Crystal microstructure, infrared absorption, and microwave electromagnetic properties of (La_(1-x)Dy_x)_(2/3)Sr_(1/3)MnO_3

The manganite perovskite polycrystal samples of （La1-xDyx）2/3Sr1/3MnO3 （x = 0, 0.1, 0.2, 0.35, and 0.5） doped with Dy were prepared by solid state reaction in atmosphere to measure their X-ray diffraction （XRD） patterns, scanning electric microscope （SEM） images, infrared absorption spectra, and microwave electromagnetic properties. The displacement of the XRD peaks of the samples was found, and the 2θ increases from 0.05o to 0.5o. The grains of undoped La2/3Sr1/3MnO3 not only have the greatest size, but also the most regular shape. The size of the grains decreases as the Dy doping content increases from 0 to 0.5. The infrared absorption spectra of all samples were measured at room temperature. An absorption peak corresponding to the stretching vibration mode of Mn-O bonds appears within the range of 591-629 cm-1. The absorption peak shifts from a higher frequency to a lower one with the decrease of the average ionic radius of A-site. The frequency de- pendence of microwave-absorbing properties, imaginary components of the complex magnetic permeability μ＂ and dielectric permeability ε＂ for all samples was measured at room temperature from 8 to 13 GHz. The results show that the loss of microwave absorption can be attrib- uted to both the magnetic and electric losses. The increase of Dy content not only enhances the microwave absorption but also causes the displacement of the absorption peaks.

Microstructure and microwave electromagnetic properties of Dy^(3+)-doped W-type hexaferrites

Ba 1 x Dy x Co 2 Fe 16 O 27 （x = 0.00, 0.05, 0.10, 0.15, and 0.20） was prepared by the solid-state method. The phase structure was studied using powder X-ray diffraction （XRD）, the electromagnetic properties were measured, and the reflection loss of Dy 3＋ -doped ferrite material was calculated using electromagnetic parameters by the transmission line theory. All XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x ≤ 0.15. The values of ε ′ and ε ″ increased slightly with Dy 3＋ ions doping. The values of μ″ and μ′ were improved with Dy 3＋ doping, exhibiting excellent microwave magnetic performance. The reasons have also been discussed using the electromagnetic theory. Dy substitution could increase microwave-absorbing performance and broaden frequency band （reflection loss （RL） -10 dB）, and the absorbing peak shifted to high-frequency position. When x = 0.2, ferrite layer exhibited the most excellent microwave-absorbing performance at a thin matching thickness of 1.5 mm. The peak value of RL was around -15 dB, and the frequency band （RL -10 dB） was about 7 GHz （from 8 to 15 GHz）.

Combustion Synthesis,Character and Electromagnetic Properties of Nano-Sized La_(0.8)Sr_(0.2)FeO_3 Perovskite

The perovskite-type nanocrystal La0.8Sr0.2FeO3 was prepared using a sol-gel auto-combustion method with citric acid as the chelating agent. The metal ions coordination compound, obtained from nitrate and citrate, underwent an auto-combustion process and voluminous ashes formed when calcining the complex in the air. Some analytical methods, which consisted of FT-IR, XRD, TEM and wave-guide, were used to characterize the gel and the final products. It was shown that metal ions and carboxyl were combined to form a homogeneous organic complex base salts in the process of gelation. The nanocrystalline had dielectric loss in the microwave frequency range of measurement.

Influence of Er^(3+) Substitution on Microwave Magnetic Performance of BaFe_(12)O_(19)

Barium hexaferrites doped with Er3+, Ba1-xErxFe12O19, x=0.0, 0.01, 0.02, 0.04, 0.06, were prepared by the conventional ceramic technology. The structure and electromagnetic properties of the calcined samples were studied using powder X-ray diffraction (XRD) and network analyzer (Agilent 8722ET). All the XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x is below 0.02. The lattice parameters of ferrites doped with Er3+ decreased, indicating that the substitution of Er3+ occurs on Ba2+ basis site and results in a contract of the crystal cell. The microwave electromagnetic properties of the samples have been studied at the frequency range from 2 to 18 GHz. It was shown that ε′ increased slightly, and the maximum of ε″ appeared at low frequency position with Er3+ doping. μ″ and μ′ were improved significantly when x=0.01, and the maxima are 2 and 1.7, respectively. The reasons were also discussed using electromagnetic theory.

Effect of liquid-solid ratio on the morphology,structure,conductivity,and electromagnetic characteristics of iron particles

Using a ball-milling technique,polymorphous iron particles were prepared by changing only the liquid-solid ratioλ.Effects of λon their morphology,structure,conductivity,and electromagnetic properties were studied.The results show that an increase ofλfrom 0 to 0.25 causes a nonlinear decrease of the conductivity in the ranges of 88.50-2.25 S cm-1 and a regular variation of the electromagnetic parameters,corresponding to the as-obtained iron particles.This is ascribed to a combination of the increased shape anisotropy and the decreased fresh surface with active atoms deriving from the weakened welding-on action and the enhanced micro-malleation action in the ball-milling process.Hereinto,the iron flakes formed at wet-milling with λ=0.08-0.25 have lower conductivity,higher permittivity and permeability,and more excellent absorption property compared with the irregular iron particles obtained at dry-milling withλ=0.It is a consequence of the synergistic effect of dielectric relaxation loss,exchange energy and conductance loss originating from the flake-shape structures.This indicates that the morphology,structure,conductivity,and electromagnetic properties of the products can be effectively controlled by changingλ.