Surendran,K P; Bijumon, P V; Mohanan, P; Sebastian,M T(Department of Electronics, April 14, 2005)
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Abstract:
The MgAl2O4 ceramics were prepared by the conventional
solid-state ceramic route and the dielectric properties
studied in the microwave frequency region (3–13 GHz).
The phase purity and crystal structure were identified using
the X-ray diffraction technique. The MgAl2O4 spinel ceramics
show interesting microwave dielectric properties (εr = 8.75,
Qux f = 68 900 GHz (loss tangent = 0.00017 at 12.3 GHz),
τf =−75 ppm/◦C). The MgAl2O4 has high negative τf, which
precludes its immediate use in practical applications. Hence
the microwave dielectric properties of MgAl2O4 spinels were
tailored by adding different mole fractions of TiO2. The
εr and Q factor of the mixed phases were increased with
the molar addition of TiO2 into the spinel to form mixtures
based on (1−x)MgAl2O4-xTiO2 (x = 0.0−1.0). For x = 0.25 in (1−x)MgAl2O4-xTiO2, the microwave quality factor
reaches a maximum value of Qux f = 105 400 GHz (loss tangent
= 0.00007 at 7.5 GHz) where εr and τf are 11.035 and
−12 ppm/◦C, respectively. The microwave dielectric properties
of the newly developed 0.75MgAl2O4-0.25TiO2 dielectric is
superior to several commercially available low loss dielectric
substrates.
Anantharaman, M R; Saravanan, S; Joseph, Mathai C; Venkitachalam, S; Prabhakaran, P V(Wiley Periodicals, July 23, 2003)
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Abstract:
Electrically conductive organic and metalloorganic
polymers are of great interest and they have applications
in electronic, optical, photonic, photoelectric, electrochemical,
and dielectric devices. Tetrameric cobalt phthalocyanine
was prepared by conventional chemical method.
The dielectric permittivity of the tetrameric cobalt phthalocyanine
sample was evaluated from the observed capacitance
values in the frequency range 100 KHz to 5 MHz and
in the temperature range of 300 to 383°K. It is found that the
system obeys the Maxwell Wagner relaxation of space
charge phenomenon. Further, from the permittivity studies
AC conductivity was evaluated. The values of AC conductivity
and DC conductivity were compared. Activation energy
was calculated. To understand the conduction mechanism
Mott’s variable range hopping model was applied to
the system. The T 1/4 behavior of the DC conductivity along
with the values of Mott’s Temperature (T0), density of states
at the Fermi energy N (EF), and range of hopping R and
hopping energy W indicate that the transport of charge
carriers are by three-dimensional variable range hopping
Description:
Journal of Applied Polymer Science, Vol. 91, 2529–2535 (2004)
In this article, we report the preparation of
conducting natural rubber (NR) with polyaniline (Pani). NR
was made into a conductive material by the compounding
of NR with Pani in powder form. NR latex was made into a
conductive material by the in situ polymerization of aniline
in the presence of NR latex. Different compositions of Pani-
NR semi-interpenetrating networks were prepared, and the
dielectric properties of all of the samples were determined
in microwave frequencies. The cavity perturbation techpique was used for this study. A HP8510 vector network analyzer
with a rectangular cavity resonator was used for this
study. S bands 2-4 GHz in frequency were used. Thermal
studies were also carried out with thermogravimetric analysis
and differential scanning calorimetry.
Anantharaman, M R; Soloman, M A; Philip, Kurian; Joy, P A(Wiley Periodicals, September 26, 2002)
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Abstract:
Fine particles of barium ferrite (BaFe12O19)
were synthesized by the conventional ceramic technique.
These materials were then characterized by the X-ray diffraction
method and incorporated in the natural rubber matrix
according to a specific receipe for various loadings of
ferrite. The rubber ferrite composites (RFC) thus obtained
have several applications, and have the advantage of molding
into complex shapes. For applications such as microwave
absorbers, these composites should have an appropriate
dielectric strength with the required mechanical and
magnetic properties. The N330 (HAF) carbon black has been
added to these RFCs for various loadings to modify the
dielectric and mechanical properties. In this article we report
the effect of carbon black on the mechanical and dielectric
properties of these RFCs. Both the mechanical and dielectric
properties can be enhanced by the addition of an appropriate
amount of carbon black
Description:
Journal of Applied Polymer Science, Vol. 89, 769–778 (2003)
Rani, Joseph(Wiley InterScience, February 18, 2006)
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Abstract:
In this paper we report the preparation and
dielectric properties of poly o-toluidine:poly vinyl chloride
composites in pellet and film forms. The composites were
prepared using ammonium persulfate initiator and HCl
dopant. The characterization is done by TGA and DSC. The
dielectric properties including dielectric loss, conductivity,
dielectric constant, dielectric heating coefficient, absorption
coefficient, and penetration depth were studied in the
microwave field. An HP8510 vector network analyzer with
rectangular cavity resonator was used for the study. Sbands (2-4 GHz), C band (5-8 GHz), and X band (8-12
GHz) frequencies were used in the microwave field. Comparisons
between the pellet and film forms of composites
were also included. The result shows that the dielectric
properties in the microwave field are dependent on the frequency
and on the method of preparation.
Subhadra, V K; Syamaprasad, U; Vallabhan, C P G(American Institute of Physics, 1983)
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Abstract:
Results of axiswise measurements of the electrical conductivity (dc and ac) and dielectric constant of NH4H2PO4 confirm the occurrence of the recently suggested high‐temperature phase transition in this crystal (at 133 °C). The corresponding transition in ND4D2PO4 observed here for the first time takes place at 141.5 °C. The mechanism involved in these transitions and those associated with the electrical conduction and dielectric anomalies are explained on the basis of the motional effects of the ammonium ions in these crystals. Conductivity values for deuterated crystals give direct evidence for the predominance of protonic conduction throughout the entire range of temperatures studied (30–260 °C).
Sagar, S; Dr.Anantharaman, M R(Cochin University of Science & Technology, August , 2010)
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Abstract:
This thesis lays importance in the investigation on the multiferroic and
thermooelectric properties of selected representatives of low bandwidth and
intermediate band width manganites. The first candidate, Strontium doped Gd manganite, is prepared by wet solid state reaction method and the second
candidate, Na doped La manganite, by citrate gel method. In addition to the above
mentioned properties, magneto resistance and dielectric properties are
investigated. Using dielectric spectroscopic the dispersion parameters are
correlated to the relaxation mechanisms and an attempt is made to obtain the grain
and grain boundary contribution to the impedance of the sample through
impedance spectroscopy studies.
Description:
Department of Physics,
Cochin University of Science & Technolog
Rani, Joseph(Wiley Inter Science, December 14, 2005)
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Abstract:
Polypyrrole/poly (vinyl chloride) semi-interpenenzrtirtg
networks of different compositions are prepared using anunonitun per
sulfate initiator at room temperature in pellet.form and lilrrt form and
their dielectric properties are studied at different microwave frequencies.
An HP 8510 Vector network analyzer interfaced with a computer
is used. The cavity-perturbation technique is employed for the
study