On the dielectric response function and dispersion relation in strongly coupled magnetized dusty plasmas

Using the generalized viscoelastic fluid model, we derive the dielectric response function in a strongly coupled dusty magnetoplasma which reveals two different dust acoustic（DA） wave modes in the hydrodynamic and kinetic limits. The effects of the strong interaction of dust grains and the external magnetic on these DA modes, as well as on the shear wave are examined. It is found that both the real and imaginary parts of DA waves are significantly modified in strongly coupled dusty magnetoplasmas. The implications of our results to space and laboratory dusty plasmas are briefly discussed.

Effective Dielectric Response of Composites with Graded Material

The effective dielectric response of linear composites containing graded material is investigated under an applied electric field E_0.For the cylindrical inclusion with gradient dielectric function,ει(r)=b+cr,randomly embedded in a host with dielectric constant εm,we have obtained the exact solution of local electric potential of the composite media regions,which obeys a linear constitutive relation D=εE,using hypergeometric function.In dilute limit,we have derived the effective dielectric response of the linear composite media.Furthermore,for larger volume fraction,the formulas of effective dielectric response of the graded composite media are given.

NUMERICAL ANALYSIS OF DIELECTRIC RESPONSE IN RELAXOR FERROELECTRICS

The dielectric response of complex perovskite relaxor ferrolectrics Pb(Mg1/3Nb2/3) O3 with respect to temperature and frequency was carefully measured. Using a normalized method of the 'universal' many-body theory, the relaxation process was analyzed around the temperature of dielectric absorption maximum. There is no structural phase transition near this temperature and the behavior is closely like that of a polar dipole medium. The functional relationship about frequency and temperature of dielectric pormittivity maximum was also fitted to discuss the dynamic behavior of polar microregion. It is confirmed that a new power exponential Arrhenius relation is better to characterize the relaxation behavior than the Vogel-Fulcher and Debye relations. Based on the polarization theory of polar dipoles, we analyzed the relaxation mechanism of ferroelectric microdomains of relaxor ferroelectrics, and get an ideal distribution function of relaxation time. Consequently, a simulated dielectric response dependence on temperature and frequencies can be expressed, which is well coincided with experiment results.

PREDICTION OF DIELECTRIC DISPERSION FOR LEAD BASED PEROVSKITES AND STUDY OF LOCAL DIELECTRIC RESPONSE IN 0.75Pb(Mg_(1/3)Nb(2/3))O_(3)-0.25PbTiO_(3)

Relaxors exhibit unique dielectric response properties such as diffuse phase transitions and strong dispersion of the dielectric constant.The origin of these properties is still not fully understood.Here,we review our work on usingfirst-principles-based methods to elucidate the connections between composition,local structure and dynamics in Pb-based relaxors.

Dielectric response of BaZrO_(3)/BaTiO_(3) superlattice

We use the first-principles-based molecular dynamic approach to simulate dipolar dynamics of BaZrO_(3)/BaTiO_(3)superlattice,and obtain its dielectric response.The dielectric response is decomposed into its compositional,as well as the in-plane and out-of-plane parts,which are then discussed in the context of chemical ordering of Zr/Ti ions.We reveal that,while the in-plane dielectric response of BaZrO_(3)/BaTiO_(3)superlattice also shows dispersion over probing frequency,it shall not be categorized as relaxor.

Effective Anisotropic Dielectric Properties of Crystal Composites

Transformation fieM method （TFM） is developed to estimate the anisotropic dielectric properties of crystal composites having arbitrary shapes and dielectric properties of crystal inclusions, whose principal dielectric axis are different from those of anisotropic crystal matrix. The complicated boundary-value problem caused by inclusion shapes is circumvented by introducing a transformation electric field into the crystal composites regions, and the effective anisotropic dielectric responses are formulated in terms of the transformation field. Furthermore, the numerical results show that the effective anisotropie dielectric responses of crystal composites periodically vary as a function of the rotating angle between the principal dielectric axes of inclusion and matrix crystal materials. It is found that at larger inclusion volume fraction the inclusion shapes induce profound effect on the effective anisotropic dielectric responses.

Effective Response of Nonlinear Composite under External AC and DC Electric Field

A perturbation method is used to study effective response of nonlinear Kerr composites, which are subject to the constitutive relation of electric displacement and electric field, Dα=εαE＋xα｜E｜^2E. Under the external AG and DC electric field Eapp = Eα（1 ＋ sinωt）, the effective nonlinear responses and local potentials are induced by the cubic nonlinearity of Kerr materials at all harmonics. As an example in three dimensions, we have investigated this kind of nonlinear composites with spherical inclusions embedded in a host. At all harmonic frequencies, the potentials in inclusion and host regions are derived. Furthermore, the formulae of the effective linear and nonlinear responses are given in the dilute Iimit.

