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

Abstract

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) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>α</mml:mi> <mml:mo>,</mml:mo> <mml:mi>γ</mml:mi> <mml:mo>−</mml:mo> </mml:math> Fe 2 O 3 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.