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One-step synthesis of Zn4Sb3 nanocrystals and Zn4Sb3–ZnSb composites
Superlattices and Microstructures 64 (2013) 433–438
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
One-step synthesis of Zn4Sb3 nanocrystals and Zn4Sb3–ZnSb composites Sudarat Sitthichai a, Titipun Thongtem b,c, Somchai Thongtem a,c,⇑, Tawat Suriwong d a
Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand c Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand d School of Renewable Energy Technology, Naresuan University, Phitsanulok 65000, Thailand b
a r t i c l e
i n f o
Article history: Received 10 June 2013 Received in revised form 1 October 2013 Accepted 7 October 2013 Available online 14 October 2013 Keywords: Zn4Sb3 nanocrystals X-ray diffraction Electron microscopy Spectroscopy
a b s t r a c t Zn4Sb3 nanocrystals were synthesized by a 900 W microwave of 4.5:3 M ratio Zn:Sb with a total mass of 1 g for 5 min. Phase, internal texture, constituents, vibration mode and energy gap were detected using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), Raman spectroscopy and UV– visible spectroscopy. In this research, Zn4Sb3 nanocrystals with a prominent vibration mode at 144 cm1 and 1.22 eV optical band gap were detected, including Zn4Sb3–ZnSb composites were also synthesized using microwave plasma for 10 min. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction In recent year, thermoelectric materials have received much attention for the conversion of energy by their temperature differences. Among them, TAGS (Te–Ag–Ge–Sb), Zn4Sb3 and skutterudites have high potential for a number of applications. Zn4Sb3 is a solid which has phase transition at different temperatures: a ? b over the temperature range of 253–263 K, b ? c at the temperature of 763 K, and c ? melt at 857 K [1,2]. The material can be used in a variety of applications, including waste heat recovery from power plants and automobile industries [3]. Different processes were used to synthesize Zn4Sb3 semiconductors: solid state synthesis of e-Zn4Sb3 bulk specimens [1], stoichiometric Zn4Sb3
⇑ Corresponding author at: Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand. Tel.: +66 053 941924; fax: +66 053 943445. E-mail address: [email protected] (S. Thongtem). 0749-6036/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.spmi.2013.10.004
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mixture of Zn and Sb heated at 973 K in vacuum for 2 h [2], semiconducting Zn4Sb3 samples processed by hot pressing [3], b-Zn4xCdxSb3 by direct melting in vacuum [4], intermetallic Zn4Sb3 phase by low temperature solution route [5], Zn4Sb3 by combustion process [6], and b-Zn4Sb3 by hot pressing [7]. In this research, Zn4Sb3 nanocrystals were synthesized by a microwave plasma process and further characterized by different methods. 2. Experimental details To synthesize nanocrystalline Zn4Sb3, 4.5:3 M ratio of Zn:Sb with a total mass of 1 g was thoroughly mixed and put in 11 mm I.D. 100 mm long silica tubes which was placed in a horizontal quartz tube as shown in Fig. 1. The horizontal quartz tube was tightly closed and evacuated to 4.3 ± 1 kPa absolute pressure for removal of air. Following the evacuation, argon was fed into this tube for 5 min, and evacuated to 4.3 ± 1 kPa absolute pressure. Subsequently, the system containing solid mixture was heated by 900 W microwave for 5 and 10 min and left cool down in the vacuum to room temperature for further characterization. The products were characterized by an X-ray diffractometer (XRD, SIEMENS D500) operating at 20 kV, 15 mA and using Cu Ka line in combination with the database of the Joint Committee on Powder Diffraction Standards (JCPDS) [8]; a scanning electron microscope (SEM, JEOL JSM6335F) equipped with an energy dispersive X-ray (EDX) analyzer operating at 15 kV; a transmission electron microscope (TEM, JEOL JEM-2010) and high resolution transmission electron microscope
Fig. 1. Diagram of the apparatus used for microwave plasma synthesis.
Fig. 2. Microwave plasma.
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435
(HRTEM) operating at 200 kV; a Raman spectrometer (T64000 HORIBA Jobin Yvon) using a 50 mW and 514.5 nm wavelength Ar green laser; and UV–visible spectrometer (Lambda 25 PerkinElmer) using a UV lamp with 1 nm resolution.
Fig. 3. XRD patterns of the products synthesized by microwave plasma for 5 and 10 min.
