Ac Conductivity Spectra Research Articles

Structural, morphological, optical and dielectric properties of sodium bismuth titanate ceramics

• The NBT ceramic was prepared by solid state reaction. • Modified Debye theory has been adopted to describe the phenomenon of relaxation. • The temperature dependence of Dc-conductivity of NBT followed the Mott’s Variable Range Hopping (VRH) law. This work focuses on the structural, optical and electrical properties of sodium bismuth titanate Bi 1/2 Na 1/2 TiO 3 (NBT) lead-free ceramic for its possible application in capacitors, batteries and as an electrolyte in SOFC. NBT material was prepared by the solid-state method. X-ray diffraction analysis performed at room temperature revealed a rhombohedral structure with R3c space group. Rietveld refinement confirmed a good agreement between the calculated and the observed pattern. Scanning electron microscopy analysis revealed a polycrystalline nature of the material with a grain size of 29.17 µm. FT-IR analysis showed the presence of different bonds. The band gap energy was extracted through diffuse reflectance spectroscopy and was found to be 2.61eV. Detailed studies of dielectric and impedance properties carried out in the frequency range of 40–10 7 Hz at different temperatures (from 400K-700K) provided many interesting properties. The dielectric loss and dielectric constant with frequency increase. This behavior could be interpreted by the Maxwell–Wagner type of polarization in agreement with Koop's theory. To explain the complex impedance plane plots, an equivalent circuit template was employed, reflecting semiconducting behavior of NBT. The Ac-conductivity spectrum satisfied Jonscher’s power law below 460K and followed Jonscher’s double power law (DPL) above 480K. The correlated barrier hopping (CBH) and small polaron hopping (SPH) models could explain the conduction mechanism at the studied temperature range. The study of the Dc-electrical conductivity confirmed that NBT followed the variable range hopping (VRH) model. The present work could give further insights into this kind of material from a physical point of view and thus enhance its presence in the industrial field.

Correlation of structure and ionic-conductivity in phosphate glass using MAS-NMR and impedance spectroscopy: Influence of sodium salt

In the process of diminishing the safety concerns of sodium-ion batteries, the development of glass-based solid electrolyte materials has received adequate interest. Nevertheless, achieving a high ionic-conductivity at room temperature for glass materials remains a challenging task because of the poor correlation between the conductivity and the glass structure. Here, we attempt to understand the effective influence of NaCl on the structure and ionic-conductivity of the phosphate-based glass network. For this study, $x\mathrm{NaCl}\text{\ensuremath{-}}(100\text{\ensuremath{-}}x$) ($31.725\phantom{\rule{4pt}{0ex}}{\mathrm{Na}}_{2}\mathrm{O}\text{\ensuremath{-}}12.69\phantom{\rule{0.16em}{0ex}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}\text{\ensuremath{-}}31.725\phantom{\rule{0.16em}{0ex}}{\mathrm{P}}_{2}{\mathrm{O}}_{5}\text{\ensuremath{-}}8.46\phantom{\rule{0.16em}{0ex}}\mathrm{NaF}\text{\ensuremath{-}}5.40\phantom{\rule{0.16em}{0ex}}{\mathrm{Na}}_{2}{\mathrm{SO}}_{4}\text{\ensuremath{-}}10\phantom{\rule{0.16em}{0ex}}{\mathrm{MoO}}_{3}$) glass systems (mol %) were selected, where $x=0$, 5, 10, 15, and 20 mol %. To investigate structural changes with the addition of different NaCl concentrations, $^{27}\mathrm{Al}, ^{23}\mathrm{Na}, ^{31}\mathrm{P}$ magic angle spinning nuclear magnetic resonance (MAS-NMR), $^{31}\mathrm{P}$ two-dimensional (2D) phase-adjusted spinning sideband (PASS), and $^{31}\mathrm{P}$ 2D J-resolved NMR techniques and Raman spectroscopic techniques were utilized. Impedance spectroscopy and ac conductivity spectra were used to assess ionic-conductivity and sodium-ion dynamics, respectively. Impedance spectral analysis reveals that the ionic-conductivity of the base glass is increased by 2.4 times (from 1.85 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ to 4.44 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ S/cm at 373 K) with the addition of 20 mol % of NaCl. Raman spectra confirm the presence of P\ensuremath{-}O\ensuremath{-}Mo and the absence of Mo\ensuremath{-}O\ensuremath{-}Mo bonds in these glass systems, and $^{31}\mathrm{P}$ 2D J-resolved spectra indicate the absence of P\ensuremath{-}O\ensuremath{-}P bonds. Upon increasing the NaCl concentration, significant changes in the shapes of $^{31}\mathrm{P}$ and $^{27}\mathrm{Al}$ MAS-NMR spectra were observed, indicating the effective influence of NaCl on the distribution of alumina and phosphorus structural units. Irrespective of the temperature, sodium-ion dynamic studies show that the mean-square displacement $\ensuremath{\langle}{R}^{2}({t}_{p})\ensuremath{\rangle}$ decreases with increasing NaCl concentration up to 10 mol % and then increases with a further increase in NaCl concentration. This investigation aids in understanding the sodium-ion dynamics and the structural information of a multicomponent glass system to enhance the room-temperature conductivity.

