Negative capacitance switching in size-modulated Fe₃O₄nanoparticles with spontaneous non-stoichiometry: confronting its generalized origin in non-ferroelectric materials

Abstract

Using phasor diagrams, a generalized theory is proposed to classify the mechanisms of negative capacitance in distinct materials, apart from Landau ferroelectrics.

On the Interplay Between Oxygen Vacancies and Small Polarons in Manganese Iron Spinel Oxides

“…Oxygen vacancy formation energies, calculated according to eq 1 , are nearly constant across all MFO cells tested ( Figure 2 a and Table 1 ), consistent with the uniform concentration of oxygen vacancies throughout the stoichiometric range, observed in X-ray photoemission spectroscopy measurements of the epitaxial thin films. 16 We note that while the formation energy is large, ∼3.5 eV ( Figure 2 a and Table 1 ), it is consistent both with reports for other spinels 22 , 53 − 57 and iron oxides. 19 , 58 , 59…”

“…For the magnetite cells ( x = 0, Fe 3 O 4 ), the results differ significantly between the cells obtained when enabling or disabling symmetry constraints from the VASP calculations, with the unconstrained cell result falling in line with the results at other stoichiometries ( Figure 2 a, empty square) and with previously reported GGA + U results, 57 while the symmetry-constrained cell is markedly lower and consistent with a value previously reported in the literature. 60 The decreased formation energy for the symmetry-constrained case is the result of a significantly higher total energy for the pristine cell (−387.38 eV) as compared to the nonconstrained case (−388.67 eV).…”

Laser‐induced Fano interference subsumed by electron–phonon coupling in orthorhombic KNbO3nano‐bricks: An ab initio vibrational and Raman spectroscopic investigation

“…This further ensures that there is hardly any change in the associated bond‐length or unit cell volume, disregarding the possibility of anharmonic effects. This is an important advantage of the current study because charge–phonon coupling can be controlled by the laser power without disturbing the system or any unintentional inception of anharmonic dissipations 49 . In fact, the static‐lattice model for crystalline solids assumes useful corrections within the harmonic phonon approximation that matches with experimental evidence in numerous circumstances 50 …”

“…This is an important advantage of the current study because charge-phonon coupling can be controlled by the laser power without disturbing the system or any unintentional inception of anharmonic dissipations. 49 In fact, the static-lattice model for crystalline solids assumes useful corrections within the harmonic phonon approximation that matches with experimental evidence in numerous circumstances. 50 The Raman spectroscopic method is useful for phonon lifetime determination, which is linked with some thermal properties, as well as quality and purity of the sample.…”

Dielectric and piezoelectric augmentation in self-poled magnetic Fe3O4/poly(vinylidene fluoride) composite nanogenerators

“…The exchange-correlation terms are entreated with the generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) functionals for both DFT and DFT+U approach [42]. The value of U is set to 3.50 eV for the strongly correlated Fe 3d electrons, as suggested in previous reports [43,44]. The PBE+D2 force field (Grimme's) method is used for dispersive force corrections [45].…”