Dielectric loss

About: Dielectric loss is a research topic. Over the lifetime, 20296 publications have been published within this topic receiving 349254 citations.

Dielectric and conductivity relaxations in PVAc based polymer electrolytes

Abstract: The polymer electrolytes composed of a blend of poly (vinyl acetate) (PVAc) and poly (methylmethacrylate) (PMMA) as a host polymer and LiClO4 as a salt are prepared by a solution casting technique. The formation of blend polymer- salt complex has been confirmed by FT-IR spectral studies. The conductivity- temperature plots are found to follow an Arrhenius nature. Arrhenius plot shows the decrease in activation energy with the increase in salt concentration. The dielectric behaviour of the sample is analysed using dielectric permittivity (e′), dielectric loss (e″) and electric modulus (M″) of the samples. The impedance cole- cole plot shows the high frequency semi- circle is due to the bulk effect of the material and the depression in the semicircle shows the non-Debye nature of the material. The bulk conductivity is found to vary between 2.5×10−5 Scm−1 to 1.7×10−3 Scm−1 with the increase of salt concentration of blend polymer samples. The migration energy derived from the dissipation factor is almost equal to the activation energy calculated from conductivity. The modulus spectrum of the samples shows the non-Debye behaviour of the polymer electrolyte films. The low frequency dispersion of the dielectric constant implies the space charge effects arising from the electrodes.

Magnetic NiFe2O4/Polypyrrole nanocomposites with enhanced electromagnetic wave absorption

Abstract: NiFe2O4/polypyrrole (NiFe2O4/PPy) nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions. These nanocomposites also exhibit significantly enhanced electromagnetic wave (EMW) absorption property in the high frequency regions. Compared with pure PPy, the enhanced negative permittivity is observed in the NiFe2O4/PPy nanocomposites with a NiFe2O4 loading of 5.0, 10.0, 20.0 and 40.0 wt%, indicating the formation of metal-like electrical conducting network in NiFe2O4/PPy nanocomposites. Moreover, the negative permittivity could be tuned by changing the NiFe2O4 loading. The minimum reflection loss (RL) of -40.8 dB is observed in the 40.0 wt% NiFe2O4/PPy composites with a thickness of only 1.9 mm. The effective absorption bandwidth below -10.0 and -20.0 dB reaches 6.08 and 2.08 GHz, respectively. The enhanced EMW absorption performance benefits from the improved independence matching, EMW attenuation capacity, and synergistic effects of conduction loss, dielectric loss (interfacial and dipole polarizations) and magnetic loss (exchange and natural resonances). This research work provides a guidance for the fabrication of nanocomposites with an excellent EMW absorption.

Fabrication and enhanced microwave absorption properties of Al2O3 nanoflake-coated Ni core–shell composite microspheres

Abstract: Core–shell composite microspheres with Ni cores and Al2O3 nanoflake shells have been successfully fabricated by the hydrothermal deposition method. The electromagnetic parameters of the Ni microspheres and Ni/Al2O3 composites are measured by a coaxial line method. The tangent losses for the Ni/Al2O3 composite are larger than those of the Ni. A significant enhancement of electromagnetic absorption (EMA) performance of Ni microspheres coated by the alumina shells was achieved over the 1–18 GHz. The reflection loss (RL) less than −10 dB of the composite was obtained over 7.5–18.0 GHz by tuning an appropriate sample thickness between 1.3 and 2.2 mm, and an optimal RL of −33.03 dB was obtained at 9.2 GHz with a thin absorber thickness of 2.0 mm. The coating of the dielectric alumina shell significantly enhanced the microwave absorption performance due to the enhancement of interface polarization between the metals and dielectric interfaces, the synergetic effect between the dielectric loss and magnetic loss and unique flake-like dielectric alumina.

Optical and dielectric properties of a nanostructured NbO2 thin film prepared by thermal oxidation

Abstract: Nanostructured NbO2 films have been prepared on Si (001) substrates by thermally oxidizing a spiral niobium coil in a vacuum of the order of 10−2 Torr. The film consists of single-crystalline NbO2 nanoslices (several tens of nanometres thick) that are aligned with each other. When excited with 512 nm light, the NbO2 film showed room-temperature photoluminescence around 700 and 825 nm. It also exhibits, interestingly, excellent dielectric properties in the frequency range from 1 kHz to 10 MHz. It has a dielectric constant comparable to that of SiO2 and Si3N4, is independent of the frequency applied, and has a dielectric loss of less than 1% in the measured frequency range, making NbO2 a potential material for applications into MOS devices. The Raman spectrum of the NbO2 phase, for the first time, is also reported.