STRUCTURAL, ELECTRONIC AND MAGNETIC PROPERTIES OF THE LINEAR CHAIN COMPOUNDS CsMI3(M = V, Cr, Mn) FROM 129I MÖSSBAUER SPECTROSCOPY

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STRUCTURAL, ELECTRONIC AND MAGNETIC

PROPERTIES OF THE LINEAR CHAIN

COMPOUNDS CsMI3(M = V, Cr, Mn) FROM 129I

MÖSSBAUER SPECTROSCOPY

J. Sanchez, J. Friedt, G. Jehanno

To cite this version:

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JOURNAL DE PHYSIQUE Colloque C2, supplement au n O 3, Tome 40, mars 1979, page C2-398

STRUCTURAL, ELECTRONIC

AND

MAGNETIC PROPERTIES

OF THE LINEAR CHAIN

COMPOUNDS CSMI

3 ( = ~

V,

Cr, ~ n ) FROM 1291

MOSSBAUER

SPECTROSCOPY

J.P. Sanchez, J.M. Friedt and G. ~ehanno*

Laboratoire de Chimie NucZBaire, Centre de Recherches NucZgaires, B.P. 20, 67037 Strasbourg Cedex, France.

'service de Physique du Solide e t de RBsonance Magne'tiqw, Centre dfE$udes Nucle'aires de Saclay, h e des Merisiers, B.P. 2, 91190 Gif-sup-Yvette, France.

Rdsumi5.- L'analyse des spectres Mgssbauer de 12'1 dans les compos6s CsM13 (M = V, Cr, Mn) a permis de dGduire la symGtrie locale de l'ion de transition. Une Qtude compldmentaire par diffraction de rayons X a montrG que CsCrI3 prdsente une transition de phase cristallographique P 165 K. Un ordre magndtique a 6tG mis en 6vidence dans CsCrI3 et CsM.n13. Les densitds de charge et de spin dans les orbitales de valence de l'iode ont 6tQ d6duites B partir des paramstres d'interactions hyperfines. Un arrangement antiferromagn6tique des moments le long de l'axe des chabes est sugg6r6 pour CsMnI3. Abstract.- The coordination symmetry of the M2+ ion in the compounds CsMI3 (M = V, Cr, Mn) is dedu- ced from 12'1 Mzssbauer spectroscopy. For CsCrI3, a crystal phase transition is observed at 165 K -

Magnetic transitions are observed for CsCrIs and CsMnIs. The hyperfine interactions parameters are interpreted for the charge and spin densities in the iodine valence orbitals. An antiferromagnetic alignement of the spins along the chain axis is suggested for CsMnIs.

The compounds CsM13 have attracted much interest in patible with either structure proposed from X-ray view of their linear chain structure which gives diffraction study performed at 300 K /I/.

rise to predominantly one dimensional electronic and magnetic properties.

From previous single crystal X-ray diffraction stu- dies of CsV13 and CsMn13, it was concluded that the space group of these compounds is either P631mmc or P63rnc /I/. However, for CsMn13, a more recent work has showed that the centrosymmetric P63/mmc space group gave the best agreement with the measured in- tensities /2/. For both structures, the transition metal ion is surrounded by a distorded octahedron

of halide ions. However, the M-1-M bridges are sym- _W,/mmc

"=a= PO122

metric for the space group P63/mmc whereas they are asymmetric for the lower symmetry P63mc space group (figure 1 )

.

The 'I Gssbauer measurements on powder samples reveal for both CsVI3 and CsMn13 a single crystallographic iodine site with a positive quadrupole coupling constant (figure 2). These results allow to conclude that both compounds crystallize in the space group P63/mmc.

