Synthesis, Structural and Physical Properties of Cu1–xZnxFe2O4 Ferrites

doi:10.4236/msa.2011.211223

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Materials Science s a nd Applications, 2011, 2, 1675-1681

doi:10.4236/msa.2011.211223 Published Online November 2011 (http://www.SciRP.org/journal/msa)

1675

Synthesis, Structural and Physical Properties of

Cu1–xZnxFe2O4 Ferrites

Shahida Akhter1*, Deba Prasad Paul1, Md. Abdul Hakim2, Dilip Kumar Saha2, Md. Al-Mamun2,

Alhamra Parveen2

1Department of Physics, University of Chittagong, Chittagong, Bangladesh; 2Materials Science Division, Atomic Energy Centre,

Dhaka, Bangladesh.

Email: *[email protected]

Received August 30th, 2011; revised October 13th, 2011; accepted October 22nd, 2011.

ABSTRACT

Zn substituted Cu-Zn ferrites with a composition Cu1–xZnxFe2O4 have been synthesized by standard double sintering

ceramic method and characterized by X-ray diffraction. The single-phase cubic spinel structure of all the samples has

been confirmed from X-ray diffraction analyses. The lattice constant is found to increase linearly with the zinc content

obeying Vegard’s law. This increase in lattice parameter is explained in terms of the sizes of component ions. It is well

known that density plays a key role in controlling the properties of polycrystalline ferrites. The X-ray and bulk densities

of the Cu-Zn ferrite is significantly decreased whereas porosity increased with increasing Zn concentration, thereby

giving an impression that zinc might be helping in the densification of the materials. SEM micrographs exhibit a de-

crease in grain size with increasing Zn content. The real part of initial permeability, μ′ increase with increasing Zn

contents upto x = 0.5 after that it decreases with higher Zn content.

Keywords: Ferrites, XRD, Lattice Parameter, Density, Porosity, Permeability

1. Introduction

Ferrites, i.e. ferrimagnetic cubic spinels, possess the com-

bined properties of magnetic materials and insulators.

Ferrites represent an important class of functional mag-

netic materials, largely used in electronic industry and

many other fields of interest, like high frequency devices,

solid state physics, mobile communications of informa-

tion technology [1-3]. By virtue of their magnetic and

semiconducting properties the copper ferrite and its solid

solutions with other ferrites are employed as magnetic

materials foe multilayer chip inductors but also for

transducers of high thermomagnetic sensitivity [4,5]. The

copper ferrite has the structure of the mineral spinel cor-

responding to the general chemical formula MeFe2O4

where Me is Cu or a diavalent ion of the transition ele-

ments and Fe is the iron trivalent ion Fe3+. As long as the

ions are distributed in this way over A (tetrahedral) and

B (octrahedral) position the spinel is known as normal.

When divalent ions are distributed on B position and

trivalents ones on A position the spinel is known as in-

verse. For instance zinc ferrite is normal and copper fer-

rite completely inverse and these are extreme cases. In

reality there is a random distribution of the ions over A

and B sites and each composition is characterized by a

degree of inversion, which very much depend on the

preparation. Mixed ferrites have different degrees of in-

version and CuZn ferrites proved to be very sensitive to

thermal treatments having different cation distribution

upon annealing and mainly upon cooling speed from

high temperatures. The objective of this work is to syn-

thesize the Zn substituted Cu-Zn ferrites and to investi-

gate the effect of zinc ions which substitute iron in ferrite,

on the structural and physical properties of Cu-Zn ferrite

by studying XRD, SEM and frequency dependence per-

meability.

2. Materials and Method

Ferrite samples of the chemical formula Cu1–xZnxFe2O4

(x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7) were prepared by

the double sintering ceramic technique. High purity re-

agent powders of CuO, ZnO, and Fe2O3 were dried at

150˚C and were weighed precisely according to their

molecular weight. Intimate mixing for the materials was

carried out for 4 hours using agate mortar and then the

materials in ethyl alcohol are poured into an agate jar

with two types of stainless steel balls of different sizes.

