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Mössbauer lattice parameters of mixed tin fluoride α-Sn2F6
Mat. Res. B u l l . , Vol. 21, p p . 999-1009, 1986. P r i n t e d in t h e USA. 0025-5408/86 $3.00 + .00 C o p y r i g h t (c) 1986 Pergamon J o u r n a l s L t d .
MOSSBAUER
L@opold
LATTICE
Fourn6s,
PARAMETERS
OF
MIXED
TIN
FLUORIDE
P a s c a l L a g a s s i @ , Y v e s Potin, and P a u l H a g e n m u l l e r
Jean
a-Sn2F 6
Grannec
L a b o r a t o i r e de C h i m i e du S o l i d e du C N R S U n i v e r s i t @ de B o r d e a u x I 351, c o u r s de la L i b @ r a t i o n 3 3 4 0 5 T a l e n c e Cedex, F r a n c e .
( R e c e i v e d May 22, 1986; Communicated b y P. Hagenmuller)
ABSTRACT
M~ssbauer resonan~9 Y-transition in ---m l x e d tln f l u o r l d e r a n g e 4.2 ~ T 4 378 '
'
I
measurements u s i n g the 23.8 k e V Sn _have. b e e n c a r r l e d out on the I± IV Sn Sn F 6 o v e r the t e m p e r a t u r e K.
F r o m the t e m p e r a t u r e d e p e n d e n c e of the i s o m e r s h i f t it is p o s s i b l e to e x t r a c t the e f f e c t i v e vibrating m a s s e s , i.e. M ~: II = 178 amu for Sn(II) and Me. f : 298 amu for S n ( I V ~ . The l a t t l c e t e m p e r a t u r e s c a l c u l a t e d f r o m the t e m p e r a t u r e d e p e n d e n c e of the a r e a of the r e s o n a n c e p e a k are 166 K a n d 211 K for Sn(II) and Sn(IV) respectively. U s i n g Mef f leads to l a t t i c e t e m p e r a t u r e s of 1 3 9 K (Sn(II)) a n a 133 K ( S n ( I V ) ) . The r e c o i l l e s s f r a c t i o n s at 293 K are 0.15 for Sn(II) and 0.31 for S n ( I V ) .
MATERIALS
INDEX
:
M6ssbauer a-Sn2F 6
resonance,
mixed
tin
fluoride,
Introduction Many bonding parameters can be d e t e r m i n e d in s o l i d s t a t e f r o m the r e l a t i o n s h i p s between structure and physical properties. F r o m t h a t p o i n t of v i e w M 6 s s b a u e r s p e c t r o s c o p y m a k e s a v a i l a b l e d a t a on the d y n a m i c a l b e h a v i o r of a t o m s in c o n d e n s e d matrix. In r e c e n t y e a r s s e v e r a l i n v e s t i g a t i o n s h a v e b e e n c a r r i e d out b y this t e c h n i q u e in o r d e r to d e t e r m i n e the l a t t i c e t e m p e r a t u r e of v a r i o u s c o m p o u n d s containing either tin(II) or tin (IV) (i to 4). T h i s d e t e r m i n a t i o n l e a d s to the L a m b - M ~ s s b a u e r f a c t o r f, the t h e r m a l e v o l u t i o n of w h i c h m a y g i v e i n f o r m a t i o n on intermolecular and intramolecular bondings in a solid. A d d i tional details concerning the lattice vibrational modes in s o l i d s h a v e b e e n e l u c i d a t e d by R a m a n s p e c t r o s c o p y (5, 6). 999
i000
L. FOURNES, et 8/.
Vol. 21, No. 8
A c c o r d i n g to an e x p e r i m e n t a l m e t h o d p r e v i o u s l y p r o p o s e d (7) it is p o s s i b l e to e x t r a c t the M 6 s s b a u e r l a t t i c e t e m p e r a t u r e and the r e c o i l l e s s f r a c t i o n f r o m the t e m p e r a t u r e d e p e n d e n c e of the a r e a of the r e s o n a n c e peak. T h i s m e t h o d a p p l i e s o n l y to a t h i n a b s o r b e r , as the l o g a r i t h m of the m e a s u r e d a r e a is s u p p o s e d to v a r y l i n e a r l y w i t h t e m p e r a t u r e in the h i g h t e m p e r a t u r e a p p r o x i mation. One may consider t h a t the h i g h t e m p e r a t u r e validity r a n g e is d e f i n e d for T > en/2, w h e r e en is the D e b y e t e m p e r a t u r e of the solid. For m o s t tl~n c o m p o u n d s ~ e_ is r e l a t i v e l y low a n d results thus in a l a r g e r l n v e s t l g a t l o n field. In m a n y c a s e s h o w e v e r t h i s m e t h o d c a n n o t e a s i l y a p p l y s i n c e the tin r e c o i l l e s s fractions are u s u a l l y v e r y w e a k at r o o m t e m p e r a t u r e or b e l o w (i)
.
velocity CmnveO ----
I
t
I
I
I
I
l,
I
t
3
I_ls°c M6ssbauer
FIG. 1 resonance spectrum of a-Sn2F 6 .
Us°oo at
293 K
e - S n 2 F 6 was p e r f o r m e d at r o o m t e m p e r a t u r e . The s h o w n in Fig. 1 l e a d s to f o l l o w i n g r e m a r k s : - the o b s e r v e d a r e a s to the l l 9 s n r e s o n a n c e to Sn(II) a n d Sn(IV) are q u i t e d i f f e r e n t
Some years ago a m i x e d tin fl~?ri~ Sn--Sn--F~ has been is61ated (8). Recently we a t t e m p t e d to characterize the different allotropic varieties which were detected by DTA (9). During this study a M6ssbauer spectrum of the l o w t e m perature form typical spectrum
lines
corresponding
- t h e s e a b s o r p t i o n s are r e l a t i v e l y large, w h e r e a s in c o m p o u n d s M S s s b a u e r e f f e c t c a n n o t be o b s e r v e d at 293 weak recoilless fraction.
m a n y tin K due to
Since divalent and tetravalent tin s p e c i e s c a n r e a d i l y be distinguished on the b a s i s of t h e i r s p e c i f i c i s o m e r shifts, it seemed w o r t h w h i l e to determine the M6ssbauer parameters and e s p e c i a l l y the r e c o i l l e s s f r a c t i o n of b o t h tin n u c l e i in e - S n ~ F 6 to t a k e a d v a n t a g e of s i m u l t a n e o u s p r e s e n c e of the two oxid~tion states. Experimental s - S n 2 F 6 has b e e n p r e p a r e d by s o l i d s t a t e r e a c t i o n f r o m a s t o i c h i o m e t r i c m i x t u r e of SnF~ a n d SnF. h o m o g e n e i z e d in a dry atmosphere of a g l o v e box. ~he s t a r t l n g m a t e r l a l s have been i n t r o d u c e d i n t o g o l d t u b e s a n d h e a t e d u n d e r v a c u u m at 100°C. The t u b e s w e r e t h e n s e a l e d a n d the r e a c t i o n s c a r r i e d out at 500°C. The f i n a l s t e p w a s a t e m p e r a t u r e q u e n c h i n g . The s a m p l e w a s c h a r a c t e r i z e d by its p o w d e r X - r a y d i f f r a c t i o n p a t t e r n u s i n g Cu K e r a d i a t i o n .
