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Growth of Sb2S3 single crystals by chemical vapour transport
Materials Chemistry and Physics, 1 7 (1987) 311-316
31l
SHORT COMMUNICATION
GROWTH OF Sb.2S3 SINGLE CRYSTALS BY CHEMICAL VAPOUR TRANSPORT
B. V E N G A T E S A N ,
N. K A N N I A H
and P. R A M A S A M Y
Crystal Growth Centre, Anna University, Madras - 600 025 (India) R e c e i v e d September 29, 1986; a c c e p t e d October 31, 1986
ABSTRACT Single crystals of a n t i m o n y t r i s u l f i d e have been grown by a chemical vapour t r a n s p o r t technique using iodine as the transporting agent. Single crystals were o b t a i n e d at a much lower t e m p e r a t u r e w h e n antimony and sulfur in the s t o i c h i o m e t r i c r a t i o were taken as the source along w i t h iodine. However when p o l y c r y s t a l l i n e antimony trisulfide was taken as the source with iodine, single crystals were not o b t a i n e d even at the m e l t i n g point of Sb2S 3. This o b s e r v a t i o n has been e x p l a i n e d on the basis of b o n d energy values.
INTRODUCTION The ferroelectric s e m i c o n d u c t o r Sb2S 3 has i n t e r e s t i n g properties such as photoconductivity,
with e l e c t r o o p ~ c a l
and ~ e c t r o m e c h a n i c a l
properties.
Sb2s 3
has become i n c r e a s i n g l y important in recent years on account of its photoe l e c t r i c properties.
Its larger p h o t o c o n d u c t i v i t y in the visible region makes
Sb2s 3 attractive for applications as a target material in TV p i c k - u p tubes of the v i d i c o n type and its s e n s i t i v i t y to X-rays is useful in X-ray detection. Zig-zag Sb - S - Sb chains are b o u n d into ribbons along the a - c plane, which ensure a perfect cleavage p e r p e n d i c u l a r to the b - axis. A quite e x t r a o r d i n a r y e n v i r o n m e n t exists for one half of the a n t i m o n y atoms, which are s u r r o u n d e d with five sulfur atoms, each of w h i c h in turn is linked to three Sb atoms.
The other
half of the Sb atoms and the remaining sulfur atoms exhibit the usual t r i v a l e n c y and b i v a l e n c y r e s p e c t i v e l y
[1,2].
~he c o m p o u n d is p r e v a l e n t l y covalent,
although an a p p r e c i a b l e ionic nature exists in the Sb - S bonds also been evidence of some r e s o n a n c e - c o v a l e n t b o n d i n g
0254-0584/87/$3.50
[3].
[2].
There has
Sb2S 3 belongs to an
© Elsevier Sequoia/Printed in The Netherlands
312 o r t h o r h o m b i c system with the space group Pbnm. It has the forbidden energy g a p 9 It is polar b e l o w 420 K (C 2V symmetry) and non polar (group
of 2.2 eV [4]. 16 (D2h)
above the curie t e m p e r a t u r e
crystal by v a c u u m e v a p o r a t i o n and liquid-gas interface
[5].
Earlier workers have g r o w n this
[6], solution [7], hydrothermal
[i0] methods.
[8], d i p - d r y [9]
These techniques yielded thin films. In
the p r e s e n t study we have grown single crystalline needles as well as platelets of Sb2S 3 by the chemical vapour transport technique using iodine as a transp o r t i n g agent.
E X P E R I M E N T A L DETAILS In the first series of experiments,
the ~ e m e n t s
Sb and S in s t o i c h i o m e t r i c
amounts and 5 m g / c m 3 of iodine have been t a k e n in a Corning glass ampoule of 18 cm length and 1 cm d i a m e t e r w i t h a very n a r r o w e x t e n s i o n at the b o t t o m to -5 initiate nucleation. A f t e r e v a c u a t i n g to i0 torr, the ampoule was sealed off and p l a c e d in a horizontal k a n t h a l - c o i l e d double zone furnace.
