Magnetically recoverable CoFe1.9Gd0.1O4 ferrite/polyaniline nanocomposite synthesized via green approach for radar band absorption

The gadolinium substituted cobalt ferrite (CoFe_1.9Gd_0.1O₄) nanoparticles and CoFe_1.9Gd_0.1O₄/Polyaniline (PANI) microwave absorber were synthesized by sol-gel auto combustion technique using lemon juice and in-situ polymerization method respectively. X-ray patterns confirmed the formation of single phase cubic structure. The crystallite size of the synthesized CoFe_1.9Gd_0.1O₄ nanoparticles are within the range of 15–68 nm. The saturation magnetization of CoFe_1.9Gd_0.1O₄ ferrite/Polyaniline (PANI) composite was reduced due to nonmagnetic PANI. The reflection loss for microwave absorbing properties of CoFe_1.9Gd_0.1O₄ ferrite nanoparticles and CoFe_1.9Gd_0.1O₄/PANI nanocomposite were investigated and minimum value of reflection loss was found to be −16.85 dB at 13.52 GHz for nanoparticles of thickness 2.5 mm and −25.59 dB at 11.92 GHz for CoFe_1.9Gd_0.1O₄/PANI nanocomposite of thickness 2.0 mm) respectively. The prepared samples have low density, high surface resistivity and enhanced attenuation constant. The nanocomposite exhibits excellent absorption performance over a broad band range in the radar band.     

Combustion-synthesized ferrites and ferroelectrics for microwave applications

The individual phases of Ni_{1 ? x} Cd _x Fe₂O₄ (x = 0.2, 0.4, 0.6) ferrite and Ba_0.8Sr_0.2TiO₃ ferroelectric (BST phase) were successfully prepared by autocombustion route. The oscillatory behavior of transmittance for the Ni-Cd ferrite was observed at about 0.44 at 8.2 GHz. The absorption study depicts the hopping phenomena of microwaves through the Ni-Cd phase. The dependence of microwave conductivity on ferrite content was discussed. The dielectric permittivity of Ni-Cd ferrites varied between 10 and 30. Compared to the Ni-Cd phase, the transmittance of the Ba_0.8Sr_0.2TiO₃ phase was found to be low. The dip in reflection loss for Ba_0.8Sr_0.2TiO₃ is equivalent to the minimum reflection or the maximum absorption of the microwave power for BST phase. The maximum microwave conductivity for Ba_0.8Sr_0.2TiO₃ was found to be about 0.459 S/cm. The high microwave permittivity for Ba_0.8Sr_0.2TiO₃ had a value of about 120.21.     

Achieving high breakdown strength and figure of merit of Ba0.6Sr0.4TiO3 films through coating a Y3Fe5O12 layer

Low tunability and figure of merit significantly limited the application of Ba_0.6Sr_0.4TiO₃ (BST) ferroelectric film, which originates from the low electric breakdown strength and high dielectric loss of BST layer. Garnet structured Y₃Fe₅O₁₂ (YIG) exhibits the merits of good microwave dielectric property and a much high resistivity, which are helpful for enhancing the breakdown strength and suppressing the dielectric loss. In this work, Y₃Fe₅O₁₂/Ba_0.6Sr_0.4TiO₃ (YIG/BST) composite films were fabricated via chemical solution deposition method. The composite films exhibited a low dielectric loss (0.006) and an almost frequency independent dielectric constant in a frequency range from 10 kHz to 1 MHz. The electric breakdown strength was significantly enhanced from less than 400 kV/cm to around 800 kV/cm through coating a YIG layer, causing an excellent tunability of 72.84% and an ultra-high figure of merit (FOM=118) at 800 kV/cm in YIG/BST film. It is physically clarified that the conduction loss plays an important role in BST film while the intrinsic loss is the dominate factor for the YIG/BST composite films.     