Synthesis, Structural and Physical Properties of CuZn Fe O Ferrites

1676 1–xx2 4

The weight ratio of material to ball was 1:5 under air

atmosphere. The jar was placed into a planetary grinding

miller, and then the materials were continuously milled

for 4 hours. The slurry was dried and was pressed into

disc shape sample. The disc shaped sample was pre-sin-

tered at 850˚C for 6 hours at a heating rate of 4˚C/minute

in air to form ferrite through chemical reaction and then

cooled down to room temperature at the same rate as that

of heating. The pre-sintered material was again crushed

and wet milled for another 4 hours in distilled water to

reduce it to small crystallites of uniform size. The mix-

ture was dried and a few drops of saturated solution of

polyvinyl alcohol were added as a binder.

The resulting powders were pressed uniaxially under a

pressure of (20 Pa) in a stainless steel dies to make pel-

lets. The pressed pellets (9 mm diameter, 3 mm thickness)

toroids (12 mm outer diameter, 8 mm inner diameter and

4 mm thickness) were then finally sintered at 950˚C for 4

hours in air and cooled in the furnace. All samples were

heated slowly in the programmable Muffle furnace (Model

HTL 10/17, Germany) at the rate of about 220˚/hours

increase to avoid cracking of the samples. Then, the tem-

perature was raised to firing temperature of 950˚C and

kept at this temperature for 4 hours. The surfaces of all

the samples were polished in order to remove any oxide

layer formed during the process of sintering. The weight

and dimensions of the pellets were measured to deter-

mine bulk densities. Phase analysis was done by X-ray

diffraction using Phillips (PW3040) X’ Pert PRO X-ray

diffractometer. The powder specimens were exposed to

CuK



radiation with a primary beam of 40 kV and 30

mA with a sampling pitch of 0.02˚ and time for each step

data collection was 1.0 sec to characterize it. A 2



scan

was taken from 10˚ to 90˚ to set possible fundamental

peaks where Ni filter was used to reduce CuK



radiation.

All the data of the samples were analyzed using com-

puter software “X PERT HIGHSCORE”. X-ray diffrac-

tion patterns were carried out to confirm the crystal struc-

ture, where no extra lines were found indicating the ab-

sence of the starting oxides or any other phases. The mi-

crostructures of the samples were done by a scanning

electron microscope (SEM) (model: FEI Inspect). The

SEM micrographs were taken on the smooth surface of

the pellet-shaped polished samples. Before taking micro-

graphs, the surface of the samples were thermally etched

at a temperature of 150˚C below the sintering tempera-

ture. Frequency dependence initial permeability of the

toroid shaped samples was measured with 6500B im-

pedance analyzer at frequency range upto 15 MHz.

3. Results and Discussion

The structural study is essential for optimizing the prop-

erties needed for various applications. The phase identi-

fication and lattice constant determination were performed

on an X-ray diffractometer. The X-ray diffraction pat-

terns of the synthesized Zn substituted mixed ferrite

Cu1–xZnxFe2O4 is shown in Figure 1. All the samples

show good crystallization, with well-defined diffraction

lines. Powder X-ray diffraction of the ferrite samples,

showing well-defined reflections without any ambiguity,

reveals the formation of single-phase cubic spinel struc-

ture and all the peaks observed match well with those of

Mg-Cu-Zn, Mg-Cu and Zn-Mg ferrites reported earlier

[6-8]. The X-ray lines show considerable broadening, in-

dicating the fine particle nature of the ferrite powder. It is

obvious that the characteristic peaks for spinel Cu-Zn

ferrites appear in all samples as the main crystalline

phase. The peaks (220), (311), (222), (400), (422), (511)

and (440) correspond to spinel phase. A strong diffrac-

tion from the planes (311), (511) and (440) as well as

weak diffraction from the planes (220), (222), (400) and

(422) appeared in the X-ray diffractograms. Generally,

for the spinel ferrites the peak intensity depends on the

concentration of magnetic ions in the lattice.

After that, using the X-ray data, the lattice constant (a0)

and hence the X-ray densities were calculated. The lattice

constant was determined through the Nelson-Rilay ex-

trapolation method. The values of the lattice constant ob-

tained from each reflected plane are plotted against Nel-

son-Rilay function [9]





12 cossincosF



 









, where



is the

Bragg’s angle and straight lines are obtained as shown in

Figure 2. The accurate values of lattice constant, a0 were

estimated from the extrapolation of these lines to F(



) =

0 or



= 90˚.

