Structural, electrical and magnetic characterizations of Ni-Cu-Zn ferrite synthesized by citrate precursor method

Fine powders of NiCuZn ferrite with composition Ni_(0.7−x)Cu_xZn_0.3Fe₂O₄ (where x=0, 0.2, 0.4 and 0.6) were prepared by the citrate precursor method. X-ray diffraction measurements confirm the formation of single-phase cubic spinel structure. The grain size was estimated by SEM micrograph which increases with Cu content. Dielectric constant (?) and loss tangent (tan δ) were measured as a function of frequency. The ? and tan δ show a decreasing trend with increase of frequency for all the samples. The DC resistivity was measured as a function of temperature. The temperature-dependent DC resistivity measurements show that the room-temperature DC resistivity of NiCuZn ferrite with x=0.2 is of the order of 10⁹ Ω cm. The AC conductivity (σ_AC) was studied as a function of frequency. The hysteresis data indicate that the maximum saturation magnetization of 38.66 emu/g is obtained for the composition with x=0.2.     

Characterization, sintering and dielectric properties of nanocrystalline zinc oxide prepared by a citric acid-based combustion route

Nanosized zinc oxide has been synthesized through a novel single step solution combustion route using citric acid as fuel. The X-ray diffraction (XRD) analysis revealed that the synthesized ZnO nanopowder has the pure wurtzite structure. The phase purity of the nanopowder has been confirmed using differential thermal analysis (DTA), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The morphology and crystalline size of the as-prepared nanopowder characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the powder consisted of a mixture of nanoparticles and nanorods. The nanocrystalline ZnO could be sintered to ∼97% of the theoretical density at 1200 °C in 4 h. The dielectric constant (ε_r) and dielectric loss (ε_i) of sintered ZnO pellets at 5 MHz were 1.38 and 9×10⁻², respectively, at room temperature.     

Hard magnetic properties of nanosized Sr(Fe,Al)12O19 hexaferrites obtained by Pechini method

In this work, we report the magnetic properties of isotropic M-type SrFe_12−xAl_xO₁₉ (x=0.0,1.5) hexaferrites synthesized by means of Pechini method. A polycrystalline distribution of fine grains was verified by Transmission Electron Microscopy for both compositions, with average sizes below 60 nm. Remarkable coercivity values within the range 500–850 kA/m were attained as a consequence of a combined effect of grain size refinement together with an enhancement of the anisotropy field afforded by the incorporation of the Al³⁺ cations into the hexagonal crystal structure.     

Low-temperature sintering and microwave dielectric properties of Ca2Zn4Ti15O36 ceramics

The sintering behavior, microstructures, and microwave dielectric properties of Ca₂Zn₄Ti₁₅O₃₆ ceramics with B₂O₃ addition were investigated. The crystalline phases and microstructures of Ca₂Zn₄Ti₁₅O₃₆ ceramics with 0-10 wt% B₂O₃ addition were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The sintering temperature of Ca₂Zn₄Ti₁₅O₃₆ ceramic was lowered from 1170 to 930 °C by 10 wt% B₂O₃ addition. Ca₂Zn₄Ti₁₅O₃₆ ceramics with 8 wt% B₂O₃ addition sintered at 990 °C for 2 h exhibited good microwave dielectric properties, i.e., a quality factor (Qf) 11,400 GHz, a relative dielectric constant (ε_r) 41.5, and a temperature coefficient of resonant frequency (τ_f) 94.4 ppm/°C.     

Improvement in electrical and magnetic properties of mixed Mg-Al-Mn ferrite system synthesized by citrate precursor technique

In the present work, mixed magnesium-manganese ferrites of composition Mg_0.9Mn_0.1Al_0.3Co_zFe_1.7−zO₄ where z=0.3, 0.5 and 0.7 have been synthesized by the citrate precursor technique. X-ray diffraction patterns of the samples confirmed the formation of single-phase spinel structure. The ferrites have been investigated for their electric and magnetic properties such as dc resistivity, Curie temperature, saturation magnetization, initial permeability and relative loss factor (RLF). Fairly constant value of initial permeability over a wide frequency range (0.1-20 MHz) and low values of the relative loss factor of the order of 10⁻⁴-10⁻⁵, in the frequency range 0.1-30 MHz, are the cardinal achievements of the present investigation. In addition to this, initial permeability was found to increase with an increase in temperature while RLF was observed to be low at these temperatures. The dc resistivity and Curie temperature were found to increase with an increase in cobalt content. The mechanisms contributing to these results are discussed in detail in this paper.     

