Dielectric behavior of Cu-Zn ferrites with Si additive

Since ferrites are highly sensitive to the additives present in or added to them, extensive work, to improve the properties of basic ferrites, has been carded out on these aspects. The present paper reports the effects of composition, frequency, and temperature on the dielectric behavior of a series of CuxZn1-xFe2O4 ferdte samples prepared by the usual ceramic technique. In order to improve the properties of the samples, low cost Fe2O3 having 0.5 wt.% Si as an additive is selected to introduce into the system. The dielectric constant increases by increasing the Cu content, as the electron exchange of Cu^2＋ 〈=〉 Cu^＋ is responsible for the conduction and the polarization. However, the addition of Si could decrease the dielectric constant as it suppresses the ceramic grain growth and promotes the quality factor at higher frequencies. Dielectric constant ε′ and loss tangent tan δ of the mixed Cu-Zn ferrite decrease with increasing frequency, attributed to the Maxwell-Wagner polarization, which increases as the temperature increases.

The dielectric behavior and efficient microwave absorption of doped nanoscale LaMnO_(3)at elevated temperature

LaMnO_(3)perovskite has great potential in microwave absorption at high temperature due to its complex doping effect and super stability.The current research mainly focuses on the doping ratio regulation,while the mechanism of doping effect at high temperature is still lack of sufficient investigation.In this work,La1−xSrxMn1−yFeyO_(3)(LaMnO_(3),La_(0.7)Sr_(0.3)MnO_(3),and La_(0.7)Sr_(0.3)Mn_(0.8)Fe_(0.2)O_(3))nanostructures with different doping sites were successfully prepared by the solid phase reaction method.Then,the high temperature dielectric test samples were obtained by mixing with cordierite(2MgO·2Al_(2)O_(3)·5SiO_(2)(MAS)).The results showed that the temperature dependence of Mn ion spin state had a significant impact on the high temperature dielectric behavior of La_(1−x)Sr_(x)Mn_(1−y)FeyO_(3).Particularly,when the thickness is only 1.9 mm,La_(0.7)Sr_(0.3)Mn_(0.8)Fe_(0.2)O_(3)/MAS can achieve the widest bandwidth of 4.2 GHz covered the entire X-band(8.2–12.4 GHz)and a minimum reflection loss(RL)value of−17.99 dB at 500℃.In order to improve the operating temperature of La_(0.7)Sr_(0.3)Mn_(0.8)Fe_(0.2)O_(3)/MAS,a cellular array structure was designed by using computer simulation technology(CST)software to introduce magnetic loss.When the outer length of the hexagon is 1 mm and the coating thickness is 1.9 mm,the widest bandwidth covers the X-band and the minimum RL value is−15.35 dB at 800℃.Therefore,La_(0.7)Sr_(0.3)Mn_(0.8)Fe_(0.2)O_(3)has a great prospect as an efficient high temperature microwave absorber.

Dielectric behavior of alumina thin film under high DC electric field prepared by sol–gel method

Dielectric behavior of aluminum oxide(Al_(2)O_(3))thin film under high DC electric field is presented and discussed.Aluminum oxide thin films were prepared starting from aluminum isopropoxide as a precursor via a wet chemistry route.Silicon substrates and silica glass substrates were used to deposit the films via spin-coating technique.The deposited films were then annealed under 450℃–700℃ for 2–3 h.Dense,crack-free and uniform films were obtained.The thickness of the films is in the range of 200–800 nm.The films obtained are in amorphous state as revealed by the X-ray diffraction patterns.Voltage–Current(V–I)characteristics of the films were used to study the dielectric behavior of the films.Very low leakage current density J under high DC electric field E can be obtained.The breakdown electric field of the films is around 1.2 MV/cm.The V–I characteristics of the films are slightly nonlinear.With platinum as bottom electrode and gold as top electrode,successive breakdown phenomena of the films under high DC electric field were observed.Each breakdown event of the film corresponds to a sharp spike at the V–I plot of the sample.The shape of the breakdown spots of the films are in crater-like with a breakdown channel of diameter around a few micrometers as revealed by SEM images.The top gold electrode at the breakdown spots either splashed out or ripped off from the breakdown spots,which isolated the breakdown spots from rest of the electrode,and made the successive breakdown of the sample possible.The breakdown spots of the sample are concentrated at the edge of the electrode with proportional spacing,which can be easily understood as the edge effect of the parallel capacitor configuration,while the uniform distribution of the breakdown spots signifies that the uniformity of the films thus prepared are satisfied.Breakdown spots apart from the electrode edge can also be observed.Most of such spots associated with ripped-off gold film electrode in large area.We suppose such breakdown took place at higher electric field after the successive breakdown at the electrode edge and the isolation of the edge part from rest of the sample.Higher energy is needed to tear off larger section of the electrode.The breakdown characteristics of the films reported in this work are useful for the further study to enhance the breakdown strength of the film.

