Modulus Spectra Research Articles

Broadband dielectric behaviour and structural characterization of PVDF/PMMA/OMMT polymer nanocomposites for promising performance nanodielectrics in flexible technology advances

Characterization of broadband dielectric behaviour of polymer nanocomposites (PNCs) is vital for the exploration of efficient nanodielectrics as energy storage, flexible dielectric substrates, and insulators in a wide range of advanced electronic device technologies. Accordingly, herein, PNC films based on poly(vinylidene fluoride) (PVDF)/ poly(methyl methacrylate) (PMMA) blend matrix (80/20 wt/wt%) dispersed with 0, 2.5, 5, and 10 wt% organo-modified montmorillonite (OMMT) nanoclay are developed by state-of-the-art homogenized solution casting method. These PVDF/PMMA/OMMT compositions based flexible PNC films are characterized in detail by employing a scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) device, x-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectrometer, differential scanning calorimeter (DSC), inductance-capacitance-resistance (LCR) meter, and impedance/material analyzer (IMA). The SEM microimages, XRD traces, and FTIR spectra evidenced appreciable homogeneity and surface morphology, intercalated and exfoliated OMMT structures, and the α, β and γ-phase crystallites of the PVDF in these complex semicrystalline PNCs. The DSC thermograms confirmed a significant alteration in the melting temperature and degree of crystallinity of the PVDF crystallites with the increased amount of OMMT in the 80PVDF/20PMMA blend host matrix. The broadband dielectric dispersion spectra over the frequency range of 20 Hz−1 GHz explained the contribution of interfacial polarization in the complex dielectric permittivity at lower experimental frequencies, whereas at higher frequencies permittivity is ruled by dipolar polarization in these composites at 27 °C. The dielectric loss angle tangent and electric modulus spectra revealed an intense structural dynamics relaxation process in the upper radio frequency region. The influence of OMMT concentration on the dielectric permittivity and electrical conductivity is explored. The detailed dielectric and electrical characterization of these innovative semicrystalline composites with important structural and thermal properties revealed their immense potential as high-performance nanodielectrics for highlighting current applications of broadband frequency range electrical and electronic device technologies.

Effects of PVP surfactant on nanosuspension stability and optical, dielectric, and rheological properties of zinc oxide nanoparticles dispersed alcohols mixture based nanofluids

Nanofluids (NFs) are state-of-the-art engineered promising properties soft materials which found vital applications in thermal management and electrical insulation, and also gaining much attention in the advances of soft optoelectronic and microelectronic device technologies. The longer-time functionality of the NF material depends on particle suspension stability which can be maintained up to some extent with the addition of appropriate surfactants. Here, we report the promising properties of the semiconductor NF (SNF) samples consisting of a highly rich ethylene glycol (EG) mixture with glycerol (Gly) (90/10 vol%) as base fluid, zinc oxide (ZnO) nanosuspension, and poly(vinyl pyrrolidone) (PVP) surfactant. These formulated 90EG + 10Gly/x wt% (ZnO + PVP) SNFs with varying concentrations (x wt%) of ZnO and PVP are characterized by employing ultraviolet-visible (UV–Vis) spectrophotometer (wavelength range 200–800 nm), precision inductance-capacitance-resistance (LCR) meter (frequency range 50 Hz to 1 MHz), and rotational rheometer (shear rate range 13–132 s−1). The UV–Vis absorbance spectra, recorded on the freshly prepared and aged SNF samples, confirmed that the added PVP enhances longer time suspension stability for ZnO nanoparticles in the H-bonded 90EG + 10Gly viscous base fluid, and also promoted the photosensitivity, electronic transition, and radiation blocking performance of these materials. The dielectric spectra revealed a huge contribution of the electrode and interfacial polarization processes to the dielectric permittivity of the SNFs at low frequencies and their dynamics is explored from the intense relaxation peaks observed in the loss angle tangent spectra. The higher experimental frequency range dielectric permittivity remains frequency independent and it is marginally affected by the ZnO and PVP concentrations in these SNFs, at 298.15 K. The electric modulus and impedance spectra of these SNFs are also provided and analyzed for the charge conductivity and interfacial relaxation processes. The ac electrical conductivity of these materials obeys the power law behaviour along with the dc conductivity part in the range from 5.4 to 6.8 × 10–7 S⋅cm−1. The rheological measurements on these SNFs, in the 303.15 K to 323.15 K, categorized them as Newtonian-type fluids with a considerable increase in dynamic viscosity by PVP dissolution. These materials showed the Arrhenius behaviour of viscous flow having activation energies in the range of 25–27 kJ⋅mol−1. The experimental results of various techniques on these green-formulated SNFs revealed their multifunctionality with great potential for the future generation of soft device technologies, in addition to highlighting their current applications of manageable heat transfer in the flow systems.