BaCO3 mediated modifications in structural and magnetic properties of natural nanoferrites

Preparing M-type barium hexaferrite and improving the magnetic response of natural ferrites by incorporating barium carbonate (BaCO₃) is ever-demanding. Series of barium carbonate doped ferrites with composition (100−x)Fe₃O₄·xBaCO₃ (x=0, 10, 20, 30 wt%) are prepared through solid state reaction method and sintered gradually at temperatures of 800 and 1000 °C. Nanoparticles of natural ferrite and commercial BaCO₃ are used as raw materials. Impacts of BaCO3 on structural and magnetic properties of these synthesized ferrites are inspected. The obtained ferrites are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) at room temperature. Uniform barium hexaferrite particles in terms of both morphology and size are not achieved. The average crystallite size of BaFe₁₂O₁₉ is observed to be within 30–600 nm. The sintering process results phase transformation from Fe₃O₄ (magnetite) to α-Fe₂O₃ (hematite) and the formation of hexagonal barium ferrite crystals. The occurrence of barium crystal is found to enhance with the increase of BaCO₃ concentrations up to 20 wt% and suddenly drop at 30 wt%. Saturation and remanent magnetization of the doped ferrites are significantly augmented up to 16.37 and 8.92 emu g⁻¹, respectively compared to their pure counterpart. Furthermore, the coercivity field is slightly decreased as BaCO₃ concentrations are increased. BaCO₃ mediated improvements in the magnetic response of natural ferrites are demonstrated.     

Synthesis, structural and electrical properties of La and Nb modified Bi4Ti3O12 ferroelectric ceramics

Polycrystalline ceramic samples of Bi_4−xLa_xTi₃O₁₂ (x=0.0, 0.5 and 1) and Bi_3.5La_0.5Ti_3−yNb_yO₁₂ (y=0.02 and 0.04) have been synthesized by standard high temperature solid state reaction method using high purity oxides and carbonates. The effect of lanthanum doping on Bi-site and Nb doping on Ti-site on the structural and electrical properties of Bi₄Ti₃O₁₂ powders was investigated by X-ray diffraction, scanning electron microscopy, dc conductivity and dielectric studies. A better agreement between the observed and calculated X-ray diffraction pattern was obtained by performing the Rietveld refinement with a structural model using the non-centrosymmetric space group Fmmm in all the cases. A better agreement between observed and calculated d-values also shows that the lattice parameters calculated using the Rietveld refinement analysis are better. The increase in lanthanum and niobium contents does not lead to any secondary phases. It is found that La³⁺ doping reduces the material grain size and changes its morphology from the plate-like form to a spherical staking like form. The substitution of Nb for Ti ions affected the degree of disorder and modified the dielectric properties leading to more resistive ceramic compounds. The shape and size of the grains are strongly influenced by the addition of niobium to the system. The activation energies of all the compounds were calculated by measuring their dc electrical conductivities. The frequency and temperature dependent dielectric behavior of all the compounds have also been studied and the results are discussed in detail. The substitution of La and Nb on the Bi and Ti sites decreased the T_c and improved the dielectric and ferroelectric behavior.     

Effect of Gd doping on structural, electrical and magnetic properties of BiFeO3 electroceramic

Room temperature multiferroic electroceramics of Gd doped BiFeO₃ monophasic materials have been synthesized adopting a slow step sintering schedule. Incorporation of Gd nucleates the development of orthorhombic grain growth habit without the appearance of any significant impurity phases with respect to original rhombohedral (R3c) phase of un-doped BiFeO₃. It is observed that, the materials showed room temperature enhanced electric polarization as well as ferromagnetism when rare earth ions like Gd doping is critically optimized (x=0.15) in the composition formula of Bi_1+2xGd_2x/2Fe_1−2xO₃. We believe that magnetic moment of Gd⁺³ ions in Gd doped BiFeO₃ tends to align in the same direction with respect to ferromagnetic component associated with the iron sub lattice. The dielectric constant as well as loss factor shows strong dispersion at lower frequencies and the value of leakage current is greatly suppressed with the increase in concentration of x in the above composition. Addition of excess bismuth and Gd (x=0.1 and 0.15) caused structural transformation as well as compensated bismuth loss during high temperature sintering. Doping of Gd in BiFeO₃ also suppresses spiral spin modulation structure, which can change Fe-O-Fe bond angle or spin order resulting in enhanced ferromagnetic property.     

A systematic study on magnetic, dielectric and magnetocapacitance properties of Ni doped bismuth ferrite

In this paper we report the structural, magnetic, magnetocapacitance and dielectric properties of BiFe_1−xNi_xO₃ nanoceramics (with x=0, 0.1) prepared by the sol-gel method. XRD analysis showed formation of single phase nanoceramics (particle size ∼50 nm by TEM). Samples of BiFe_1−xNi_xO₃ were divided into two parts—one of them quenched in liquid nitrogen and another sintered in the normal way. We observed the enhancement in magnetic and dielectric properties of quenched sample. The splitting of zero field cool (ZFC) and field cool (FC) magnetization curves at low temperature reveals spin- glass behavior. Quenched sample showed the enhancement of blocking temperature.     

