Summary:MgGd0.1 of the additives. The variation of dielectric properties

Summary:MgGd0.1
Fe1.9 O4 ferrite with improved electrical and dielectric
properties has been synthesized by conventional ceramic technique. X-ray
analysis explains the single-phase inverse spinel structure of the ferrite. The
dc resistivity is increased by arrangement of magnitude as compared to
Magnesium ferrite. The dielectric loss of the model explained that at room
temperature is only 3 × 10?3 at 3 MHz. If th resistance is high and
low dielectric loss that can be complementary to better constitutional
Stoichiometry, size and character of the additives. The variation of dielectric
properties of the model as a purpose of frequency in the class 0.1–20 MHz has
been deliberate at different temperatures. The electric and dielectric property
has been studied as a purpose of temperature. Possible methods participating to
the results have been explained slightly in the paper.

1. 
Introduction: Spinel ferrites have been studied
extensively because they play a vital role in the technological applications.
Gd–Mg ferrites have emerged as one of the most important material due to its
high dc resistivity and low dielectric losses. It is very important in many
applications to control the dc resistivity of the spinel ferrites. For this
purpose two major possibilities are available, controlling the sintering
temperature and substitution. The dc resistivity of MgGd0.1Fe1.9O4
ferrite is increased by one order of magnitude as compared to Mg ferrite. These
useful properties of the spinel ferrites depend upon the choice of the cation
along with Fe2+, Fe3+ ions and their distribution between
tetrahedral (A) and octahedral

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(B) sites of the spinel
lattice, preparation methods, chemical com-position, sintering temperature,
rate of sintering and nature of the additives. All the ferrites have high dc
resistance. It is used in the formation of the transformers central parts and
chokes. All the ferrites having extremely low dielectric loss are very helpful
for microwave statement. In the paper ,the difference of electric and
dielectric properties of the model as a purpose of frequency at varied
temperatures. In addition to this, the effects of temperature on the electric
and dielectric properties were investigated and reported in the present work.

2. 
Experimental details: Mg–Gd ferrite of
composition MgGd0.1 Fe1.9 O4 was prepared by
using the standard ceramic technique. Analytical grade reagents MgO, Gd2
O3 and Fe2 O3 were weighted in appropriate
proportions and mixed thoroughly by wet blending with de-ionized water in an
agate mortar and pestle. The mixed powders were dried and calcinated at 800 ?
C for 3 h to improve the homogeneity of the constituents. After cooling to room
temperature the samples were mixed with a small quantity of polyvinyl alcohol
as a binder and milled. The powders were compressed into pellets uniaxially
under a pressure of 3–8 ton/in.2 in a stainless steel die. The
pellets were finally sintered at 1000 ? C for 3 h and were cool down
to room temperature. The single-phase nature of the prepared samples was checked
by X-ray diffraction studies, which were made by Cu-K radiation of wavelength
1.54 Å using Riga Ku-Denki X-ray diffraction meter. The surfaces of the pellet
were polished and coated with silver paste; they acted as good contacts and
electrodes for measuring the electric and dielectric properties. The dielectric
constant and dielectric loss were determined by Agilent Technologies 4285A Precision
LCR meter at room temperature in the frequency range from 0.075 to 20 MHz. The
dc resistivity of the samples at different temperatures was measured by using a
Keithley Model 2611 in the temperature range 293–473 K.

