z
K n s t a l l o g n N C S j l S (2003) 173-174
173
© by Oldenbourg Wissenschaftsverlag, München
Crystal structure of yttrium borosilicide,
Y
5
SÌ2-xB
8
(.χ =
0 . 1 3 )
1 Ro<Ter. R. Jardin, V. Babizhetskyy, S. Députier, J. Bauer and R. Guérin*
UMR CNRS-Université No 6511, Campus de Beaulieu, Laboratoire de Chimie du Solide et Inorganique Moléculaire, Avenue du Général Ledere, F-35042
Rennes Cedex, France
Received June 2, 2003, accepted and available on-line June 11, 2003; CSD-No. 409707
9 ^ 9
Τ
'
Source of material
9 ^
H
ThB 4
slab
*
U 3 Si 2
slab
Suitable amounts of p o w d e r and freshly filed chips of the constituents in the n o m i n a l atomic percentage Y:Si:B=5:2:8 w e r e m i x e d
together and p r e s s e d into pellets. S a m p l e s melting w a s p e r f o r m e d
in an arc furnace using a non-consumable thoriated tungsten electrode under Ti/Zr-gettered argon atmosphere. To ensure homogeneity, the samples were turned over and re-melted several times. Shiny
black platelet-like single crystals could be extracted f r o m molten
samples after crushing and used for structure determination.
Discussion
ThB 4
slab
Abstract
B
8Sii. 8 7 Y 5 , tetragonal, PAImbm (No. 127), a = 7.2234(2) Á,
c = 8.0961(3) Â, V = 4 2 2 . 4 Â 3 , Ζ = 2, Rgt(F) = 0.040,
WÄreffF2) = 0.095, 7 ' = 293 K.
T h e ternary c o m p o u n d Y5SÌ2-a-B8 belongs to the f a m i l y of rare
earth borosilicides R5S12B8 (R = S m , Gd, Tb, Dy), w h i c h w e h a v e
recently discovered [1, 2], This f a m i l y of c o m p o u n d s crystallizes
in the n e w structure type Gd5Si2B8. T h e structure determination
concludes to the occurrence of t w o yttrium ( Y1, Y2) and three boron (B1, B2, B3) independent positions. On the other h a n d , there
is only one silicon position, w h i c h has b e e n f o u n d slightly deficient (τ = 0.935(9)). T h e structure Y5S12B8 can b e easily described as an intergrowth structure of TI1B4 [3] and U3S12 [4]
related slabs of composition YB4 and Y3S12, f o l l o w i n g each other
along the [001] direction (top figure). F o r example, the structure
composition is c o n f i r m e d by the resulting equation: 2YB4 +
Y3S12 = Y5S12B8. T h e salient characteristic of the structure results
f r o m the occurrence of t w o ordered independent b o r o n and silic o n sublattices. T h e silicon atoms within the U3S12 related slab
f o r m S i — S i pairs with a S i — S i distance of 2.358(4) A (middle
figure). T h e boron atoms within the ThB4 related slab f o r m distorted Bö octahedra, which are built f r o m four B 2 (square basis)
and two Β 3 atoms. These octahedra, which are inserted in yttrium
cubes, are close to ideal local Oh symmetry, as shown by the
inter-octahedral B 2 — B 3 and B 2 — B 2 distances which are quite
similar (1.81(1) Â and 1.84(1) Â, respectively; ave. 1.83(1) Â). T h e
last boron atoms, namely the Β1 atoms, lie in the same ζ = 1/2 as the
B 2 squares to which they are connected. E a c h Β1 a t o m is connected to another Β1 atom and to t w o Β 2 atoms which belong to
two different octahedra, i.e. each Β1 atom is three-coordinated (sp 2
hybridisation). T h e B l — B 2 and B l — B1 distances of 1.76(1) Â
a n d 1 . 8 2 ( 2 ) Â, r e s p e c t i v e l y , a r e s l i g h t l y s h o r t e r t h a n t h e
intra-octahedron ones. A s a result, the boron sublattice can b e described as m a d e of Bô octahedra w h i c h are linked together in the
(a, b) plane through boron atoms which f o r m Β — Β pairs (bottom
figure). It is worth noting that the Β — Β pairs (ζ = 1/2) are situated
almost straight up the S i — S i ones (z = 0). Finally, the Β 1 and B 2
atoms generate a two-dimensional planar (2-D) network which can be
described as made of fused squares and heptagons (bottom figure).