Green biopolymer and plasticizer for solid electrolyte preparation: FTIR, electrochemical properties and EDLC characteristics

In this study a green electrolyte was developed by incorporating methylcellulose (MC) polymer with potassium thiocyanate as ion provider and plasticized with glycerol to enhance salt dissociation. The purpose of glycerol addition was to improve DC conductivity and to enhance the performance of an electric double-layer capacitor (EDLC) device. The electrochemical and structural characteristics of the green electrolyte were examined. The broadening of the FTIR bands and a decrease in intensity indicated the interaction between the electrolyte components. The suitability of the electrolyte films for device applications was confirmed by measuring ionic conductivity using electrochemical impedance spectroscopy (EIS) skills. A significant amount of charge was concentrated at the electrode–electrolyte interface because of the high dielectric constant of the electrolyte. The loss tangent (tan δ) and modulus (M“) spectra obtained from electrical impedance spectroscopy showed distinct peaks associated with ion relaxation processes. The results of the transference number measurement (TNM) experiment indicated that ions were more influential than electrons. The stability of the film under different voltage conditions was evaluated using the linear sweep voltammetry (LSV) method. The performance of the EDLC was determined through cyclic voltammetry (CV) and charge–discharge evaluations. The CV pattern of the device at low scan rates showed a non-Faradaic mode of charge storage with a nearly rectangular shape. The newly constructed EDLC exhibited an initial capacitance per unit mass of 79F/g, a utilization efficiency of 87%, a power density of 1950 W/kg, and an energy storage density of 12.1 Wh/kg.

Effect of nanodispersed zinc oxide concentrations on the structural, optical, dielectric, viscous, and acoustic properties of ethylene glycol– glycerol mixture based nanofluids

Nanofluids (NFs) are green-formulated innovative soft materials, enormously used for thermal management medium in energy harvesting/ storage and heat transport, as high breakdown voltage insulators/ nanodielectrics in electrical and energy storage systems, and in the advances of soft condensed matter device technologies. In this study, NFs consisting of ethylene glycol (EG) and glycerol (Gly) mixture in equal volumes as the base fluid and semiconductive zinc oxide (ZnO) nanoparticles with increasing concentrations from 0.005 to 1.00 wt% are prepared and characterized by employing different advanced techniques. X-ray diffraction (XRD) patterns recorded directly on these NFs confirmed the homogeneity and nanosuspension stability of ZnO particles in the hydrogen-bonded supramolecular 3D structure of viscous EG–Gly base fluid. The UV-Vis absorbance spectra explained the ZnO concentration tunable photo sensing and UV blocking properties of these semiconductive nanofluids. The 20 Hz to 1 MHz range dielectric spectra revealed high static dielectric permittivity of these NFs, at 298.15 K, confirming them as promising nanodielectric for electric energy storage devices. The dielectric dissipation factor, electric modulus, and impedance spectra confirmed that these EG–Gly/ZnO NFs have electrode polarization and conductivity relaxation processes around 200 Hz and 20 kHz, respectively. The electrical conductivity is observed in the range of 0.32– 0.65 μS/cm with a noticeable increase at the higher ZnO concentration which infers appreciable insulation performance of these NFs. The rheological measurements demonstrated Newtonian behavior of these NFs with a dynamic viscosity of about 69 mPa.s, at 298.15 K. Ultrasound velocity and various acoustic parameters of these NF materials are marginally altered with varying the ZnO concentration and revealed appreciable thermal conductivity of 0.31 W·m–1·K–1, at ambient temperature. The temperature dependent viscosity measurements of EG–Gly/1.00 wt% ZnO sample demonstrated its Arrhenius behavior with high activation energies for both the viscous and relaxation processes. These experimental results establish the EG–Gly/ZnO nanofluids as multifunctional materials for highlighting current applications and also in futuristic soft condensed matter technologies.

