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Microwave-assisted synthesis and investigation of SnO2 nanoparticles
Materials Letters 63 (2009) 896–898
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Microwave-assisted synthesis and investigation of SnO2 nanoparticles T. Krishnakumar a, R. Jayaprakash a,⁎, M. Parthibavarman a, A.R. Phani b, V.N. Singh c, B.R. Mehta c a b c
Nanotechnology Laboratory, Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore, Tamilnadu-641 020, India Nano-RAM Technologies, Vijayanagar, Bangalore 560040, India Thin Film Laboratory, Department of Physics, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi-110016, India
a r t i c l e
i n f o
Article history: Received 7 December 2008 Accepted 14 January 2009 Available online 20 January 2009 Keywords: Microwave technique Nanoparticles Tin dioxide Transmission Electron Microscopy Monocrystalline
a b s t r a c t Microwave technique was adopted for preparation of tin dioxide nanoparticles with particles size ranging from 10 to 11 nm within 10 min. The formation of monocrystalline SnO2 nanoparticles was confirmed by the XRD (X-Ray Diffraction) and TEM (Transmission Electron Microscopy) as well as with SAED (Selected Area Electron Diffraction) analysis. The structure of the SnO2 crystal was found to be Cassiterite type tetragonal structure. The FT-IR results further supported the formation of tin dioxide from tin hydroxyl group without any post annealing. The samples were further characterized by thermo gravimetric analysis (TGA), electrical resistance measurements and photoluminescence spectrum. © 2009 Published by Elsevier B.V.
1. Introduction Answer to nanotechnology refers to the manipulation of living and non-living matter at the level of the nanometer (nm), one billionth of a meter. In the nanoscale region, quantum physics takes over from classical physics and the properties of elements change character in novel and unpredictable ways. Generally, nanotechnology refers to mechanical engineering on a molecular scale, but it is a slippery and ambiguous term. Sometimes it refers to today's applied nanotechnology, such as the use of nanoparticles in cosmetics or industrial coatings. Tin dioxide is a stable and largely n-type semiconductor material with bandgap of (Eg ≈ 3.7 eV) and it has been widely used in various applications such as gas sensor [1–3], photosensors [4], antistatic coating [5] etc. The nanosized tin dioxide has great potential in wide applications, due to its higher surface to volume ratio. Tin oxide nanomaterials have been prepared by many techniques namely; chemical precipitation [6], microwave technique [7], combustion route [8], sol–gel [9], solvothermal [10], hydrothermal [11], sonochemical [12] and mechanochemical [13]. In the present investigation we have adopted cost-effective and simple microwave technique due to its unique properties. Microwaves generate high power densities, enabling efficient production at decreased production cost. Microwave systems are more compact and thus require smaller equipment space. Microwave energy is precisely controllable and can be turned on and off instantly, eliminating the need for warm-up and cooldown. This increases production run times, reduces both cleaning
⁎ Corresponding author. Tel.: +91 0422 2692349. E-mail address: [email protected] (R. Jayaprakash). 0167-577X/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.matlet.2009.01.032
times and chemical costs. Microwaves are a non-contact drying technology. Microwave energy is selectively absorbed by areas of greater moisture. This results in more uniform temperature and moisture profiles, improved yields and enhanced product performance. The use of industrial microwave systems avoids combustible gaseous by-products, eliminating the need for environmental concerns and improved working conditions. Srivastava et al. [14] has obtained tin dioxide after thermally treating at 600 °C for 3 h by using microwave technique. Cirera et al. [15] have prepared tin dioxide nanoparticles by microwave technique after conventionally treating at higher temperatures of order of 450 °C to 1000 °C for 8 h. Wu et al. [16] have prepared tin mono oxide (SnO) nanoparticles by using microwave technique. In this work, we have prepared tin dioxide nanoparticles in short time (10 min) by using reducing agent without any post-synthesis modifications. Hydrazine hydrate is a convenient reductant because the by-products are typically nitrogen gas and water. When hydrazine hydrate is added in the precursor solution, it mixed well with the precursor solution and increased the pH of the solution. Hydrazine hydrate absorbs more microwave energy than ammonia which results in increased reaction rate. To the best our knowledge this is the first report by microwave technique which deals with preparation of tin dioxide nanoparticles within 10 min without any post-synthesis annealing. 2. Experimental Tin hydroxyl solution was prepared by dissolving tin (II) chloride in deionized water with 0.1 M concentration. Then pH of the solution was maintained between 7 and 9 using hydrogen hydrate diluted with deionized water. The resulting precipitate was washed with deionized
T. Krishnakumar et al. / Materials Letters 63 (2009) 896–898
897
water more than five times till no chlorine ions were detected in the sliver nitrate test. The resulting precipitate was transferred into Teflon lined household microwave oven (2.45 GHz) with power up to 1 kW and irradiated for 10 min. Finally light gray coloured precipitate was filtered and dried at 80 °C. The crystalline structure of the powder was analyzed by X-Ray Diffraction (XRD) using the CuKα wavelength of 1.5406 Å. The morphology of the powder was observed by Transmission Electron Microscopy (TEM) and Selected-Area electron diffraction (SAED) pattern was used for deterring the crystallinity. The Fourier Transformed infrared spectra (FT-IR) of the samples were collected using a 5DX FTIR spectrometer. The Photoluminescence spectra of the samples were collected from Cary Eclipse (el02045776) Fluorescence spectrometer in the wavelength range of 400 to 800 nm. 3. Results and discussion Thermogravimetric analysis of microwave synthesized tin dioxide has been carried out to analyze the amount of weight loss in the sample and it is shown in Fig. 1(A). The observed weight loss between room temperature to 250 °C may be due to the elimination of ammonia, physically absorbed water and chemically bonded water which reflects the endothermic peak [17]. The second weight loss above 250 °C corresponds to completion of any reactions involving and burning out of carbon nanotubes [18]. Fig. 1(B) shows the electrical resistance of tin dioxide nanoparticles as a function of heating temperature. The synthesized tin dioxide nanopowder was pressed in the form of pellet and electrode contact was made using Fig. 2. XRD pattern of tin dioxide nanoparticles (A) before exposure to microwave (B) after exposure to microwave for 10 min.
silver paste. The linear decrease of resistance was observed with increase in temperature. This was due to desorption of physically adsorbed water which releases the charge carriers with increase of temperature. The low temperature conductivity was due to migration − − + of charges such as O2− 2 , O , OH , H3O [19]. The average crystallite size and structure were calculated from XRay Diffraction pattern which is shown in Fig. 2. The XRD pattern of SnO2 samples before microwave treatment (dried precipitate) show the presence of tin hydroxyl groups and the pattern matches well with the Sn6O4(OH)4 structure. The XRD pattern of the sample after microwave treatment (as-prepared) shows the formation of tin dioxide nanocrystals. As prepared sample has exhibited the following
Fig. 1. Tin dioxide nanoparticles (A) TGA curve (B) Electrical resistance vs heating temperature.
Fig. 3. TEM micrograph of tin oxide exposed to microwave for 10 min (inset) corresponding SAED pattern of tin dioxide nanoparticles.
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T. Krishnakumar et al. / Materials Letters 63 (2009) 896–898
Fig. 4. FT-IR spectrum of tin dioxide nanoparticles (A) before exposure to microwave (B) after exposure to microwave for 10 min.
