Structural, morphological and dielectric properties of ErNbO4 prepared by the sol-gel method

In this work, ErNbO4 samples were prepared using the sol-gel method, through the citrate route, and heat-treated at temperatures between 700 and 1600 °C. The structure was studied by X-ray diffraction and Raman spectroscopy. The crystallite size was estimated using the Rietveld refinement and the Sherrer's formula, presenting values from 31.27 to 86.65 nm and from 40.96 to 78.23 nm, respectively. The morphology was studied by scanning electron microscopy. The measurement of the complex permittivity was made using the small perturbation technique, with a cavity operating in TE105 mode, at resonant frequency of 2.7 GHz. The increase of the treatment temperature promoted the increase of the dielectric constant and the dielectric losses were still maintained with low values, allowing their potential application in electric storage devices. The dielectric constant of ErNbO4 in a zero porosity sample case was estimated and compared with the experimental values.publishe

Electrical, morphology and structural properties of biodegradable nanocomposite polyvinyl-acetate/ cellulose nanocrystals

In this work, the dielectric properties and the electrical conductivity of polyvinyl acetate (PVAc) polymer doped with cellulose nanocrystals (CNC), extracted from the date palm rachis, are reported. We investigate the filler effect on the molecular mobility of the PVAc polymer chains and the charge transport properties of this material. PVAc/CNC films structure was characterized by powder X-Ray diffraction (XRD), showing the crystalline behavior of the cellulose filler. The dielectric properties were investigated using impedance spectroscopy, in the frequency range of 102–106 Hz and temperatures from 200 to 350 K. A β relaxation, assigned to the motions of the -OCOCH3 side groups, and α relaxation, associated with the glass transition of the PVAc matrix, can be detected.publishe

Relaxation processes in TiO2–V2O5–P2O5 glass-ceramics

Bulk samples of the ternary TiO2–V2O5–P2O5 system have been synthesized by the melt-quenching technique. X-ray diffraction and scanning electron microscopy with energy-dispersive spectroscopy were applied for structure and composition identification, whereby the presence of NASICON and Rutile type structures were identified. Dielectric properties were measured using impedance spectroscopy, at frequencies from 10 mHz to 1 MHz, and temperatures between 40 °C and 190 °C. Different relaxation models were applied to fit the experimental data. The electrical conductivity and activation energy of the glass matrix and crystalline particles were calculated and correlated to the structure of the material. The impedance spectra were analyzed with the complex dielectric modulus and the Distribution Function of Relaxation Times method to corroborate and complement the results of equivalent circuit models. The grain conductivity was shown to reach 10-1 S/m at 190 °C for the NASICON sample.publishe

Crystal Structure, Ionic Conductivity, Dielectric Properties and Electrical Conduction Mechanism of the Wyllieites Na_1.5Mn_3.5(AsO₄)₃ and Na_1.5Mn₃Fe_0.5(AsO₄)₃

Na1.5MnII3MnIII0.5(AsO4)3 and Na1.5MnII3FeIII0.5(AsO4)3 compounds were synthesized via a high-temperature solid-state combustion reaction. The obtained samples were submitted to structural, morphological, and electrical characterizations. X-ray diffraction measurements revealed that both compounds crystallize in the monoclinic system with the space group P21/c. The lattice parameters were determined to be a = 6.78344 Å, b = 12.93830 Å, c = 11.22825 Å, and β = 98.5374° for Na1.5MnII3MnIII0.5(AsO4)3, and a = 6.76723 Å, b = 12.9864 Å, c = 11.256 Å, and β = 98.8636° for Na1.5Mn2+3Fe3+0.5(AsO4)3. The structures consist of octahedral MnII and MnIII or FeIII ions connected by sharing edges, forming infinite chains. These chains are further connected by AsO4 tetrahedra, resulting in a three-dimensional anionic framework with tunnels parallel to the a-direction and cavities according to the c-direction. The structural models were validated using bond valence and charge distribution analyses. In addition to the structural characterization, the electric results depended on the crystal structures, indicating the potential of the studied materials for being used in several applications

BaTiO3—Gd3Fe5O12 Composites: Exploring the Dielectric Properties in a Broad Frequency Range

International audienceThis study presents the dielectric properties of a barium titanate–gadolinium ferrite composite material, obtained through a solid-state reaction method. The aim of this research was to create a composite material with enhanced dielectric properties compared to each individual component, and to investigate the electrical properties of the composites, using impedance spectroscopy. The structural and morphologic properties were analyzed using X-ray diffraction and scanning electron microscopy, respectively. Impedance spectroscopy measurements were performed over a wide frequency range (100–0.1 GHz) and temperature (45–170 °C) to evaluate the electrical behavior of the material. The dielectric relaxations were analyzed using the Havriliak–Negami function, and the key electrical parameters such as relaxation frequency, dielectric strength, and electrical conductivity were extracted. Several relaxation processes were identified, which depend on the mixture of the initial titanate and ferrite materials, and a correlation between structural, morphologic, and electrical properties was exposed. The sample with the highest dielectric constant was the 25 wt% gadolinium ferrite composite, with ε′ close to 240 and loss tangent values below 0.1, affording it the more appropriate composition for energy storage devices such as lead-free dielectric capacitors

Thermal and dielectric properties of carbon nanotubes/graphite/polyester ternary composites