Ionic transport and segmental dynamics in poly(ethylene oxide) based polymer electrolytes: Dependence on molecular weight of host polymer matrix

We have investigated the ion transport and segmental dynamics in poly(ethylene oxide) (PEO) and sodium tetrafluoroborate (NaBF4) salt based solid polymer electrolytes as a function of molecular weight of PEO polymer matrix at a fixed salt concentration (EO/Na = 18) using broadband dielectric spectroscopy. The molecular weight (Mv) of PEO polymer matrix was varied from 1 × 105 to 6 × 105 g/mol. The ionic conductivity of the PEO based electrolytes obtained from the complex impedance plot showed a correlation with the glass transition temperature, crystallinity and ion diffusion coefficient. The AC conductivity spectra were analyzed by using the universal power law model, except the low frequency region, where the electrode polarization contribution was dominant. The temperature dependence of ionic conductivity and the hopping frequency followed the Vogel-Tammann-Fulcher (VTF) relation, indicating a coupling between the ion transport and the segmental dynamics of polymer chains. The segmental dynamics was investigated using the derivative dielectric constant spectra. The modulus spectra were well described by the Havriliak-Nigami and the Kohlrausch-Williams-Watts functions. The temperature dependence of the conductivity relaxation time also followed the VTF relation. The ion transport in PEO based polymer electrolytes with higher molecular weight was found more cooperative than that of the other polymer electrolytes.

Effect of pH on Structure, Optical, and Dielectric Properties of BaTiO3 Nanoparticles

AbstractBarium titanate (BTA) nanoparticles are prepared by low‐temperature hydrothermal technique with varying pH from 9 to 12. The X‐ray diffraction (XRD) patterns confirm that the BTA nanoparticles with pH ranging from 9 to 11 show the existence of few small secondary phases (*) related to tetragonal structure along with the prominent cubic phases. But for sample with pH = 12, the XRD patterns confirm the presence of cubic phases without secondary phases. The morphology evidences the existence of almost spherical‐shaped grains (field‐emission scanning electron microscopy), and nanoparticles (high‐resolution transmission electron microscopy) in case of all samples. The energy dispersive spectra confirm the presence of Ba, Ti, and O elements among all samples. Besides, the photocatalytic activity is noticed for all samples. Using the Tauc's plots, optical band gap is determined. The dielectric constant (at pH = 12) is ≈15.10 while the dielectric loss is ≈1.231 suggesting the sample is suitable for charge stored capacitor applications. The dielectric modulus and impedance spectra are recorded in order to evaluate the polarization and conduction mechanism.

Structure and electrical properties of AM(PO3)4: A = Li, Na and M = Ce and Pr

In this manuscript, preparation, crystal structure and electrical properties of two types of AIMIII(PO3)4 metaphosphates, namely LiCe(PO3)4 and LiPr(PO3)4 (monoclinic, C2/c), and NaCe(PO3)4 (monoclinic, P21/n) have been reported. All the compounds were prepared by conventional solid-state reaction and characterized by powder X-ray diffraction. The electrical properties of these materials were studied by impedance spectroscopy. The dc-conductivity (σdc) of all compounds show similar increasing trend with temperature and is attributed mainly to the alkali metal ion diffusion. However, a discontinuity in the temperature dependent σdc is observed at higher temperature in all of them. The activation energy (eV) for alkali ion conductivity in LiCe(PO3)4, LiPr(PO3)4 and NaCe(PO3)4 respectively, is 1.14, 1.18 and 0.84, up to certain temperature (∼973K), and increases to 1.31, 1.35 and 1.51 at higher temperature. The analysis of ac-conductivity and modulus spectra indicated a correlated movement of ions in the structure. It is observed that structure and electrical properties of these metaphosphates are dependent more on the nature and ionic radii of the alkali ions than the rare-earth ions.

Structural, Frequency and Temperature Dependent Dielectric Properties of Zn2+ Substituted Ni-Co Based Spinel Ferrite (ZnxNi0.8−xCo0.2Fe2O4)

Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8−xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard’s law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8−xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan δ) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxation. Rise in Zinc concentration leads to a decrease in dielectric constant (ε r) due to the declining of Fe3+–O–M2+ conducting network (M is Co or Ni). Here, we report a low loss tangent factor of the order of for the sample Ni0.6Zn0.2Co0.2Fe2O4 make this composition suitable for high frequency-applications at room temperature. The activation energy is calculated from electric modulus formalism and DC electrical conductivity and found to increase with further substitution of Zn2+ concentration.