miller indices [110], [101], [200], [210], [211], [301], [202] which matches well with JCPDS card # 41–1445 and structure of the crystal was found to be Cassiterite type tetragonal of SnO2 crystal. The result confirmed the formation of tin dioxide nanocrystals from tin hydroxyl within 10 min without any annealing. The average crystallite size of the tin dioxide crystal was calculated from Debye–Scherrer formula and found to be 10 nm ± 2 nm. The broadening of FWHM in the XRD spectrum indicates formation of smaller particles after the microwave irradiation. This is obvious as the tin oxide nanoparticles have been obtained from tin hydroxide nanoparticles by dehydration. The lattice parameters of the crystal were calculated as a = 4.739(3) Å and c = 3.221(2) Å [15] which matches well with the standard values of (a = 4.74 Å, c = 3.19 Å) tin oxide. The morphology and particle size of the tin dioxide nanoparticles were observed using TEM micrograph (Fig. 3). The presence of monodispersed spherical shaped particles with particles size ranging from 10 to 11 nm was observed. The corresponding SAED pattern was shown in inset and it has bright spots, which indicates the crystalline nature. The calculated particles size from XRD investigation matches well with the particles size observed from TEM micrograph. These results suggest the formation of monocrystalline tin dioxide nanoparticles. The FT-IR spectrum further supports the presence of tin hydroxyl and tin dioxide functional group for before and after microwave treated samples, respectively. The FT-IR spectra of samples before microwave treatment (dried precipitate) and after microwave treatment are shown in Fig. 4(A and B). The adsorption band at 550 cm− 1 in Fig. 4(A) was ascribed to the presence of tin hydroxyl group (νSn–OH) [16]. The microwave irradiated sample had the broad absorption band at 613 cm− 1 (Fig. 4(B)), which is attributed to oxide-bridge functional group (νOSnO) [17]. This elucidates that the microwave energy had transformed the tin hydroxyl group to oxide group. The peak at 1617 cm− 1 was ascribed to the vibration of NO−3 ions. The absorption band at 3419 cm− 1 attributed to νOH stretching vibration of surface hydroxyl group or adsorbed water [18] which has been observed due to the readsorption of water molecules from ambient atmosphere. The oxygen deficiency and lattice distortion of the tin dioxide samples were analyzed using photoluminescence spectrum and it is shown in Fig. 5. The photoluminescence spectrum was recorded using 385 nm excitation source. The emission at 432 nm is attributed to the residual stresses within the tin dioxide nanocrystals that originate from the lattice distortion. The emission observed at 433 nm is attributed to the Sn interstitials [19]. The emissions observed at
Fig. 5. Photoluminescence spectrum of tin dioxide nanoparticles exposed to microwave for 10 min.
483 nm, and 475 nm were related to the oxygen deficiency [20]. Different types of oxygen vacancies exist, among them the 527 nm peak is attributed to V+O oxygen vacancies [21]. 