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Characterization and transport properties of mixed ferrite

system Mn1-xCuxFe2O4 0.0≤ x ≤ 0.7

Journal: Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal

Chemistry

Manuscript ID: Draft

Manuscript Type: Original Paper

Date Submitted by the Author: n/a

Complete List of Authors: Azab, Ali; National Research Center,

Keywords: ferrite, Electrical

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Characterization and transport properties of mixed

ferrite system Mn1-xCuxFe2O4 0.0≤ x ≤ 0.7

M.A. Ahmeda, A. A. Azabb, E.H. El-Khawasc, E. Abd El Bast c

a:Materials Science lab(1), Physics Department, Faculty of Science, Cairo University, Giza, Egypt.

b: Solid State Electronics Laboratory, Solid State Physics Department, Physics Division, National Research Center, Dokki, Cairo, 12311 Egypt. c: Basic Science Department, Higher Technological Institute, tenth of Ramadan City, Egypt.

Abstract:

A series of Cu doped Mn ferrites with the formula Mn1-xCuxFe2O4 (0.0 ≤x ≤ 0.7)

were synthesized by citrate auto combustion method. The structural characterization and

morphology of the samples were examined by X-ray diffraction (XRD), energy

dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM). XRD and

EDX confirmed the formation of single-phase cubic spinel structure. The electrical

conductivity(σ), dielectric constant (ε′) and dielectric loss factor (ε′′) were studied as a

function of temperature at different frequencies ranged from 100 kHz to 5 MHz.

Increasing is observed in the values of σ, ε′ and ε′′ with substitution of copper up to

x=0.3. Above this value, a decrease in σ, ε′ and ε′′ was detected.

Keywords: Nano ferrite, SEM, EDX, conductivity and dielectric

1. Introduction

Mixed metallic oxides especially spinels having the general formula AB2O4 are

very important materials for technological applications. Mixed copper ferrites have high

electrical resistivities and consequently low eddy currents as well as dielectric losses,

They have several applications such as radio frequency coils, transformer cores, rod

antennas and magnetic cores of read-write heads for high speed digital tapes [1, 2, 3]. The

studies of dielectric properties of ferrites offer much valuable information on the behavior

of localized electrical charge carriers. This leads to a good explanation and also an

understanding of the mechanism involved in dielectric behavior of ferrites. It is well

known that the conductivity and the dielectric properties of ferrites are strongly

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dependent on frequency and temperature [4, 5]. Hence, the study of such properties at

different frequencies, temperatures and chemical compositions provide valuable

information about the kind and amount of additives required to obtain high quality

materials for many applications. The properties of the nanocrystalline materials are

varied from those of corresponding bulk materials, due to their small grain size. Also in

these materials a large percentage of atoms are available at their grain boundaries and

therefore there are more chances for interaction between the grains [6]. In the present

work we aimed to reach the critical concentration of Cu in the compound at which we optimize

the transport properties to be more applicable.

2. Experimental methods

The spinel ferrite of Mn1-xCuxFe2O4; (x= 0.0, 0.1, 0.3, 0.5, 0.7) was prepared by

citrate auto combustion method[6]. An aqueous solution of; Mn(NO3)2.4H2O,

Cu(NO3)2.3H2O and Fe(NO3)3.9H2O from Aldrich were used. Citrate complexes of the

metal ions components were mixed in stoichiometric ratios of metal nitrates and citric

acid with a ratio (1:1) with constant stirring to form the citrate-precursor mixture. The pH

value of the precursor solution was adjusted to about 7 by using a drop of ammonia

solution. The solution again stirred during heating the sample and then transformed into

Xero-gel; the dried gel burns itself to form the powder, after which the powders were

pressed into pellets using uniaxial press of pressure 1.9 x108 Nm-2. X-ray diffraction

(XRD) were carried out at room temperature on a Proker D8 with Cu kα radiation (k =

1.5418 Å) in 2θ ranged 20–80o. Elemental analysis and surface morphology were

analyzed by EDX spectroscopy and scanning electron microscope (SEM: Model JEOL-

JSM6400 F).

The samples were good polished to obtain uniform parallel surfaces. Contacts on

the sample surface were made by silver paste and then cheked for good conduction. The

real part of dielectric constant (ε′) and the ac conductivity (σ) were measured by the two

probe method using LCR meter model Hioki type 3532 (Japan) as a function of the

temperature from 300 to 750K at different frequencies ranging from 100 kHz to 5MHz.

The dc conductivity was measured for the investigated samples in the same range of

temperature as that of ac conductivity. The temperature of the samples was measured

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using a K-type thermocouple connected to a digit-sense thermometer (USA) with

junction in contact with the sample.