Vol. 21, No. 8
~-Sn2F 6
I001
The M 6 s s b a u e r r e s o n a n c e s p e c t r a w e r e o b t a i n e d w i t h a c o n s ac[~eration HALDER-type spectrometer with a room temperaC a - - - S n O 3 s o u r c e in a t r a n s m i s s i o n g e o m e t r y . 2 The s a m p l e c o n t a i n e d 15 mg n a t u r a l tin per cm , a c o n c e n t r a t i o n for w h i c h l i n e b r o a d e n i n g due to t h i c k n e s s e f f e c t s is hardly noticeable.
tant ture
The s p e c t r a in the t e m p e r a t u r e r a n g e 4.2 < T ~ 293 K w e r e r e c o r d e d w i t h a v a r i a b l e t e m p e r a t u r e c r y o s t a t . B e t w e e n 293 and 378 K a s t u d y of the t e m p e r a t u r e d e p e n d e n c e was c a r r i e d out in a specially built reactor using a flow system. For the i n v e s t i g a t i o n of ~-Sn^F_ the r e a c t o r was p r e v i o u s l y filled with b a r g o n d r i e d up by p J o s p h o r o u s p e n t o x l d e .
The d e t a i l s of the r e a c t o r are gi~ ,~~ , ~ 7 ~ 1 ~ 1 < ! ven in Fig. 2. The eocto cons t o a nickel cylinder water" I| with a 30 m m i n n e r diameter (a). The ~ /~ f u r n a c e b o d y is c o m posed of a larger ......... / ~ "thermocoax"heating ...... coil (b). The w i n dows for Y -ray . ..~_.~ transmission use a u:z-multilayer composite material (c). It is _ m a d e of h i g h p u r i t y aluminium deposited on polymer foils. The w i n d o w s are p r o tected against overI| Y / / / / / / / / ~ V/~////////~ heating by cooling L ~ ~ _ ~ _ _ ~ _ ~ coils (d) . The sam~ ~ ~s~let ple is put on a ~ ~ boron nitride holder I (e). The disk and absorber are p l a c e d in a cylindrical FIG. 2 nickel holder kept D e s i g n of a f u r n a c e for the M 6 s s b a u e r in the c e n t e r of the r e s o n a n c e i n v e s t i g a t i o n of e - S n 2 F 6. r e a c t o r (f). A c h r o mel-alumel thermocouple c a p a b l e of m e a s u r i n g w i t h i n ± I°C a c c u r a c y is i n s e r t e d i n t o the m i d d l e n e a r the s a m p l e (g). A t u b e a l l o w s to i n t r o d u c e the gas (h). The r e a c t o r is put in a dry g l o v e b o x for p r e p a r i n g the e x p e r i m e n t . It is t h e n h e l d v e r t i c a l l y on the top of a t r a n s d u c e r c a r r y i n g a i0 mCi s o u r c e . The s p e c t r a w e r e f i t t e d to the sum of L o r e n t z i a n s by l e a s t s q u a r e r e f i n e m e n t . All i s o m e r s h i f t s g i v e n b e l o w r e f e r to C a S n O 3 at 293 K.
~
1002
L. FOURNES, et al.
Results 1 - M6ssbauer
parameters
of
and discussion ~-Sn2F 6
The s t r u c t u r e of e - S n ^ F 6 M ~ s s b a u e r r e s o n a n c e studyl~as~ r a n g e 4.2 ~ T < 378 K. ~ ~Sn g i v e n in Fig. 3. The r e l e v a n t
~
i
-T
-6
~
-¢
"8
L
i
i
i
i
Vol. 21, No. 8
-a i i
has not b e e n so far d e t e r m i n e d . The b e e n c a r r i e d out in the t e m p e r a t u r e s p e c t r a at v a r i o u s t e m p e r a t u r e s are p a r a m e t e r s a p p e a r in T a b l e I.
-s l
Q rl
•
•
I
A
S
•
7
i
i
i
i
i
i
h
L/
5. C.W
M6ssbauer
resonance
spectra
5. (,,)
Fig. 3 of e - S n 2 F 6 at v a r i o u s
temperatures.
Vol. 21, No. 8
-Sn2F6
TABLE M@ssbauer
parameters
1003
I of
~ - S n 2 F 6.
Sn(II)
Sn(IV)
T(K)
6(mm.s -I )
A(mm.s -I )
r(mm.s -I)
6(mm.s -I )
A(mm.s -I)
r(mm.s -I)
378 323 293 240 160 77 4.2
4.088(9) 4.094(8) 4.103(5) 4.119(7) 4.134(6) 4.162(5) 4.169(5)
0.429(9) 0.452(8) 0.493(5) 0.504(7) 0.565(6) 0.610(5) 0.645(5)
1.10(2) 1.11(2) 1.12(1) i.Ii(i) 1.12(1) i.i0(i) 1.17(1)
-0.402(9) -0.396(8) -0.392(5) -0.385(7) -0.371(6) -0.360(5) -0.352(5)
0.652(9) 0.673(8) O.68O(5) 0.719(7) 0.730(6) 0.759(5) 0.796(5)
0.98(2) 0.97(2) 0.95(1) 1.02(1) 1.03(1) i.ii(i) 1.20(1)
: i s o m e r shift r e l a t i v e to C a S n O 3 at A : quadrupole splittinq r : l i n e w i d t h at half-height.