The growth zone
was c l e a n e d by initially m a i n t a i n i n g the temperature higher than the source zone for 24 hours.
A f t e r this, the t e m p e r a t u r e g r a d i e n t was reversed.
The source
t e m p e r a t u r e was m a i n t a i n e d at 490°C and that of the growth zone was m a i n t a i n e d at 410°C.
The experiment was r e p e a t e d with the growth zone at 420°C, keeping
the source zone at 490°C. In the second series of experiments,
about 2 g of a p o l y c r y s t a l l i n e a n t i m o n y
t r i s u l f i d e sample was p l a c e d in a C o m i n g
ampoule of the same dimensions.
The
temperature of the source zone was kept at 550°C while the growth zone temperature was 480°C.
RESULTS A N D DISCUSSION In the first series of e x p e r i m e n t s single crystal needles of length 8 m m and thickness 0.i to 0.2 m m were o b t a i n e d after I00 hours when the source zone t e m p e r a t u r e was 490°C and that of the growth zone was 420°C (Fig.l). shows a b u n c h of needles w i t h branching. ses towards the source zone.
Figure 2
The thickness of the needles decrea-
W h e n the growth zone t e m p e r a t u r e was m a i n t a i n e d
at 410 ° C, platelets of length 8 m ~ and b r e a d t h 0.i m m were o b t a i n e d
(Fig. 3a).
As the length of the p l a t e l e t increases the breadth sharply decreases towards the source zone (Fig. 3b).
This may be due to the slight v a r i a t i o n of
s u p e r s a t u r a t i o n with the t e m p e r a t u r e gradient.
The crystals were confirmed
by X-ray d i f f r a c t i o n analysis a n d found to be single crystals with an o r t h o r h o m b i c p o i n t g r o u p of s y m m e t r y w i t h lattice p a r a m e t e r s b = 1.131 ; values
[ii].
a = 1.122 ;
c = 0.383 n m w h i c h are in g o o d a c c o r d a n c e w i t h the l i t e r a t u r e
313
Fig.
Fig.
i.
2.
Needles of Sb2S 3 ( x i00).
A bunch of needles of Sb2S 3 ( x I00).
314
Fig.
Fig.
3a.
3b.
Platelets
Platelets
of Sb2S 3 ( x i00).
of Sb2S 3
( x i00).
315 W h e n p o l y c r y s t a l l i n e Sb2s 3 was t a k e n as the source m a t e r i a l a l o n g w i t h icdine, single c r y s t a ~ w e r e
n o t o b t a i n e d e v e n at a source t e m p e r a t u r e of 550°C.
This
c a n be e x p l a i n e d o n the b a s i s of b o n d e n e r g y values. W h e n the e l e m e n t s are t a k e n in the s t o i c h i o m e t r i c r a t i o w i t h iodine, the f o l l o w i n g c h e m i c a l t r a n s p o r t r e a c t i o n occurs
2 Sb(s )
+
3 S(s )
+
3 12
~
"
2 SbI 3
(g)
3 [ S2(g )
+
(i)
(g)
N o w iodine reacts w i t h a n t i m o n y t o f o r m the v o l a t i l e a n t i m o n y iodide.
This
i n v o l v e s t h e f i s s i o n of S b - S b b o n d s and the f o r m a t i o n of Sb-I bonds. W h e n the p o l y c r y s t a l l i n e Sb2s 3 was t a k e n as the source, the f o l l o w i n g chemical transport reaction should have occurred
Sb2S3(s )
+
3 12 (g)
2 SbI3(g )
+
3
(2)
S2(g)
In this case the f o r m a t i o n of SbI 3 w o u l d involve the f i s s i o n of Sb-S b o n d s w i t h the f o r m a t i o n of Sb-I bonds. B o n d d i s s o c i a t i o n e n e r g y is the energy r e q u i r e d to b r e a k a bond. s t a n d a r d d i s s o c i a t i o n e n e r g y of a S b - S b b o n d is 71.5 ± 1.5 K c a l / m o l s t a n d a r d d i s s o c i a t i o n e n e r g y of a Sb-S b o n d is 90.5 K c a l / m o l
The [12].
