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CHALCOGENIDE AND OXYCHALCOGENIDE GLASSES : EVOLUTION OF THE GALLIUM SURROUNDING WITH THE OXYGEN CONTENT
S. Benazeth, M. Tuilier, H. Dexpert, M. Guittard, D. Carre
To cite this version:
S. Benazeth, M. Tuilier, H. Dexpert, M. Guittard, D. Carre. CHALCOGENIDE AND OXYCHALCOGENIDE GLASSES : EVOLUTION OF THE GALLIUM SURROUNDING WITH THE OXYGEN CONTENT. Journal de Physique Colloques, 1986, 47 (C8), pp.C8-419-C8-422.
�10.1051/jphyscol:1986884�. �jpa-00226206�
JOURNAL DE PHYSIQUE
Colloque C8, suppl6ment au n o 12, Tome 47, dbcembre 1986
CHALCOGENIDE AND OXYCHALCOGENIDE GLASSES : EVOLUTION OF THE GALLIUM SURROUNDING WITH THE OXYGEN CONTENT
S. BENAZETH, M.H. TUILIER*, H. DEXPERT*, M. GUITTARD and D. CARRE
Laboratoire d e Chimie Minerale Structurale (U.A. ZOO), Faculte des Sciences Pharmaceutiques et Biologiques de Paris V ,
4, Avenue de llObservatoire , F-75270 Paris Cedex 0 6 , France 'LURE (CNRS, MEN, CEA), Url.iversite Paris-Sud, F-91405 Orsay Cedex , France
R"esum6
L'analvse structurale des verres de sulfure de terre rare par EXAFS met en dvidence un environnement sulfur6 tgtragdrique pour le gallium. Lorsqu'on opere une substitution partielle du soufre par l'oxygene, cet environnement kvolue
:le gal- lium se place dans des sites octa6driques distordus. De plus, nous avons pu pr6pa- rer un materiau existant 5 la msme composition dans les deux dtats, vitreux et cris- tallin
;l'analyse a alors r6vgl6 un polyedre de coordination plus r6gulier dans 1'6tat vitreux.
Abstract
Structural analysis of rare earth sulfide glasses shows a sulfur tetrahedral surrounding for the gallium atomwhen sulfur is svbstituted by oxygen this surroun- ding changes
:gallium occupies excentred position in octahedral sites. Moreover, we could prepare a material within the two states (glassy and crystalline) for an identical composition
:analysis revealed a more regular coordination polyhedron for the glass.
Introduction
We synthetised glasses by addition of gallium sulfide to rare earth sulfi- des (1). More extended glass forming regions occur by substituting sulfur atoms by oxygen atoms
(2);The glasses may then be obtained after slow cooling (5'/min) with
(v*) or without (V1) thermic effect by D.T.A. in increasing temperature (Fig. 1).
From the vibration spectra (11, different structural informations have been already given and present some discrepancies. EXAFS studies have been undertaken at K edge gallium and LIII edge lanthanum to better describe local order around these atoms. This paper just describes gallium surrounding.
Experimental
Powder samples were sifted (diametral granulations < 25 pm) both for glassy and crystalline types and then disposed between two pieces of adhesive tape. The four gLassy samples studied have a constant metallic composition (n
=Ga/(Ga + La)
=0.64) and various ones for the oxygen and sulfur atoms (0,< m
=0/(0 + S) < , 0.45).
