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A simple solvothermal route to copper chalcogenides
July 2000
Materials Letters 44 Ž2000. 366–369 www.elsevier.comrlocatermatlet
A simple solvothermal route to copper chalcogenides Z.H. Han, Y.P. Li, H.Q. Zhao, S.H. Yu, X.L. Yin, Y.T. Qian ) Department of Chemistry and Structure Research Laboratory, UniÕersity of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China Received 30 October 1999; received in revised form 8 February 2000; accepted 9 February 2000
Abstract Using copperŽI. chloride, sodium oxalate and elemental chalcogen, copper chalcogenide powders were synthesized through a simple solvothermal route. Pseudocubic Cu 1.80 S and orthorhombic Cu 31S16 single phases synthesized in ethylenediamine ŽEn. are made up of polyhedral particles, cubic Cu 2yx Se synthesized in pyridine ŽPy. was irregular in shape, while Cu 1.75Te synthesized in distilled water appeared to be spherical. Other chalcogenides were also formed under different conditions. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Copper chalcogenide; Solvothermal; Synthesis
1. Introduction Many applications have been found for copper sulfides, such as photovoltaic cells w1x, copper ion selective microelectrodes w2x, and sensors for detecting hydrogen sulfide in the atmosphere w3x. Although the reports concerning copper selenides and tellurides were relatively less, they could also be used for various purposes w4,5x. In recent years, the spectroscopy of copper sulfides was investigated w6,7x, the electron excitation energy in copper selenide clusters was calculated w8x, and the structure of copper telluride cluster was studied w9x. Meanwhile, a number of synthetic techniques have been developed for copper chalcogenides. Copper sulfide nanoparticles were synthesized in Triton-X 100 water-in-oil microemulsion w10x, whereas nanocrystalline copper
)
Corresponding author. E-mail address: [email protected] ŽY.T. Qian..
selenide powders were obtained in ethylenediamine ŽEN. w11x. Using mixtures of metallic copper and chalcogen as reactants, copper chalcogenide powders were systematically prepared through the sonochemical processes w12x, mechanical alloying with high energy w13x, as well as reactions in liquid ammonia w14x. This paper introduces a simple solvothermal route to well-crystallized copper chalcogenide powders, such as Cu 1.80 S, Cu 31 S 16 , Cu 2yx Se and Cu 1.75Te, employing copper salt rather than metallic copper in various solvents.
2. Experimental Analytically pure CuCl, Na 2 C 2 O4 , together with S, Se, or Te served as initial materials. An appropriate amount of the reactants was ground and put into a stainless steel autoclave with a capacity of 35 ml.
00167-577Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 0 6 0 - 4
Z.H. Han et al.r Materials Letters 44 (2000) 366–369
367
out on a Drmax-gA rotation anode X-ray diffractometer with Ni-filtered Cu K a radiation. In order to observe the morphology of crystallites in a single phase, an X-650 scanning electron microanalyzer was employed to take the scanning electron microscopy ŽSEM..
3. Results and discussion
Fig. 1. XRD patterns of typical samples: Ža. pseudocubic Cu 1.80 S synthesized at 1808C in En, Žb. orthorhombic Cu 31 S16 synthesized at 1808C in En, Žc. cubic Cu 2y x Se synthesized at 2408C in Py, Žd. hexagonal Cu 1.75Te synthesized at 180 in water.