The
[13].
The f i s s i o n of a S b - S b b o n d is m o r e p o s s i b l e e v e n at a lower t e m p e r a t u r e c o m p a r e d to the f i s s i o n of a Sb-S bond.
Hence the f o r m a t i o n of the v o l a t i l e
i n t e r m e d i a t e compounds, n a m e l y SbI 3 and $2, is easier w h e n the elements are the source m a t e r i a l s .
Hence c h e m i c a l t r a n s p o r t of the m a t e r i a l t a k e s place at
a m u c h lower t e m p e r a t u r e of 490°C. T h e g a s e o u s i n t e r m e d i a t e compounds are d r i f t e d t o w a r d s the g r o w t h zone due to the t e m p e r a t u r e gradient.
Now the s y s t e m is s h i f t e d f r o m the e q u i l i b r i u m
c o n d i t i o n d u e t o the change in temperature.
2 SbI 3 (g)
+
3 ~ S2(g)
2 SbI 3
+
3 ~ S2(g ) ,
•
'
+
Sb2S3(s)
2 Sb(s )
+
There are two p o s s i b l e reactions,
(3)
3 12 (g)
3 S(s )
(g)
+
3 12
(4) (g)
Of t h e s e the t h i r d e q u a t i o n i n v o l v e s the f o r m a t i o n of t h e Sb-S b o n d and the fourth e q u a t i o n i n v o l v e s the f o r m a t i o n of the S b - S b bond.
From the b o n d e n e r g y
v a l u e s the f o r m a t i o n of the Sb-S b o n d is m o r e f a v o u r e d t h a n the S b - S b b o n d due t o h i g h e n e r g y release.
The s y s t e m w i t h the lowest e n e r g y is m o r e stable and
its f o r m a t i o n is h i g h l y favourable.
As the Sb-S b o n d is formed, m o r e e n e r g y
is r e l e a s e d a n d h e n c e a h i g h l y stable Sb2s 3 is formed as single c r y s t a l s at the g r o w t h zone.
The fourth e q u a t i o n is not possible.
316 When polycrystalline Sb2s 3 was taken as the source, the single crystals were not obtained even at 550°C.
From the foregoing arguments it is clear that the
formation of SbI 3 is not achieved even at the melting point of Sb2S 3 i.e. 550°C due to the high dissociation energy of Sb-S bond.
Hence the transport
was not observed and the crystals were not formed. We have not carried out the experiment above 550°C, because it will not then be a transport reaction.
Instead it would be a physical vapour deposition i.e.
crystal growth due to the deposition of vapour in equilibrium with the solid or liquid.
CONCLUSION Chemical vapour transport facilitates the growth of antimony trisulphide crystals.
The single crystals Of Sb2s 3 are formed at a much lower temperature
when the source material consists of the elements rather than polycrystalline material.
ACKNOWLEDGEMENT One of the authors (BV) thanks the C.S.I.R. for the award of the research fellowship.
REFERENCES 1
A.F. Wells, Structural Inor@anic Chemistry,
2
S. Scavnicar, Z. Krist., 114 (1960) 85.
2nd edn., Oxford, 1950, p.400.
3
A. Karpus and I.V. Batarunas, Chemical Bonds in Semiconductors and Solids, Consultants Bureau, New York, 1967, p.203.
4
A.G. Khasabov and I.Ya. Nikiforov, Kristallo~rafiya~
5
J. Grigas, J. Meskauskas and A. Orliukas, Phys. Status Solidi A, 37 (1976) K39.
6
L.S. Nadezhina, E.L. Grinzaid and E.A. Pikus, Zh. Prikl. Khim., 55 (1982) 489.
7
M.M. Abou Sekkina, Z.M. Hanafi and M.A. Moharm, Indian J. Phys. Part A, 54 (1980) 462.
