Effective Dielectric Response of Nonlinear Composites of Coated Metal Inclusions

The effective dielectric response of the composites in which nondilute coated metal particles are randomly embedded in a linear host is investigated. Two types of coated particles are considered, one is that the core is nonlinear, the other is that the shell is nonlinear. We derive general expressions for the effective linear dielectric function and the effective third-order nonlinear susceptibility, and take one step forward to perform numerical calculations on the coated metal/dielectric composites. Numerical results show that the effective linear and nonlinear dielectric responses can be greatly enhanced near the surface plasmon resonant frequency. Moreover, the resonant peaks are found within a range from 0.46ωp to 0.57ωp for spherical particles and from 0.59ωp to 0.70ωp for cylindrical inclusions. In the frequency region, the resonant peak can achieve the maximum, according to an optimal structural parameter and volume fraction. The resonant frequency exhibits a redshift with the increasing structural parameter k or volume fraction f or dimensionality factor D.     

Optical Reskponse of Metal—Dielectric Composite Containing Interfacial Layers

A phenomenological approach nto investigate the effect of interfacial layers on the absorption of metaldielectric composite at elevated temperatures is put forward by making use of a model in which weakly nonlinear spherical metallic particles with linear concentric shells are randomly embedded in a linear host.Corresponding formulae in terms of the interfacial factor are derived in detail by incorporating Taylor expansion and Drude model.We take Ag/MgF2 composite as numerical calculation.It is concluded that such absorption is dependent not only on the temperature,but also on the properties of interfacial layers.Many other interesting phenomena are shown.     

Dielectric relaxation in polyvinylidenefluoride–polysulfone blends

Dielectric properties of polymer blend of polyvinylidenefluoride (PVDF) and polysulfone (PSF) of different wt. % have been studied to understand the molecular motion and their relaxation behavior in the frequency range of 100 Hz to 10 kHz at different temperatures between 30 and 190 °C. The dielectric constant of the blend decreased with frequency and increased with the increasing temperature and PSF content in the blend. The magnitude of dielectric loss also increased with increase in temperature and PSF content. The observed characteristic has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending of PSF with PVDF. At constant frequency and temperature, the blend follows a linear relationship between logarithm of their dielectric constant and different ratios of blend. The appearance of a peak for each concentration in dielectric loss suggests the presence of relaxing dipoles in the blend. In addition of PSF with PVDF, the peak shifts toward higher frequency side suggesting the speed up the relaxation process. AC dielectric data is also combined with thermally stimulated depolarization current (TSDC) data which is generally studied for low-frequency dielectric properties of polymers blends so as to produce the results in a wide frequency range. The glass transition temperature (T_g) of the blend was studied by differential scanning calorimetric technique (DSC), the T_g was compared and correlated with TSDC peak. The blend samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to study the formation of blend and micro structural properties of the materials. The shifting of peak toward lower diffraction angle side confirms the reduction in particle size with increasing amorphous content in the blend.     

Microdischarges Near Metal–Insulator Interfaces

Some statistical features of microdischarges running near the metal-insulator interfaces have been discussed. The study has verified an exponential character of statistical distributions of the time intervals between microdischarge pulses, power-law distribution of voltage peaks of these pulses (height of pulses) and very weak correlation effects among pulses, i.e. weak time-height correlation, time autocorrelation and height autocorrelation. A statistical parameter of the power law distribution of the heights of microdischarge pulses proved to be sensitive to the voltage load of the insulating interface metal-insulator.     

Metal–insulator transition in Si–MOS structures

A survey is presented on recent investigations of the metal-to-insulator transition in two-dimensional systems with special emphasis on n-Si–MOS structures. Experimental facts are presented and the currently open questions on the nature of this transition are addressed.     

Dielectric Properties of Lithium–Titanium Ferrite Ceramics

The temperature dependences of the real and imaginary parts of the complex dielectric permittivities of ceramic Li–Ti ferrospinel are measured within the frequency range 10²–10⁶ Hz. The empirical expressions describing these dependences are derived and the frequency-independent electrophysical parameters of the material under study are obtained. The best agreement between the experimental and calculation data is achieved when the time constant and the static dielectric permittivity are decreasing functions of frequency. A model of relaxational processes accounting for this result is proposed. A certain role in polarization of the relaxation agents, whose reorientation is controlled by tunneling electron transitions inside the two-valence iron ion – three-valence metal ion, is assumed. It is stated that under certain conditions, the relaxation agent reorientation is likely to possess a collective character. The temperature dependences and are derived for a number of dc currents at different electric field strengths. Sharp variations in the dielectric characteristics of the ceramics are found.     

