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Structural analysis of the Mn–Zn ferrites using XRD technique
Materials Science and Engineering B 118 (2005) 84–86
Structural analysis of the Mn–Zn ferrites using XRD technique Uzma Ghazanfara , S.A. Siddiqia , G. Abbasb,∗ a
Centre of Excellence in Solid State Physics, University of Punjab, Pakistan b LPRC, UMIST, Manchester, UK
Abstract Manganese–zinc ferrite samples, Mnx Zn1−x Fe2 O4 , with x = 0.66, 0.77, 0.88, 0.99 were prepared by conventional double-sintering method, using low cost Fe2 O3 with 0.5 wt.% of Si as an impurity, to improve their properties. The chemical phase analysis has been carried out by X-ray powder diffraction (XRD) method, which confirms the formation of the ferrite structure. Lattice constant increases proportionally to the Mn content (x). The mass density of the ferrites was found to be increasing, whereas X-ray density depends on the lattice constant and molecular weight of the samples and tends to decrease with increasing Mn concentration. The porosity, calculated using both densities, also shows a decreasing behaviour with increase in manganese content. © 2004 Published by Elsevier B.V. Keywords: Manganese–zinc ferrite; X-ray powder diffraction; Silicon impurity
1. Introduction The use of ferrites has very well been established in many branches of telecommunications and electronics engineering embracing a very wide diversity of compositions, properties and applications. Among these, fine ferrites, made of oxides of manganese, zinc and iron have been of interest due to their applications in various fields. Manganese–zinc ferrites belong to the group of soft ferrite materials characterized by high magnetic permeabilities and low losses. These materials are extensively used in microwave devices, computer memory chips, magnetic recording media, fabrication of radio frequency coils, transformer cores and rod antennas, etc. [1,2]. Some of the principal mechanical properties of a representative selection of ferrite specimens have been determined by Snelling [2]. According to him sintered density of Mn–Zn ferrite is 4800 kg/m3 and porosity is 8%, whereas in view of Mangalaraya [3], typical porosity range for ferrites is 7–25%. Another researcher, Abdullah [4] in his research shows an increase of the lattice constant and decreasing trend of density with x. In the present work, we have studied the mass ∗
Corresponding author. E-mail address: [email protected] (G. Abbas).
0921-5107/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.mseb.2004.12.018
and X-ray densities along with porosity measurements of the ferrites prepared by using low cost, locally available Fe2 O3 and having 0.5 wt.% of Si as an impurity. These ferrites are used to check the effect of silicon impurity on their practical applications because sometimes ferrites are required to exhibit high density as well as high electrical resistance, apart from their purely magnetic properties. Investigations undertaken, particularly by Heck [5], show that the behaviour of mixed ferrites with suitable additions varied. He prepared some compositions, which unite high resistance with high density. Some researchers [6–8] have already shown in their work the improvement in different properties of Mn–Zn ferrite by using SiO2 as an impurity, especially to improve microstructural characteristics, homogenous grain growth, less porosity, high density and resistivity, as also discussed in our work [9]. The present work differs from all the previous studies in two ways: firstly, the different compositions (x = 0.66, 0.77, 0.88, 0.99) of alloying metals (Mn and Zn) in the ferrites (Mnx Zn1−x Fe2 O4) were used. Secondly, in all the previous studies pure ferrites were used and SiO2 was added to improve the resistivity of ferrite. However, in the present studies low price, low purity, locally available iron oxide containing Si as an impurity was used. In this way the overall cost of the ferrite produced was reduced markedly.
U. Ghazanfar et al. / Materials Science and Engineering B 118 (2005) 84–86
85
Fig. 2. Plot showing lattice parameters vs. Mn concentration for Mn–Zn ferrite system. Fig. 1. XRD patterns of Mn–Zn ferrite (Mnx Zn1−x Fe2 O4 ) with x = 0.66, 0.77, 0.88, 0.99.