CONDUCTIVITY AND DIELECTRIC BEHAVIOR OF PLiAMPS-BASED SEMI-IPN SINGLE ION CONDUCTOR PLASTICIZED WITH POLY(SILOXANE-G-ETHYLENE OXIDE)

Comb poly(siloxane-g-ethylene oxide)(PSi-PE)with high chain segmental mobility,as a plasticizer,was introduced into poly(lithium 2-acrylamido-2-methyl-1-propanesulfonate)(PLiAMPS)-based semi-interpenetrating polymer network single-ion conductors.The structures of PSi-PE and PLiAMPS were characterized by FTIR spectroscopy.The distribution of PSi-PE in polyelectrolyte matrix was investigated through observing the residual surface morphology of conductor membrane after being etched by toluene.AC impedance and dielectric behavior measurements were used to investigate the impact of PSi-PE on the ionic conductivity and to analyze the mechanism of conductivity variation.Compared with the unplasticized membranes,the ionic conductivity of the membrane with the addition of 35 wt.%PSi-PE was improved by 20 times.Meanwhile,the dielectric constant(ε)of the membrane was increased to 1330 and the relaxation time was decreased to 0.012 s.The changes of dielectric properties reflect directly the effect of PSi-PE on the dissociation ability of Liþand the chain segmental mobility,which well explains the reasons of ionic conductivity variation.

Influences of nanoparticles and chain length on thermodynamic and electrical behavior of fluorine liquid crystals

Hydrogen-bonded polar nematic liquid crystal series with the general formula n OBAF(n = 7-12) is studied. The mesomorphic characterization is demonstrated through differential scanning calorimetry(DSC) and polarized optical microscopy(POM). The complexes with short alkyl chains(n = 7, 8) present a wide nematic range and monotropic smectic F mesophase, whereas the longer alkyl chain(n = 10-12) analogues show high melting and low clearing mesomorphic liquid crystals. The thermal range of the mesophase and the birefringence increase with chain length decreasing. Furthermore, the effect of the nanoparticles(LiNbO_(3)) on the thermal and the electrical behavior of 8OBAF are investigated. The presence of LiNbO_(3) nanoparticles increases the conductivity and reduces the resistivity of the complex.

Identification of the Intrinsic Dielectric Properties of Metal Single Atoms for Electromagnetic Wave Absorption

Atomically dispersed metals on N-doped carbon supports(M-N_(xCs)) have great potential applications in various fields.However,a precise understanding of the definitive relationship between the configuration of metal single atoms and the dielectric loss properties of M-N_(xCs) at the atomic-level is still lacking.Herein,we report a general approach to synthesize a series of three-dimensional(3D)honeycomb-like M-N_xC(M=Mn,Fe,Co,Cu,or Ni) containing metal single atoms.Experimental results indicate that 3D M-N_(xCs) exhibit a greatly enhanced dielectric loss compared with that of the NC matrix.Theoretical calculations demonstrate that the density of states of the d orbitals near the Fermi level is significantly increased and additional electrical dipoles are induced due to the destruction of the symmetry of the local microstructure,which enhances conductive loss and dipolar polarization loss of 3D M-N_(xCs),respectively.Consequently,these 3D M-N_(xCs) exhibit excellent electromagnetic wave absorption properties,outperforming the most commonly reported absorbers.This study systematically explains the mechanism of dielectric loss at the atomic level for the first time and is of significance to the rational design of high-efficiency electromagnetic wave absorbing materials containing metal single atoms.

Enhancing Dielectric and Mechanical Behaviors of Hybrid Polymer Nanocomposites Based on Polystyrene,Polyaniline and Carbon Nanotubes Coated with Polyaniline

The dielectric and mechanical properties of hybrid polymer nanocomposites of polystyrene/polyaniline/carbon nanotubes coated with polyaniline （pCNTs） have been investigated using impedance analyzer and extensometer. The blends of PS/PANI formed the heterogeneous phase separated morphology in which pCNTs are dispersed uniformly. The incorporation of a small amount of pCNTs into the blend of PS/PANI has remarkably increased the dielectric properties. Similarly, the AC conductivity of PS/PANI is also increased five orders of magnitude from 1.6 × 10^-10 to 2.0×10^-5 S.cm-1 in the hybrid nanocomposites. Such behavior of hybrid nanocomposites is owing to the interfacial polarization occurring due to the presence of multicomponent domains with varying conductivity character of the phases from insulative PS to poor conductor PANI to highly conductive CNTs. Meanwhile, the tensile modulus and tensile strength are also enhanced significantly up to 55% and 160%, respectively, without much loss of ductility for three phase hybrid nanocomposites as compared to the neat PS. Thereby, the hybrid nanocomposites of PS/PANI/pCNTs become stiffer, stronger and tougher as compared to the neat systems.