293 K
The v a l u e s of the tin(II) M ~ s s b a u e r p a r a m e t e r s d i f f e r from those observed for m a n y o t h e r tin f l u o r i d e s (I0 to s ~))', The i s o m e r s h i f t at 293 K is r e l a t i v e l y h i g h (6 = 4.10 mm . but of t h~ same o r d e r of m a g n i t u d e as that o ~ SnF^, BF_ (6 = 3.98 m m . s - ) (13) or S n ( S b m 6 ) ~ ( 6 : 4.50 mm.s---) (i~). O ~ the o t h e r hand the quadrupole splitting ( A : 0.49 m m . s -~) is low c o m p a r a t i v e l y to the v a l u e s u s u a l l y o b t a i n e d for tin(II) f l u o r i des (i0, ii). N e v e r t h e l e s s for S n ( S b F 6 ) 2, w h e r e Sn(II) o c c u p i e s an ideal o c t a h e d r a l site, no q u a d r u p o l ~ s p l i t t i n g a p p e a r s . For t e t r a v a l e n t tin, if the v a l u e s of the i s o m e r shift are q u i t e s i m i l a r to t h o s e o b s e r v e d for e x a m p l e for SnFa (15) or K p S n F ~ (16) at r o o m t e m p e r a t u r e , on the c o n t r a r y t~e q u a d r u p o l e s ~ l i t [ i n g is d i f f e r e n t f r o m t h o s e r e p o r t e d for those c o m p o u n d s . A c c o r d i n g to the o b t a i n e d r e s u l t s tin(II) c o u l d be c o n s i d e red in ~ - S n 2 F _ as h a v i n g a s l i g h t l y d i s t o r t e d e n v i r o n m e n t . In the same w a y ~he q u a d r u p o l e s p l i t t i n g for tin(IV) s u g g e s t s for this c a t i o n a w e a k a s y m m e t r y of the o c t a h e d r a l site. The i s o m e r s h i f t s o b s e r v e d for the two o x i d a t i o n s t a t e s a s c e r t a i n the fact that the S n ( I V ) - F b o n d s h a v e a r e l a t i v e l y c o v a l e n t c h a r a c t e r , while the S n ( I I ) - F b o n d s are s t r o n g l y ionic. This r e s u l t was a l r e a d y s u g g e s t e d by B i r c h a l l et al. for c o m p o u n d s o b t a i n e d from SnF 2 and L e w i s a c i d s (13). Nevertheless, for the m i x e d tin f l u o r i d e it seems that at room_temperature a s h a r p ionic f o r m u l a t i o n such as (Sn)Z+(SnF~)Z~is~ot r e a l l y s u i t a b l e (13). A b e t t e r f o r m u l a t i o n w o u l d be ~Sn±±sn±VF ] i m p l y i n g f l u o r i n e b r i d g e s of 6-x Sn(II)-F-Sn(IV) type. Such b r l d g e s w o u l d a c c o u n t for a l a r g e r r i g i d i t y of the l a t t i c e and lead to r e c o i l l e s s f r a c t i o n s r e l a t i v e l y h i g h for tin n u c l e i .
1004
L. FOURNES, et al.
2 - Temperature
dependence
of the
isomer
shift
F r o m the t e m p e r a t u r e d e p e n d e n c e of wing relationship allows to c a l c u l a t e m a s s M e f f (17, 3), w h i c h is a s s o c i a t e d c i t e d m o r i o n of the M 6 s s b a u e r a t o m : d6 _
3 E0kB
Vo]. 21, No. 8
the i s o m e r s h i f t f o l l o an e f f e c t i v e vibrating w i t h the t h e r m a l l y ex-
[i] 2
dT
2 Mef f _ c
where E 0 Boltzmann
is the n u c l e a r constant.
transition
energy
for
( r a m sI )
(ram ..4+
Sr(~v] 4,16 - 0,36
4,14
4,12 -o, a8
.-~
4,10 4,08 0,40 L--.
i
i
i
I
100
200
300
400
FIG. 4 T e m p e r a t u r e d e p e n d e n c e of the s h i f t s of ~ - S n 2 F 6.
d6
-
--ISn(II)l = -(2.3 dt d6[sn(IV)~l dt
+ 0.i)
= -(1.39
i
T(K)
isomer
tin
and
kB
the
Fig. 4 s h o w s the v a r i a t i o n of the i s o m e r s h i f t vs temperature for 7 7 < T ( 3 7 8 K. (77 K c o r r e s p o n d i n g to the lower l i m i t of the high temperature validity range). The s o l i d l i n e s have been obt a i n e d by l i n e a r regression using the f i f t e e n experimental data with a correlation coefficient of 0.98 for Sn(II) a n d 0.99 for Sn (IV). The slop~ have respectively the values :
x i0 - 4 m m . s - i K -I
± 0.06)
x 1 0 - 4 m m . s - i K -I
From those values and relationship e f f e c t i v e v i b r a t i n g m a s s e s for b o t h tin M e f f [ S n ( I I ) ] = 178
± i0 amu
M e f f [ S n ( I V ) ] = 298
+ 14 amu
[i] we m a y nuclei :
determine
the
Vol. 21, No. 8
The relative
~-Sn2F 6
results obtained t o S n O (3) :
d6
2.46
for
× 10-4mm.s-iK
-I
Sn(II)
and
]005
are
Mef f
very
=
168
close
± 18
to
those
amu
dt 3 - Lattice
temperature
determination
For a thin absorber the temperature dependence ofl~e recoilless fraction for the 23.8 keV y-ray transition in Sn is well represented by the temperature dependence of t h e a r e a of the resonance peak : dLnf
_ dLnA
dt
[2]
dT
where A is t h e a r e a n o r m a l i z e d to a c o n v e n i e n t so t h a t s a m p l e c o m p a r i s o n s c a n be m a d e e a s i l y . In
the
dhnA
_
high 6 E
temperature
validity
limit
r
reference
point
:
[3]
k B o2
dt
where E is t h e r e c o i l e n e r g y f o r y - r a y a b s o r p t i o n in t h e a b s o r 0 ber and r @ the Debye temperature. Herber proposes to r e p l a c e D D by a lattlce temperature @M more closely connected to the m a s s notion. Substitution for the recoil energy in terms of the M6ssbauer y - r a y e n e r g y l e a d s to :
and
E -
2 E0
r
2Mc 2
equation
[3]
dLnA dt
becomes
:
-3E~
[4]
kBMC20~
A representative d a t a s e t of t h e t e m p e r a t u r e dependence of the area under the resonance c u r v e is g i v e n in Fig. 5 (the a r e a s have been normalized using the values at 77 K s e l e c t e d as t h e validity limit of t h e h i g h - t e m p e r a t u r e range). The correlation coefficient to t h e l i n e a r r e g r e s s i o n l e a d i n g to b o t h s o l i d l i n e s is ~ r ~ 9 f o r fifteen values in e a c h c a s e . U s i n g t h e a t o m i c m a s s of ± JSn l e a d s to f o l l o w i n g data :
M As
[Sn(II)]
a comparison,
: 166 for
-+ 8 K a n d SnO
-
0
M
0
M
[Sn(IV)]
: 229
K
(3)
: 211
-+ i0
K
"
1006
L. F O U R N E S ,
et al.
Vo]. 21, No. 8
Lo-[A(T K)]
Lo~[A(TK) ]
' °LA~IJ
~[A--T~-K!
o
Sn('@
0
snOv)
_0,5
-0,,5
SnO0~
_1,0
-I, 0
_I,5
2bo
.... 160
S u b s t i t u t i o n of M by the relationship [4] y i e l d s :
~TCK)
effective
vibrating
under
mass
Mef f into
3E~
dt By u s i n g
4~0
FIG. 5 of the n o r m a l i z e d area curve for ~ - S n 2 F 6.
