Real Part Of Dielectric Constant Research Articles

The Effect of Thickness on Some Optical Properties of Sb2S3 Thin Films Prepared by Chemical Bath Deposition

Sb2S3 thin films have been prepared by chemical bath deposition on a glas sub Absorbance and transmittance spectra were recorded in the wavelength range (30-900) nm. The effects of thickness on absorption coefficient, reflectance, refractive index, extinction coefficient, real and imaginary parts of dielectric constant were estimated. It was found that the reflectivity, absorption coefficient , extinction coefficient, real part of dielectric constant and refractive index, all these parameters decrease as the thickness increased, while the imaginary part of the dielectric constant increase as the thickness increased.

Structural and Optical Properties of SnS2:Cu Thin films prepared by chemical Spbay Pyrolysis

Thin filis have been prepared from the tin disulphide (SnS2 ), the pure and the doped with copper (SnS2:Cu) with a percentages (1,2,3,4)% by using ahemical spray pyrolysis techniqee on substrate of glass heated up to(603K)and sith thicknesses (0.7±0.02)?m ,after that the films were treated thermally with a low pressure (10-3mb) and at a temperature of (473K) for one hour. The influence of both doping with copper and the thermal treatment on some of the physical characteristics of the prepared films(structural and optical) was studied. The X-ray analysis showed that the prepared films were polycrystalline Hexagonal type. The optical study that included the absorptance and transmitance spectra in the weavelength range (300-900)nm demonstrated that the value of absorption coefficient (?) was greater than (104 cm-1) for the pure and doped films and that the electronic transitions at the fundamental absorption edge were of the indirect kind whether allowed or forbidden and the value of the optical energy gap in the case of the indirect transition, the allowed decreased from (2 eV) to (1.8,1.7,1.5,1.2)eV at the doping percentages (1,2,3,4)% respectively, also it was found that the value of energy gap for the pure and doped films increased after annealing. Tthe absorption and transmission spectra were used to find the optical constant including refractive index(n), extinction coefficient (k), imaginary and real part of dielectric constant (?1 &?2) , and it was found that all the optical constant was affected by changing the doping percentages; in addition to being affected after treating the films thermally

A double-layer light shutter consisting of polymer dispersed liquid crystal and azo dye/quantum dot

We have developed a double-layer liquid crystal light shutter and investigated its temperature dependent morphological, electro-optical, and dielectric properties. The optical layers of the shutter are in direct contact, reducing optical losses. The shutter comprises a polymer dispersed liquid crystal film adjacent to an azo dye methyl red and CdSeS/ZnS quantum dot doped cholesteric liquid crystal layer. This novel double-layer light shutter device is switchable between opaque and transparent states at room temperature, and it exhibits low threshold and saturation voltages. Both the threshold (Vth) and saturation (Vsat) voltages are found to decrease with increasing temperature. The electrical characteristics of the shutter, namely the real part of dielectric constant (ε′) and the ac conductivity (σac) also increase with temperature in the low frequency region. Our results show that this double-layer light shutter has interesting potential for simple electro-optical devices and smart window applications.

Effect of Cobalt Doping on the Dielectric Properties and Electrical Conductivity of Nickel Tungstate

The study investigates the influence of cobalt doping on the structural and dielectric properties of NiWO4. Pristine and Co-doped nickel tungstate samples are synthesized via the direct chemical precipitation method. X-ray diffractogram is employed to analyze the structural variations introduced by doping. The impact of doping on dielectric properties is analyzed by examining the frequency response curves of the dielectric constant's real part and the loss tangent. Nyquist curves are used to study the relaxation process and the conduction mechanism taking place within pure and doped samples. An equivalent circuit is formulated and analyzed based on impedance spectroscopy to examine the physical processes occurring within the pure and doped samples. The introduction of cobalt dopants in the lattice of nickel tungstate results in a change in the conduction mechanism of nickel tungstate, leading to higher conductivity in the Co-doped nickel tungstate samples. Co-doping improves the electrical properties and conductivity of nickel tungstate and makes it a promising candidate in microelectronic devices.[copyright information to be updated in production process]