8
V.I. Popolitov and G.F. Plakhov, Izv. Akad. Nauk SSSR, Neorq. Mater.q 19 (1983) 1651.
9
B.B. Nayak and H.N. Acharya, Thin Solid Films, 122 (1984) 93.
i0
S.H. Pawar, Shobha Tamhankar, P.N. Bhosale and M.D. Uplane, Indian J. Pure Appl. Phys.~ 21 (1983) 665.
Ii
ASTM 1~owder diffraction file (1965), ASTM Publication @ PDIS - 15i, printed in Baltimore, Md. (1965).
12
G. De Maria, J. Drowart and M.G. Inghram, J. Chem. Phys.~ 31 (1959) 1076.
13
F.M. Faure, M.J. Mitchell and R.W. Bartlett, High Temp. Sci.~ 4 (1972) 181.
16 (1971) 41.
31l
SHORT COMMUNICATION
GROWTH OF Sb.2S3 SINGLE CRYSTALS BY CHEMICAL VAPOUR TRANSPORT
B. V E N G A T E S A N ,
N. K A N N I A H
and P. R A M A S A M Y
Crystal Growth Centre, Anna University, Madras - 600 025 (India) R e c e i v e d September 29, 1986; a c c e p t e d October 31, 1986
ABSTRACT Single crystals of a n t i m o n y t r i s u l f i d e have been grown by a chemical vapour t r a n s p o r t technique using iodine as the transporting agent. Single crystals were o b t a i n e d at a much lower t e m p e r a t u r e w h e n antimony and sulfur in the s t o i c h i o m e t r i c r a t i o were taken as the source along w i t h iodine. However when p o l y c r y s t a l l i n e antimony trisulfide was taken as the source with iodine, single crystals were not o b t a i n e d even at the m e l t i n g point of Sb2S 3. This o b s e r v a t i o n has been e x p l a i n e d on the basis of b o n d energy values.
INTRODUCTION The ferroelectric s e m i c o n d u c t o r Sb2S 3 has i n t e r e s t i n g properties such as photoconductivity,
with e l e c t r o o p ~ c a l
and ~ e c t r o m e c h a n i c a l
properties.
Sb2s 3
has become i n c r e a s i n g l y important in recent years on account of its photoe l e c t r i c properties.
Its larger p h o t o c o n d u c t i v i t y in the visible region makes
Sb2s 3 attractive for applications as a target material in TV p i c k - u p tubes of the v i d i c o n type and its s e n s i t i v i t y to X-rays is useful in X-ray detection. Zig-zag Sb - S - Sb chains are b o u n d into ribbons along the a - c plane, which ensure a perfect cleavage p e r p e n d i c u l a r to the b - axis. A quite e x t r a o r d i n a r y e n v i r o n m e n t exists for one half of the a n t i m o n y atoms, which are s u r r o u n d e d with five sulfur atoms, each of w h i c h in turn is linked to three Sb atoms.
The other
half of the Sb atoms and the remaining sulfur atoms exhibit the usual t r i v a l e n c y and b i v a l e n c y r e s p e c t i v e l y
[1,2].
~he c o m p o u n d is p r e v a l e n t l y covalent,
although an a p p r e c i a b l e ionic nature exists in the Sb - S bonds also been evidence of some r e s o n a n c e - c o v a l e n t b o n d i n g
0254-0584/87/$3.50
[3].
[2].
There has
Sb2S 3 belongs to an
© Elsevier Sequoia/Printed in The Netherlands
312 o r t h o r h o m b i c system with the space group Pbnm. It has the forbidden energy g a p 9 It is polar b e l o w 420 K (C 2V symmetry) and non polar (group
of 2.2 eV [4]. 16 (D2h)
above the curie t e m p e r a t u r e
crystal by v a c u u m e v a p o r a t i o n and liquid-gas interface
[5].
Earlier workers have g r o w n this
[6], solution [7], hydrothermal
[i0] methods.
