The dielectric behavior of polyvinylidene fluoride (PVDF), nanocrystalline nickel (nc-Ni) composites has been investigated over a broad frequency range of 40Hz–10MHz. High effective dielectric constant (εeff=2050) and low loss (tanδ=10) at 100Hz have been observed near the percolation threshold. To the best of our knowledge, this is the highest εeff value reported to date among the PVDF based metal-polymer composites. The dielectric properties have been explained by using boundary layer capacitor effect and percolation theory while the dielectric anomalies are attributed to process of fabrication leading to thick insulating layer between the filler particles forming a gap in effective tunneling range of two filler particles and also making a difficulty in probability of higher order tunneling.

The effect of processing conditions and filler particle size/surface area on the dielectric behavior of polyvinyledene fluoride/nickel composites is reported. Large enhancement of low frequency dielectric constant with reduction in metal particle size in a metal-polymer composite is observed. Enhancement in the dielectric constant has been attributed to increase in interfacial area and consequent interfacial polarization with reduction in metal particle size. The increased interparticle contacts from the nearest neighbors result in enhanced tunneling probability leading to lowering of percolation threshold for nanosized nickel/polyvinyledene fluoride composites as compared to micron nickel/polyvinyledene fluoride composites.

We report a comprehensive study on the structure and magnetic properties of ultrafine Ni nanoparticles prepared by the borohydride reduction method. A spontaneous surface oxide layer of NiO encapsulates the Ni particles, as these have been prepared under ambient atmosphere. From the x-ray diffraction ͑XRD͒ pattern, the "as-prepared" sample has been identified as Ni in a tetragonal crystal structure, stabilized by the incorporation of oxygen atoms in the Ni lattice. On annealing this sample in air at different temperatures, the XRD patterns showed an interesting feature: unexpected fcc Ni peaks appeared together with the usual NiO peaks. Anomalous behavior is also observed in the M-H curves, with the as-prepared sample showing a linear response with field and low values of magnetization and the annealed samples showing ferromagnetism with large coercivity ͑290 Oe͒ and high magnetization values. These surprising and seemingly contradictory observations have been coherently explained on the basis of a proposed phenomenological model. Furthermore, we attribute the observed low magnetization values of the as-prepared sample to an antiferromagnetic superexchange interaction between some of the Ni atoms, mediated by the dissolved oxygen atoms in the Ni lattice.

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Articles you may be interested in Tunability of optical memory in ferroelectric liquid crystal containing polyvinylpyrrolidone capped Ni nanoparticles for low power and faster device operation Effect of interstitial oxygen on the crystal structure and magnetic properties of Ni nanoparticles Abstract. In the present paper, we have studied the improvement in dielectric and optical properties of nematic liquid crystal (NLC) by doping of nickel oxide (NiO) nanoparticles. We have observed the dielectric and optical properties of pure and doped cells in order to understand the influence of NiO nanoparticles in the pure NLC. The experimental results have been analyzed through dielectric spectroscopic and optical texural methods.Detailed studies of dielectric parameters such as dielectric permittivity, dielectric loss and dielectric loss factor as a function of frequency with temperature were carried out. It has been observed that on doping the nanoparticles in NLC, the value of dielectric parameters (dielectric permittivity, dielectric loss and dielectric loss factor) decreases. The impedance and resistance of both pure and nanoparticles doped NLC cells were studied and found that for doped NLC, these parameter have low value. In addition to this, optical textures of the pure and doped samples have also been observed with a polarizing optical microscope at room temperature. All the results i.e. related to the investigation of dielectric and electro-optic properties have been explained by using existing theory of NLC.

The temperature variation of the electrical resistivity ρ and the Seebeck coefficient S of Heusler-type Fe 2 VAl 1−x Si x (0 x 1) alloys has been investigated. We have shown that the transport parameters are very sensitive to doping. For the x = 0 sample, high values of ρ and negative temperature coefficient of resistivity (TCR) have been observed. As the Si concentration increases, ρ decreases and the TCR changes its sign, while S shows significant changes in magnitude as well as sign when Al is replaced with Si. These changes appear to be reminiscent of a metal to semiconductor transition. It has been shown that the conventional transport theories proposed for intermetallic alloys or semiconductors cannot explain the transport behaviour in the whole temperature range of the present study. Low-temperature resistivity data of x = 0-0.02 samples could be described with a gapless semiconductor model. The strong composition dependence of S and ρ is attributed to the sharp variations in electronic density of states at the Fermi energy. It is also shown that by optimum doping one can achieve very large values of power factor (P). The estimated power factor at room temperature is observed to be highest (2.23 × 10 −3 W mK −2 ) for x = 0.06 and comparable to that of conventional thermoelectric material. At lower temperatures P is found to be even higher than that of conventional thermoelectric material.

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