Sintering characteristics, phase transitions, and microwave dielectric properties of low-firing [(Na_(0.5)Bi_(0.5))_(x)Bi_(1-x)](W_(x)V_(1-x))O_(4) solid solutionceramics

A series of high-k[(Na_(0.5)Bi_(0.5))_(x)Bi_(1-x)](W_(x)V_(1-x))O_(4)(abbreviated as NBWV(x value))solid solution ceramics with a scheelite-like structure are synthesized by a modified solid-state reaction method at the temperature range of 680-760 C.A monoclinic(0≤x<0.09)to tetragonal scheelite(0.09≤x≤1.0)structural phase transition is confirmed by X-ray difraction(XRD),Raman,and infrared(IR)analyses.The effect of structural deformation and order-disorder caused by Na^(+)/Bi^(3+)/W^(6+) complex substitution on microwave dielectric properties is investigated in deail.The compositional series possess a wide range of variable relative permittivity(er=24.8-80)and temperature coefficient of resonant frequency(TCF value,-271.9-188.9 ppm/℃).The maximum permittivity of 80 and a high Qxf value of~10,000 GHz are obtained near the phase boundary at x=0.09.Furthermore,the temperature-stable dielectric ceramics sintered at 680 C with excellent microwave dielectric properties of ε_(r)=80.7,Qxf=9400 GHz(at 4.1 GHz),and TCF value=-3.8 ppm/℃ are designed by mixing the components of x=0.07 and 0.08.In summary,similar sinterability and structural compatibility of scheelite-like solid solution systems make it potential for low-temperature co-fired ceramic(LTCC)applications.

Damping Properties of Piezoelectric and Electrical Conductive of BaTiO_3/VGCF/CPE Composites: Effect of Carbon Fiber

A new damping composite of CPE/BaTiO3/VGCF has been developed on the basis of the piezo- effect and conductivity mechanism. The conductivity of composites varied with the VGCF content are tested and analyzed.The results indicate that the conductivity of composites grows up slowly as the VGCF content is in the range of 10%-20%. It is very useful for industrial application to control the conductivity of composites by adjusting the VGCF content. In addition, at the range of - 50 - 120°C,the dependence of loss factor on the VGCF content varied with the temperature are tested and analyzed by dynamic mechanical and dielectric behavior measurement of the composites, and expected results are obtained.

Preparation,crystallization,microstructure and dielectric properties of lead bismuth titanate borosilicate glass ceramics

Various bulk and transparent glasses were prepared by rapid melt quenching technique in the glass system 55[(Pb_(x)Bi_(1-x))TiO_(3)]-44[2Si_(O)2B_(2)O_(3)]-La2O3(x=0-0.7).The X-ray diffraction(XRD)studies of the glass samples confirmed the amorphous nature.The differential thermal analyses(DTA)were carried out from room temperature to 900℃with a heating rate of 10℃/min.The DTA patterns of the samples showed one or more exothermic sharp peaks shifting towards lower temperature side with increasing concentration of bismuth oxide(BiO).On the basis of DTA results,the solid solution of bismuth titanum oxide(Bi_(2)Ti_(2)O_(7))/lead bismuth titanium oxide(Pb3Bi4Ti6O21)was precipitated in borosilicate glassy matrix as a major phase.The glasses were subjected to 4 h and 8 h heat treatment schedules to convert into glass ceramics.XRD analysis of these glass ceramic samples showed that the major crystalline phase of the entire glass ceramic samples with 0≤x≤0.5 is found to have cubic crystal structure,while it is tetragonal for glass ceramic sample with x=0.7.The scanning electron microscopy(SEM)micrographs indicated the uniform distribution of Bi_(2)Ti_(2)O_(7)and Pb3Bi4Ti6O21 crystallites in the glassy matrix.

Sintering characteristics and microwave dielectric properties of 0.5Ca_(0.6)La_(0.267)TiO_3-0.5Ca(Mg_(1/3)Nb_(2/3))O_3 ceramics prepared by reaction-sintering process

0.5 Ca（0.6La0.267TiO3-0.5 Ca（Mg1/3Nb2/3）O3（5 CLT-5 CMN） ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = ＋8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.