Investigation and treatment of carbon pollution in LiZn ferrite ceramics prepared by spark plasma sintering

In this study, lithium–zinc ferrite (LZF) ceramics were prepared by spark plasma sintering. Problem of carbon pollution was effectively resolved by annealing decarburization, formation of BN-coated carbon paper, and formation of protective layer of different metal foils (Ti, Mo, W, and Ta). The effects of carbon pollution and different protective layers on microstructure and dielectric and magnetic properties of LZF ceramics were studied comprehensively. Results reveal that annealing decarburization and BN-coated carbon paper could significantly improve resistance and saturation magnetization (Ms) of LZF, while real part of dielectric constant (ε′) and dielectric loss (tanδ) were significantly reduced. X-ray diffraction patterns indicate that all selected protective layers can provide good spinel-phase LZF ceramics. The utilization of metallic foil as protective layer can effectively reduce carburization, improve the resistance of LZF ceramics, and reduce ε′ and tanδ values. X-ray photoemission spectroscopy and Raman spectroscopy results reveal that cations with the highest valence state replace Fe3+ at B-site. The use of metal foil protective layer leads to the infiltration of metal ions into LZF lattice, leading to the increase in the lattice constant and decrease in the Ms value. This study deepens the understanding of carburization during SPS, providing a reference scheme for future applications.

Optically tunable dielectric response of TiO2:MAPbI3 nanocomposite thin films

We report on the optically tunable dielectric response of TiO2:MAPbI3 nanocomposite thin films via the electron injection from the CH3NH3PbI3 (MAPbI3) crystals to the TiO2 nanoparticles. The equivalent circuit analysis shows that the dielectric responses can be classified into the inner regions of dielectric media and the TiO2/MAPbI3 interfaces. Optical photos, atomic-force microscopic images, photoluminescence spectra, Raman scattering spectra, and X-ray diffraction patterns show that the TiO2:MAPbI3 thin film contains two different regions. The brighter and darker regions consist of isolated MAPbI3 rods and TiO2:MAPbI3 nanocomposites, respectively. It is noted that the real part of dielectric constant of the TiO2:MAPbI3 (3:1) composite thin film largely increases from 397 to 557 at the frequency of 40 kHz with one sun illumination, which opens a way to create optically tunable devices such as active antennas and active filters.

Comparison of the Real Part of Dielectric Constants with Different Materials to Decrease the Emittance and a Virtual Dielectric Constant to Reproduce Reflectance

This paper analyzes how the real part of the dielectric constant affects the emittance or temperature in some materials. A two-layer configuration was implemented on a glass substrate, with theory and experiment, on a sunny day in Mexico. Furthermore, the transfer matrix method was used as theory, changing the material on the top of the substrate and below a film of zinc sulfide. As a result, for a larger real part of the dielectric constant, the emittance decreased in analytical results, and therefore a decrease in temperature was obtained in the experiment. Furthermore, a virtual dielectric constant was obtained from the experimental reflectance in a bilayer system reproducing this system analytically with one layer having different thickness. The finite-difference time-domain (FDTD) method was used to obtain the optimal length of equilateral pyramids on the surface of a flat film by changing the materials to improve the reflectance or decrease the emittance. It was concluded that for a wavelength of the incident source, optimal dimensions of the triangles on the surface exist.

Exploring gas sensing, magnetic and dielectric properties of Ni2+ modified Mn–Zn ferrites

