- Email: [email protected]
Effect of reaction time on particle size and dielectric properties of manganese substituted CoFe2O4 nanoparticles
Journal of Physics and Chemistry of Solids 74 (2013) 110–114
Contents lists available at SciVerse ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Effect of reaction time on particle size and dielectric properties of manganese substituted CoFe2O4 nanoparticles E. Ranjith Kumar a, R. Jayaprakash a,n, T. ArunKumar a, Sanjay Kumar b a b
Department of Physics, Nanotechnology Laboratory, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore-641020, Tamil Nadu, India Centre for Appropriate Management, Chandragupt Institute of Management Chajubagh, Patna-800 001, Bihar, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 January 2012 Received in revised form 5 July 2012 Accepted 9 August 2012 Available online 23 August 2012
An auto-combustion route was adopted for preparing nanosize manganese substituted cobalt ferrite. The synthesis of the nanoparticles was carried out using different fuel ratio for combustion process. The prepared samples were characterized using XRD and TEM. The impact of fuel ratio on the formation of Co0.6Mn0.4Fe2O4 nanoparticles was analyzed in terms of particle size. The particle is achieved towards smaller range of size as 3–51 nm only at the 50% fuel ratio. The 75% and 100% fuel combustion ratio are not supported to attain the particle size on these ranges. The dielectric loss and low value of dielectric constant have been measured in the frequency range of 50 Hz–1 MHz. & 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Magnetic materials A. Nanostructures B. Chemical synthesis C. X-ray diffraction D. Dielectric properties
1. Introduction Preparation of nanosized spinel ferrite particle has become an important component of modern ceramic research. Various physical properties of ferrites are greatly influenced by the distribution of cations among the sublattices, nature of grain, grain boundaries, voids, inhomogenetities, surface layers and contacts, etc. The important properties of the ferrite materials such as their high value of resistivity and low eddy current losses are conducive to high frequency applications [1]. Owing to dielectric behavior, they are sometimes called multiferroics. They are important commercially because they can be applied in many devices such as phase shifter, high frequency transformer cores, switches, resonators, computers, TVs, and mobile phones [2]. Spinel ferrites with small dimensions, lightweight and modified structures are important components for many electronic products. The size reduction and compact arrangement of electronic devices in a smaller area have a welcoming feature in nanotechnology [3]. There are several methods for synthesizing nanosized magnetic spinel ferrite particles, such as co-precipitation [4], sol–gel [5], aerosol [6], polymerized complex method [7], microemulsion [8], combustion method [9], hydrazine method [10], reverse micelle method[11], wet chemical method [12], microwave-induced
n
Corresponding author. Tel.: þ91 9486313118. E-mail address: [email protected] (R. Jayaprakash).
0022-3697/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jpcs.2012.08.008
combustion [13], microwave refluxing method [14] and microwave hydrothermal method [15]. In the present work, an innovative autocombustion method is used to synthesize manganese doped cobalt nanosized spinel ferrite particles in 3–67 nm range with the use of urea. Although the use of auto-combustion method for preparing nanoparticles is described in earlier report [9], here we have varied the fuel ratio and determinants the impact on the particle size. Being a high resistance material, Mn doped in CoFe2O4 become a very good dielectric behavior. The dielectric properties such as dielectric constant and dissipation factor (D) are important for fabricating non conducting materials like ceramic.
2. Experimental details Nanocrystalline manganese doped cobalt ferrite has been prepared with the chemical formula Co0.6Mn0.4Fe2O4 was prepared by an auto-combustion technique. The analytical grade manganese nitrate [Mn (NO3)2 6H2O], cobalt nitrate [Co (NO3)2 6H2O], ferric nitrate [Fe (NO3)3 9H2O], and urea [CO(NH2)2] were used as raw materials. Urea is added for different percentage such as 50%, 75% and 100%. Subsequently, 5.02 g of manganese nitrate, 8.37 g of cobalt nitrate, 40.4 g of ferric nitrate and urea were dissolved in deionized water to form mixed solution, using a magnetic stirrer. Then the mixture was heated at 160 1C to dehydrate until selfignition takes place. Being ignited in air at room temperature, the dried gel burnt in a self propagating combustion, giving rise to the evolution of a large amount of gases and producing a dry and loose
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
111
Fig. 1. Indexed XRD pattern of Co0.6Mn0.4Fe2O4 nanoparticles prepared by auto combustion technique. (A) fuel ratio-50%, (B) fuel ratio-75%, and (C) fuel ratio-100%.
ferrite powder. Throughout the process no pH adjustment was made. To determine the influence of heat treatment on particle size and dielectric properties, a portion of the as-burnt ferrite powders was annealed at 600 1C and 900 1C for 5 h with the help of muffle furnace. The as-burnt and sintered Co–Mn ferrite powders were subjected to XRD analyses with Rigaku X-ray diffraction unit (Model ULTIMA III) to explore the structural properties. Transmission Electron Microscopy (TEM) and Selected-area Electron Diffraction (SAED) were recorded on a Technai G20-stwin Higher Resolution Electron Microscope (HRTEM) using an accelerating voltage of 200 kV. The dielectric properties of as-burnt and sintered samples were measured using a Digital LCR meter (Model TH2816A) in the frequency range from 50 Hz to 1 MHz.