Polyaniline (PANI)–Co0.5Mn0.5Fe2O4 nanocomposite: Synthesis,characterization and magnetic properties evaluation

Polyaniline (PANI)/Cobalt-manganese ferrite, (PANI)/Co_0.5Mn_0.5Fe₂O₄, nanocomposite was synthesized by oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate (APS). Microwave assisted synthesis method was used for the fabrication of core CoFe₂O₄ nanoparticles. The structural, morphological, thermal and magnetic properties of the nanocomposite were investigated in detail by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The average crystallite size of (PANI)/Co_0.5Mn_0.5Fe₂O₄ nanocomposite by the line profile method was 20±9 nm. The magnetization measurements revealed that (PANI)/Co_0.5Mn_0.5Fe₂O₄ nanocomposite has superparamagnetic behavior with blocking temperature higher than 300 K. The saturation magnetization of the composite is considerably low compared to that of CoFe₂O₄ nanoparticles due to the partial replacement of Co²⁺ ions and surface spin disorder. As temperature decreases, both coercivity and strength of antiferromagnetic interactions increase which results in unsaturated magnetization of the nanocomposite.     

Effect of La-Ni substitution on structural,magnetic and microwave absorption properties of barium ferrite

In this paper, La-Ni substituted barium ferrite nanoparticles were prepared by a co-precipitation method. The morphology, structure, magnetic and microwave absorption properties of samples were accomplished by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and vector network analysis. From the results evaluation, it can be seen that the magnetoplumbite structure for all of the samples have been formed and the average crystallite sizes of Ba_1−xLa_xFe_12−xNi_xO₁₉ nanoparticles within in the range of 50.9–65.5 nm. Ba_0.9La_0.1Fe_11.9Ni_0.1O₁₉ exhibits a remarkable reflection loss of −13.5 dB at 13.05 GHz with a matching thickness of 1.5 mm. The reflection loss results indicate that Ba_0.9La_0.1Fe_11.9Ni_0.1O₁₉ nanoparticles may be used as a potential for thin microwave absorbers.     

Microwave dielectric properties of (Ba1−xSrx)(Mg0.5W0.5)O3 ceramics

The densification, microstructural evolution and microwave dielectric properties of (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ ceramics with x=0, 0.25, 0.5 and 0.75 are investigated in this study. The sintering temperature of the (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ is significantly reduced from 1575 °C to 1400 °C as the x value increases from 0 to 0.25 and 0.50; this result is accompanied by the formation of the (Ba_1−ySr_y)WO₄ phase and a small quantity of second phase surrounding the grains. The grain size of the (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ ceramics is increased by raising the Sr²⁺ content, which significantly lowers the sintering temperature. The microstructure of the (Ba_0.75Sr_0.25)(Mg_0.5W_0.5)O₃ ceramic displays the smallest average grain size of approximately 0.8 μm, with a narrow grain size distribution. Without long annealing time, very high Q×f values are obtained for the (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ ceramics sintered at 1400–1575 °C for a duration of only 2 h. The (Ba_0.75Sr_0.25)(Mg_0.5W_0.5)O₃ ceramic sintered at 1400 °C results in the best microwave dielectric properties, including ε_r of 20.6, Q×f of 152,600 GHz and τ_f of +24.0 ppm/°C.     

(Ba0.5Sr0.5)TiO3 modification on etched aluminum foil for electrolytic capacitor

A new method was proposed to form (Ba_0.5Sr_0.5)TiO₃–Al₂O₃ composite oxide film on etched aluminum foils. The specimens were covered with (Ba_0.5Sr_0.5)TiO₃ (BST) layer by dip-coating in citrate solution and subsequent heat-treatment under 400–650 °C, finally by anodizing in a hot boracic acid and borate solution. The BST powders heated under different temperatures were characterized by X-ray diffraction (XRD) and the specific capacitance of the coated specimens heat-treated under different temperatures and times was measured. It is found that the specific capacitance increases initially with enhancing the temperature and reaches to maximum at 550 °C, but slightly decreases with the heat-treatment time. The capacitance was increased by about 35% after BST coating.     

