Using phasor diagrams, a generalized theory is proposed to classify the mechanisms of negative capacitance in distinct materials, apart from Landau ferroelectrics.
One major discipline of contemporary research in energy harvesting and conversion aims in developing lead-free, biocompatible, easily scalable, flexible and high power-denisty nanogenerators via utilizing poly(vinylidene fluoride) as an electroactive host-network due to its large breakdown strength, interesting polytype electrical order and thermoplastic nature. In this work, surfacefunctionalized magnetite nanoparticles (MNPs) of two different size having exotic electret and sizedependent magnetic properties are mixed with PVDF gel to fabricate self-poled composite piezoelectric films, which can obstruct electromagnetic interference also for smart device applications. A four-fold enhancement of its polar β-phase is verified from XRD and Raman spectra against incorporation of Fe 3 O 4 . Dielectric analysis suggests higher dielectric constant and lower dissipation for the films with tiny MNPs embedded in PVDF. The observations are duly validated from first principles studies. The physisorption process is recognized via geometrical optimization of Fe 3 O 4 /PVDF composite structure and significant amount of charge-transfer is demonstrated by the Mulliken charge-analysis. Open-circuit voltage and short-circuit current attain enhancement upto an order due to adequate ion-dipole and dipole-dipole interactions between the polar nanoscopic surface of Fe 3 O 4 and PVDF. Finally, the nanogenerators are employed to light up commercial LEDs.
An analytic dielectric introspection in two cardinal ferric oxide polymorphs, viz. hematite and maghemite, is conducted using a three-fold line of direction. Firstly, dc field-dependent radio/audio-frequency impedance and dielectric spectra of polycrystalline MIM pellets, comprising near-stoichiometric (meticulously characterized)
α
,
γ
−
Fe2O3 nanoparticles, are analysed by employing the Cole–Davidson model, Jonscher’s power law and equivalent circuitry to quantify non-Debye dipolar relaxations, small polaron hopping conduction, grain core–boundary resistivity correlations and field-driven delocalization/de-trapping of carriers. Bias-tuned low-frequency enhancement of the dielectric constant by augmenting Maxwell–Wagner polarization is demonstrated for both samples, a prerequisite for conquering classical energy-storage bottleneck. Secondly, the optical dielectric function and associated parameters are evaluated under a density functional theory + U framework, to physically designate particular resonant absorption, dissipation, electronic polarization and decay. In doing so, a new crystallographically consistent and energetically stable vacancy-ordered maghemite-type supercell is constructed to accomplish reasonable computational cost. Thirdly, intrinsic anisotropy in materials sensitive to photonic excitations is videographed by simulating energy-dispersive evolution of the quadric surface to project real/imaginary dielectric tensors. The authors anticipate that this intensive technique will pictorially demonstrate anisotropic deviations in the dielectric ellipsoid, fostering materials physics over linear and nonlinear dielectrics.
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