Tetrahedral 8a Sites Research Articles

Enhancing Lithium Conductivity Using High-Valence Cations in Cubic Spinel Halide Solid Electrolytes.

Halide solid electrolytes for all-solid-state batteries have recently emerged as competitors to oxide and sulfide solid electrolytes due to their excellent electrochemical properties. This ab initio study unveils the dynamic nature of Li2Sc2/3Cl4, a rare superionic conductor among cubic spinel halide materials. Li ions in Li2Sc2/3Cl4 prefer to occupy some of the tetrahedral 8a, octahedral 16c, and octahedral 16d sites, leading to disordered Li distribution. Li ions in Li2Sc2/3Cl4 diffuse through the single-ion diffusion mechanism rather than the concerted diffusion mechanism, providing a high conductivity of 1.36 mS cm-1. Li ions at the 16d site diffuse as actively as those at the 8a/16c site, an unexpected result that runs counter to the conventional view. In Li2MgCl4, the same cubic spinel as Li2Sc2/3Cl4, Li ions at the 8a/16c site diffuse actively, but those at the 16d site are almost immobile, resulting in a very low conductivity of 5.3 × 10-4 mS cm-1. The extremely higher conductivity in Li2Sc2/3Cl4 than in Li2MgCl4 is because the concentration of Sc3+/Mg2+ cations blocking the movement of Li ions at the 16d site is lower in Li2Sc2/3Cl4 than in Li2MgCl4. Designing cubic spinel materials containing high-valence cations is proposed as a way to increase conductivity by reducing the concentration of multivalent cations that impede Li diffusion. This study sheds new light on how to control conductivity using site-dependent Li mobility in solid electrolytes.

Study of the cationic substitution effect on the magnetic properties of the ferrite MnxZn1-xFe2O4 nanoparticles prepared by TREG-mediated solvothermal route

MnxZn1-xFe2O4 (x = 0–1) solid solution was prepared using the TREG-mediated solvothermal method. 10–12 nm spherical superparamagnetic particles (except for ZnFe2O4) were obtained. At room temperature, the ferrites have lower magnetic saturation (Ms) than magnetite. However, at 10 K, it is precisely the opposite. DRX and EXAFS showed that incorporating Zn2+ ions in tetrahedral A-sites provokes a redistribution of Mn and Fe ions in octahedral B-sites of the mixed spinel structure. For Zn concentrations from x = 0.5 and below, the Mn and Fe ions are almost equally distributed between A and B-sites. Therefore, at low Zn concentrations, the small migration of Fe and Mn ions to B-sites increases the magnetic moment of B sub-lattices and, consequently, the total magnetic saturation. In addition, Mn2+ oxidized to Mn3+ and, simultaneously, Fe3+ reduced to Fe2+, affecting the magnetic properties. The increment of Zn concentration severely reduces the magnetization.

Rietveld refinement and cation distribution of Zn-Al substituted NiFe2O4 ferrite nanoparticles

A series of Zn-Al co-substituted nickel ferrites having general formula Ni1-xZnxFe2-yAlyO4 with x = y = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 were successfully synthesized by wet chemical sol–gel auto combustion method. The X-ray diffraction pattern with Rietveld refinement has confirmed the formation of monophase cubic spinel structured samples with space group Fd-3 m. It is found that the lattice constant (a) decreases from 8.3399 Å to 8.2801 Å with an increase in Zn-Al content. The crystallite sizes are decreased from 25 nm to 18 nm with Zn-Al content. The X-ray density is decreased from 5.3679 to 4.9642 g/cm3 and porosity is decreased from 32.23 to 30.68 % with Zn-Al substitution. The cation distribution attributed that the dopant Zn2+ preferentially occupies tetrahedral A-site and dopant Al3+ preferentially occupies octahedral B-site for all the composition of Zn-Al. The average grain size (G) is observed to be increased from 36 nm to 43 nm. The saturation magnetization (Ms) is decreased from 48.51 to 1.05 emu/g with Zn-Al composition. The coercivity (Hc) of the sample is decreased from 104 to 26.31 Oe and the remenance ratio is decreased from 0.23 to 0.03 Zn-Al content. The variations in dielectric properties are explained on the basis of Maxwell and Wagner’s type of interfacial polarization effects. The magnetic and dielectric properties of nickel ferrite nanoparticles are strongly influenced by the Zn-Al co-substitution, which is valuable in technological applications.

