Dielectric Constant Permittivity Research Articles

A phenomenological thermodynamic energy density function for ferroelectric wurtzite Al1−xScxN single crystals

A Landau–Devonshire thermodynamic energy density function for ferroelectric wurtzite aluminum scandium nitride (Al1−xScxN) solid solution is developed. It is parametrized using available experimental and theoretical data, enabling the accurate reproduction of composition-dependent ferroelectric properties, such as spontaneous polarization, dielectric permittivity, and piezoelectric constants, for both bulk and thin films. The maximum concentration of Sc for the wurtzite structure to remain ferroelectric is found to be 61 at. %. A detailed analysis of Al1−xScxN thin films reveals that the ferroelectric phase transition and properties are insensitive to substrate strain. This study lays the foundation for quantitative modeling of novel ferroelectric wurtzite solid solutions.

A low-cost dual bandpass planar filter for WiMAX and mobile communications

This study proposes a new design of low-cost dual-bandpass filter for worldwide interoperability and microwave access (WiMAX) band at <br /> 3.50 GHz and mobile communications band at 1.19 GHz. A high pass filter and a stopband filter make up the new dual-bandpass filter structure. Different theoretical studies were carried out for the design of the proposed filter. This filter’s base is a RO5880 substrate with a dielectric permittivity constant of 2.2, loss tangent of 0.0009 and 1.6 mm thickness. High mashing density was used to validate the various simulated structures while accounting for two numerical methods: the moment technique and the finite integration method. The final circuit's overall dimensions are 60×178,3 mm<sup>2</sup>.

Semiconducting CdS quantum dots as a guest in a four ring bent-core nematic medium: modified dielectric and elastic properties

The nematic phase of the bent-core family proves to be particularly fascinating due to its distinct properties in comparison to its calamitic counterpart. Here we revealed after the dispersion of semiconducting CdS QD an achiral unsymmetrical (4′-fluoro phenyl azo) phenyl-4-yl 3-[N-(4′-n-hecyloxy two hydroxybenzylidene)amino]-2-methylbenzoate (6-2M-F) a bent-core nematic (BCN) liquid-crystalline medium made of bent-shaped molecules with short cores and low bend angles. These molecules are on the cusp between conventional bent-core molecules and rod-like molecules, with characteristics somewhere in between, resembling hockey sticks. The threshold voltage dielectric permittivity and elastic constants of pure BCN have been considerably influenced by semiconductor nanoparticles. The threshold voltage of nano-disperse BCN has decreased with QD doping, and we know that the low operation voltage is one of the key considerations in the development of mobile liquid crystal display technology. Similar to other BCNs with smectic-like clusters previously described, the elastic anisotropy for 6-2M-F is negative; however, the insertion of CdS QDs causes the anisotropy to become very positive (bend elastic constant > splay elastic constant ). While the parallel component of permittivity has declined with doping, the perpendicular component of permittivity has increased, leading to a considerable reduction in dielectric anisotropy in the nanocomposite, which implies the effect on nematic ordering due to the interaction between CdS QDs and the LC molecules.

Оптическая спектроскопия тонких пленок оксида цинка, легированных медью

The results of a comparative study of the optical properties of the thin films of zinc oxide ZnO, taking into account the influence of their copper doping, are presented. Using the experimental spectra of optical transmission, spectral dependences of the refractive and extinction index of the studied material, as well as components of complex dielectric permittivity constant, were calculated. The revealed features of the obtained dispersion curves are associated with the behavior of the impurity injected into the ZnO matrix.

Optical spectroscopy of thin zinc oxide films doped with copper

The results of a comparative study of the optical properties of the thin films of zinc oxide ZnO, taking into account the influence of their copper doping, are presented. Using the experimental spectra of optical transmission, spectral dependences of the refractive and extinction index of the studied material, as well as components of complex dielectric permittivity constant, were calculated. The revealed features of the obtained dispersion curves are associated with the behavior of the impurity injected into the ZnO matrix. Keywords: zinc oxide, optical transmission, refractive index, dielectric permittivity.

