Investigation of the structure and dielectric properties of doped barium titanates.

This work examined the influence of zirconium concentration on barium titanate (BZT) BaZrxTi1-xO3, with (x = 0, 0.15, 0.50, 0.75, and 1), produced by the tartrate precursor technique. The Fourier transform infrared (FTIR) spectra support the X-ray diffraction (XRD) results regarding formation of the perovskite structure. Grain size grows with Zr concentration, suggesting that the presence of Zr ions enlarges the grains. The transmission electron microscopy (TEM) images demonstrated that, due to their nano size, nanocrystallites are agglomerated in most images with irregular morphologies and average particle sizes from 20.75 nm to 63.75 nm. Increasing Zr content diminished the piezoelectric coefficient (d33) and the grain size. The value of d33 decreases by increasing Zr content, and there is an inverse relationship between grain size and d33. The remnant polarization of BZT increases with increasing Zr4+ content, which may be suitable for permanent memory device applications.

Microstructure and high frequency electromagnetic parameters of the soft/soft (CoFe2O4) x : (Ni0.4Cu0.2Zn0.4Fe2O4) y nanocomposites.

The soft/soft (CoFe2O4) x : (Ni0.4Cu0.2Zn0.4Fe2O4) y (CFO x /NCZO y ) nanocomposites (NCs) based on spinel ferrites were produced by the sol-gel method with varying phase's ratio (x : y = 0 : 1; 1 : 1; 2 : 1; 3 : 1; 1 : 3; 1 : 2 and 1 : 0). All NCs consisted of 2 single phases (initial spinels) without any impurities and the absence of chemical interaction between phases. Structural features were investigated and analyzed. The varying of the structural parameters was non-linear and correlated well with the lattice parameter for initial components. There were two maxima observed for all NCs on particle size distribution. It was demonstrated that an increase in the CFO content leads to an increase in the most probable size of the coarse fraction and a decrease in the most probable grain size of the fine fraction. An increase in the NCZO content leads to a decrease in the average size of both fine and coarse fractions. This is obviously due to the large number of defects in the NCZO crystal lattice. The high frequency electromagnetic parameters (real and imaginary parts of the permittivity and permeability, reflection losses) were analyzed in the range of 2-10 GHz. The increase of the energy losses with frequency increase was observed. The nature of the attenuation of the reflected energy associated with the electromagnetic absorption processes due to magnetic losses. Maximal values of the electromagnetic absorption were observed for CFO2/NCZO1 (-18.9 dB). This correlates with the lattice parameters of the composites. The result of the electromagnetic characteristics opens broad perspectives for practical applications such kind of NCs for antenna technology (5G technology) and for electromagnetic absorbing coatings.

Combined Effect of Microstructure, Surface Energy, and Adhesion Force on the Friction of PVA/Ferrite Spinel Nanocomposites.

Nanocomposite films based on spinel ferrite (Mg0.8Zn0.2Fe1.5Al0.5O4) in a PVA matrix were obtained. An increase in the spinel concentration to 10 wt.% caused an avalanche-like rise in roughness due to the formation of nanoparticle agglomerates. The lateral mode of atomic force microscopy (AFM) allowed us to trace the agglomeration dynamics. An unexpected result was that the composite with 6 wt.% of filler had a low friction coefficient in comparison with similar composites due to the successfully combined effects of low roughness and surface energy. The friction coefficient decreased to 0.07 when the friction coefficient of pure PVA was 0.72. A specially developed method for measuring nano-objects' surface energy using AFM made it possible to explain the anomalous nature of the change in tribological characteristics.

Structure, Morphology and Electrical/Magnetic Properties of Ni-Mg Nano-Ferrites from a New Perspective.

Using the auto combustion flash method, Ni1-x+2Mgx+2Fe2+3O4 (x = 0, 0.2, 0.6, 0.8 and 1) nano-ferrites were synthesized. All samples were thermally treated at 973 K for 3 h. The structural analysis for the synthesized samples was performed using XRD, high-resolution transmission electron microscopy (HRTEM), and FTIR. Scanning electron microscopy (SEM) was undertaken to explore the surface morphology of all the samples. The thermal stability of these samples was investigated using thermogravimetric analysis (TGA). XRD data show the presence of a single spinel phase for all the prepared samples. The intensity of the principal peak of the spinel phase decreases as Mg content increases, showing that Mg delays crystallinity. The Mg content raised the average grain size (D) from 0.084 µm to 0.1365 µm. TGA shows two stages of weight loss variation. The vibrating sample magnetometer (VSM) measurement shows that magnetic parameters, such as initial permeability (µi) and saturation magnetization (Ms), decay with rising Mg content. The permeability and magnetic anisotropy at different frequencies and temperatures were studied to show the samples' magnetic behavior and determine the Curie temperature (TC), which depends on the internal structure. The electrical resistivity behavior shows the semi-conductivity trend of the samples. Finally, the dielectric constant increases sharply at high temperatures, explained by the increased mobility of charge carriers, and decreases with increasing frequency.

