Structural, Magnetic, and Optical Properties of Zinc- and Copper-Substituted Nickel Ferrite Nanocrystals

Ferrite nanocrystals are an interesting material due to their rich physical properties. Here we add non-magnetic dopants Zn and Cu to nickel ferrite nanocrystals, Ni_1?x M _x Fe₂O₄ (0??x??1, M=Cu, Zn), and study how relevant properties of the samples are modified accordingly. Basically, these dopings cause a rearrangement of Fe⁺³ ions into the two preexisting octahedral and tetrahedral sites. In fact, this, we show, induces pertinent magnetic properties of the doped samples. In the case of the Cu-doping, the Jahn?CTeller effect also emerges, which we identify through the Fourier Transform Infra-Red Spectroscopy of the samples. Moreover, we show an increase in the lattice parameters of the doped samples, as well a superparamagnetic behavior for the doped samples is shown, while the Jahn?CTeller effect precludes a similar behavior in the CuFe₂O₄ nanocrystals. The influences of Zn and Cu substitutions are investigated on the optical properties of nickel ferrite nanocrystals by photoluminescence measurement at room temperature.     

Sintering and properties of SrBi2(Ta1−x V x )2O9 ceramics

The effects of vanadium doping on the sintering, microstructure, dielectric properties, and ferroelectric properties of SrBi₂(Ta_1–x V _x )₂O₉ ceramics were investigated. The densification and grain-growth processes of the vanadium doped ceramics were shifted to a lower temperature range. For the ceramics with relative density 90%, the dielectric constant is 120–125 and 100–130 for the undoped and doped ceramics, respectively, and the dielectric loss tangent is below 1%. As compared with the undoped ceramics, the ferroelectric properties can be significantly improved by doping with an appropriate amount of vanadium and sintering at 1000°C. The variations of dielectric and ferroelectric properties are influenced by the incorporation of vanadium into crystal lattice and several microstructural factors.     

Effect of annealing conditions and concentration of oxygen vacancies on vanadium doped SrBi2Ta2O9

This paper studied the annealing effects on the dielectric characteristics of vanadium doped SrBi₂Ta₂O₉ (SBT). SBT was synthesized at 1000 °C and vanadium doped SBT at 900 °C by solid-state reaction. Crystallization structure and phase purity of the prepared ceramic samples was observed by X-ray diffraction analysis. XRD analysis indicated a single layered perovskite structure without any secondary phases up to 15% of vanadium doping in SBT ceramics. Detailed dielectric study on vanadium doped SBT ceramics indicated that post-sinter annealing enhances the peak dielectric permittivity, which is attributed to the increased homogeneity in the system at atomic scale upon annealing. Annealing for larger time interval suppresses the permittivity growth beyond transition temperature which gives a direct evidence for the existence of lower valance state of vanadium (V⁺⁴) in as-sintered SBTV ceramics and also the permittivity growth is related to the oxygen ions or oxygen vacancies created during sintering. UV–Vis spectroscopy was also performed to confirm the lower valance state of the vanadium ions in the ceramics.     

Effects of Gd2O3 on structure and magnetic properties of Ni-Mn ferrite

The emulsion method was used to prepare nanocrystalline Ni_0.7Mn_0.3Gd _x Fe_2-x O₄ ferrites. The growth of particles, the structure and the magnetic properties were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Furthermore, the influence of Gd₂O₃ on magnetic properties of Ni-Mn ferrite powders has been investigated in detail. When the crystallite sizes are about 30–40 nm, all the samples have the similar Ms values. The variational rules of saturation magnetization (Ms) and coercivity (Hc) along with doped-Gd contents at different sintering temperatures show that the maximum Gd ions content doped into ferrite lattices is x = 0.06. When Gd-doped content x is larger than 0.06, the doped Gd ions can’t enter into the ferrite lattice totally but reside at grain boundary, as the ionic radii of the Gd³⁺ ions are larger than that of Fe³⁺ ions. The ferrimagnetism have not disappeared completely, even if the crystallite size is 7.8 nm.     