Figure 3 shows the variation of lattice constant with

Zn concentration. A linear increase was evidenced in the

lattice constant with increasing Zn2+ ion concentration

from 8.365 Å for Cu-Zn ferrite for x = 0.0 to 8.439 Å for

x = 0.7. The increase in lattice constant with content of

Zinc indicates that the present system obeys the Vegard’s

law [10]. An increase in lattice constant with an increase

in the content of Zn can be attributed to the ionic size

differences since the unit cell has to expand when sub-

stituted by ions with large ionic size. Since the ionic

x=0.0

20 30 40 50 60 70

Position (2)

Intensity (A.U)

x=0.1

x=0.4

x=0.2

x=0.3

x=0.5

x=0.6

440

511

422

400

222

311

220

x=0.7

Figure 1. XRD pattern of Cu1–xZnxFe2O4 (x = 0.0 - 0.7).

Synthesis, Structural and Physical Properties of Cu1–xZnxFe2O4 Ferrites

1677

Figure 2. Variati on of lattice parameter with N-R function.

Figure 3. Vari ati on “a” with Zn content.

radius of Zn2+ ions ( = 0.82 Å) [11] is larger than

that of Cu2+ ions ( = 0.73 Å) [12], the substitution is

expected to increase the lattice constant with the increase

in x throughout the concentration studied. A similar lin-

ear variation has also been observed in Zn-Mg [8], Li-Mg

[13]; Zn-Mg-Cu [14]; Zn-Mg [15]; and Li-Cd [16] ferrites.

It was reported [17] that the value of lattice constant of

CuFe2O4 is 8.380 Å. Our experimental value is 8.365 Å,

which is almost similar to the reported value. This slight

difference in the value of the lattice constant is may be

due to the different scattering source, different sintering

and preparation techniques.

R

2

The bulk density,



B, was measured by usual mass and

dimensional consideration whereas X-ray density,



was calculated for each sample using the expression [18]





where, M is the molecular weight of the corresponding

composition, N is Avogadro’s number, V = a3 is the

volume of the cubic unit cell and Z is the number of

molecules per unit cell, which is 8 for the spinel cubic

structure. The porosity percentage was then calculated

from



B and



x values using the expression [19]

1 100











Density plays a key role in controlling the properties

of polycrystalline ferrites [20,21]. The variation of X-ray

and bulk densities is shown in Figure 4. By substituting

Zn in Cu-Zn ferrite, a decrease of X-ray and bulk densi-

ties is observed. The X-ray density depends upon the

Synthesis, Structural and Physical Properties of CuZn Fe O Ferrites

1678 1–x x2 4

Figure 4. X-ray and bulk de nsities with Zn conte nt.

lattice constants and molecular weight of the samples. As

lattice constants increase linearly with the increase of Zn

content, X-ray density decrease owing to the stoichiome-

tery of the sample. Similar decrease pattern is observed

by A. A. Pandit et al. in Mg-Mn ferrite [22]. It is also

observed form Figure 4 that the X-ray densities are lar-

ger in magnitude than corresponding to bulk densities.

This may be due to the existence of pores which were

formed and developed during the sample preparation or

the sintering process [23].

The effect of Zn ion on bulk density and on the poros-

ity is shown in Table 1 and Figure 5. By incorporating

Zn into Cu-Zn ferrite, a significant decrease of the bulk

density can be obtained. The highest density 5.124 g/cm3

whereas lowest porosity 5.61% is obtained for the com-

position of x = 0.0 i.e for pure Cu-ferrite. The porosity

value of all the samples is less than 12% that indicates

the existence of very few pores in the samples. The po-

rosity is found to increase from 5.61% for x = 0.0 to

10.18% for x = 0.7. Moreover this increase in porosity

and decrease in bulk density is due to the increase in

grain size, because the grains may be of irregular shape

and as the sintering proceeds the grain growth takes place

[24]. The intergrainular pores as developed during sin-

tering must also be capable of moving with the grain

boundaries as the growth occurs, requires that the pores

move together and coalesce, and a different transport

mechanism has been indicated. This consists of the trans-

port of gaseous oxygen across the pores and the diffusion

of cations around the pores; it is facilitated by high con-

centration of cation vacancies i.e. excess of Fe2O4. Hence

it is conclude that porosity increase with the addition of

Zn content due to the creation of more cation vacancies

with the reduction of oxygen vacancies [25].

