Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

We report scanned probe investigations on the ferroelectric properties of individual single-crystalline barium titanate nanowires. We show that nonvolatile electric polarization can be reproducibly induced and manipulated on these nanowires, thereby demonstrating that nanowires as small as 10 nm in diameter retain ferroelectricity. The coercive field for polarization reversal is determined to be ∼7 kV/cm, and the retention time for the induced polarization exceeds 5 days. These nanowires should provide promising materials for fundamental investigations on nanoscale ferroelectricity, and they may also be useful in nanoscale nonvolatile memory applications.

Ferroelectric Properties of Individual Barium Titanate Nanowires Investigated by Scanned Probe Microscopy

The dielectric properties of MnxNi0.5−xZn0.5Fe2O4 ferrites with x varying from 0.05 to 0.4 synthesized by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. An increase in the dielectric constant is observed with the increase in Mn concentration except for x=0.3. Dispersion in the dielectric constant with frequency in the range of 100 Hz–1 MHz is observed. Resonance peaks were observed in tan δ∈ versus frequency curves for all samples. A shift in the resonance frequency towards higher frequency is observed with increase in temperature. The peak height also increases with increase in temperature. Possible mechanisms contributing to these processes have been discussed. From the temperature variation of the dielectric relaxation, activation energies for various samples have been calculated and compared with those obtained from dc resistivity.

Dielectric properties of Mn-substituted Ni–Zn ferrites

Structural, electrical and magnetic properties of Co-Cu ferrite nanoparticles

Effect of lattice strain on structure, morphology and magneto-dielectric properties of spinel NiGdxFe2−xO4 ferrite nano-crystallites synthesized by sol-gel route

Ferroelectric and dielectric properties of barium titanate (BaTiO3) bulk ceramics and thin films have been investigated. The bulk ceramics and thin film samples have been prepared from barium acetate [Ba(CH3COO)2] and titanium(IV)isopropoxide [Ti(CH3)2CHO)4] precursors by sol-gel technique. The as-grown bulk powder and thin films were found to be amorphous, which crystallized to tetragonal phase after annealing at 700°C in air for one hour. The values of the spontaneous polarization (Ps), remanant polarization (Pr) and coercive field (Ec) of the bulk ceramics were found to be 19.0, 12.6 μC cm−2 and 30 kV cm−1 respectively. In the case of the film, the values of Ps, Pr and Ec were respectively found to be 14.0, 3.2 μC cm−2 and 53 kV cm−1. The capacitance-voltage (C-V) characteristics of the film also showed polarization hysteresis. The values of the dielectric constant (e) of the bulk ceramic and thin film at 1 kHz were found to be 1235 and 370 respectively. Both the films and ceramics showed dielectric anomaly peaks at 125°C, showing ferroelectric to paraelectric phase transition.

Ferroelectric and dielectric properties of sol-gel processed barium titanate ceramics and thin films

The effect of fatigue on the electrical properties of sol-gel derived ferroelectric barium titanate (BaTiO3) thin films have been investigated. At room temperature, the resistivity, breakdown field, dielectric constant (e), and loss tangent (tan δ) decreases after fatigue while the coercive field increases. Fatigue also influences the dielectric properties of the film at high temperatures. The sharpness and magnitude of the peak in the dielectric constant at the transition temperature decreases after fatigue. The loss tangent of the virgin film showed a peak at the transition temperature while it is absent in the case of the fatigue film. The phenomena are explained in terms of (i) the accumulation of point charge defect, (ii) the pinning of domain wall mobility, and (iii) the space charge layer models of fatigue.

Fatigue in sol-gel derived barium titanate films

The lattice constant, dc resistivity, dielectric constant, saturation magnetization and Curie temperature were studied on a series of Cr-substituted Li-Sb ferrite systems. The dc resistivity increases with increase of the chromium level. A change in slope was observed in the variation of resistivity with temperature and hence two regions of different activation energy. The study of dielectric permittivity with frequency showed dispersion for the whole system. The saturation magnetization and the Curie temperature were found to decrease with increase of the substitution level.

https://iopscience.iop.org/article/10.1088/0022-3727/32/17/303/pdf

H. N. K. Sarma

Papers

Ferroelectric and dielectric properties of sol-gel processed barium titanate ceramics and thin films

Fatigue in sol-gel derived barium titanate films

Electrical and magnetic studies of the spinel system Li0.5+tCrxSbtFe2.5-x-2tO4

Influence of Co2+ on the electrical and magnetic properties of Li–Sb ferrites

Effects of Cobalt substitution on the dielectric properties of Li–Zn ferrites