In the present report, pristine and Ni2+ modified Manganese Zinc ferrites (Mn–Zn ferrites) [Mn0·5Zn0.5NixFe 2-xO4, where x = 0.0, 0.025, 0.05] were synthesized using combustion method. Structural characterization revealed all the composition exhibit face-centered cubic crystallinity with space group Fd3‾m without any secondary phases. FTIR spectra showed high frequency bend located at 652 cm−1 which confirmed the formation of Mn0·5Zn0.5NixFe2-xO4 (x = 0.0, 0.025, 0.05) NPs as the high frequency kink attributes to Fe/Ni–O stretching vibration in cubic ferrite structure. Surface morphology and granular microstructure of all the compositions was determined using Scanning Electron Microscopy (SEM) and it was observed that compositions possessed porous micro-grains with average size of ∼20 μm. The average particle size increased from 5.5 ± 0.34 nm to 11.29 ± 0.12 nm with Ni2+ substitution in Mn–Zn ferrites. The optical energy band (Eg) slightly increased from 1.925 to 2.036 eV with increasing Ni2+ content as derived from UV–Visible spectral studies. The saturation magnetization enhanced with increasing Ni2+ concentration in the crystal framework of Mn–Zn ferrites. The real part of dielectric constant also increases with increasing Ni2+ concentration in the Mn–Zn ferrites. The gas sensing response of all the compositions was also analyzed for liquified petroleum gas (LPG). The sensitivity of all the compositions was also investigated on LPG, carbon monoxide (CO), and acetone gases and it was observed that the composition with higher concentration of Ni2+ depicted maximum response against all the gases, but in case of LPG the sensor showed maximum response. The sensing response was also checked at different operating temperature and time. The observed results support the potential candidature of Mn0·5Zn0.5NixFe 2-xO4, where x = 0.0, 0.025, and 0.05 NPs as LPG gas sensor.

Improvement of Optical Confinement for Terahertz Vertical-Cavity Surface-Emitting Laser with Square-Lattice Photonic Crystal Structure

A new method proposed to enhance the optical confinement of the terahertz band in a vertical cavity surface emitting laser involves introducing a square-lattice photonic crystal structure. This structure’s filling factor was optimized by computing the energy band structure and optical band values of the photonic crystal. The optimal optical band value is 0.436–0.528 a/λ. At a specific carrier concentration, the real part of dielectric constant of GaAs/AlGaAs materials will gradually increase with the increase of Al elements. By adjusting the length of the resonant cavity, a vertical cavity surface emitting laser with two wavelengths can be created without utilizing current injection. Additionally, the photonic crystal structure’s control effect on the transverse mode of the vertical cavity surface emitting laser and the release effect of the PN junction light confinement were analyzed. Numerical calculations indicated that incorporating a cubic photonic crystal structure in the vertical cavity surface emitting laser resulted in a 2× increase in the difference frequency intensity and a 6.33× increase in the optical field intensity.

Structural, electronic and optical study of Zr:CeO2 thin films by computational and experimental approach

Transition metal oxide shows some exceptional optical and electronic properties explore in recent investigations. In this context, the current study presents first principal and experimental investigations of pure and Zr doped CeO2 thin films. The simulations were performed using density functional theory based Wien2k-code with PBE-GGA approximation. The uniform and well-distributed granular thin films were grown for experimental investigations. The simulations and experimental results show a good resemblance in outcomes. The density of states predicts the p-d hybridization between Ce and O atoms while band structure reduce with Zr incorporation in CeO2 structure. Crystallographic analysis reveals the presence of crystalline cubic phase with space-group 225-F-m3m in thin films. Experimentally observed bandgap follows the reducing trend with Zr incorporation as predicted by simulations data and found as 2.38 eV for pure CeO2 and 1.51 eV for 6.25% Zr doping content. Optical parameters were recorded as a function of photon energy which strongly influenced by Zr concentration. The sharp increase in optical absorption and real part of dielectric constant in Zr containing composition makes these materials more efficient and favorable for photovoltaic and optoelectronic applications.

Plasmonic Ring Resonator Sensor With High Sensitivity and Enhanced Figure of Merit Using an Ag–Si–Ag Bus Waveguide

