NiFe2O4 Ceramics Research Articles

Tuning in structural, optoelectronic, magnetic and ferroelectric properties of NiFe2O4 ceramics engineering nanomaterials by substitution of rare earth element, Pr3+ prepared by sol–gel method

Tuning in structural, optoelectronic, magnetic and ferroelectric properties of NiFe2O4 ceramics engineering nanomaterials by substitution of rare earth element, Pr3+ prepared by sol–gel method

Pseudocapacitive behavior of ferrimagnetic NiFe2O4-carbon nanotube electrodes prepared with a multifunctional dispersing agent

We investigate the pseudocapacitive properties of ferrimagnetic NiFe2O4 ceramics in a 0.5 ​M Na2SO4 aqueous electrolyte. These ceramics have a high capacitance of 2.33 Fcm−2 since a more efficient colloidal technique is applied, which enhances the current response of the electrode in the negative potential range. NiFe2O4 is co-dispersed with multiwalled carbon nanotubes (MWCNTs) using Celestine Blue (CB) dye as a multifunctional co-dispersant. The capacitance measurements are performed by cyclic voltammetry, impedance spectroscopy and galvanostatic charge-discharge. The experiments reveal the synergistic effects of NiFe2O4 and conductive MWCNTs additives and the benefit they provide through co-dispersion with CB, which acts as an electron transfer mediator, enhancing pseudocapacitance. The mass ratio of NiFe2O4 and MWCNTs in the composite electrodes is varied to optimize the capacitance enhancement, lower electrical resistance at a high active mass loading of 40 ​mg ​cm−2, and achieve favorable capacitance retention at high charge-discharge rates. The results reveal a path for the development of pseudocapacitive ferrimagnetic ceramic composites that have advanced functionality.

Role of Mg2+ and In3+ substitution on magnetic, magnetostrictive and dielectric properties of NiFe2O4 ceramics derived from nanopowders.

The effect of Mg2+ and In3+ substitution on the structural, magnetic, magnetostrictive and dielectric properties of NiFe2O4 samples derived through sintering of nanocrystalline ceramic powders is investigated. Namely, NiFe2O4, NiMg0.2Fe1.8O4 and NiIn0.2Fe1.8O4 nanopowders were synthesized by a tartrate-gel route followed by calcination at 500 °C, pelletization and sintering at 1200 °C for 2 h. The average particle size was found to decrease from ∼13 nm (for NiFe2O4) to ∼9 nm and ∼7 nm for as-synthesized Mg2+ and In3+ substituted NiFe2O4 samples (after calcination), respectively. However, after sintering a better grain growth occurs for the In3+ substituted sample, as confirmed through the microscopy and dielectric results. Due to the replacement of smaller Fe3+ cations by larger In3+ and Mg2+ cations at the tetrahedral (Td) and octahedral (Oh) interstitial positions, respectively, in the spinel structure of NiFe2O4, the lattice parameters increase in both the cases. The Td site occupation of In3+ leads to higher magnetization for the NiIn0.2Fe1.8O4 sample, but Oh site occupation of Mg2+ leads to lower magnetization for the NiMg0.2Fe1.8O4 sample, in comparison to the pure NiFe2O4 sample. Furthermore, the Curie temperatures (TC) and magnetocrystalline anisotropy constants (K1) for both the samples are considerably lower than the parent compound, with all the parameters being the lowest for the In3+ substituted sample because the Td occupation of non-magnetic In3+ drastically decreases the A-O-B magnetic superexchange interactions. The above alteration to the magnetic interactions alters the magnitude of maximum magnetostriction (λmax), which is explained based on the occupation of the Mg2+ and In3+ cations in our samples. The obtained magnetostriction properties of our samples are very useful for magnetostriction based sensor application.