Hydrothermal synthesis of Cu-substituted Ni ferrites: Structural, morphological, and magnetic properties

Cu-substituted Ni ferrite systems are produced following a hydrothermal synthetic route carried out at relatively mild conditions (i.e., below 200 °C). Different degrees of substitution were investigated, ranging from bare Ni ferrite to a complete Cu-substituted system (by replacing 100% of Ni with Cu). Morphological and structural characterisations point out that the introduction of Cu in the Ni ferrite (below 50% substitution) causes a gradual reduction of the average diameter of the ferrite polyhedral nanoparticles maintaining the Ni ferrite structure. At higher content of Cu, instead, the morphology evolves toward the co-presence of iron oxides (magnetite and hematite) and copper oxide (tenorite), without the formation of bare Cu ferrite. The partially substituted Ni ferrite nanomaterials exhibit a mostly superparamagnetic behaviour in all samples, registering a reduction of the values of magnetisation saturation by increasing the Cu content. Transmission Mössbauer spectroscopy performed on these nanomaterials evidenced a gradual lowering of the Fe fraction occupying the octahedral sites and a consequent increment of the Fe fraction in the tetrahedral sites. Quantitative analysis confirms the gradual reduction of the Ni content within the ferrite samples, coupled with the opposite increment of the Cu content, whereas the Fe content is lower in the case of Ni75-Cu25 sample. This particular behaviour can be associated with the influence of Cu substitution in the Ni ferrite structure, with preferential replacement of Fe from the octahedral B-sites toward the tetrahedral A-sites.

Fascinating study of elastic, FTIR, and antimicrobial properties of silver nanochromite at different annealing temperatures

AbstractIn this work, Ag0.5Cr2.5O4 nanochromite is fabricated utilizing a simple process (flash technique) at various annealing temperatures (room and 900 °C). The particle sizes of the materials under study were shown to be in the nanoscale range by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). Fourier transform infrared (FTIR) analysis was performed to verify the fabrication of the examined nanosamples and evaluate the bands behavior. The tetrahedral A-site (622.9 cm−1 for room temperature, 630.6 cm−1 for 900 °C) and the octahedral B-site (557.3 cm−1 for room temperature, 563.1 cm−1 for 900 °C) were the two prominent bands measured by FTIR analysis. The elastic characteristics of Ag0.5Cr2.5O4 nanoparticles were examined using FTIR measurements, revealing that the interatomic bonding of the atoms at 900 °C is higher than at room temperature. In addition, the elastic characteristics may be understood by analyzing the transverse and longitudinal velocities. Both Gram-positive and Gram-negative bacteria were effectively inhibited by the samples evaluated for antibacterial properties; however, neither sample showed any antifungal activity. Therefore, it is highly suggested that the investigated samples could be used in different applications, particularly biological ones.

Surface Phase Conversion in a High-Entropy Layered Oxide Cathode Material

High-entropy transition-metal oxides are potentially interesting cathode materials for lithium-ion batteries, among which high-entropy layered oxides are considered highly promising because there exist two-dimensional ion transport channels that may, in principle, enable fast ion transport. However, high-entropy layered oxides reported to date exhibit fast capacity fading in initial cycles and thus are hardly of any practical value. Here, we investigate the structural and property changes of a five-element layered oxide, LiNi0.2Co0.2Mn0.2Fe0.2Al0.2O2, using electrochemical and physical characterization techniques. It is revealed that the M3O4 phase formed at the surface of LiNi0.2Co0.2Mn0.2Fe0.2Al0.2O2 due to the migration of metal ions from octahedral sites of the transition-metal layer to tetrahedral 8a and octahedral sites of the lithium layer hinders the intercalation of lithium ion, which leads to the low initial Coulombic efficiency and fast decay of reversible capacity. This mechanism could be generally applicable to other high-entropy layered oxides with different elemental compositions.

