- Email: [email protected]
Effect of Gd3+ substitution on dielectric properties of nano cobalt ferrite
Materials Letters 65 (2011) 3191–3192
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 ev i e r. c o m / l o c a t e / m a t l e t
Effect of Gd 3+ substitution on dielectric properties of nano cobalt ferrite Anu Rana a,⁎, O.P. Thakur a, Vinod Kumar b a b
School of Applied Sciences, Netaji Subhas Institute of Technology, New Delhi, India DCR Univ. Sci. Tech., Murthal, Haryana, India
a r t i c l e
i n f o
Article history: Received 29 September 2010 Accepted 21 June 2011 Available online 28 June 2011 Keywords: Nano-particles Ferrite Dielectric constant Dielectric loss Co-precipitation
a b s t r a c t CoGdxFe2 − xO4 (x = 0.0, 0.1, 0.3, 0.5) nano magnetic ferrite particles were synthesized by chemical coprecipitation method. The variation of dielectric parameters like dielectric constant, dielectric loss, capacitance and resistance for different Gd 3+ compositions has been measured at room temperature for frequency dependence in the range of 100 Hz to 10 MHz using impedance analyzer. Results of measurements reveal strong dependence of dielectric parameters on frequency and Gd 3+ ion content. Dielectric constant, dielectric loss, capacitance and resistance decrease with increasing frequency for all the CoGdxFe2 − xO4 compositions. Increase in Gd3+ ion composition in material, increases the values of dielectric constant, dielectric loss and capacitance while decreases the electrical resistance of nano-particles. A qualitative explanation is given for the composition and frequency dependence of dielectric parameters. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Magnetic nanoparticles are gaining importance due to their potential applications in high-density magnetic recording, magnetic fluid, biomedical and microwave applications etc. [1–3]. Physical and chemical properties of any material are mainly dependent on the chemical composition as well as processing. The abnormal dielectric behavior of the zinc substituted spinel cobalt ferrite as a function of frequency and composition was reported by Ahmed et al. [4]. A strong correlation between conduction mechanism and the dielectric behavior of ferrites has been reported by Iwauchi [5]. In view of the wide-ranging applications, Gd 3+ doped cobalt ferrites were chosen for study. Detailed investigation of the Gd 3+ ion composition and frequency dependence of the dielectric constant and dielectric loss tangent are carried out in the frequency range of 100 Hz to 10 MHz and the results are presented in paper.
2. Experimental Polycrystalline samples of gadolinium substituted cobalt ferrite having the chemical formula CoGdxFe2 − xO4 where x = 0, 0.1, 0.3, 0.5 are prepared by co-precipitation method using cobalt chloride, gadolinium chloride and ferric nitrate. High purity salts of CoCl2, Fe (No3)3·9H2O and GdCl3·6H2O were taken as an initial materials. 1 M aqueous solutions were prepared and mixed in respective stoichiom-
⁎ Corresponding author. E-mail address: [email protected] (A. Rana). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.076
etry composition. The solution mixture is kept for heating at 60 °C to make it homogenous. Precipitation is accomplished with constant stirring and adding ammonia solution drop by drop. The nano-particle formation took place by the conversion of metal salts into hydroxides which occurred immediately. Thus, the particles are collected by using filtration of solutions and are washed several times with double distilled water to remove unwanted salts residual. The precipitated nano-particles were dried at 85 °C for 1 h. The samples are further annealed at 300 °C to improve the crystalline properties of the material. The structural parameters of the samples are characterized using powder X-ray diffraction technique. The frequency dependent dielectric losses and dielectric constant were studied on impendence analyzer (Wayne KERR, UK) in the frequency range of 100 Hz to 10 MHz. 3. Result and discussion Structural parameter confirms the single phase formation of the material. The X-ray diffraction pattern of as obtained and annealed samples of CoGdxFe2 − xO4 (where x = 0, 0.1, 0.3, 0.5) are shown in Fig. 1. The diffraction pattern of as obtained sample shows single phase formation and poor crystallinity of the material. The crystallinity decreases with the increase in Gd ion concentration. The lattice parameter increases with the increase of Gd ion concentration which is attributed to larger ionic radius of Gd 3+ (0.938 nm) as compared to Fe 3+ (0.065 nm) creating the asymmetric behavior thus decreasing the crystalline properties. The dielectric constant, έ, decreases with increase in frequency for all the concentration as shown in Fig. 2. The variation of dielectric loss factor, tanδ with frequency for different gadolinium concentration is shown in Fig. 3. The general trend for all composition is that the
3192
A. Rana et al. / Materials Letters 65 (2011) 3191–3192
120
10
x=0.1
Dielectric loss (tan )
x=0.3 x=0.5
(311)
80
Counts / a.u
Gd0.0 Gd0.1 Gd0.3 Gd0.5
x=0.0
100
60
40
20
10
10
10
0 10
20
30
40
50
60
70
10 10
2
10
10
10
10
Frequency (Hz)
Fig. 1. X-ray diffraction pattern of the different concentration Gd3+ ion doped cobalt ferrite nano materials.