Impact of the Nanocarbon on Magnetic and Electrodynamic Properties of the Ferrite/Polymer Composites.

Binary and ternary composites (CM) based on M-type hexaferrite (HF), polymer matrix (PVDF) and carbon nanomaterials (quasi-one-dimensional carbon nanotubes-CNT and quasi-two-dimensional carbon nanoflakes-CNF) were prepared and investigated for establishing the impact of the different nanosized carbon on magnetic and electrodynamic properties. The ratio between HF and PVDF in HF + PVDF composite was fixed (85 wt% HF and 15 wt% PVDF). The concentration of CNT and CNF in CM was fixed (5 wt% from total HF + PVDF weight). The phase composition and microstructural features were investigated using XRD and SEM, respectively. It was observed that CM contains single-phase HF, γ- and ß-PVDF and carbon nanomaterials. Thus, we produced composites that consist of mixed different phases (organic insulator matrix-PDVF; functional magnetic fillers-HF and highly electroconductive additives-CNT/CNF) in the required ratio. VSM data demonstrate that the main contribution in main magnetic characteristics belongs to magnetic fillers (HF). The principal difference in magnetic and electrodynamic properties was shown for CNT- and CNF-based composites. That confirms that the shape of nanosized carbon nanomaterials impact on physical properties of the ternary composited-based magnetic fillers in polymer dielectric matrix.

Investigation of AC-Measurements of Epoxy/Ferrite Composites.

A pure ferrite and epoxy samples as well as the epoxy/ferrite composites with different 20 wt.%, 30 wt.%, 40 wt.%, and 50 wt.% weight ferrite contents have been prepared by the chemical co-precipitation method. AC-conductivity and dielectric properties such as the dielectric constant and dielectric loss of the prepared samples have been studied. The obtained results showed that the samples had a semiconductor behavior. The dielectric constant of the composites has been calculated theoretically using several models. For the composite sample that contains 20 wt.% of ferrites, these models give satisfactory compliance, while for the composite samples with a higher percentage of nanofillers, more than 30 wt.% theoretical results do not coincide with experimental data. The investigated polymer has very low conductivity, so this type of polymer can be useful for high-frequency applications, which can reduce the losses caused by eddy current. Thus, the prepared samples are promising materials for practical use as elements of microwave devices.

Functional Magnetic Composites Based on Hexaferrites: Correlation of the Composition, Magnetic and High-Frequency Properties.

The paper describes preparation features of functional composites based on ferrites, such as "Ba(Fe1-xGax)12O19/epoxy," and the results of studying their systems; namely, the correlation between structure, magnetic properties and electromagnetic absorption characteristics. We demonstrated the strong mutual influence of the chemical compositions of magnetic fillers (Ba(Fe1-xGax)12O19 0.01 < x < 0.1 solid solutions), and the main magnetic (coercivity, magnetization, anisotropy field and the first anisotropy constant) and microwave (resonant frequency and amplitude) characteristics of functional composites with 30 wt.% of hexaferrite. The paper presents a correlation between the chemical compositions of composites and amplitude-frequency characteristics. Increase of Ga-content from x = 0 to 0.1 in Ba(Fe1-xGax)12O19/epoxy composites leads to increase of the resonant frequency from 51 to 54 GHz and absorption amplitude from -1.5 to -10.5 dB/mm. The ability to control the electromagnetic properties in these types of composites opens great prospects for their practical applications due to high absorption efficiency, and lower cost in comparison with pure ceramics oxides.

Correlation Between Composition and Electrodynamics Properties in Nanocomposites Based on Hard/Soft Ferrimagnetics with Strong Exchange Coupling.

In this work, Sr0.3Ba0.4Pb0.3Fe12O19/(CuFe2O4)x (x = 2, 3, 4, and 5) as strongly exchange-coupled nanosized ferrites were fabricated using a one-pot sol⁻gel combustion method (citrate sol-gel method). The X-ray diffraction (XRD) powder patterns of the products confirmed the occurrence of pure, exchange-coupled ferrites. Frequency dependencies of the microwave characteristics (MW) were investigated using a co-axial method. The non-linear behavior of the MW with the composition transformation may be due to different degrees of Fe ion oxidation on the spinel/hexaferrite grain boundaries and strong exchange coupling during the hard and soft phases.