Influence of Elastic and Optical Properties on AgFeO2 and AgCrO2 Delafossite to be Applied in High-Frequency Applications

Nanometric AgFeO2 and AgCrO2 delafossite were easily prepared by the flash auto-combustion method. The two main bands estimated from FTIR (Fourier-transform infrared) analysis were the tetrahedral A-site (573 cm−1 for AgFeO2, 630 cm−1 for AgCrO2) and the octahedral B-site (484 cm−1 for AgFeO2, 595 cm−1 for AgCrO2). This study is mainly focused on the elastic properties evaluated from the FTIR analysis and showed that AgCrO2 delafossite is more elastic than AgFeO2 delafossite. The elastic properties can be explained by studying the longitudinal and transverse velocities. Owing to the optical properties results, AgCrO2 delafossite is a promising material to be applied in optical devices. However, AgFeO2 delafossite is a promising material in magnetic applications because it showed a large switching field distribution by 9-fold more than that of AgCrO2 delafossite. Moreover, high-frequency applications were calculated from the magnetic analysis and showed that both samples could be applied in ultra-high microwave applications.

Highly active urchin-like MCo2O4 (M = Co, Cu, Ni or Zn) spinel for toluene catalytic combustion

MCo2O4 (M = Co, Cu, Ni or Zn) spinel catalysts have been prepared using a chemical co-precipitation method and applied in toluene combustion. The physicochemical properties of the MCo2O4 catalysts was discussed to explore the impact of substitution on the tetrahedral A-site ions. The results of the activity evaluation show that the catalytic performances of Co3O4, CuCo2O4 and NiCo2O4 with urchin-like morphology are far superior than ZnCo2O4 nanoparticles. The CuCo2O4 catalyst exhibited the mostsuperior performance for toluene combustion, and the toluene conversion rate reached 90% at 230 °C. When compared to the other catalysts, the optimal activity of CuCo2O4 was attributed to the presence of more reactive oxygen species, a higher concentration of Co3+ ions on catalyst surface and better reducibility at relative lower temperature. Moreover, the catalytic activity of the CuCo2O4 catalyst did not decrease significantly in the long-term test, demonstrating its excellent stability.

Cobalt content dependences of cationic distribution and local fields in CoxFe3−xO4—Hyperfine interaction studies

Co content (x) dependences of cationic distribution and local fields at the tetrahedral A-site and octahedral B-site nuclei in Co ferrites, CoxFe3−xO4 (x = 0–1.0), were investigated by means of hyperfine interaction techniques. A combined investigation by 57Fe transmission and 57Co emission Mössbauer spectroscopies revealed that about 6% of Co2+ ions occupy the A sites for the sample with Co contents of x = 0 and 1.0. This observation evidently suggests that the site selectivity of Co2+ ions is independent of x for samples prepared on the same heat treatment condition. For hyperfine interaction parameters, obvious x dependence was observed for the B-site Fe nuclei, reflecting variation of the atomic ratio of Fe3+/Fe2+ changing with x, whereas for the A-site Fe nuclei, the parameters hardly change along with x. Contrary to the x-independence for the A-site Fe nuclei, however, it was demonstrated by perturbed angular correlation spectroscopy with the nonmagnetic probe 111Cd(←111In) that the hyperfine field at the A site significantly changes along with x. These contradictory results on the A-site fields verify that the nonmagnetic probe can distinguish a subtle change in the local fields with higher sensitivity.