2. Experimental details Mnx Zn1−x Fe2 O4 (x = 0.66, 0.77, 0.88, 0.99) ferrites were prepared in a polycrystalline form by high temperature solid-state reaction method. The parent oxides, ZnO and MnO are 99.99% pure, whereas locally available, low cost Fe2 O3 is relatively impure and contains a very small proportion (0.5 wt.%) of silicon impurity. These were mixed in required proportions in agate mortar and the powder mixture was pressed into pellets of 16 mm diameter under a uni-axial pressure of 124 MPa. The samples were sintered by the conventional double-sintering method. The final sintering was done at 1473 K for 6 h in a muffle furnace and the samples were furnace cooled. X-ray diffraction (XRD) patterns were taken to identify the phases formed and to confirm the completion of the chemical reaction by using Rigaku XRD D/MAX-IIA diffractometer with Cu K␣ radiation. The samples were rotated through an angle of 20–70◦ at a scanning speed of 2.9 × 10−4 rad/s. In the present work, the surface of the pellets was cleaned with SiC grinding paper in order to remove any contamination and the lattice parameters and X-ray densities of the samples were calculated from the diffraction pattern (Fig. 1) using Eq. (1) [2]. The sintered density was determined from the mass and bulk volume of the samples. By comparing the values of both densities, the porosity for each sample was determined.
different sources of research [2,5–8,11] that small-amount (a few mol%) additions of SiO2 are often used particularly in this ferrite (Mn–Zn) to improve the magnetic, electrical and mechanical properties. In the present studies locally available low cost iron oxide with 0.5 wt.% of Si was used to reduce the costs and get better results. The values of the lattice constant as a function of manganese concentration are plotted in Fig. 2 for various Mnx Zn1−x Fe2 O4 ferrites. The data reported are an average of at least three readings. It can be seen that lattice parameter increases proportionally to the manganese content x, which may be a direct consequence of the larger ionic radius ˚ as compared to Zn2+ (0.82 A), ˚ as also of Mn2+ (0.91 A) discussed by different authors [1,11]. The X-ray densities were calculated using the relation [12]. dx =
8M Na3
(1)
where 8 represents the number of molecules in a unit cell of spinel lattice, M the molecular weight of the sample, a the lattice parameter of the ferrite and N the Avogadro’s number. The X-ray density (dx) depends on the lattice constant and molecular weight of the sample, whereas, the mass density (d) of the samples is being calculated from the geometry and mass of the samples. Both densities dx and d as a function of Mn concentration are plotted in Fig. 3. It can be seen from the figure that the X-ray density decreases with the increase
3. Results and discussion The diffraction pattern of Mnx Zn1−x Fe2 O4 ferrites shown in Fig. 1 is taken after final sintering and shows the formation of Mn–Zn ferrite along with some peaks of Zinc silicate (Zn2 SiO4 ). The lattice parameter for different compositions have been calculated using the values of d-spacing, which were calculated by using Bragg law and compared to values reported in JCPDS (Joint Committee on powder Diffraction Standards) cards [10]. However, as far as the authors are aware, no data are available in the literature to compare the values of the lattice parameter of Mn–Zn ferrite of this composition (x = 0.66, 0.77, 0.88, 0.99). It is observed from
Fig. 3. Plot showing X-ray (dx) and mass (d) densities vs. Mn concentration for Mn–Zn ferrite system.
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U. Ghazanfar et al. / Materials Science and Engineering B 118 (2005) 84–86
4. Conclusions
Fig. 4. Porosity plotted against Mn concentration for Mn–Zn ferrites.
of Mn-content x, as it is inversely proportional to the lattice constant, which increases with increasing Mn concentration. Mass density of the ferrite was found to be increasing with x which may be due to the ionic difference between Mn and Zn, as reported in the literature [1,2,4,5] or due to the difference in the specific gravity of Mn (7.21 g/cm3 ) and Zn (7.133 g/cm3 ), as described in CRC book [13]. The percentage porosity (P) of the samples was calculated using the equation [12]: P=
1 − bulk density X-ray density
(2)
and is plotted against Mn-concentration in Fig. 4. The data reported are an average of at least three reading shows a decreasing trend with increasing Mn concentration from x = 0.66 to 0.99. This is due to the fact that the value of X-ray density is decreasing because the lattice constant is increasing with the increase of Mn content. Hence the ratio d/dx increases which leads to the decrease in porosity, another reason might be the difference in melting points of the oxides used, i.e. the melting point of MnO has a smaller value than that of the ZnO [13]. At sintering temperature of 1473 K, the number of pores is reduced, as a result of which individual grains come closer to each other and the effective area of grain-to-grain contact increases. This in turn results in greater densification or less porosity, as also described by Moinuddin in his work [14].
