- Email: [email protected]
Growth of hollow SbSI crystals from the vapour
432
Journal of Crystal Growth 79(1986) 432-435 North-Holland, Amsterdam
GROWTH OF HOLLOW SbSI CRYSTALS FROM THE VAPOUR D. ARIVUOLI, F.D. GNANAM and P. RAMASAMY Crystal Growth Centre, Anna University, Madras-600 25, india
Antimony sulphoiodide hollow crystals were grown from the vapour. The size of the needles ranged from I to 1.5 cm in length and 0.5 to 1 mm in cross section. The conditions under which the hollow crystals were formed were also established.
1. Introduction Interest in ferroelectrics of V—VT—Vu group compounds is mainly due to their semiconducting properties. SbSI is found to be superior to many known ferroelectrics by virtue of its characteristic properties; pyroelectric [1], piezoelectric [2], electro-optic [3] and photoelectric [4]. The combination of all these properties favours efficient fabrication of optical light modulators, low-pressure high-sensitivity pick-up cartridges, piezo-electric elements, etc. When compared with other ferroelectric materials discovered so far it has the maximum piezo-electric modulus, Single crystal and polycrystalline SbSI differ very strongly in their piezoelectric properties [5]. The possibility of producing SbSI piezo ceramics was considered [6] as it possesses interesting properties for practical purposes. SbSI ceramics are characterised by a strongly pronounced temperature hysteresis over a broad temperature range [7]. The anisotropy of the growth rate along different directions leads to the formation of needle or plate morphology. The (001) face of a needle is generally not well defined and also not smooth. According to Donges [8], SbSI forms a close hexagonal packing consisting of iodine and sulphur molecules and antimony cations are accommodated in the voids. The sulphur atom is surrounded by four antimony atoms while the iodine is quadruply coordinated by antimony. As half of the anions (sulphur are small in size and are double charged, they are strongly attracted by the Sb atom, and they partially force away the singly
charged iodine atoms. Due to the different charges and sizes of these atoms, there arises a strong bond leading to the occurrence of double chains (Sb2S2 12),,. The chains are linked by the screw axis in such a way that the antimony in one chain contacts the sulphur in the neighbouring chain. The binding in the chains is of the covalent-ion type and weak Van der Waals bonds between the neighbouring chain. The phase diagram of antimony sulphur iodine shows that the binary systems, Sb2S3—Sb13, SbSI—S and SbSI—Sb, are stable [9], while Sb2S3 reacts with iodine to form SbSI [10] at 623 K. As the phase diagram shows, SbSI melts congruently at 673 ±5 K. The slope in the liquidus curve in the vicinity of the compound leads to substantial dissociation in the melt. The crystalline SbSI evaporates incongruently by the simple dissociation scheme, 3 ~ Sb2S3(s) + Sb13(g). The homogeneity region of SbSI has a maximum at 49.9—50.2 mol% of Sb2 S3 at a temperature of 653 K. The ferroelectric transition is also found to vary from 291 to 294 K in the same range of composition. SbSI can be prepared by fusing stoichiometric amounts of (1) Sb13—Sb2S3, (2) Sb, S and 1, (3) Sb13, Sb and S, and (4) Sb2 S3, I and Sb. When elements are used as starting materials care has to be taken to avoid self-heating of the material, due to the rapid increase in the reactions accompanied by a sharp rise in pressure in the ampoule, which may initiate an explosion. Another method of
0022-0248/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
D. Arivuoli eta!.
/
Growth of hollow SbSI crystalsfrom the vapour
433
synthesising SbSI is by reacting Sb2 S3 with I, at high temperatures. 1.1. Hollow crystals Hollow crystals have stimulated the interest of many researchers due to the complexity in the growth mechanism. Hollow crystals were reported for Il—VI compounds grown from the vapour [11] and for CsCl and NaCl grown from solution [12]. Ice hollow crystals were also reported [13] and they show some dependence on the conditions of growth, like supersaturation and temperature. Hollow needles of selenium [14] are also obtained by hydrothermal crystallization. Hollow crystals in the V—VI compounds like Sb2S3, Bi2S3 and As2Te3 [15,16], in the mixed system Sb2S3—Sb2Se3 [17], and also in Bi2Se2S have been reported. Hollow crystals in V—VT—Vu group compounds like BiSI [18] and SbSBr were also observed. 2. Exlenment Antimony sulphoiodide polycrystalline material was prepared both (1) directly from elements and (2) reacting Sb2 S3 with Sb and iodine. The elements of purity Sb (99.999%) S(99.999%) analar grade (99.9%) resublimed iodine and Sb2 S3 (99.99%) were used. They were mixed in the stoichiometric ratio in glass ampoule and of sealed 5 aTorr. In the case the in a vacuum of i0 elementary substances, the ampoule containing temperature was raised to 170°C in 6 h and then increased slowly to 450°Cand kept for a day in order to homogenize the melt. It was cooled to room temperature and confirmed as SbSI by wide angle X-ray analysis by the agreement of reflections with the reported values [19]. About 10 g of the sample were taken in a glass tube of length 15 cm and diameter 10 mm, sealed at a pressure of i0~ Torr. Hollow crystals were grown in a twozone horizontal furnace by sublimation. The source zone was kept at 420°Cand the growth zone at 340, 330, 320 and 300°C.