Effects of cobalt doping on structural, optical, electrical and electrochemical properties of Li4Ti5O12 anode

Cobalt-doped Li4Ti5O12 (LTO) i.e Li4Ti5−xCoxO12 (x = 0, 0.05, 0.1, 0.15, 0.2) powders have been synthesized by solid state reactions and examined for effects of Cobalt (Co) concentration on structural, optical, electrical and electrochemical properties of LTO. X-ray diffraction (XRD), Raman spectroscopy and field-emission scanning electron microscopy (FESEM) evaluate phase composition and morphology of samples. Optical study reveals reduction in bandgap Eg of LTO from 3.4 to 2.7 eV for x = 0.15, with Eg extension into visible region around 515–740 nm due to increased conduction electrons and energy levels from 3d7 orbitals of Co and induced oxygen vacancies. Electronic conductivity of sample with x = 0.15 increases by 104 as compared to LTO due to conversion of Ti4+ to Ti3+ ions and increased Ti4+-Vo-Ti3+ hopping centers. Ionic conductivity and diffusivity increase upto 2.0×10−7Scm−1 and 4.6×10−12cm2s−1 for x = 0.15, owing to increased lattice spacing by substitution of Ti4+ with Co2+. Frequency dependent conductivity suggests hopping of Li+ ions as dominant conduction in LTO. Thermally activated Li+ ions follow different conduction mechanisms in different temperature regimes. Low activation energies Ea of 0.3–0.5 eV indicate conduction of ions through interstitial pathways i.e 8a-16c-8a. High Ea of 0.7–1.15 eV suggest hopping of ions through vacancy/defect mediated channels or other long routes. Electrochemical tests demonstrate unexpected degradation in electrochemical performance for dilute dopant concentration; x = 0.05 and 0.1, as compared to LTO, which is attributed to substitution of Co2+ ions at Li+ tetrahedral (8a) sites. However, for x = 0.15 electrochemical activity gets better indicating substitution of more of Co2+ ions at Ti4+ octahedral sites.

Cation distribution and bond energy of intermediate spinel Mg(Zn0.5Ti0.5)2xGa(2−2x)O4 microwave dielectric ceramics

Substitution of Ga3+ by [Zn0.5Ti0.5]3+ in MgGa2O4 improved the comprehensive properties of the resultant spinel. A continuous solid solution with a spinel structure was formed in Mg(Zn0.5Ti0.5)2xGa(2−2x)O4 (0 ≤ x ≤ 1); here, Zn2+ occupied the tetrahedral 8a site while Ti4+ occupied the octahedral 16d site, resulting in a decrease in the degree of inversion λ from 0.86 to 0. The optimal sintering temperature decreased from 1460 °C to 1220 °C, and the dielectric constant (εr) increased from 8.8 to 14.9; these changes could be ascribed to the greater polarizability of [Zn0.5Ti0.5]3+ relative to that of Ga3+. The temperature coefficient of resonant frequency (τf) of the material remarkably increased from −64.1 ppm/°C to −16.8 ppm/°C, which may be attributed to the increase in dielectric polarizability/molecular volume, bond energy, and bond valence in B-sites. The high-quality factor (Q × f) slightly decreased from 89,253 GHz to 73,432 GHz with decreasing λ and packing fraction. Optimal microwave dielectric properties were obtained from the sample with x = 1 and sample sintered at 1220 °C; in this case, εr = 14.9, Q × f = 73,432 GHz, and τf = −16.8 ppm/°C.

