Lanthanum doped Manganese-Zinc spinel ferrite nanoparticles for microwave and soft magnet applications
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Dielectric loss
Hexa-spinel ferrite composites with various mass ratios (1:1, 1:2, 1:5, and 1:8) of the two constituent phases Ba2Ni2Fe12O22 and CuFe2O4 were prepared by Sol-Gel auto combustion technique. The effects of composition on the crystallography, particle morphology, and Dielectric constant were investigated. The XRD patterns of the composites reveal that all the composites were consisted of two phases: hexagonal and spinel. The absence of new phase proved that there was no chemical reaction between spinel and hexagonal ferrites. The SEM photographs show that the two kinds of phases were distributed homogenously. All the samples show the frequency dependent phenomena, i.e. the dielectric constant decreases with increasing frequency and then reaches a constant value.
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Abstract In the present work, nanocrystalline Sb 3+ ions doped Ni 0.2 Ba 0.1 Co 0.7 Fe 2−x Sb x O 4 (0 ≦ x ≦ 0.1, step by 0.025) ferrites were prepared via sol-gel method. The spinel-phase structure of samples can be confirmed by X-ray diffraction (XRD) patterns. The composition and structure were further studied by fourier transform infrared spectroscopy (FTIR). There were two typical characteristic bands ν 1 and ν 2 related to the stretching vibrations in spinel ferrite in FTIR spectra. Energy dispersive spectrometer (EDS) analyzed the elements of samples. It indicated that the elements of Ni, Ba, Co, Fe, O and Sb existed in the samples. Vibrating sample magnetometer was used to characterize magnetic properties. The saturation magnetization decreased from 57.65 emu/g to 44.50 emu/g with the increasing Sb 3+ ions content, which is attributed to Fe 3+ ions replaced by the Sb 3+ ions. Remanent magnetization and coercivity first decreased and then increased slightly.
Nanocrystalline material
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In this work, 0-3 lead zirconate titanate (PZT) was mixed with normal Portland cement to produce 0-3 connectivity composites. The effect of temperature on the dielectric properties such as the dielectric constant and dielectric loss was determined. It was found that with increasing PZT content the Tc increases where the optimum dielectric constant was observed and that at the temperature up to 100°C there is a significant change in the dielectric properties in PZT-cement composites. This is due to the loss of water molecules at up to 100°C. At above 100°C, the dielectric properties of the composites were found to have a similar behavior to that of PZT ceramic with Tc being ≈420°C.
Lead zirconate titanate
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Zirconate
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Ceramic/polymer composites made of nanosized CaCu3Ti4O12 (CCTO) powders as filler and P(VDF-TrFE) copolymers as matrix were fabricated by solution casting method followed by a hot-press process. The hot-press process results in a better morphological uniformity in the composites. The morphology of the composites was investigated using scanning electron microscopy, while the dielectric propeorties of the composites at temperatures from room temperature to 125°C were characterized at frequencies from 100 Hz to 1 MHz. It is found that the composites exhibit a relatively high dielectric constant with a small dielectric loss. For example, the flexible composites with 50 vol.% CCTO, the dielectric constant at 1 kHz is 60 with a loss about 0.05.
Dielectric loss
High-κ dielectric
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The mixed polycrystalline ferrites , were obtained using the standard double sintering technique of mixing high purity of metal oxides , and for different concentration of Ni content. Double probe electrode method was used to measure the AC electrical conductivity ( ), real dielectric constant ( e' ), the imaginary dielectric constant ( e ''), the complex dielectric constant ( e *) and the dielectric loss tangent (tan δ ) over a variable angular frequency in range of at room temperature. for the given samples shows a continuous increasing with the increasing of the applied angular frequency. The results obtained from the dielectric parameter for all the samples decreases with increasing of frequency, which indicated to normal spinel ferrite behavior. The variation of AC and dielectric parameters were explained on the basis of electronic exchange between or . The experimental results reveal that the electrical and dielectric properties, which can be dramatically, changed by substitution of the Ni content in spinel ferrite. These improved properties of the mixed Zn-Ni spinel ferrite suggest uses as a soft ferrite material, which is proving an interesting material for technological and scientific applications.
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Influence of Ca substitution on structural, magnetic and dielectric properties of Ba 3 Co 2-x Ca x Fe 24 O 41 (where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), prepared by Sol-Gel auto-combustion method, has been investigated in present studies. The obtained powder was sintered at 950 oC for 4 hrs. in the static air atmosphere. Structural analysis of Ca-doped Ba 3 Co 2-x Ca x Fe 24 O 41 powders revealed pure Z-type hexaferrite phase at low temperature. The frequency dependent dielectric constant (Єʹ) and magnetic properties such as remanent magnetization (Mr), saturation magnetization (Ms) and coercivity (Hc) were studied. It is observed that coercivity increased gradually with increase in calcium content. The real dielectric constant (Єʹ) and dielectric loss tangent (tan δ) were studied in the frequency range of 20Hz to 2MHz. The dielectric parameters for all samples show normal dielectric behavior as observed in hexaferrites. Contents of Paper
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Stoichiometry
Magnetic Relaxation
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The series of Cr-Zn nano ferrites having the general composition CrxZnFe2-xO4 (0 ≤ x ≤ 0.5) have been synthesized successfully in the nanocrystalline form using the sol-gel method. The samples were sintered at 900°C for 3 hours. The effect of chromium substitution on dielectric properties of Zn-ferrites is reported in this paper. The analysis of XRD patterns revealed the formation of single phase cubic spinel structure for all the Cr-Zn ferrite samples. The FTIR spectra show two strong absorption bands in the range of 400 - 600 cm-1, which corroborate the spinel structure of the samples. The average grain size was found to be in the nanometer range and of the order of 43 - 63 nm obtained using TEM images. The lattice parameter and crystallite size decrease with increase in Cr concentration (x). The investigation on dielectric constant (ε'), dissipation factor (D) and ac conductivity (σac) was carried out at a fixed frequency 1 kHz and in the frequency range of 100 Hz to 1 MHz at room temperature using LCR meter. The plots of dielectric constant (ε') versus frequency show the normal dielectric behavior of spinel ferrites. The value of ac conductivity (σac) increases with increase in frequency for all the compositions. The appearance of the peak for each composition in the dissipation factor versus frequency curve suggests the presence of relaxing dipoles in the Cr-Zn nano ferrite samples. It is also found that the shifting of the relaxation peak towards lower frequency side with an increase in chromium content (x) is due to the strengthening of dipole-dipole interactions. The composition and frequency dependence of the dielectric constant, dielectric loss and ac-conductivity are explained based on the Koop’s two-layer model, Maxwell-Wagner polarization process, and Debye relaxation theory.
Nanocrystalline material
Dielectric loss
Dissipation factor
Lattice constant
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Lattice constant
Dielectric loss
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