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Pb(Zr0.5, Ti0.5)O3 nanofibres by electrospinning
Materials Letters 59 (2005) 3085 – 3089 www.elsevier.com/locate/matlet
Pb(Zr0.5, Ti0.5)O3 nanofibres by electrospinningB N. Dharmaraj a,b,*, C.H. Kim b, H.Y. Kim b a
b
Department of Chemistry, Government Arts College, Udumalpet-642 126, India Inorganic/Organic Nanomaterials Research Laboratory, Department of Textile Engineering, Chonbuk National University, Chonju 561-756 , South Korea Received 17 January 2005; accepted 26 May 2005 Available online 5 July 2005
Abstract Lead zirconate titanate Pb(Zr0.5, Ti0.5)O3 nanofibres with diameters ranging from 200 – 300 nm have been synthesized by calcination of the electrospun lead zirconate titanate/polyvinyl acetate composite fibres. The morphology and crystalline phase features of these lead zirconate titanate (PZT) nanofibres have been studied by various physico-chemical methods such as SEM, AFM, XRD and FT – IR. The formation of perovskite PZT phase was observed at temperatures as low as 550 -C. D 2005 Elsevier B.V. All rights reserved. Keywords: Piezoelectric; Lead zirconate titanate (PZT) nanofibres; Electrospinning; Calcination; X-ray diffraction
1. Introduction Perovskite lead zirconate titanate (PZT) based materials exhibit various properties, such as pyroelectric, piezoelectric, ferroelectric, elasto-optic effect, linear and quadratic electrooptic effect depending on the chemical compositions, and hence is used in wide range of applications [1]. Piezoelectric ceramics have been used as sensor and actuator materials in smart material and structural systems, non-volatile ferroelectric memory devices, micro-electromechanical systems (MEMS), because they have the ability to transform energy from electrical to mechanical and vice versa [2 – 5]. Fibrous PZT has potential for utilization in high performance hydrophones and ultrasonic transducer applications, because the fine fibrous geometry offers the possibility of composite fabrication where damping and reinforcement is combined [6]. Uniaxially oriented sol-gel derived PZT fibres with diameters smaller than 30 (Am) have been successfully integrated into planar fibre architectures, embedded with i
This work was presented at the Korea – Japan joint forum (KJF-2003) at Pusan National University, Pusan, South Korea. * Corresponding author. Department of Chemistry, Government Arts College, Udumalpet-642 126, India. Tel.: +82 63 270 2351; fax: +82 63 270 2348. E-mail address: [email protected] (N. Dharmaraj). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.05.040
inter-digitated electrodes [7]. Lead zirconate titanate thin films and powders can be synthesized in many different ways, such as through metallo-organic decomposition (MOD) [8,9], co-precipitation [10], sol-gel [11], hydrothermal reactions [12] and reactive calcinations [13]. Among these methods, sol-gel processing is the widely used process for PZT thin films because of its control over stoichiometry and microstructure [14]. Additionally, this method is simple with versatile laboratory equipments. Earlier studies showed that the formation of perovskite phase in PZT powders occurs only at temperatures of about 800 -C [15]. In contrast to the multiplicity of synthesis methods used for PZT thin films and powders, only a few ways have been found for the PZT fibres, all with diameters larger than 10 (Am)[6– 19]. In order to realize potential applications of PZT fibres, the fabrication of fine-scale fibres is becoming an increasingly important aspect. Interestingly, the electrostatic deposition method (electrospinning) yields fibres distributed in the micro- and nanoscopic range in diameter and macroscopic in length [20]. Recently, some novel metal oxide fibres with nano- to submicron scale diameter have been prepared by electrospinning technique and characterized with various sophisticated instruments [20 –25]. This study aims to synthesize perovskite lead zirconate titanate fibres with ultra-fine dimensions in the neighbour-
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N. Dharmaraj et al. / Materials Letters 59 (2005) 3085 – 3089
hood of 200 – 300 nm diameter, at low temperature using sol-gel processing and electrospinning technique.