Low-temperature dielectric relaxation mechanism and correlated barrier hopping transport in neodymium perovskite chromite

Herein, neodymium chromite (NdCrO3) has been synthesized by the sol–gel auto-combustion method. The Rietveld analysis of the X-ray diffraction pattern has shown that NdCrO3 crystalizes in the perovskite structure with orthorhombic unit cell and Pbnm space group symmetry. The electrical transport properties have been investigated by complex impedance spectroscopy over the experimental frequency and temperature ranging from 40 to 1 × 106 Hz and 158–283 K, respectively. The equivalent circuit modeling of Nyquist plots revealed the contribution of grains and grain boundaries to the charge conduction and the relaxation mechanism of NdCrO3, respectively. The AC conductivity analysis divulged the correlated barrier hopping transport mechanism in the NdCrO3. The imaginary electrical modulus spectra fitted by the Kohlrausch, Williams, and Watts function presented the non-Debye type nature of the relaxation mechanism in the material. The dielectric permittivity has exhibited the Maxwell–Wagner type polarization of the material, and the loss factor has exhibited an increasing trend with temperature.

Temperature-driven complex dielectric and polaron-hopping mediated electrical conduction in aurivillius Gd2MoO6

In this work, aurivillius gadolinium molybdate (Gd2MoO6) was synthesized by the conventional solid-state route which was accompanied by cutting-edge characterization i.e., structural, and electrical, to give insight into the material characteristics required for possible high-temperature applications. The single-phase crystalline nature with monoclinic symmetry (C2/c, Space group-15) of Gd2MoO6 was confirmed by the X-ray diffraction (XRD) pattern. The average particle size was obtained to be ∼0.495 µm. The electrical conductivity and dielectric properties of a Gd2MoO6 plate capacitor were investigated in the frequency range between 10 Hz and 1 MHz and temperature from 473 to 773 K. A high dielectric constant (ε') of ∼3272 and low dielectric loss (δ) of ∼200 was observed at the low frequency and high-temperature regions, respectively. The Maxwell–Wagner interfacial polarization was found to be responsible for the decrease of the dielectric constant with increasing frequency. The behavior with the temperature of the frequency exponent (n) from the fitted conductivity spectra by Jonscher power law corresponds to the non-overlapping small polaron tunneling model between 473–673 K and correlated barrier hopping model at/over 673 K. The non-exponential Kohlrausch Williams-Watts function was introduced to fit the imaginary modulus (M′′) spectra and the activation energy was obtained to be 0.81 eV for grain and 0.94 eV for grain boundary conduction. The Nyquist plots(Z′vs.Z′′) differentiate the grain and grain boundary contribution and were fitted with the combinations of resistance (R), capacitance (C), and constant phase element (Q) in an equivalent circuit model(RC)(RCQ). Typical negative temperature coefficient of resistance behaviors of Gd2MoO6 suggest its possible application as thermistors in modern electronics circuits.

Investigation on electrical transport and dielectric relaxation mechanism in TbCrO3 perovskite orthochromite

Herein, the TbCrO3 (TCO) chromite was synthesized by the sol-gel auto-combustion route and sintered at 900 °C. The Rietveld analysis of the room temperature powder X-ray diffraction profile confirmed the single-phase formation of the material crystallized in the orthorhombic phase of the perovskite structure with Pbnm space group symmetry. The surface morphology, the elemental composition, and the chemical states of the compound were investigated by field emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy, respectively. The electronic density of states, band structure, and electron density were analyzed by Density Functional Theory. The electrical transport and dielectric relaxation mechanism were investigated using complex impedance spectroscopy over the experimental frequency and temperature ranging from 40-1.2x106Hz and 138−273 K, respectively. Two semicircular arcs in the impedance complex plane plots were modeled to an equivalent circuit configured by RG∥QG+RGB∥QGB which were attributed to the contributions of the highly resistive grain boundaries and relatively conducting grains in the material. The electrical conductivity as a function of frequency followed Jonscher’s universal power law behavior and an increasing nature of the temperature-dependent frequency exponent suggested small polaron hopping as the electrical conduction mechanism of the material. The least capacitive response of the TCO system was investigated by the complex electrical modulus formalism and the frequency-dependent imaginary modulus spectra were modeled by the Kohlrausch–Williams–Watts function, which resolved the thermally activated peaks of bulk and interface effects to the dielectric relaxation mechanism. The dielectric constant exhibited Maxwell-Wagner interfacial polarization effects and the dielectric loss factor showed frequency dispersion at all temperatures.