Effect of Zr:Sn ratio in the lead lanthanum zirconate stannate titanate ceramics on microstructure and electric properties

The effect of variations of the Zr:Sn ratio on the microstructure and electric properties of lead lanthanum zirconate stannate titanate (PLZST) antiferroelectric ceramics were investigated. The precursor powders were synthesized by the modified coprecipitation method and all the samples were pure perovskite phase in the XRD patterns. The ceramics sintered at 1100 °C exhibited the highest relative density. With the increasing of Sn⁴⁺ content, the grain size of the ceramics was decreased in the SEM and the maximum dielectric constant and the corresponding temperature were decreased. The P-E hysteresis loops indicated that it is helpful to steady the antiferroelectric phase by increasing Sn⁴⁺ content.     

Structural and electrical properties of high-energy ball-milled NASICON type Li1.3Ti1.7Al0.3(PO4)2.9(VO4)0.1 ceramics

Nano-crystallites of Li_1.3Ti_1.7Al_0.3(PO₄)_2.9(VO₄)_0.1 NASICON type material are prepared by means of solid-state reaction of a stoichiometric mixture after milling it for 22 and 55 h. The milling reduces the average crystallite size of the ceramic to 80 and 60 nm, respectively. Mechanical milling changes structural parameters and the strain induced at the grain-boundaries plays a major role in improving electrical conductivity. An order of magnitude increase in electrical conductivity is observed in the material milled for 55 h compared to the unmilled material, which is also reflected in permittivity loss. Modulus and permittivity representations substantiate the constriction effect of grain-boundaries observed in the complex impedance representation.     

Electronic transport and magnetic studies of La1−xCax−0.08Sr0.04Ba0.04MnO3

Lanthanum based mixed valence manganite system La_1−xCa_x−0.08Sr_0.04Ba_0.04MnO₃ (LCSBMO; x=0.15, 0.24 and 0.33) synthesized through the sol-gel route is systematically investigated in this paper. The electronic transport and magnetic susceptibility properties are analyzed and compared, apart from the study of unit cell structure, microstructure and composition. Second order phase transition is observed in all the samples and significant difference is observed between the insulator to metal transition temperature (T_MI) and paramagnetic (PM) to ferromagnetic (FM) transition temperature (T_C). In contrast to the insulating FM behaviour usually observed in La_1−xCa_xMnO₃ (LCMO) for x=0.15, a clear insulator to metal transition is observed for LCSBMO for the same percentage of lanthanum. The temperature dependent resistivity of polycrystalline pellets, when obeying the well studied law ρ=ρ_o+ρ₂T² for T<T_MI, is observed to differ significantly in the values of ρ_o and ρ₂, with the electrical conductivity increasing with x. The variable range hopping model has been found to fit resistivity data better than the small polaron model for T>T_MI. AC magnetic susceptibility study of the polycrystalline powders of the manganite system shows the highest PM to FM transition of 285 K for x=0.33.     

Structural and optical characterization of CdS nanoparticles prepared by chemical precipitation method

In the present study we have synthesized CdS semiconducting quantum dots by the chemical precipitation method using Thioglycerol as the capping agent. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) are employed to characterize the size, morphology and crystalline structure of the as-prepared material. The synthesized QPs have a mixture of cubical and hexagonal crystal symmetry with 12 nm average diameter. Ultraviolet-visible (UV-vis) absorption spectroscopy is used to calculate the band gap of the material and blue shift in absorption edge. Confinement of the optical phonon modes in the QPs is studied by Raman spectroscopy, while FTIR for identification of chemical bonds in the nanomaterial. Multiple cadmium and sulphur defects were observed by employing the photoluminescence (PL) method.     

Studies of dielectric and impedance properties of KCa2V5O15 ceramics

A polycrystalline sample, KCa₂V₅O₁₅, with tungsten bronze structure was prepared by a mixed-oxide method at low temperature (i.e., at 630 °C). A preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound was studied by scanning electron microscopy (SEM). Two dielectric anomalies at 131 and 275 °C were observed in the temperature dependency of dielectric response at various frequencies, which may be attributed to the ferroelastic-ferroelectric and ferroelectric-paraelectric transitions, respectively. The nature of variation of the electrical conductivity, and value of activation energy of different temperature regions, suggest that the conduction process is of mixed-type (i.e., ionic-polaronic and space charge generated from the oxygen ion vacancies). The impedance plots showed only bulk contributions, and non-Debye type of relaxation process occurs in the material. A hopping mechanism of electrical transport processes in the system is evident from the modulus analysis. The activation energy of the compound (calculated both from loss and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers.     