2. Experimental 2.1. Materials Lead acetete trihydrate (99% Aldrich), zirconium (IV) npropoxide (70 wt.% solution in 1-propanol, Aldrich) and titanium (IV) isopropoxide (97% Aldrich) were used as precursors. 2-Methoxyethanol was used as a solvent to facilitate the dehydration by boiling and acetic acid was used as the chelating agent for the alkoxides. 2.2. Preparation of PZT sol The preparation of PZT sol was carried out as reported earlier [26]. Lead acetate trihydrate (1 mol, 3.79 g) was dissolved in 2-methoxyethanol (10 ml) by heating and stirring at 70 -C. The water of crystallization was removed by distillation and again refluxed for 1 h and then cooled down to 70 -C and this forms the lead precursor. A solution containing 2-methoxyethanol, acetic acid, zirconium (IV) npropoxide (0.5 mol, 1.63 g in 10 ml of 2-methoxyethanol) and titanium (IV) isopropoxide (0.5 mol 1.42 g in 10 ml of 2methoxyethanol) were then prepared and this forms the zirconium/titanium precursor. The acetic acid to alkoxide molar ratio was kept at 1 : 1. Pb and Zr/Ti precursor solutions
were then mixed and refluxed at 80 -C for 3 h. To this solution, water of hydrolysis (water / alkoxide ratio = 1.5) was added and final refluxing has been done for 6 h at 80 -C. The clear golden yellow coloured PZT sol was then filtered and used for further processing. Poly(vinyl acetate) (PVAc) (18 wt.%) solution was prepared in methanol/ethanol (80 / 20 wt. ratio) mixture. 2.3. Preparation of the PZT/PVAc composite nanofibres The solution needed for electrospinning was prepared by stirring the lead zirconate titanate sol and PVAc (18 wt.% in methanol/ethanol (80 / 20)) solution in the weight ratio of 0.8 : 1, for 5 h at room temperature. The viscous solution thus obtained was placed in a hypodermic syringe. The positive terminal of a variable high voltage power supply was attached to a copper wire inserted into the solution in the syringe, whereas the ground iron drum covered with an aluminium foil served as counter electrode. The distance between the tip of the syringe and collector was 17 cm. The syringe was placed at an angle of 25- to horizontal in order to get uniform flow of the solution. When the voltage applied between the two electrodes reached 17 kV, lead zirconate titanate/PVAc composite fibres with several centimeter length have been accumulated on the surface of the aluminium foil. The as-prepared lead zirconate titanate/ PVAc composite fibres were collected and calcinated at different temperatures to get lead zirconium titanate fibres with nano- to sub-micron diameters.
Fig. 1. SEM images of PZT nanofibres: (a) as-prepared composite fibres, (b) fibres calcinated at 550 -C, (c) fibres calcinated at 650 -C, and (d) fibres calcinated at 700 -C.
N. Dharmaraj et al. / Materials Letters 59 (2005) 3085 – 3089
3087
• (110)
2.4. Characterization of samples
X
pyrochlore
• (112)
• (102)
x
• (200)
• (111)
• (100)
(111)
• perovskite
Intensity
SEM images of the samples were recorded by JEOL GSM-5900 scanning electron microscope. Tapping mode AFM images were obtained from Nanoscope(R)-IV instrument. Powder X-ray diffraction patterns of the fibres were obtained from Shimadzu Lab-X 600 X-ray diffractometer using Cu – Ka radiation. FT – IR spectra of the samples (as pellets in KBr) have been recorded in BIO-Rad Win instrument. The as-prepared composite fibres were calcinated at different temperatures at a heating rate of 2 -C/min in air.
d c
3. Results and discussion
b a
3.1. Scanning electron microscopic images (SEM) 10
Fig. 1 shows the SEM images of the PZT nanofibres. The asprepared PZT/PVAc composite fibres have a cylindrical geometry with diameters in the range of 300 – 400 nm. After calcination at 550 -C, the surface of the fibres became rough due to the removal organic components and crystallization of perovskite phase. The
20
30
40
50
60
70
2θ (degree) Fig. 3. XRD patterns of PZT nanofibres: (a) as-prepared composite fibres, (b) fibres calcinated at 550 -C, (c) fibres calcinated at 650 -C, and (d) fibres calcinated at 700 -C.
Fig. 2. One dimensional and three dimensional AFM images of PZT/PVAc as-prepared composite fibres.