Steering of Magnetic Interactions in Ni0.5Zn0.5Fe2–x(Mn)xO4 Nanoferrites via Substitution-Induced Cationic Redistribution

Ni0.5Zn0.5Fe2O4 is one of the most versatile and technologically indispensable soft magnetic materials; however, a detailed investigation on the effect of substitution-induced cation redistributionon the magnetic and ferromagnetic resonance (FMR) properties of Ni–Zn-nanoferrites (NFs) remains elusive. Herein, we demonstrate that the modulation of the superexchange interactions via dopant-driven cationic redistribution is an efficient way to maneuver the static and dynamic magnetic properties of Mn-substituted Ni0.5Zn0.5Fe2–x(Mn)xO4 NFs. Employing a combination of Raman and X-ray photoelectron spectroscopies, the effect of Mn-doping on cation distribution is revealed. It was found that Mn2+ cations initially occupy tetrahedral A-sites; however, as substitution of Mn increases from Mn = 0.1 to 0.5, the higher percentage of Mn-cation exhibits the Mn3+ oxidation state and preferably occupies the octahedral B-sites. The Mössbauer study elucidates that the Fe3+–O–Mn2+ superexchanges are weaker than the Fe3+–O–Fe3+ superexchange. We demonstrate that the Mn-substitution-driven redistribution of cations is responsible for the remarkable decrease in magnetocrystalline anisotropy. Composition-dependent FMR studies reveal that the substitution of the Fe3+ cation by the Mn2+ cation weakens the magnetic coupling, causing shifts in the FMR relaxation frequency. The analysis of magnetic relaxation suggests that there are two kinds of interparticle interactions present in these NFs, namely, dipolar interaction and the surface spin interaction (broken superexchange). The superparamagnetic NFs with Mn = 0.1 substitution exhibit a magnetization value as high as 58 emu/g along with a very low coercivity of ∼20 Oe, making them an excellent candidate for a broad range of technological applications.

One-pot Cajanus cajan (L.) Millsp. leaf extract-mediated preparation of MgFe2O4 nanoparticles: Optical, structural, morphological and particle size analyses

In this study, MgFe2O4 nanoparticles were successfully prepared through one-pot synthesis using Cajanus cajan (L.) Millsp. Leaf extract (CLE) as a source of weak bases and stabilizing agents. The optical property, structure, morphology, and particle size of the nanoparticles were analyzed. Several characterizations were performed to investigate the formation of nanoparticles. The absorption peaks at 576 cm−1 and 427 cm−1 were attributed to Mg–O vibration stretching at the tetrahedral (8a) site and Fe–O vibration stretching at the octahedral site (16d) of MgFe2O4 spinel structure, respectively. The most prominent diffraction pattern of MgFe2O4 with a spinel structure was found at 2θ = 35.55 in the crystal plane (311). The optical bandgap of MgFe2O4 was obtained to be 2.12 eV. The values of Hc, Mr, and Ms were 110.38 Oe; 1.4 emu/g; and 13.74 emu/g, respectively. All characterizations are in good agreement that MgFe2O4 nanoparticles were formed with a spherical shape with a particle size distribution of approximately 12–20 nm. Importantly, we designed a simple, cost-effective, and eco-friendly approach for synthesizing MgFe2O4 nanoparticles.

Effect of coordination environment on the localization behavior and band tail states of Zn0.7In0.3Fe2O4 and Zn0.3In0.7Fe2O4 nanoparticles

The interplay of the coordination environment and localization behavior in ferrites is one of the fascinating and least discussed problems. We report on the effect of the coordination environment on the localization behavior, band tail states, and the optical constants in the UV–Vis regime. X-ray diffraction data confirm the spinal structure with general formula AB2O4. Mossbauer spectroscopy data confirm the existence of Fe ion in the + 3 oxidation state occupying both the tetrahedral and octahedral positions. The Indium (In3+) ions prefer to reside in the tetrahedral A-site. Incorporation of excess In3+ ions causes excess migration of Fe+3 ions to the octahedral B-site and results in the t2g orbital splitting. This lowers the octahedral symmetry from FeO6 to FeO5 dominant coordination environment, which has a strong impact on the magnetic and optical behavior. UV–Vis diffuse reflectance spectroscopy was employed to determine the bandgap and band tail states, which are the key parameters in understanding the localization behavior.

