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Effect of Temperature on the Properties of La2O3 Nanostructures
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 2 (2015) 1021 – 1025
5th International Conference on Perspectives in Vibrational Spectroscopy
Effect of temperature on the properties of La2O3 nanostructures S. Karthikeyan, A. Dhayal Raj*, A. Albert Irudayaraj, D. Magimai Antoni Raj PG & Research Department of Physics, Sacred Heart College(Autonomous), Tirpattur, Vellore-635 601, Tamil Nadu, India
Abstract In recent years, the synthesis of Lanthanum oxide (La 2O3) nanoparticles by using simple reflux method using Lanthanum nitrate (LaN3O9.6H2O), urea (NH2CONH2) and double distilled water as starting and strong materials. The solution obtained was transferred to a round bottom flask which was maintained at a constant reaction temperature and time. The effect of calcinations temperature on the properties of Lanthanum oxide (La2O3) nanoparticles have been explored and reported. The phase and structure of the lanthanum oxide has been identified using X-ray powder diffraction(XRD). The surface properties and morphology has been investigated using a scanning electron microscopy (SEM) technique. The properties of the synthesized nanostructures have been investigated and reported. Fourier transform infrared spectroscopy (FTIR) analysis confirms the present of functional group. The vibrational behaviours of the bonds are further analyzed using FTIR. Thermal stability of the samples have been investigated using TG/DTA analysis and the UV-Vis spectroscopy technique has been exploited to study about the optical absorption of the samples. © The Authors. ElsevierLtd. Ltd. All rights reserved. © 2014 2015 Published by Elsevier Conference Committee Members of the 5th 5th International Conference on on Selection and and Peer-review Peer-reviewunder underresponsibility responsibilityofofthethe Conference Committee Members of the International Conference Perspectives in Perspectives in Vibrational VibrationalSpectroscopy. Spectroscopy. Keywords: Lanthanum Oxide; Nanoslabs; SEM; Structure; FTIR; Polycrystalline;
*Corresponding author: E-mail address: [email protected]
1. Introduction Rare earth oxides (RE) have been intensively investigated due to their excellent mechanical, chemical, thermal, optical and electrical properties [1,2]. There is a great interest in the study of the influence of many factors on luminescent materials, such as synthesis methods, hosts influence, europium ion concentration, thermal treatments and several others. Currently the microstructure and the macrostructure of these materials are produced by a combination of those factors, which have an effect on the luminescence properties. In particular, in nanocrystalline
2214-7853 © 2015 Published by Elsevier Ltd. Selection and Peer-review under responsibility of the Conference Committee Members of the 5th International Conference on Perspectives in Vibrational Spectroscopy. doi:10.1016/j.matpr.2015.06.030
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S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
powders [3]. The RE doped oxides are some of the most promising luminescent materials, their technological applications are the principal motivation for the research into rare earth luminescence. Lanthanum oxide (La 2O3) is potentially useful material for various optical and electronic applications, such as high k gate dielectric material, capacitors, non-volatile memories (NVMs), optical filters and waveguides. The La 2O3 films are promising material for integration into future NVMs because they are expected to crystallize above 500ºC in the monoclinic phase which has a higher most of rare earth oxides crystallize [4,5]. In recent years the preparation and properties of nanocrystalline La2O3 have attracted much interest from a practical point of view [6,7]. The La2O3 film has been prepared using various deposition techniques such as chemical vapor deposition, ultrasonic spray pyrolysis technique, electron beam evaporation, etc [8,9]. Rare earth oxides are used as a component in various optical, electrical and magnetic applications such as optical wave guide optical filters and capacitors [10]. La2O3 is also used in production of PTCR (positive temperature coefficient in resistance). All these applications need nanosized La 2O3 powders. It is also well-known that the functional properties of these materials depend on particle size. The properties of lanthanum in general are greatly affected by the characteristics of the powder, such as particle size, morphology, purity and chemical composition. Wet chemical synthesis of ultrafine ceramic powders continues to be a subject of intense research activity as the products exhibit several advantages over powder derived from conventional lanthanum routes. Using chemical methods, e.g. co-precipitation, sol-gel, hydrothermal and