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N. Dharmaraj et al. / Materials Letters 59 (2005) 3085 – 3089
[4,20,26,27]. The coexistence of pyrochlore and perovskite phases between 600 to 850 -C was in consistent with those reported for PZT fibres [20,27].
a
Transmittance
3.4. FT – IR spectra
b c
d
500
1000
Wavenumber
1500
2000
(cm-1)
Fig. 4. FT – IR spectra of PZT nanofibres: (a) as-prepared composite fibres, (b) fibres calcinated at 550 -C, (c) fibres calcinated at 650 -C, and (d) fibres calcinated at 700 -C.
samples obtained after calcinations at 650 and 700 -C showed a little decrease in the fibre diameter and reaches as minimum as 200 – 300 nm and were broken to short length. 3.2. Atomic force microscopy (AFM) The surface topography of the PZT/PVAc composite fibres was also studied by tapping mode atomic force microscopy (TMAFM). Fig. 2 represents the AFM images and the height profiles of the corresponding as-electrospun PZT/PVAc composite fibres marked on the images. It can be seen from the AFM images that the aselectrospun PZT/PVAc composite fibres (Fig. 2) have uniform, smooth surfaces with cylindrical structure possessing the diameters in the range of 300 – 400 nm as was seen in SEM photographs. Our attempt to obtain AFM images of the calcinated samples went unsuccessful owing to their surface roughness. The three dimensional (3D) image of the fibre sample was also presented. 3.3. X-ray diffraction studies (XRD) The crystallographic structures of the fibres were systematically examined by X-ray diffraction spectra (Fig. 3) to determine the crystalline phases present in them at various temperatures. No peaks were confirmed in the pattern of the PZT/PVAc composite fibres, characteristic of its amorphous nature (Fig. 3a). After calcination at 550 -C, it was observed that the crystallization of perovskite phase began to form at this temperature along with a trace of pyrochlore phase at 2h = 28.9 (Fig. 3b). The relative intensity of perovskite peaks is far stronger with respect to pyrochlore peaks. Further, by increasing the calcination temperature to 650 and 700 -C, (Fig. 3c and d), the fibres displayed sharp and intense peaks indicating well crystalline perovskite lead zirconate titanate phase. In a typical powder process, the PZT perovskite phase was formed at temperature of about 800 -C [15]. Therefore, sol-gel derived PZT fibres obtained thorough electrospinning followed by calcination treatment produced the perovskite phase at lower temperature (550 -C) than in the conventional synthesis method. All the peaks corresponding to tetragonal perovskite phase were well matched with previously reported data
The formation of PZT nanofibres was also confirmed by FT – IR spectra. The spectrum of the PZT/PVAc composite fibres (Fig. 4a) has multiple strong absorption bands in the region 1000 to 1750 cm 1, corresponding to the stretching and bending vibrations of PVAc. After calcinations at 550 -C, the spectra showed that the organic bands diminish greatly indicating the decomposition of polymer templates, but a new band characteristic of PZT peaks appeared between 500 – 750 cm 1 (Fig. 4b [20]. Further increase in the calcinations treatment temperature to 650 -C revealed that the organic bands almost disappeared while the broad PZT band becomes more intense (Fig. 4c). The FT – IR spectra of the fibres obtained after 700 -C, have also showed an intense PZT band and its width has been found to be narrow in the range 550 – 700 cm 1 (Fig. 4d).
4. Conclusion Ultra-fine lead zirconate titanate Pb(Zr0.5, Ti0.5)O3 fibres with diameters in the range of 200 – 300 nm have been successfully prepared by calcinating the sol-gel derived, electrospun PZT/PVAc composite fibres. Sol-gel processing resulted in low perovskite crystallization temperature (550 -C) as compared to other conventional synthesis methods. A good correlation was observed between XRD and FT – IR spectra in the formation of perovskite lead zirconate titanate nanofibres.