3. Results and discussion 3.1. Structural characterization Fig. 1 represents the powder X-ray diffraction patterns of Co0.6Mn0.4Fe2O4 for as-burnt powder (sample A) and powders annealed at 600 1C (sample B) and 900 1C (sample C). All the peaks (220), (311), (400), (511) and (440) could be indexed with the standard pattern for MnFe2O4 and CoFe2O4 reported in JCPDS card no. 38-0430 and 74-208, respectively [16,17]. XRD pattern reveals that as-burnt powder is a single phase ferrite with spinel structure. On increasing the sintering temperature the diffraction peaks become narrower and sharper suggesting that there is an increase in particle size and crystallinity upon annealing [18]. From the results, at annealing temperature of 600 1C, the Co–Mn ferrite phase formed contained some secondary peaks, which are due to the a-Fe2O3 phase [19]. The average particle size of powders has been calculated from the diffraction peak of the (311) plane in the XRD profile, in accordance with Debye– Scherrer formula [20]: t¼
0:9l : bcos y
ð1Þ
where t is the average particle, l is the X-ray wave length (0.1542 nm), b is full width at half maximum(FWHM) and y is the Bragg angle of the (311) plane. It has been observed that the
Table 1 The effect of fuel ratio in particle size for different samples (A—as burnt), (B—annealed at 600 1C) and (C—annealed at 900 1C). Fuel ratio %
50 75 100
Particle size, t (nm) calculated from XRD Sample A
Sample B
Sample C
TEM particle Lattice parameter, a (A) ˚ size(nm) for sample C Sample Sample Sample A B C
3 14 18
9 20 20
52 57 67
54 60 65
8.4102 8.4140 8.4142
8.3547 8.3721 8.3748
8.3998 8.3856 8.3821
powders of synthesized ferrites consist of nanocrystalline particles with the size in the range of 3–67 nm. Also it has been observed that the particle size increases with increase in the sintering temperature which is in consistent with the recent reports [21]. The lattice parameter (a) has been calculated from X-ray diffraction data using the formula [22]: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 1 2 2 2 h þk þl ð2Þ ¼ 2 a2 d where d is the lattice spacing and h, k and l are the miller indices of the plane. The lattice parameter (a) of ferrite samples for different fuel ratio is listed in Table 1. The crystal parameter such as particle size and lattice parameter (a) of the as-burnt powders and annealed powders are predicted. Auto-combustion route produces better crystallized ferrites with designed properties. Also the average particle sizes of auto combustion samples are smaller. This observation is extended for the samples preparation in different combustion fuel ratio such as 50%, 75% and 100%. The XRD results for these samples reveals that the average particle size is less for the samples prepared by 50% fuel ratio than the other fuel ratio (75% and 100%) see Table 1. Thus impact of fuel ratio on Co0.6Mn0.4Fe2O4 influences the change in particle size. Fig. 2 shows the graphical representation of particle size with respect to temperature and it is found that increase in particle size as the temperature and the fuel ratio were raised. On considering with reaction time according to fuel ratio, the 100% fuel ratio makes combustion reaction faster, than the 50% fuel ratio.
112
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
Fig. 2. Variation of particle size of Co0.6Mn0.4Fe2O4 nanoparticles with respect to annealing temperature for different combustion fuel ratio: 50% (black squares), 75% (black points), 100% (black triangles).
900 1C. The maximum value of the dielectric constant in the range 378–484 is obtained for all samples at 50 Hz. A rapid decrease in dielectric constant is observed in low frequency at 200 Hz and gradually decreases up to 40 kHz then it retains a constant value. This behavior is almost similar for all the samples prepared under three different fuel ratios. From XRD results it is found that the particle size of the material increases with increase in the annealing temperature for various fuel ratios. Due to the impact of the fuel ratio the dielectric properties decreases with increase in particle size. The observed change in the dielectric constant can be explained on the basis of hoping conduction between Fe3 þ and Fe2 þ , Mn2 þ and Mn3 þ , Co2 þ and Co3 þ pairs of ions. A maximum polarization is occurred at low frequency range for these ions and it shows that dielectric constant to an optimum value [23]. According to Koops the decrease in dielectric constant for increase in frequency can be expressed by considering the solid as composed of well conducting grains which is separated by the poorly conducting grain boundaries [24]. The hope of electrons to reach the grain boundary and if the resistance of grain boundary is high enough then electrons pile up at the grain boundaries which causes polarization. The further increase of applied field shows that the electrons reverse their direction of motion and reduces the chance of electrons to approach the grain boundary and decreases the polarization. Thus this study reveals that the value of dielectric constant slowly decreases at lower frequencies and remains constant at higher frequencies [25]. Fig. 4 shows the variation in dielectric loss factor of Mn doped CoFe2O4 for different fuel ratios (50%, 75% and 100%) sintered at 900 1C. Both the dielectric constant and dielectric loss decrease as the frequency increases. This decrease indicates the normal behavior of ferrite samples. The decrease takes place when the jumping frequency of electric charge carriers cannot follow the alteration of applied AC electric field beyond a certain critical frequency [26]. 3.3. Transmission electron microscopy Fig. 5(A–C) show TEM micrograph of Co0.6Mn0.4Fe2O4 for different fuel ratios (50%, 75% and 100%) annealed at 900 1C. Few particles appear in spherical shape; however, some elongated
Fig. 3. Variation of dielectric constant of Co0.6Mn0.4Fe2O4 nanoparticles with respect to log frequency for different combustion fuel ratio: 50% (black squares), 75% (black points), 100% (black triangles).