Fig. 1. Irregularly shaped hollow needle(x 112.5).
Well developed (220) prism faces were obtained for the growth zone temperature of 340°C [20]. For the growth zone temperature of 330°C, irregular shaped hollow needles are obtained, as shown in fig. 1. Fig. 2 shows the hollow needle produced when the growth temperature was 320°C. One side of these crystals consists of many hollow needles with a new type of morphology. When the
3. Results and discussion After two days, hollow crystals of SbSI were obtained, depending on the growth conditions.
Fig. 2. Hollow needle for the growth zone temperature of 320°C(x 112.5).
434
D. Arivuoli eta!.
_
/
Growth of hollow SbSI crystalsfrom the vapour
_
1
I Fig. 5. Higher magnification of fig. 4 (X 855). Fig. 3. Hollow needles for the growth zone temperature of 300°C(x112.5).
temperature was kept at 300°C, hollow crystals as shown in fig. 3 are obtained, with many needles branching from the main needle. Fig. 4 shows the layer growth patterns with a gradual rising or elevation towards the hollow part. Fig. 5 is a higher magnification of fig. 4 showing growth layers gradually rising in height when they approach the hollow part. On some of the needle surfaces, layers with elevated mounds are seen just near the start of the hollow. In some needles growth hillocks arranged parallel to the opening are observed as depicted by fig. 6. The SbSI crystal growth mechanism differs in various crystallographic directions. Along the [0011 direction, growth can take place without the for-
mation of two-dimensional nuclei since in the structure there is a screw component in this (2~ screw axis) direction [21]. The [hk0] faces can grow either by formation of 2D nucleation or on dislocations and other crystal surface defects. Thus different minimum supersaturations are required for growth to proceed in the [001] and perpendicular directions. For growth along the c-directions, small supersaturations will be sufficient since it is a K-face [22] and grows more rapidly, but a critical supersaturation is necessary for the formation of the 2D nuclei in the other faces. Just before the creation of the cavity, the layers increase in height as they approach the cavity. The higher magnification shows them as triangular hillocks. The crystal consists of bundles of whiskers arranged parallel to the c-axis. At some point due
a
~.,‘
Fig. 4. Growth layers just before the hollow ( X 315).
-T
~
_
Fig. 6. Growth hillocks arranged parallel to the opening ( X 315).
D. Arivuoli eta!.
/ Growth of hollow SbSI crystals from thevapour
to dislocation or impurity, some of the whiskers are completely retarded from growing further and the other whiskers, which are able to continue, form the outer lateral surface. When the hinderance is at the centre, a complete hollow with well-defined hollow prisms is formed. If the hinderance is just near the edges, there is a chance of getting an open lateral surface. The surface of some of the hollow crystals shows pits due to vapour etching. In some of the needles pits were lined up parallel to the cavity.
4. Conclusion The morphology of the SbSI hollow crystal was found to depend on the temperature differences. The growth mechanism of the hollow crystals is explained on the basis of crevice creation occurring due to dislocations and impurities.
Acknowledgment
[2] D. Berlincourt, H. Jaffe, [3] [4] [5] [6]
435
W.I. Merz and R. Nitsche,
AppI.