Acknowledgements We gratefully acknowledge The Korean Federation of Science and Technology Societies (KOFST), Ministry of Science and Technology, Republic of Korea, for awarding Brain Pool Fellowship (041S-4-12, 2004) to one of the authors (N. Dharmaraj).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
G.H. Haertling, J. Am. Ceram. Soc. 82 (1999) 797. J. Tani, T. Takagi, J. Qiu, Appl. Mech. Rev. ASME 51 (1998) 505. J. Qui, J. Tani, J. Intell. Mater. Syst. Struct. 6 (1995) 474. J. Qui, J. Tani, Y. Kobayashi, T.Y. Um, H. Takahashi, Smart Mater. Struct. 12 (2003) 331. A.J. Molson, J.H. Herbert, Electroceramics, Chapman and Hall, London, 1990. S. Yoshikawa, S. Ulgargaraj, P. Moses, J. Witham, R. Meyer, T. Shrout, J. Intell. Mater. Syst. Struct. 6 (1995) 152. D. Sporn, A. Schoenecker, Mater. Res. Innov. 2 (1999) 303. J. Fukushima, K. Kodaira, T. Matsushita, J. Mater. Sci. 19 (1984) 595. S.-Y. Chen, I.-W. Chen, J. Am. Ceram. Soc. 81 (1998) 97. K.R.M. Rao, A.V.P. Rao, Mater. Lett. 28 (1996) 463. V.R. Palkar, M.S. Multani, Mater. Res. Bull. 14 (1979) 1353.
N. Dharmaraj et al. / Materials Letters 59 (2005) 3085 – 3089 [12] T.R.N. Kutty, R. Balachandran, Mater. Res. Bull. 19 (1984) 1479. [13] C.A. Randall, N. Kim, J.P. Kucera, W.W. Cao, T.R. Shrout, J. Am. Ceram. Soc. 81 (1998) 677. [14] Y. Xu, J.D. Mackenzie, Integr. Ferroelectr. 1 (1992) 17. [15] T. Um, Y. Kobayashi, J. Qiu, J. Tani, H. Takahashi, J. Jpn. Soc. Powder Powder Metall. 47 (2000) 674. [16] H. Takeguchi, C. Nakaya, Ferroelectrics 68 (1986) 53. [17] D.J. Waller, A. Safari, R. Card, M.P.O. Toole, J. Am. Ceram. Soc. 73 (1990) 3503. [18] U. Selvaraj, A.V. Prasadarao, S. Komareni, K. Brooks, K.S. Kurtz, J. Mater. Res. 7 (1992) 992. [19] R. Meyer Jr., T. Shrout, S. Yoshikawa, J. Am. Ceram. Soc. 81 (1998) 861. [20] Y. Wang, J.J. Santiago-Aviles, Nanotechnology 15 (2004) 32.
3089
[21] H. Guan, C. Shao, S. Wen, B. Chen, J. Gong, X. Yang, Inorg. Chem. Commun. 6 (2003) 1302. [22] H.G. Guan, C. Shao, B. Chen, J. Gong, X. Yang, Inorg. Chem. Commun. 6 (2003) 1409. [23] P. Viswanathamurthi, N. Bhattarai, H.Y. Kim, D.R. Lee, S.R. Kim, M.A. Morris, Chem. Phys. Lett. 374 (2003) 79. [24] P. Viswanathamurthi, N. Bhattarai, H.Y. Kim, D.R. Lee, Scripta Mater. 49 (2003) 577. [25] P. Viswanathamurthi, N. Bhattarai, H.Y. Kim, D.R. Lee, Nanotechnology 15 (2004) 320. [26] R. Thomas, S. Mochizuki, T. Mihara, T. Ishida, Mater. Lett. 57 (2003) 2007. [27] Y. Wang, S. Serrano, J. Santiago, Mater. Res. Soc. Symp. Proc. 702 (2002) 359.