Effect of W ion doping on magnetic and dielectric properties of Ni-Zn ferrites by “one-step synthesis”

W-doped Ni-Zn ferrites with a nominal composition of Ni_0.5Zn_0.5W_xFe_2−xO₄ (where x = 0, 0.02, 0.04, 0.06, and 0.08) were prepared by one-step synthesis through the incorporation of WO₃ into the raw powders. The magnetic and dielectric properties of the as-prepared Ni-Zn ferrites were investigated. All samples have a typical spinel cubic structure. With increasing amount of W ions doped, the lattice constant decreases, while the grain size increases. The density and diameter shrinkage of the samples raise with small amount of W ions doped, but drop down with large amount of W ions doped. However, an uneven abnormal growth and closed pores were observed when too much of WO₃ was added. The saturation magnetization of the samples increases with small amount of W ions doped, but decreases with large amount of W ions doped, and the coercivity shows an opposite trend. The Curie temperature raises with increasing amount of W ions doped. Both the real and imaginary parts of permeability of the ferrites decrease with increasing amount of W ions doped, while the natural resonance changes very little. Both the dielectric constant and dielectric loss present a decrease with small amount of W ions doped, but increase with large amount of W ions doped.     

The evolution of structure and properties in GdMn(1−x)TixO3 ceramics

In this work, the effects of Ti doping on the microstructure, dielectric, and magnetic properties of GdMn_(1?x)Ti_xO₃ (x?=?0.00–0.15) ceramic samples synthesized using a solid-state reaction were investigated. All the experimental samples formed a single-phase structure, and no structural transformation occurred within the experimental doping range; however, Ti doping caused lattice shrinkage. Ti doping reduced the grain size, and the microstructure of the synthesized samples appeared more compact in scanning electron microscopy images. The lattice distortion of GdMn_(1?x)Ti_xO₃ caused by Ti substitution at the Mn sites resulted in changes in the Raman vibration modes. X-ray photoelectron spectroscopy results showed that the valence state transition of the Ti and Mn ions occurred and the concentration of Ti⁴⁺, Mn³⁺ ions and oxygen vacancies changed due to the charge compensation induced by Ti doping. Ti doping had a significant influence on the size and concentration of cation vacancies in the GdMn_(1?x)Ti_xO₃ samples. Appropriate Ti doping was shown to reduce the dielectric loss, improve the frequency stability of the dielectric constant, and significantly affect the long-range ordering of Gd³⁺ magnetic moments and clearly reduce magnetization.

     

Electrical Properties of Nanophase Ferrites Doped with Rare Earth Ions

The electrical properties of nanocrystalline nickel ferrites doped with rare earth ions having a general chemical formula Ni _x Fe _(3?x)O₄ have been studied. The AC electrical conductance has been measured as a function of frequency in the range of 0.05–900 kHz at room temperature of 296 K. The conductance was found to be dependent on concentration of nickel ions. Doping of these samples with rare earth ions has shown a change in the electrical conductance. The results are discussed in the light of a hopping model.     

Anomalous electrical properties of nanocrystalline Ni–Zn ferrite

Nanocrystalline powders of Ni–Zn ferrite (NZFO) having the chemical formula Ni _x Zn_1−x Fe₂O₄, where x varies as 1, 0.8, 0.6, 0.4, 0.2, and 0, were synthesized by chemical co-precipitation technique. The samples synthesized were characterized by X-ray diffraction (XRD) technique at several stages. As prepared samples at room temperature show absence of Bragg peak indicating that there was no crystalline phase formation of ferrite. The XRD pattern of the samples sintered at 400 °C clearly showed the characteristic Bragg peaks of spinel cubic structure. XRD patterns were further analyzed to calculate the lattice constant, porosity, and jump length of charge carriers. Electrical dc resistivity measurements were carried out with respect to temperature using two probe method. NZFO samples showed abnormal electrical behavior at room temperature. Also abnormal electrical behavior with increase in temperature in the range 600–800 K was observed. Variation of dielectric constant and loss tangent with frequency were studied at room temperature. The electrical and dielectric behavior of the Ni–Zn samples is discussed in the light of literature.     

XRD, Magnetic and M?ssbauer Spectral Studies of?Ag x Ni1?x Fe2O4 Ferrite Nanoparticles

Nanophase Ag _x Ni_1?x Fe₂O₄ (x=0,0.2) ferrites were prepared by glycothermal method. The NiFe₂O₄ (x=0) nanosized sample was also produced by high-energy ball milling for comparison of properties. Structural investigations of the samples were carried out by X-ray diffraction. The experiment reveals that pure Ag-Ni ferrite materials with grain sizes of about 8 nm can be obtained after annealing at relatively low temperature of about 500?°C. The nanosized compounds produced by glycothermal reaction indicate superparamagnetic behavior. A higher value of coercive field (910 Oe) is observed in x=0 milled sample with similar particle size. The zero field cooled (ZFC) and field cooled (FC) magnetization measurements reveals spin glass like behavior of the nanosized compounds.     