Fig. 4. (a) SEM image and (b) EDX spectrum of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
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3. Results and discussion During microwaving of argon gas at 4.3 ± 1 kPa absolute pressure, molecules and atoms were ionized and turned into plasma (Fig. 2), containing charged particles or ions inside the horizontal quartz tube. Fig. 3 shows XRD patterns of the products synthesized from 4.5:3 M ratio of Zn:Sb by 900 W microwave plasma for 5 and 10 min. The spectra were indexed and compared with the JCPDS database Nos. 34-1013 and 05-0714 for Zn4Sb3 and ZnSb, respectively [8]. In this research, the product was pure Zn4Sb3 for 5 min microwaving. Zn and Sb combined to form Zn4Sb3. During heating up, a temperature of solids was gradually increased and some Zn evaporated. Thus no Zn residue was detected in the product. When the time was lengthened from 5 to 10 min, additional ZnSb was also detected and the product was Zn4Sb3–ZnSb composites. Possibly, some Zn4Sb3 transformed into ZnSb with the evaporation of nascent Zn. It is very interesting to note that their peaks were very sharp implying that the products were very good crystals, composed of arrays of Zn and Sb atoms residing in crystal lattices. A typical SEM image of Zn4Sb3 synthesized by microwave plasma for 5 min is shown in Fig. 4a. This bulky product was composed of nanoparticles, oriented in different directions. Its EDX spectrum (Fig. 4b) shows the characteristic peaks of Zn (Ka1,2 at 8.63 keV, Kab at 9.66 keV, La at 1.01 keV) and Sb (La at 3.61 keV, Lb1 at 3.84 keV, Lb2 at 4.10 keV), suggesting that the product contained only zinc and antimony as fundamental elements. Quantitative EDX analysis shows that the atomic ratio of Zn:Sb was 57.14:42.86 (very close to 4:3), confirming that the as-synthesized product was really crystalline Zn4Sb3. In addition to the above analysis, Cu of the stub at 8.04 keV (Ka1,2), sputtered Au for conductivity improving at 2.12 keV (Ma), and adsorbed O at 0.53 keV (Ka1,2) were also detected [9]. Fig. 5 is a TEM image of the Zn4Sb3 product which was composed of a number of nanoparticles oriented in different directions. Their image appeared as different colors: dark, white and gray. Several
Fig. 5. TEM and HRTEM images of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
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437
interference fringes of randomly across planes of nanoparticles [10] were also detected. Each of the nanoparticles was specified as single crystal having a number of the (2 2 0) parallel planes (inset of Fig. 5) with 0.306 nm apart. This implied that the bulky product is really a cluster of single crystalline nanoparticles, and the atoms of each were uniformly arranged in systematic array. For b-Zn4Sb3 rhombohedral crystal system with R-3c space group containing 22 atoms per primitive unit cell. The decomposition of the irreducible lattice modes at q = 0 is represented according to the following:
Cv ð36f Þ ¼ 3A1g þ 3A2g þ 6Eg þ 3A1u þ 3A2u þ 6Eu Cv ð18eÞ ¼ A1g þ 2A2g þ 3Eg þ A1u þ 2A2u þ 3Eu Cv ð12cÞ ¼ A1g þ A2g þ 2Eg þ A1u þ A2u þ 2Eu For b-Zn4Sb3, the vibration become:
Cv ðZn4 Sb3 Þ ¼ 5A1g þ 6A2g þ 11Eg þ 5A1u þ 6A2u þ 11Eu
Fig. 6. Raman spectrum of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
Fig. 7. The (a h m)2 vs hm plot of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
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The irreducible acoustic modes are A2u + Eu, the IR active modes are 5A2u + 10Eu, and the 16 Raman active modes are 5A1g + 11Eg [4]. The Raman spectrum of Zn4Sb3 synthesized by exposure to microwave plasma for 5 min is shown in Fig. 6. The spectrum shows prominent peaks at 108 and 144 cm1 and a broad shallow peak at 256 cm1. The peak at 144 cm1 is associated with the b-Zn4Sb3 phase based on previous reports at 152 cm1 [5] and 155 cm1 [6]. The shift in the location of this peak could relate to the nanostructure of the reaction product of this work, which led to the change in bond length, defect structure, and degree of crystallinity in comparison to larger Zn4Sb3 grains produced by other processes. The UV–visible light absorption spectrum (Fig. 7) of nanocrystalline Zn4Sb3 synthesized by microwave processing for 5 min was consistent with a direct energy gap of 1.22 eV, in accordance with the report of Caillat et al. [7]. 