Pb(Zr0.5, Ti0.5)O3 nanofibres by electrospinningB N. Dharmaraj a,b,*, C.H. Kim b, H.Y. Kim b a
b
Department of Chemistry, Government Arts College, Udumalpet-642 126, India Inorganic/Organic Nanomaterials Research Laboratory, Department of Textile Engineering, Chonbuk National University, Chonju 561-756 , South Korea Received 17 January 2005; accepted 26 May 2005 Available online 5 July 2005
Abstract Lead zirconate titanate Pb(Zr0.5, Ti0.5)O3 nanofibres with diameters ranging from 200 – 300 nm have been synthesized by calcination of the electrospun lead zirconate titanate/polyvinyl acetate composite fibres. The morphology and crystalline phase features of these lead zirconate titanate (PZT) nanofibres have been studied by various physico-chemical methods such as SEM, AFM, XRD and FT – IR. The formation of perovskite PZT phase was observed at temperatures as low as 550 -C. D 2005 Elsevier B.V. All rights reserved. Keywords: Piezoelectric; Lead zirconate titanate (PZT) nanofibres; Electrospinning; Calcination; X-ray diffraction
1. Introduction Perovskite lead zirconate titanate (PZT) based materials exhibit various properties, such as pyroelectric, piezoelectric, ferroelectric, elasto-optic effect, linear and quadratic electrooptic effect depending on the chemical compositions, and hence is used in wide range of applications [1]. Piezoelectric ceramics have been used as sensor and actuator materials in smart material and structural systems, non-volatile ferroelectric memory devices, micro-electromechanical systems (MEMS), because they have the ability to transform energy from electrical to mechanical and vice versa [2 – 5]. Fibrous PZT has potential for utilization in high performance hydrophones and ultrasonic transducer applications, because the fine fibrous geometry offers the possibility of composite fabrication where damping and reinforcement is combined [6]. Uniaxially oriented sol-gel derived PZT fibres with diameters smaller than 30 (Am) have been successfully integrated into planar fibre architectures, embedded with i
This work was presented at the Korea – Japan joint forum (KJF-2003) at Pusan National University, Pusan, South Korea. * Corresponding author. Department of Chemistry, Government Arts College, Udumalpet-642 126, India. Tel.: +82 63 270 2351; fax: +82 63 270 2348. E-mail address: [email protected] (N. Dharmaraj). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.05.040
inter-digitated electrodes [7]. Lead zirconate titanate thin films and powders can be synthesized in many different ways, such as through metallo-organic decomposition (MOD) [8,9], co-precipitation [10], sol-gel [11], hydrothermal reactions [12] and reactive calcinations [13]. Among these methods, sol-gel processing is the widely used process for PZT thin films because of its control over stoichiometry and microstructure [14]. Additionally, this method is simple with versatile laboratory equipments. Earlier studies showed that the formation of perovskite phase in PZT powders occurs only at temperatures of about 800 -C [15]. In contrast to the multiplicity of synthesis methods used for PZT thin films and powders, only a few ways have been found for the PZT fibres, all with diameters larger than 10 (Am)[6– 19]. In order to realize potential applications of PZT fibres, the fabrication of fine-scale fibres is becoming an increasingly important aspect. Interestingly, the electrostatic deposition method (electrospinning) yields fibres distributed in the micro- and nanoscopic range in diameter and macroscopic in length [20]. Recently, some novel metal oxide fibres with nano- to submicron scale diameter have been prepared by electrospinning technique and characterized with various sophisticated instruments [20 –25]. This study aims to synthesize perovskite lead zirconate titanate fibres with ultra-fine dimensions in the neighbour-
3086
N. Dharmaraj et al. / Materials Letters 59 (2005) 3085 – 3089
hood of 200 – 300 nm diameter, at low temperature using sol-gel processing and electrospinning technique.