Microstructures and Properties of 3Y‐TZP/Ba0.5Sr0.5Fe12O19 Composites Prepared by Two Methods

Two composites of Ba_0.5Sr_0.5Fe₁₂O₁₉ grains dispersed in a 3 mol% yttria‐doped zirconia (3Y‐TZP) matrix are prepared by two methods. The mechanical and electromagnetic properties of the both composites are investigated. The maximum values of the bending strength and the fracture toughness are 786 MPa and 8.6 MPa m^1/2, respectively. The maximum value of the magnetization is 17.2 emu/g. In addition, the distribution of the Ba_0.5Sr_0.5Fe₁₂O₁₉ phase is described using the box dimension of the fractal theory. The impedance spectra of the both composites are fitted using the equivalent circuit model with a constant phase element (CPE). The obtained p value of the CPE can indirectly reflect the morphology of the Ba_0.5Sr_0.5Fe₁₂O₁₉ phase in both composites according to the universal relaxation law.     

Synthesis,characterization and magnetic properties of polythiophene/SrFe12-x(ZrZn)0.5xO19 nanocomposite as a microwave absorber

Ferrites are an important group of magnetic materials which are used as absorbers. The incorporation of ferrite and conducting polymer achieves great enhancement in microwave absorption properties. The nanocomposites of hexagonal ferrites embedded by conducting polymers such as polypyrrole, polyaniline and polythiophene (PTH) have been paid much attention. In the present study, strontium hexagonal ferrite doped by Zr and Zn with the final formula of SrFe_12-x(ZrZn)_0.5xO19 considering x = 0.9 and embedded by PTH was produced to achieve a nanocomposite with the highest microwave absorbing ability. In this study, after synthesis of SrFe₁₂O₁₉(ZrZn)_0.5xO19 and PTH, the nanocomposite was prepared by in situ polymerization. Wrapping the ferrite particles and PTH chains could form nanocomposite properly, and therefore acceptable interactions were observable between SrFe_12-x(ZrZn)_0.5xO19ferrite particles and PTH polymer chains in the composites. Assessing the X-ray diffraction (XRD) patterns of SrFe_12-x(ZrZn)_0.5xO19, PTH, and PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite indicated that the PTH characteristic peak shifts slightly and its peak intensity reduces, which may be attribute to the coating of PTH polymer chains onto SrFe_12-x(ZrZn)_0.5xO19 particles. We revealed also lower magnetic properties in the obtained nanocomposite. The morphological assessment also suggested that PTH could effectively coat the SrFe_12-x(ZrZn)_0.5xO19 particles. The synergistic effect of SrFe_12-x(ZrZn)_0.5xO19 particle plus PTH leads to microwave absorption percentage higher than 95% by PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite. Overall, nanocomposite creating by coupling interaction between SrFe_12-x(ZrZn)_0.5xO19 particles (x = 0.9) and PTH can effectively lead to achieve the highest rate of absorption of electromagnetic waves.     

Synthesis,characterization, and magneto‐electric properties of (1−x)BCZT‐xCFO ceramic particulate composites

Synthesis of a new magnetoelectric [(1?x)(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃‐xCoFe₂O₄] (weight fraction x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1) ceramic particulate composites with its structural characterization and magneto‐electric properties have been reported here in this study. Lead free piezoelectric (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) and ferrimagnetic CoFe₂O₄ (CFO) were synthesized using sol‐gel and combustion methods respectively. (1?x)BCZT‐xCFO magnetoelectric composites were then synthesized by mixing of the calcined individual ferroic phases with required weight fractions. Powder X‐ray diffraction studies indicate the coexistence of BCZT and CFO phases in the composites sintered at 1300°C. 0.5BCZT‐0.5CFO composite showed high strain sensitivity (dλ/dH) of 52×10^?9 Oe^?1, which is comparable to that of pure CFO (50×10^?9 Oe^?1). A high piezoelectric voltage constant (g₃₃) of 8×10^?3 V m/N was measured for 0.8BCZT‐0.2CFO sample. All the composites showed magnetoelectric effect and a high magnetoelectric coupling coefficient (α_ME) of 6.85 mV/cm Oe was measured for 0.5BCZT‐0.5CFO composite at 1 kHz and a large ME coefficient of 115 mV/cm Oe at its resonance frequency. The effect of microstructure on the magnetoelectric properties of [(1?x)BCZT‐(x)CFO] composites has been studied and reported here as a function of its piezoelectric (BCZT)/ferrite (CoFe₂O₄) content.     