4. Conclusions Zn4Sb3 was successfully synthesized by solid state processing of Zn and Sb powders in a microwave plasma for 5 min. Extending the processing time to 10 min resulted in some loss of Zn from the material, producing a composite of Zn4Sb3 and ZnSb. The product was an agglomeration of nanocrystalline grains of Zn4Sb3 with an energy gap of 1.22 eV. Acknowledgements We wish to thank the Thailand’s Office of the Higher Education Commission for providing financial support through the National Research University (NRU) Project for Chiang Mai University (CMU), and the National Research Council of Thailand (NRCT) for providing financial support for graduate research program, including the Graduate School of CMU for a general support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
S.C. Ur, P. Nash, I.H. Kim, J. Alloys Compd. 361 (2003) 84–91. Y. Mozharivskyj, A.O. Pecharsky, S. Bud’ko, G.J. Miller, Chem. Mater. 16 (2004) 1580–1589. M. Chitroub, F. Besse, H. Scherrer, J. Alloys Compd. 460 (2008) 90–93. R. Viennois, M.C. Record, V. Izard, J.C. Tedenac, J. Alloys Compd. 440 (2007) L22–L25. A. Denoix, A. Solaiappan, R.M. Ayral, F. Rouessac, J.C. Tedenac, J. Solid State Chem. 183 (2010) 1090–1094. F. Rouessac, R.M. Ayral, J. Alloys Compd. 530 (2012) 56–62. T. Caillat, J.P. Fleurial, A. Borshchevsky, J. Phys. Chem. Solids 58 (1997) 1119–1125. Powder Diffract. File, JCPDS-ICDD, 12 Campus Boulevard, Newtown Square, PA 19073–3273, USA, 2001. Oxford Instr. Anal., Halifax Rd., High Wycombe Bucks HP12 3SE, UK. K. Yu, J. Zhao, Y. Guo, X. Ding, H. Bala, Y. Liu, Z. Wang, Mater. Lett. 59 (2005) 2515–2518.
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
One-step synthesis of Zn4Sb3 nanocrystals and Zn4Sb3–ZnSb composites Sudarat Sitthichai a, Titipun Thongtem b,c, Somchai Thongtem a,c,⇑, Tawat Suriwong d a
Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand c Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand d School of Renewable Energy Technology, Naresuan University, Phitsanulok 65000, Thailand b
a r t i c l e
i n f o
Article history: Received 10 June 2013 Received in revised form 1 October 2013 Accepted 7 October 2013 Available online 14 October 2013 Keywords: Zn4Sb3 nanocrystals X-ray diffraction Electron microscopy Spectroscopy
a b s t r a c t Zn4Sb3 nanocrystals were synthesized by a 900 W microwave of 4.5:3 M ratio Zn:Sb with a total mass of 1 g for 5 min. Phase, internal texture, constituents, vibration mode and energy gap were detected using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), Raman spectroscopy and UV– visible spectroscopy. In this research, Zn4Sb3 nanocrystals with a prominent vibration mode at 144 cm1 and 1.22 eV optical band gap were detected, including Zn4Sb3–ZnSb composites were also synthesized using microwave plasma for 10 min. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction In recent year, thermoelectric materials have received much attention for the conversion of energy by their temperature differences. Among them, TAGS (Te–Ag–Ge–Sb), Zn4Sb3 and skutterudites have high potential for a number of applications. Zn4Sb3 is a solid which has phase transition at different temperatures: a ? b over the temperature range of 253–263 K, b ? c at the temperature of 763 K, and c ? melt at 857 K [1,2]. The material can be used in a variety of applications, including waste heat recovery from power plants and automobile industries [3]. Different processes were used to synthesize Zn4Sb3 semiconductors: solid state synthesis of e-Zn4Sb3 bulk specimens [1], stoichiometric Zn4Sb3
⇑ Corresponding author at: Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand. Tel.: +66 053 941924; fax: +66 053 943445. E-mail address: [email protected] (S. Thongtem). 0749-6036/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.spmi.2013.10.004