A multifunctional transition metal based double perovskite Ba2(FeW)O6: Structural, microstructural, optical, electrical and ferroelectric properties

In this article, synthesis (solid-state reaction) and characterizations (XRD, SEM-EDX, RAMAN, UV–Vis, LCR & P-E measurements) of a polycrystalline double perovskite Ba2(FeW)O6 are reported. The prepared sample crystallizes in tetragonal symmetry with an average crystallite size of 60.7 nm and lattice strain of 0.00045 respectively. Vibrational modes of the molecules in the prepared sample are investigated using Raman spectroscopy. Analysis of scanning electron microscope (SEM) and energy dispersive analysis of x-ray (EDX) supports homogenous distribution of grains and compositional consistency. Optical investigation calibrates direct energy bandgap of 2.72 eV; which may be suitable for photocatalytic and photovoltaic devices. Dielectric, impedance, and modulus spectra have been studied over a wide range of frequencies (1 kHz–1 MHz) and temperatures (25 °C–500 °C). Wide dielectric dispersion at low-frequency encounters space charge polarization with the Maxwell-Wager effect. Study of impedance plots reveals negative temperature coefficient resistance (NTCR) character while existence of non-Debye relaxation mechanism is confirmed from modulus plots. Frequency dependence ac conductivity obeys Jonscher's Power Law (JPL) and confirms the presence of a non-overlapping small polaron and correlated barrier hopping process (CBH). The study of activation energy (Ea), sensitivity factor (α) and thermistor constant (β) values from resistance versus temperature supports NTC thermistor behaviour and explore the possible applications related to temperature-based sensors.

Scaling studies of temperature dependence of electric conductivity and electric modulus spectra of solid solution Sr2-xLaxSnO4 (x ≤ 0.10) Ruddlesden Popper Oxide

The mixed ionic and electronic conductor oxide with formula Sr2-xLaxSnO4 (S2LS) within x ≤ 0.10 were synthesized via the conventional ceramic route and investigated. The structural analysis revealed the formation of single-phase materials with a tetragonal crystal structure. The presence of Sn in the form of Sn4+/Sn2+ ions and oxygen vacancies in the synthesized samples were investigated by X-ray photoelectron spectroscopy. The alternating current (AC) conductivity and modulus spectra of S2LS systems were obtained as functions of frequency and temperature and further scaled. The AC conductivity data were analyzed using Jonscher's power law (JPL) fitting to determine the hopping frequencies, DC conductivities, and power exponents. The obtained activation energy value suggests the dependence of conductivity primarily on the mobility of charge carriers. The conductivity spectra were analyzed using various formalisms, viz., Ghosh scaling and Rolling scaling, to understand the conduction mechanism. The scaling behaviors of AC conductivity and modulus spectra reflect the temperature-independent conduction mechanism of the system.

The study of structural, dielectric, impedance and modulus properties of La0·8Pb0·2FeO3 doped by 25% Mg into the B-site

The sample of La0·8Pb0·2Fe0·75Mg0·25O3 was synthesized via the sol-gel route. The Refinement using the Rietveld method confirms that the structure is orthorhombic with space group Pnma. The dielectric properties (ε) and modulus (M) of the material were studied a wide range of temperatures and frequencies range. The constant dielectric values of our compound were lower than those for LaFeO3. Indeed, relatively reduced values of the dielectric constant, not exceeding 102 F/m, were usually achieved when intrinsic ionic and electronic polarization mechanisms were employed in the studied structure. Dielectric losses were described by the Giuntini theory. The imaginary modulus spectra were adjusted using the exponential function provided by Kohlrausch-Williams Watts (KWW) relaxation function, which determined the presence of thermally activated relaxation. The comparative display of the normalized impedance and electric modulus revealed the existence of short-range movement of the charge carrier. Relaxation phenomena of the non-Debye type were confirmed in the material by studying the modulus.