Magneto-optical properties and Mössbauer Investigation of BaxSryPbzFe12O19 Hexaferrites

Ba_0.3Sr_0.4Pb_0.3Fe₁₂O₁₉, Ba_0.4Sr_0.3Pb_0.3Fe₁₂O₁₉ and Ba_0.3Sr_0.3Pb_0.4Fe₁₂O₁₉ hexaferrites were synthesized via sol-gel auto combustion. XRD (X-ray powder diffraction) powder patterns of the products confirmed the formation of M-type hexaferrites without any secındary phase. The crystallite sizes of the products were calculated as 37–41 nm by Scherrer equation. SEM (Scanning electron microscopy) analyses revelaed the hexagonal morphology and 200–400 nm grain size of the prodcuts. The magnetic hysteresis (σ-H) curves exhibit the ferromagnetic features for all hexaferrites. Especially, Ba_0.3Sr_0.4Pb_0.3Fe₁₂O₁₉ and Ba_0.4Sr_0.3Pb_0.3Fe₁₂O₁₉ samples have suitable magnetic characteristics (saturation magnetizations as 42.58 and 38.55 emu/g, coercive fields as 1950 and 2978 Oe, larger squareness ratios (SQR) as 0.447 and 0.454, respectively) for high density magnetic recording applications and permanent magnet fabrication. Effective crystalline anisotropy constants (K_eff) are between 3.18×10⁵–3.54×10⁵ Erg/g. The observed 17000 Oe Ha (anisotropy field) reveal that products are hard magnet. Tauc plots were plotted to determine the Eg (direct optical energy band gap) of the samples. The E_g values are 1.46, 1.51, 1.69 eV belonging to Ba_0.3Sr_0.4Pb_0.3Fe₁₂O₁₉, Ba_0.4Sr_0.3Pb_0.3Fe₁₂O₁₉, and Ba_0.3Sr_0.3Pb_0.4Fe₁₂O₁₉ hexaferrites respectively.     

Preparation of La1?x Sr x CoO3 Oxide Electrode Material and its Influence on the Structure and Dielectric Performance of the Supported Ba1?x Sr x TiO3 Thin Films

Using the sol–gel method, La_1−x Sr _x CoO₃ (LSCO) electrode films were first fabricated on the Si (100) substrates, followed by the growth of Ba_1−x Sr _x TiO₃ (BST) thin films on the LSCO electrode film. The crystal structure and surface morphology of these films were characterized by XRD and SEM. The effects of Sr-doping and annealing temperature on the structure and electric resistivity of the LSCO films and the dielectric properties of the BST films were studied. Results show that the La_0.5Sr_0.5CoO₃ electrode annealed at 750 °C has the lowest electric resistivity, 1.1 × 10⁻³Ω cm. The relative permittivity of the La_0.5Sr_0.5CoO₃-supported BST films first increases and then decreases with Sr-doping. The relative permittivity of the BST film decreases while the dielectric loss increases with frequency. Among the studied BST films, Ba_0.5Sr_0.5TiO₃ has the largest relative permittivity and the smallest dielectric loss (95 and 0.1, respectively) when the frequency is 1 kHz.     

Investigation on microwave absorption characteristics of ternary MWCNTs/CoFe2O4/FeCo nanocomposite coated with conductive PEDOT-Polyaniline Co-polymers