colloid emulsion technique have been confirmed to efficiently control the morphology and chemical composition of prepared powder. The main advantages of these methods are the increased homogeneity and high surface area of the resulting powders, which lead to relatively high reactivity and hence low sintering temperatures. There are not many reports on preparation of La2O3 nanoparticles. However all these methods formed La2O3 only at temperatures much above 110°C. The method of gel to crystalline conversion is reported in the literature [11] and final products are formed at around 110°C. 2. Experimental All the materials were obtained from commercial suppliers and were used without further purification. Lanthanum oxide (La2O3) has been synthesized by a simple reflux method using Lanthanum nitrate (LaN3O9.6H2O) and Urea (NH2CONH2) as starting and strong materials. The effect of precursor concentration on the properties of Lanthanum oxide (La2O3) nanoparticles have been explored and reported. In a typical synthesis, required mole of Lanthanum nitrate and 0.01 Mole of Urea were dissolved in 500 ml double distilled water. The precursor solution was transferred into a round bottom flask and maintained at a constant temperature of 110°C for 24 hours. The samples are prepared with different precursor (lanthanum nitrate) concentrations namely 0.01 and 0.1 Mole. Finally, the prepared nanoparticles were calcinated at 500°C for 1 hour. The prepared samples were characterized by XRD, SEM, FTIR TG/DTA and UV-Visible analysis. 3. Results and Discussion 3.1 Structural analysis Powder XRD is useful for conforming the identity of a solid material and determining the crystallinity and phase purity. Fig.1 shows the XRD patterns of the La2O3 nanoparticles prepared by Reflux method with different reaction temperatures. The XRD pattern in figure 1 (a) corresponds to the sample prepared at 6 hours reaction time exhibiting a polycrystalline nature. The well defined higher intensity peaks in the XRD pattern presented in Fig. 1 (b) indicate that the sample prepared with 12 hours reaction time also exhibit polycrystalline nature with a higher degree of crystallinity. The peaks obtained for both the samples, exactly match with those reported in JCPDS 500602. The crystallites were found to have a monoclinic structure. The crystallite sizes as calculated from the XRD patterns were 5 nm and 18 nm for the sample prepared with 6 hours and 12 hours, respectively.
S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
1023
Fig. 1 XRD pattern of La2O3 nanoparticles prepared with a) 6 hours and b) 12 hours
3.2 Morphological analysis The SEM image of the samples prepared with 6 hours and 12 hours reaction time are presented in fig.2 ( a and b) respectively. The increase in reaction time has altered the morphology of the samples. For longer duration the nanoslab like structures formed seem to allign themselves in to flower like morphologies as can be seen from fig.2b. The formation of these flower like morphologies may offer more surface for the reactions to occur and hence will be of great interest in the field of gas sensors and catalysis.
a
b
Fig. 2 Morphological Analysis pattern of La 2O3 nano particles prepared with a reaction time of a) 6 hours and b) 12 hours
3.3 Vibrational analysis Fig. 3 (a)&(b) show the FTIR spectra of La2O3 nanoparticles prepared with reaction temperatures 6 hours and 12 hours, respectively. From the FTIR spectrum, one can observe the absorption due to the molecular vibration. The FTIR spectrum of La2O3 nanoparticles were recorded in the range of 450 cm-1 to 4000 cm-1. The frequency of various vibrational frequencies around 500 to 1000 cm-1 confirm the formation of La2O3. The obtained peaks are in match with the earlier reported values thus confirming the formation of La 2O3 phase.
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S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
3500
3000
2500
1500
(1079.8) (1043.4)
(1457.1)
2000
(861.5) (818.7) (726.2) (692.8)
(838.1) (808.1)
(699.8)
(1628) (3500)
(1621.8)
(3430.1)
(2475.4)
(1764.4)
a
4000
(1076.8)
(1771.1)
(2484.7)
(%) T ransmittance
(2920.8)
b
1000
500
Wavenumber (cm-1)
Fig. 3 FTIR spectra of La2O3 nanoparticles prepared with a) 6 hours and b) 12 hours
3.4 Optical analysis The optical absorbance spectrum of La2O3 nanoparticles for the wavelength length range 200-1100 nm was recorded using UV-Visible spectrophotometer. Fig. 4 (a) & (b) shows the UV absorption spectrum of La 2O3 nanoparticles prepared with a reaction time of 6 hours and 12 hours respectively. The UV-Vis results are in correlation with the SEM results. The sample prepared with a higher reaction time of 12 hours having flower like morphology shows a higher absorption when compared to the sample with nanoslab like morphology. This can be accounted with the large surface area expected to be offered by the flower like morphologies.