A plasmonic miniaturized ring resonator based on Ag-analyte-Ag ring cavity coupled with an Ag-Si-Ag input bus waveguide has been numerically analyzed for bulk refractive index and surface adlayer sensing applications. The opto-geometric parameters of the sensor structure have been thoroughly optimized to maximize field confinement in the sensing zone, which significantly improves the sensitivity. Using an Ag-Si-Ag input bus waveguide results in the reduction of propagation loss which offers an improved quality factor and figure of merit due to narrowing of full width at half maximum (FWHM) of the transmission spectrum. The average bulk refractive index sensitivity over biologically relevant refractive index range (1.33-1.38 RIU) and gas-sensitivity (1-1.01 RIU) values are 1757.71 nm/RIU with an FWHM of 37 nm, and 1787.14 nm/RIU with an FWHM of 24 nm, respectively. We have also investigated the optimized sensor's performance as an adlayer biosensor and the maximum adlayer sensitivity obtained is 2.72 nm/nm. We have also analyzed the sensor's optical tolerance by incorporating a 10% change in Ag's and Si's real part of dielectric constants. Owing to excellent sensitivity and high figure of merit the proposed sensor may find applications in designing highly sensitive on-chip nano-sensors with improved detection limit.

Influence of sintering temperature on electrical properties of Fe substituted NdCrO3 relaxor perovskite ceramic materials

Temperature-dependent dielectric properties of NdCr1-xFexO3 (0 ≤x≤1) (NCFO) perovskite nanocrystalline materials were successfully studied at 1 kHz, 10 kHz, 100 kHz, and 1 MHz selected frequencies. Temperature dependent real part of dielectric constant (ε′) curves of all samples exhibit step like relaxations. Capacitance (C) have been calculated for x = 0, 0.5, 1 samples of both 450 °C, 900 °C sintered systems at 1 kHz & 315 K and are found to be 4.5x 10-11 F, 1.5x 10-10 F, 3.7x 10-12 F; 1.4x 10-9 F, 2.6x 10-10, 9.3x 10-12 F respectively. Temperature variation real part of impedance (Z′), dielectric loss (tan δ) and imaginary part of modules (M″) plots have shown relaxor behavior. These plots obeyed Arrhenius law, and activation energies (Ea) are found to be in the order of 0.7–0.94 eV indicating semiconductor behavior. It is also noticed that ac conductivity (σac) is progressively increased with augment in temperature. σac have been estimated for x = 0, 0.5, 1 samples of both 450 °C and 900 °C sintered systems at 10 kHz & 315 K which are 4.5x 10-5 S/m, 1x 10-3 S/m, 1.4x 10-7 S/m; 1.8x 10-3 S/m, 1.2x 10-2 S/m, 1x 10-6 S/m respectively. High sintered (900 °C) samples possess high grain growth, and densification, which leads to significant structural and structural and electrical properties. Significant results of samples are suitable for high-power-density capacitors and microwave applications.

Effect of Alkaline earth oxides on the ionic conductivity of Boro-Tellurite glasses for solid state ion batteries

The complex impedance spectroscopy studies (electrical impedance, a.c. conductivity, dielectric constant, loss tangent) of the boro-tellurite glasses were measured as a function of the alkaline earth oxide content at broad range of frequencies and temperatures. Three series of boro-tellurite glasses containing BaO/SrO viz. BaO-TeO2-TiO2-B2O3 (BTTB), BaO-TeO2-B2O3 (BTB) and SrO-TeO2-TiO2-B2O3 (STTB) were prepared by the melt quenching method. The prepared glasses were characterized by XRD, DSC, density, FTIR and complex impedance spectroscopy experimental techniques. The XRD spectra exhibited no characteristic sharp peaks indicating the amorphous nature of the prepared glass samples. The glass transition temperature (Tg) values were evaluated from the DSC thermograms. The density values were found to increase with BaO content while they decreased with SrO content. This variation was attributed to the different density values of BaO and SrO. FTIR spectra revelated the presence of different structural units like BO3 and BO4. Impedance studies demonstrated that the replacement of TeO2 by the BaO content enhanced the ionic conductivity. The impedance plots of BTTB, BTB and STTB glasses exhibited nearlys semicircles. The bulk resistance (Rb) was calculated from the impedance plots. It was observed that the Rb values decrease with increasing BaO in BTTB and BTB glasses, while it increased with SrO in STTB glasses which may be attributed to the variation of mobile charge carriers. The Rb values vary as BTB > BTTB > STTB. The capacitance calculated from the impedance plots increased with increasing BaO mol% and decreasing SrO mol%. The capacitance also increased with increasing temperature. The power law exponent (k) values decrease with increasing temperature. Therefore, the ac conduction mechanism may follow correlated barrier hopping model. The real part of dielectric constant has high values at low frequencies, which decreased rapidly with surge of frequency. At high frequencies the contribution of charge accumulation is minimum resulting in constant