In this study, ternary MWCNTs/CoFe₂O₄/FeCo nanocomposite coated with conductive PEDOT-polyaniline (PA@MW/F/C) co-polymers were synthesized by microwave-assisted sol-gel followed in-situ polymerization methods. The phases, crystal structures, morphologies, magnetic and electromagnetic features of the as-prepared samples were identified via XRD, SEM, XPS, VSM, and VNA respectively. Absorption characteristics were investigated in the frequency (12–18 GHz) Ku band. XRD, VSM and SEM analysis confirmed the partial reduction process of CoFe₂O₄ and successfully decorated magneto-dielectric particles with co-polymers. By measuring electromagnetic features of the samples, it was found that coating magneto-dielectric particles with conductive co-polymers improved the permittivity and dielectric constant, accordingly affecting the impedance matching characteristic and attenuation constant performance. Moreover, exchange coupling behavior was found significant impacts on the microwave absorption properties. PA@MW/F/C coated nanocomposite revealed the maximum reflection loss of ?90 dB at 13.8 GHz with 4 GHz effective bandwidth and 1.5 mm thickness. Due to the enhanced interfacial polarization, impedance matching and exchange coupling effects of the as-prepared nanocomposite, it owns excellent microwave absorption properties, which can be applied as an absorber with distinguishing features (strong absorption, thin thickness, and broadest effective bandwidth).     

Dielectric Properties and Low‐Temperature Sintering of the Ba0.6Sr0.4TiO3 Ceramics with B2O3/CuO Additions

The sintering behaviors and dielectric properties of Ba_0.6Sr_0.4TiO₃ ceramics were investigated as a function of B₂O₃ and CuO content. The addition of both B₂O₃ and CuO reduced the sintering temperature of Ba_0.6Sr_0.4TiO₃ about 500°C. It was suggested that a liquid phase BaCu(B₂O₅) was formed and assisted the densification of Ba_0.6Sr_0.4TiO₃ ceramics. Ba_0.6Sr_0.4TiO₃ ceramics co‐doped with 3.0 mol% B₂O₃, and 2.0 mol% CuO, sintered at 950°C for 5 h, had a dense microstructure and showed good microwave dielectric properties of a moderate dielectric constant (ε = 1048), low dielectric loss (0.0090) and high tunability (42.2%) at dc electric field of 30 kV/cm.     

Improvement of dielectric loss of (Ba,Sr)(Ti,Zr)O3 ferroelectrics for tunable devices

(Ba_0.6Sr_0.4)(Ti_1−xZr_x)O₃ (0.05 ≤ x ≤ 0.3) ferroelectric materials have cubic perovskite structure and show paraelectric properties at room temperature. Curie point shifted to a negative value as increasing Zr content in (Ba_0.6Sr_0.4)(Ti_1−xZr_x)O₃ system. When Zr substituted 0.1 mol, the dielectric constant, dielectric loss, tunability, Curie point and FOM were 4500, 0.0005, 63%, −1.6 °C and 1260, respectively. This composition shows excellent microwave dielectric properties than those of (Ba_0.6Sr_0.4)TiO₃ ferroelectrics, which are limelight materials for tunable devices such as varactors, phase shifters and frequency agile filters, etc.     

Effect of lemon juice on microstructure,phase changes,and magnetic performance of CoFe2O4 nanoparticles and their use on release of anti-cancer drugs

Cobalt ferrite magnetic nanoparticles were synthesized and developed by a modified Pechini method using iron nitrate, cobalt nitrate, ethylene glycol (EG), and sucrose with different volumes of lemon juice (10, 20, 30, 40, 50, 60, and 70 ml) as the source of chelating agent as well as nonmagnetic elements such as Ca and Mg ions. The XRD patterns confirmed that all samples synthesized by different contents of extracted lemon juice had a cubic crystal structure with single-phase spinel. Scanning electron microscopy revealed that cobalt ferrite nanoparticles had a semi-spherical morphology. Also, the vibrating sample magnetometer indicated that the saturation magnetization of CoFe₂O₄ nanoparticles prepared with different values of extracted lemon juice increased from 18.6 emu/g for 10 ml extracted lemon juice to 75.7 emu/g for 50 ml extracted lemon juice, after which the saturation magnetization diminished. Afterwards, the CoFe₂O₄ nanoparticles were coated with polyethylene glycol (PEG) and doxorubicin (DOX) drugs, whereby drug delivery was detected at different pH levels. The CoFe₂O₄-PEG-DOX nanocomposite could release doxorubicin by more than 42% at pH = 5.4 in 75 h.     

