Tunable Dielectric Properties of Nickel Ferrite Derived via Crystallographic Site Preferential Cation Substitution

Abstract

We report on the tunable dielectric properties achieved in cation-substituted nickel ferrite (NiFe 2 O 4 ; NFO) by selectively engineering the crystallographic site occupation of the dopant cation in the NFO ceramics. The NFO, Mg-substituted NFO (NiMg 0.2 Fe 1.8 O 4 ; NMFO), and In-substituted NFO (NiIn 0.2 Fe 1.8 O 4 ; NIFO) nanocrystals were synthesized by employing a tartrate-gel chemical route, followed by calcination at 500 °C. High-resolution transmission electron microscopy (HRTEM) analyses indicate the crystal quality of NFO, NMFO, and NIFO nanomaterials. The HRTEM data revealed that all of the ferrite materials were nanocrystalline with sizes in the range of 15−25 nm. Coupled with HRTEM analyses, X-ray diffraction analyses indicate the formation of single-phase spinel-structured NFO, NMFO, and NIFO materials without any detectable impurities. Chemical analysis performed using Mossbauer spectroscopy indicates that Mg 2+ occupies the octahedral site, while In 3+ preferably occupies the tetrahedral site of the spinel-structured NFO. The Fourier transform infrared (FTIR) absorption bands corresponding to metal−oxygen (M−O) intrinsic stretching vibration in the octahedral unit (MO 6 ) and the tetrahedral unit (MO 4 ), respectively, were noted in all of the samples. However, the trend in the frequency shift of these bands in Mg-and In-substituted NFO materials is different due to the occupation of different sites of Mg and In as confirmed by Mossbauer studies. The electronic structure and chemical valence state analysis using X-ray photoelectron spectroscopy (XPS) corroborates with chemical bonding analyses performed by FTIR and cation distribution evaluation carried out by Mossbauer spectroscopy. The energy-dispersive X-ray spectrometry (EDS) data, in addition to XPS and FTIR analyses, further validate the formation of uniform and chemically homogeneous samples. The corresponding cation distribution revealed from Mossbauer studies correlates with the variation of dielectric properties of the doped NFO samples with respect to intrinsic NFO. At room temperature, the dielectric constant (ε) of NFO and NMFO is found to be nearly the same and constant over a wide range of frequencies. However, in NIFO, ε decreases with the applied frequency. The differences are attributed to the size effect and site preference of dopants (Mg 2+ and In 3+ ). Irrespective of the dopants, an increase in the temperature enhances the dielectric constant, which is due to an increase in the number of free charge carriers. A thermally activated electrical conduction mechanism was operative in NFO, NMFO, and NIFO materials. The activation energies for NFO, NFMO, and NIFO were 18.84, 34.48, and 57.14 meV, respectively. The enhanced dipolar effect of In 3+ at the tetrahedral site compared to Mg 2+ at the octahedral site may be the origin of the relatively higher value of activation energy in NIFO compared to intrinsic and Mg-substituted NFO.

Structural, Magnetic, and Magnetostriction Properties of Flexible, Nanocrystalline CoFe2O4 Films Made by Chemical Processing

“…To further assess the chemical bonding and structural quality of CFO films, we relied on spectroscopic characterization, particularly Raman scattering, which provides direct information on chemical bonding. − Cation distribution, which is one of the primary factors, strongly affects the magnetic properties of spinel ferrites. ,,, As the spinel ferrite exhibits two crystallographically distinguishable sites (tetrahedral and octahedral), the magnetic cations’ distribution among these sites dictates the magnetization of the spinel ferrite samples . Raman spectroscopy can be employed as an effective tool to identify the cation distribution and also the phase formation of the nano and bulk ferrite samples .…”

“…16 , 19 , 23 , 35 As the spinel ferrite exhibits two crystallographically distinguishable sites (tetrahedral and octahedral), the magnetic cations’ distribution among these sites dictates the magnetization of the spinel ferrite samples. 35 Raman spectroscopy can be employed as an effective tool to identify the cation distribution and also the phase formation of the nano and bulk ferrite samples. 32 Therefore, Raman scattering measurements on CFO films on mica substrates are expected to provide information on their structural quality and chemical bonding.…”

Influence of Exfoliated Boron Nitride for Fabrication of a Lightweight Wideband Microwave Absorbing Material

“…The fitted Ni 2p core-level spectrum shows two satellite peaks and the two spin–orbit doublet peaks (Figure d). The peaks at ∼852.3 and ∼870 eV corresponding to the Ni 2p3/2 and Ni 2p1/2, respectively, indicate the presence of Ni 2+ in 15-NiFBN. , Figure e depicts the deconvoluted XPS spectra of Fe. The presence of two peaks at ∼708.5 and ∼721.7 eV confirms the Fe 3+ state of iron in NiFe 2 O 4 . , Moreover, the deconvoluted XPS spectra of Fe show two satellite peaks at ∼716.1 and ∼729.9 eV (Figure e).…”

“…3 and ∼870 eV corresponding to the Ni 2p3/2 and Ni 2p1/2, respectively, indicate the presence of Ni 2+ in 15-NiFBN 48,52. Figure4edepicts the deconvoluted XPS spectra of Fe.…”

Effective Enhancement of the Ferroelectric Performance of Polar Co-Gallate MOF by Doping M2+ Ions (M = Mg, Mn, Ni) into Framework Nodes

“…The survey spectrum and high resolution of Co-Gallate and partial M-doped Co-Gallate (M = Mg, Mn, and Ni) are shown in Figures S2–S4 and . For Mg-doped Co-Gallate, the characteristic peak of Mg 1s at 1304.8 eV is found for 5% Mg-doped Co-Gallate and 7% Mg-doped Co-Gallate, which corresponds to the +2 valence of Mg element (Figure S2), indicating the successful insertion of Mg 2+ ions into parent Co-Gallate . Although the high-resolution of Mg elements is not performed because the signal is weak, the binding energy of O 1s and Co 2p exhibits an obvious change compared to that of parent Co-Gallate when Mg 2+ ions are doped into framework nodes.…”