Dielectric properties of Al-substituted Co ferrite nanoparticles

A series of polycrystalline spinel ferrites with composition, CoFe_2−x Al _x O₄ (0 ≤ x ≤ 1), have been synthesized by sol-gel method. The effect of Al-substitution on structural and dielectric properties is reported in this paper. X-ray diffraction analysis revealed the nanocrystalline nature in the prepared ferrite samples. The particle size, D, decreases with increase in Al-content. The lattice parameter, a and X-ray density, d _x , decreased with increase in Al-content. The dielectric properties for all the samples have been studied as a function of frequency in the range 100 Hz–10 MHz. Dielectric properties such as dielectric constant, ɛ′, dielectric loss, ɛ″ and dielectric loss tangent, tan δ, have been studied for nanocrystalline ferrite samples as a function of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrites proposed by this technique possess lower value than that of the ferrites prepared by other methods for the same composition. The low dielectric behaviour makes ferrite materials useful in high frequency applications.     

Electrical and dielectric properties of nano crystalline Ni–Co spinel ferrites

Nanocrystalline samples of Ni_xCo₁–_xFe₂O₄, where x = 1, 0.8, 0.6, 0.4, 0.2 and 0, were synthesized by chemical co-precipitation method. The spinel cubic phase formation of Ni–Co ferrite samples was confirmed by X-ray diffraction (XRD) data analysis. All the Bragg lines observed in XRD pattern belong to cubic spinel structure of ferrite. Scanning Electron Microscopy (SEM) technique was used to study the surface morphology of the Ni–Co ferrite samples. Nanocrystalline size of Ni–Co ferrite series was observed in SEM images. Pellets of Ni–Co ferrite were used to study the electrical and dielectric properties. The resistivity measurements were carried out on the samples in the temperature range 300–900 K. Ferrimagnetic to paramagnetic transition temperature (T_c) for all samples was noted from resistivity data. The activation energy below and above T_c was calculated. The dielectric constant (ɛ′) measurements with increasing temperature show two peaks in the temperature range of measurements for all samples under investigation. The peaks observed show frequency and compositional dependences as a function of temperature. Electrical and dielectric properties of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples show unusual behavior in temperature range of 500–750 K. To our knowledge, nobody has discussed such anomalies for nanocrystalline Ni_xCo₁–_xFe₂O₄ at high temperature. Here, we discuss the mechanism responsible for electrical and dielectric behavior of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples.     

Effect of Ce Doping on the Magnetic Properties of NiFe2O4 Nanoparticles

In the present work, effect of different concentration of Ce ions on the magnetic properties of nickel ferrite nanoparticles is discussed. A series of NiCe _x Fe_2?x O₄ (x=0.0–0.10) samples were prepared by a chemical route. XRD patterns show that all the samples are in pure spinel phase except that with x=0.10. This indicates that rare earth ions have limited solubility in the spinel lattice. Magnetic properties are studied by electron paramagnetic resonance spectroscopy (EPR) and the results are explained in terms of a magnetic moment obtained by a vibrating sample magnetometer. Mössbauer spectroscopy was performed to have an idea about the distribution of ions between the tetrahedral and octahedral sites. Magnetic moment is found to decrease after doping with Ce ions. It was found that the samples show mixed spinel nature rather than the pure inverse character. Doping with Ce ions reduces the EPR linewidth of pure nickel ferrite, which indicates that eddy current losses are reduced.     

Synthesis,structural and optical characterization of Ni-doped ZnO nanoparticles

Nanocrystalline Zn_1−x Ni _x O (x = 0.00, 0.02, 0.04, 0.06, 0.08) powders were synthesized by a simple sol–gel autocombustion method using metal nitrates of zinc, nickel and glycine. Structural and optical properties of the Ni-doped ZnO samples annealed at 800 °C are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis using X-rays (EDAX), UV–visible spectroscopy and photoluminescence (PL). X-ray diffraction analysis reveals that the Ni-doped ZnO crystallizes in a hexagonal wurtzite structure and secondary phase (NiO) was observed with the sensitivity of XRD measurement with the increasing nickel concentration (x ≥ 0.04). The lattice constants of Ni-doped ZnO nanoparticles increase slightly when Ni²⁺ is doped into ZnO lattice. The optical absorption band edge of the nickel doped samples was observed above 387 nm (3.20 eV) along with well-defined absorbance peaks at around 439 (2.82 eV), 615(2.01 eV) and 655 nm (1.89 eV). PL measurements of Ni-doped samples illustrated the strong UV emission band at ~3.02 eV, weak blue emission bands at 2.82 and 2.75 eV, and a strong green emission band at 2.26 eV. The observed red shift in the band gap from UV–visible analysis and near band edge UV emission with Ni doping may be considered to be related to the incorporation of Ni ions into the Zn site of the ZnO lattice.     