Gd0.1
10
Fig. 3. Plot of dielectric loss tangent (tanδ) vs. frequency for Co–Gd ferrites with different Gd3+ ion concentrations.
The dielectric constant and dielectric loss increases with increasing compositions of gadolinium are explained on the basis of space charge polarization, presence of higher conductivity phases (grains) in the insulating matrix (grain boundaries) causing localized accumulation of charge under the influence of an electric field. The variation of dielectric constant έ, dielectric loss, and resistance with frequency has been studied. Significant changes are observed for all the concentrations of gadolinium ions in the whole range of frequency.
Gd0.0
Dielectric costant
10
Gd0.3 Gd0.5 10
4. Conclusion
10
1x10
1x10
1x10
1x10
1x10
1x10
frequency (Hz) Fig. 2. Plot of real part of dielectric constant vs. frequency for Co–Gd ferrites with different Gd3+ ion concentrations.
dielectric constant (έ) and dielectric loss decreases with increasing frequency. This can be explained that well conducting grains are separated by the poorly conducting grain boundaries in the material. The electron reaches the grain boundary by hopping and the resistance of grain boundary is relatively more. The electrons pile up at grain boundaries where they produce polarization. When the frequency of applied field is increased, the electrons reverse their direction of motion more often which decreases probability of electrons reaching the grain boundary and as a result polarization decreases, therefore, decreasing the dielectric constant and dielectric loss of the developed materials with the increase in frequency [6–8].
CoGdxFe2 − xO4 (x= 0.0, 0.1, 0.3, 0.5) nano magnetic ferrite particles were synthesized by chemical co-precipitation method. The variation of dielectric constant and dielectric loss for different Gd3+ compositions have been measured at room temperature for frequency dependence in the range of 100 Hz to 10 MHz using impedance analyzer. Results confirm strong dependence of the studied parameters on frequency and Gd 3+ ion content. Increase in Gd3+ ion composition in the developed ferrite material increases the values of dielectric constant and dielectric loss. References [1] Han DH, Luo HL, Yang Z. J Magn Magn Mater 1996;161:376. [2] Sousa MH, Tourinbo FA. J Phys Chem B 2001;105:168. [3] Dong-Hyun K, David EN, Duane TJ, Christopher SB. J Magn Magn Mater 2008;320: 2390. [4] Ramana Reddy AV, Ranga Mphan G, Ravinder D, Boyanov BS. J Mat Sci 1999;34: 3169. [5] Iwuchi K. Jpn J Appl Phys 1971;10:1520. [6] Mazeuand SA, Dawoad HA. Matter Chem Phys 2003;82:557. [7] Zhi Y, Chen A. J Appl Phys 2002;91:5325. [8] Ranga Mohan G, Ravinder D, Ramama Reddy AV, Boyanov BS. Mater Lett 1999;40: 39.
