Ranu Pal; Sandeep Kumar Singh; M.J. Akhtar; Kamal K. Kar
Abstract
Efforts to use microwaves in material processing are gradually increasing. However, the phenomenon associated with the processing is less understood. The conversion of electromagnetic energy into heat depends largely on the dielectric properties of the material being treated. Therefore, the fundamental ...
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Efforts to use microwaves in material processing are gradually increasing. However, the phenomenon associated with the processing is less understood. The conversion of electromagnetic energy into heat depends largely on the dielectric properties of the material being treated. Therefore, the fundamental knowledge of these properties is essential for processing of materials using microwaves. In this study, first the dielectric evolution of silicon carbide (SiC) infused epoxy nanocomposites prepared at room temperature with 0-0.3 wt% content of SiC was measured. Secondly, the dielectric properties of the prepared nanocomposites after heating for 10 min in microwaves at a power of 500 W were investigated in order to see the effect of microwave curing. The dielectric properties of all the samples were measured at the microwave frequency of 2.45 GHz using the advanced cavity perturbation method attached to a vector Network Analyzer (VNA). The results indicate that the dielectric properties of the resultant nanocomposites increase with the increase in SiC content as compared to the neat epoxy sample. However, the dielectric properties were found to be decrease after microwave curing signaling the maximum possible extent of curing. This indicates that reinforcement of SiC nanoparticles in epoxy makes them ideal candidates for efficient microwave curing of nanocomposites. Lastly, the determination of thermal properties also confirms the maximum possible extent of curing of epoxy using SiC as nanofillers. Copyright © 2018 VBRI Press.
Shobhna Choudhary; Ram J. Sengwa
Abstract
The dielectric and electrical spectra of solution cast prepared nanocomposite films comprising poly(vinyl alcohol) (PVA) as polymer matrix and zinc oxide (ZnO) as inorganic nanofiller (PVA–x wt% ZnO (x = 0, 1, 3 and 5)) have been investigated in the frequency range from 20 Hz to 1 MHz. Anomalous ...
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The dielectric and electrical spectra of solution cast prepared nanocomposite films comprising poly(vinyl alcohol) (PVA) as polymer matrix and zinc oxide (ZnO) as inorganic nanofiller (PVA–x wt% ZnO (x = 0, 1, 3 and 5)) have been investigated in the frequency range from 20 Hz to 1 MHz. Anomalous increase is observed in real part of complex permittivity with increase of ZnO concentration, whereas relaxation peak corresponding to PVA chain segmental motion is appeared in the intermediate frequency region of dielectric loss tangent and the loss part of electric modulus spectra of the nanocomposites. These results confirm that the interaction of ZnO nanoparticles with hydroxyl groups of PVA acts as exciter for polymer chain segmental dynamics in the nanocomposites. The temperature dependent dielectric investigations on PVA–3 wt% ZnO film reveal that the dielectric polarization and chain segmental dynamics increase with the increase of temperature. The dielectric relaxation and conductivity activation energies values of the film are determined from the Arrhenius relation, which are found equal. The X-ray diffraction study confirms that the crystalline phase of PVA matrix abruptly reduces with doping of only 1 wt% ZnO which suggests that the interaction of polymer-nanoparticles significantly alter the hydrogen bonded crystalline structure of pristine PVA matrix. The dielectric and electrical results showed that these nanodielectrics are potentially useful as an electrical insulation material for various electronic devices. Copyright © 2017 VBRI Press.
Richa Sharma; N. C. Mehra; R. P. Tandon
Abstract
In the present work, the composite series (1-x) Ba0.94Ca0.06TiO3 - (x) Ni0.7Co0.1Zn0.2Fe2O4 (where x = 0.1, 0.2, 0.3 and 0.4 wt. fraction) was synthesized by solid state reaction method followed by conventional sintering. The structure and morphology of prepared samples were examined using X-ray diffractometer ...
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In the present work, the composite series (1-x) Ba0.94Ca0.06TiO3 - (x) Ni0.7Co0.1Zn0.2Fe2O4 (where x = 0.1, 0.2, 0.3 and 0.4 wt. fraction) was synthesized by solid state reaction method followed by conventional sintering. The structure and morphology of prepared samples were examined using X-ray diffractometer (XRD) and scanning electron microscopy (SEM), respectively. In addition, dielectric constant (ε΄) and loss tangent (tan δ) of prepared samples were measured as a function of frequency and temperature. The room temperature values of dielectric constant (ε΄) of composite samples are found to decrease from 529.29 to 159.52 as ferrite content increased from x = 0.1 to x = 0.4 at 1 kHz frequency. Moreover, in the dielectric constant vs. temperature plots of the composite samples, ferroelectric to paraelectric phase transition of pure Ba0.94Ca0.06TiO3 is observed. Furthermore, ferroelectric and magnetic properties of the composite samples were studied at room temperature. With increasing addition of the ferrite content in the composites, the ferroelectric properties get weakened and the magnetic behavior of the composite samples improved. The maximum values of saturation magnetization ( ) and remanant magnetization ( ) are 22.52 emu/gm and 3.39 emu/gm, respectively, for composite sample containing 0.4 wt. fraction Ni0.7Co0.1Zn0.2Fe2O4. Copyright © 2017 VBRI Press.