4. Conclusion In summary, tin dioxide nanoparticles were synthesized by microwave-assisted technique within 10 min. The formation of single crystalline tin dioxide nanoparticles has been confirmed by TEM micrograph with SAED pattern and XRD spectrum. The samples were further characterized by TGA, FT-IR and electrical resistance measurements. Further, this method can be highly perpetrated for synthesis of semiconducting nanoparticles in short time using a simple technique. References [1] Cirera A, Vila A, Dieguez A, Cabot A, Cornet A, Morante JR. Sens Actuators B 2000;64:65–9. [2] Phani AR, Manorama S, Rao VJ. Mater Chem Phys 1999;58:101–8. [3] Phani AR, Manorama S, Rao VJ. J Phys Chem Solids 2000;61:985–93. [4] Pandey PC, Upadhyay BC, Pandey CMD, Pathak HC. Sens Actuators B: Chem 1999;56:112–20. [5] Cho Young-Sang, Yi Gi-Ra, Hong Jeong-Jin, Jang Sung Hoon, Yang Seung-Man. Thin Solid Films 2006;515:1864–71. [6] Yu Dabin, Wang Debao, Yu Weichao, Qian Yitai. Mater Lett 2006;58:84–7. [7] Krishnakumar T, Jayaprakash R, Pinna Nicola, Singh VN, Mehta BR, Phani AR. Mater Lett 2009;63:242–5. [8] Fraigi LB, Lamas DG, Walsoe de Reca NE. Mater Lett 2001;47:262–6. [9] Korosi L, Papp S, Meynen V, Cool P, Vansant EF, Dekany I. Colloids Surf A: Physicochem Eng Asp 2005;268:147–54. [10] Han Zhaohui, Guo Neng, Li Fanqing, Zhang Wanqun, Zhao Huaquiao, Qian Yitai. Mater Lett 2001;48:99–103. [11] Sakai Go, Baik Nam Seok, Miura Norio, Yamazoe Noboru. Sens Actuators B 2001;77: 116–21. [12] Hu Xian Luo, Zhu Ying-Ji, Wang Shi-Wei. Mater Chem Phys 2004;88:421–6. [13] Cukrov LM, Mc Cormick PG, Galatsis K, Wlodarski W. Sens Actuators B 2007;77: 491–5. [14] Srivastava Abhilasha, Lakshmikumar ST, Srivastava AK, Jain Rashmi Kiran. Sens Actuators B 2007;126:583–7. [15] Cirera A, Vila A, Cornet A, Morante JR. Mater Sci Eng C 2001;15:203–5. [16] Wu Dien-Shi, Han Chih-Yu, Wang Shi-Yu, Wu Nae-Lih, Rusakova IA. Mater Lett 2002;53:155–9. [17] Lin Yung-Jen, Wu Ching-Jiunn. Surf Coat Technol 1996;88:239–47. [18] Krishnakumar T, Pinna Nicola, PrasannaKumari K, Perumal K, Jayaprakash R. Mater Lett 2008;62:3437–40. [19] Gu F, Wang SF, Lu MK, Cheng XF, Liu SF, Zhou GJ, et al. J Cryst Growth 2004;262: 182–5. [20] Sakurai Y. J Non-Cryst Solids 2006;352:5391–8. [21] Zhou JX, Zhang MS, Hong JM, Yin Z. Solid State Commun 2006;138:242–6.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Microwave-assisted synthesis and investigation of SnO2 nanoparticles T. Krishnakumar a, R. Jayaprakash a,⁎, M. Parthibavarman a, A.R. Phani b, V.N. Singh c, B.R. Mehta c a b c
Nanotechnology Laboratory, Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore, Tamilnadu-641 020, India Nano-RAM Technologies, Vijayanagar, Bangalore 560040, India Thin Film Laboratory, Department of Physics, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi-110016, India
a r t i c l e
i n f o
Article history: Received 7 December 2008 Accepted 14 January 2009 Available online 20 January 2009 Keywords: Microwave technique Nanoparticles Tin dioxide Transmission Electron Microscopy Monocrystalline
a b s t r a c t Microwave technique was adopted for preparation of tin dioxide nanoparticles with particles size ranging from 10 to 11 nm within 10 min. The formation of monocrystalline SnO2 nanoparticles was confirmed by the XRD (X-Ray Diffraction) and TEM (Transmission Electron Microscopy) as well as with SAED (Selected Area Electron Diffraction) analysis. The structure of the SnO2 crystal was found to be Cassiterite type tetragonal structure. The FT-IR results further supported the formation of tin dioxide from tin hydroxyl group without any post annealing. The samples were further characterized by thermo gravimetric analysis (TGA), electrical resistance measurements and photoluminescence spectrum. © 2009 Published by Elsevier B.V.