The "'I ~6ssbauer spectra of CsCr13 measured below

100 K reveal the existence of two non-equivalent crystallographic iodine sites with relative occupa- tion 1 : 2 (figure 2). The 27.8 keV Gssbauer reso- nance cannot be measured at higher temperatures because of the sharp decrease of the Debye-Waller factor. The occurence of two iodine sites is incom-

Fig.1 : Partial view of the linear chain showing the coordination symmetry of the transition metal ion for various space group.

Indeed, our investigation of the powder X-ray diffraction of CsCrI3 as a function of temperature reveals a crystal phase transition at 165

+

5 K from a high temperature hexagonal phase (a = 8.12 c = 6.85

1)

to a low temperature phase of lower symmetry (likely orthorhombic). In the low temperature phase the coordination of the cr2+ ion is de- duced from the ~gssbauer results to be an axially disforted octahedron (figure I), similar for ins- tance to that of Cu in CsCuC13 which crystallizes in the P6122 space group. A static Jahn-Teller

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d i s t o r t i o n may e x p l a i n t h e c r y s t a l phase t r a n s i t i o n . Table I F i g . 2 : Msssbauer s p e c t r a of 1 2 9 ~ i n CsMI.3. a ) CsCrI3 a t 77 K b) CsMn13 a t 21 K c) CsMnIB a t 1.4 K a s s u m e d value.

Charge and s p i n d e n s i t i e s a t '"I i n C s M I , (M = V , C r , Mn). N s and Np+ r e p r e s e n t t h e charge d e n s i t i e s i n t h e 5 s and 5pr v a l e n c e o r b i t a l s of i o d i n e . f c and f n a r e t h e s p i n d e n s i t i e s i n t h e 5p0 and 5pT o r b i t a l s r e s p e c t i v e l y . f,-f,

-

1.5~10-' References N PV 1.90 2* 1.84 1.90 / I / Mc Pherson, G.L., S i n d e l , L.J., Quarls, H.F., F r e d e r i c k , C.B. and Doumit, C . J . , Inorg. Chem.

14 (1975) 1831.

-

C o m p o u n d C S V 1 3 a

-

s i t e c s C r 1 3 b - s i t e C s M n 1 3

Magnetic o r d e r i n g i s observed i n CsCrI3 and CsMnT.3; t h e 3d-order temperatures a r e 18 and 10 K r e s p e c t i - v e l y . Due t o t h e poor s p e c t r a l r e s o l u t i o n connected w i t h t h e low symmetry of t h e

cr2+

i o n , t h e a n a l y s i s of t h e magnetic d a t a i n CsCrIs i s u n c e r t a i n . I n CsMn13, t h e i n t e r p r e t a t i o n of t h e t r a n s f e r r e d hyper- f i n e f i e l d a t t h e 12'1 nucleus i n d i c a t e s an a n t i - ferromagnetic s p i n arrangement w i t h i n t h e c h a i n s , with t h e magnetic moments of t h e Kn2+ i o n s d i r e c t e d p a r a l l e l t o t h e c h a i n a x i s .

The charge d e n s i t i e s i n t h e valence o r b i t a l s of

Npz

*

2 1.81 2 2 N, 1.99 1.99 1.99 2 i o d i n e a r e o b t a i n e d from t h e a n a l y s i s of t h e isomer s h i f t and quadrupole i n t e r a c t i o n parameters. The

N PZ 1.84 1.93 1.80 1.84

/ 2 / S e i f e r t , H . J . and Kischka, K.H., Thennochim. Acta, i n p r e s s .

/ 3 / Sanchez, J . P . , Djermouni, B . , F r i e d t , J . M . and Shenoy, G.K., Hyperfine I n t e r a c t i o n s

1

(1976) 313; F r i e d t , J.M. Sanchez, J . P . , and Shenoy,G.K., J . Chem. Phys.

65

(1976) 5093.

s p i n d e n s i t i e s a r e e v a l u a t e d from t h e t r a n s f e r r e d magnetic h y p e r f i n e i n t e r a c t i o n 1 3 1 . Q u a n t i t a t i v e e s -