Temperature dependence the r e s o n a n c e
dLnA
3~o
kBMef fc 2 8~2 Mef f v a l u e s
extracted
from
equation
[11 one
obtains:
!
eM[Sn(II) ] = 139
~ 3K
and
e~[Sn(IV)]
= 133
-% 3K.
It seems t h e r e f o r e that the m e t h o d t a k i n g into a c c o u n t the e f f e c t i v e v i b r a t i n g m a s s leads to l a t t i c e t e m p e r a t u r e s v a l u e s e L significantly lower than those deduced from e q u a t i o n ~. A~ a n a l o g o u s r e s u l t has b e e n o b s e r v e d for SnO :e. = 2 2 9 K and e.' = 193K (3) . One may a s c e r t a i n a c t u a l l y that for ~ lot of c o mM p o u n d s the l a t t i c e temperatures d e d u c e d from e q u a t i o n J4J are h i g h e r than those d e t e r m i n e d by o t h e r t e c h n i q u e s , in p a r t i c u l a r R a m a n spectroscopy (6).
4 - Temperature
dependence
of the r e c o i l l e s s
fractions
For a thin a b s o r b e r in the t e m p e r a t u r e range w h e r e high temperature limiting equation ~ is valid, there is a correspondence b e t w e e n r e c o i l l e s s f r a c t i o n f and 8M , n a m e l y :
f = exp
-3EgT 2 kBMC2eM
[6]
Vol. 21, No. 8
At of
u-Sn2F 6
293 K u s e of the form : f = exp
the
atomic
mass
1007
for
tin
leads
x 10 4
-5.248
to a r e l a t i o n s h i p
171
02 M
so t h a t t h e ~. v a l u e s p r e v i o u s l y calculated lead respectively to: f[Sn(II);293mK] "= 0 . 1 5 ± 0 . 0 1 a n d f [ S n ( I V ) ; 2 9 3 K ] : 0.31 ± 0.02. If the Sn atomic mass is replaced by the effective vibrating mass and if we consider the c o r r e s p o n d i n g lattice temperature e M' , f b e c o m e s f[Sn(II)]
-3.652
= exp
x 104
e'2[Sn(II)] M
f[Sn(IV)]
181
-2.096
: exp
x
104
0'2[Sn(IV)] M This 0.01
approach gives, as and f[Sn(IV) ; 293
expected K] : 0 . 3 1 TABLE
Summary
of
llgsn
: f[Sn(II) i 0.02.
; 293
)
data
-(2.3±0.i)xi0
(K-l)
d Log[A(TK)/A(77K)]
:
0.15
±
II
M6ssbauer
for
~ - S n 2 F 6.
Sn(II) d6(mm.s-iK-i dT
K~
-(6.5±0. 3)xl0
Sn(IV) -4
-3
-(1.39±0.06)xi0 -(4.0±0.2)xi0
-4 -3
dT Meff(uma)
% (K) v
oM f
(K)
(293
K)
176±10
298±14
166±8
211!i0
139±3
133±3
0.15±0.01
0.31±0.02
The main results obtained for ~-Sn_F_ are s u m m a r i z e d in z b .. T a b l e II. T h e t h e r m a l e v o l u t i o n of t h e L a m b - M o s s b a u e r factors f deduced from the equation 161 c a n be r e p r e s e n t e d by : f : exp
-1.791
x 102 2
T
°M T i t h 0 M [ S n ( I I ) ] : 166 + 8 K a n d 8 m [ S n ( I V ) ] : 211-+ i0 ne t e m p e r a t u r e dependence is s h o w n in Fig. 6.
K.
1008
L. FOURNES, et al.
o,4
The low t e m p e r a t u r e v a l u e s of the r e c o i l l e s s ~ractions obtained for ~ - S n 2 F 6 are relatively high: f[Sn(II);77K]=0.61±0,02, f[Sn(IV);77K]=0.75±0.02, if c o m p a r e d with those of SnF^ [4] : f [ S n ( I I ) ; 293K]=0~07 and f [Sn(II) ; 7 7 K ] = 0 . 5 0 . S u c h a r e s u l t is in g o o d a g r e e m e n t w i t h the p r e v i o u s l y a s s u m p t i o n : the strong rigidity of the lattice l e a d s to h i g h v a l u e s of f. The L a m b Mossbauer factors become e q u a l o n l y at v e r y l o w temperatures (Fig. 6) : at 4.2 K for e x a m p l e the areas corresponding to Sn(II) and Sn(IV) are s i m i l a r (Fig. 3).
SnC~
O,2
J
0
i
100
200
FIG.
L
,
300
400
Vol. 21, No. 8
T(K)
6
T h e r m a l e v o l u t i o n of the f f a c t o r s for e - S n 2 F 6
References 1 - M. C o r d e y - H a y e s , C h e m i c a l a p p l i c a t i o n s of M ~ s s b a u e r s p e c troscopy, V.I. Goldanskii a n d R.H. H e r b e r Ed., A c a d e m i c P r e s s , 314 (1968). 2 - R.H. H e r b e r , A.E. S m e l k i n s o n , M.J. S i e n k o a n d L.F. S c h n e e m e y e r , J. C h e m . P h y s . , 68, 3705 (1978). 3 - R.H.
Herber,
Phys.
Rev.
B,
27,
4 - T. B i r c h a l l , G. D ~ n ~ s , K. H y p e r f i n e I n t e r a c t i o n s , 29,
7,
4013
(1983).
Ruebenbauer 1327 (1986).
and
J.
Pannetier,
5 - Y. H a z o n y a n d I.J. G r u v e r m a n 107 (1973).
R.H. H e r b e r , M ~ s s b a u e r e f f e c t m e t h o d o l o g y , a n d C.W. S e i d e l Ed., P l e n u m Press, vol. 8,
6 - A.J. R e i n (1975).
R.H.
and
7 - R.H. Herber Weissberger (1972).
and and
Herber,
J.
Chem.
Phys.,
63,
2,
1021
Y. H a z o n y , Techniques of C h e m i s t r y , A. B.W. Rossiter Ed., Wiley, vol.l, 278
8 - R. S a b a t i e r , A.M. H e b r a r d Sc., 279, 1121 (1974).
and
J.C.
Cousseins,
C.R.
Acad.
9 - J. G r a n n e c , P. L a g a s s i ~ , Y. Potin, L. F o u r n ~ s a n d P. H a g e n m u l l e r , Mat. Res. Bull., to be p u b l i s h e d . 10 - J.D. ii
-
Donaldson
a n d B.J.
Senior,
J. Chem.
Soc.
A,1796(1966).
T. B i r c h a l l , G. D ~ n ~ s , K. R u e b e n b a u e r a n d J. P a n n e t i e r , J. C h e m . Soc., D a l t o n T r a n s . , 12, 2296 (1981).