Influence of gadolinium (Gd3+) ion substitution on structural, magnetic and electrical properties of cobalt ferrites

In present work, CoFe2-xGdxO4 nanoparticles with compositions x = 0.0, 0.02, 0.04, 0.06, 0.08 and 0.1 were successfully synthesized by a sol-gel auto-combustion route sintered at 700 °C for 5 h. The effect of Gd3+ substitution on structural, morphological, magnetic and dielectric properties has been investigated. The X-ray diffraction with Rietveld refinement reveals that Gd-substituted Co-ferrites are prepared in a single-phase cubic spinel structure. Fourier transform infrared and Raman spectra confirm the single-phase formation of cubic spinel structure. It is observed that the lattice constants decrease from 8.3776 to 8.3711 Å with the substitution of Gd composition from x = 0.0 to 0.1. This is because of the distortion of the lattice structure with the introduction of Gd3+ ions. The crystallite size calculated from X-ray diffraction decreases from 29 to 19 nm with Gd3+ composition which confirms the formation of nanocrystalline samples. These values are good agreement with crystallite size calculated by the Williamson Hall method. The distribution of cations among the octahedral B and tetrahedral A-site was estimated by the computational method. Field emission scanning electron microscopy (FE-SEM) also confirmed the nanostructural nature in the range of 200–300 nm. Energy dispersive analysis (EDAX) proves chemical purity and stoichiometry. Fourier transform infrared spectra show the main vibration band of spinel structure. Gd-doped Co-ferrite shows the characteristics Raman active modes of spinel structure. Magnetic study reveals that saturation magnetization decreases from 77.37 to 51.38 emu/g with an increase of Gd composition in cobalt ferrites. It is observed that the coercivity of samples is increased from 976 to 1281 Oe with Gd substitution. Dielectric properties measured from LCR-Q meter exhibits the Maxwell–Wagner model.

Structural Properties and Cation Distribution in Co2+ and Ho3+ Ions Induced Nanocrystalline ZnFe2O4

Nanocrystalline CoyZn1-yHozFe2-zO4 (where y = 0.0, 0.25, 0.5, 0.75, 1.00 and z=0.0, 0.03, 0.06, 0.08, 0.1) ferrites were prepared by sol-gel auto combustion method at pH of 8. Samples were obtained by annealing at relatively low temperature 600 °C for 4 h and characterized by thermo gravimetric/differential thermal analysis (TG/DTA) all the samples were annealed at 600 °C for 4 h. The prepared samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. Particle size measured from XRD and TEM are in good agreement with each other. The TEM study reveals the fine particle nature of the ferrites with little agglomerations. The cation distribution suggests that Zn2+ ion mainly on tetrahedral-A sites, Ho3+ ions shows strong preference towards octahedral-B site, Co2+ and Fe3+ ions are randomly distributed at the tetrahedral-A and octahedral-B site. FT-IR study confirmed two main absorption bonds in the frequency range 400-600 cm-1, assigned due to the tetrahedral-A and octahedral-B stretching vibrations.

Structural, optical, elastic and magnetic properties of Ce and Dy doped cobalt ferrites

Abstract The CoCexDyxFe2-2xO4 (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05) have been prepared by sol-gel auto-combustion technique. The structural result confirmed the formation of single phase cubic spinel structure showed by XRD. Crystallite size obtained from the XRD is in the range of 24–28 nm, whereas particle size obtained from the transmission electron microscopy is in the range of 20–30 nm. It is also found that the cation distribution of CoCexDyxFe2-2xO4 resulted in the Fe3+ and Co ions occupy both tetrahedral A-site and octahedral B-site, whereas Ce and Dy cation distributed in both of them. The photoluminescence (PL) analysis reveals that all prepared samples contain four bands; (i) peak centered at 412 nm corresponding to ultraviolet (UV) band i.e. near band edge emission, (ii) a high intensity peak centered at 434 nm belonging to violet band, (iii) a low intensity and sharpness peak positioned at 466 nm refers to blue band, and (iv) a broad and very low intensity peak observed at 502 nm assigned to green band. FTIR results of the prepared samples showed that two vibration bands between 600 cm−1 and 400 cm−1 belonging to the stretching vibration of tetrahedral metal-oxygen bond (vA) and stretching vibration of octahedral site (vB) respectively. Mossbauer spectroscopy has also been performed to investigate the hyperfine structure of undoped, Ce and Dy co-doped cobalt nano ferrites. The higher values of MS and Hhf for x = 0.01 composition can be attributed to the occupation of Dy3+ ions in octahedral site whereas the Ce3+ ions occupied to tetrahedral site.

