Field-enhanced polarization in polytype ferric oxides: confronting anisotropy in dielectric ellipsoid dispersion

Abstract

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.

Laser‐induced Fano interference subsumed by electron–phonon coupling in orthorhombic KNbO3 nano‐bricks: An ab initio vibrational and Raman spectroscopic investigation

“…Its sluggish rising trend can be noted from Figure 6E. Miscellaneous local mechanisms such as lattice disorder, crystal field effects, material‐specific anisotropic deviations, commensurate or incommensurate interaction of phonons with spins, charge carriers and surrounding phonons can lead to phonon damping 57–59 . Electron–phonon coupling has a general tendency of renormalizing the peak‐wavenumbers that supports the functional form of Einstein's approximation for gap renormalization 20 .…”

“…Miscellaneous local mechanisms such as lattice disorder, crystal field effects, material-specific anisotropic deviations, commensurate or incommensurate interaction of phonons with spins, charge carriers and surrounding phonons can lead to phonon damping. [57][58][59] Electron-phonon coupling has a general tendency of renormalizing the peak-wavenumbers that supports the functional form of Einstein's approximation for gap renormalization. 20 Nevertheless, the effect of disorder, shallow defect states, phonon confinement, and crystal field interactions are predominantly disregarded in this work.…”

Impact of tetra ethyl ortho-silicate and magnesium nitrate hexahydrate on dielectric characteristics of forsterite powder

“…However, ò ∞ of sample S3 is lower than S2. This behavior is probably caused by the rise in carrier density induced by the electric field [41]. Further, the value of α decreases as we move from sample S1 to S3.…”

“…However, as the frequency increases, the ability of the driving signal to induce a response diminishes. This phenomenon is attributed to the delay in the material's response, leading to a rapid decay in the system, which is a characteristic of Maxwell-Wagner interfacial polarization (MWIP) [41]. MWIP arises due to the presence of space-charge effects in dielectric structures that are inhomogeneous.…”

“…The Debye relaxation theory is one of the earliest models used to understand the dielectric response of a group of ideal, non-interacting dipoles as a function of the excitation frequency. However, in real-world scenarios, interactions occur between neighboring dipoles or with the surrounding environment, leading to a distribution of relaxation times and asymmetrical broadening of loss peaks [41]. The Cole-Cole model with a distribution variable (α) is introduced in order to overcome such discrepancies.…”