3. Results and discussion

3.1 Structure characterization

Figure (1) illustrates XRD patternes of Mn1-xCuxFe2O4 (0.0 ≤x ≤ 0.7), it reveals

single phase spinel structure. Details of structure analysis as well as microstructure

were reported in our previously published work [7].

Figure (2) shows SEM micrograph of Mn1-xCuxFe2O4 (0.0 ≤x ≤ 0.7). The data

reveals cluster size variation with increasing Cu 2+ content. From a close look to the

micrograph one find that, there is nearly stable values from 0 ≤ x ≤0.3 after which a

peculiar increase was found at x=0.5. This peculiarity does not appear for all clusters,

while the rest of the clusters have nearly the same size. This can be due to rearrange of

iron ions between A and B sites as well as the migration of Mn2+ (after changing Mn3+) to

B site. It was expected that at higher Cu content, the process is reversible. Also Cu2+

plays role after changing valance to Cu1+. The composition of Cu doped Manganes

ferrites has been examined using the energy dispersion X-ray analysis (EDX). X-ray

analysis spectra of Mn1-xCuxFe2O4 (x=0, 0.3 and 0.5) samples are shown in Fig.(3). From

the EDX spectrum, the presence of Mn, Cu, Fe and O are confirmed, the appearance of

Pt is due to platinum coating for SEM measurements. The quantitative analysis of EDX

spectrum at table (1) revealed the relative atomic ratio of all elements. These values are

close to the expected for MnFe2O4, Mn0.9Cu0.1Fe2O4 and Mn0.5Cu0.5Fe2O4.

3.2 Electrical properties

Figure (4) shows the dc conductivity of Mn1-xCuxFe2O4 ,(0 ≤ x ≤ 0.7). The

observed increase in dc conductivity with increasing temperature assure semiconducting

like behavior of Mn1-xCuxFe2O4. The increase in electrical conductivity (σdc) with

temperature is ascribed to the increase in the thermally activated mobility of charge

carriers. The activation energy for the thermally activated hopping process was obtained

by fitting the dc conductivity data with the Arrhenius relation [8].

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σdc (T) = σ0 exp(-ΔE/kBT)

where σ0 is the pre-exponential constant, ∆E is the activation energy for dc

conductivity, T is the absolute temperature and kB is the Boltzmann’s constant. The

activation energy for low temperature region (EI) and high temperate region (EII) are

calculated and listed in table (2). From the reported data it is observed that, the activation

energy EII is higher than EI. This trend is attributed to higher lattice vibrating which

increase the scattering of charge carriers resulting in decreasing conductivity and

increasing EII.

Figure(5) shows ac conductivity of Mn1-xCuxFe2O4(0 ≤ x ≤ 0.7) as a function of

temperature and different frequency. From the reported data it is observed that, the data

reveals that σac increase with both frequency and temperature. The hopping of electron

between Fe2+ and Fe3+ ions on the B sites played role in conduction mechanism in spinel

ferrites [9]. In general, the increase in conductivity with increasing frequency can be

explained on the basis of Maxwell-Wagner theory [10, 11] and Koop’s model [12, 13].

Accordingly the theory of dielectric structure was formed by two conducting layers

separated by ultra thin insulating layer, which forms the grain boundaries. The non-

conducting layer or grain boundary is formed by oxygen ions. These grain boundaries are

more active at lower frequencies, hence the hopping frequency of Fe2+ and Fe3+ ion is less

at lower frequencies. As the applied frequency increases the conductive grains became

more active by promoting the hopping between Fe2+ and Fe3+ cations, thereby increasing

the hopping frequency. Thus, we observe a gradual increase in conductivity with

frequency. The increase in conductivity does not means that the amount of charge carriers

increases, but only the rate of hopping of charge carriers between Fe2+ and Fe3+ ions

increases[14]. As temperature increases the mobility of hopping ions as well as

conductivity.

The dielectric properties can vary widely in ferrites as a function of temperature,

frequency of applied electric field, crystal structure, humidity and other external factors.

The dielectric response of ferrite materials can be described by the dielectric constant as a

complex quantity composed of a real and an imaginary component:

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ε = ε′ - jε′′

where the first term ε' is the real part of dielectric constant representing the amount of

energy stored in a dielectric material, while the second term ε'' is the imaginary part of

dielectric constant which describes the dissipated energy. Fig.(6) shows the effect of

temperature on dielectric constant (ε') for Mn1-xCuxFe2O4 (0 ≤ x ≤ 0.7) ferrites at different

frequencies. It is clear that ε' increases with temperature to reach maximum value for the

samples x=0.0 ,0.1, 0.3, with the peak value shifted to higher temperature with increasing

frequency. The decrease of dielectric constant with increasing frequency is observed in

the case of copper ferrites and this is a normal behavior of spinel ferrites[15-17]. This

attributed to the Maxwell–Wagner interfacial type of polarization [10, 11], which is in

agreement with Koops phenomenological theory [13]. The decrease in polarization with

increasing of frequency is due to the fact that, beyond a certain frequency of the electric

field, the electronic exchange between Fe2+ and Fe3+ cannot follow the alternating field,

therefore the real part of dielectric constant (ε') decreases with increasing frequency . It

is also noticed from Fig.(6) that the dielectric constant increases with temperature. It is

explained due to thermal activation which enhances the number of dipoles available for

polarization when the sample is at a high temperature.