Variable range hopping and modulus relaxation in NiFe2O4 ceramics

Nickel ferrite ceramics prepared from combustion derived powders have been investigated using dielectric, impedance, and modulus spectroscopy over a wide frequency (0.1 Hz–1 MHz) and temperature range (173–473 K). Step-like dielectric response ε'T,f is related to the surface barrier layer capacitor (SBLC) effect. Dielectric relaxation peaks in ε″(f) masked by the huge dielectric loss are revealed by εder″(f) derived from the ε′(f) data following Kramers – Kronig transformations. Multiple relaxations are evidenced from the asymmetric nature of εder″(f) peaks. Impedance Cole-Cole analysis reveals two relaxation processes corresponding to grain and grain-boundary effects. A maximum in the grain capacitance (Cg) at 293 K is attributed to the collective influence of electron and hole charge carriers on dielectric polarization. The modulus analysis reveals distinctly three relaxations occurring at temperatures T ≥ 323 K, and only two relaxations for T < 323 K. The variation of modulus relaxation frequencies ln(fmax) with (1/T) suggests different conduction mechanisms for temperature above and below 323 K. The two relaxations observed in the entire temperature range originate due to hopping of holes and electrons at equivalent B-sites of NiFe2O4, while the third relaxation seen only at temperatures T > 323 K is attributed to defect hopping. The present analysis based on modulus relaxation, dc conductivity, and power law exponent sT indicates two different conduction mechanisms for Nickel ferrite NiFe2O4 with variable range hopping dominating at lower temperatures, and thermally activated hopping at higher temperatures.

Magnetoelectric response in lead-free Na0.4K0.1Bi0.5TiO3/NiFe2O4 laminated composites

Lead-free Na0.4K0.1Bi0.5TiO3 (NKBT) and NiFe2O4 (NFO) ceramics are synthesized by solid-state reaction, and the laminated NKBT/NFO composites have been prepared by gluing the sintered discs with silver-epoxy. The measured parameters, dielectric constant (ε′) ∼1450 at 1 kHz, remanent polarization (Pr)∼39 μC/cm2, coercive electric field (Ec)∼27 kV/cm and maximum strain (Smax)∼0.3 % of NKBT along with saturation magnetization (Ms)∼49 emu/g, coercive magnetic field (Hc)∼27 Oe and magnetostriction (λ)∼-30 ppm of NFO, makes them suitable materials to evaluate as laminated magnetoelectric (ME) composites. A maximum ME response of 37, 67 and 86 mV/cm Oe at Hdc∼350−400 Oe field and 1 kHz frequency is observed for NKBT/NFO, NKBT/NFO/NKBT and NFO/NKBT/NFO layered composites, respectively. The high ME response at reasonable fields implies that NKBT/NFO laminated composite is a worthy lead-free candidate for ME sensor and energy harvesting applications.

Fabrication of high‐density NiFe2O4 ceramics by slip casting and pressureless sintering

ABSTRACTHigh‐density NiFe2O4 ceramics with homogeneous microstructure were produced by slip casting and pressureless sintering. The slurry stability, sintering behavior, and microstructure of NiFe2O4 ceramics were investigated. A stable slurry can be obtained by adding 12.5 wt% NiFe2O4 nanoparticle and 5 wt% nano‐binder at a slurry pH around 11.0. The linear shrinkage and linear shrinkage rate for both NiFe2O4 ceramic green bodies shaped by cold press molding and slip casting showed nearly the same trends. The temperature associated with the maximum linear shrinkage rate of slip casted green body was 1263.5°C, which was lower than that of cold press molded sample (1272.0°C). The sintering activation energy of slip casted green body was also lower than that of cold press molded sample (279.18 vs 288.47 kJ mol−1), owing to high density and homogeneity of slip‐casted green compact. A high‐density NiFe2O4 ceramics with uniform grain size distribution can be produced by slip casting and pressureless sintering at 1350°C for 6 hours, attributed to the ability of slip casting to minimize agglomerates and micropores. It demonstrated that slip casting was more suitable to prepare high‐density NiFe2O4 ceramics with good homogeneity.

Influences of annealing temperature on dielectric, magnetic and magnetoelectric coupling properties of 0.7Bi0.5Na0.5TiO3-0.3NiFe2O4 ceramics

Multiferroic 0.7Bi0.5Na0.5TiO3-0.3NiFe2O4 ceramics were prepared by sol-gel method with various temperatures ranging from 950 to 1100 °C. The influence of annealing temperature on structure, morphology, dielectric, magnetic and magnetoelectric coupling effect was investigated. The refinement of x-ray diffraction data and the thermogravimetric-differential thermal analysis indicated the coexistence of perovskite and spinel phases with annealing temperature above 950 °C. Increasing grain size in surface morphology measurement was closely related to the increasing annealing temperature. Enhancement in dielectric properties was observed with increasing annealing temperature. The room-temperature ferromagnetic properties were also detected with saturated magnetic hysteresis loops under different annealing temperatures. Finally, magnetoelectric coupling effect was confirmed in the samples. The possible factors for room-temperature multiferroic properties were discussed with increasing annealing temperature. This study showed that annealing temperature could evidently affect the multiferroic properties in 0.7Bi0.5Na0.5TiO3-0.3NiFe2O4 solid solution.

