Yazar "Sarac, Mehmet F." seçeneğine göre listele

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    Cr-substituted nanocrystalline Ni-Co ferrites: tuning dielectric, magnetic, structural, X-band microwave absorption, and characteristic properties
    (Springer, 2023) Teber, Ahmet; Sarac, Mehmet F.
    The structural, characteristic, dielectric, and magnetic features of Co0.5Ni0.5CrxFe2 - xO4 (0.0 <= x <= 1.0 with a step of 0.2 x-concentration) nanoparticles are prepared via the hydrothermal method. The investigation of characteristics, structural, and magnetic features of the produced nanoparticles are examined through XRD, FT-IR, SEM-EDS, TEM-SAED, and VSM, respectively. AC conductivity and the dielectric investigations are also reported. According to the XRD measurements, all samples have the M-type hexagonal crystal structure nanocrystallites of between 27 and 97 nm. Refined structural parameters using Rietveld analysis are carried out using the TOPAS refinement program. A good match was observed between the diffraction patterns obtained and calculated by Rietveld analysis. Moreover, the morphological analyses indicate that the relatively small spherical structures of Ni-Co ferrites particles can be seen to change from spherical to relatively oval-shaped with increasing chromium content. The results of the FT-IR study show that the spinel structure has formed as predicted because the expected range of absorption bands is present. According to magnetic measurements, Cr-substituted Ni-Co ferrite nanostructures reveal a relatively soft ferromagnetic property. The coercive field (H-c) variation has a propensity to decrease in relation to the Cr-concentration. The electromagnetic constitutive parameters are calculated from measured S-parameters (S-11 and S-21) using network analyzer and the return losses of the samples are then obtained to determine microwave absorption properties. According to the dielectric and magnetic tangent losses or dissipation factors, both dielectric and magnetic features can mutually reinforce in terms of microwave absorption properties in the X-band. The Cr2O3 impurity peaks obtained by XRD analysis have an effect on the microwave absorption properties. The results of the microwave absorption based on each concentration reveal that there exist electromagnetic wave absorptions between approximately 11 GHz and 12.4 GHz in the X-band. The absorption trend is also towards the Ku-band.
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    Electrical, Magnetic, Microstructural, and Characteristic Properties of Zirconium-Substituted Co0.5Ni0.5ZrxFe2-xO4Spinel Ferrite Nanostructures
    (Springer Heidelberg, 2023) Teber, Ahmet; Sarac, Mehmet F.
    The effect of zirconium (Zr) substitution in nickel-cobalt ferrites, Co0.5Ni0.5ZrxFe2-xO4 (0.0 <= x <= 1.0) produced by the hydrothermal method on the electrical, magnetic, microstructural and characteristic properties are reported. A secondary phase as tetragonal-ZrO2 phase in the crystal system is detected and have both M-type hexagonal and tetragonal nanocrystallites between 32 and 67 nm. Refined structural parameters using Rietveld analysis are carried out, resulting in lattice parameters, the unit cell volume, parameter ratios, and the crystallite size using the TOPAS refinement program. In addition, residuals for the R-Bragg factor and goodness of fit (chi(2)) value for each concentration are represented. The Rietveld analysis determines that the predicted and actual diffraction patterns are in accord. Furthermore, the Zr effect is presented in unit volume as seen by the drop in peak intensity that occurs (with the addition of Zr) due to the lattice tension. Moreover, the morphological analyses indicate that the shape transformed from agglomerated clusters to oval-shaped structures and a reduction in grain size. Fourier transform infrared (FT-IR) analysis in the range of 4000-450 cm(-1) correlates with the presence of the hexagonal spinel ferrite structure. The dielectric parameters, such as the relative permittivity, tangent loss, and ac conductivity, are experimentally measured with the oscillation voltage level of 0.05 V in the frequency range of 0.1-10 MHz. The dielectric permittivities and tangent losses of the specimens decreased with an increment in frequency. Magnetic measurements reveal that the values of coercivity (H-c) have the propensity to increase relating to the zirconium concentration.
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    Yttrium-substituted Co0.5Ni0.5YxFe2-xO4 ferrites as microwave absorbers by investigating structural, magnetic, dielectric, and absorption characteristics
    (Elsevier, 2023) Teber, Ahmet; Sarac, Mehmet F.
    The effect of Yttrium Substitution on Co0.5Ni0.5YxFe2-xO4 (0.0 <= x <= 1.0) Ferrites as Microwave Absorbers was investigated to include structural, magnetic, dielectric and X-band absorption properties. The main objective of this work is to enhance microwave absorption properties of materials with interesting dielectric/magnetic be-haviors by doping rare earth element of Yttrium based on transition metals. The hydrothermal method was used to create Yttrium (Y) substituted nanoparticles, and the effects of Y-ion substitution on the characteristics, structural, magnetic features were examined by XRD, FT-IR, SEM-EDS, TEM-SAED, and VSM, respectively. Electromagnetic properties were obtained from microwave scattering parameters measured via a metal-backed transmission line and Nicholson-Ross Weir techniques using a vector network analyzer (VNA) in conjunction with an X-band waveguide set. Return loss (RL) values of the samples were obtained from the electromagnetic constitutive parameters (permittivity and permeability). According to the XRD measurements, hexagonal crystal structure of ferrite and YFeO3 as secondary phase nanocrystal sizes are between 11 and 67 nm. Refined structural parameters using Rietveld analysis are carried out using the TOPAS refinement program. A good match was observed between the diffraction patterns obtained and calculated by Rietveld analysis. Moreover, the morphological analyses indicate that the relatively small spherical structures of Ni-Co ferrites particles can be seen to change from spherical to hexagonal-shaped with increasing yttrium concentration. The results of the FT-IR study show that the spinel structure has formed as predicted because the expected range of absorption bands is present. According to magnetic measurements, the coercivity (Hc) results show a modest increase in porosity as the Y-content rises. The results revealed that the minimum RL value and bandwidth vary significantly with the amount of Yttrium in the mixture, indicating that the obtained structures will be useful for broadband microwave applications.