2. Experimental 2.1. Materials Lead acetete trihydrate (99% Aldrich), zirconium (IV) npropoxide (70 wt.% solution in 1-propanol, Aldrich) and titanium (IV) isopropoxide (97% Aldrich) were used as precursors. 2-Methoxyethanol was used as a solvent to facilitate the dehydration by boiling and acetic acid was used as the chelating agent for the alkoxides. 2.2. Preparation of PZT sol The preparation of PZT sol was carried out as reported earlier [26]. Lead acetate trihydrate (1 mol, 3.79 g) was dissolved in 2-methoxyethanol (10 ml) by heating and stirring at 70 -C. The water of crystallization was removed by distillation and again refluxed for 1 h and then cooled down to 70 -C and this forms the lead precursor. A solution containing 2-methoxyethanol, acetic acid, zirconium (IV) npropoxide (0.5 mol, 1.63 g in 10 ml of 2-methoxyethanol) and titanium (IV) isopropoxide (0.5 mol 1.42 g in 10 ml of 2methoxyethanol) were then prepared and this forms the zirconium/titanium precursor. The acetic acid to alkoxide molar ratio was kept at 1 : 1. Pb and Zr/Ti precursor solutions
were then mixed and refluxed at 80 -C for 3 h. To this solution, water of hydrolysis (water / alkoxide ratio = 1.5) was added and final refluxing has been done for 6 h at 80 -C. The clear golden yellow coloured PZT sol was then filtered and used for further processing. Poly(vinyl acetate) (PVAc) (18 wt.%) solution was prepared in methanol/ethanol (80 / 20 wt. ratio) mixture. 2.3. Preparation of the PZT/PVAc composite nanofibres The solution needed for electrospinning was prepared by stirring the lead zirconate titanate sol and PVAc (18 wt.% in methanol/ethanol (80 / 20)) solution in the weight ratio of 0.8 : 1, for 5 h at room temperature. The viscous solution thus obtained was placed in a hypodermic syringe. The positive terminal of a variable high voltage power supply was attached to a copper wire inserted into the solution in the syringe, whereas the ground iron drum covered with an aluminium foil served as counter electrode. The distance between the tip of the syringe and collector was 17 cm. The syringe was placed at an angle of 25- to horizontal in order to get uniform flow of the solution. When the voltage applied between the two electrodes reached 17 kV, lead zirconate titanate/PVAc composite fibres with several centimeter length have been accumulated on the surface of the aluminium foil. The as-prepared lead zirconate titanate/ PVAc composite fibres were collected and calcinated at different temperatures to get lead zirconium titanate fibres with nano- to sub-micron diameters.
Fig. 1. SEM images of PZT nanofibres: (a) as-prepared composite fibres, (b) fibres calcinated at 550 -C, (c) fibres calcinated at 650 -C, and (d) fibres calcinated at 700 -C.
N. Dharmaraj et al. / Materials Letters 59 (2005) 3085 – 3089
3087
• (110)
2.4. Characterization of samples
X
pyrochlore
• (112)
• (102)
x
• (200)
• (111)
• (100)
(111)
• perovskite
Intensity
SEM images of the samples were recorded by JEOL GSM-5900 scanning electron microscope. Tapping mode AFM images were obtained from Nanoscope(R)-IV instrument. Powder X-ray diffraction patterns of the fibres were obtained from Shimadzu Lab-X 600 X-ray diffractometer using Cu – Ka radiation. FT – IR spectra of the samples (as pellets in KBr) have been recorded in BIO-Rad Win instrument. The as-prepared composite fibres were calcinated at different temperatures at a heating rate of 2 -C/min in air.
d c
3. Results and discussion
b a
3.1. Scanning electron microscopic images (SEM) 10
Fig. 1 shows the SEM images of the PZT nanofibres. The asprepared PZT/PVAc composite fibres have a cylindrical geometry with diameters in the range of 300 – 400 nm. After calcination at 550 -C, the surface of the fibres became rough due to the removal organic components and crystallization of perovskite phase. The
20
30
40
50
60
70
2θ (degree) Fig. 3. XRD patterns of PZT nanofibres: (a) as-prepared composite fibres, (b) fibres calcinated at 550 -C, (c) fibres calcinated at 650 -C, and (d) fibres calcinated at 700 -C.
Fig. 2. One dimensional and three dimensional AFM images of PZT/PVAc as-prepared composite fibres.
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N. Dharmaraj et al. / Materials Letters 59 (2005) 3085 – 3089
[4,20,26,27]. The coexistence of pyrochlore and perovskite phases between 600 to 850 -C was in consistent with those reported for PZT fibres [20,27].
a
Transmittance
3.4. FT – IR spectra
b c
d
500
1000
Wavenumber
1500
2000
(cm-1)
Fig. 4. FT – IR spectra of PZT nanofibres: (a) as-prepared composite fibres, (b) fibres calcinated at 550 -C, (c) fibres calcinated at 650 -C, and (d) fibres calcinated at 700 -C.