1. Structural analysis with XRD indicates that the system confirms the formation of Mn–Zn ferrite structure with lattice constant increasing proportionally to the manganese content. 2. The increase in manganese concentration x favours the formation of Mn–Zn ferrites with higher density. 3. X-ray density depends on the lattice constant and molecular weight of the samples shows a decreasing trend with increasing Mn content. 4. Porosity, calculated using both densities, also shows a decrease with increase in Mn concentration.
References [1] T. Abbas, Y. Khan, M. Ahmad, S. Anwar, Solid State Commun. 82 (1992) 701. [2] E.C. Snelling (Ed.), Soft Ferrites, Properties and Applications, 2nd ed., Butter Worth and Co. (Publisher) Ltd., London, 1988. [3] R.V. Mangalaraya, S.A. Kumar, P. Manohar, Mater. Lett. 58 (2004) 1593. [4] M.H. Abdullah, S.H. Ahmad, Sains-Malaysiana 22 (1993) 1. [5] C. Heck (Ed.), Magnetic Materials and Their Applications, Butterworth Co., Ltd., London, 1974. [6] K. Hirota, T. Aoyana, S. Enomoto, J. Magnet. Magnetic Mater. 205 (1999) 283. [7] J. Nie, H. Li, Z. Feng, H. He, J. Magnet. Magnetic Mater. 265 (2003) 172. [8] Y.S. Cho, D. Schaffer, V.L. Burdick, V.R.W. Amarakoon, Mater. Res. Bull. 34 (1999) 2361. [9] G. Uzma, S.A. Siddiqi, Study of dc resistivity behaviour of Mn–Zn ferrite in relation with activation energies and drift mobility, in preparation. [10] P. Bayliss, D.C. Erd, M.E. More, A. Sabina, D.K. Smith, Mineral Powder Diffraction File, JCPDS, USA, 1986. [11] Modern Ferrite Technology Alex Goldman, Van Nostrand Reinhold (Publisher) Ltd., New York, 1990. [12] M.U. Islam, I. Ahmad, T. Abbas, Proceedings of the Sixth International Symposium on Advanced Materials, 1999, p. 155. [13] D.R. Lide, CRC Handbook of Chemistry and Physics, 76th ed., CRC Press, London, 1995. [14] M.K. Moinuddin, S.R. Murthy, J. Alloys Compd. 194 (1993) 105 (JALCOM 539).
Structural analysis of the Mn–Zn ferrites using XRD technique Uzma Ghazanfara , S.A. Siddiqia , G. Abbasb,∗ a
Centre of Excellence in Solid State Physics, University of Punjab, Pakistan b LPRC, UMIST, Manchester, UK
Abstract Manganese–zinc ferrite samples, Mnx Zn1−x Fe2 O4 , with x = 0.66, 0.77, 0.88, 0.99 were prepared by conventional double-sintering method, using low cost Fe2 O3 with 0.5 wt.% of Si as an impurity, to improve their properties. The chemical phase analysis has been carried out by X-ray powder diffraction (XRD) method, which confirms the formation of the ferrite structure. Lattice constant increases proportionally to the Mn content (x). The mass density of the ferrites was found to be increasing, whereas X-ray density depends on the lattice constant and molecular weight of the samples and tends to decrease with increasing Mn concentration. The porosity, calculated using both densities, also shows a decreasing behaviour with increase in manganese content. © 2004 Published by Elsevier B.V. Keywords: Manganese–zinc ferrite; X-ray powder diffraction; Silicon impurity
1. Introduction The use of ferrites has very well been established in many branches of telecommunications and electronics engineering embracing a very wide diversity of compositions, properties and applications. Among these, fine ferrites, made of oxides of manganese, zinc and iron have been of interest due to their applications in various fields. Manganese–zinc ferrites belong to the group of soft ferrite materials characterized by high magnetic permeabilities and low losses. These materials are extensively used in microwave devices, computer memory chips, magnetic recording media, fabrication of radio frequency coils, transformer cores and rod antennas, etc. [1,2]. Some of the principal mechanical properties of a representative selection of ferrite specimens have been determined by Snelling [2]. According to him sintered density of Mn–Zn ferrite is 4800 kg/m3 and porosity is 8%, whereas in view of Mangalaraya [3], typical porosity range for ferrites is 7–25%. Another researcher, Abdullah [4] in his research shows an increase of the lattice constant and decreasing trend of density with x. In the present work, we have studied the mass ∗
Corresponding author. E-mail address: [email protected] (G. Abbas).