Radiation from a dipole perpendicular to the interface between two planar semi-infinite magnetoelectric media

We consider two semi-infinite magnetoelectric media with constant dielectric permittivity separated by a planar interface, whose electromagnetic response is described by non-dynamical axion electrodynamics and investigate the radiation of a point-like electric dipole located perpendicularly to the interface. We start from the exact Green's function for the electromagnetic potential, whose far-field approximation is obtained using a modified steepest descent approximation. We compute the angular distribution of the radiation and the total radiated power finding different interference patterns, depending on the relative position dipole-observer, and polarization mixing effects which are all absent in the standard dipole radiation. They are a manifestation of the magnetoelectric effect induced by axion electrodynamics. We illustrate our findings with some numerical estimations employing realistic media as well as some hypothetical choices in order to illuminate the effects of the magnetoelectric coupling which is usually very small.

Theory of nonlinear transverse-magnetic guided waves in a plane waveguide filled with nonhomogeneous nonlinear medium

The paper focuses on electromagnetic transverse-magnetic wave propagation in a plane waveguide filled with nonlinear nonhomogeneous medium. The waveguide is located between two half-spaces which are characterized by constant dielectric permittivities. The dielectric permittivity of the medium within the waveguide is described by Kerr law; in addition, it is assumed that the linear part of the permittivity depends on the transverse coordinate. The problem under consideration is to find so called propagation constants of the waveguide and describe their properties. In the paper it is shown that Kerr nonlinearity produces guiding modes that do not exist in the linear limit.

On the Maxwell-wave equation coupling problem and its explicit finite-element solution

It is well known that in the case of constant dielectric permittivity and magnetic permeability, the electric field solving the Maxwell’s equations is also a solution to the wave equation. The converse is also true under certain conditions. Here we study an intermediate situation in which the magnetic permeability is constant and a region with variable dielectric permittivity is surrounded by a region with a constant one, in which the unknown field satisfies the wave equation. In this case, such a field will be the solution of Maxwell’s equation in the whole domain, as long as proper conditions are prescribed on its boundary. We show that an explicit finite-element scheme can be used to solve the resulting Maxwell-wave equation coupling problem in an inexpensive and reliable way. Optimal convergence in natural norms under reasonable assumptions holds for such a scheme, which is certified by numerical exemplification.

Piezoelectric voltage constant and sensitivity enhancements through phase boundary structure control of lead-free (K,Na)NbO3-based ceramics

The piezoelectric voltage constant (g33) is a material parameter critical to piezoelectric voltage-type sensors for detecting vibrations or strains. Here, we report a lead-free (K,Na)NbO3 (KNN)-based piezoelectric accelerometer with voltage sensitivity enhanced by taking advantage of a high g33. To achieve a high g33, the magnitudes of piezoelectric charge constant d33 and dielectric permittivity εr of KNN were best coupled by manipulating the intrinsic polymorphic phase boundaries effectively with the help of Bi-based perovskite oxide additives. For the KNN composition that derives benefit from the combination of εr and d33, the value of g33 was found to be 46.9 × 10−3 V·m/N, which is significantly higher than those (20 – 30 × 10−3 V·m/N) found in well-known polycrystalline lead-based ceramics including commercial Pb(Zr,Ti)O3 (PZT). Finally, the accelerometer sensor prototype built using the modified KNN composition demonstrated higher voltage sensitivity (183 mV/g) when measuring vibrations, showing a 29% increase against the PZT-based sensor (142 mV/g).