[8], d i p - d r y [9]
These techniques yielded thin films. In
the p r e s e n t study we have grown single crystalline needles as well as platelets of Sb2S 3 by the chemical vapour transport technique using iodine as a transp o r t i n g agent.
E X P E R I M E N T A L DETAILS In the first series of experiments,
the ~ e m e n t s
Sb and S in s t o i c h i o m e t r i c
amounts and 5 m g / c m 3 of iodine have been t a k e n in a Corning glass ampoule of 18 cm length and 1 cm d i a m e t e r w i t h a very n a r r o w e x t e n s i o n at the b o t t o m to -5 initiate nucleation. A f t e r e v a c u a t i n g to i0 torr, the ampoule was sealed off and p l a c e d in a horizontal k a n t h a l - c o i l e d double zone furnace.
The growth zone
was c l e a n e d by initially m a i n t a i n i n g the temperature higher than the source zone for 24 hours.
A f t e r this, the t e m p e r a t u r e g r a d i e n t was reversed.
The source
t e m p e r a t u r e was m a i n t a i n e d at 490°C and that of the growth zone was m a i n t a i n e d at 410°C.
The experiment was r e p e a t e d with the growth zone at 420°C, keeping
the source zone at 490°C. In the second series of experiments,
about 2 g of a p o l y c r y s t a l l i n e a n t i m o n y
t r i s u l f i d e sample was p l a c e d in a C o m i n g
ampoule of the same dimensions.
The
temperature of the source zone was kept at 550°C while the growth zone temperature was 480°C.
RESULTS A N D DISCUSSION In the first series of e x p e r i m e n t s single crystal needles of length 8 m m and thickness 0.i to 0.2 m m were o b t a i n e d after I00 hours when the source zone t e m p e r a t u r e was 490°C and that of the growth zone was 420°C (Fig.l). shows a b u n c h of needles w i t h branching. ses towards the source zone.
Figure 2
The thickness of the needles decrea-
W h e n the growth zone t e m p e r a t u r e was m a i n t a i n e d
at 410 ° C, platelets of length 8 m ~ and b r e a d t h 0.i m m were o b t a i n e d
(Fig. 3a).
As the length of the p l a t e l e t increases the breadth sharply decreases towards the source zone (Fig. 3b).
This may be due to the slight v a r i a t i o n of
s u p e r s a t u r a t i o n with the t e m p e r a t u r e gradient.
The crystals were confirmed
by X-ray d i f f r a c t i o n analysis a n d found to be single crystals with an o r t h o r h o m b i c p o i n t g r o u p of s y m m e t r y w i t h lattice p a r a m e t e r s b = 1.131 ; values
[ii].
a = 1.122 ;
c = 0.383 n m w h i c h are in g o o d a c c o r d a n c e w i t h the l i t e r a t u r e
313
Fig.
Fig.
i.
2.
Needles of Sb2S 3 ( x i00).
A bunch of needles of Sb2S 3 ( x I00).
314
Fig.
Fig.
3a.
3b.
Platelets
Platelets
of Sb2S 3 ( x i00).
of Sb2S 3
( x i00).
315 W h e n p o l y c r y s t a l l i n e Sb2s 3 was t a k e n as the source m a t e r i a l a l o n g w i t h icdine, single c r y s t a ~ w e r e
n o t o b t a i n e d e v e n at a source t e m p e r a t u r e of 550°C.
This
c a n be e x p l a i n e d o n the b a s i s of b o n d e n e r g y values. W h e n the e l e m e n t s are t a k e n in the s t o i c h i o m e t r i c r a t i o w i t h iodine, the f o l l o w i n g c h e m i c a l t r a n s p o r t r e a c t i o n occurs
2 Sb(s )
+
3 S(s )
+
3 12
~
"
2 SbI 3
(g)
3 [ S2(g )
+
(i)
(g)
N o w iodine reacts w i t h a n t i m o n y t o f o r m the v o l a t i l e a n t i m o n y iodide.