T h e Y 1 atoms are octahedrally surrounded by t w o boron and f o u r
silicon atoms, while the Y 2 ones are twelve-coordinated by nine
b o r o n and three silicon atoms, but in a m o r e c o m p l e x arrangement.
Correspondence author (e-mail: [email protected])
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174
Y5SÌ2-.vBB
Table 1. Data collection and handling.
Crystal:
Wavelength:
μDiffractometer, scan mode:
20max:
N(hkl)measured, N(hkl)unique:
Criterion for I0bs, N(hkl)gt:
N(param) refined:
Programs:
shiny black platelet,
size 0.036 χ 0.052 χ 0.052 mm
Mo Ka radiation (0.71073 Â)
341.70 cm" 1
Kappa CCD-Nonius, 0/20
69.76°
1730, 534
/obs > 2 a(Iobs), 436
28
SIR97 [5], SHELXL-97 [6],
DIAMOND [7]
Table 2. Atomic coordinates and displacement parameters (in À 2 ).
Atom
Site Occ.
Y(l)
Y(2)
Si
B(l)
B(2)
B(3)
2a
8k
4g
4h
8;
4e
X
0
0.81897(4)
0.935(9) 0.3846(2)
0.9109(8)
0.6724(7)
0
y
0
-x+1/2
-x+1/2
x+1/2
0.4597(8)
0
ζ
í/ll
U22
Í/33
0
0.72410(6)
0
1/2
1/2
0.337(1)
0.0136(3)
0.0077(2)
0.0112(8)
0.012(2)
0.009(2)
0.009(2)
Un
Un
Un
Un
0.010(2)
Un
0.0057(4)
0.0069(3)
0.009(1)
0.010(4)
0.004(2)
0.010(3)
Un
0
-0.0004(2)
0.0001(8)
0.005(3)
-0.002(2)
0
Un
0
0.0002(1)
0
0
0
0
t/23
0
-Un
0
0
0
0
Acknowledgment. V. Babizhetskyy on leave from Ivan Franko National University of L'viv (Ukraine) thanks the Centre National de la Recherche
Scientifique (France) for a research fellowship.
References
1. Babizhetskyy, V.; Roger,J.; Députier, S.; Jardin, R.; Bauer, J.; Guérin, R.:
Solid state phase equilibria in the Gd-Si-B system at 1270 K. J. Solid
State Chem., in print.
2. Babizhetskyy, V.; Roger, J.; Députier, S.: Guérin, R.; Jardin, R.; Bauer, J.;
Hiebl, K.; Jardin, C.; Halet, J. F.; Saillard, J. Y.: Crystal structure, physical
properties and theoretical calculations of the new ternary compound
Gd5SÌ2B8. Angew. Chem., submitted.
3. Zalkin, Α.; Templeton, D. Η.: The crystal structures of CeB-i, ThB4 and
UB 4 . Acta Crystallogr. 6 (1953) 269-272.
4. Zachariasen, W. H.: Crystal chemical studies of the 5f-series of elements.
8. Crystal structure studies of uranium silicides and of CeS¡2, NpS¡2 and
PuSi 2 . Acta Crystallogr. 2 (1949) 94-97.
5. Altomare, Α.; Burla, M. C.; Camalli, M.; Carrozzini,Β.; Cascarano, G.L.;
Giacovazzo, C.; Guagliardi, Α.; Moliterni, A. G. G.; Polidori, G.; Rizzi, R.:
SIR97: A new tool for crystal structure determination and refinement. J.
Appi. Crystallogr. 32 (1999) 115-119.
6. Sheldrick, G. M.: SHELXL-97. Program for the Refinement of Crystal
Structures. University of Göttingen, Germany 1997.
7. Brandenburg, K.: DIAMOND Version 2.le, Crystal Impact GbR, Bonn,
Germany 1996-2001.
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