Search

Barium hexaferrite is known to be a very good ferromagnetic material. However, it shows very good dielectric properties, i.e., the dielectric constant is comparable to that of the ferroelectric material. However, its crystal symmetry does not allow it to be a ferroelectric material. Hence, the electrical properties have revived the considerable research interest on these materials, not only for academic interest, but also for technological applications. There are a few reports on temperature dependent dielectric behavior of these materials. However, the exact cause of dielectric as well as electrical conductivity is yet to be established. Hence, Al (very good conducting material) substituted barium hexaferrite (BaFe12-xAlxO19, x=0.0-4.0) has been prepared by following the modified sol-gel method to understand the ac and DC electrical properties of these materials. The crystal structure and parameters have been studied by employing the XRD and FTIR techniques. There are two transition temperatures, which have been observed in the temperature dependent ac dielectric and DC resistivity measurement. The response of dielectric behaviors to temperature is similar to that of the ferroelectric material; however, the dielectric polarization is due to the polaron hopping, which is evident from the DC resistivity analysis. Hence, the present observations lead to understand the electrical properties of barium hexaferrite. The frequency dependent dielectric dispersion can be understood by the modified Debye model. More interestingly, the dielectric constant decreases and DC resistivity increases with the increase in the Al concentration, which has the correlation between bond length modifications in the crystal due to substitution. [ABSTRACT FROM AUTHOR]

(1 − x)PVA–(x)CFO nanocomposite thick films with x = 0 to 0.1 (i.e., 0% to 10%) have been prepared by employing the solvent casting method. The polyvinyl alcohol (PVA), cobalt ferrite (CFO), and PVA–CFO nanocomposites were characterized by x-ray diffraction pattern analysis, Raman spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. X-ray diffraction pattern analysis revealed the coexistence of both PVA and CFO in the nanocomposites, indicating that no major chemical reaction occurred between them. The morphology and elemental composition were analyzed by field-emission scanning electron microscopy (FE-SEM) and energy-dispersive spectroscopy (EDS), respectively. The real and imaginary parts of the dielectric constant were measured over a wide range of frequencies (100 Hz to 1 MHz) and temperatures (30°C to 130°C). The dielectric constant of PVA increased on loading CFO nanofiller into the polymer matrix. The resistivity was measured for all samples from room temperature to 130°C. The electric polarization was measured using a ferroelectric hysteresis (P–E) loop tracer. The highest polarization was observed for the 2% CFO nanofiller loading in the PVA polymer matrix. The activation energy was calculated by analyzing the dielectric data, being lower than that obtained from the analysis of the temperature-dependent resistivity data. Also, the leakage current increased with increase of the CFO filler loading in the nanocomposite. [ABSTRACT FROM AUTHOR]

The polymer nanocomposites have potential applications in flexible electronics due to its interesting dielectric properties. Hence, flexible nanocomposite films of polyvinylidene fluoride (PVDF) polymer and barium hexaferrite (BHF) nanoparticles with high dielectric constant were prepared by the solution cast method. The dielectric behavior of the materials has been understood by employing the impedance spectroscopy technique. The co-existence of α and β phases of PVDF has been observed from the XRD (X-ray Diffractometer) and FTIR (Fourier-transform infrared spectroscopy) analysis. The ratio of α and β phases of PVDF has a great influence on dielectric, ferroelectric and energy storage density of PVDF-BHF nanocomposites and, it depends upon the concentration of BHF in the nanocomposites. FE-SEM (Field Emission Scanning Electron Microscopy) micrographs reveal that the microstructure of the composite depends upon the concentration of BHF in the PVDF matrix. Dielectric properties of nanocomposite highly depends on microstructure of the PVDF-BHF nanocomposite. This observation has been well explained by considering the BLCs (Barrier Layer capacitances) model. Interestingly, the dielectric constant has been enhanced eighteen (18) times at 1 KHz to that of dielectric constant of PVDF. The dielectric constant increases due to the electrostatics and interfacial interaction between the local electric field of the BHF nanoparticle and CH2/CF2 dipole of PVDF chain. The present study opens a new window for the possible use of PVDF-BHF nanocomposite in dielectric and energy storage device applications. [ABSTRACT FROM AUTHOR]

The barium hexaferrite (BaFe 12 O 19) is synthesized by the modified sol-gel method. The nanoparticle BHF with different average particle sizes have been prepared by using the high energy planetary ball mill. The X-ray diffraction (XRD) patterns reveal that all the materials crystallize to hexagonal crystal symmetry with P6 3 /mmc space group. It is observed that the maximum magnetization decreases with the decrease in the average particle size of BHF. However, the maximum dielectric constant is found to be for the BHF with average particle size ~24 nm. [ABSTRACT FROM AUTHOR]