Here the reaction time increases for 75% fuel ratio which is more than 100% fuel ratio. Similarly 50% fuel ratio takes higher reaction time, than the 75% and 100% fuel ratio. It suggests that the higher combustion reaction time produces smaller particle sizes. It conforms from the XRD pattern for 50% fuel ratio. Similarly the increases in particle size according to fuel ratio observed from the annealing temperature. 3.2. Dielectric properties The dielectric properties were measured for the samples prepared under different fuel ratio such as 50%, 75% and 100% using impedance analyzer in frequency range of 50 Hz to 1 MHz. Fig. 3 shows the variation in dielectric constant of Mn doped CoFe2O4 for different fuel ratios (50%, 75% and 100%) annealed at
Fig. 4. Variation of dielectric loss of Co0.6Mn0.4Fe2O4 nanoparticles with respect to log frequency for different combustion fuel ratio: 50% (black squares), 75% (black points), 100% (black triangles).
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
113
Fig. 5. TEM micrographs (A–C) and SAED pattern (D–F) of Co0.6Mn0.4Fe2O4 ferrite for different fuel ratios (50%, 75% and 100%) annealed at 900 1C.
particles are also present as shown in the TEM images. Some moderately agglomerated particles as well as separates particles are present in the images. Agglomeration is understood in terms of increase in size with annealing temperature and hence some degree of agglomeration at the higher annealing temperature is unavoidable [27]. From the TEM images the size for the separate particles are in the range of 50–70 nm. The particle size from the TEM report matches well with the size estimated from XRD measurement. Fig.5(D–F) shows the SAED pattern of Co0.6Mn0.4Fe2O4 samples prepared for different fuel ratios (50%, 75% and 100%) at 900 1C. Thus the bright spots indicate the good crystallinity of the samples with equal lattice arrangement. The SAED patterns of the high-resolution TEM image confirm that the nanoparticles correspond to face centered cubic structure. Fig. 6 shows the TEM image of as-burnt sample of Co0.6Mn0.4Fe2O4 for 50% fuel ratio with the particle size 8 nm.
4. Conclusion The nanocrystalline manganese substituted cobalt ferrite samples are prepared by auto-combusted techniques. Indexed powder XRD pattern revealed that the samples prepared by this route were ferrite nanoparticles with cubic spinel structure. It was seen that the particle size of synthesized ferrite samples was in the range of 3–67. The average particle size was less for the samples prepared by 50% fuel ratio than the other fuel ratio (75% and 100%) suggesting the impact of fuel ratio to the size of the particles. The results confirmed that the particle size of sample increase with the increase of annealing temperature. The presences of few separate spherical as well as agglomerated particles are rescored from the TEM images. The good crystallinity of the sample was confirmed by the occurrence of bright spot in SAED pattern. The dielectric properties of Co0.6Mn0.4Fe2O4
114
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
Fig. 6. TEM micrograph of as-burnt Co0.6Mn0.4Fe2O4 nanoparticle for 50% fuel ratio.
samples were analyzed. Measurements of the dielectric constant and dielectric loss in the 50 Hz–1MHz frequency range showed higher magnitude, at lower measuring frequencies, decreasing with increase in frequency, essentially becoming constant above 1 kHz. References [1] Y. Yamamoto, J. Makino, Core losses and magnetic properties of Mn–Zn ferrites with fine grain sizes, J. Magn. Magn. Mater. 133 (1994) 500. [2] X. Stanciulea, J. Neamtu, M. Feder, E. Segal, P. Cristea, L. Gai, Considerations on the sintering of manganese–zinc ferrite for power applications, J. Mater. Sci. Lett. 11 (1992) 961. [3] S.R. Murthy, Low temperature sintering of Mg–Cu–Zn ferrite and its electrical and magnetic properties, Bull. Mater. Sci. 24 (2001) 379. [4] Y. Il Kim, D. Kim, C.S. Lee, Synthesis and characterization of CoFe2O4 magnetic nanoparticles prepared by temperature-controlled coprecipitation method, Phys. B 337 (2003) 42–51. [5] X.H. Huang, Z.H. Chen, CoFe2O4 nanoparticles hosted in silica xerogels, Scr. Mater. 54 (2006) 169–173.