The selected solvent filled the autoclave up to 85% of its total volume. During the experiment, En, pyridine ŽPy., or distilled water was used for the solvent. The autoclave was maintained under suitable temperatures for 12 h before it was air-cooled to ambient temperature. The products were collected, washed with distilled water, and dried in vacuum at 608C. X-ray diffraction ŽXRD. of the powders was carried
Quite a few single phases of copper chalcogenides were obtained under controlled conditions. Fig. 1 shows XRD patterns of typical samples. According to the indexing results, phase-pure pseudocubic Cu 1.80 S and orthorhombic Cu 31 S16 powders were synthesized in En at 1808C, cubic Cu 2y x Se was synthesized in Py at 2408C, and hexagonal Cu 1.75Te was synthesized in water at 1808C. The sharp diffraction peaks of the powders imply their good crystallinity. Table 1 lists refined cell constants of the phases, the parameters are all close to the reported data w15x. Influential factors on the product were investigated. Different ratio of the starting materials could derive different products. When the molar ratio of copperŽI. chloride, sodium oxalate and sulfur was 4:1:2, orthorhombic Cu 31 S 16 was given at 1808C. When the ratio became 1:1:1, however, pseudocubic Cu 1.80 S was afforded even if the reaction was performed at the same temperature and in the same solvent. By changing the ratio of reactants, mixed Cu x S powders were formed. If the quantity of initial selenium was more than that required for Cu 2y x Se single phase, a mixture of Cu 2y x Se, CuSe and CuSe 2 would be generated. Various reaction media, including organic and inorganic solvents, may be applicable to the synthesis of copper chalcogenides, al-
Table 1 Experimental results of copper chalcogenides synthesized under various conditions Starting materials
Molar ratio
Solvent
Temperature Ž8C.
Product
˚. Cell constants ŽA
CuCl q Na 2 C 2 O4 q S CuCl q Na 2 C 2 O4 q S CuCl q Na 2 C 2 O4 q Se CuCl q Na 2 C 2 O4 q Te
1:1:1 4:1:2 2:1:1 2:3:2
En En Py H 2O
180 180 240 180
Cu 1.80 S Cu 31 S16 Cu 2yx Se Cu 1.75Te
a s 27.859 a s 26.936, b s 15.696, c s 13.548 a s 5.733 a s 4.166, c s 21.583
368
Z.H. Han et al.r Materials Letters 44 (2000) 366–369
Fig. 2. SEM images of powders of copper chalcogenides: Ža. Cu 1.80 S, Žb. Cu 31 S16 , Žc. Cu 2yx Se, Žd. Cu 1.75Te.
though the selected solvent usually favors certain copper chalcogenide. Moreover, the reaction temperature exerts an effect to the product distribution. Copper selenides could be prepared not only in Py, but also in En or water. As for the synthesis of copper tellurides, En was another suitable reaction medium besides Py, in which Cu 1.80Te was formed at 1808C and Cu 2.86Te 2 was formed at higher temperature, 2208C. The powders of sulfides, selenide and telluride are composed of particles with different morphologies. Fig. 2 refers to the TEM images of Cu 1.80 S, Cu 31 S 16 , Cu 2y x Se, and Cu 1.75Te single phases. Cu 1.80 S and Cu 31 S16 crystals seem to be polyhedral, whereas Cu 2y x Se particles are agglomerated considerably and irregular in shape. In contrast to the sulfides and selenide, Cu 1.75Te powders appeared to be spherical, the particles are much smaller and the mean size is no more than 250 nm. The sulfides have a larger dimension than any other sample. Seen from magni-
Fig. 3. SEM images of bigger crystals of copper sulfides: Ža. Cu 1.80 S, Žb. Cu 31 S16 .
fied images of bigger Cu 1.80 S and Cu 31 S 16 crystals shown in Fig. 3, their polyhedral morphology becomes clearer, in particular, the polyhedron of Cu 31 S16 obviously comprises 14 faces. It is notable that copper chalcogenides prepared by the solvothermal method are usually non-stoichiometric. Adjusting the solvent, the molar ratio of starting materials and employed temperature can control the chemical composition depending on reaction conditions. As-prepared non-stoichiometric copper chalcogenides may possess different electronic properties and in turn show different performance when using microelectrodes and sensors. Furthermore, the special morphologies of the copper chalcogenides very likely influence the applications as well. 4. Conclusion A solvothermal route has been developed to synthesize copper chalcogenide powders with good crystallinity. This is a simple and convenient method because the preparative steps can be easily operated without employing complicated equipment. Single phases including Cu 1.80 S, Cu 31 S 16 , Cu 2yx Se, and Cu 1.75Te were successfully produced under controlled conditions via this route. Furthermore, an even large range of copper chalcogenides such as Cu x S, CuSe, CuSe 2 , Cu 1.80Te and Cu 2.86Te 2 were obtained in the form of mixtures. Considering the phase distribution are dependent on the reaction conditions, more copper chalcogenide single phases are expected to be prepared, provided that the preparative conditions are properly controlled.