Phys. Letters 4 (1964) 61. R. Kern, J. Phys. Chem. Solids 23 (1962) 249. R. Nitsche, H. Roetschi and P. Wild. Appl. Phys. Letters 4 (1964) 210. K. Harnano and T. Shimmi, J. Phys. Soc. Japan 33 (1972) 118. K. Okazaki and S. Narushima, J. Cerain. Assoc. Japan 76
(1968) 19. [7] MS. Novikov, NP. Kachalov, IN. Polandov, A.A. Grekov and L.N. Syrkin, Vestn. Mosk. Univ. Ser. Khim. 76(1968) 19. [8] E. Donges, Z. Anorg. Aligem. Chem. 265 (1951) 56. [9] T. Mon and H. Taniura, J. Phys. Soc. Japan 19 (1964) 1247. [10] L.M. Belyaev, V.A. Lyakhovitsakaya, G.B. Netesov, MV. Mokhosoev and SM. Aleikima, Izv. Akad. Nauk SSSR, Neorg. Mater. 1 (1965) 2178. [11] [12] [13] [14]
S. Simov, J. Mater. Sci. 11(1976) 2319. H. Iwanaga, T. Yoshiie, T. Yamaguchi and N. Shibata, J. Crystal Growth 51(1981) 438. D. Shaw and B.J. Mason, Phil. Mag. 46 (1955) 249. 374. ED. Koib and R.A~Laudise, J. Crystal Growth 8 (1971) 191. [15] A. Goumann and P. Bohac, S. Crystal Growth 15 (1972) 304. [16] D. Arivuoli, F.D. Gnanaxn and P. Raniasamy, I. Mater. Sci. Letters, in press. [17] D. Arivuoli, F.D. Gnanain and P. Rainasamy, S. Mater.
One of the authors (D.A.) thanks the University Grants Commission for the financial assistance to carry out this work.
Sci. Letters, in press. [18] D. Arivuoli, F.D. Gnanam and P. Ran3asa!ny, S. Mater. Sci., in press. [19] A. Kukuchi, Y. Oka and E. Sawaguchi, J. Phys. Soc.
References
Japan 23 (1967) 337. [201 D. Arivuoli, F.D. Gnanain and P. Raniasainy, J. Mater. Sci., in press. [21] H. Neels, W. Schmitz, H. Hottinan, R. Rosner and W. Topp, Kristall Tech. 6 (1971) 225. [22] P. Hartman and W.G. Perdok, Acta Cryst. 8 (1955) 49, 521.
[1] B.P. Grigas, I.P. Grigas and R.P. Belyatskar, Fiz. Tverd. Tela 9 (1967) 1532.
Journal of Crystal Growth 79(1986) 432-435 North-Holland, Amsterdam
GROWTH OF HOLLOW SbSI CRYSTALS FROM THE VAPOUR D. ARIVUOLI, F.D. GNANAM and P. RAMASAMY Crystal Growth Centre, Anna University, Madras-600 25, india
Antimony sulphoiodide hollow crystals were grown from the vapour. The size of the needles ranged from I to 1.5 cm in length and 0.5 to 1 mm in cross section. The conditions under which the hollow crystals were formed were also established.
1. Introduction Interest in ferroelectrics of V—VT—Vu group compounds is mainly due to their semiconducting properties. SbSI is found to be superior to many known ferroelectrics by virtue of its characteristic properties; pyroelectric [1], piezoelectric [2], electro-optic [3] and photoelectric [4]. The combination of all these properties favours efficient fabrication of optical light modulators, low-pressure high-sensitivity pick-up cartridges, piezo-electric elements, etc. When compared with other ferroelectric materials discovered so far it has the maximum piezo-electric modulus, Single crystal and polycrystalline SbSI differ very strongly in their piezoelectric properties [5]. The possibility of producing SbSI piezo ceramics was considered [6] as it possesses interesting properties for practical purposes. SbSI ceramics are characterised by a strongly pronounced temperature hysteresis over a broad temperature range [7]. The anisotropy of the growth rate along different directions leads to the formation of needle or plate morphology. The (001) face of a needle is generally not well defined and also not smooth. According to Donges [8], SbSI forms a close hexagonal packing consisting of iodine and sulphur molecules and antimony cations are accommodated in the voids. The sulphur atom is surrounded by four antimony atoms while the iodine is quadruply coordinated by antimony. As half of the anions (sulphur are small in size and are double charged, they are strongly attracted by the Sb atom, and they partially force away the singly
charged iodine atoms. Due to the different charges and sizes of these atoms, there arises a strong bond leading to the occurrence of double chains (Sb2S2 12),,. The chains are linked by the screw axis in such a way that the antimony in one chain contacts the sulphur in the neighbouring chain. The binding in the chains is of the covalent-ion type and weak Van der Waals bonds between the neighbouring chain. The phase diagram of antimony sulphur iodine shows that the binary systems, Sb2S3—Sb13, SbSI—S and SbSI—Sb, are stable [9], while Sb2S3 reacts with iodine to form SbSI [10] at 623 K. As the phase diagram shows, SbSI melts congruently at 673 ±5 K. The slope in the liquidus curve in the vicinity of the compound leads to substantial dissociation in the melt. The crystalline SbSI evaporates incongruently by the simple dissociation scheme, 3 ~ Sb2S3(s) + Sb13(g). The homogeneity region of SbSI has a maximum at 49.9—50.2 mol% of Sb2 S3 at a temperature of 653 K. The ferroelectric transition is also found to vary from 291 to 294 K in the same range of composition. SbSI can be prepared by fusing stoichiometric amounts of (1) Sb13—Sb2S3, (2) Sb, S and 1, (3) Sb13, Sb and S, and (4) Sb2 S3, I and Sb. When elements are used as starting materials care has to be taken to avoid self-heating of the material, due to the rapid increase in the reactions accompanied by a sharp rise in pressure in the ampoule, which may initiate an explosion. Another method of