0921-5107/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.mseb.2004.12.018
and X-ray densities along with porosity measurements of the ferrites prepared by using low cost, locally available Fe2 O3 and having 0.5 wt.% of Si as an impurity. These ferrites are used to check the effect of silicon impurity on their practical applications because sometimes ferrites are required to exhibit high density as well as high electrical resistance, apart from their purely magnetic properties. Investigations undertaken, particularly by Heck [5], show that the behaviour of mixed ferrites with suitable additions varied. He prepared some compositions, which unite high resistance with high density. Some researchers [6–8] have already shown in their work the improvement in different properties of Mn–Zn ferrite by using SiO2 as an impurity, especially to improve microstructural characteristics, homogenous grain growth, less porosity, high density and resistivity, as also discussed in our work [9]. The present work differs from all the previous studies in two ways: firstly, the different compositions (x = 0.66, 0.77, 0.88, 0.99) of alloying metals (Mn and Zn) in the ferrites (Mnx Zn1−x Fe2 O4) were used. Secondly, in all the previous studies pure ferrites were used and SiO2 was added to improve the resistivity of ferrite. However, in the present studies low price, low purity, locally available iron oxide containing Si as an impurity was used. In this way the overall cost of the ferrite produced was reduced markedly.
U. Ghazanfar et al. / Materials Science and Engineering B 118 (2005) 84–86
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Fig. 2. Plot showing lattice parameters vs. Mn concentration for Mn–Zn ferrite system. Fig. 1. XRD patterns of Mn–Zn ferrite (Mnx Zn1−x Fe2 O4 ) with x = 0.66, 0.77, 0.88, 0.99.
2. Experimental details Mnx Zn1−x Fe2 O4 (x = 0.66, 0.77, 0.88, 0.99) ferrites were prepared in a polycrystalline form by high temperature solid-state reaction method. The parent oxides, ZnO and MnO are 99.99% pure, whereas locally available, low cost Fe2 O3 is relatively impure and contains a very small proportion (0.5 wt.%) of silicon impurity. These were mixed in required proportions in agate mortar and the powder mixture was pressed into pellets of 16 mm diameter under a uni-axial pressure of 124 MPa. The samples were sintered by the conventional double-sintering method. The final sintering was done at 1473 K for 6 h in a muffle furnace and the samples were furnace cooled. X-ray diffraction (XRD) patterns were taken to identify the phases formed and to confirm the completion of the chemical reaction by using Rigaku XRD D/MAX-IIA diffractometer with Cu K␣ radiation. The samples were rotated through an angle of 20–70◦ at a scanning speed of 2.9 × 10−4 rad/s. In the present work, the surface of the pellets was cleaned with SiC grinding paper in order to remove any contamination and the lattice parameters and X-ray densities of the samples were calculated from the diffraction pattern (Fig. 1) using Eq. (1) [2]. The sintered density was determined from the mass and bulk volume of the samples. By comparing the values of both densities, the porosity for each sample was determined.
different sources of research [2,5–8,11] that small-amount (a few mol%) additions of SiO2 are often used particularly in this ferrite (Mn–Zn) to improve the magnetic, electrical and mechanical properties. In the present studies locally available low cost iron oxide with 0.5 wt.% of Si was used to reduce the costs and get better results. The values of the lattice constant as a function of manganese concentration are plotted in Fig. 2 for various Mnx Zn1−x Fe2 O4 ferrites. The data reported are an average of at least three readings. It can be seen that lattice parameter increases proportionally to the manganese content x, which may be a direct consequence of the larger ionic radius ˚ as compared to Zn2+ (0.82 A), ˚ as also of Mn2+ (0.91 A) discussed by different authors [1,11]. The X-ray densities were calculated using the relation [12]. dx =
8M Na3
(1)
where 8 represents the number of molecules in a unit cell of spinel lattice, M the molecular weight of the sample, a the lattice parameter of the ferrite and N the Avogadro’s number. The X-ray density (dx) depends on the lattice constant and molecular weight of the sample, whereas, the mass density (d) of the samples is being calculated from the geometry and mass of the samples. Both densities dx and d as a function of Mn concentration are plotted in Fig. 3. It can be seen from the figure that the X-ray density decreases with the increase
3. Results and discussion The diffraction pattern of Mnx Zn1−x Fe2 O4 ferrites shown in Fig. 1 is taken after final sintering and shows the formation of Mn–Zn ferrite along with some peaks of Zinc silicate (Zn2 SiO4 ). The lattice parameter for different compositions have been calculated using the values of d-spacing, which were calculated by using Bragg law and compared to values reported in JCPDS (Joint Committee on powder Diffraction Standards) cards [10]. However, as far as the authors are aware, no data are available in the literature to compare the values of the lattice parameter of Mn–Zn ferrite of this composition (x = 0.66, 0.77, 0.88, 0.99). It is observed from
Fig. 3. Plot showing X-ray (dx) and mass (d) densities vs. Mn concentration for Mn–Zn ferrite system.