1. Introduction Answer to nanotechnology refers to the manipulation of living and non-living matter at the level of the nanometer (nm), one billionth of a meter. In the nanoscale region, quantum physics takes over from classical physics and the properties of elements change character in novel and unpredictable ways. Generally, nanotechnology refers to mechanical engineering on a molecular scale, but it is a slippery and ambiguous term. Sometimes it refers to today's applied nanotechnology, such as the use of nanoparticles in cosmetics or industrial coatings. Tin dioxide is a stable and largely n-type semiconductor material with bandgap of (Eg ≈ 3.7 eV) and it has been widely used in various applications such as gas sensor [1–3], photosensors [4], antistatic coating [5] etc. The nanosized tin dioxide has great potential in wide applications, due to its higher surface to volume ratio. Tin oxide nanomaterials have been prepared by many techniques namely; chemical precipitation [6], microwave technique [7], combustion route [8], sol–gel [9], solvothermal [10], hydrothermal [11], sonochemical [12] and mechanochemical [13]. In the present investigation we have adopted cost-effective and simple microwave technique due to its unique properties. Microwaves generate high power densities, enabling efficient production at decreased production cost. Microwave systems are more compact and thus require smaller equipment space. Microwave energy is precisely controllable and can be turned on and off instantly, eliminating the need for warm-up and cooldown. This increases production run times, reduces both cleaning
⁎ Corresponding author. Tel.: +91 0422 2692349. E-mail address: [email protected] (R. Jayaprakash). 0167-577X/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.matlet.2009.01.032
times and chemical costs. Microwaves are a non-contact drying technology. Microwave energy is selectively absorbed by areas of greater moisture. This results in more uniform temperature and moisture profiles, improved yields and enhanced product performance. The use of industrial microwave systems avoids combustible gaseous by-products, eliminating the need for environmental concerns and improved working conditions. Srivastava et al. [14] has obtained tin dioxide after thermally treating at 600 °C for 3 h by using microwave technique. Cirera et al. [15] have prepared tin dioxide nanoparticles by microwave technique after conventionally treating at higher temperatures of order of 450 °C to 1000 °C for 8 h. Wu et al. [16] have prepared tin mono oxide (SnO) nanoparticles by using microwave technique. In this work, we have prepared tin dioxide nanoparticles in short time (10 min) by using reducing agent without any post-synthesis modifications. Hydrazine hydrate is a convenient reductant because the by-products are typically nitrogen gas and water. When hydrazine hydrate is added in the precursor solution, it mixed well with the precursor solution and increased the pH of the solution. Hydrazine hydrate absorbs more microwave energy than ammonia which results in increased reaction rate. To the best our knowledge this is the first report by microwave technique which deals with preparation of tin dioxide nanoparticles within 10 min without any post-synthesis annealing. 2. Experimental Tin hydroxyl solution was prepared by dissolving tin (II) chloride in deionized water with 0.1 M concentration. Then pH of the solution was maintained between 7 and 9 using hydrogen hydrate diluted with deionized water. The resulting precipitate was washed with deionized
T. Krishnakumar et al. / Materials Letters 63 (2009) 896–898
897
water more than five times till no chlorine ions were detected in the sliver nitrate test. The resulting precipitate was transferred into Teflon lined household microwave oven (2.45 GHz) with power up to 1 kW and irradiated for 10 min. Finally light gray coloured precipitate was filtered and dried at 80 °C. The crystalline structure of the powder was analyzed by X-Ray Diffraction (XRD) using the CuKα wavelength of 1.5406 Å. The morphology of the powder was observed by Transmission Electron Microscopy (TEM) and Selected-Area electron diffraction (SAED) pattern was used for deterring the crystallinity. The Fourier Transformed infrared spectra (FT-IR) of the samples were collected using a 5DX FTIR spectrometer. The Photoluminescence spectra of the samples were collected from Cary Eclipse (el02045776) Fluorescence spectrometer in the wavelength range of 400 to 800 nm. 3. Results and discussion Thermogravimetric analysis of microwave synthesized tin dioxide has been carried out to analyze the amount of weight loss in the sample and it is shown in Fig. 1(A). The observed weight loss between room temperature to 250 °C may be due to the elimination of ammonia, physically absorbed water and chemically bonded water which reflects the endothermic peak [17]. The second weight loss above 250 °C corresponds to completion of any reactions involving and burning out of carbon nanotubes [18]. Fig. 1(B) shows the electrical resistance of tin dioxide nanoparticles as a function of heating temperature. The synthesized tin dioxide nanopowder was pressed in the form of pellet and electrode contact was made using Fig. 2. XRD pattern of tin dioxide nanoparticles (A) before exposure to microwave (B) after exposure to microwave for 10 min.