Reuse is restricted to non-commercial and no derivative uses.Binary and ternary composites were synthesized using a polyester matrix reinforced by two types of carbon inclusions, namely, carbon nanotubes (CNT) and graphite (Gt) (CNT/Gt/Polyester). Thermal analyses were performed, using thermogravimetry and differential scanning calorimetry, which allowed us to observe significant changes in glass transition temperatures and degradation temperatures of the composites. Dielectric measurements were performed in a frequency range from 100 Hz to 1 MHz and temperature from –33 to 107°C. The dielectric permittivity values of the CNT/Gt/Polyester ternary composites, compared to the Gt/Polyester binary composites, indicate that the addition of CNT particles to the Gt/Polyester binary system significantly improved the dielectric permittivity, due to the enhanced interfacial polarization of the host matrix, while the frequency dependence of the electrical modulus spectra revealed a Maxwell–Wagner–Sillars dielectric relaxation process that was found to follow the Cole–Davidson approach.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Project I3N, UIDB/50025/2020 and UIDP/50025/2020, FCT/MEC and the financial support from the Diputación General de Aragón under project T03_20R (Grupo Reconocido).Peer reviewe

Electrical properties of lithium ferrite nanoparticles dispersed in a styrene-isoprene-styrene copolymer matrix

The main goal of this work was the preparation and study of a composite material by dispersing lithium ferrite particles in a polymeric matrix. The matrix selected was styrene-b-isoprene-b-styrene (SIS) copolymer. Lithium ferrite (LiFe5O8) is an attractive material for several potential technological applications, due to its physical properties LiFe5O8crystallites were obtained by controlled heat-treatments of homogeneous Li2O-Fe2O3powders prepared by wet ball-milling method and using lithium and iron nitrates as raw materials. To achieve an effective dispersion of particles, we modified its surface. The structure of the composites, containing modified and unmodified ferrite particles, was studied by XRD and Raman spectroscopy. The dielectric properties were analyzed in the frequency range between 10?1 and 106Hz, and as a function of the temperature between ?73 and 127 �C. The frequency dependence of the ac conductivity is characterized by a low frequency region of constant conductivity followed by a frequency dependent conductivity. This behavior was interpreted using the Jonscher power law.Scopu

Studies on thermal and dielectric properties of Gt/CNT/polyester ternary composites

Abstract of the poster presented at the Nanoscience and Nanotechnology in Security and Protection Against CBRN Threats, (NATO Advanced Study Institute (SPS.ASI 985611), Sozopol, Bulgaria, 12th - 20th September 2019.This study focuses on the development of polyester reinforced with the combined inclusion of two types of fillers, carbon nanotubes (CNT) and graphite (Gt) nanocomposites. Morphological observations revealed that the replacement of Gt with CNT reduces the Gt aggregations. Electrical and dielectric properties of these ternary composites were analyzed using the impedance spectroscopy formalism over a frequency range from 100 Hz to 1MHz and temperature range from 300 to 400 K. The frequency dependence of electrical conductivity obeys the universal dynamic response. Positive and negative temperature coefficients in resistivity phenomena were observed at temperatures below and above the glass transition point respectively. It was found that the mechanism responsible for the changes in resistivity is predominantly due to the tunneling effect. The dielectric relaxation phenomena appeared in the impedance spectra were interpreted using the Cole-Cole model. The calculated relaxation parameters reveal that, with substitution of Gt by CNT, the PTC effect that related to these composites shows significant changes

Effect of structural properties in the electrical impedance spectrum of multi-walled carbon nanotube/graphite/polyester ternary composites

The aim of this study is to establish a connection or correlation between the electrical and structural properties of ternary composites, which were prepared by adding multi-walled carbon nanotubes (MWCNT) and graphite (Gr) as conductive fillers to an insulating polyester matrix. The study utilized small-angle neutron scattering, infrared and Raman spectroscopy for structural characterization. Electrical measurements were conducted within a frequency range of 100 Hz to 1 MHz and a temperature range of 200–380 K. The alternating current (AC) conductivity showed a frequency dependence following Jonscher's power law. The temperature dependence of the AC conductivity suggested that the electrical conduction within the material is a thermally activated process. The temperature-dependent behavior of the direct current (DC) conductivity suggests that below and above the critical temperature, there is a pronounced positive and negative temperature coefficient of resistivity, respectively. In comparison to MWCNT/polyester or Gr/polyester composites, the percolation threshold of the MWCNT/Gr/polyester composite is much lower. Additionally, applying the Arrhenius equation to analyze the temperature dependence of DC conductivity reveals that the inclusion of MWCNT and Gr in the polyester matrix results in a decrease in activation energy.Authors acknowledge financial support from Spanish MICINN/AEI under Project PID2019- 104272RB-C51/AEI/10.13039/501100011033, Diputación General de Aragón for Project T03_20R (Grupo Reconocido), and FEDER through the COMPETE 2020 Programme and National Funds through FCT—Portuguese Foundation for Science and Technology under the Project UID/CTM/50025/2019.Peer reviewe

Thermal and dielectric behavior of ternary composites Carbon nanotubes/Graphite/Polyester

Poster presented at the Fifth International Symposium on Dielectric Materials and Applications, ISyDMA’5, 15-17 april 2020 (virtual meeting), organised by the Faculty of Science Semlalia Cadi Ayyad University, Morocco.Ternary composites composed of a polyester matrix were synthesized with the combined inclusion of two types of fillers, namely, multi-walled carbon nanotubes and graphite. Thermal analysis was performed, using thermogravimetric analysis and differential scanning calorimetry, which allowed us to observe changes in the glass transition temperatures and degradation temperatures of the composites. Electrical and dielectric measurements were carried out in a frequency range from 100 Hz to 1 MHz and temperatures from -33 to 107 ºC. The dielectric response was analyzed using the electrical modulus Cole-Cole formalisms, depending on the temperatures and on the concentration of filler in the polymer matrix