Z.H. Han et al.r Materials Letters 44 (2000) 366–369
Acknowledgements Financial support from the Natural Science Foundation of China and Anhui Provincial Natural Science Foundation is gratefully acknowledged.
References w1x M.I. Schimmel, O.L. Bottechia, H. Wendt, J. Appl. Electrochem. 28 Ž1998. 299. w2x M. Kupper, J.W. Schultze, J. Electroanal. Chem. 427 Ž1997. 129. w3x S.I. Krichmar, V.M. Bezpalchenko, Ind. Lab. 61 Ž1995. 521. w4x M.A. Korzhuev, Phys. Solid State 40 Ž1998. 217. w5x W. Tremel, H. Kleinke, V. Derstroff, C. Reisner, J. Alloys Compd. 219 Ž1995. 73.
369
w6x T. Pauporte, J. Vedel, Solid State Ionics 109 Ž1998. 125. w7x S. Saito, H. Kishi, K. Nie, H. Nakamaru, F. Wagatsuma, T. Shinohara, Phys. Rev. B: Condens. Matter 55 Ž1997. 14527. w8x A. Schafer, M. Kollwitz, R. Ahlrichs, J. Chem. Phys. 104 ¨ Ž1996. 7113. w9x J.F. Corrigan, D. Fenske, Angew. Chem., Int. Ed. 36 Ž1997. 1981. w10x S.K. Haram, A.R. Mahadeshwar, S.G. Dixit, J. Phys. Chem. 100 Ž1996. 5868. w11x W. Wang, Y. Geng, P. Yan, F. Liu, Y. Xie, Y. Qian, J. Am. Chem. Soc. 121 Ž1999. 4062. w12x T. Ohtani, T. Nonaka, M. Araki, J. Solid State Chem. 138 Ž1998. 131. w13x T. Ohtani, K. Maruyama, K. Ohshima, Mater. Res. Bull. 32 Ž1997. 343. w14x G. Henshaw, I.P. Parkin, G.A. Shaw, Chem. J. Soc., Dalton Trans. 231 Ž1997.. w15x PDF-2 database, International Center for Diffraction Data, Swarthmore, PA 19081, 1990.
Materials Letters 44 Ž2000. 366–369 www.elsevier.comrlocatermatlet
A simple solvothermal route to copper chalcogenides Z.H. Han, Y.P. Li, H.Q. Zhao, S.H. Yu, X.L. Yin, Y.T. Qian ) Department of Chemistry and Structure Research Laboratory, UniÕersity of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China Received 30 October 1999; received in revised form 8 February 2000; accepted 9 February 2000
Abstract Using copperŽI. chloride, sodium oxalate and elemental chalcogen, copper chalcogenide powders were synthesized through a simple solvothermal route. Pseudocubic Cu 1.80 S and orthorhombic Cu 31S16 single phases synthesized in ethylenediamine ŽEn. are made up of polyhedral particles, cubic Cu 2yx Se synthesized in pyridine ŽPy. was irregular in shape, while Cu 1.75Te synthesized in distilled water appeared to be spherical. Other chalcogenides were also formed under different conditions. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Copper chalcogenide; Solvothermal; Synthesis
1. Introduction Many applications have been found for copper sulfides, such as photovoltaic cells w1x, copper ion selective microelectrodes w2x, and sensors for detecting hydrogen sulfide in the atmosphere w3x. Although the reports concerning copper selenides and tellurides were relatively less, they could also be used for various purposes w4,5x. In recent years, the spectroscopy of copper sulfides was investigated w6,7x, the electron excitation energy in copper selenide clusters was calculated w8x, and the structure of copper telluride cluster was studied w9x. Meanwhile, a number of synthetic techniques have been developed for copper chalcogenides. Copper sulfide nanoparticles were synthesized in Triton-X 100 water-in-oil microemulsion w10x, whereas nanocrystalline copper
)
Corresponding author. E-mail address: [email protected] ŽY.T. Qian..
selenide powders were obtained in ethylenediamine ŽEN. w11x. Using mixtures of metallic copper and chalcogen as reactants, copper chalcogenide powders were systematically prepared through the sonochemical processes w12x, mechanical alloying with high energy w13x, as well as reactions in liquid ammonia w14x. This paper introduces a simple solvothermal route to well-crystallized copper chalcogenide powders, such as Cu 1.80 S, Cu 31 S 16 , Cu 2yx Se and Cu 1.75Te, employing copper salt rather than metallic copper in various solvents.