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mixture of Zn and Sb heated at 973 K in vacuum for 2 h [2], semiconducting Zn4Sb3 samples processed by hot pressing [3], b-Zn4xCdxSb3 by direct melting in vacuum [4], intermetallic Zn4Sb3 phase by low temperature solution route [5], Zn4Sb3 by combustion process [6], and b-Zn4Sb3 by hot pressing [7]. In this research, Zn4Sb3 nanocrystals were synthesized by a microwave plasma process and further characterized by different methods. 2. Experimental details To synthesize nanocrystalline Zn4Sb3, 4.5:3 M ratio of Zn:Sb with a total mass of 1 g was thoroughly mixed and put in 11 mm I.D. 100 mm long silica tubes which was placed in a horizontal quartz tube as shown in Fig. 1. The horizontal quartz tube was tightly closed and evacuated to 4.3 ± 1 kPa absolute pressure for removal of air. Following the evacuation, argon was fed into this tube for 5 min, and evacuated to 4.3 ± 1 kPa absolute pressure. Subsequently, the system containing solid mixture was heated by 900 W microwave for 5 and 10 min and left cool down in the vacuum to room temperature for further characterization. The products were characterized by an X-ray diffractometer (XRD, SIEMENS D500) operating at 20 kV, 15 mA and using Cu Ka line in combination with the database of the Joint Committee on Powder Diffraction Standards (JCPDS) [8]; a scanning electron microscope (SEM, JEOL JSM6335F) equipped with an energy dispersive X-ray (EDX) analyzer operating at 15 kV; a transmission electron microscope (TEM, JEOL JEM-2010) and high resolution transmission electron microscope
Fig. 1. Diagram of the apparatus used for microwave plasma synthesis.
Fig. 2. Microwave plasma.
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435
(HRTEM) operating at 200 kV; a Raman spectrometer (T64000 HORIBA Jobin Yvon) using a 50 mW and 514.5 nm wavelength Ar green laser; and UV–visible spectrometer (Lambda 25 PerkinElmer) using a UV lamp with 1 nm resolution.
Fig. 3. XRD patterns of the products synthesized by microwave plasma for 5 and 10 min.
Fig. 4. (a) SEM image and (b) EDX spectrum of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
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3. Results and discussion During microwaving of argon gas at 4.3 ± 1 kPa absolute pressure, molecules and atoms were ionized and turned into plasma (Fig. 2), containing charged particles or ions inside the horizontal quartz tube. Fig. 3 shows XRD patterns of the products synthesized from 4.5:3 M ratio of Zn:Sb by 900 W microwave plasma for 5 and 10 min. The spectra were indexed and compared with the JCPDS database Nos. 34-1013 and 05-0714 for Zn4Sb3 and ZnSb, respectively [8]. In this research, the product was pure Zn4Sb3 for 5 min microwaving. Zn and Sb combined to form Zn4Sb3. During heating up, a temperature of solids was gradually increased and some Zn evaporated. Thus no Zn residue was detected in the product. When the time was lengthened from 5 to 10 min, additional ZnSb was also detected and the product was Zn4Sb3–ZnSb composites. Possibly, some Zn4Sb3 transformed into ZnSb with the evaporation of nascent Zn. It is very interesting to note that their peaks were very sharp implying that the products were very good crystals, composed of arrays of Zn and Sb atoms residing in crystal lattices. A typical SEM image of Zn4Sb3 synthesized by microwave plasma for 5 min is shown in Fig. 4a. This bulky product was composed of nanoparticles, oriented in different directions. Its EDX spectrum (Fig. 4b) shows the characteristic peaks of Zn (Ka1,2 at 8.63 keV, Kab at 9.66 keV, La at 1.01 keV) and Sb (La at 3.61 keV, Lb1 at 3.84 keV, Lb2 at 4.10 keV), suggesting that the product contained only zinc and antimony as fundamental elements. Quantitative EDX analysis shows that the atomic ratio of Zn:Sb was 57.14:42.86 (very close to 4:3), confirming that the as-synthesized product was really crystalline Zn4Sb3. In addition to the above analysis, Cu of the stub at 8.04 keV (Ka1,2), sputtered Au for conductivity improving at 2.12 keV (Ma), and adsorbed O at 0.53 keV (Ka1,2) were also detected [9]. Fig. 5 is a TEM image of the Zn4Sb3 product which was composed of a number of nanoparticles oriented in different directions. Their image appeared as different colors: dark, white and gray. Several