Vol. 21, No. 8
a-Sn2F 6
1009
12
- T. B i r c h a l l , G. D @ n 6 s , K. J.Chem. Scc., D a l t o n T r a n s . ,
13
- T. A,
Birchall, P.A.W. 1777 (1971).
14
- T. D.
B i r c h a l l , J.E. V e k r i s , B. F r l e c , D. G a n t a r H a n z e l , J. F l u o r i n e C h e m . , 27, 61 (1985).
15
- Y. C a l a g e , L. 1209 (1978).
16
- H.A. C a r t e r , A.M. Q u r e s c h i , J. C h e m . , 48, 2853 (1970).
J.R.
17
- G.K. S h e n o y , s h i f t s , G.K. i01 (1978).
G.M. K a l v i u s , M 6 s s b a u e r i s o m e r W a g n e r Ed., N o r t h - H o l l a n d ,
Dean
Benmiloud
Ruebenbauer and 9, 1831 (1981). and
and
F.E. W a g n e r a n d S h e n o y a n d F.E.
R.J.
J.
J.
Gillespie,
Pannetier, Sams
and
Pannetier, J.
Soc.
and J.
F.
Chem.
Phys.,
Aubke,
39,
Canad.
MOSSBAUER
L@opold
LATTICE
Fourn6s,
PARAMETERS
OF
MIXED
TIN
FLUORIDE
P a s c a l L a g a s s i @ , Y v e s Potin, and P a u l H a g e n m u l l e r
Jean
a-Sn2F 6
Grannec
L a b o r a t o i r e de C h i m i e du S o l i d e du C N R S U n i v e r s i t @ de B o r d e a u x I 351, c o u r s de la L i b @ r a t i o n 3 3 4 0 5 T a l e n c e Cedex, F r a n c e .
( R e c e i v e d May 22, 1986; Communicated b y P. Hagenmuller)
ABSTRACT
M~ssbauer resonan~9 Y-transition in ---m l x e d tln f l u o r l d e r a n g e 4.2 ~ T 4 378 '
'
I
measurements u s i n g the 23.8 k e V Sn _have. b e e n c a r r l e d out on the I± IV Sn Sn F 6 o v e r the t e m p e r a t u r e K.
F r o m the t e m p e r a t u r e d e p e n d e n c e of the i s o m e r s h i f t it is p o s s i b l e to e x t r a c t the e f f e c t i v e vibrating m a s s e s , i.e. M ~: II = 178 amu for Sn(II) and Me. f : 298 amu for S n ( I V ~ . The l a t t l c e t e m p e r a t u r e s c a l c u l a t e d f r o m the t e m p e r a t u r e d e p e n d e n c e of the a r e a of the r e s o n a n c e p e a k are 166 K a n d 211 K for Sn(II) and Sn(IV) respectively. U s i n g Mef f leads to l a t t i c e t e m p e r a t u r e s of 1 3 9 K (Sn(II)) a n a 133 K ( S n ( I V ) ) . The r e c o i l l e s s f r a c t i o n s at 293 K are 0.15 for Sn(II) and 0.31 for S n ( I V ) .
MATERIALS
INDEX
:
M6ssbauer a-Sn2F 6
resonance,
mixed
tin
fluoride,
Introduction Many bonding parameters can be d e t e r m i n e d in s o l i d s t a t e f r o m the r e l a t i o n s h i p s between structure and physical properties. F r o m t h a t p o i n t of v i e w M 6 s s b a u e r s p e c t r o s c o p y m a k e s a v a i l a b l e d a t a on the d y n a m i c a l b e h a v i o r of a t o m s in c o n d e n s e d matrix. In r e c e n t y e a r s s e v e r a l i n v e s t i g a t i o n s h a v e b e e n c a r r i e d out b y this t e c h n i q u e in o r d e r to d e t e r m i n e the l a t t i c e t e m p e r a t u r e of v a r i o u s c o m p o u n d s containing either tin(II) or tin (IV) (i to 4). T h i s d e t e r m i n a t i o n l e a d s to the L a m b - M ~ s s b a u e r f a c t o r f, the t h e r m a l e v o l u t i o n of w h i c h m a y g i v e i n f o r m a t i o n on intermolecular and intramolecular bondings in a solid. A d d i tional details concerning the lattice vibrational modes in s o l i d s h a v e b e e n e l u c i d a t e d by R a m a n s p e c t r o s c o p y (5, 6). 999
i000
L. FOURNES, et 8/.
Vol. 21, No. 8
A c c o r d i n g to an e x p e r i m e n t a l m e t h o d p r e v i o u s l y p r o p o s e d (7) it is p o s s i b l e to e x t r a c t the M 6 s s b a u e r l a t t i c e t e m p e r a t u r e and the r e c o i l l e s s f r a c t i o n f r o m the t e m p e r a t u r e d e p e n d e n c e of the a r e a of the r e s o n a n c e peak. T h i s m e t h o d a p p l i e s o n l y to a t h i n a b s o r b e r , as the l o g a r i t h m of the m e a s u r e d a r e a is s u p p o s e d to v a r y l i n e a r l y w i t h t e m p e r a t u r e in the h i g h t e m p e r a t u r e a p p r o x i mation. One may consider t h a t the h i g h t e m p e r a t u r e validity r a n g e is d e f i n e d for T > en/2, w h e r e en is the D e b y e t e m p e r a t u r e of the solid. For m o s t tl~n c o m p o u n d s ~ e_ is r e l a t i v e l y low a n d results thus in a l a r g e r l n v e s t l g a t l o n field. In m a n y c a s e s h o w e v e r t h i s m e t h o d c a n n o t e a s i l y a p p l y s i n c e the tin r e c o i l l e s s fractions are u s u a l l y v e r y w e a k at r o o m t e m p e r a t u r e or b e l o w (i)
.
velocity CmnveO ----
I
t
I
I
I
I
l,
I
t
3
I_ls°c M6ssbauer
FIG. 1 resonance spectrum of a-Sn2F 6 .