Studies on nano crystalline copper doped Nickel Zinc ferrites for optoelectronic applications

Investigation of optical and dielectric properties of nanocrystalline Ni0.65Zn0.35 Cu x Fe(2-2x/3) O4 (for x = 0.00–0.05 in steps of 0.01) ferrites synthesized using hydrothermal route is successfully carried out. Two distinct analytical spectroscopic methods with Dichloro – 5,6-Dicyano – 1,4-Benzo quinone (DDQ) and Bromo Phenol Blue (BPB) are adopted to observe the UV–visible absorption spectroscopy in the dispersed solutions of all samples. The formation of ion pair complex in the presence of BPB results in two distinct absorption edges in the visible region, around 440 nm and 580 nm in the present ferrite samples. Application of Tauc's formalism gives rise to two optical band gap values Eg1 and Eg2 in the range of 2.12–2.40 eV and 3.583–3.674 eV, respectively. The formation of charge transfer complex with all sample solutions in presence of DDQ reagent results in sharp absorption edges in the UV-region around 306 nm wavelength. An initial rise followed by continuous drop in band gap values ranging from 3.814 to 3.824 eV is observed from Tauc's plots. The optimum refractive index (n) values calculated for the three types of band gap values using empirical relations display the optical absorption potentiality of Ni–Cu–Zn nano ferrites in both Visible and UV – regions. Variation of band gap values is ascribed to the lattice strain effect, quantum confinement and narrowing band gap effects. Real part of dielectric constant (ε′), dielectric loss factor (tanδ) and ac-conductivity(σac) are studied for all samples at room temperature with in the frequency range of 42 Hz to 5 MHz. The values of ε′ and tanδ are observed to decrease with increase in frequency, while that of σac are found to increase with increase in frequency. Improved dielectric properties, existence of optical band-gap values observed in the present Ni–Cu–Zn ferrites promote these materials for their utility in optoelectronic devices and high frequency applications.

Preparation and wave attenuation properties of GR/Fe93.5Si3.5Gd3 composite powders

In this paper, different graphene (GR)/Fe93.5Si3.5Gd3 composite powders were prepared via high-energy ball milling. Through the analysis of the structural morphology and electromagnetic parameters of the composite powder, the effects of ball milling time and graphene on the wave absorption properties of the composite powder were investigated. It is shown that in the ball-milled composite powder, graphene is compounded with the alloy powder in an amorphous state, and the particle size of the composite powder decreases with the increase of ball milling time. Moreover, the addition of graphene and the introduction of high-energy ball milling did improve the electromagnetic parameters of the composite powder. With other conditions guaranteed to be the same, the real part of dielectric constant of the composite powder rises by up to 472.94% and the real part of permeability increases by up to 23.80%. The optimized change of electromagnetic parameters increases the conduction loss of the composite powder, together with the combined effect of spatial polarization and orientation polarization, it increases the dielectric loss of the composite powder. The magnetic loss of the composite powder is also greatly improved by the change of the main mode of magnetic loss to natural resonance. The increase in dielectric loss and magnetic loss has greatly improved the electromagnetic wave absorption performance of the composite powder. Among them, at 0.3 ∼ 8.5 GHz, the electromagnetic loss of 1.0 wt% GR/Fe93.5Si3.5Gd3 ball milled for 24 h reaches 1.20 ∼ 11.78. With other conditions being the same, it is respectively 718.06% and 708.22% higher than the composite powder without graphene and the composite powder with the shortest ball milling time, showing excellent microwave attenuating performance.