samples obtained after calcinations at 650 and 700 -C showed a little decrease in the fibre diameter and reaches as minimum as 200 – 300 nm and were broken to short length. 3.2. Atomic force microscopy (AFM) The surface topography of the PZT/PVAc composite fibres was also studied by tapping mode atomic force microscopy (TMAFM). Fig. 2 represents the AFM images and the height profiles of the corresponding as-electrospun PZT/PVAc composite fibres marked on the images. It can be seen from the AFM images that the aselectrospun PZT/PVAc composite fibres (Fig. 2) have uniform, smooth surfaces with cylindrical structure possessing the diameters in the range of 300 – 400 nm as was seen in SEM photographs. Our attempt to obtain AFM images of the calcinated samples went unsuccessful owing to their surface roughness. The three dimensional (3D) image of the fibre sample was also presented. 3.3. X-ray diffraction studies (XRD) The crystallographic structures of the fibres were systematically examined by X-ray diffraction spectra (Fig. 3) to determine the crystalline phases present in them at various temperatures. No peaks were confirmed in the pattern of the PZT/PVAc composite fibres, characteristic of its amorphous nature (Fig. 3a). After calcination at 550 -C, it was observed that the crystallization of perovskite phase began to form at this temperature along with a trace of pyrochlore phase at 2h = 28.9 (Fig. 3b). The relative intensity of perovskite peaks is far stronger with respect to pyrochlore peaks. Further, by increasing the calcination temperature to 650 and 700 -C, (Fig. 3c and d), the fibres displayed sharp and intense peaks indicating well crystalline perovskite lead zirconate titanate phase. In a typical powder process, the PZT perovskite phase was formed at temperature of about 800 -C [15]. Therefore, sol-gel derived PZT fibres obtained thorough electrospinning followed by calcination treatment produced the perovskite phase at lower temperature (550 -C) than in the conventional synthesis method. All the peaks corresponding to tetragonal perovskite phase were well matched with previously reported data
The formation of PZT nanofibres was also confirmed by FT – IR spectra. The spectrum of the PZT/PVAc composite fibres (Fig. 4a) has multiple strong absorption bands in the region 1000 to 1750 cm 1, corresponding to the stretching and bending vibrations of PVAc. After calcinations at 550 -C, the spectra showed that the organic bands diminish greatly indicating the decomposition of polymer templates, but a new band characteristic of PZT peaks appeared between 500 – 750 cm 1 (Fig. 4b [20]. Further increase in the calcinations treatment temperature to 650 -C revealed that the organic bands almost disappeared while the broad PZT band becomes more intense (Fig. 4c). The FT – IR spectra of the fibres obtained after 700 -C, have also showed an intense PZT band and its width has been found to be narrow in the range 550 – 700 cm 1 (Fig. 4d).
4. Conclusion Ultra-fine lead zirconate titanate Pb(Zr0.5, Ti0.5)O3 fibres with diameters in the range of 200 – 300 nm have been successfully prepared by calcinating the sol-gel derived, electrospun PZT/PVAc composite fibres. Sol-gel processing resulted in low perovskite crystallization temperature (550 -C) as compared to other conventional synthesis methods. A good correlation was observed between XRD and FT – IR spectra in the formation of perovskite lead zirconate titanate nanofibres.
Acknowledgements We gratefully acknowledge The Korean Federation of Science and Technology Societies (KOFST), Ministry of Science and Technology, Republic of Korea, for awarding Brain Pool Fellowship (041S-4-12, 2004) to one of the authors (N. Dharmaraj).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
G.H. Haertling, J. Am. Ceram. Soc. 82 (1999) 797. J. Tani, T. Takagi, J. Qiu, Appl. Mech. Rev. ASME 51 (1998) 505. J. Qui, J. Tani, J. Intell. Mater. Syst. Struct. 6 (1995) 474. J. Qui, J. Tani, Y. Kobayashi, T.Y. Um, H. Takahashi, Smart Mater. Struct. 12 (2003) 331. A.J. Molson, J.H. Herbert, Electroceramics, Chapman and Hall, London, 1990. S. Yoshikawa, S. Ulgargaraj, P. Moses, J. Witham, R. Meyer, T. Shrout, J. Intell. Mater. Syst. Struct. 6 (1995) 152. D. Sporn, A. Schoenecker, Mater. Res. Innov. 2 (1999) 303. J. Fukushima, K. Kodaira, T. Matsushita, J. Mater. Sci. 19 (1984) 595. S.-Y. Chen, I.-W. Chen, J. Am. Ceram. Soc. 81 (1998) 97. K.R.M. Rao, A.V.P. Rao, Mater. Lett. 28 (1996) 463. V.R. Palkar, M.S. Multani, Mater. Res. Bull. 14 (1979) 1353.
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