2. Experimental Analytically pure CuCl, Na 2 C 2 O4 , together with S, Se, or Te served as initial materials. An appropriate amount of the reactants was ground and put into a stainless steel autoclave with a capacity of 35 ml.
00167-577Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 0 6 0 - 4
Z.H. Han et al.r Materials Letters 44 (2000) 366–369
367
out on a Drmax-gA rotation anode X-ray diffractometer with Ni-filtered Cu K a radiation. In order to observe the morphology of crystallites in a single phase, an X-650 scanning electron microanalyzer was employed to take the scanning electron microscopy ŽSEM..
3. Results and discussion
Fig. 1. XRD patterns of typical samples: Ža. pseudocubic Cu 1.80 S synthesized at 1808C in En, Žb. orthorhombic Cu 31 S16 synthesized at 1808C in En, Žc. cubic Cu 2y x Se synthesized at 2408C in Py, Žd. hexagonal Cu 1.75Te synthesized at 180 in water.
The selected solvent filled the autoclave up to 85% of its total volume. During the experiment, En, pyridine ŽPy., or distilled water was used for the solvent. The autoclave was maintained under suitable temperatures for 12 h before it was air-cooled to ambient temperature. The products were collected, washed with distilled water, and dried in vacuum at 608C. X-ray diffraction ŽXRD. of the powders was carried
Quite a few single phases of copper chalcogenides were obtained under controlled conditions. Fig. 1 shows XRD patterns of typical samples. According to the indexing results, phase-pure pseudocubic Cu 1.80 S and orthorhombic Cu 31 S16 powders were synthesized in En at 1808C, cubic Cu 2y x Se was synthesized in Py at 2408C, and hexagonal Cu 1.75Te was synthesized in water at 1808C. The sharp diffraction peaks of the powders imply their good crystallinity. Table 1 lists refined cell constants of the phases, the parameters are all close to the reported data w15x. Influential factors on the product were investigated. Different ratio of the starting materials could derive different products. When the molar ratio of copperŽI. chloride, sodium oxalate and sulfur was 4:1:2, orthorhombic Cu 31 S 16 was given at 1808C. When the ratio became 1:1:1, however, pseudocubic Cu 1.80 S was afforded even if the reaction was performed at the same temperature and in the same solvent. By changing the ratio of reactants, mixed Cu x S powders were formed. If the quantity of initial selenium was more than that required for Cu 2y x Se single phase, a mixture of Cu 2y x Se, CuSe and CuSe 2 would be generated. Various reaction media, including organic and inorganic solvents, may be applicable to the synthesis of copper chalcogenides, al-
Table 1 Experimental results of copper chalcogenides synthesized under various conditions Starting materials
Molar ratio
Solvent
Temperature Ž8C.
Product
˚. Cell constants ŽA
CuCl q Na 2 C 2 O4 q S CuCl q Na 2 C 2 O4 q S CuCl q Na 2 C 2 O4 q Se CuCl q Na 2 C 2 O4 q Te
1:1:1 4:1:2 2:1:1 2:3:2
En En Py H 2O
180 180 240 180
Cu 1.80 S Cu 31 S16 Cu 2yx Se Cu 1.75Te
a s 27.859 a s 26.936, b s 15.696, c s 13.548 a s 5.733 a s 4.166, c s 21.583
368
Z.H. Han et al.r Materials Letters 44 (2000) 366–369
Fig. 2. SEM images of powders of copper chalcogenides: Ža. Cu 1.80 S, Žb. Cu 31 S16 , Žc. Cu 2yx Se, Žd. Cu 1.75Te.