Selectively doped piezoelectric ceramics with tunable piezoelectricity via suspension-enclosing projection stereolithography

The macroscopic piezoelectric properties of piezoelectric materials can be regulated via localized control of microstructures to introduce site-specific electric displacement vectors, but much of the current research is centered around design and manipulation of meso-scale architectural units that are inherently limited in achieving high functionality. In this study, we propose a stereolithography-based additive manufacturing (AM) strategy to spatially tune the properties of piezoelectric ceramics at a grain-microstructural scale through selectively incorporating dopants into the ceramic materials for tailoring the grain development. The effects of different doping parameters (including ceramic solid loading, dopant type, and dopant concentration) on the microstructures and properties of printed piezoelectric ceramics are investigated. The thermodynamics and kinetics of different doping additives in the dopant-ceramic interaction are experimentally and numerically studied to enable location-specific inhibition of microstructures. Our results indicate that a doping concentration of 2 wt% promoted the homogeneity of local grain growth, resulted in a higher compressive strength and lower porosity, and improved dielectric permittivity and piezoelectric voltage constant in printed piezoelectric ceramics. Moreover, our results suggest that thermochemically stable particles (e.g., ZrO2) with a high melting point and a low vapor pressure exhibited micro-scale diffusion behaviors, in contrast to millimeter-scale diffusion behaviors of common doping additives (e.g., ZnO), which are more suitable as a locally incorporated dopant for achieving location-specific property tuning. Test cases of selectively doped piezoelectric components in predefined patterns highlight the potential of the proposed approach in creating novel piezoelectric materials with programmable location-specific properties.

Structural, optical, and dielectric properties for Mg0·6Cu0·2Ni0·2Cr2O4 chromite spinel

In this work, the structural, optical, and dielectric properties for Mg0·6Cu0·2Ni0·2Cr2O4 chromite sample prepared by sol-gel process were investigated. The XRD characterization for this sample confirmed the development of the face-centered cubic spinel structure with Fd3‾m space group. From the UV–Vis optical absorbance, the synthesized chromite shows significantly lower direct band gap energy and has an appropriate absorption rate in the visible light region. The variations of penetration depth, extinction coefficient, refractive coefficient, dispersion energy parameters, and dielectric permittivity constants were also interpreted. The Non-Overlapping Small Polaron Tunneling (NSPT) and the Correlated Barrier Hopping (CBH) are the suitable models to describe the conduction process for the prepared sample. The behavior of dielectric constants has been interpreted based on the Maxwell-Wagner's theory of interfacial polarization. The behavior of imaginary part of impedance (Z″) shows a dielectric-relaxation phenomenon in the sample with activation energies near to those determined from the conductivity study.

Stress-induced phase transitions in nanoscale CuInP2S6

Using Landau-Ginsburg-Devonshire approach and available experimental results we reconstruct the thermodynamic potential of the layered ferroelectric CuInP$_2$S$_6$ (CIPS), which is expected to be applicable a wide range of temperatures and applied pressures. The analysis of temperature dependences of the dielectric permittivity and lattice constants for different applied pressures unexpectedly reveals the critically important role of the nonlinear electrostriction in this material. With the nonlinear electrostriction included we calculated temperature and pressure phase diagrams and spontaneous polarization of bulk CIPS. Using the coefficients of the reconstructed four-well thermodynamic potential, we study the strain-induced phase transitions in thin epitaxial CIPS films, as well as the stress-induced phase transitions in CIPS nanoparticles, which shape varies from prolate needles to oblate disks. We reveal the strong influence of the mismatch strain, elastic stress and shape anisotropy on the polar properties and phase diagrams of nanoscale CIPS. Also, we derived analytical expressions, which allow the elastic control of the nanoscale CIPS polar properties. Hence obtained results can be of particular interest for the strain-engineering of nanoscale layered nanoferroelectrics.

Evoking or suppressing electromechanical instabilities in soft dielectrics with deformation-dependent dielectric permittivity

Soft dielectric films subjected to the electromechanical loads can easily have large deformations that are accompanied by a variety of failure modes. The functions of soft dielectric actuators and harvesters are limited due to the existence of electromechanical instabilities. In this paper, we study the large deformation and electromechanical instabilities of a soft dielectric film by prescribing its deformation in one direction. The prescribed deformation can enhance the film stability; even more, it can avoid pull-in instability in dielectric films with constant dielectric permittivity. However, the prescribed stretch would bring another failure mode, i.e., loss of tension, in the prescribed direction. So far, the co-existence of pull-in instability and loss of tension is seldom reported in dielectric films with a prescribed deformation. We find that the deformation-dependent dielectric permittivity has a considerable impact on electromechanical behaviors. The competition between pull-in instability and loss of tension exists in dielectric films with a permittivity that increases with deformation. Our stability analyses find the conditions under which the deformation-dependent dielectric permittivity evokes pull-in instability or suppresses loss of tension.