Us°oo at
293 K
e - S n 2 F 6 was p e r f o r m e d at r o o m t e m p e r a t u r e . The s h o w n in Fig. 1 l e a d s to f o l l o w i n g r e m a r k s : - the o b s e r v e d a r e a s to the l l 9 s n r e s o n a n c e to Sn(II) a n d Sn(IV) are q u i t e d i f f e r e n t
Some years ago a m i x e d tin fl~?ri~ Sn--Sn--F~ has been is61ated (8). Recently we a t t e m p t e d to characterize the different allotropic varieties which were detected by DTA (9). During this study a M6ssbauer spectrum of the l o w t e m perature form typical spectrum
lines
corresponding
- t h e s e a b s o r p t i o n s are r e l a t i v e l y large, w h e r e a s in c o m p o u n d s M S s s b a u e r e f f e c t c a n n o t be o b s e r v e d at 293 weak recoilless fraction.
m a n y tin K due to
Since divalent and tetravalent tin s p e c i e s c a n r e a d i l y be distinguished on the b a s i s of t h e i r s p e c i f i c i s o m e r shifts, it seemed w o r t h w h i l e to determine the M6ssbauer parameters and e s p e c i a l l y the r e c o i l l e s s f r a c t i o n of b o t h tin n u c l e i in e - S n ~ F 6 to t a k e a d v a n t a g e of s i m u l t a n e o u s p r e s e n c e of the two oxid~tion states. Experimental s - S n 2 F 6 has b e e n p r e p a r e d by s o l i d s t a t e r e a c t i o n f r o m a s t o i c h i o m e t r i c m i x t u r e of SnF~ a n d SnF. h o m o g e n e i z e d in a dry atmosphere of a g l o v e box. ~he s t a r t l n g m a t e r l a l s have been i n t r o d u c e d i n t o g o l d t u b e s a n d h e a t e d u n d e r v a c u u m at 100°C. The t u b e s w e r e t h e n s e a l e d a n d the r e a c t i o n s c a r r i e d out at 500°C. The f i n a l s t e p w a s a t e m p e r a t u r e q u e n c h i n g . The s a m p l e w a s c h a r a c t e r i z e d by its p o w d e r X - r a y d i f f r a c t i o n p a t t e r n u s i n g Cu K e r a d i a t i o n .
Vol. 21, No. 8
~-Sn2F 6
I001
The M 6 s s b a u e r r e s o n a n c e s p e c t r a w e r e o b t a i n e d w i t h a c o n s ac[~eration HALDER-type spectrometer with a room temperaC a - - - S n O 3 s o u r c e in a t r a n s m i s s i o n g e o m e t r y . 2 The s a m p l e c o n t a i n e d 15 mg n a t u r a l tin per cm , a c o n c e n t r a t i o n for w h i c h l i n e b r o a d e n i n g due to t h i c k n e s s e f f e c t s is hardly noticeable.
tant ture
The s p e c t r a in the t e m p e r a t u r e r a n g e 4.2 < T ~ 293 K w e r e r e c o r d e d w i t h a v a r i a b l e t e m p e r a t u r e c r y o s t a t . B e t w e e n 293 and 378 K a s t u d y of the t e m p e r a t u r e d e p e n d e n c e was c a r r i e d out in a specially built reactor using a flow system. For the i n v e s t i g a t i o n of ~-Sn^F_ the r e a c t o r was p r e v i o u s l y filled with b a r g o n d r i e d up by p J o s p h o r o u s p e n t o x l d e .
The d e t a i l s of the r e a c t o r are gi~ ,~~ , ~ 7 ~ 1 ~ 1 < ! ven in Fig. 2. The eocto cons t o a nickel cylinder water" I| with a 30 m m i n n e r diameter (a). The ~ /~ f u r n a c e b o d y is c o m posed of a larger ......... / ~ "thermocoax"heating ...... coil (b). The w i n dows for Y -ray . ..~_.~ transmission use a u:z-multilayer composite material (c). It is _ m a d e of h i g h p u r i t y aluminium deposited on polymer foils. The w i n d o w s are p r o tected against overI| Y / / / / / / / / ~ V/~////////~ heating by cooling L ~ ~ _ ~ _ _ ~ _ ~ coils (d) . The sam~ ~ ~s~let ple is put on a ~ ~ boron nitride holder I (e). The disk and absorber are p l a c e d in a cylindrical FIG. 2 nickel holder kept D e s i g n of a f u r n a c e for the M 6 s s b a u e r in the c e n t e r of the r e s o n a n c e i n v e s t i g a t i o n of e - S n 2 F 6. r e a c t o r (f). A c h r o mel-alumel thermocouple c a p a b l e of m e a s u r i n g w i t h i n ± I°C a c c u r a c y is i n s e r t e d i n t o the m i d d l e n e a r the s a m p l e (g). A t u b e a l l o w s to i n t r o d u c e the gas (h). The r e a c t o r is put in a dry g l o v e b o x for p r e p a r i n g the e x p e r i m e n t . It is t h e n h e l d v e r t i c a l l y on the top of a t r a n s d u c e r c a r r y i n g a i0 mCi s o u r c e . The s p e c t r a w e r e f i t t e d to the sum of L o r e n t z i a n s by l e a s t s q u a r e r e f i n e m e n t . All i s o m e r s h i f t s g i v e n b e l o w r e f e r to C a S n O 3 at 293 K.
~
1002
L. FOURNES, et al.
Results 1 - M6ssbauer
parameters
of
and discussion ~-Sn2F 6
The s t r u c t u r e of e - S n ^ F 6 M ~ s s b a u e r r e s o n a n c e studyl~as~ r a n g e 4.2 ~ T < 378 K. ~ ~Sn g i v e n in Fig. 3. The r e l e v a n t
~
i
-T
-6
~
-¢
"8
L
i
i
i
i
Vol. 21, No. 8
-a i i
has not b e e n so far d e t e r m i n e d . The b e e n c a r r i e d out in the t e m p e r a t u r e s p e c t r a at v a r i o u s t e m p e r a t u r e s are p a r a m e t e r s a p p e a r in T a b l e I.
-s l
Q rl
•
•
I
A
S
•
7
i
i
i
i
i
i
h
L/
5. C.W
M6ssbauer
resonance
spectra
5. (,,)
Fig. 3 of e - S n 2 F 6 at v a r i o u s
temperatures.
Vol. 21, No. 8
-Sn2F6
TABLE M@ssbauer
parameters
1003
I of
~ - S n 2 F 6.
Sn(II)
Sn(IV)
T(K)
6(mm.s -I )
A(mm.s -I )
r(mm.s -I)
6(mm.s -I )
A(mm.s -I)
r(mm.s -I)
378 323 293 240 160 77 4.2
4.088(9) 4.094(8) 4.103(5) 4.119(7) 4.134(6) 4.162(5) 4.169(5)
0.429(9) 0.452(8) 0.493(5) 0.504(7) 0.565(6) 0.610(5) 0.645(5)
1.10(2) 1.11(2) 1.12(1) i.Ii(i) 1.12(1) i.i0(i) 1.17(1)
-0.402(9) -0.396(8) -0.392(5) -0.385(7) -0.371(6) -0.360(5) -0.352(5)
0.652(9) 0.673(8) O.68O(5) 0.719(7) 0.730(6) 0.759(5) 0.796(5)
0.98(2) 0.97(2) 0.95(1) 1.02(1) 1.03(1) i.ii(i) 1.20(1)
: i s o m e r shift r e l a t i v e to C a S n O 3 at A : quadrupole splittinq r : l i n e w i d t h at half-height.
