term of a random distribution of 13% of S3Cu-CuS3 and 87% of octahedral MnS6 sites.Recently the crystal structure of Cu05Cr0.5PS3 was reevaluated in the same way [5] .In this case the Cr ions were found to be located in ordered crystallographic positions and the random distribution involved octahedral Cu ions,Cu-Cu pair and thus metal-free sites.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19868169

C8-876 JOURNAL DE PHYSIQUE

The use in conjunction of EXAFS and X-ray diffraction presented in these studies - already published

is illustrated in figure I.It can be generalized for all the partially substituted compounds of the MnPS3 familly involving some structural disorder as in the compounds presented in section 11.

Mismatch b e t w e e n EHRFS and X-Ray Diffraction

2.64 A

CU-S 2.22 A 2.07 A

Rueraged H R D structure

Corrected structure w i t h EHAFS distances (values in parentheses are e s t i m a t e d b y assuming homothetic Cu and M n sites 1

FIGURE I

diamagnetic CdPS3 matrix,with a cd2+ ionic radius (0.97 A) much larger than

~ i (0.72 A) ~ + .Optical properties, XANES spectra and X-ray powder diffraction of the series are already published [6-b1.The nickel edge EXAFS results presented in this work are obtained in the fluorescence mode since the cadmium matrix is too much absorbant for transmission.The spectra were recorded on the EXAFS I1 port at LURE with a NaI scintillation detector kindly provided by Dr R.Cortes.

Optical and XANES spectra support a regular dependence of the ligand field upon the susbtitution rate x and a simple correlation between x and the Ni-S distance

(

assumed to follow Vegardts law ),was expected.It turns out that neither powder diffraction unit cell dimensions nor fluorescence EXAFS Ni-S distances follow this law (table I).EXAFS Ni-S distances are significantly shorter than expected from a continuous x dependence and than the averaged crystallographic metal-sulfur distance h his result comfirms the random distribution of the diluted Ni ions.

The stuctural properties of NiXCdl-,PS3 derivatives where completed by their magnetic properties [6-a1.These compounds exhibit a ferromagnetic behaviour.This indicates that the Nickel ions are not isolated and must be coupled as dimers or linear chains.(2D Ni clusters would lead to antiferromagnetic properties).The complete structural picture of these compounds,each technique giving as fraction of the total information,is then a random distribution of small chains of coupled ions with a local structure similar to that of pure Nips3 (fig(11)).

*the 20% compound was synthetized using the soft chemistry method

131

FIGURE I I

m o e e e s e

Ni

@ cd

C8-878 JOURNAL DE PHYSIQUE

A s

a l r e a d y d e p i c t e d with v a r i o u s systems (metal a l l o y s [ 7 ] , semi-conductors [8] and a l k a l i halides[9]),EXAFS is needed t o probe t h e l o c a l s t r u c t u r e of p a r t i a l l y s u b s t i t u t e d M P S 3 cornpounds,since X r a y d i f f r a c t i o n g i v e s o n l y an average p i c t u r e of t h e s t r u c t u r e . I n some f a v o r a b l e c a s e s ( a s Cuo.26 Mn0.87PS3 s i n g l e c r y s t a l s

t h e use of t h e s e two s t r u c t u r a l techniques a r e s u f f i c i e n t t o g i v e a complete p i c t u r e

more d i f f i c u l t c a s e s o t h e r p h y s i c a l p r o p e r t i e s a r e a l s o needed.

[I] A. MICHALOWICZ and R. CLEMENT ,

1norg.Chem (1982) ,a, 3872 [2] A. MICHALOWICZ and R. CLEMENT

J.of Inclusion Phenomena , (1986) in press [3] R. CLEMENT and A. MICHALOWICZ

Rev.Chim.Min, (1984) ,a, 426

[4] Y. MATHEY,A. MICHALOWICZ,A. TOFFOLI and G-VLAIC, Inorg-Chem. (1984) ,=, ⁸⁹⁷

[5] Y. MATHEY,H. MERCIER,A. MICHALOWICZ and A. LEBLANC J.Phys.Chem.Solids, (1985) ,GI 1025

[6] a) H. MERCIER , Th&se, Universit6 Paris-Sud, (1985) , ^ORSAY

b) H. MERCIER and Y. MATHEY Nouv. J. Chim., (1986) , ^{in press}

[7] D. RAOUX,A. .FONTAINE,P. LAGARDE,A. SADOC,Phys. Rev., (1981),~,5547 [8] J.C. MIKKELSEN, JR. and J. B. BOYCE ,Phys.Rev, (1983) ,a, 7130

[9] a) T . ^{MURATA, P} . ^LAGARDE, A. FONTAINE, D . ^RAOUX, "EXAFS and Near Edge Spectroscopy I1 ",Springer Verlag1(1983),p 271

b) T. MURATA, "EXAFS and Near Edge Spectroscopy I11 ", Springer Verlag,

0

(1985) , p 432