[6] S. Singhal, J. Singh, S.K. Barthwal, K. Chandra, Preparation and characterization of nanosize nickel-substituted cobalt ferrites (Co1 xNixFe2O4), J. Solid State Chem. 178 (2005) 3183–3189. [7] S.M. Montemayor, L.A. Garcia-Cerda, J.R. Torres-Lubian, Preparation and characterization of cobalt ferrite by the polymerized complex method, Mater. Lett. 59 (2005) 1056–1060. [8] E.J. Choi, Y. Ahu, S. Kim, D.H. An, Superparamagnetic relaxation in CoFe2O4 nanoparticles, J. Magn. Magn. Mater. 262 (2003) L198–L202. [9] A.F. Junior, E.C.O. Lima, Synthesis of nanoparticles of CoxFe(3 x)O4 by combustion reaction method, J. Magn. Magn. Mater. 308 (2007) 198–202. [10] L. Satyanarayana, K.M. Reddy, S.V. Manorama, Synthesis of nanocrystalline Ni1 xCoxMnxFe2 xO4: a material for liquefied petroleum gas sensing, Sens. Actuators B 89 (2003) 62–67. [11] P. Poddar, J. Gass, D.J. Rebar, S. Srinath, H. Srikanth, Magnetocaloric effect in ferrite nanoparticles, J. Magn. Magn. Mater. 307 (2006) 227–231. [12] K. Maaz, A. Mumtaz, S.K. Hasanain, A. Ceylan, Synthesis and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles prepared by wet chemical route, J. Magn. Magn. Mater. 308 (2007) 289–295. [13] Y.-P. Fu, K.-Y. Pan, C.-H. Lin, Microwave-induced combustion synthesis of Ni0.25Cu0.25Zn0.5 ferrite powders and their characterizations, Mater. Lett. 57 (2002) 291–296. [14] Y. Xuan, Q. Li, G. Yang, Synthesis and magnetic properties of Mn–Zn ferrite nanoparticles, J. Magn. Magn. Mater. 312 (2007) 464–469. [15] C.-K. Kim, J.-H. Lee, S. Katoh, Synthesis of Co-, Co–Zn and Ni–Zn ferrite powders by the microwave-hydrothermal method, Mater. Res. Bull. 36 (2001) 2241–2250. [16] X. Hou, J. Feng, Y. Ren, Z. Fan, M. Zhang, Synthesis and adsorption properties of spongelike porous MnFe2O4, Colloids Surf. A 363 (2010) 1–7. [17] Y. Qu, H. Yang, N. Yang, Y. Fan, H. Zhu, G. Zou, The effect of reaction temperature on the particle size, structural and magnetic properties of coprecipitated CoFe2O4 nanoparticles, Mater. Lett. 60 (2006) 3548–3552. [18] X. Huang, Z. Chen, Preparation of CoFe2O4/SiO2 nanocomposites by sol–gel method, J. Cryst. Growth 271 (2004) 287–293. [19] M.M. Hessien, M.M. Rashad, K. El-Barawy, I.A. Ibrahim, Influence of manganese substitution and annealing temperature on the formation, microstructure and magnetic properties of Mn–Zn ferrites, J. Magn. Magn. Mater. 320 (2008) 1615–1621. [20] M.A. Gabal, Y.M. Al Angari, S.S. Al-Juaid, A study on Cu substituted Ni–Cu–Zn ferrites synthesized using egg-white, J. Alloys Compds. 492 (2010) 411–415. [21] H.E. Zhang, B.F. Zhang, G.F. Wang, X.H. Dong, Y. Gao, The structure and magnetic properties of Zn1 xNixFe2O4 ferrite nanoparticles prepared by sol–gel auto-combustion, J. Magn. Magn. Mater. 312 (2007) 126–130. [22] P.P. Hankare, U.B. Sankpal, R.P. Patil, A.V. Jadhav, K.M. Garadkar, B.K. Chougule, Magnetic and dielectric studies of nanocrystalline zinc substituted Cu–Mn ferrites, J. Magn. Magn. Mater. 323 (2011) 389–393. [23] A. Thakur, P. Mathur, M. Singh, Study of dielectric behaviour of Mn–Zn nano ferrites, J. Phys. Chem. Solids 68 (2007) 378–381. [24] C.G. Koops, On the dispersion of resistivity and dielectric constant of some semiconductors at audiofrequencies, Phys Rev. 83 (1951) 121. [25] S.R. Kulkarni, C.M. Kanamadi, B.K. Chougule, Dielectric and magnetoelectric properties of (x)Ni0.8Co0.1Cu0.1Fe2O4/(1 x)PbZr0.8Ti0.2O3 composites, Mater. Res. Bull. 40 (2005) 2064–2072. [26] A.M. Abdeen, Dielectric behaviour in Ni–Zn ferrites, J. Magn. Magn. Mater. 192 (1999) 121. [27] L. Ai, J. Jiang, Influence of annealing temperature on the formation, microstructure and magnetic properties of spinel nanocrystalline cobalt ferrites, Curr. Appl. Phys. 10 (2010) 284–288.