Ram J. Sengwa; Shobhna Choudhary
Abstract
Dielectric dispersion and relaxation behaviour of aqueous solution grown polymeric nanocomposite films consisting of poly(vinyl alcohol) (PVA) and alumina (Al2O3) (PVA–x wt% Al2O3 (x = 0, 1, 3 and 5)) have been studied in the frequency range from 20 Hz to 1 MHz by employing dielectric relaxation ...
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Dielectric dispersion and relaxation behaviour of aqueous solution grown polymeric nanocomposite films consisting of poly(vinyl alcohol) (PVA) and alumina (Al2O3) (PVA–x wt% Al2O3 (x = 0, 1, 3 and 5)) have been studied in the frequency range from 20 Hz to 1 MHz by employing dielectric relaxation spectroscopy (DRS). It is found that at constant frequency, the real part of complex permittivity increases nonlinearly with the increase of Al2O3 nanoparticles concentrations in the PVA matrix, whereas it decreases with increase of frequency at constant concentration of Al2O3. The temperature dependent investigation on PVA–3 wt% Al2O3 film reveals that the dielectric properties increase with the increase of temperature confirming its thermally activated dielectric behaviour. The ac electrical conductivity of the nanocomposites increases and the impedance values decreases with the increase of frequency which are moderately affected by Al2O3 concentrations(x = 0 to 5 wt%) and temperatures (30 to 60 °C). The dc conductivity and relaxation time of PVA chain segmental motion of the nanocomposites obey the Arrhenius behaviour. The X-ray diffraction (XRD) study reveals that the crystallite size and amorphous phase of PVA increase with the increase of Al2O3 concentration in the PVA–Al2O3 nanocomposites. Results of this study confirm the suitability of PVA–Al2O3 nanocomposite materials as tunable nanodielectric for their use as insulator and substrate in the fabrication of microelectronic devices operated at audio and radio frequencies. Copyright © 2017 VBRI Press.
Pragya Pandit; Pargin Bangotra
Abstract
In this paper we investigate the effect of lanthanum doping on structural, dielectric and electrical properties of lead magnesium niobate - lead titanate, 0.65Pb(Mg1/3Nb2/3O3)- 0.35PbTiO3 (x=0, 0.02, 0.05) ferroelectric ceramics. Dielectric and AC impedance spectroscopic measurements were ...
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In this paper we investigate the effect of lanthanum doping on structural, dielectric and electrical properties of lead magnesium niobate - lead titanate, 0.65Pb(Mg1/3Nb2/3O3)- 0.35PbTiO3 (x=0, 0.02, 0.05) ferroelectric ceramics. Dielectric and AC impedance spectroscopic measurements were carried out on pure and lanthanum doped PMN/PT ceramics over a wide temperature (30o- 450o C) and frequency interval (10 Hz-1 MHz). Pure and lanthanum doped Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x/4)]O3, (x=0, 0.02, 0.05) ceramics were prepared by solid state reaction route using columbite precursor method. X-ray diffraction revealed tetragonal (P4mm) phase for pure PMN/PT ceramics and transition to pseudo cubic phase (Pm3m) was observed with increased lanthanum doping. The dielectric response of the lanthanum modified PMN/PT ceramics was interpreted in terms of modified curie weiss law. Modulus spectroscopy revealed the deviation of dielectric behavior from ideal Debye behaviour. Activation energies calculated from dielectric relaxation and modulus spectroscopy suggested that charge transport processes are due to oxygen ion hopping.The AC conductivity of the PMN/PT ceramics initially increased for 2 mol% of lanthanum doping followed by a subsequent decrease with further 5 mol% of lanthanum doping. The value of the activation energies calculated from the temperature dependance of ac conductivity was in the range from 1.20-1.48 ev which is due to doubly ionized oxygen vacancies. The overall structural, electrical and dielectric behaviour of Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x/4)]O3, (x=0, 0.02, 0.05) ceramics is correlated to the relaxor nature induced by lanthanum doping.
Asheesh K. Sharma; Jayanth K. Swamy; Anjana Jain
Abstract
Piezoelectric polymer-ceramic composite materials are promising candidate for transducer application because of their inherent capability of combining the favourable properties of both ceramic and polymer materials. Present work discusses the dielectric properties of such composite films developed from ...
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Piezoelectric polymer-ceramic composite materials are promising candidate for transducer application because of their inherent capability of combining the favourable properties of both ceramic and polymer materials. Present work discusses the dielectric properties of such composite films developed from two piezoelectric materials viz. Poly(vinylidene fluoride) (PVDF) as a matrix and Lead Zirconate Titanate (PZT) as filler in PVDF. PVDF-PZT composite films were prepared by solvent casting method followed by hot pressing for better packing and connectivity of ceramic phase in the composite and hence improved piezoelectric properties in the material. The dielectric parameters of these films are evaluated by the measurement of dielectric constants (ε¢ and ε¢¢), intrinsic impedance, capacitance and dielectric loss, etc. as function of frequency at room temperature. The temperature dependence of the dielectric properties is studied as well from 40˚C to 75˚C. It was found that dielectric properties like permittivity and capacitance were quite stable in the frequency range 100 Hz-100 kHz. A variation of 20 to 50% in dielectric properties was observed, for increase in temperature with respect to room temperature, which may be accounted to pyroelectric behaviour of material.