Structural Peculiarities and Thermoelectric Study of Iron Indium Thiospinel.

The homogeneity range of ternary iron indium thiospinel at 873 K was investigated. A detailed study was focused on two distinct series (y=z): 1) a previously reported charge‐balanced (In0.67+0.33y□0.33−0.33y)tetr[In2−zFez]octS4 (A1‐series; □ stands for vacancy; the abbreviations “tetr” and “oct” indicate atoms occupying tetrahedral 8a and octahedral 16d sites, respectively) and 2) a new charge‐unbalanced (In0.67+y□0.33−y)tetr[In2−zFez]octS4 (A2‐series). Fe atoms were confirmed to exclusively occupy an octahedral position in both series. An unusual reduction of the unit cell parameter with increasing Fe content is explained by differences in the ionic radii between Fe and In, as well as by an additional electrostatic attraction originating from charge imbalance (latter only in A2‐series). The studied compound is an n‐type semiconductor, and its charge carrier concentration increases or decreases for larger Fe content within the A1‐ and A2‐series, respectively. The thermal conductivity κ tot is significantly reduced upon increasing vacancy concentration, whereas the change of power factor is insufficient to drastically improve the thermoelectric figure of merit.

Impact of rare earth europium (RE-Eu3+) ions substitution on microstructural, optical and magnetic properties of CoFe2−xEuxO4 nanosystems

In this study, pure cobalt ferrite (CoFe2O4) nanoparticles and europium doped CoFe2O4 (CoFe2−xEuxO4; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe3+) ions by trivalent rare earth europium (RE-Eu3+) ions on the microstructure, optical and magnetic properties of the produced CoFe2O4 nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu2O3 phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ1 and υ2) and tetrahedral A-site (υ3) around 415 cm−1, 470 cm−1 and 600 cm−1 respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu3+ ions within CoFe2O4 host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu3+ added to CoFe2O4 in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe2−xEuxO4, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe2O4 have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu3+ in CoFe2O4 lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe2O4 samples. Substitution of Fe3+ ions in CoFe2O4 nanoparticles with RE-Eu3+ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.

The influence of cationic surfactant CTAB on optical, dielectric and magnetic properties of cobalt ferrite nanoparticles

In the present work, the influence of cationic surfactant CTAB (cetyltrimethylammonium bromide) on size, shape and coalescence behaviour of cobalt ferrite nanoparticles (CFNPs) synthesized via hydrothermal method is reported. Pure CFNPs show no additional peaks, whereas α-Fe2O3 phase is observed in CTAB added CFNPs upon annealing. FT-IR analysis confirms the formation of M − O vibrational bands (metal -oxygen) at tetrahedral A-site and octahedral B-site for both samples. SEM observations reveal less agglomeration and smaller particle size for surfactant added CFNPs. Raman spectral study confirms the formation of cubic spinel structure and Raman active modes of CTAB added CFNPs. UV–Vis spectra indicate a decrease in the energy band gap with annealing. The dielectric constant of surfactant added CFNPs decreases with increasing applied frequencies for both real and imaginary, but ac conductivity increases with increasing frequencies. Two sextet patterns of Fe3+ trivalent ions from tetrahedral and octahedral sites are observed in Mössbauer spectra. VSM study indicate the ferrimagnetic nature of CTAB added CFNPs. The electrochemical analysis reveals the pseudocapacitive nature of working electrode prepared by CTAB added CFNPs.