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 ev i e r. c o m / l o c a t e / m a t l e t
Effect of Gd 3+ substitution on dielectric properties of nano cobalt ferrite Anu Rana a,⁎, O.P. Thakur a, Vinod Kumar b a b
School of Applied Sciences, Netaji Subhas Institute of Technology, New Delhi, India DCR Univ. Sci. Tech., Murthal, Haryana, India
a r t i c l e
i n f o
Article history: Received 29 September 2010 Accepted 21 June 2011 Available online 28 June 2011 Keywords: Nano-particles Ferrite Dielectric constant Dielectric loss Co-precipitation
a b s t r a c t CoGdxFe2 − xO4 (x = 0.0, 0.1, 0.3, 0.5) nano magnetic ferrite particles were synthesized by chemical coprecipitation method. The variation of dielectric parameters like dielectric constant, dielectric loss, capacitance and resistance for different Gd 3+ compositions has been measured at room temperature for frequency dependence in the range of 100 Hz to 10 MHz using impedance analyzer. Results of measurements reveal strong dependence of dielectric parameters on frequency and Gd 3+ ion content. Dielectric constant, dielectric loss, capacitance and resistance decrease with increasing frequency for all the CoGdxFe2 − xO4 compositions. Increase in Gd3+ ion composition in material, increases the values of dielectric constant, dielectric loss and capacitance while decreases the electrical resistance of nano-particles. A qualitative explanation is given for the composition and frequency dependence of dielectric parameters. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Magnetic nanoparticles are gaining importance due to their potential applications in high-density magnetic recording, magnetic fluid, biomedical and microwave applications etc. [1–3]. Physical and chemical properties of any material are mainly dependent on the chemical composition as well as processing. The abnormal dielectric behavior of the zinc substituted spinel cobalt ferrite as a function of frequency and composition was reported by Ahmed et al. [4]. A strong correlation between conduction mechanism and the dielectric behavior of ferrites has been reported by Iwauchi [5]. In view of the wide-ranging applications, Gd 3+ doped cobalt ferrites were chosen for study. Detailed investigation of the Gd 3+ ion composition and frequency dependence of the dielectric constant and dielectric loss tangent are carried out in the frequency range of 100 Hz to 10 MHz and the results are presented in paper.
2. Experimental Polycrystalline samples of gadolinium substituted cobalt ferrite having the chemical formula CoGdxFe2 − xO4 where x = 0, 0.1, 0.3, 0.5 are prepared by co-precipitation method using cobalt chloride, gadolinium chloride and ferric nitrate. High purity salts of CoCl2, Fe (No3)3·9H2O and GdCl3·6H2O were taken as an initial materials. 1 M aqueous solutions were prepared and mixed in respective stoichiom-
⁎ Corresponding author. E-mail address: [email protected] (A. Rana). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.076
etry composition. The solution mixture is kept for heating at 60 °C to make it homogenous. Precipitation is accomplished with constant stirring and adding ammonia solution drop by drop. The nano-particle formation took place by the conversion of metal salts into hydroxides which occurred immediately. Thus, the particles are collected by using filtration of solutions and are washed several times with double distilled water to remove unwanted salts residual. The precipitated nano-particles were dried at 85 °C for 1 h. The samples are further annealed at 300 °C to improve the crystalline properties of the material. The structural parameters of the samples are characterized using powder X-ray diffraction technique. The frequency dependent dielectric losses and dielectric constant were studied on impendence analyzer (Wayne KERR, UK) in the frequency range of 100 Hz to 10 MHz. 3. Result and discussion Structural parameter confirms the single phase formation of the material. The X-ray diffraction pattern of as obtained and annealed samples of CoGdxFe2 − xO4 (where x = 0, 0.1, 0.3, 0.5) are shown in Fig. 1. The diffraction pattern of as obtained sample shows single phase formation and poor crystallinity of the material. The crystallinity decreases with the increase in Gd ion concentration. The lattice parameter increases with the increase of Gd ion concentration which is attributed to larger ionic radius of Gd 3+ (0.938 nm) as compared to Fe 3+ (0.065 nm) creating the asymmetric behavior thus decreasing the crystalline properties. The dielectric constant, έ, decreases with increase in frequency for all the concentration as shown in Fig. 2. The variation of dielectric loss factor, tanδ with frequency for different gadolinium concentration is shown in Fig. 3. The general trend for all composition is that the
3192
A. Rana et al. / Materials Letters 65 (2011) 3191–3192
120
10
x=0.1
Dielectric loss (tan )
x=0.3 x=0.5
(311)
80
Counts / a.u
Gd0.0 Gd0.1 Gd0.3 Gd0.5
x=0.0
100
60
40
20
10
10
10
0 10
20
30
40
50
60
70
10 10
2
10
10
10
10
Frequency (Hz)
Fig. 1. X-ray diffraction pattern of the different concentration Gd3+ ion doped cobalt ferrite nano materials.