Contents lists available at SciVerse ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Effect of reaction time on particle size and dielectric properties of manganese substituted CoFe2O4 nanoparticles E. Ranjith Kumar a, R. Jayaprakash a,n, T. ArunKumar a, Sanjay Kumar b a b
Department of Physics, Nanotechnology Laboratory, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore-641020, Tamil Nadu, India Centre for Appropriate Management, Chandragupt Institute of Management Chajubagh, Patna-800 001, Bihar, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 January 2012 Received in revised form 5 July 2012 Accepted 9 August 2012 Available online 23 August 2012
An auto-combustion route was adopted for preparing nanosize manganese substituted cobalt ferrite. The synthesis of the nanoparticles was carried out using different fuel ratio for combustion process. The prepared samples were characterized using XRD and TEM. The impact of fuel ratio on the formation of Co0.6Mn0.4Fe2O4 nanoparticles was analyzed in terms of particle size. The particle is achieved towards smaller range of size as 3–51 nm only at the 50% fuel ratio. The 75% and 100% fuel combustion ratio are not supported to attain the particle size on these ranges. The dielectric loss and low value of dielectric constant have been measured in the frequency range of 50 Hz–1 MHz. & 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Magnetic materials A. Nanostructures B. Chemical synthesis C. X-ray diffraction D. Dielectric properties
1. Introduction Preparation of nanosized spinel ferrite particle has become an important component of modern ceramic research. Various physical properties of ferrites are greatly influenced by the distribution of cations among the sublattices, nature of grain, grain boundaries, voids, inhomogenetities, surface layers and contacts, etc. The important properties of the ferrite materials such as their high value of resistivity and low eddy current losses are conducive to high frequency applications [1]. Owing to dielectric behavior, they are sometimes called multiferroics. They are important commercially because they can be applied in many devices such as phase shifter, high frequency transformer cores, switches, resonators, computers, TVs, and mobile phones [2]. Spinel ferrites with small dimensions, lightweight and modified structures are important components for many electronic products. The size reduction and compact arrangement of electronic devices in a smaller area have a welcoming feature in nanotechnology [3]. There are several methods for synthesizing nanosized magnetic spinel ferrite particles, such as co-precipitation [4], sol–gel [5], aerosol [6], polymerized complex method [7], microemulsion [8], combustion method [9], hydrazine method [10], reverse micelle method[11], wet chemical method [12], microwave-induced
n
Corresponding author. Tel.: þ91 9486313118. E-mail address: [email protected] (R. Jayaprakash).
0022-3697/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jpcs.2012.08.008
combustion [13], microwave refluxing method [14] and microwave hydrothermal method [15]. In the present work, an innovative autocombustion method is used to synthesize manganese doped cobalt nanosized spinel ferrite particles in 3–67 nm range with the use of urea. Although the use of auto-combustion method for preparing nanoparticles is described in earlier report [9], here we have varied the fuel ratio and determinants the impact on the particle size. Being a high resistance material, Mn doped in CoFe2O4 become a very good dielectric behavior. The dielectric properties such as dielectric constant and dissipation factor (D) are important for fabricating non conducting materials like ceramic.
2. Experimental details Nanocrystalline manganese doped cobalt ferrite has been prepared with the chemical formula Co0.6Mn0.4Fe2O4 was prepared by an auto-combustion technique. The analytical grade manganese nitrate [Mn (NO3)2 6H2O], cobalt nitrate [Co (NO3)2 6H2O], ferric nitrate [Fe (NO3)3 9H2O], and urea [CO(NH2)2] were used as raw materials. Urea is added for different percentage such as 50%, 75% and 100%. Subsequently, 5.02 g of manganese nitrate, 8.37 g of cobalt nitrate, 40.4 g of ferric nitrate and urea were dissolved in deionized water to form mixed solution, using a magnetic stirrer. Then the mixture was heated at 160 1C to dehydrate until selfignition takes place. Being ignited in air at room temperature, the dried gel burnt in a self propagating combustion, giving rise to the evolution of a large amount of gases and producing a dry and loose
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
111
Fig. 1. Indexed XRD pattern of Co0.6Mn0.4Fe2O4 nanoparticles prepared by auto combustion technique. (A) fuel ratio-50%, (B) fuel ratio-75%, and (C) fuel ratio-100%.
ferrite powder. Throughout the process no pH adjustment was made. To determine the influence of heat treatment on particle size and dielectric properties, a portion of the as-burnt ferrite powders was annealed at 600 1C and 900 1C for 5 h with the help of muffle furnace. The as-burnt and sintered Co–Mn ferrite powders were subjected to XRD analyses with Rigaku X-ray diffraction unit (Model ULTIMA III) to explore the structural properties. Transmission Electron Microscopy (TEM) and Selected-area Electron Diffraction (SAED) were recorded on a Technai G20-stwin Higher Resolution Electron Microscope (HRTEM) using an accelerating voltage of 200 kV. The dielectric properties of as-burnt and sintered samples were measured using a Digital LCR meter (Model TH2816A) in the frequency range from 50 Hz to 1 MHz.