This
i n v o l v e s t h e f i s s i o n of S b - S b b o n d s and the f o r m a t i o n of Sb-I bonds. W h e n the p o l y c r y s t a l l i n e Sb2s 3 was t a k e n as the source, the f o l l o w i n g chemical transport reaction should have occurred
Sb2S3(s )
+
3 12 (g)
2 SbI3(g )
+
3
(2)
S2(g)
In this case the f o r m a t i o n of SbI 3 w o u l d involve the f i s s i o n of Sb-S b o n d s w i t h the f o r m a t i o n of Sb-I bonds. B o n d d i s s o c i a t i o n e n e r g y is the energy r e q u i r e d to b r e a k a bond. s t a n d a r d d i s s o c i a t i o n e n e r g y of a S b - S b b o n d is 71.5 ± 1.5 K c a l / m o l s t a n d a r d d i s s o c i a t i o n e n e r g y of a Sb-S b o n d is 90.5 K c a l / m o l
The [12].
The
[13].
The f i s s i o n of a S b - S b b o n d is m o r e p o s s i b l e e v e n at a lower t e m p e r a t u r e c o m p a r e d to the f i s s i o n of a Sb-S bond.
Hence the f o r m a t i o n of the v o l a t i l e
i n t e r m e d i a t e compounds, n a m e l y SbI 3 and $2, is easier w h e n the elements are the source m a t e r i a l s .
Hence c h e m i c a l t r a n s p o r t of the m a t e r i a l t a k e s place at
a m u c h lower t e m p e r a t u r e of 490°C. T h e g a s e o u s i n t e r m e d i a t e compounds are d r i f t e d t o w a r d s the g r o w t h zone due to the t e m p e r a t u r e gradient.
Now the s y s t e m is s h i f t e d f r o m the e q u i l i b r i u m
c o n d i t i o n d u e t o the change in temperature.
2 SbI 3 (g)
+
3 ~ S2(g)
2 SbI 3
+
3 ~ S2(g ) ,
•
'
+
Sb2S3(s)
2 Sb(s )
+
There are two p o s s i b l e reactions,
(3)
3 12 (g)
3 S(s )
(g)
+
3 12
(4) (g)
Of t h e s e the t h i r d e q u a t i o n i n v o l v e s the f o r m a t i o n of t h e Sb-S b o n d and the fourth e q u a t i o n i n v o l v e s the f o r m a t i o n of the S b - S b bond.
From the b o n d e n e r g y
v a l u e s the f o r m a t i o n of the Sb-S b o n d is m o r e f a v o u r e d t h a n the S b - S b b o n d due t o h i g h e n e r g y release.
The s y s t e m w i t h the lowest e n e r g y is m o r e stable and
its f o r m a t i o n is h i g h l y favourable.
As the Sb-S b o n d is formed, m o r e e n e r g y
is r e l e a s e d a n d h e n c e a h i g h l y stable Sb2s 3 is formed as single c r y s t a l s at the g r o w t h zone.
The fourth e q u a t i o n is not possible.
316 When polycrystalline Sb2s 3 was taken as the source, the single crystals were not obtained even at 550°C.
From the foregoing arguments it is clear that the
formation of SbI 3 is not achieved even at the melting point of Sb2S 3 i.e. 550°C due to the high dissociation energy of Sb-S bond.
Hence the transport
was not observed and the crystals were not formed. We have not carried out the experiment above 550°C, because it will not then be a transport reaction.
Instead it would be a physical vapour deposition i.e.
crystal growth due to the deposition of vapour in equilibrium with the solid or liquid.
CONCLUSION Chemical vapour transport facilitates the growth of antimony trisulphide crystals.
The single crystals Of Sb2s 3 are formed at a much lower temperature
when the source material consists of the elements rather than polycrystalline material.
ACKNOWLEDGEMENT One of the authors (BV) thanks the C.S.I.R. for the award of the research fellowship.
REFERENCES 1
A.F. Wells, Structural Inor@anic Chemistry,
2
S. Scavnicar, Z. Krist., 114 (1960) 85.
2nd edn., Oxford, 1950, p.400.
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