Parameters Identification for Extended Debye Model of XLPE Cables Based on Sparsity-Promoting Dynamic Mode Decomposition Method

To identify the parameters of the extended Debye model of XLPE cables,and therefore evaluate the insulation performance of the samples,the sparsity-promoting dynamicmode decomposition(SPDMD)methodwas introduced,aswell the basics and processes of its applicationwere explained.The amplitude vector based on polarization current was first calculated.Based on the non-zero elements of the vector,the number of branches and parameters including the coefficients and time constants of each branch of the extended Debye model were derived.Further research on parameter identification of XLPE cables at different aging stages based on the SPDMD method was carried out to verify the practicability of the method.Compared with the traditional differential method,the simulation and experiment indicated that the SPDMD method can effectively avoid problems such as the relaxation peak being unobvious,and possessing more accuracy during the parameter identification.And due to the polarization current being less affected by the measurement noise than the depolarization current,the SPDMD identification results based on the polarization current spectral line proved to be better at reflecting the response characteristics of the dielectric.In addition,the time domain polarization current test results can be converted into the frequency domain,and then used to obtain the dielectric loss factor spectrum of the insulation.The integral of the dielectric loss factor on a frequency domain can effectively evaluate the insulation condition of the XLPE cable.

Exploring the electromechanical response and electric field-induced dielectric anomalies in PMN-PT electroceramics

Electromechanical and dielectric properties of PMN-PT ferroelectric ceramics are investigated.In particular,dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency.Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves,e(E),which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature.A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90°and 180°domains walls.

Complex dielectric modulus and relaxation response at low microwave frequency region of dielectric ceramic Ba_(6-3x)Nd_(8+2x)Ti_(18)O_(54)

The desirable characteristics of Ba_(6-3x)Nd_(8+2x)Ti_(18)O_(54)include high dielectric constant,low loss tangent,and high quality factor developed a new field for electronic applications.The microwave dielectric properties of Ba_(6-3x)Nd_(8+2x)Ti_(18)O_(54),with x?0:15 ceramics at different sintering temperatures(600–1300C)were investigated.The phenomenon of polarization produced by the applied electric field was studied.The dielectric properties with respect to frequency from 1MHz to 1.5 GHz were measured using Impedance Analyzer,and the results were compared and analyzed.The highest dielectric permittivity and lowest loss factor were defined among the samples.The complex dielectric modulus was evaluated from the measured parameters of dielectric measurement in the same frequency range,and used to differentiate the contribution of grain and grain boundary.

Doping effect of rare-earth(lanthanum, neodymium and gadolinium) ions on structural,optical, dielectric and magnetic properties of copper nanoferrites

Copper and rare earth-doped(RE = La, Gd, Nd) CuFe1.85RE0.15O4nano ferrites were prepared using the so nochemical method. The effective doping of rare-earth(La3+, Nd3+, Gd3+) ions with copper nanoferrites was confirmed by X-ray diffraction. The tetrahedral and octahedral sites of the nano ferrites were identified through the Fourier transform infrared spectra. The doping of rare-earth elements enhances the optical bandgap energy of the nanoferrites that are observed through Ultraviolet-DRS spectra. The oxidation state of the elements Cu 2 p, La 3 d, Nd 3 d, Gd 3 d, Fe 2 p and O 1 s was analyzed. Scanning electron microscopy images indicate a spherical morphology with agglomeration to some elongate. The values of dielectric constant and conductivity decrease considerably due to doping rare-earth ions in copper nanoferrites. Low saturation magnetization and high coercivity values of rare earth-doped copper nanoferrites are observed from the typical hysteresis curves.

Structural,microstructural and dielectric characterizations of(Bi_(0.5)Na_(0.5))TiO_(3) based lead-free ferroelectric ceramics

(1-x)(Bi_(0.5)Na_(0.5))TiO_(3)-xBaTiO_(3) lead-free ceramics have been obtained from the conventional solid-state reaction sintering method.The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques.Results revealed well-crystallized ceramic samples with perovskite structure.Microstructural properties,obtained from scanning electron microscopy measurements,have shown high density with very low porosity level.The dielectric response,analyzed as a function of the temperature and several frequencies,showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system.Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties.