Fig. 5. TEM and HRTEM images of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
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437
interference fringes of randomly across planes of nanoparticles [10] were also detected. Each of the nanoparticles was specified as single crystal having a number of the (2 2 0) parallel planes (inset of Fig. 5) with 0.306 nm apart. This implied that the bulky product is really a cluster of single crystalline nanoparticles, and the atoms of each were uniformly arranged in systematic array. For b-Zn4Sb3 rhombohedral crystal system with R-3c space group containing 22 atoms per primitive unit cell. The decomposition of the irreducible lattice modes at q = 0 is represented according to the following:
Cv ð36f Þ ¼ 3A1g þ 3A2g þ 6Eg þ 3A1u þ 3A2u þ 6Eu Cv ð18eÞ ¼ A1g þ 2A2g þ 3Eg þ A1u þ 2A2u þ 3Eu Cv ð12cÞ ¼ A1g þ A2g þ 2Eg þ A1u þ A2u þ 2Eu For b-Zn4Sb3, the vibration become:
Cv ðZn4 Sb3 Þ ¼ 5A1g þ 6A2g þ 11Eg þ 5A1u þ 6A2u þ 11Eu
Fig. 6. Raman spectrum of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
Fig. 7. The (a h m)2 vs hm plot of nanocrystalline Zn4Sb3 synthesized by microwave plasma for 5 min.
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The irreducible acoustic modes are A2u + Eu, the IR active modes are 5A2u + 10Eu, and the 16 Raman active modes are 5A1g + 11Eg [4]. The Raman spectrum of Zn4Sb3 synthesized by exposure to microwave plasma for 5 min is shown in Fig. 6. The spectrum shows prominent peaks at 108 and 144 cm1 and a broad shallow peak at 256 cm1. The peak at 144 cm1 is associated with the b-Zn4Sb3 phase based on previous reports at 152 cm1 [5] and 155 cm1 [6]. The shift in the location of this peak could relate to the nanostructure of the reaction product of this work, which led to the change in bond length, defect structure, and degree of crystallinity in comparison to larger Zn4Sb3 grains produced by other processes. The UV–visible light absorption spectrum (Fig. 7) of nanocrystalline Zn4Sb3 synthesized by microwave processing for 5 min was consistent with a direct energy gap of 1.22 eV, in accordance with the report of Caillat et al. [7]. 4. Conclusions Zn4Sb3 was successfully synthesized by solid state processing of Zn and Sb powders in a microwave plasma for 5 min. Extending the processing time to 10 min resulted in some loss of Zn from the material, producing a composite of Zn4Sb3 and ZnSb. The product was an agglomeration of nanocrystalline grains of Zn4Sb3 with an energy gap of 1.22 eV. Acknowledgements We wish to thank the Thailand’s Office of the Higher Education Commission for providing financial support through the National Research University (NRU) Project for Chiang Mai University (CMU), and the National Research Council of Thailand (NRCT) for providing financial support for graduate research program, including the Graduate School of CMU for a general support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
S.C. Ur, P. Nash, I.H. Kim, J. Alloys Compd. 361 (2003) 84–91. Y. Mozharivskyj, A.O. Pecharsky, S. Bud’ko, G.J. Miller, Chem. Mater. 16 (2004) 1580–1589. M. Chitroub, F. Besse, H. Scherrer, J. Alloys Compd. 460 (2008) 90–93. R. Viennois, M.C. Record, V. Izard, J.C. Tedenac, J. Alloys Compd. 440 (2007) L22–L25. A. Denoix, A. Solaiappan, R.M. Ayral, F. Rouessac, J.C. Tedenac, J. Solid State Chem. 183 (2010) 1090–1094. F. Rouessac, R.M. Ayral, J. Alloys Compd. 530 (2012) 56–62. T. Caillat, J.P. Fleurial, A. Borshchevsky, J. Phys. Chem. Solids 58 (1997) 1119–1125. Powder Diffract. File, JCPDS-ICDD, 12 Campus Boulevard, Newtown Square, PA 19073–3273, USA, 2001. Oxford Instr. Anal., Halifax Rd., High Wycombe Bucks HP12 3SE, UK. K. Yu, J. Zhao, Y. Guo, X. Ding, H. Bala, Y. Liu, Z. Wang, Mater. Lett. 59 (2005) 2515–2518.