silver paste. The linear decrease of resistance was observed with increase in temperature. This was due to desorption of physically adsorbed water which releases the charge carriers with increase of temperature. The low temperature conductivity was due to migration − − + of charges such as O2− 2 , O , OH , H3O [19]. The average crystallite size and structure were calculated from XRay Diffraction pattern which is shown in Fig. 2. The XRD pattern of SnO2 samples before microwave treatment (dried precipitate) show the presence of tin hydroxyl groups and the pattern matches well with the Sn6O4(OH)4 structure. The XRD pattern of the sample after microwave treatment (as-prepared) shows the formation of tin dioxide nanocrystals. As prepared sample has exhibited the following
Fig. 1. Tin dioxide nanoparticles (A) TGA curve (B) Electrical resistance vs heating temperature.
Fig. 3. TEM micrograph of tin oxide exposed to microwave for 10 min (inset) corresponding SAED pattern of tin dioxide nanoparticles.
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T. Krishnakumar et al. / Materials Letters 63 (2009) 896–898
Fig. 4. FT-IR spectrum of tin dioxide nanoparticles (A) before exposure to microwave (B) after exposure to microwave for 10 min.
miller indices [110], [101], [200], [210], [211], [301], [202] which matches well with JCPDS card # 41–1445 and structure of the crystal was found to be Cassiterite type tetragonal of SnO2 crystal. The result confirmed the formation of tin dioxide nanocrystals from tin hydroxyl within 10 min without any annealing. The average crystallite size of the tin dioxide crystal was calculated from Debye–Scherrer formula and found to be 10 nm ± 2 nm. The broadening of FWHM in the XRD spectrum indicates formation of smaller particles after the microwave irradiation. This is obvious as the tin oxide nanoparticles have been obtained from tin hydroxide nanoparticles by dehydration. The lattice parameters of the crystal were calculated as a = 4.739(3) Å and c = 3.221(2) Å [15] which matches well with the standard values of (a = 4.74 Å, c = 3.19 Å) tin oxide. The morphology and particle size of the tin dioxide nanoparticles were observed using TEM micrograph (Fig. 3). The presence of monodispersed spherical shaped particles with particles size ranging from 10 to 11 nm was observed. The corresponding SAED pattern was shown in inset and it has bright spots, which indicates the crystalline nature. The calculated particles size from XRD investigation matches well with the particles size observed from TEM micrograph. These results suggest the formation of monocrystalline tin dioxide nanoparticles. The FT-IR spectrum further supports the presence of tin hydroxyl and tin dioxide functional group for before and after microwave treated samples, respectively. The FT-IR spectra of samples before microwave treatment (dried precipitate) and after microwave treatment are shown in Fig. 4(A and B). The adsorption band at 550 cm− 1 in Fig. 4(A) was ascribed to the presence of tin hydroxyl group (νSn–OH) [16]. The microwave irradiated sample had the broad absorption band at 613 cm− 1 (Fig. 4(B)), which is attributed to oxide-bridge functional group (νOSnO) [17]. This elucidates that the microwave energy had transformed the tin hydroxyl group to oxide group. The peak at 1617 cm− 1 was ascribed to the vibration of NO−3 ions. The absorption band at 3419 cm− 1 attributed to νOH stretching vibration of surface hydroxyl group or adsorbed water [18] which has been observed due to the readsorption of water molecules from ambient atmosphere. The oxygen deficiency and lattice distortion of the tin dioxide samples were analyzed using photoluminescence spectrum and it is shown in Fig. 5. The photoluminescence spectrum was recorded using 385 nm excitation source. The emission at 432 nm is attributed to the residual stresses within the tin dioxide nanocrystals that originate from the lattice distortion. The emission observed at 433 nm is attributed to the Sn interstitials [19]. The emissions observed at
Fig. 5. Photoluminescence spectrum of tin dioxide nanoparticles exposed to microwave for 10 min.
