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Nickel ferrite loaded (NiFe2O4) segmented polyurethane (SPU) nanocomposites prepared by melt mixing method using microcompounder at temperature 185 °C in recirculation mode to ensure proper dispersion and distribution of nanoparticles at optimized residency time of 5 min. Three different weight percentages of nanocomposites (3, 5, and 10 wt %) was prepared and studied the electromagnetic property of nanocomposites obtained from complex permittivity and permeability. The effect of nanofiller (NiFe2O4) has been studied to assess their thermal properties using thermogravimetric analysis, differential scanning calorimetry, and thermomechanical analysis. The nanocomposites (NiFe2O4/SPU) have further been studied using FE‐SEM, and the micrographs show embedded NiFe2O4 filler uniformly dispersed in SPU matrix without agglomeration (size 20–40 nm). It is also evident that further loading of nanofiller resulted in saturation effect yielding no applicable change in thermal behavior and revealed lesser melting enthalpy due to the coalescence of the nanofillers. X‐ray diffraction and vibrating sample magnetometer also support the formation of the nanocomposite. The electric and magnetic properties of NiFe2O4 incorporated nanocomposite (NiFe2O4/SPU) may have potential application in microwave absorption. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48645. [ABSTRACT FROM AUTHOR]

Electromagnetic absorbers based on carbonaceous materials, i.e., carbon black, polyaniline, polypyrrole, carbon fiber, etc., are prominently employed to attenuate incident electromagnetic waves. In the current work, exfoliated graphite (EG) was synthesized with swollen expanded volume from graphite flake by using a simple and inexpensive method. After synthesis, a series (8.9, 22.9, 33.3, 41.4 and 44.7 volume percentage) of EG–epoxy composites were prepared using a wet mixing method. EG and the prepared composites were characterized by x-ray diffraction analysis, field-emission scanning electron microscopy, and energy-dispersive x-ray analysis. An Agilent vector network analyzer (model PNA E8364B) was employed to compute the complex permittivity (εr = ε′ − jε″) of the prepared composites in the frequency range of 2 GHz to 18 GHz. The dielectric loss of the prepared EG–epoxy composites was quantified in terms of the loss tangent (tanδe = ε″/ε′). Their radar absorption properties were evaluated in terms of the return loss (RL), which in turn was calculated for varying thicknesses of the prepared composites using the computed complex permittivity data. The measured minimum RL was −26.4 dB for the absorber with thickness of 4.0 mm, and the bandwidth achieved was 5.2 GHz for RL ≤ − 10 dB in the effective frequency region of 8 GHz to 14 GHz. The matching frequency shifted towards downwards with increasing EG content in the epoxy thermosetting matrix according to both the calculated and measured data. Consequently, the prepared composites exhibited good complex permittivity, dielectric tangent loss, and microwave absorption and could be utilized in the design of electromagnetic interference shielding and absorbers for stealth applications. [ABSTRACT FROM AUTHOR]

Ferroelectric Sr1−xBaxBi2(Nb0.5Ta0.5)2O9 and Sr0.5Ba0.5Bi2(Nb1−yTay)2O9 were synthesized by solid state reaction route. X-ray diffraction studies confirm the formation of single phase layered perovskite solid solutions over a wide range of compositions (x=y=0.0, 0.25, 0.50, 0.75 and 1). The lattice parameters and the Curie temperature (Tc) have been found to have linear dependence on x and y. Transmission electron microscopy (TEM) suggest the lowering of orthorhombic distortion with increasing Ba2+ substitution. Variations in microstructural features as a function of x and y were monitored by scanning electron microscopy (SEM). The dielectric constant at room temperature increases with increase in both x and y. Interestingly Ba2+ substitution on Sr2+ site induces diffused phase transition and diffuseness increases with increasing Ba2+ concentration. [Copyright &y& Elsevier]

In the present study, lead-free piezoelectric (1-x)[(Bi 0.96 La 0.04 ) 0.5 Na 0.5 TiO 3 ]-(x)[Ba 0.90 Ca 0.10 TiO 3 ] ceramics with x ≤ 0.20 have been prepared at optimum temperature (950°C–1050 °C) by employing semi-wet technique. The effect of Ba 0.90 Ca 0.10 TiO 3 (BCT) content on the phase formation, surface morphology, dielectric and piezoelectric properties is systematically investigated and characterized by X-ray diffraction (XRD), Raman Spectroscopy, Field emission Scanning electron micrographs (FE-SEM), Impedance analyzer. XRD analysis shows phase transformation from rhombhohedral to tetragonal with the addition of BCT and the average grain size decreases with BCT content, x. Temperature dependent dielectric behavior exhibits two phase transitions, i.e. depolarization temperature; T d and phase transition temperature; T m . The phase transitions; T m tends to diffuse with increasing x and exhibited a broad frequency dependent maximum upto x ≤ 12. Optimum piezoelectric and dielectric properties (i.e., d 33 = 165 pC/N, k p = 39%, k t = 47% and k 33 = 57%, ε r = 1585, tan δ = 0.07) in the studied system have been obtained. [ABSTRACT FROM AUTHOR]