Gd0.1
10
Fig. 3. Plot of dielectric loss tangent (tanδ) vs. frequency for Co–Gd ferrites with different Gd3+ ion concentrations.
The dielectric constant and dielectric loss increases with increasing compositions of gadolinium are explained on the basis of space charge polarization, presence of higher conductivity phases (grains) in the insulating matrix (grain boundaries) causing localized accumulation of charge under the influence of an electric field. The variation of dielectric constant έ, dielectric loss, and resistance with frequency has been studied. Significant changes are observed for all the concentrations of gadolinium ions in the whole range of frequency.
Gd0.0
Dielectric costant
10
Gd0.3 Gd0.5 10
4. Conclusion
10
1x10
1x10
1x10
1x10
1x10
1x10
frequency (Hz) Fig. 2. Plot of real part of dielectric constant vs. frequency for Co–Gd ferrites with different Gd3+ ion concentrations.
dielectric constant (έ) and dielectric loss decreases with increasing frequency. This can be explained that well conducting grains are separated by the poorly conducting grain boundaries in the material. The electron reaches the grain boundary by hopping and the resistance of grain boundary is relatively more. The electrons pile up at grain boundaries where they produce polarization. When the frequency of applied field is increased, the electrons reverse their direction of motion more often which decreases probability of electrons reaching the grain boundary and as a result polarization decreases, therefore, decreasing the dielectric constant and dielectric loss of the developed materials with the increase in frequency [6–8].
CoGdxFe2 − xO4 (x= 0.0, 0.1, 0.3, 0.5) nano magnetic ferrite particles were synthesized by chemical co-precipitation method. The variation of dielectric constant and dielectric loss for different Gd3+ compositions have been measured at room temperature for frequency dependence in the range of 100 Hz to 10 MHz using impedance analyzer. Results confirm strong dependence of the studied parameters on frequency and Gd 3+ ion content. Increase in Gd3+ ion composition in the developed ferrite material increases the values of dielectric constant and dielectric loss. References [1] Han DH, Luo HL, Yang Z. J Magn Magn Mater 1996;161:376. [2] Sousa MH, Tourinbo FA. J Phys Chem B 2001;105:168. [3] Dong-Hyun K, David EN, Duane TJ, Christopher SB. J Magn Magn Mater 2008;320: 2390. [4] Ramana Reddy AV, Ranga Mphan G, Ravinder D, Boyanov BS. J Mat Sci 1999;34: 3169. [5] Iwuchi K. Jpn J Appl Phys 1971;10:1520. [6] Mazeuand SA, Dawoad HA. Matter Chem Phys 2003;82:557. [7] Zhi Y, Chen A. J Appl Phys 2002;91:5325. [8] Ranga Mohan G, Ravinder D, Ramama Reddy AV, Boyanov BS. Mater Lett 1999;40: 39.