Influence of Co ion doping on the microstructure, magnetic and dielectric properties of Ni1-xCoxFe2O4 ceramics

Ni1-xCoxFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8) ceramics were prepared by chemical co-precipitation method and the effect of Co ion doping on the microstructure, magnetic and dielectric properties has been investigated. The results show that the synthesized ceramics display only spinel phase of Ni1-xCoxFe2O4, without other apparent impurities found. The lattice of Ni1-xCoxFe2O4 crystal structure was distorted as a result of the incorporation of Co ion, and the lattice parameters increase with the increase of Co ion content. The grain size decreases slightly with increasing the content of Co ion, indicating a change of particle size and morphology at higher doping content. The results of impedance analysis shows that the sample doped with 80 at.%Co possesses the maximal dielectric constant, while the pure NiFe2O4 sample shows the minimal value when the frequency is below 0.1MHz. The M-H loops of these ceramics exhibit highly magnetic nature and the saturation magnetization. The remnant magnetization increases linearly with the increase of Co-concentration in nickel ferrite while the coercive field (Hc) shows non-monotonic variation with Co content. The minimal and maximal values of Hc can be obtained when the Co concentrations are 40 and 80 at.%, respectively. The highest value of the saturation magnetization is 63 emu/g obtained with 80 at.% Co doping while the lowest value is ~31 emu/g for the pure NiFe2O4 ceramics. The abnormal magnetic behaviour is due to the A-B super exchange interaction when magnetic Co2+ ions are added.

Adjustability of resonance frequency by external magnetic field and bias electric field of sandwich magnetoelectric PZT/NFO/PZT composites

Sandwich magnetoelectric composites of PZT/NFO/PZT (PNP) have been prepared by laminating PZT5, NiFe2O4, and PZT5 ceramics in turn with polyvinyl alcohol (PVA) paste. A systematic study of structural, magnetic and ferroelectric properties is undertaken. Structural studies carried out by X-ray diffraction indicate formation of cubic perovskite phase of PZT5 ceramic and cubic spinel phase of NiFe2O4 ceramic. As increasing the content of PZT5 phase, ferroelectric loops and magnetic loops of PNP composites showed increasing remnant electric polarizations and decreasing remnant magnetic moments separately. Both external magnetic fields and bias voltages could regulate the basal radial resonance frequency of the composites, which should be originated with the transformation and coupling of the stress between the piezoelectric phase and magnetostrictive phase. Such magnetoelectric composite provides great opportunities for electrostatically tunable devices.

Electrical Properties of NiFe2O4 Ceramics and Size Dependent Metal to Semiconductor Transition

Electrical Properties of NiFe₂O₄ Ceramics and Size Dependent Metal to Semiconductor Transition

Properties of NiFe2O4 ceramics from powders obtained by auto-combustion synthesis with different fuels

Nickel ferrite (NiFe2O4) powders derived by auto-combustion synthesis using three different fuels (citric acid, glycine and dl-alanine) have been characterized. The sintering behavior of ceramics using these powders has been compared. Oxygen balance (OB) setting for the chemical reaction is found to regulate the combustion reaction rate. A rapid reaction rate and a high flame temperature are achieved with dl alanine fuel yielding single phase NiFe2O4 powder in the as-burnt stage, whereas powders derived with citric acid and glycine fuels show poor crystallinity and necessitate post-annealing. The powder particles are largely agglomerated with a non-uniform distribution in shape and size, and the average particle size is estimated in the range ~ 54–71nm. Powders derived from dl-alanine fuel show better phase purity, smaller crystallite size, larger surface area and superior sintering behavior. Additional Raman modes discerned for dl-alanine derived powder support a 1:1 ordering of Ni2+ and Fe3+ at the octahedral sites relating to microscopic tetragonal P4122 symmetry expected theoretically for the formation of NiFe2O4 with inverse spinel structure. Microstructure of sintered ceramics depends on the precursor powders that are used and sintering at 1200°C is found to be optimum. Citric acid and glycine derived powders yield high saturation magnetization (Ms~47–49emu/g), but poor dielectric properties, whereas dl-alanine derived powders yield ceramics with high resistivity (~3.4×108Ωcm), low dielectric loss (tanδ~0.003 at 1MHz) and high magnetization (46emu/g). Dielectric dispersion and impedance analysis show good correlation with the changes in the ceramic microstructure.