Figure (7) shows the dielectric loss factor (ε'') of Mn1-xCuxFe2O4 (0 ≤ x ≤ 0.7), ε''

have the same behavior of ε' where ε'' increases with temperature and decreases with

frequency. This is because the dielectric loss arises when the polarization lag behind the

applied alternating field which is caused by the impurities and imperfections in the

crystal. According to the phenomenological Koop’s theory [13], this was explained on

the basis of the fact that, in the low frequency region, where the resistivity is high and the

grain boundary effect is dominant, more energy is required for electron exchange

between Fe2+ and Fe3+ ions, as a result the loss is high. In the high frequency region,

when the resistivity is low and grains themselves have a dominant role, a small energy is

required for electron transfer between the two Fe ions at the octahedral site. The

dielectric loss shows its maximum value (Debye relaxation) at samples x=0, 0.1 and 0.5.

Debye relaxation occurs when hopping frequency of charge carriers becomes

approximately equal to the frequency of an externally applied field [18]. Also at lower

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frequencies, high dielectric loss may be because of impurities, crystal defects and

moisture.

Figure (8) shows the composition dependence of Mn1-xCuxFe2O4 (0 ≤ x ≤ 0.7) on

the conductivity and dielectric constant values in which they increased up to x=0.3 and

after that they decreased. This is the same behavior of the magnetic properties in the

previous work [7]. The increase of conductivity in ferrite compound is mainly due to the

hopping electron between ions of the same element present at different valence state.

Mn2+ + Fe3+ ↔ Mn3+ + Fe2+

Cu2+ ↔ Cu+ + e+

Also, this may be attributed to the decrease in the lattice parameter with increasing Cu

content [7]. The hopping length L (B–B distance) is affected directly on the conductivity

whenever the length L decreases the conductivity will increase. Another reason for

decreasing the conductivity is the exchange interaction between Mn2+ and Fe3+ at B-site

resulting in decreasing the ratio of Fe3+/Fe2+ .

Conclusion

The X-ray and EDX measurements confirmed synthesis of Mn1-xCuxFe2O4 in

spinel structure by citrate auto combustion method. SEM images showed that the cluster

size increased with increasing Cu2+ up to x=0.5. The ac conductivity, dielectric constant

and dielectric loss factor increase with Cu2+ substitution up to x=0.3 and then decreased.

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Table (1) EDAX results of Mn1-xCuxFe2O4

Comp. x

Weight% Atomic% Mn Cu Fe O Mn Cu Fe O

0 18.36 0 33.24 48.4 8.45 0 15.05 76.5 0.1 19.93 2.33 42.64 35.1 10.81 1.09 22.74 65.35

0.5 7.94 9.62 31.3 51.14 3.57 3.73 13.83 78.87

Table (2) The values of activation energy E1 and E11 as afunction of frequency at different concentrations of Mn1-xCuxFe2O4 (0 ≤ x ≤ 0.7) Freq x=0.0 x=0.1 x=0.3 x=0.5 x=0.7 Act.En. EI EII EI EII EI EII EI EII EI EII

dc 0.391 0.774 0.369 0.626 0.369 0.614 0.016 0.626 0.369 0.595 100kHz 0.129 0.516 0.069 0.297 ----- 0.270 ----- 0.172 0.069 0.344 800kHz 0.129 0.516 0.069 0.297 ----- 0.258 ----- 0.172 0.065 0.258 2MHz 0.086 0.573 0.069 0.319 ----- 0.310 0.029 0.129 0.258 0.258

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References:

[1] Raghavender, A.T.; Shirsath, Sagar E.; Vijaya Kumar, K. J. Alloys Compd. 2011,

509, 7004.

[2] Jnaneshwara, D.M.; Avadhani, D.N.; Daruka Prasad B.; Nagabhushana, B.M.;

Nagabhushana, H.; Sharma, S.C.; Prashantha,S.C.; Shivakumara, C. J. Alloys Compd.

2014, 587, 50.

[3] Panda, R.K.; Behera, D. J. Alloys Compd. 2014, 587, 481.

[4] Ahmed, M. A.; Okasha, N.; J. Magn. Magn. Mater. 2014, 321, 3436.