Temperature dependence of the transverse piezoelectric properties in the [001]-poled 0.25Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystal with alternating current treatment

In this work, the transverse piezoelectric properties of the pre-direct current poled (DCP) 0.25Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (0.25PIN-0.42PMN-0.33PT) single crystals were enhanced by the alternating current treatment (ACT) of 10 kVp/cm (5.8 kVrms/cm), 50 Hz, and 20 cycles. The transverse piezoelectric constant d31 of −1560 pC/N and electromechanical coupling coefficient k31 of 0.92 at room temperature were achieved in the DCP-ACT crystal, which were, respectively, 80% and 11% higher than those of the DCP crystal (d31=−870pC/N,k31=0.83) . Meanwhile, the elastic compliance constant S11E and dielectric permittivity ε33T/ε0 of the DCP-ACT crystal were, respectively, 78% and 46% higher than those of the DCP crystal. Based on the temperature dependence of dielectric properties and resonance curves, the d31, ε33T/ε0, and S11E of the DCP-ACT crystal were higher than those of the DCP crystal in the R phase region. The DCP-ACT crystal also showed a higher TFerro (110 °C) than the DCP crystal (96 °C), which was related to the intermediate phase induced by ACT. The d31 at Tferro of the DCP-ACT crystal can be −3810 pC/N, which was 2.3 times that of the DCP crystal (−1680 pC/N). In the T phase region, the DCP-ACT crystal presented a high ε33T/ε0 and attenuated impedance resonance. Moreover, ACT also affected the ferroelectric to paraelectric phase transition. This could be related to the nanoscale heterogeneous polar region induced by ACT, which enhanced the inhomogeneous state in the relaxor-based ferroelectric single crystal. ACT is a potential way for improving the transverse piezoelectric properties of the PIN-PMN-PT single crystal.

Analysis of dielectric properties of zinc aluminum silicate based ceramic nanoparticles

Abstract Zinc Aluminate (ZnAl2O4) is a class of spinel group which has unusual characteristics and recognised as the microwave dielectric ceramic. Zinc Aluminate based silicon (ZnAl2O4) compound nanomaterial is suitable for the microwave applications due to its low dielectric permittivity low tangent loss and the improved conductivity. In this work, we present the sol–gel synthesis of ZnAl2O4SiO2 ceramic nanoparticles and investigations using X-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscopy (FESEM). XRD study revealed the amorphous nature of the sample. Raman measurement showed the vibration peaks of TiO2-Eg modes originated at 143 cm−1 and 631 cm−1 along with a peak at 391 cm−1 ascribed to the B1g mode of SiO2. We noticed almost constant dielectric permittivity at room temperature with the increased frequency however, an increased permittivity is observed with the increased frequency at increased temperature from 40 to 150 °C. In a similar fashion, we observed low dielectric loss in higher frequency regime at increased temperature from 40 to 150 °C. Furthermore, we explored the conductivity and impedance analysis of ZnAl2O4SiO2 ceramic nanoparticles in the view of their applicability as the microwave ceramic material.

High temperature and low voltage AC poling for 0.24Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 piezoelectric single crystals manufactured by continuous-feeding Bridgman method

Alternating current poling (ACP) in air by changing poling temperature (70–130 °C) and voltages (2–6 kVrms/cm) on pseudo-ternary 0.24 Pb(In1/2Nb1/2)O3-0.46 Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 (PIMN-0.30PT) single crystals (SCs) manufactured by continuous-feeding Bridgman (CF BM) method was investigated. Free dielectric permittivity (εT33/ε0) and piezoelectric constant (d33) were improved to be 7000 and 2340 pC/N, which were 29% higher than those of direct current poling (DCP) at 90 °C with 4 kV/cm (εT33/ε0 = 5440, d33 = 1810 pC/N). However, phase change temperature (Tpc) decreased from 94 °C to 78 °C as opposite results reported by other groups. We demonstrated that the high temperature (HT) ACP improved piezoelectric performance of CF BM SCs, however, the Tpc were different from other crystal growth method. The well-designed ACP process was a promising method for mass production not only to enhance the electrical properties for the pseudo-ternary SCs but also reduce the risk of breakdown and realizes organic solvent-free poling process.