0.7
Absorbance (Arbitr. Units)
0.6 0.5 0.4 0.3
b
0.2
a
0.1 200
400
600
800
1000
Wavelength (nm)
Fig. 4 Optical Analysis of La2O3 nano particles prepared with a reaction time of a) 6 hours b) 12 hours
4. Conclusion The structures of the prepared samples were obtained from XRD pattern as monoclinic crystal system and the prepared samples exhibit polycrystalline nature. The morphology of the prepared samples were studied using SEM. The SEM images showed Nanoplate like morphologies and the average diameter of the thickness was found to be around 50-80 nm at the optimized condition. FTIR results show the presence of La2O3 is evident from the stretching
S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
1025
vibration peaks at 556cm-1 and 570 cm-1. Therefore, as expected with increase in reaction temperature and time, the particle size increases. However there must be a compromise between the crysallinity and size of the prepared samples. References [1] J. Gouteron, D. Michel, A.M. Lejus, J. Zarembowitch, J. Solid State Chem. 38 (1981) 288-296. [2] E.A.d. Morais, L.V.A. Scalvi, A.A. Cavalheiro, A. Tabata, J.B.B. Oliveira, J. Non-Cryst. Solids 354 (2008) 4840-4845. [3] G. Wakefield, H.A. Keron, P.J. Dobson, J.L. Hutchison, J. Colloid Interface Sci. 215 (1999) 179-182. [4] S. W. Kang, S. W. Rhee, J. Electrochem. Soc. 149 (2002) C345. [5] S. Wang, W. Wang, Y. Qian, Thin Solid Films 372 (2000) 50-53. [8] J.B. Chen, A.D. Li, Q.Y. Shao, H.Q. Ling, D.Wu, Y.Wang, Y.J. Bao, M.Wang, Z.G. Liu,N.B. Ming, Appl. Surf. Sci. 233 (2004) 91-98. [9] C. Yang , H. Fan, Y. Xi , S. Qiu , Y.Fu, Thin Solid Films 517 (2009) 1677-1680. [10] Q.Z. Wu, Y. Shen, J.F. Liao, Y.G. Li, Mater. Lett. 58 (2004) 2688-2691. [11] S. Wang, W. Wang, Y. Qian, Thin Solid Films 372 (2000) 50-53.
ScienceDirect Materials Today: Proceedings 2 (2015) 1021 – 1025
5th International Conference on Perspectives in Vibrational Spectroscopy
Effect of temperature on the properties of La2O3 nanostructures S. Karthikeyan, A. Dhayal Raj*, A. Albert Irudayaraj, D. Magimai Antoni Raj PG & Research Department of Physics, Sacred Heart College(Autonomous), Tirpattur, Vellore-635 601, Tamil Nadu, India
Abstract In recent years, the synthesis of Lanthanum oxide (La 2O3) nanoparticles by using simple reflux method using Lanthanum nitrate (LaN3O9.6H2O), urea (NH2CONH2) and double distilled water as starting and strong materials. The solution obtained was transferred to a round bottom flask which was maintained at a constant reaction temperature and time. The effect of calcinations temperature on the properties of Lanthanum oxide (La2O3) nanoparticles have been explored and reported. The phase and structure of the lanthanum oxide has been identified using X-ray powder diffraction(XRD). The surface properties and morphology has been investigated using a scanning electron microscopy (SEM) technique. The properties of the synthesized nanostructures have been investigated and reported. Fourier transform infrared spectroscopy (FTIR) analysis confirms the present of functional group. The vibrational behaviours of the bonds are further analyzed using FTIR. Thermal stability of the samples have been investigated using TG/DTA analysis and the UV-Vis spectroscopy technique has been exploited to study about the optical absorption of the samples. © The Authors. ElsevierLtd. Ltd. All rights reserved. © 2014 2015 Published by Elsevier Conference Committee Members of the 5th 5th International Conference on on Selection and and Peer-review Peer-reviewunder underresponsibility responsibilityofofthethe Conference Committee Members of the International Conference Perspectives in Perspectives in Vibrational VibrationalSpectroscopy. Spectroscopy. Keywords: Lanthanum Oxide; Nanoslabs; SEM; Structure; FTIR; Polycrystalline;
*Corresponding author: E-mail address: [email protected]
1. Introduction Rare earth oxides (RE) have been intensively investigated due to their excellent mechanical, chemical, thermal, optical and electrical properties [1,2]. There is a great interest in the study of the influence of many factors on luminescent materials, such as synthesis methods, hosts influence, europium ion concentration, thermal treatments and several others. Currently the microstructure and the macrostructure of these materials are produced by a combination of those factors, which have an effect on the luminescence properties. In particular, in nanocrystalline