3. Results and discussion 3.1. Structural characterization Fig. 1 represents the powder X-ray diffraction patterns of Co0.6Mn0.4Fe2O4 for as-burnt powder (sample A) and powders annealed at 600 1C (sample B) and 900 1C (sample C). All the peaks (220), (311), (400), (511) and (440) could be indexed with the standard pattern for MnFe2O4 and CoFe2O4 reported in JCPDS card no. 38-0430 and 74-208, respectively [16,17]. XRD pattern reveals that as-burnt powder is a single phase ferrite with spinel structure. On increasing the sintering temperature the diffraction peaks become narrower and sharper suggesting that there is an increase in particle size and crystallinity upon annealing [18]. From the results, at annealing temperature of 600 1C, the Co–Mn ferrite phase formed contained some secondary peaks, which are due to the a-Fe2O3 phase [19]. The average particle size of powders has been calculated from the diffraction peak of the (311) plane in the XRD profile, in accordance with Debye– Scherrer formula [20]: t¼
0:9l : bcos y
ð1Þ
where t is the average particle, l is the X-ray wave length (0.1542 nm), b is full width at half maximum(FWHM) and y is the Bragg angle of the (311) plane. It has been observed that the
Table 1 The effect of fuel ratio in particle size for different samples (A—as burnt), (B—annealed at 600 1C) and (C—annealed at 900 1C). Fuel ratio %
50 75 100
Particle size, t (nm) calculated from XRD Sample A
Sample B
Sample C
TEM particle Lattice parameter, a (A) ˚ size(nm) for sample C Sample Sample Sample A B C
3 14 18
9 20 20
52 57 67
54 60 65
8.4102 8.4140 8.4142
8.3547 8.3721 8.3748
8.3998 8.3856 8.3821
powders of synthesized ferrites consist of nanocrystalline particles with the size in the range of 3–67 nm. Also it has been observed that the particle size increases with increase in the sintering temperature which is in consistent with the recent reports [21]. The lattice parameter (a) has been calculated from X-ray diffraction data using the formula [22]: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 1 2 2 2 h þk þl ð2Þ ¼ 2 a2 d where d is the lattice spacing and h, k and l are the miller indices of the plane. The lattice parameter (a) of ferrite samples for different fuel ratio is listed in Table 1. The crystal parameter such as particle size and lattice parameter (a) of the as-burnt powders and annealed powders are predicted. Auto-combustion route produces better crystallized ferrites with designed properties. Also the average particle sizes of auto combustion samples are smaller. This observation is extended for the samples preparation in different combustion fuel ratio such as 50%, 75% and 100%. The XRD results for these samples reveals that the average particle size is less for the samples prepared by 50% fuel ratio than the other fuel ratio (75% and 100%) see Table 1. Thus impact of fuel ratio on Co0.6Mn0.4Fe2O4 influences the change in particle size. Fig. 2 shows the graphical representation of particle size with respect to temperature and it is found that increase in particle size as the temperature and the fuel ratio were raised. On considering with reaction time according to fuel ratio, the 100% fuel ratio makes combustion reaction faster, than the 50% fuel ratio.
112
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
Fig. 2. Variation of particle size of Co0.6Mn0.4Fe2O4 nanoparticles with respect to annealing temperature for different combustion fuel ratio: 50% (black squares), 75% (black points), 100% (black triangles).
900 1C. The maximum value of the dielectric constant in the range 378–484 is obtained for all samples at 50 Hz. A rapid decrease in dielectric constant is observed in low frequency at 200 Hz and gradually decreases up to 40 kHz then it retains a constant value. This behavior is almost similar for all the samples prepared under three different fuel ratios. From XRD results it is found that the particle size of the material increases with increase in the annealing temperature for various fuel ratios. Due to the impact of the fuel ratio the dielectric properties decreases with increase in particle size. The observed change in the dielectric constant can be explained on the basis of hoping conduction between Fe3 þ and Fe2 þ , Mn2 þ and Mn3 þ , Co2 þ and Co3 þ pairs of ions. A maximum polarization is occurred at low frequency range for these ions and it shows that dielectric constant to an optimum value [23]. According to Koops the decrease in dielectric constant for increase in frequency can be expressed by considering the solid as composed of well conducting grains which is separated by the poorly conducting grain boundaries [24]. The hope of electrons to reach the grain boundary and if the resistance of grain boundary is high enough then electrons pile up at the grain boundaries which causes polarization. The further increase of applied field shows that the electrons reverse their direction of motion and reduces the chance of electrons to approach the grain boundary and decreases the polarization. Thus this study reveals that the value of dielectric constant slowly decreases at lower frequencies and remains constant at higher frequencies [25]. Fig. 4 shows the variation in dielectric loss factor of Mn doped CoFe2O4 for different fuel ratios (50%, 75% and 100%) sintered at 900 1C. Both the dielectric constant and dielectric loss decrease as the frequency increases. This decrease indicates the normal behavior of ferrite samples. The decrease takes place when the jumping frequency of electric charge carriers cannot follow the alteration of applied AC electric field beyond a certain critical frequency [26]. 3.3. Transmission electron microscopy Fig. 5(A–C) show TEM micrograph of Co0.6Mn0.4Fe2O4 for different fuel ratios (50%, 75% and 100%) annealed at 900 1C. Few particles appear in spherical shape; however, some elongated
Fig. 3. Variation of dielectric constant of Co0.6Mn0.4Fe2O4 nanoparticles with respect to log frequency for different combustion fuel ratio: 50% (black squares), 75% (black points), 100% (black triangles).