Effect of vanadium doping on the electric properties of barium titanate hafnate ceramics

Pure and V-doped barium titanate hafnate (BaHf_0.1Ti_0.9O₃, short for BHT) ceramics were prepared by sol–gel method. The microstructures, dielectric and ferroelectric properties of BaHf_0.1V _x Ti_0.9?x O₃ (x = 0, 0.02, 0.05, 0.08, 0.1) ceramics have been investigated. From the X-ray patterns it implies that V⁵⁺ ions have entered the unit cell maintaining the perovskite structure of solid solution. The a-axis and c-axis lattice constants gradually increase and the tetragonality gradually decreases with the increasing of vanadium content. The content of vanadium has an inconspicuous effect on the grain size and the Curie temperature. The addition of vanadium can decrease the dielectric loss of BHT ceramics. It is found that well-behaved hysteresis loops can be observed in all samples at room temperature. The coercive electric field gradually decreases and then increases with the increasing of vanadium content.     

Characterization of Nano-Particle Co<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> Synthesized Using Alove Vera Gel

Nano-particle Co_1?x Zn _x Fe₂O₄ (x = 0.0, 0.3, 0.5, 0.7, and 1.0) samples were prepared via combustion route using Alove Vera Gel. XRD, IR, and SAED analysis represents single-phase formation of ferrite samples, and nano-sizes of the particles in the range of 6 to 13 nm were confirmed using XRD data and TEM images. Decrease in lattice constant with increasing Zn content reflects formation of compositionally homogeneous samples. Dielectric constant and dielectric loss study showed promising results. The room temperature Mossbauer spectrum showed mixed superparamagnetic and ordered ferromagnetic behavior. The possible modification in the cation distributions was seen in the nano-particle ZnFe₂O₄ sample obtained in the present work compared to conventional bulk samples.     

Superparamagnetic Behavior of Zinc-Substituted Nickel Ferrite Nanoparticles and its Effect on Mossbauer and Magnetic Parameters

Zinc-substituted nickel ferrite (Ni _1?x Zn _x Fe ₂ O ₄ with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) nanoparticles were synthesized by solgel auto-combustion technique at low temperature and characterized by using X-ray diffraction, scanning electron microscopy, pulse field hysteresis loop technique, and Mossbauer spectroscopy. X-ray diffraction studies confirmed the formation of single-phase spinel structure of the prepared ferrite samples with average crystallite size of 30 nm, very close to that of the critical size for nanoparticles exhibiting superparamagnetism. Scanning electron micrographs of the ferrite samples showed uniform spherical morphology of nanograins with homogenous microstructure. Further investigations on magnetic properties by pulse field hysteresis loop technique and Mossbauer spectroscopy indicated the presence of superparamagnetic phases in the ferrite samples attributed to occupation of octahedral [B] sites by zinc ions in these Ni–Zn samples and also to the nanometer sizes of the ferrite particles. Magnetic behavior of the Ni–Zn ferrite system is in agreement, initially, with Neel’s two-sublattice collinear model and then with the Yafet–Kittel model for samples with higher zinc content (x ≥ 0.4). Value of hyperfine splitting is found to decrease with increase in zinc content and is attributed to the reduction in particle size giving rise to superparamagnetism. Other Mossbauer parameters like quadrupole splitting and the isomer shift are within the reported range for those of ferrites with spinel structure.     

The effect of Ti<Superscript>4+</Superscript> ions and gamma radiation on the structure and electrical properties of Mg ferrite

Ferrite samples of the general formula Mg_1+x Ti _x Er _y Fe_2−2x−y O₄; 0.1 ≤ x ≤ 0.9, y = 0.025 were prepared using the standard ceramic method. The final sintering temperature was 1,200 °C with heating rate 4 °C/min during 100 h. X-ray diffraction analysis was carried out to assure the formation of the spinel structure. The effect of Ti⁴⁺ ion concentration on the structural and the electrical properties of the investigated samples is studied. It change the iron ion concentration from 2 to 2−2x thereby decreasing the number of ferrous ions on octahedral sites, with a consequent decrease the dielectric constant. The most important result of γ-irradiation on the electrical properties is the change of ratio on the octahedral site leading to increase the conductivity as well as the dielectric constant. The variation of the thermoelectric power with a temperature is performed, the common feature of all compositions is the fluctuation of Seebeck coefficient between positive and negative over the whole range of temperature. This indicates that the charge carriers are electrons and holes, depending on both the temperature range and the additive in the ferrite samples.     