483 nm, and 475 nm were related to the oxygen deficiency [20]. Different types of oxygen vacancies exist, among them the 527 nm peak is attributed to V+O oxygen vacancies [21]. 4. Conclusion In summary, tin dioxide nanoparticles were synthesized by microwave-assisted technique within 10 min. The formation of single crystalline tin dioxide nanoparticles has been confirmed by TEM micrograph with SAED pattern and XRD spectrum. The samples were further characterized by TGA, FT-IR and electrical resistance measurements. Further, this method can be highly perpetrated for synthesis of semiconducting nanoparticles in short time using a simple technique. References [1] Cirera A, Vila A, Dieguez A, Cabot A, Cornet A, Morante JR. Sens Actuators B 2000;64:65–9. [2] Phani AR, Manorama S, Rao VJ. Mater Chem Phys 1999;58:101–8. [3] Phani AR, Manorama S, Rao VJ. J Phys Chem Solids 2000;61:985–93. [4] Pandey PC, Upadhyay BC, Pandey CMD, Pathak HC. Sens Actuators B: Chem 1999;56:112–20. [5] Cho Young-Sang, Yi Gi-Ra, Hong Jeong-Jin, Jang Sung Hoon, Yang Seung-Man. Thin Solid Films 2006;515:1864–71. [6] Yu Dabin, Wang Debao, Yu Weichao, Qian Yitai. Mater Lett 2006;58:84–7. [7] Krishnakumar T, Jayaprakash R, Pinna Nicola, Singh VN, Mehta BR, Phani AR. Mater Lett 2009;63:242–5. [8] Fraigi LB, Lamas DG, Walsoe de Reca NE. Mater Lett 2001;47:262–6. [9] Korosi L, Papp S, Meynen V, Cool P, Vansant EF, Dekany I. Colloids Surf A: Physicochem Eng Asp 2005;268:147–54. [10] Han Zhaohui, Guo Neng, Li Fanqing, Zhang Wanqun, Zhao Huaquiao, Qian Yitai. Mater Lett 2001;48:99–103. [11] Sakai Go, Baik Nam Seok, Miura Norio, Yamazoe Noboru. Sens Actuators B 2001;77: 116–21. [12] Hu Xian Luo, Zhu Ying-Ji, Wang Shi-Wei. Mater Chem Phys 2004;88:421–6. [13] Cukrov LM, Mc Cormick PG, Galatsis K, Wlodarski W. Sens Actuators B 2007;77: 491–5. [14] Srivastava Abhilasha, Lakshmikumar ST, Srivastava AK, Jain Rashmi Kiran. Sens Actuators B 2007;126:583–7. [15] Cirera A, Vila A, Cornet A, Morante JR. Mater Sci Eng C 2001;15:203–5. [16] Wu Dien-Shi, Han Chih-Yu, Wang Shi-Yu, Wu Nae-Lih, Rusakova IA. Mater Lett 2002;53:155–9. [17] Lin Yung-Jen, Wu Ching-Jiunn. Surf Coat Technol 1996;88:239–47. [18] Krishnakumar T, Pinna Nicola, PrasannaKumari K, Perumal K, Jayaprakash R. Mater Lett 2008;62:3437–40. [19] Gu F, Wang SF, Lu MK, Cheng XF, Liu SF, Zhou GJ, et al. J Cryst Growth 2004;262: 182–5. [20] Sakurai Y. J Non-Cryst Solids 2006;352:5391–8. [21] Zhou JX, Zhang MS, Hong JM, Yin Z. Solid State Commun 2006;138:242–6.