Dielectric and magnetic properties of Nickel ferrite ceramics using crystalline powders derived from DL alanine fuel in sol–gel auto-combustion

Dielectric and magnetic properties of NiFe2O4 ceramics prepared with powders using DL-alanine fuel in the sol–gel auto combustion technique are studied. DL-alanine fuel yields crystalline as-burnt powders, and when used for ceramic processing yields varying microstructure at different sintering temperatures. The dielectric properties are influenced by the resulting microstructure and the magnetic properties show slight change in saturation magnetization Ms (~44 – 46emu/g). The coercive fields, dielectric losses and dispersion are reduced considerably at higher sintering temperatures (1200–1300°C). The influence of changing microstructure is analyzed through dielectric response, complex impedance analysis and electrical modulus spectroscopy in the frequency range (10−2–107Hz) to understand the interactions from the grain and grain boundary phases. Sintering at 1200°C, is found to be optimum, yields lower losses & reduced dielectric dispersion, and high resistivity (3.4×108Ωcm).

Effect of sintering atmosphere on composition and properties of NiFe2O4 ceramic

NiFe2O4 ceramics were prepared in different sintering atmospheres. The phase compositions, microstructures and mechanical properties were studied. The results show that the stoichiometric compound NiFe2O4 cannot be obtained in vacuum or atmospheres with oxygen contents of 2×10−5, 2×10−4 and 2×10−3, respectively. All the samples sintered in above-mentioned atmospheres contain phases of NiFe2O4 and NiO. With increasing oxygen content, NiFe2O4 content in the ceramic increases, while NiO content appears a contrary trend. In vacuum, NiFe2O4 ceramic has average grain size of 3.94 μm, and bending strength of 85.12 MPa. The changes of the phase composition and mechanical properties of NiFe2O4 based cermets are mainly caused by the alteration of their properties of NiFe2O4 ceramic.

Effect of TiO2 Doping on the Sintering Process, Mechanical and Magnetic Properties of NiFe2O4 Ferrite Ceramics

TiO2‐doped NiFe2O4 samples were prepared via ball‐milling and two‐step sintering processes. Besides NiFe2O4 phase, two new phases, NiTiO3 and Fe2TiO5, formed in TiO2‐doped samples. The temperature of sintering onset for 1.0 wt% TiO2‐doped samples is 230°C lower than that of undoped samples. Early‐stage synthesis process of TiO2‐doped NiFe2O4 ceramics is controlled by grain boundary diffusion mechanism. Increasing TiO2 content from 0 to 1.0 wt%, the apparent activation energy decreased from 813.919 KJ/mol to 639.361 KJ/mol. The values of relative density and bending strength reached their maximum value with 1.0 wt% TiO2. Saturation magnetization, residual magnetization ratio and coercivity decrease with increasing TiO2 content.

Microstructure and mechanical properties of NiFe2O4 ceramics reinforced with ZrO2 particles with different sintering temperatures

NiFe2O4 ceramics reinforced with ZrO2 particle was fabricated by conventional high-temperature solid state reaction. Effect of the sintering temperature (1100–1500°C) on the microstructure and mechanical properties of the ZrO2/NiFe2O4 composite ceramics was investigated in detail. The fracture surfaces of NiFe2O4 composite ceramics were observed by scanning electron microscopy (SEM). Elemental analysis of micro-structural phases was performed using energy dispersive spectroscopy (EDS), attached with SEM. Flexural strength by three-point bending techniques and fracture toughness were measured. It was indicated that when the sintering temperature was above 1400°C, phase transformation causing crack can directly lead to the strength degradation. The grain size of ZrO2 increases with increasing of the sintering temperature. The samples sintering at 1400°C had the highest flexural strength of 192±10MPa and fracture toughness of 3.38±0.05MPam1/2 due to densification, phase transformation.

Synthesis and characterization of dense and fine nickel ferrite ceramics through two-step sintering

Two-step sintering (TSS) has been employed in the current study to suppress the accelerated grain growth of NiFe2O4 nanopowder compacts in the final sintering stage. Experiments are conducted to determine the appropriate temperatures for each step. The temperature range from 1200°C to 1300°C is effective for the first-step sintering (T1) due to its highest densification rate. The second-step sintering temperature (T2) should be within the kinetic window, where grain boundary diffusion is maintained but grain boundary migration is suppressed. The grain sizes of high density (≥98% theoretical density) NiFe2O4 compacts produced by TSS are smaller than 700nm, while that of those formed by CS are over 2.5μm. The evidence indicates that the saturation magnetization of nearly full NiFe2O4 ceramics is independent of grain size and likewise high, with the corresponding values of approximately 54emu/g. The Vickers hardness and fracture toughness both increase with the decrease of grain size and porosity.