Here the reaction time increases for 75% fuel ratio which is more than 100% fuel ratio. Similarly 50% fuel ratio takes higher reaction time, than the 75% and 100% fuel ratio. It suggests that the higher combustion reaction time produces smaller particle sizes. It conforms from the XRD pattern for 50% fuel ratio. Similarly the increases in particle size according to fuel ratio observed from the annealing temperature. 3.2. Dielectric properties The dielectric properties were measured for the samples prepared under different fuel ratio such as 50%, 75% and 100% using impedance analyzer in frequency range of 50 Hz to 1 MHz. Fig. 3 shows the variation in dielectric constant of Mn doped CoFe2O4 for different fuel ratios (50%, 75% and 100%) annealed at
Fig. 4. Variation of dielectric loss of Co0.6Mn0.4Fe2O4 nanoparticles with respect to log frequency for different combustion fuel ratio: 50% (black squares), 75% (black points), 100% (black triangles).
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
113
Fig. 5. TEM micrographs (A–C) and SAED pattern (D–F) of Co0.6Mn0.4Fe2O4 ferrite for different fuel ratios (50%, 75% and 100%) annealed at 900 1C.
particles are also present as shown in the TEM images. Some moderately agglomerated particles as well as separates particles are present in the images. Agglomeration is understood in terms of increase in size with annealing temperature and hence some degree of agglomeration at the higher annealing temperature is unavoidable [27]. From the TEM images the size for the separate particles are in the range of 50–70 nm. The particle size from the TEM report matches well with the size estimated from XRD measurement. Fig.5(D–F) shows the SAED pattern of Co0.6Mn0.4Fe2O4 samples prepared for different fuel ratios (50%, 75% and 100%) at 900 1C. Thus the bright spots indicate the good crystallinity of the samples with equal lattice arrangement. The SAED patterns of the high-resolution TEM image confirm that the nanoparticles correspond to face centered cubic structure. Fig. 6 shows the TEM image of as-burnt sample of Co0.6Mn0.4Fe2O4 for 50% fuel ratio with the particle size 8 nm.
4. Conclusion The nanocrystalline manganese substituted cobalt ferrite samples are prepared by auto-combusted techniques. Indexed powder XRD pattern revealed that the samples prepared by this route were ferrite nanoparticles with cubic spinel structure. It was seen that the particle size of synthesized ferrite samples was in the range of 3–67. The average particle size was less for the samples prepared by 50% fuel ratio than the other fuel ratio (75% and 100%) suggesting the impact of fuel ratio to the size of the particles. The results confirmed that the particle size of sample increase with the increase of annealing temperature. The presences of few separate spherical as well as agglomerated particles are rescored from the TEM images. The good crystallinity of the sample was confirmed by the occurrence of bright spot in SAED pattern. The dielectric properties of Co0.6Mn0.4Fe2O4
114
E. Ranjith Kumar et al. / Journal of Physics and Chemistry of Solids 74 (2013) 110–114
Fig. 6. TEM micrograph of as-burnt Co0.6Mn0.4Fe2O4 nanoparticle for 50% fuel ratio.
samples were analyzed. Measurements of the dielectric constant and dielectric loss in the 50 Hz–1MHz frequency range showed higher magnitude, at lower measuring frequencies, decreasing with increase in frequency, essentially becoming constant above 1 kHz. References [1] Y. Yamamoto, J. Makino, Core losses and magnetic properties of Mn–Zn ferrites with fine grain sizes, J. Magn. Magn. Mater. 133 (1994) 500. [2] X. Stanciulea, J. Neamtu, M. Feder, E. Segal, P. Cristea, L. Gai, Considerations on the sintering of manganese–zinc ferrite for power applications, J. Mater. Sci. Lett. 11 (1992) 961. [3] S.R. Murthy, Low temperature sintering of Mg–Cu–Zn ferrite and its electrical and magnetic properties, Bull. Mater. Sci. 24 (2001) 379. [4] Y. Il Kim, D. Kim, C.S. Lee, Synthesis and characterization of CoFe2O4 magnetic nanoparticles prepared by temperature-controlled coprecipitation method, Phys. B 337 (2003) 42–51. [5] X.H. Huang, Z.H. Chen, CoFe2O4 nanoparticles hosted in silica xerogels, Scr. Mater. 54 (2006) 169–173.