Dielectric, ferroelectric, magnetic and magnetoelectric properties of PMN-PT based ME composites

A systematic study of magnetoelectric composite system (x) CoFe₂O₄+(1−x) Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ with x=0, 0.15, 0.30, 0.45 and 1 was carried out. The lattice strain was calculated using Williamson and Hall equation, which depends on the content of constituent phases in composites. The microstructure was studied using scanning electron microscopy. The ferroelectric transition temperature was independent of the content of individual phases, suggesting that the ferroelectric character is maintained in the composite. Observed P–E and M–H loops indicate that the multiferroic nature of magnetoelectric ceramics is dependent on the content of individual phases. The variation of magnetostriction with dc magnetic field was studied. The maximum magnetoelectric voltage coefficient of 7.2 mV/cm Oe is obtained for the synthesized composites. The magnetoelectric measurements are well explained with magnetostrictive behavior of the magnetic phase.     

Microwave solid synthesis and electrical properties of Aurivillius-type oxide-ion conductor

A new oxide-ion conductor of Aurivillius-type structure, namely BISRVOX (Bi₂Sr_xV_1−xO_{5.5-(3x/2)-δ}, 0≤x≤0.20), was successively synthesized by the microwave-assisted solid state reaction. 25 min of microwave irradiation was found to be quite sufficient to ensure the completion of reaction. Powder X-ray diffraction and differential thermal analysis showed better structural properties for the microwave-prepared samples compared to those obtained from the conventional solid synthesis route. Interestingly, the highly conducting γ-phase was effectively stabilized for x≥0.10. AC impedance spectroscopy evidenced the superiority of the microwave heating over conventional solid synthesis routes in exhibiting high oxide-ion performance.     

Investigations on the electrical and structural properties of polyaniline doped with camphor sulphonic acid

Polyaniline is chemically synthesised and doped with camphor sulphonic acid. FTIR studies carried out on these samples indicate that the aromatic rings are retained after polymerisation. The percentage of crystallinity for polyaniline doped with camphor sulphonic acid has been estimated from the X-ray diffraction studies and is around 56% with respect to polyaniline emeraldine base. The change in dielectric permittivity with respect to temperature and frequency is explained on the basis of interfacial polarisation. AC conductivity is evaluated from the observed dielectric permittivity. The values of AC and DC conductivity and activation energy are calculated. The activation energy values suggested that the hopping conduction is the prominent conduction mechanism in this system.     

Densification and magnetic properties of low-fire NiCuZn ferrites

The mixing of (Ni_0.38Cu_0.12Zn_0.50)Fe₂O₄ powders with Bi₂O₃ was performed using the solid-state mixing as well as wet chemical coating processes such as ammonia precipitation coating, urea precipitation coating, and solution coating. Ferrites prepared from the wet chemical coating processes could be densified at a lower sintering temperature without significant impact on the microstructural evolution compared with that prepared by solid-state mixing. In addition, samples prepared from the wet chemical coating process have a higher B_r and B_s and a lower H_c compared with that from solid-state mixing. Considering both the effects of sintering temperature and sintered density (>95% T.D.), ferrites with 1.5 wt% Bi₂O₃ addition by ammonia precipitation coating sintered at 900°C can provide the best permeability and quality factor (191 and 68.2, respectively) among all the cases studied.     

Spinel-type solid solutions involving Mn and Ti:Crystal chemistry, magnetic and electrochemical properties

This study reports the structural and magnetic properties of spinel systems Li₄Mn_5−xTi_xO₁₂ (“4-5-12” series) and LiNi_0.5Mn_1.5−xTi_xO₄ (“LNMTO” series), both based on Mn⁴⁺ substitution by Ti⁴⁺. Intermediate compositions covering the whole range of compositions (0≤x≤5 and 0≤x≤1.5, respectively) were prepared by solid state reaction. The 4-5-12 system forms a continuous spinel solid solution, whereas the spinel phase range in LNMTO stops before the end member “LiNi_0.5Ti_1.5O₄”, which is multi-phased with a major hexagonal phase component. Cell parameters and (Mn,Ti)-O distances increase monotonically with titanium content in both series. In the LNMTO series, the end member LiNi_0.5Mn_1.5O₄ is known to form a superstructure with Ni/Mn cation ordering. Neutron diffraction and Raman spectroscopy show that this order is lost when Ti is substituted, even at low level (x=0.15). The LNMTO crystal chemistry is also complicated by the presence of partial cation inversion, and the presence of a secondary rocksalt-type phase that modifies the spinel stoichiometry. Magnetic properties are characterized by a competition between ferromagnetic and antiferromagnetic interactions; no magnetic ordering is achieved, in agreement with B-site cation frustration and disorder. Electrochemical measurements show that the Ti^3+/4+ and Mn^3+/4+ redox couples behave independently in the 4-5-12 series, and that titanium decreases the high-potential electrochemical redox activity of LNMTO because of its blocking character for electron transfer to and from the nickel sites in the spinel structure.