293 K
The v a l u e s of the tin(II) M ~ s s b a u e r p a r a m e t e r s d i f f e r from those observed for m a n y o t h e r tin f l u o r i d e s (I0 to s ~))', The i s o m e r s h i f t at 293 K is r e l a t i v e l y h i g h (6 = 4.10 mm . but of t h~ same o r d e r of m a g n i t u d e as that o ~ SnF^, BF_ (6 = 3.98 m m . s - ) (13) or S n ( S b m 6 ) ~ ( 6 : 4.50 mm.s---) (i~). O ~ the o t h e r hand the quadrupole splitting ( A : 0.49 m m . s -~) is low c o m p a r a t i v e l y to the v a l u e s u s u a l l y o b t a i n e d for tin(II) f l u o r i des (i0, ii). N e v e r t h e l e s s for S n ( S b F 6 ) 2, w h e r e Sn(II) o c c u p i e s an ideal o c t a h e d r a l site, no q u a d r u p o l ~ s p l i t t i n g a p p e a r s . For t e t r a v a l e n t tin, if the v a l u e s of the i s o m e r shift are q u i t e s i m i l a r to t h o s e o b s e r v e d for e x a m p l e for SnFa (15) or K p S n F ~ (16) at r o o m t e m p e r a t u r e , on the c o n t r a r y t~e q u a d r u p o l e s ~ l i t [ i n g is d i f f e r e n t f r o m t h o s e r e p o r t e d for those c o m p o u n d s . A c c o r d i n g to the o b t a i n e d r e s u l t s tin(II) c o u l d be c o n s i d e red in ~ - S n 2 F _ as h a v i n g a s l i g h t l y d i s t o r t e d e n v i r o n m e n t . In the same w a y ~he q u a d r u p o l e s p l i t t i n g for tin(IV) s u g g e s t s for this c a t i o n a w e a k a s y m m e t r y of the o c t a h e d r a l site. The i s o m e r s h i f t s o b s e r v e d for the two o x i d a t i o n s t a t e s a s c e r t a i n the fact that the S n ( I V ) - F b o n d s h a v e a r e l a t i v e l y c o v a l e n t c h a r a c t e r , while the S n ( I I ) - F b o n d s are s t r o n g l y ionic. This r e s u l t was a l r e a d y s u g g e s t e d by B i r c h a l l et al. for c o m p o u n d s o b t a i n e d from SnF 2 and L e w i s a c i d s (13). Nevertheless, for the m i x e d tin f l u o r i d e it seems that at room_temperature a s h a r p ionic f o r m u l a t i o n such as (Sn)Z+(SnF~)Z~is~ot r e a l l y s u i t a b l e (13). A b e t t e r f o r m u l a t i o n w o u l d be ~Sn±±sn±VF ] i m p l y i n g f l u o r i n e b r i d g e s of 6-x Sn(II)-F-Sn(IV) type. Such b r l d g e s w o u l d a c c o u n t for a l a r g e r r i g i d i t y of the l a t t i c e and lead to r e c o i l l e s s f r a c t i o n s r e l a t i v e l y h i g h for tin n u c l e i .
1004
L. FOURNES, et al.
2 - Temperature
dependence
of the
isomer
shift
F r o m the t e m p e r a t u r e d e p e n d e n c e of wing relationship allows to c a l c u l a t e m a s s M e f f (17, 3), w h i c h is a s s o c i a t e d c i t e d m o r i o n of the M 6 s s b a u e r a t o m : d6 _
3 E0kB
Vo]. 21, No. 8
the i s o m e r s h i f t f o l l o an e f f e c t i v e vibrating w i t h the t h e r m a l l y ex-
[i] 2
dT
2 Mef f _ c
where E 0 Boltzmann
is the n u c l e a r constant.
transition
energy
for
( r a m sI )
(ram ..4+
Sr(~v] 4,16 - 0,36
4,14
4,12 -o, a8
.-~
4,10 4,08 0,40 L--.
i
i
i
I
100
200
300
400
FIG. 4 T e m p e r a t u r e d e p e n d e n c e of the s h i f t s of ~ - S n 2 F 6.
d6
-
--ISn(II)l = -(2.3 dt d6[sn(IV)~l dt
+ 0.i)
= -(1.39
i
T(K)
isomer
tin
and
kB
the
Fig. 4 s h o w s the v a r i a t i o n of the i s o m e r s h i f t vs temperature for 7 7 < T ( 3 7 8 K. (77 K c o r r e s p o n d i n g to the lower l i m i t of the high temperature validity range). The s o l i d l i n e s have been obt a i n e d by l i n e a r regression using the f i f t e e n experimental data with a correlation coefficient of 0.98 for Sn(II) a n d 0.99 for Sn (IV). The slop~ have respectively the values :
x i0 - 4 m m . s - i K -I
± 0.06)
x 1 0 - 4 m m . s - i K -I
From those values and relationship e f f e c t i v e v i b r a t i n g m a s s e s for b o t h tin M e f f [ S n ( I I ) ] = 178
± i0 amu
M e f f [ S n ( I V ) ] = 298
+ 14 amu
[i] we m a y nuclei :
determine
the
Vol. 21, No. 8
The relative
~-Sn2F 6
results obtained t o S n O (3) :
d6
2.46
for
× 10-4mm.s-iK
-I
Sn(II)
and
]005
are
Mef f
very
=
168
close
± 18
to
those
amu
dt 3 - Lattice
temperature
determination
For a thin absorber the temperature dependence ofl~e recoilless fraction for the 23.8 keV y-ray transition in Sn is well represented by the temperature dependence of t h e a r e a of the resonance peak : dLnf
_ dLnA
dt
[2]
dT
where A is t h e a r e a n o r m a l i z e d to a c o n v e n i e n t so t h a t s a m p l e c o m p a r i s o n s c a n be m a d e e a s i l y . In
the
dhnA
_
high 6 E
temperature
validity
limit
r
reference
point
:
[3]
k B o2
dt
where E is t h e r e c o i l e n e r g y f o r y - r a y a b s o r p t i o n in t h e a b s o r 0 ber and r @ the Debye temperature. Herber proposes to r e p l a c e D D by a lattlce temperature @M more closely connected to the m a s s notion. Substitution for the recoil energy in terms of the M6ssbauer y - r a y e n e r g y l e a d s to :
and
E -
2 E0
r
2Mc 2
equation
[3]
dLnA dt
becomes
:
-3E~
[4]
kBMC20~
A representative d a t a s e t of t h e t e m p e r a t u r e dependence of the area under the resonance c u r v e is g i v e n in Fig. 5 (the a r e a s have been normalized using the values at 77 K s e l e c t e d as t h e validity limit of t h e h i g h - t e m p e r a t u r e range). The correlation coefficient to t h e l i n e a r r e g r e s s i o n l e a d i n g to b o t h s o l i d l i n e s is ~ r ~ 9 f o r fifteen values in e a c h c a s e . U s i n g t h e a t o m i c m a s s of ± JSn l e a d s to f o l l o w i n g data :
M As
[Sn(II)]
a comparison,
: 166 for
-+ 8 K a n d SnO
-
0
M
0
M
[Sn(IV)]
: 229
K
(3)
: 211
-+ i0
K
"
1006
L. F O U R N E S ,
et al.