Dielectric properties of composite based on ferroelectric copolymer of poly(vinylidene fluoride-trifluoroethylene)and ferroelectric ceramics of barium lead zirconate titanate

A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene)copolymer P(VDFTrFE)and ferroelectric ceramics of barium lead zirconate titanate(BPZT)solid solution is presented in this work.The composite films containing up to 50 vol.%of BPZT grains with size
1
m were prepared by the solvent cast method.Frequency dependences of real and imaginary components of the complex permittivity were determined.The concentration dependence of the dielectric constant was discussed.

Boosted microwave absorption performance of transition metal doped TiN fibers at elevated temperature

Due to the temperature and frequency response of electromagnetic(EM)loss,how to realize the effective design of microwave absorption materials(MWAMs)at elevated temperature is highly desirable for practical applications.Herein,transition metaldoped titanium nitride(M-TiN,M=Fe or Co)fibers were fabricated,the distortion of TiN lattice could cause the adjustable charge enrichment,which played a profound influence on the dielectric response and EM microwave absorption(EMWA)performances.Benefiting from the negative correlation between dielectric loss and temperature,more loss mechanism could be introduced,which would effectively enhance dielectric loss and EMWA performances at elevated temperature.The optimal EMWA performances of Fe-TiN fibers/polydimethylsiloxane(PDMS)composites were realized with a wide temperature range(298–423 K):the reflection loss(RL)could reach 99%(RL<−20 dB)at 12.2 GHz with 1.8 mm,when the filler content was only 15.0 wt.%.Compared with the undoped-TiN fibers/PDMS and Co-TiN fibers/PDMS composites,the excellent EMWA of Fe-TiN fibers/PDMS composite could be attributed to the reasonably synergistic polarization loss and conduction loss.Based on systematic analysis of the variable-temperature EM parameters and EMWA performances,the optimization of EMWA performances in wide temperature domain could be realized by introducing appropriate polarization loss and its compensating.Hopefully,this work provides a new strategy for regulating the dielectric response and designing effective MWAMs at elevated temperature.

Terahertz frequency selective surfaces using heterostructures based on two-dimensional diffraction grating of single-walled carbon nanotubes

For single-walled carbon nanotubes(SWCNTs)with a length of 1-50μm,the surface plasmon-polariton(SPP)resonance is within the terahertz frequency range;therefore,SWCNT lattices can be used to design frequency-selective surface(FSS).A numerical model of electromagnetic wave diffraction on a two-dimensional periodic SWCNT lattice can be described by an integro-differential equation of the second-order with respect to the surface current along SWCNT.The equation can be solved by the Bubnov-Galerkin method.Frequency dependence of reflecting and transmitting electromagnetic waves for FSSs near the SPP resonance is studied numerically.It is shown that the resonances are within the lowerfrequency part of the terahertz range.We also estimate the relaxa-tion frequency of an individual SWCNT and demonstrate the applic-ability of the Kubo formula for graphene conductivity to array of strips similar in size to SWCNTs under consideration.

First-order phase transition and unexpected rigid rotation mode in hybrid improper ferroelectric(La,Al)co-substituted Ca_(3)Ti_(2)O_(7) ceramics

Ca_(3)Ti_(2)O_(7) with Ruddlesden-Popper structure exhibits the largest polarization among the known hybrid improper ferroelectrics.However,the high Curie temperature impedes the thorough study of phase transition through dielectric characterization.According to the previous theoretical design rule,the Curie temperature can be suppressed by increasing the tolerance factor.So,in the present work,high-quality Ca_(3-x)LaxTi_(2-x)Al_(x)O_(7)(x=0.0,0.1,0.2,0.3)ceramics with increased tolerance factors were successfully prepared.The amplitude of oxygen octahedral tilt mode indeed decreases with increasing tolerance factors,leading to a degeneration of ferroelectric polarization.However,the unexpected rigid rotation mode causes the composition-invariable coercive fields.The Curie temperatures decrease linearly with increasing x and tolerance factors.The variable-temperature dielectric constant confirms first-order improper ferroelectric transitions in Ca_(3)Ti_(2)O_(7)-based ceramics.The results of variable temperature Xray diffraction reveal the coexistence of two-phases below Curie temperature.The present work confidently confirms the first-order improper ferroelectric transition in Ca_(3)Ti_(2)O_(7)-based ceramics by combining results of variable-temperature dielectric response and in-situ X-ray powder diffraction.