Dielectric Constant Estimation of Lunar Surface Using Mini-RF and Chandrayaan-2 SAR Data

A new dielectric constant estimation approach for the lunar surface using Mini-RF synthetic aperture radar (SAR) data and Chandrayaan-2 SAR data is presented in this work. Both the SAR systems are based on a hybrid-polarimetry (hybrid-pol) configuration that transmits a circularly polarized wave and coherently measures the backscattered wave by dual orthogonal linearly polarized channels. From the three-component hybrid-pol SAR decomposition technique, the ratio of the Fresnel reflection coefficients for horizontal and vertical polarization transmission can be estimated. This ratio, which is referred to as the co-polarization ratio, is used by the proposed methodology to find the real value of the dielectric constant. For performance validation, the proposed method is implemented on the Mini-RF hybrid-pol SAR data acquired over Apollo 17 landing sites. The values of the real part of dielectric constant are estimated for six different regions covering the collection sites of six Apollo 17 samples: 72 441, 73 241, 74 241, 75 081, 76 001, and 79 135. The results obtained using the proposed method are found to be in good agreement with the laboratory-measured results of the corresponding samples. Furthermore, the proposed methodology is also implemented on the Chandrayaan-2 hybrid-pol SAR data acquired over the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Biot crater</i> region. Various small areas possessing different possible surface characteristics, situated inside and outside the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Biot crater</i> , are being analyzed for validation.

Shielding performance of MnxNi0.8–xZn0.2Fe2O4 (0.1≤x≤0.7) for electromagnetic interference (EMI) in X-band frequency

A series of MnxNi0.8–xZn0.2Fe2O4 (0.1≤x≤0.7) nanoferrites were prepared by sol-gel auto combustion method. The TGA-DSC studies revealed the weight loss up to 700 °C and after no weight loss was found confirming the complete ferrite phase. Therefore, the as-burnt samples subjected to conventional sintering at 900 °C for 2h. The traces of XRD patterns revealed that formation of ferrite phase co-existed with secondary phases. The complex permittivity and permeability of present ferrite systems are found to be dependent of Mn2+ ion concentration. The real part of dielectric constant (ε′) for the all compositions are in the range of 5.184–6.951 at 8.2 GHz while it is 5.269–7.663 at 12.4 GHz. The values of ε′ at 8.2 GHz are slightly lower than the values at 12.4 GHz. The imaginary part of dielectric constant (ε″) was found to be in the range of 0.046–0.315 for all compositions over the entire range of X-band frequency (8.2–12.4 GHz). Compared to the variation of ε′, the variation of ε″ is more disorder. The number of semicircles in Cole-Cole plots is a witness of multiple di-electric relaxations of EM energy dissipation. The real part of magnetic permeability (μ′) is increasing, while imaginary part of magnetic permeability (μ″ ) is decreasing for all compositions as frequency is increasing from 8.2 to 12.4 GHz. Compared to the other ferrite compositions, the ferrite with low content of Mn2+ i.e. Mn0.1Ni0.7Zn0.2Fe2O4 ferrite system has higher value of μ″ and seems to be invariant over the entire X-band frequency range. The total effective shielding (SET) for all compositions is found to be in the range 37–12 dB. The highest values of SET 37 dB at 8.2 GHz and 28 dB at 12.4 GHz were reported for the ferrite composition Mn0.1Ni0.7Zn0.2Fe2O4. The shielding studies revealed that Mn–Ni–Zn ferrite systems are effectively suppressing electromagnetic interference (EMI) in X-band frequency. Comparatively, the ferrite system Mn0.1Ni0.7Zn0.2Fe2O4 is useful for the fabrication of EMI suppressor.

Effect of the cobalt ferrite and carbon fiber powder doping ratio on the electromagnetic properties of coated polyaniline-based polyester–cotton fabric