Vo]. 21, No. 8
Lo-[A(T K)]
Lo~[A(TK) ]
' °LA~IJ
~[A--T~-K!
o
Sn('@
0
snOv)
_0,5
-0,,5
SnO0~
_1,0
-I, 0
_I,5
2bo
.... 160
S u b s t i t u t i o n of M by the relationship [4] y i e l d s :
~TCK)
effective
vibrating
under
mass
Mef f into
3E~
dt By u s i n g
4~0
FIG. 5 of the n o r m a l i z e d area curve for ~ - S n 2 F 6.
Temperature dependence the r e s o n a n c e
dLnA
3~o
kBMef fc 2 8~2 Mef f v a l u e s
extracted
from
equation
[11 one
obtains:
!
eM[Sn(II) ] = 139
~ 3K
and
e~[Sn(IV)]
= 133
-% 3K.
It seems t h e r e f o r e that the m e t h o d t a k i n g into a c c o u n t the e f f e c t i v e v i b r a t i n g m a s s leads to l a t t i c e t e m p e r a t u r e s v a l u e s e L significantly lower than those deduced from e q u a t i o n ~. A~ a n a l o g o u s r e s u l t has b e e n o b s e r v e d for SnO :e. = 2 2 9 K and e.' = 193K (3) . One may a s c e r t a i n a c t u a l l y that for ~ lot of c o mM p o u n d s the l a t t i c e temperatures d e d u c e d from e q u a t i o n J4J are h i g h e r than those d e t e r m i n e d by o t h e r t e c h n i q u e s , in p a r t i c u l a r R a m a n spectroscopy (6).
4 - Temperature
dependence
of the r e c o i l l e s s
fractions
For a thin a b s o r b e r in the t e m p e r a t u r e range w h e r e high temperature limiting equation ~ is valid, there is a correspondence b e t w e e n r e c o i l l e s s f r a c t i o n f and 8M , n a m e l y :
f = exp
-3EgT 2 kBMC2eM
[6]
Vol. 21, No. 8
At of
u-Sn2F 6
293 K u s e of the form : f = exp
the
atomic
mass
1007
for
tin
leads
x 10 4
-5.248
to a r e l a t i o n s h i p
171
02 M
so t h a t t h e ~. v a l u e s p r e v i o u s l y calculated lead respectively to: f[Sn(II);293mK] "= 0 . 1 5 ± 0 . 0 1 a n d f [ S n ( I V ) ; 2 9 3 K ] : 0.31 ± 0.02. If the Sn atomic mass is replaced by the effective vibrating mass and if we consider the c o r r e s p o n d i n g lattice temperature e M' , f b e c o m e s f[Sn(II)]
-3.652
= exp
x 104
e'2[Sn(II)] M
f[Sn(IV)]
181
-2.096
: exp
x
104
0'2[Sn(IV)] M This 0.01
approach gives, as and f[Sn(IV) ; 293
expected K] : 0 . 3 1 TABLE
Summary
of
llgsn
: f[Sn(II) i 0.02.
; 293
)
data
-(2.3±0.i)xi0
(K-l)
d Log[A(TK)/A(77K)]
:
0.15
±
II
M6ssbauer
for
~ - S n 2 F 6.
Sn(II) d6(mm.s-iK-i dT
K~
-(6.5±0. 3)xl0
Sn(IV) -4
-3
-(1.39±0.06)xi0 -(4.0±0.2)xi0
-4 -3
dT Meff(uma)
% (K) v
oM f
(K)
(293
K)
176±10
298±14
166±8
211!i0
139±3
133±3
0.15±0.01
0.31±0.02
The main results obtained for ~-Sn_F_ are s u m m a r i z e d in z b .. T a b l e II. T h e t h e r m a l e v o l u t i o n of t h e L a m b - M o s s b a u e r factors f deduced from the equation 161 c a n be r e p r e s e n t e d by : f : exp
-1.791
x 102 2
T
°M T i t h 0 M [ S n ( I I ) ] : 166 + 8 K a n d 8 m [ S n ( I V ) ] : 211-+ i0 ne t e m p e r a t u r e dependence is s h o w n in Fig. 6.
K.
1008
L. FOURNES, et al.
o,4
The low t e m p e r a t u r e v a l u e s of the r e c o i l l e s s ~ractions obtained for ~ - S n 2 F 6 are relatively high: f[Sn(II);77K]=0.61±0,02, f[Sn(IV);77K]=0.75±0.02, if c o m p a r e d with those of SnF^ [4] : f [ S n ( I I ) ; 293K]=0~07 and f [Sn(II) ; 7 7 K ] = 0 . 5 0 . S u c h a r e s u l t is in g o o d a g r e e m e n t w i t h the p r e v i o u s l y a s s u m p t i o n : the strong rigidity of the lattice l e a d s to h i g h v a l u e s of f. The L a m b Mossbauer factors become e q u a l o n l y at v e r y l o w temperatures (Fig. 6) : at 4.2 K for e x a m p l e the areas corresponding to Sn(II) and Sn(IV) are s i m i l a r (Fig. 3).
SnC~
O,2
J
0
i
100
200
FIG.
L
,
300
400
Vol. 21, No. 8
T(K)
6
T h e r m a l e v o l u t i o n of the f f a c t o r s for e - S n 2 F 6
References 1 - M. C o r d e y - H a y e s , C h e m i c a l a p p l i c a t i o n s of M ~ s s b a u e r s p e c troscopy, V.I. Goldanskii a n d R.H. H e r b e r Ed., A c a d e m i c P r e s s , 314 (1968). 2 - R.H. H e r b e r , A.E. S m e l k i n s o n , M.J. S i e n k o a n d L.F. S c h n e e m e y e r , J. C h e m . P h y s . , 68, 3705 (1978). 3 - R.H.
Herber,
Phys.
Rev.
B,
27,
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4013
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Pannetier,
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R.H. H e r b e r , M ~ s s b a u e r e f f e c t m e t h o d o l o g y , a n d C.W. S e i d e l Ed., P l e n u m Press, vol. 8,
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and
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12
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13
- T. A,
Birchall, P.A.W. 1777 (1971).
14
- T. D.
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15
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J.R.
17
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G.M. K a l v i u s , M 6 s s b a u e r i s o m e r W a g n e r Ed., N o r t h - H o l l a n d ,
Dean
Benmiloud
Ruebenbauer and 9, 1831 (1981). and
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R.J.
J.
J.
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and
Pannetier, J.
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