Dielectric relaxation in NBT–ST ceramic composite materials

Lead-free piezoelectric ceramic composites (1-x) Na_0.5Bi_0.5TiO₃-xSrTiO₃, where x?=?0.05, 0.10, 0.15 and 0.2, are prepared by mixing independently-prepared individual phases through sol–gel method. X-ray diffraction revealed the coexistence of rhombohedral and cubic phases. Surface morphology of the composites is observed using SEM, and both the phases are observed in the samples. Spectroscopic studies of the composites are characterized based on Fourier transform infrared, and vibration bands are analyzed at room temperature in the wave number region 500–3,000 cm^?1. Dielectric properties of these composites are measured from room temperature to 400 °C in the frequency range 1–10 kHz, and these studies indicate the presence of defect clusters within the composite materials. P–E hysteresis loops of these samples were measured as a function of temperature and observed large anomalies in the behavior compared to pure sodium bismuth titanate (NBT) (the host material). Unlike NBT, all the composites exhibited excellent P–E loops. In addition, decrease in remanence polarization is observed, with increase of SrTiO₃ at room temperature. Piezoelectric parameter d₃₃ is measured on poled composites.     

Dielectric response of water confined in metal–organic frameworks

Dielectric response of water confined in metal–organic frameworks was investigated in broad temperature range from 140 to 410 K and from 20 Hz to 1 MHz using a capacitance bridge. Several dispersion regions of characteristic shape were found, caused by freezing–melting of adsorbed water molecules, which disappear after a prolonged heating at 410 K. Temperature dependencies of relaxation time of confined water molecules were obtained and are compared to those of water confined in MCM-41 mesoporous molecular sieves.     

Dielectric properties of PIN–PT ceramics under compressive stress

Lead indium niobate, Pb(In_1/2Nb_1/2)O₃ or (PIN), is an interesting ferroelectric material, because it can be changed from a disordered state to ordered state by long-time thermal annealing. However, the temperature related to the maximum dielectric constant (T_max) of PIN in relaxor phase is low (at 1 kHz, T_max = 66 °C). In this study, to increasing T_max of PIN, lead titanate, PbTiO₃(PT) was thus added to PIN with compositions (1 − x)PIN–xPT (for x = 0.1–0.5). The influence of stress on the dielectric properties of (1 − x)PIN–xPT ceramics was then investigated. The dielectric properties were measured under various uniaxial compressive stress up to 400 MPa. The results showed that the superimposed compression load reduced the dielectric constant in 0.9PIN–0.1PT. For the other compositions, the dielectric constants first increased with the compressive stress, and then decreased when the stress was further increased up to 400 MPa. The dielectric loss tangent of all composition was found to decrease with increasing compressive stress.     

Waveguide Modes in a Planar Graphene–Dielectric Thin-Layer Structure

Particular features of waveguide propagation of modes in a planar structure that consists of alternating layers of a dielectric and graphene are investigated. Within the effective-medium approximation, dispersion relations are obtained for symmetric and antisymmetric waveguide modes. Based on their numerical analysis, the frequency dependences of the propagation and decay constants, of the group and phase velocities, and of the energy flux carried by waveguide modes are constructed. The influence of the fraction of graphene in the structure on the behavior of waveguide modes is analyzed.     

Dielectric relaxation and ion transport in silver–boro-tellurite glasses

Glass systems of composition xAg₂SO₄–20Ag₂O–(80?x) [0.50 B₂O₃–0.50 TeO₂], where x = 5, 10, 15, 20, 25 and 30 mol% have been prepared by melt-quenching technique. Frequency- and temperature-dependent conductivity measurements have been carried out in the frequency range 10 Hz to 10 MHz and at a temperature range of 303–353 K, respectively. DC conductivities exhibit Arrhenius behavior over the entire temperature range with a single activation barrier. Addition of Ag₂SO₄ expands the glass network and, consequently, conductivity increases. This suggests that the structure and network expansion are the key parameters for enhancing conductivity. Impedance spectra of these glasses show a single semicircle, indicating one type of conduction. AC conductivity behavior of the glasses was analyzed using both single power law and Kolhrauh–William–Watts (KWW) stretched exponential relaxation function. The power law exponent (s) is temperature-dependent, while the stretched exponent (β) is insensitive to temperature. Scaling behavior has also been carried out using reduced plots of conductivity with frequency, which suggests the ion transport mechanism remains unaffected by temperature and composition.     

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 carried 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 ferrite samples prepared by the usual ceramic technique. In order to improve the properties of the samples, low cost Fe2O3having 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 Cu2+= 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.     

Negative Differential Resistance and Other Features of Spin-Dependent Electron Transport in Double-Barrier Hybrid Superconductor–Ferromagnetic Metal–Normal Metal Structures

Spin-dependent electronic transport is theoretically investigated for double-barrier hybrid structures S–IF–F–IF–N and S–IF–N–IF–N, where S is a superconductor; F and N are ferromagnetic and normal metals, respectively; and IF is the spin-active barrier. It is shown that in the case of strong superconducting proximity effect and sufficiently thin F layers, the differential resistance of such structures can become negative at some voltages, and the voltage dependence of the current can have an N-shaped form. Characteristic feature of the differential resistance is its asymmetric dependence on voltage, which is most clearly manifested at strong polarization of at least one of the barriers. The influence of impurity spin–orbit scattering processes in the N-layer located between the barriers is investigated. The study was carried out for the case of diffusion electron transport.     