Optimization Analysis of Electrostatic Cloaking Problems

Under consideration are the inverse problems of electrostatics which arise in designing two-dimensional multilayer shielding and cloaking devices. Using optimization, we reduce these inverse problems to the finite-dimensional extremal problems in which the roles of control parameters are played by the constant dielectric permittivities of the layers. Basing on particle swarm optimization, we develop some numerical algorithm for solving these problems. We also show that the devices designed by the algorithm have the highest cloaking efficiency and simplicity of technical implementation.

Silver nanoparticles dispersed in nematic liquid crystal: an impact on dielectric and electro-optical parameters

In the present study, nematic liquid crystal (NLC) 4′-(Octyloxy)-4-biphenylcarbonitrile dispersed with three different concentrations of silver nanoparticles (Ag NPs) is characterized by electro-optical and dielectric spectroscopy method. The dispersion of Ag NPs into NLC material leads to the change in physical parameters such as dielectric permittivity, photoluminescence, threshold voltage, response time and splay elastic constant. The AC conductivity and threshold voltage of Ag NPs-dispersed composite system have increased significantly. The increase in the AC conductivity for the composite system is attributed to the Ag NPs-assisted induced charge transfer mechanism in the system. Moreover, the increase in AC conductivity value for Ag NPs/NLC composite system discloses its importance in photovoltaic solar cell.

Electric dipole image forces in three-layer systems: The classical electrostatic model.

General exact analytical expressions have been derived for the image force energy Wi(Z, φ) of a point dipole in a classical three-layer system composed of dispersionless media with arbitrary constant dielectric permittivities εi. Here, i = 1-3 is the layer number, and Z and φ are the dipole coordinate and orientation angle, respectively. It was found that the long-range asymptotics Wi(Z→∞,φ) in both covers (i = 1, 3) are reached unexpectedly far from the interlayer (i = 2). Another specific feature of the solution consists in that the interference of the fields created by polarization charges emerging at both interfaces leads to the appearance of a constant contribution inside the interlayer with a non-standard dependence on the dipole orientation angle φ. It was shown that by changing the dielectric constants of the structure components, one can realize two peculiar regimes of the Wi(Z, φ) behavior in the covers; namely, there arises either a potential barrier preventing adsorption or a well far from the interface, both being of a totally electrostatic origin, i.e., without involving the Pauli exchange repulsion, which is taken into account in the conventional theories of physical adsorption. The results obtained provide a fresh insight into the physics of adsorption in physical electronics, chemical physics, and electrochemistry.

Non-Coulombic behavior of electrostatic charge-charge interaction in three-layer heterostructures

Electrostatic interaction energy WQ1Q2 between two point charges Q1 and Q2 in a three-layer planar system was calculated on the basis of the Green's function method in the classical electrostatic model with constant dielectric permittivities εi (i=1,2,3) for all constituent media. Two significant particular cases of charge configurations were analyzed in more detail: (i) when the both charges are in the same medium and their perpendicular coordinates are equal, Z1=Z2, and (ii) the charges are located at different interfaces and interact across the slab. It was demonstrated that the WQ1Q2 dependences on the charge-charge distance S and its projection R on the XY plane [S2=R2+(Z1−Z2)2] differ from the classical Coulombic one. This phenomenon occurs due to the appearance of polarization charges at both interfaces, making the problem a many-body one. Numerical calculations demonstrated that both the underscreening and overscreening of the electrostatic charge-charge interaction is possible depending on the charge arrangement and the relationships between εi’s in the layers. The deviations from the Coulomb law were found to be especially large when the dielectric constants of the covers are much larger or much smaller than that in the interlayer.