Effect of rare earth yttrium substitution on the structural,dielectric and electrical properties of nanosized nickel aluminate

In this communication, we have systematically investigated the effect of yttrium substitution on the structural, dielectric and electrical properties of nanosized NiAl_2−2xY_2xO₄ series (where x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.07 and 0.10). All the samples were prepared by chemical coprecipitation method. Powder X-ray diffraction (XRD) confirmed the formation of single phase cubic spinel structure in all the samples. Replacement of Al³⁺ ions by Y³⁺ ions results in a slight increase of lattice parameter. It was inferred that the substitution of yttrium suppressed the crystallite size growth. Transmission electron microscopy (TEM) validated the nanocrystalline nature of the samples. The Fourier transform infrared spectroscopy (FTIR) confirmed the preference of Y³⁺ ions at the octahedral B site. Room temperature dielectric properties, namely dielectric constant (?′), dielectric loss (tan δ), ac conductivity (σ_a.c.) and electrical modulus (M″) were studied as a function of applied frequency in the range from 1 kHz to 1 MHz. These studies indicate that all the samples show usual dielectric dispersion which is due to Maxwell–Wagner type Interfacial Polarization. The ac conductivity measurement suggests that the conduction mechanism is due to small polaron hopping. The electrical modulus results clearly indicate the presence of non-Debye type of dielectric relaxation in all the samples. The dc electrical resistivity measured in the temperature range of 303–373 K was found to increase with temperature and yttrium content.     

Enhanced dielectric temperature stability and energy-storage properties of (Y0.5Nb0.5)4+ co-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free relaxor ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1?x(Y_0.5Nb_0.5)_xO₃ (abbreviated as BNTBT-100xYN) lead-free relaxor ceramics were designed and prepared using a traditional solid-state sintering technique. The influences of the introduction of (Y_0.5Nb_0.5)⁴⁺ complex ions for the dielectric properties and energy storage performances of BNTBT-100xYN ceramics were systematically studied. All samples exhibited a typical pseudo-cubic symmetry structure and obtained the dense microstructure with the uniform distribution of all elements. The ergodic relaxor behavior of all ceramics was observed and revealed a trend of increase as a function of composition. It accelerated the improvement of the temperature stability of the dielectric constant. All samples showed a single grain conduction mechanism and the activation energy decreased with the addition of composition. It is related to the generation of oxygen vacancies induced by the defect dipoles. BNTBT-6YN ceramic revealed excellent dielectric temperature stability within the temperature range from 87 to 479 °C and the loss tangent less than 0.05 between 25 °C and 474 °C. Besides, a high recoverable energy density of?~?0.91 J/cm³ with the corresponding efficiency of?~?78.5% at applied 115 kV/cm field was achieved for BNTBT-5YN ceramic. Hence, BNTBT-5YN and BNTBT-6YN ceramics will become one of the outstanding dielectric ceramics for the electronic components.

     

Catalytic Activity of the Spinel Ferrite Nanocrystals on the Growth of Carbon Nanotubes

We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe₂O₄) (ii) ferrite where cobalt was substituted by nickel (Ni _x Co_1?x Fe₂O₄, with x=0, 0.2, 0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc (Zn _y Ni_1?y Fe₂O₄ with y=1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray diffraction patterns show that the ferrite samples have been crystallized in the cubic spinel structural phase. We obtained the size of grains by field emission scanning electron microscopy images and their magnetic properties by vibrating sample magnetometer. Next, carbon nanotubes were grown on these nanocatalysts by the catalytic chemical vapor deposition method. We show that the catalytic activity of these nanocrystals on the carbon nanotube growth depend on cation distributions in the octahedral and tetrahedral sites, structural isotropy, and catalytic activity due to cations. Our study may have applications in finding a suitable candidate of doped ferrite nanocrystals as catalysts for carbon nanotube growth. More interestingly, the yield of fabrication of carbon nanotubes can be considered as an indirect tool to study catalytic activity of ferrites.