Structural and magnetic properties sensitively depend

on the microstructure of ferrites. Grain size of the micro-

structures is the most important parameter affecting the

magnetic properties of ferrites. Figure 6 shows the SEM

Table 1. Lattice Constant, Bulk density, X-ray density and

porosity of the system Cu1–xZnxFe2O4.

content

(x)

Lattice

Constant,

a0 (Å)

Bulk Density,



B (gm/cm3)

X-ray

Density,



(gm/cm3)

Porosity

(%)

Grain

size

(μm)

0.0 8.36535.124 5.43 5.61 3.822

0.1 8.37245.067 5.42 6.49 3.577

0.2 8.38635.029 5.40 6.79 3.325

0.3 8.39344.974 5.39 7.65 2.902

0.4 8.40834.928 5.36 8.09 2.396

0.5 8.41644.868 5.35 9.02 2.047

0.6 8.42954.787 5.33 10.18 1.565

0.7 8.4396 4.716 5.31 11.26 1.277

Figure 5. Bulk density and Porosity with Zn content .

photographs of Cu-Zn ferrites substitute with Zn content

of 0.0, 0.2, 0.4 and 0.6 respectively. The average grain

size was obtained by line intercept method using SEM.

As shown in Figure 6, the microstructures revealed that

the grain size was influenced by the Zn substitution.

Fro m Table 1, it is observed that with the increase of Zn

substitution, the grain size decreased. In general, the

grain sizes of all samples are smaller than 4 μm, which is

superior to reduce thickness of each layer in multilayer

chip inductors leading to further miniaturization.

The structural and magnetic properties of soft ferrites

are influenced by the composition, additives and micro-

structures of the materials. Among these factors, the mi-

crostructures have great effect on structural and magnetic

properties. It is generally known that the larger grain

sizes, the higher the saturation magnetization and initial

permeability. Figure 7 shows permeability increased

with the increase of Zn content upto x = 0.5 and after that

it decrease. However, the variation of initial permeability

with Zn content was not consistent with the variation of

microstructures, the bulk density and the above empirical

Synthesis, Structural and Physical Properties of Cu1–xZnxFe2O4 Ferrites

1679

x = 0.0 x = 0.2

x = 0.4 x = 0.6

Figure 6. SEM micrographs of Cu1–xZnxFe2O4 ferrites (x = 0.0, 0.2, 0.4, 0.6).

Figure 7. Variation of initial permeability at with Zn con-

tent 10 KHz.

principle. This phenomenon might be explained by the

following equation:



MaKb







where μi is the initial permeability, Ms is the saturation

magnetization, K is the crystal anisotropy constant, λ is

the magnetostriction constant, and σ is the inner stress.

Nam et al. studies [26] that Zn substitution within small

range in composition plays a crucial role in properties of

NiCuZn ferrites by reducing magnetostriction effects.

Therefore with the increase of Zn content, the increase of

the initial permeability of CuZn ferrites was attributed to

the decrease of magnetostriction constant. The same

conclusions have been confirmed by Nakano’s [27] and

Xiwei qi’s [28] studies. From microstructures we could

see that the grain sizes tended to become smaller and the

distributions of pores were more even which might help

to diminish inner stress and lead to an increase of initial

permeability. In comparison with the reported results of

NiCuZn ferrites prepared by the same method [26], low

temperature sintered CuZn ferrites posses higher initial

permeability and better grain structure. The higher initial

permeability, low cost, low sintering temperature and

smaller grain size characteristics make the Zn substituted

CuZn ferrites be the most potential candidate material for

Multilayer chip inductor (MLCI) industry.

Synthesis, Structural and Physical Properties of CuZn Fe O Ferrites

1680 1–x x2 4

4. Conclusions

A series of Cu1–xZnxFe2O4 ferrites have been synthesized.

The presence of Zn ions causes appreciable changes in

the structure and physical properties of the Zn-substituted

Cu-Zn ferrite. XRD results indicate the single phase of

pure cubic spinel structure. The lattice constant is found

to increase linearly with increasing Zn content in the

mixed Cu-Zn ferrite system obeying Vegard’s law due to

larger ionic radius of Zn2+ compared to Cu2+. X-ray den-

sity decrease with increasing Zn content as lattice con-

stant increase. A remarkable decrease in the value of

bulk density has been found with increasing Zn substitu-

tion Cu-Zn ferrite attaining 98% of theoretical density for

the sample x = 0.0. The porosity is found to increase for

the Zn substitution due to the creation of more cation

vacancies with the reduction of oxygen vacancies. With

the increase of Zn substitution, the grain sizes decreased.

The increases of initial permeability of CuZn ferrites

with Zn content were attributed to the decrease of mag-

netostriction constant.

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