Influence of 4ZnO–B2O3 Addition on Dielectric Properties and Microstructures of Barium Strontium Titanate

This study investigates the effect of 4ZnO–B₂O₃ on the sintering behavior, dielectric properties, and microstructures of Ba_0.6Sr_0.4TiO₃ (BST) ceramics. These ceramics were sintered in air at temperatures ranging from 900°C to 1080°C. BST ceramics with 4ZnO–B₂O₃ addition can be sintered to a theoretical density higher than 95% at 1050°C. A secondary phase (Ba₂ZnTi₅O₁₃) is produced in the BST ceramics during 4ZnO–B₂O₃ addition. Compositional analysis using TEM-EDX of the BST ceramics with 3 wt% 4ZnO–B₂O₃ revealed that the Zn ion is generally located at the triple points. This result indicates that BaO, TiO₂, and ZnO form a liquid phase that acts as a secondary phase at the lower sintering temperatures. The amount of secondary phase was observed to increase as the amount of 4ZnO–B₂O₃ additives increased. In addition, the original Ba_0.6Sr_0.4TiO₃ phase was shifted to the Ba_0.5Sr_0.5TiO₃ phase by the addition of 3 wt% 4ZnO–B₂O₃ at 1050°C. The Ba_0.6Sr_0.4TiO₃ ceramic with 2 wt% 4ZnO–B₂O₃ sintered at 1050°C in air for 2 h exhibited dielectric properties of ɛ_r=1883 and dissipation loss=0.36%. Moreover, BST with 1 wt% 4ZnO–B₂O₃ addition sintered at 1080°C exhibits dielectric properties of ɛ_r=2330, dissipation loss=0.29%, and bulk density >95% of theoretical density.     

Thickness effects on microwave properties of (Ba,Sr)TiO3 films for frequency agile technologies

We fabricated (Ba_0.6Sr_0.4)TiO₃ (BST) thin films of various thicknesses on sapphire (−1 1 2 0) substrates using metal-organic decomposition method. These films showed grain growth from 160 to 650 nm with an increase in the thickness from 90 to 1050 nm. At microwave frequencies, the measured capacitances of the planar capacitors decreased with the film thickness because the electro-magnetic field propagates across high permittivity BST films to the low permittivity sapphire substrate. However, we found that the BST-thin film permittivity remained large up to 90 nm thick, based on electro-magnetic field analysis using the finite element method. On the other hand, the BST thin film tunability decreased with the film thickness.     

Property optimization of Ba0.4Sr0.6TiO3–BaMoO4 composite ceramics for tunable microwave applications

(1 ? x)Ba_0.4Sr_0.6TiO₃–xBaMoO₄ ceramics with x = 5, 10, 20, 30, 40 and 60 wt% were prepared by traditional solid-state reaction method. Two crystalline phases, a cubic perovskite structure Ba_0.4Sr_0.6TiO₃ (BST) and a tetragonal scheelite structure BaMoO₄ (BM) were obtained by XRD analysis. The microwave dielectric properties of Ba_0.4Sr_0.6TiO₃–BaMoO₄ composite ceramics were investigated systematically. The results show that the composite ceramics exhibited promising microwave properties. The dielectric constant can be adjusted in the range from 900 to 78, while maintaining relatively high tunability from 27.3% to 12.8% under a direct current electric field of 60 kV/cm and Q values from 619 to 67 in the gigahertz frequency region.     

Ball milling–based piezocatalysis using .5Ba(Zr0.2Ti0.8)O3–.5(Ba0.7Sr0.3)TiO3 ceramics

One of the newly light on processes utilized in applications for cleaning water is piezocatalysis. Mechanical vibrations generated through ultrasonication are generally used to separate out the charges in ferroelectric ceramics. The current research presents a novel prospective methodology of ball milling, where it is used as a facile and green technique for water remediation. The movement of the planetary ball mill imparts enough force such that reactive species are produced which are responsible for organic dye degradation. One of the results in the parametric analysis showed that by using 0.30 g of the 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Sr_0.3)TiO₃ (BST–BZT) powder, 62% of the methylene blue (MB) dye was degraded in 60 minutes.