3. 
Results and discussion: The X-ray diffraction
patterns for the ferrite powder obtained on calcination at 1000 ? C
corresponded to that of the single-phase inverse spinel structure for the
compositions MgGdx Fe2?x O4 (x
= 0.00 and 0.1). The diffraction peaks are quite sharp because of the
micrometer size of the crystallite. The particle size of the sample has been
estimated from the broadening of XRD peaks using the Scherrer equation. The
average particle size is about 0.1–1 m at 1000 ? C. The variation of
dc resistivity with temperature. High dc resistivity of ?7
× 108_
cm is obtained at room temperature, and decreases with increase in temperature.
The higher value of dc resistivity is due to Gd3+ content in Mg
ferrite. Gd3+ content doping reduces the iron ion concentration from
2 to 1.9 thereby reduces the number of Fe3+ ions on theoctahedral
sites which play a dominant role in the mechanism of conduction. The inset
shows the variation of dc resistivity of MgFe2O4 (Pure Mg
ferrite) with temperature. The resistivity of the sample decreases with
increase in temperature according to Arrhenious equation . Increasing
temperature leads to decrease in resistivity, which is the normal behavior of
semiconducting materials. Increase in temperature of the sample will help the
trapped charges to be liberated and participate in the conduction process, with
the result of decreasing the resistivity. This decrease in resistivity could be
related to the increase in the drift mobility of the thermally activated
electrons according to the hopping conduction mechanism and not to thermally
creation of the charge carriers. The hopping conduction mechanism between Fe2+
? Fe3++e?1 is the main source of electron hopping
in the process. Activation energy, E was calculated from the slope of
the graph. The value of activation energy for the sample is 0.4497 eV. In
ferrite samples, the activation energy is often associated with the variation
of mobility of charge carriers rather than with their concentration. The charge
carriers are considered as localized at the ions or vacant sites and conduction
occurs via a hopping process. The hopping depends upon the activation energy,
which is associated with the electrical energy barrier experienced by the
electrons during hop-ping. The variation of dielectric constant as purpose of
frequency in the range 0.1_20 MHz at various temperatures. Initially dielectric
constant decreases slowly with frequency up to 1 MHz and becomes almost
constant up to 6 MHz. The increase in dielectric constant above 6 MHz may
indicate the beginning of a possible presence of resonance with peaks occurring
at higher frequencies. The initial decrease in dielectric constant with
frequency up to (1 MHz) can be explained by the phenomenon of dipole
relaxation. The resonance may arise due to the matching of the frequency of
charge transfer between Fe2+ ? Fe3+ ions, and that of the
applied electric field. These changes can also be elaborated on the basis of
space charge polarization model of Wagner and Maxwell . The variation of
dielectric constant with temperature at different frequencies. The dielectric
constant increases with temperature at all frequencies. The hopping of the
charge carriers is thermally activated with t he rise in temperature; hence,
the dielectric polarization increases, causing an increase in dielectric
constant. At lower frequencies (100 kHz), the increase in dielectric constant
is very large with an increase in temperature, while at higher frequency range
(1–12 MHz), the increase in dielec-tric constant is small. The dielectric
constant of any materials, in general, is directly related to dielectric
polarization. The higher the polarization, the higher the dielectric constant
of the mate-rial. There are four primary mechanisms causing polarizations:
electronic polarization, ionic polarization, dipolar polarization and space
charges polarization. Their occurrence depends upon the electric frequency of
the applied field. At low frequencies, space charges polarization and dipolar
polarization are known to play the vital role 19
and both these polarizations are temperature dependent. At high frequencies,
ionic polarizations are main contributors, and their temperature dependence is
insignificant. The change of dielectric loss with frequency at different
temperatures. The dielectric loss factor decreases initially with increasing
frequency followed by the appearance of a resonance with peaks occurring at
higher frequencies. The initial decrease in dielectric loss (tan ?) with an
increase in frequency is in accordance with the Koops phenomenological model. The
resonance may arise due to the matching of hopping frequency with the frequency
of the external electric field. Hudson has shown that, the dielectric losses in
ferrites are reflected in the conductivity measurements where the materials of
high conductivity exhibiting higher losses and vice-versa. The change of
dielectric loss as a function of temperature at different frequencies. The
dielectric loss also shows the same trend as the dielectric constant curves,
and can be explained online similar to those advanced for explaining dielectric
constant. The low values of dielectric constant, dielectric loss and high value
of dc resistivity are due to the Gd3+ ion content in Mg ferrite.
This result is explained in view of the hopping conduction mechanism between Fe2+
? Fe3+ + e?1, Gd3+ ions do not
participate in conduction and polarization process but limit the degree of
hop-ping by blocking up Fe2+ ? Fe3+ + e?1
pattern on the octahedral sites. This is due to the reduction in the
concentration of Fe ions inthe system due to the doping of Gd3+ ions
in Mg ferrite.

4. 
Conclusions

Single-phase MgGd0.1Fe1.904
ferrite has been synthesized by conventional ceramic method. The particle size
was calculated from the most intense peak (3 1 1) using the Scherrer equation.
The dc resistivity studied shown that ferrite is increased by one order of
magnitude as compared to undoped Magnesium ferrite. High value of dc
resistivity makes this ferrite suitable for the highfrequency applications
where vortex current losses become appreciable. Gd–Mg ferrites may be used in
television yokes and fly back transformers because of their higher resistivity
which eliminates the need for taped insulation between yoke and winding.
Temperature dependent dc resistivity decreases with an increase in temperature
ensuring the normal behavior of semiconducting materials. The value of dielectric
loss in the presently studied ferrite at room temperature is only 0.003 at 3
MHz. Low values of dielectric constant and dielectric losses exhibited by this
ferrite suggest its utility in microwave communications.