[5] Ahmed, M.A.; Ateia, E.; Salah, L.M.; El-Gamal, A.A. Mater. Chem. Phys. 2005, 92,

310.

[6] N.M. Deraz, M.M. Hessien, J. Alloys Compd. 475 (2009) 832.

[7] Azab, A.; El-Khawas, E.H. Journal of Applied Sciences Research. 2013, 9(3) 1683.

[8] Savic, S. M.; Nikolic, M. V.; Aleksic, O. S.; Slankamenac, M. P.; Zivanov, M. B.;

Nikolic, P. M. Sci. Sinter. 2008, 40, 27.

[9] Younas, M.; Nadeem M.; Atif M.; Grossinger R. J. Appl. Phys. 2011, 109, 93704.

[10] Electricity and Magnetism; Maxwell, J. C. Oxford University Press, New York

1973; p 88.

[11] Wagner, K. W. Archive fur Elektrotechnik 2. 1914, 371.

[12] Muthu, K. S.; Lakshminarasimhan, N. Ceram. Int. 2013, 39, 2309.

[13] Koops, C. G. Phys. Rev. 1951, 83, 121.

[14] Hashim Alimuddin, M.; Shirsath, Sagar E.; Shalendra Kumar; Ravi Kumar,

Shirsath, Aashis S.; Jyoti Shah, Kotnala, R.K. J. Alloys Comp. 2013, 549, 348.

[15] Ahmed, M.A.; Ateia, E.; Salah, L.M.; El-Gamal, A.A. Materials Chemistry and

Physics. 2005, 92, 310.

[16] Ahmed, M.A.; Okasha, N. J. Magn. Magn. Mater. 2009, 321, 3436.

[17] Ahmed, M.A.; Mansour, S.F; Afifi, M. J. Magn. Magn. Mater. 2012, 324, 4.

[18] Cvejic Z.; Rakic, S.; Jankov, S.; Skuban, S.; Kapor, A.; J. Alloys Comp. 2009, 480,

241.

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Table (1) EDAX results of Mn1-xCuxFe2O4

Comp. x

Weight% Atomic%

Mn Cu Fe O Mn Cu Fe O

0 18.36 0 33.24 48.4 8.45 0 15.05 76.5

0.1 19.93 2.33 42.64 35.1 10.81 1.09 22.74 65.35

0.5 7.94 9.62 31.3 51.14 3.57 3.73 13.83 78.87

Table (2) The values of activation energy E1 and E11 as afunction of frequency at

different concentrations of Mn1-xCuxFe2O4 (0 ≤ x ≤ 0.7)

Freq x=0.0 x=0.1 x=0.3 x=0.5 x=0.7

Act.En. EI EII EI EII EI EII EI EII EI EII

dc 0.39

1

0.77

4

0.36

9

0.62

6

0.36

9

0.61

4

0.01

6

0.62

6

0.36

9

0.59

5

100kH

z

0.12

9

0.51

6

0.06

9

0.29

7

----- 0.27

0

----- 0.17

2

0.06

9

0.34

4

800kH

z

0.12

9

0.51

6

0.06

9

0.29

7

----- 0.25

8

----- 0.17

2

0.06

5

0.25

8

2MHz 0.08

6

0.57

3

0.06

9

0.31

9

----- 0.31

0

0.02

9

0.12

9

0.25

8

0.25

8

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Fig.(1):a)X-ray diffraction pattern of the Mn1-xCuxFe2O4 compound 0.0≤ x ≤0.7.

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Fig. (2): SEM micrograph of the Mn1-xCuxFe2O4 compound 0.0≤ x ≤0.7.

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Fig. (3): EDX spectrum of the Mn1-xCuxFe2O4 compound at x= 0.0, 0.1, 0.5.

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Fig. (4): The dependence of dc conductivity on the reciprocal

temperature ofMn1-xCuxFe2O4 compound.

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Fig(5): Variation of ac conductivity with the reciprocal of absolute temperature as

a function of frequency of Mn1-xCuxFe2O4 compound 0.0≤ x ≤0.7.

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’ with the absolute temperature as a

a function of frequency of Mn1-xCuxFe2O4 compound 0.0≤ x ≤0.7.

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Fig(7): Variation of dielectric loss factor ε” with the absolute temperature as a

function of frequency of Mn1-xCuxFe2O4 compound 0.0≤ x ≤0.7.

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Fig.(8a-c) :(a) Variation of dc conductivity with Cu

2+ content.

(b,c) Variation of ac conductivity and dielectric constant with

Cu2+

content at two absolute temperatures 323K, 373K

And frequency 100 kHz of Mn1-xCuxFe2O4 compound 0.0≤ x ≤0.7.

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