Ultrafast synthesis and sintering of materials in a single running experiment approach by using electric fields

Processing of materials in the form of ceramics normally involves several steps including calcination at a relatively low temperature for synthesis of the end-product powder and sintering at a high temperature for densification.The work we have been developing introduces a novel approach enabling synthesis plus sintering of materials in a single running experiment by using electric fields,ending with dense ceramics that display grains noticeably finer than in conventional processing.This new paradigm is fully illustrated with experiments conducted on amorphous CaCu3Ti4O12 precursor powder,shown to experience,on heating,crystallization through intermediate phases,followed by chemical reaction leading to synthesis of the end-product powder,plus densification depending on field adjustment.The processing time and furnace temperature are considerably reduced,demonstrating that enhanced synthesis and sintering rates applied under field input.Similar results found in Bi2/3Cu3Ti4O12are also shown.The different factors that may contribute to this unique scenario,including Joule heating,defect generation,and reduction of free energy for nuclei formation promoted by the applied field,are briefly discussed.Overall,the findings we bring here are exclusive as they show an exploitable way that allows rapid processing of materials with good control over particle and grain coarsening.

Room-temperature ferroelectricity in A-site ordered Ruddlesden-Popper Li_(2)CaTa_(2)O_(7) ceramics

In the present work,the crystal structure,ferroelectric and dielectric properties of the dense single-phase Li_(2)CaTa_(2)O_(7) ceramics with A-site ordered double-layer Ruddlesden-Popper structures have been investigated by the experiments and first-principles calculations.A polar Pna21 phase was determined by the Rietveld refinement against the X-ray diffraction pattern at room temperature,and it was confirmed by its lowest calculated energy and rigid phonon modes.The ferroelectricity was found by observing the ferroelectric hysteresis loop at room temperature,and its remanent polarization was similar to the value calculated from the Berry phase and Born effective charge approaches.The ferroelectricity is a nonconventional proper one since its polarization is induced from the displacement of oxygen anions instead of tantalum cations based on the individual atomic polarization.A first-order transition from an antiferroelectric to paraelectric phase around 900 K was found by the DSC and variable-temperature dielectric measurements.From the present work,the room-temperature ferroelectricity is experimental confirmed in the present ceramics,inspiring the search for new ferroelectricity in the ceramics with A-site ordered Ruddlesden-Popper structures.

Large electromechanical strain at high temperatures of novel <001> textured BiFeGaO3-BaTiO3 based ceramics

BiFeGaO3-BaTiO3(BFG-BT)based ceramics with a large piezoelectric coefficient are potential high performance lead-free piezoelectric compounds.In this work,textured and random BFG-BT ceramics were realized by the solid state reaction method with and without BaTiO3(BT)templates.Textured ceramics were obtained by a reactive templated grain growth(RTGG)method leading to a high-temperature electromechanical strain of S=0.27%at 40 kV/cm and to an effective piezoelectric coefficient(d33*)up to 685 pm/V at 180℃.The easy movement of oriented domains enhanced the electromechanical strain under an applied electric field in textured sample(Lotgering factor f=66.3%).Structural investigations reveal that the proportion and degree of distortion of BFG-BT rhombohedral phase(R3c)reached its maximum in textured ceramics,resulting in large ferrodistortive displacements under electric fields.In addition,the dense nanodomains with low domain wall energies,inferred from the high-resolution transmission electron microscope(HR-TEM)observations,contribute to the extra displacement of the textured sample under an applied electric field.In textured ceramics,the remnant polarization was stable(about 17μC/cm2)from room temperature to 180℃,contributing to the stable ferroelectric property at high temperatures.Through the introduction of BT templates,high-density nanodomains were formed and the Burns temperature was enhanced in textured ceramics.The electromechanical strain,polarization and dielectric behavior were correlated to the textured or random forms of the BFG-BT based ceramics.

Influence of ionic radius of rare-earths on the structural and electrical properties of Ba_5RTi_3Nb_7O_(30)(R=rare-earth) ferroelectric ceramics

In the present report, BasRTi3Nb7030 （R=La, Nd, Sm, Eu, Dy） compounds were synthesized by solid-state reaction method in order to know the effect of ionic radius of rare-earths on their structural, dielectric, ferroelectric, pyroelectric, piezoelectric and con- ductive properties. X-ray diffraction analysis revealed the formation of the compounds having orthorhombic structure. Scanning elec- tron micrographs showed the formation of fine granular microstructure in all the compounds with a decrease in the average grain size with increasing ionic radius of the substituted rare-earths. Detailed dielectric studies showed that the dielectric constant （er） increased while Curie temperature （To） decreased as the ionic radius of the rare-earths increased. With the decrease in the ionic radius of the rare-earths, remanent polarization （2Pr）, piezoelectric （d33） and pyroelectric coefficients were observed to increase in BasRTi3Nb7030 compounds. The temperature variation of dc conductivity suggested that the compounds had negative temperature coefficient of re- sistance （NTCR） behaviour.