0022-0248/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
D. Arivuoli eta!.
/
Growth of hollow SbSI crystalsfrom the vapour
433
synthesising SbSI is by reacting Sb2 S3 with I, at high temperatures. 1.1. Hollow crystals Hollow crystals have stimulated the interest of many researchers due to the complexity in the growth mechanism. Hollow crystals were reported for Il—VI compounds grown from the vapour [11] and for CsCl and NaCl grown from solution [12]. Ice hollow crystals were also reported [13] and they show some dependence on the conditions of growth, like supersaturation and temperature. Hollow needles of selenium [14] are also obtained by hydrothermal crystallization. Hollow crystals in the V—VI compounds like Sb2S3, Bi2S3 and As2Te3 [15,16], in the mixed system Sb2S3—Sb2Se3 [17], and also in Bi2Se2S have been reported. Hollow crystals in V—VT—Vu group compounds like BiSI [18] and SbSBr were also observed. 2. Exlenment Antimony sulphoiodide polycrystalline material was prepared both (1) directly from elements and (2) reacting Sb2 S3 with Sb and iodine. The elements of purity Sb (99.999%) S(99.999%) analar grade (99.9%) resublimed iodine and Sb2 S3 (99.99%) were used. They were mixed in the stoichiometric ratio in glass ampoule and of sealed 5 aTorr. In the case the in a vacuum of i0 elementary substances, the ampoule containing temperature was raised to 170°C in 6 h and then increased slowly to 450°Cand kept for a day in order to homogenize the melt. It was cooled to room temperature and confirmed as SbSI by wide angle X-ray analysis by the agreement of reflections with the reported values [19]. About 10 g of the sample were taken in a glass tube of length 15 cm and diameter 10 mm, sealed at a pressure of i0~ Torr. Hollow crystals were grown in a twozone horizontal furnace by sublimation. The source zone was kept at 420°Cand the growth zone at 340, 330, 320 and 300°C.
Fig. 1. Irregularly shaped hollow needle(x 112.5).
Well developed (220) prism faces were obtained for the growth zone temperature of 340°C [20]. For the growth zone temperature of 330°C, irregular shaped hollow needles are obtained, as shown in fig. 1. Fig. 2 shows the hollow needle produced when the growth temperature was 320°C. One side of these crystals consists of many hollow needles with a new type of morphology. When the
3. Results and discussion After two days, hollow crystals of SbSI were obtained, depending on the growth conditions.
Fig. 2. Hollow needle for the growth zone temperature of 320°C(x 112.5).
434
D. Arivuoli eta!.
_
/
Growth of hollow SbSI crystalsfrom the vapour
_
1
I Fig. 5. Higher magnification of fig. 4 (X 855). Fig. 3. Hollow needles for the growth zone temperature of 300°C(x112.5).