[6] S. Singhal, J. Singh, S.K. Barthwal, K. Chandra, Preparation and characterization of nanosize nickel-substituted cobalt ferrites (Co1 xNixFe2O4), J. Solid State Chem. 178 (2005) 3183–3189. [7] S.M. Montemayor, L.A. Garcia-Cerda, J.R. Torres-Lubian, Preparation and characterization of cobalt ferrite by the polymerized complex method, Mater. Lett. 59 (2005) 1056–1060. [8] E.J. Choi, Y. Ahu, S. Kim, D.H. An, Superparamagnetic relaxation in CoFe2O4 nanoparticles, J. Magn. Magn. Mater. 262 (2003) L198–L202. [9] A.F. Junior, E.C.O. Lima, Synthesis of nanoparticles of CoxFe(3 x)O4 by combustion reaction method, J. Magn. Magn. Mater. 308 (2007) 198–202. [10] L. Satyanarayana, K.M. Reddy, S.V. Manorama, Synthesis of nanocrystalline Ni1 xCoxMnxFe2 xO4: a material for liquefied petroleum gas sensing, Sens. Actuators B 89 (2003) 62–67. [11] P. Poddar, J. Gass, D.J. Rebar, S. Srinath, H. Srikanth, Magnetocaloric effect in ferrite nanoparticles, J. Magn. Magn. Mater. 307 (2006) 227–231. [12] K. Maaz, A. Mumtaz, S.K. Hasanain, A. Ceylan, Synthesis and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles prepared by wet chemical route, J. Magn. Magn. Mater. 308 (2007) 289–295. [13] Y.-P. Fu, K.-Y. Pan, C.-H. Lin, Microwave-induced combustion synthesis of Ni0.25Cu0.25Zn0.5 ferrite powders and their characterizations, Mater. Lett. 57 (2002) 291–296. [14] Y. Xuan, Q. Li, G. Yang, Synthesis and magnetic properties of Mn–Zn ferrite nanoparticles, J. Magn. Magn. Mater. 312 (2007) 464–469. [15] C.-K. Kim, J.-H. Lee, S. Katoh, Synthesis of Co-, Co–Zn and Ni–Zn ferrite powders by the microwave-hydrothermal method, Mater. Res. Bull. 36 (2001) 2241–2250. [16] X. Hou, J. Feng, Y. Ren, Z. Fan, M. Zhang, Synthesis and adsorption properties of spongelike porous MnFe2O4, Colloids Surf. A 363 (2010) 1–7. [17] Y. Qu, H. Yang, N. Yang, Y. Fan, H. Zhu, G. Zou, The effect of reaction temperature on the particle size, structural and magnetic properties of coprecipitated CoFe2O4 nanoparticles, Mater. Lett. 60 (2006) 3548–3552. [18] X. Huang, Z. Chen, Preparation of CoFe2O4/SiO2 nanocomposites by sol–gel method, J. Cryst. Growth 271 (2004) 287–293. [19] M.M. Hessien, M.M. Rashad, K. El-Barawy, I.A. Ibrahim, Influence of manganese substitution and annealing temperature on the formation, microstructure and magnetic properties of Mn–Zn ferrites, J. Magn. Magn. Mater. 320 (2008) 1615–1621. [20] M.A. Gabal, Y.M. Al Angari, S.S. Al-Juaid, A study on Cu substituted Ni–Cu–Zn ferrites synthesized using egg-white, J. Alloys Compds. 492 (2010) 411–415. [21] H.E. Zhang, B.F. Zhang, G.F. Wang, X.H. Dong, Y. Gao, The structure and magnetic properties of Zn1 xNixFe2O4 ferrite nanoparticles prepared by sol–gel auto-combustion, J. Magn. Magn. Mater. 312 (2007) 126–130. [22] P.P. Hankare, U.B. Sankpal, R.P. Patil, A.V. Jadhav, K.M. Garadkar, B.K. Chougule, Magnetic and dielectric studies of nanocrystalline zinc substituted Cu–Mn ferrites, J. Magn. Magn. Mater. 323 (2011) 389–393. [23] A. Thakur, P. Mathur, M. Singh, Study of dielectric behaviour of Mn–Zn nano ferrites, J. Phys. Chem. Solids 68 (2007) 378–381. [24] C.G. Koops, On the dispersion of resistivity and dielectric constant of some semiconductors at audiofrequencies, Phys Rev. 83 (1951) 121. [25] S.R. Kulkarni, C.M. Kanamadi, B.K. Chougule, Dielectric and magnetoelectric properties of (x)Ni0.8Co0.1Cu0.1Fe2O4/(1 x)PbZr0.8Ti0.2O3 composites, Mater. Res. Bull. 40 (2005) 2064–2072. [26] A.M. Abdeen, Dielectric behaviour in Ni–Zn ferrites, J. Magn. Magn. Mater. 192 (1999) 121. [27] L. Ai, J. Jiang, Influence of annealing temperature on the formation, microstructure and magnetic properties of spinel nanocrystalline cobalt ferrites, Curr. Appl. Phys. 10 (2010) 284–288.