Morphological, structural, optical, broadband frequency range dielectric and electrical properties of PVDF/PMMA/BaTiO3 nanocomposites for futuristic microelectronic and optoelectronic technologies

Polymer blend nanocomposite (PBNC) films consisted of fluoropolymer poly(vinylidene fluoride) (PVDF) and plexiglass polymer poly(methyl methacrylate) (PMMA) blend host matrix (fixed composition blend of PVDF/PMMA = 80/20 wt/wt%) with barium titanate (BaTiO3) ceramic nanofiller of varying concentrations (x = 0, 2.5, 5, 10, and 15 wt%) were prepared via a state-of-the-art solution-cast method. Scanning electron microscope (SEM) images evidenced high homogeneity of these PBNC films and a huge alteration in the spherulite morphology of the PVDF with the increase in dispersed BaTiO3 concentration in the polymer blend matrix. The X-ray diffraction (XRD) patterns identified the presence of electro-active polar β- and γ-phases of the PVDF crystallites in all the composite materials which are supported by the results of Fourier transform infrared (FTIR) spectra. The differential scanning calorimeter (DSC) thermograms explained the high melting temperature of these overlapped PVDF polymorphs and the degree of crystallinity altered anomalously with the variation of nanofiller concentration. The absorbance of ultraviolet-visible (UV-Vis) radiations enhanced while the direct energy band gap of the 80PVDF/20PMMA blend matrix and also the semiconducting BaTiO3 was found to decrease with the increased concentration of nanomaterial in the host polymer matrix. The ambient temperature broadband dielectric spectra covering the frequency range from 20 Hz to 1 GHz explain that the real part of complex dielectric permittivity reduced with a huge dispersion at higher radio frequencies where the dielectric loss tangent and electric modulus spectra exhibited an intense chain segmental relaxation process. The electrical conductivity of these PBNC films increased with frequency augmented and illustrated a small variation for different concentration composites. The experimental results demonstrated that these PVDF/PMMA/BaTiO3 films could be potential candidates for frequency tunable nanodielectric, electromagnetic interference shielders, a flexible dielectric substrate, thermal insulators, and bandgap regulated materials for futuristic microelectronic, capacitive energy storage, and optoelectronic technologies.

Investigation on dielectric properties of sandwich-structured fluoroelastomer/PVDF films containing graphene

The sandwich-structured FKM/PVDF film with different GNP components fabricated via the hot-pressing technique were studied by dielectric relaxation spectroscopy over a range of frequency (20 Hz-30 MHz) and temperature (25–205 °C). Compared with single-layered PVDF film, the curie transition temperature (Tc) and melting temperature (Tm) of sandwich-structured FKM/PVDF films obviously increase, but their crystallinities decrease. The permittivities of sandwich-structured FKM/PVDF films are higher than single-layered PVDF film throughout whole temperature range, and the dielectric losses of three films have a little change. In addition, the Cole-Cole plots and electric modulus spectra of all films reveal the non-Debye relaxation behavior. σdc of sandwich-structured FKM/PVDF films increase slightly compared to single-layered PVDF film, and σac decreases. Both Eτ and Eσ of sandwich-structured FKM/PVDF films slightly decrease due to the combined effect between the high conductivity of GNP and the barrier effect of layer/layer interface. A higher Ue of 8.1 J/cm3 can be obtained at 350 MV/m for sandwich-structured film with 0.5% GNP. The sandwich-structured FKM/PVDF films with low content GNP have potential application in dielectric material.

Effect of La and Se in tailoring the energy storage properties of BFO nanostructures

Simultaneous rare-earth doping at A and B sites have impacted various properties of BFO at room temperature. In this work, the dielectric and magnetic properties of BFO, are tailored by doping La and Se. Bi0.92La0.08Fe1−xSexO3, (x = 0%, 10%, 25%, 50%, 100%) nanostructures are prepared using sol-gel technique. Structural analysis reveals that increased doping has reduced and eliminated the secondary phases of nanostructures. Absorption spectra showed a wide blue shifted absorption, indicating multiple electron transitions and the bandgap values decreased upon doping. Improved room temperature dielectric properties with increased doping indicates these nanostructures as viable candidates in energy storage applications. The improvements in ac-conductivity, impedance and modulus spectrum of doped nanostructures are observed. Specific capacitance of 36.22 F/g for Bi0.92La0.08Fe1O3 at 10 mV/s and 21.48F/g for the Bi0.92La0.08Fe0.9Se0.1O3 sample was observed. Weak ferromagnetism is observed in M-H loops with increased Se concentration that also finds applications in magnetic storage devices.