The m
=0.14 compound (melilite type) exists both within glassy and crystalline states. In order to ensure model for Ga-S surrounding, we used of a crystalline corn;
pound La6Ga3.33S,, where gallium is shared between tetrahedral and octahedral sites.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986884
JOURNAL DE PHYSIQUE
Figure 1 - Phase diagram of the system La2S3-La203-Ga 2 3 0 -Ga 2 3
Sand glass forming region
Spectra were registered in transmission mode, at room temperature, using synchrotron radiation, emitted by the DCI storage ring at LURE. EXAFS spectra origin (see for instance, figure 8) was-chosen at maximum K edge gallium and measurements stretched over
500ev. The data, after clasgical treatment, were Fourier transfor- med using k3 weighting and an identical Haning window (22, 33, 460,
500eV) for all studied samples (Figures 2 to 7). The peaks situated on the graphs at Rapp
1.30A
are attributed to oxygen neighbours and the higher other ones at Rapp
E1.85 to sulfur neighbours. Their relative intensities depend on
mvalues. By using least- square procedures fitting we adjusted a structural calculated EXAFS model to the one-shell filtered experimental EXAFS (see for instance figures 9 -
10).Amplitude and phase shifts for the Ga-S pair are extracted, following the same EXAFS analysis, from a crystalline reference compound. We were governed in the choice of that refe- rence by existence of a quasi-regular Ga-S tetrahedral coordination. Among numerous crystalline compounds synthetised in the laboratory, La6GapMnnS1k (4) was the best, in that point of view the simple binary com~ound Ga2S3 was thus excluded ( 5 ) . For the Ga-0 pair, GanOs was notbnvenient because in the more stable phasis, gallium occupies both tetrahedral and octahedral sites and this behaviour is frequent for oxygen surrounded gallium. ?or this reason we used of theoretical parameters for that pair.
Discussion
The main results for evolution of sulfur and oxygen number neighbours N(O + S) are presented in table I.
\hen m
= 0we found that gallium is fourfold coordinated. For increasing m values,
N ( S )decreases. In order to interpret that behaviour we studied La6Ga3.33S1,:
in that crystalline compound gallium occupies a such distorted octahedron that it is
better described by a triangular coordination. We applied that model, which agrees
with a lower sulfur coordination, to the glassy samples. Therefore, for the highest
m values, gallium shows both tetrahedral and octahedral coordinations for oxygen and
sulfur atoms, and competition sites phenomena explain glass stability in that
region (Figure 1).
Table
I1presents comparative results for melilite type compounds. We observe that the oxygen and sulfur neighbourhood contributions are better resolved in the glassy state. The local surrounding remains the same and is consistent with diffrac- tion X structural analysis results (6). Nevertheless the isotropy of the coordina- tion polyhedra increases in the glass. as evidenced by the smaller disorders, 1 aa1 ,com- pared to the crystal.
Table I - Procedure fitting results for various m
Table I1 - Procedure fitting results for m
=0.14 (crystal - glass)
Np'5 - 0.5
4.0
4.0
3.9
3.6
2.9
1
References
1)
J. Flahaut, M. Guittard, A.M. Loireau-Lozac'h Glass Technology, 6, 149-156 (1983) .
2 )
M. Guittard, S. Jaulmes,
A.M.Loireau-Lozac'h, A. Mazurier, F. Berguer
et J. Flahaut
1 0 1
6)0.07
0.08
0.07 I b o l ( i \ )
-
0
0.04
0.04
0.06
0.04 Compound
0
a - z
0 Ln6CoZYn2Sl4 Ref conlt,uut~d
0
0.14
J.
Sol. State Chem., 58 276-289 (1985
3) G. Collin, J. ~tienne;-3. Flahaut, M. kittard, P. Laruelle
E o ( e v )
:
t ev10380
10380
10383 10382
10185 10383
10388 10385
Rev. Chim. Min., 10, 225-238
( 1 9 7 3 ) .4) N. Rodier,
M.GuiFfard, J. Flahaut C.R. Acad. Sc. Paris, 296, 65-70 (1983).
5) G. Collin, J. F l a h a u t , X Guittard,
A.M.Loireau-Lozac'h Mat. Res. Bull. fi, 285-292 (1976).
6)
A .Mazurier, M. Guittard, S. Jaulmes Act. Cryst. G, 379-382 (1982).
N
4.0
4.0
0.1 3 . 2
0.75
2 . 2 9 N e ~ p . h b a u r
S
S
0 S
2.8
0.9 2 .O
R ( A )
.
2 0.02 A
2.27
2.27
1.86 2.28
C8-422 JOURNAL DE PHYSIQUE
PSEUDO RADIAL DISTRIBUTION FUNCTIONS
Fig. 2
m = 0crystal Fig. 3 rn
= 0glass Fig.
8EXAFS
(m = 0 . 1 4 )glass
Fig.
4 m = 0 . 1 4crystal Fig. 5
rn = 0 . 1 4glass Fig.
9Ga-S pair FIT
(m = 0 . 1 4 )glass
F i g . 6 m = 0 . 4 0