2214-7853 © 2015 Published by Elsevier Ltd. Selection and Peer-review under responsibility of the Conference Committee Members of the 5th International Conference on Perspectives in Vibrational Spectroscopy. doi:10.1016/j.matpr.2015.06.030
1022
S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
powders [3]. The RE doped oxides are some of the most promising luminescent materials, their technological applications are the principal motivation for the research into rare earth luminescence. Lanthanum oxide (La 2O3) is potentially useful material for various optical and electronic applications, such as high k gate dielectric material, capacitors, non-volatile memories (NVMs), optical filters and waveguides. The La 2O3 films are promising material for integration into future NVMs because they are expected to crystallize above 500ºC in the monoclinic phase which has a higher most of rare earth oxides crystallize [4,5]. In recent years the preparation and properties of nanocrystalline La2O3 have attracted much interest from a practical point of view [6,7]. The La2O3 film has been prepared using various deposition techniques such as chemical vapor deposition, ultrasonic spray pyrolysis technique, electron beam evaporation, etc [8,9]. Rare earth oxides are used as a component in various optical, electrical and magnetic applications such as optical wave guide optical filters and capacitors [10]. La2O3 is also used in production of PTCR (positive temperature coefficient in resistance). All these applications need nanosized La 2O3 powders. It is also well-known that the functional properties of these materials depend on particle size. The properties of lanthanum in general are greatly affected by the characteristics of the powder, such as particle size, morphology, purity and chemical composition. Wet chemical synthesis of ultrafine ceramic powders continues to be a subject of intense research activity as the products exhibit several advantages over powder derived from conventional lanthanum routes. Using chemical methods, e.g. co-precipitation, sol-gel, hydrothermal and colloid emulsion technique have been confirmed to efficiently control the morphology and chemical composition of prepared powder. The main advantages of these methods are the increased homogeneity and high surface area of the resulting powders, which lead to relatively high reactivity and hence low sintering temperatures. There are not many reports on preparation of La2O3 nanoparticles. However all these methods formed La2O3 only at temperatures much above 110°C. The method of gel to crystalline conversion is reported in the literature [11] and final products are formed at around 110°C. 2. Experimental All the materials were obtained from commercial suppliers and were used without further purification. Lanthanum oxide (La2O3) has been synthesized by a simple reflux method using Lanthanum nitrate (LaN3O9.6H2O) and Urea (NH2CONH2) as starting and strong materials. The effect of precursor concentration on the properties of Lanthanum oxide (La2O3) nanoparticles have been explored and reported. In a typical synthesis, required mole of Lanthanum nitrate and 0.01 Mole of Urea were dissolved in 500 ml double distilled water. The precursor solution was transferred into a round bottom flask and maintained at a constant temperature of 110°C for 24 hours. The samples are prepared with different precursor (lanthanum nitrate) concentrations namely 0.01 and 0.1 Mole. Finally, the prepared nanoparticles were calcinated at 500°C for 1 hour. The prepared samples were characterized by XRD, SEM, FTIR TG/DTA and UV-Visible analysis. 3. Results and Discussion 3.1 Structural analysis Powder XRD is useful for conforming the identity of a solid material and determining the crystallinity and phase purity. Fig.1 shows the XRD patterns of the La2O3 nanoparticles prepared by Reflux method with different reaction temperatures. The XRD pattern in figure 1 (a) corresponds to the sample prepared at 6 hours reaction time exhibiting a polycrystalline nature. The well defined higher intensity peaks in the XRD pattern presented in Fig. 1 (b) indicate that the sample prepared with 12 hours reaction time also exhibit polycrystalline nature with a higher degree of crystallinity. The peaks obtained for both the samples, exactly match with those reported in JCPDS 500602. The crystallites were found to have a monoclinic structure. The crystallite sizes as calculated from the XRD patterns were 5 nm and 18 nm for the sample prepared with 6 hours and 12 hours, respectively.