Geotechnical and thermal analysis and complex impedance spectroscopy characterization of pure Moroccan bentonite material for civil engineering applications

Combined modulus and impedance spectra are employed in the present work to explore electrical inhomogeneity and carriers’ behaviors in a pure bentonite Moroccan clay based on equivalent circuit. It has been clearly observed that the electrical properties change due to the increase of temperature from 300 °C to 700 °C. The frequency-dependent imaginary modulus M" and imaginary impedance Z" curves has only one peak at each temperature indicating the predominance of the contribution of grains to the total electrical conduction in bentonite. The positions of these peaks move to higher frequencies when the temperature increases in relation with the distribution of relaxation time. Moreover, the activation energy for the conduction process in bentonite is determined from the slope of ln(ρdc) versus of 1/T in the order of 700 meV in good agreement with that obtained from the proposed equivalent circuit. On the other hand, let’s present a geotechnical study that show that our material is a swelling clay, very plastic and could be used as a binder. The external stress dependence of the bulk density, Young’s module and maximum stress are analysed. The thermal conductivity determined following the device of Lee's disks where two copper disks of thickness of 15 mm and diameter of 30 mm were used

Synthesis, morphological, electrical, and conduction mechanism studies of a sodium cerium diphosphate compound.

A NaCeP2O7 compound was successfully synthesized by a high-temperature reaction with the solid-state method. Analyzing the XRD pattern, of the studied compound, confirms the orthorhombic phase with the Pnma space group. The examination of SEM images reveals that the majority of grains are around 500 to 900 nm with a uniform distribution. As for the EDXS analysis, all chemical elements were detected and found in the appropriate ratio. The curves of temperature-dependent imaginary modulus M'' versus angular frequency reveal the presence of one peak at each temperature, proving that the dominant contribution is associated with the grains. The frequency dependence of the conductivity of alternating current is explained using Jonscher's law. The close values of the activation energies obtained from the jump frequency and extracted from the dielectric relaxation of the modulus spectra, as well as from the continuous conductivity imply that the transport takes place by the Na+ ions hopping mechanism. The charge carrier concentration in the title compound has been evaluated and shown to be independent of temperature. The exponent s increases with the increase in temperature; this behavior proves that the non-overlapping small polaron tunneling (NSPT) is the appropriate conduction mechanism model.

High Ionic Conduction and Polarity-Induced Piezoresponse in Layered Bimetallic Rb4Ag2BiBr9 Single Crystals

The emergence of lead-free metal-halide perovskites in modern-day energy research is primarily due to their competent semiconducting and optoelectronic properties, as well as their nontoxicity and improved stability in ambient operating conditions. However, a detailed understanding of ion transport dynamics and the relaxation behavior of these materials is still elusive. In this article, we report on the single-crystal (SC) growth of a bimetallic two-dimensional layered Rb4Ag2BiBr9 and explore its dielectric, piezoelectric, and ferroelectric properties. The dielectric attributes are investigated by studying the temperature-dependent complex impedance, complex electric modulus, and AC conductivity over an extensive frequency range from 4 Hz to 8 MHz. The role of grain and grain boundaries in the effective impedance is established using the Maxwell–Wagner equivalent circuit model from the Nyquist plots. The observed electric modulus spectra are studied using the Havriliak–Nigami and the Kohlrausch–Williams–Watts formalisms to understand the ionic transport and relaxation mechanisms in Rb4Ag2BiBr9. The DC conductivity and relaxation time show Arrhenius-like behavior with the inverse temperature validating the hopping motion of ions. The values of the activation energy required for ion hopping are calculated independently from the relaxation time, hopping frequency, and DC conductivity Arrhenius plots and are in good agreement with a value of 0.47 eV. The scaling of the temperature-dependent conductivity and electric modulus spectra into a single master curve demonstrates the congruence of the ionic conduction and the relaxation phenomena at different temperatures for Rb4Ag2BiBr9. This SC demonstrates decent thermal and ambient stability up to 500 °C and 12 months, respectively. The pristine orthorhombic Rb4Ag2BiBr9 SC shows a piezoelectric amplitude value of ∼564 pm at the maximum applied bias (±10 V), and a saturation polarization of ∼0.14 nC/cm2 estimated from the piezoelectric force microscopy and polarization hysteresis loop measurement, respectively. The ferroelectric and semiconducting attributes of this material can be harnessed for prospective applications as a thin film in designing mechanical energy harvesters as well as functional photoferroelectrics, such as optical switches and ferroelectric photovoltaics.