though the selected solvent usually favors certain copper chalcogenide. Moreover, the reaction temperature exerts an effect to the product distribution. Copper selenides could be prepared not only in Py, but also in En or water. As for the synthesis of copper tellurides, En was another suitable reaction medium besides Py, in which Cu 1.80Te was formed at 1808C and Cu 2.86Te 2 was formed at higher temperature, 2208C. The powders of sulfides, selenide and telluride are composed of particles with different morphologies. Fig. 2 refers to the TEM images of Cu 1.80 S, Cu 31 S 16 , Cu 2y x Se, and Cu 1.75Te single phases. Cu 1.80 S and Cu 31 S16 crystals seem to be polyhedral, whereas Cu 2y x Se particles are agglomerated considerably and irregular in shape. In contrast to the sulfides and selenide, Cu 1.75Te powders appeared to be spherical, the particles are much smaller and the mean size is no more than 250 nm. The sulfides have a larger dimension than any other sample. Seen from magni-
Fig. 3. SEM images of bigger crystals of copper sulfides: Ža. Cu 1.80 S, Žb. Cu 31 S16 .
fied images of bigger Cu 1.80 S and Cu 31 S 16 crystals shown in Fig. 3, their polyhedral morphology becomes clearer, in particular, the polyhedron of Cu 31 S16 obviously comprises 14 faces. It is notable that copper chalcogenides prepared by the solvothermal method are usually non-stoichiometric. Adjusting the solvent, the molar ratio of starting materials and employed temperature can control the chemical composition depending on reaction conditions. As-prepared non-stoichiometric copper chalcogenides may possess different electronic properties and in turn show different performance when using microelectrodes and sensors. Furthermore, the special morphologies of the copper chalcogenides very likely influence the applications as well. 4. Conclusion A solvothermal route has been developed to synthesize copper chalcogenide powders with good crystallinity. This is a simple and convenient method because the preparative steps can be easily operated without employing complicated equipment. Single phases including Cu 1.80 S, Cu 31 S 16 , Cu 2yx Se, and Cu 1.75Te were successfully produced under controlled conditions via this route. Furthermore, an even large range of copper chalcogenides such as Cu x S, CuSe, CuSe 2 , Cu 1.80Te and Cu 2.86Te 2 were obtained in the form of mixtures. Considering the phase distribution are dependent on the reaction conditions, more copper chalcogenide single phases are expected to be prepared, provided that the preparative conditions are properly controlled.
Z.H. Han et al.r Materials Letters 44 (2000) 366–369
Acknowledgements Financial support from the Natural Science Foundation of China and Anhui Provincial Natural Science Foundation is gratefully acknowledged.
References w1x M.I. Schimmel, O.L. Bottechia, H. Wendt, J. Appl. Electrochem. 28 Ž1998. 299. w2x M. Kupper, J.W. Schultze, J. Electroanal. Chem. 427 Ž1997. 129. w3x S.I. Krichmar, V.M. Bezpalchenko, Ind. Lab. 61 Ž1995. 521. w4x M.A. Korzhuev, Phys. Solid State 40 Ž1998. 217. w5x W. Tremel, H. Kleinke, V. Derstroff, C. Reisner, J. Alloys Compd. 219 Ž1995. 73.
369
w6x T. Pauporte, J. Vedel, Solid State Ionics 109 Ž1998. 125. w7x S. Saito, H. Kishi, K. Nie, H. Nakamaru, F. Wagatsuma, T. Shinohara, Phys. Rev. B: Condens. Matter 55 Ž1997. 14527. w8x A. Schafer, M. Kollwitz, R. Ahlrichs, J. Chem. Phys. 104 ¨ Ž1996. 7113. w9x J.F. Corrigan, D. Fenske, Angew. Chem., Int. Ed. 36 Ž1997. 1981. w10x S.K. Haram, A.R. Mahadeshwar, S.G. Dixit, J. Phys. Chem. 100 Ž1996. 5868. w11x W. Wang, Y. Geng, P. Yan, F. Liu, Y. Xie, Y. Qian, J. Am. Chem. Soc. 121 Ž1999. 4062. w12x T. Ohtani, T. Nonaka, M. Araki, J. Solid State Chem. 138 Ž1998. 131. w13x T. Ohtani, K. Maruyama, K. Ohshima, Mater. Res. Bull. 32 Ž1997. 343. w14x G. Henshaw, I.P. Parkin, G.A. Shaw, Chem. J. Soc., Dalton Trans. 231 Ž1997.. w15x PDF-2 database, International Center for Diffraction Data, Swarthmore, PA 19081, 1990.