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U. Ghazanfar et al. / Materials Science and Engineering B 118 (2005) 84–86
4. Conclusions
Fig. 4. Porosity plotted against Mn concentration for Mn–Zn ferrites.
of Mn-content x, as it is inversely proportional to the lattice constant, which increases with increasing Mn concentration. Mass density of the ferrite was found to be increasing with x which may be due to the ionic difference between Mn and Zn, as reported in the literature [1,2,4,5] or due to the difference in the specific gravity of Mn (7.21 g/cm3 ) and Zn (7.133 g/cm3 ), as described in CRC book [13]. The percentage porosity (P) of the samples was calculated using the equation [12]: P=
1 − bulk density X-ray density
(2)
and is plotted against Mn-concentration in Fig. 4. The data reported are an average of at least three reading shows a decreasing trend with increasing Mn concentration from x = 0.66 to 0.99. This is due to the fact that the value of X-ray density is decreasing because the lattice constant is increasing with the increase of Mn content. Hence the ratio d/dx increases which leads to the decrease in porosity, another reason might be the difference in melting points of the oxides used, i.e. the melting point of MnO has a smaller value than that of the ZnO [13]. At sintering temperature of 1473 K, the number of pores is reduced, as a result of which individual grains come closer to each other and the effective area of grain-to-grain contact increases. This in turn results in greater densification or less porosity, as also described by Moinuddin in his work [14].
1. Structural analysis with XRD indicates that the system confirms the formation of Mn–Zn ferrite structure with lattice constant increasing proportionally to the manganese content. 2. The increase in manganese concentration x favours the formation of Mn–Zn ferrites with higher density. 3. X-ray density depends on the lattice constant and molecular weight of the samples shows a decreasing trend with increasing Mn content. 4. Porosity, calculated using both densities, also shows a decrease with increase in Mn concentration.
References [1] T. Abbas, Y. Khan, M. Ahmad, S. Anwar, Solid State Commun. 82 (1992) 701. [2] E.C. Snelling (Ed.), Soft Ferrites, Properties and Applications, 2nd ed., Butter Worth and Co. (Publisher) Ltd., London, 1988. [3] R.V. Mangalaraya, S.A. Kumar, P. Manohar, Mater. Lett. 58 (2004) 1593. [4] M.H. Abdullah, S.H. Ahmad, Sains-Malaysiana 22 (1993) 1. [5] C. Heck (Ed.), Magnetic Materials and Their Applications, Butterworth Co., Ltd., London, 1974. [6] K. Hirota, T. Aoyana, S. Enomoto, J. Magnet. Magnetic Mater. 205 (1999) 283. [7] J. Nie, H. Li, Z. Feng, H. He, J. Magnet. Magnetic Mater. 265 (2003) 172. [8] Y.S. Cho, D. Schaffer, V.L. Burdick, V.R.W. Amarakoon, Mater. Res. Bull. 34 (1999) 2361. [9] G. Uzma, S.A. Siddiqi, Study of dc resistivity behaviour of Mn–Zn ferrite in relation with activation energies and drift mobility, in preparation. [10] P. Bayliss, D.C. Erd, M.E. More, A. Sabina, D.K. Smith, Mineral Powder Diffraction File, JCPDS, USA, 1986. [11] Modern Ferrite Technology Alex Goldman, Van Nostrand Reinhold (Publisher) Ltd., New York, 1990. [12] M.U. Islam, I. Ahmad, T. Abbas, Proceedings of the Sixth International Symposium on Advanced Materials, 1999, p. 155. [13] D.R. Lide, CRC Handbook of Chemistry and Physics, 76th ed., CRC Press, London, 1995. [14] M.K. Moinuddin, S.R. Murthy, J. Alloys Compd. 194 (1993) 105 (JALCOM 539).