In this project, firstly, polyaniline-based polyester–cotton fabric was prepared by in situ polymerization using polyester–cotton fabric as the base fabric, aniline as the monomer, ammonium persulfate as the oxidizer, and camphor sulfonic acid as the dopant. Secondly, cobalt ferrite/carbon fiber powder-coated polyaniline-based polyester–cotton fabric was prepared by the textile coating process using polyaniline-based polyester–cotton fabric as the base fabric, PU2540-type polyurethane as the adhesive, and cobalt ferrite and carbon fiber powder as functional particles. Finally, the effect of the cobalt ferrite and carbon fiber powder doping ratio on the shielding effectiveness, reflection loss, dielectric constant real part, imaginary part, and loss angle tangent of cobalt ferrite/carbon fiber powder-coated polyaniline-based polyester–cotton fabric was studied by using the controlled variable method with emphasis on the cobalt ferrite/carbon fiber powder doping ratio. The results show that in the frequency range of 0.01–3.0 GHz, when the doping ratio of cobalt ferrite to carbon fiber powder is 0:3, the reflection loss of cobalt ferrite/carbon fiber powder-coated polyaniline-based polyester–cotton fabric reaches the minimum value at 1.49 GHz, the minimum reflection loss is –21.4 dB, and the effective absorption band is 1.25–1.94 GHz. In the test band, the shielding efficiency, reflection loss, the real part and imaginary part of the dielectric constant, and the loss angle tangent of the carbon fiber powder-coated polyaniline-based polyester–cotton fabric are larger than those of cobalt ferrite-coated polyaniline-based polyester–cotton fabric. The smaller the doping ratio of cobalt ferrite to carbon fiber powder, the larger value of the shielding efficiency, reflection loss, the real part and imaginary part of the dielectric constant, and loss angle tangent of the cobalt ferrite/carbon fiber powder-coated polyaniline-based polyester–cotton fabric.

Electronic, optical, mechanical, and thermal properties of diphenylacetylene-based graphyne nanosheet using density functional theory

In this paper, the structural stability, electronic, optical, mechanical, and thermal properties of diphenylacetylene-based graphyne (DPAG) nanosheet are investigated using first-principle calculations based on density functional theory (DFT). The absolute value of the calculated cohesive energy reveals that DPAG nanosheet is a structurally stable two-dimensional material. Also, in the results of phononic dispersion curves, the absence of imaginary frequencies confirms the dynamic stability of this novel material. In addition, the theoretical electronic band structure and density of states reveal the semiconducting nature of DPAG nanosheet. The optical analysis shows that the first absorption peaks of the imaginary and real parts of dielectric constants along the in-plane and out-of-plane polarizations of DPAG monolayer occur in the visible range of the electromagnetic spectrum. On the other hand, the DPAG nanosheet exhibits orthotropic elastic behavior with four independent constants comparable with the data of similar materials available in the literature. Moreover, DFT calculations of the lattice thermal conductivity of DPAG reveals an anomalously very low thermal conductivity of this nanosheet showing its perfect thermal non-conductivity. Our results provide deep insights into the potential applications of DPAG nanosheet for the design of new optoelectronic/nanoelectronic devices.

Understanding the interaction in functionalized multi-walled carbon nanotube/polyaniline composite by impedance study at low temperature

The impedance, modulus spectroscopy and dielectric properties of polyaniline (PANI) and composite with multi-walled carbon nanotube (MWCNT) of different degrees of functionalization are studied from 300 to 4.2 K in the frequency range 40 Hz–5 MHz. At low temperature (T 100 K), grain and grain boundary relaxation peaks are observed in PANI. In composites, MWCNT forms a network between less and highly conducting grains, increases dc conductivity, and shows no relaxation peak at low temperature. The chemical functionalization of MWCNT increases the polar interaction between MWCNT and PANI, shifts the relaxation peaks towards lower frequency and slows the relaxation process. The relaxation process is manifested as non-Debye type and it tends towards Debye type with increasing temperature in functionalized muti-walled carbon nanotube (fMWCNT) PANI composites, and explained by Bergman’s theory. The relaxation barrier energy at the interface of fMWCNT and PANI increases with increasing degree of functionalization which is the effect of enhanced interfacial (Maxwell Wagner–Sillars) polarization. In MWCNT composite, the real part of dielectric constant shows high negative value below 10 K at lower frequency (950 Hz) and it becomes positive due to functionalization of MWCNT. An additional crossover from positive to negative occurs in both MWCNT and fMWCNT, PANI composite above temperature 60 K and frequency 500 Hz. This crossover shifts towards higher temperature and frequency with increasing degree of functionalization. The negative value and crossover of dielectric constant are explained by Drude–Sommerfeld model.