Metal–insulator transition in boron-doped amorphous carbon films

Boron-doped amorphous graphite-like carbon (GLC) films have been prepared with different boron concentrations. Electrical transport measurements in the temperature range 1.3–300?K on the films shows a doping-induced metal–insulator (MI) transition. On the metallic side of the transition, the experimental data are interpreted in terms of weak localization and the effect of electron–electron interactions. Data on the insulator side of transition are analyzed in terms of hopping conduction. Critical behaviour is observed near the transition, with the resistivity obeying a power-law temperature dependence.     

Field-Induced Metal–Insulator Transition in β-EuP_3

Metal-insulator transition(MIT) is one of the most conspicuous phenomena in correlated electron systems.However such a transition has rarely been induced by an external magnetic field as the field scale is normally too small compared with the charge gap.We present the observation of a magnetic-field-driven MIT in a magnetic semiconductor β-EuP_3.Concomitantly,we find a colossal magnetoresistance in an extreme way:the resistance drops billionfold at 2K in a magnetic field less than 3T.We ascribe this striking MIT as a field-driven transition from an antiferromagnetic and paramagnetic insulator to a spin-polarized topological semimetal,in which the spin configuration of Eu~(2+)cations and spin-orbital coupling play a crucial role.As a phosphorene-bearing compound whose electrical properties can be controlled by the application of field,β-EuP_3 may serve as a tantalizing material in the basic research and even future electronics.     

Red-Emitting Ru(II) Metal–Ligand Complexes

A series of Ru(N–N)₂(dcbp or mcmabp) complexes were synthesized where N-N represents a diimine ligand, dcbp is 4,4-dicaboxylic 2,2-bipyridine, and mcmabp is 4,4-2,2-bipyridine monocarboxy amide. The N-N ligand was either 2,2-bipyridine (bpy), 4,4-dimethyl-2,2-bipyridine (dmbp), or 4,4,5,5-tetramethyl-2,2-bipyridine (tmbp). We observed a red shift in both the absorption and emission with the presence of dcbp in the mixed ligand complex when compared to Ru(bpy)₃. Conversion of one of the carboxylic groups in dcbp to amide resulted in further red shifts. A red shift in the absorption and the emission was also observed with increasing numbers of electrons donating methyl substitutions on bpy. The lifetimes of the complexes decreased as expected with the red shift emission. The tris heteroleptic Ru (tmphen)(tmbp)(dcbp or mcmabp) were the most red-shifted among the complexes. Because of the red shift in the absorption, the maxima in the fundamental anisotropies of the mixed ligand Ru complexes are now coincident with the maxima in the absorption. Overall we have been able to make an Ru complex which emits at about 700 nm in all aqueous environment and has a lifetime of about 220 ns.     

Josephson Tunnel Junctions with an Integral Superconductor–Insulator–Normal Metal Shunt

Physics of the Solid State - This study is devoted to the investigation of tunneling superconductor–insulator–superconductor (SIS) Josephson junctions with a new type of shunt based on...     

A comparison study between two types of nuclear detectors having (Metal–Organic thin films–Silicon) and (Metal–Silicon) structures

Nuclear detectors having metal–organic thin film–semiconductor structures have been prepared and tested. The organic thin films (50–200 nm) were thermally sublimed and deposited onto silicon slides (n-type 1000 Ω.cm). The prepared detectors show remarkable performance and their energy resolution was highly improved in comparison to metal–semiconductor (Schottky type) detectors manufactured on identical substrates and under similar conditions.     

Improved Dielectric Breakdown Strength of Covalently-Bonded Interface Polymer–Particle Nanocomposites

Interfacial covalent bonding is an effective approach to increase the electrical resistance of a polymer–particle composite to charge flow and dielectric breakdown. A bifunctional tether reagent bonded to an inorganic oxide particle surface assists with particle dispersion within a thermosetting epoxy polymer matrix but then also reacts covalently with the polymer matrix. Bonding the particle surface to the polymer matrix resulted in a composite that maintained the pure polymer glass transition temperature, compared to modified or unmodified particle dispersions that lacked covalent bonding to the polymer matrix, which depressed the polymer glass transition to lower temperatures. The added interfacial control, directly bonding the particle to the polymer matrix, appears to prevent conductive percolation across particle surfaces that results in a reduced Maxwell–Wagner relaxation of the polymer–particle composite and a reduced sensitivity to a dielectric breakdown event. The inclusion of 5 vol% particles of higher permittivity produces a composite of enhanced dielectric constant and, with surface modification to permit surface cross-linking into the polymer, a polymer–particle composite with a Weibull E ₀ dielectric breakdown strength of 25% greater than that of the pure polymer resulted. The estimated energy density for the cross-linked interface composite was improved 260% compared to the polymer alone, 560% better than a polymer–particle composite synthesized using bare particles, and 80% better than a polymer–particle composite utilizing bare particles with a dispersant.     

Annular Multi-Tip Field Emitters with Metal–Fullerene Protective Coatings

Technical Physics - A technology of creation of annular silicon field emitters with bilayer metal–fullerene coating has been developed and their performance has been studied. It has been...