temperature was kept at 300°C, hollow crystals as shown in fig. 3 are obtained, with many needles branching from the main needle. Fig. 4 shows the layer growth patterns with a gradual rising or elevation towards the hollow part. Fig. 5 is a higher magnification of fig. 4 showing growth layers gradually rising in height when they approach the hollow part. On some of the needle surfaces, layers with elevated mounds are seen just near the start of the hollow. In some needles growth hillocks arranged parallel to the opening are observed as depicted by fig. 6. The SbSI crystal growth mechanism differs in various crystallographic directions. Along the [0011 direction, growth can take place without the for-
mation of two-dimensional nuclei since in the structure there is a screw component in this (2~ screw axis) direction [21]. The [hk0] faces can grow either by formation of 2D nucleation or on dislocations and other crystal surface defects. Thus different minimum supersaturations are required for growth to proceed in the [001] and perpendicular directions. For growth along the c-directions, small supersaturations will be sufficient since it is a K-face [22] and grows more rapidly, but a critical supersaturation is necessary for the formation of the 2D nuclei in the other faces. Just before the creation of the cavity, the layers increase in height as they approach the cavity. The higher magnification shows them as triangular hillocks. The crystal consists of bundles of whiskers arranged parallel to the c-axis. At some point due
a
~.,‘
Fig. 4. Growth layers just before the hollow ( X 315).
-T
~
_
Fig. 6. Growth hillocks arranged parallel to the opening ( X 315).
D. Arivuoli eta!.
/ Growth of hollow SbSI crystals from thevapour
to dislocation or impurity, some of the whiskers are completely retarded from growing further and the other whiskers, which are able to continue, form the outer lateral surface. When the hinderance is at the centre, a complete hollow with well-defined hollow prisms is formed. If the hinderance is just near the edges, there is a chance of getting an open lateral surface. The surface of some of the hollow crystals shows pits due to vapour etching. In some of the needles pits were lined up parallel to the cavity.
4. Conclusion The morphology of the SbSI hollow crystal was found to depend on the temperature differences. The growth mechanism of the hollow crystals is explained on the basis of crevice creation occurring due to dislocations and impurities.
Acknowledgment
[2] D. Berlincourt, H. Jaffe, [3] [4] [5] [6]
435
W.I. Merz and R. Nitsche,
AppI.
Phys. Letters 4 (1964) 61. R. Kern, J. Phys. Chem. Solids 23 (1962) 249. R. Nitsche, H. Roetschi and P. Wild. Appl. Phys. Letters 4 (1964) 210. K. Harnano and T. Shimmi, J. Phys. Soc. Japan 33 (1972) 118. K. Okazaki and S. Narushima, J. Cerain. Assoc. Japan 76
(1968) 19. [7] MS. Novikov, NP. Kachalov, IN. Polandov, A.A. Grekov and L.N. Syrkin, Vestn. Mosk. Univ. Ser. Khim. 76(1968) 19. [8] E. Donges, Z. Anorg. Aligem. Chem. 265 (1951) 56. [9] T. Mon and H. Taniura, J. Phys. Soc. Japan 19 (1964) 1247. [10] L.M. Belyaev, V.A. Lyakhovitsakaya, G.B. Netesov, MV. Mokhosoev and SM. Aleikima, Izv. Akad. Nauk SSSR, Neorg. Mater. 1 (1965) 2178. [11] [12] [13] [14]
S. Simov, J. Mater. Sci. 11(1976) 2319. H. Iwanaga, T. Yoshiie, T. Yamaguchi and N. Shibata, J. Crystal Growth 51(1981) 438. D. Shaw and B.J. Mason, Phil. Mag. 46 (1955) 249. 374. ED. Koib and R.A~Laudise, J. Crystal Growth 8 (1971) 191. [15] A. Goumann and P. Bohac, S. Crystal Growth 15 (1972) 304. [16] D. Arivuoli, F.D. Gnanaxn and P. Raniasamy, I. Mater. Sci. Letters, in press. [17] D. Arivuoli, F.D. Gnanain and P. Rainasamy, S. Mater.
One of the authors (D.A.) thanks the University Grants Commission for the financial assistance to carry out this work.
Sci. Letters, in press. [18] D. Arivuoli, F.D. Gnanam and P. Ran3asa!ny, S. Mater. Sci., in press. [19] A. Kukuchi, Y. Oka and E. Sawaguchi, J. Phys. Soc.
References
Japan 23 (1967) 337. [201 D. Arivuoli, F.D. Gnanain and P. Raniasainy, J. Mater. Sci., in press. [21] H. Neels, W. Schmitz, H. Hottinan, R. Rosner and W. Topp, Kristall Tech. 6 (1971) 225. [22] P. Hartman and W.G. Perdok, Acta Cryst. 8 (1955) 49, 521.
[1] B.P. Grigas, I.P. Grigas and R.P. Belyatskar, Fiz. Tverd. Tela 9 (1967) 1532.