S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
1023
Fig. 1 XRD pattern of La2O3 nanoparticles prepared with a) 6 hours and b) 12 hours
3.2 Morphological analysis The SEM image of the samples prepared with 6 hours and 12 hours reaction time are presented in fig.2 ( a and b) respectively. The increase in reaction time has altered the morphology of the samples. For longer duration the nanoslab like structures formed seem to allign themselves in to flower like morphologies as can be seen from fig.2b. The formation of these flower like morphologies may offer more surface for the reactions to occur and hence will be of great interest in the field of gas sensors and catalysis.
a
b
Fig. 2 Morphological Analysis pattern of La 2O3 nano particles prepared with a reaction time of a) 6 hours and b) 12 hours
3.3 Vibrational analysis Fig. 3 (a)&(b) show the FTIR spectra of La2O3 nanoparticles prepared with reaction temperatures 6 hours and 12 hours, respectively. From the FTIR spectrum, one can observe the absorption due to the molecular vibration. The FTIR spectrum of La2O3 nanoparticles were recorded in the range of 450 cm-1 to 4000 cm-1. The frequency of various vibrational frequencies around 500 to 1000 cm-1 confirm the formation of La2O3. The obtained peaks are in match with the earlier reported values thus confirming the formation of La 2O3 phase.
1024
S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
3500
3000
2500
1500
(1079.8) (1043.4)
(1457.1)
2000
(861.5) (818.7) (726.2) (692.8)
(838.1) (808.1)
(699.8)
(1628) (3500)
(1621.8)
(3430.1)
(2475.4)
(1764.4)
a
4000
(1076.8)
(1771.1)
(2484.7)
(%) T ransmittance
(2920.8)
b
1000
500
Wavenumber (cm-1)
Fig. 3 FTIR spectra of La2O3 nanoparticles prepared with a) 6 hours and b) 12 hours
3.4 Optical analysis The optical absorbance spectrum of La2O3 nanoparticles for the wavelength length range 200-1100 nm was recorded using UV-Visible spectrophotometer. Fig. 4 (a) & (b) shows the UV absorption spectrum of La 2O3 nanoparticles prepared with a reaction time of 6 hours and 12 hours respectively. The UV-Vis results are in correlation with the SEM results. The sample prepared with a higher reaction time of 12 hours having flower like morphology shows a higher absorption when compared to the sample with nanoslab like morphology. This can be accounted with the large surface area expected to be offered by the flower like morphologies.
0.7
Absorbance (Arbitr. Units)
0.6 0.5 0.4 0.3
b
0.2
a
0.1 200
400
600
800
1000
Wavelength (nm)
Fig. 4 Optical Analysis of La2O3 nano particles prepared with a reaction time of a) 6 hours b) 12 hours
4. Conclusion The structures of the prepared samples were obtained from XRD pattern as monoclinic crystal system and the prepared samples exhibit polycrystalline nature. The morphology of the prepared samples were studied using SEM. The SEM images showed Nanoplate like morphologies and the average diameter of the thickness was found to be around 50-80 nm at the optimized condition. FTIR results show the presence of La2O3 is evident from the stretching
S. Karthikeyan et al. / Materials Today: Proceedings 2 (2015) 1021 – 1025
1025
vibration peaks at 556cm-1 and 570 cm-1. Therefore, as expected with increase in reaction temperature and time, the particle size increases. However there must be a compromise between the crysallinity and size of the prepared samples. References [1] J. Gouteron, D. Michel, A.M. Lejus, J. Zarembowitch, J. Solid State Chem. 38 (1981) 288-296. [2] E.A.d. Morais, L.V.A. Scalvi, A.A. Cavalheiro, A. Tabata, J.B.B. Oliveira, J. Non-Cryst. Solids 354 (2008) 4840-4845. [3] G. Wakefield, H.A. Keron, P.J. Dobson, J.L. Hutchison, J. Colloid Interface Sci. 215 (1999) 179-182. [4] S. W. Kang, S. W. Rhee, J. Electrochem. Soc. 149 (2002) C345. [5] S. Wang, W. Wang, Y. Qian, Thin Solid Films 372 (2000) 50-53. [8] J.B. Chen, A.D. Li, Q.Y. Shao, H.Q. Ling, D.Wu, Y.Wang, Y.J. Bao, M.Wang, Z.G. Liu,N.B. Ming, Appl. Surf. Sci. 233 (2004) 91-98. [9] C. Yang , H. Fan, Y. Xi , S. Qiu , Y.Fu, Thin Solid Films 517 (2009) 1677-1680. [10] Q.Z. Wu, Y. Shen, J.F. Liao, Y.G. Li, Mater. Lett. 58 (2004) 2688-2691. [11] S. Wang, W. Wang, Y. Qian, Thin Solid Films 372 (2000) 50-53.