New insight into the colossal dielectric permittivity and AC conductivity behavior of polycrystalline non-ferroelectric ceramics

The correlation of polarization with AC conductivity behavior of polycrystalline non-ferroelectric ceramics is more satisfied to be interpreted by three zones indicated in permittivity and AC conductivity spectra. These three zones concerning the dielectric and conductivity processes governing the response to an AC field have been identified in terms of the cluster model within the framework of percolation theory. Colossal dielectric permittivity of non-ferroelectric materials can be attributed to hopping polarization aligned via developing percolation clusters with high electron concentrations. The physical origin of the correlation between dielectric permittivity and AC conductivity of polycrystalline ceramics with respect to the effect of grain boundary has been clarified.

The H+ ion transport study in polymer blends incorporated with ammonium nitrate: XRD, FTIR, and electrical characteristics

The present study gained insights into H+ ion transport through non-destructive techniques. The XRD outcome reveals that poly(2-ethyl-2-oxazoline) (POZ) reduced the crystalline phase of chitosan (CS) effectively. Films of ion-conducting polymer blend electrolytes were created from CS:POZ complexed with ammonium nitrate (NH4NO3) as an H+ supplier by using the solution casting method. X-ray diffraction was used to study the structural alterations that occurred. The degrees of crystallinity were estimated from the deconvoluted XRD pattern. Measurement of electrical impedance was carried out for the electrolytes. From FTIR measurement, free ion and ion pair values were calculated. Several ion transport parameters (ITP), such as number density (n), ionic mobility (μ), and diffusion coefficient (D), were determined. It was found that the maximum conductivity was 3.87 × 10−6 S cm−1 at 30 percent NH4NO3. The DC conductivity pattern changes linearly with temperature. Dielectric and electric modulus were studied in detail. It was discovered that the loss tangent peak transferred to a upper side of frequency when the salt concentration was increased. Long-range conductivity relaxation was seen in the Mi spectra. The lack of a full semicircle arc on the Argand figure suggested non-Debye ion dynamics. The observed AC conductivity (σac) spectra showed three different zones. In the high-frequency range, the σac value follows a power law (σac=Aωs).

Li ion transport properties of amorphous/crystalline Li-La-Zr-Nb-O solid electrolyte thick films prepared by suspension plasma spraying

Amorphous Li-La-Zr-O films are considered very attractive as a solid-state electrolyte in future batteries due to their low processing temperatures and resistance to Li-dendrite formation. The knowledge of amorphous Li-La-Zr-O phases is limited and thick films and bulk samples of amorphous Li-La-Zr-O have yet to be explored. Only thin film forms (~0.5 μm) of these amorphous Li-La-Zr-O phases have been prepared. In this work, we investigated the Li-ion transport properties of amorphous/crystalline mixtures of Li-La-Zr-Nb-O thick films (30 to 55 μm) prepared by the suspension plasma spray process. The process was manipulated to alter the amorphous Li-La-Zr-Nb-O content in the as-deposited films. Properties of the films that contained mostly amorphous Li-La-Zr-Nb-O (~76 wt%) were compared vs. mostly cubic Li garnet-type oxide (~55 wt%). The latter showed Li-ion transport properties that were similar to previously reported properties of cubic Li-garnet type oxides whereas the amorphous Li-La-Zr-Nb-O films exhibited significantly different properties. Their AC conductivity spectra show a Jonscher power law (JPL) behavior with the dimensionless exponent of ~0.92 that is followed by superlinear power law (SLPL) behavior with the dimensionless exponent of ~1.65 in the high frequency regime. These behaviors have not been reported earlier for the amorphous Li-La-Zr-Nb-O phases. Both of the JPL and SLPL behaviors have thermally activated characteristic with the activation energies of 0.76 eV and 0.64 eV, respectively. A lower value of ~0.45 eV was evaluated for the activation energy by solid-state 7Li NMR spectroscopy. The effect of temperature on the Li-ion dynamic process was studied by scaling the conductivity spectra and it was found to be temperature independent.

Influence of V2O5 concentration on structural and electrical transport properties of semiconducting ternary glass and glass-ceramics nanocomposite system

The effects of V2O5 concentration on semiconducting xV2O5–(1-x) (0.25Nd2O3–0.75ZnO) glass nanocomposites were investigated by structural, optical, and electrical conductivity studies. The composition dependency of physical attributes like density, molar volume, bond dissociation energy, number of bonds per unit volume, etc., was established. Using X-ray diffraction and field-emission scanning electron microscopy, we identified the presence of different nanocrystallites and amorphousness. DC electrical conductivity was caused by the small polaron hopping due to the presence of V4+ and V5+ valence states, enhanced as the small polaron radius was reduced with rising V2O5 concentration. The non-overlapping small polaron tunnelling (NSPT) model was the preferred AC conduction process, and reducing nature of tunnelling distance enhanced AC conductivity with increasing V2O5 concentration. We modified the existing NSPT model to get reasonable values for fitting parameters. The scaled AC conductivity spectra revealed temperature independence and the composition-dependent conductivity relaxation process of small polarons.

Electrical transport properties of La doped BiFeO3-NaNbO3 composite

ABSTRACT The composites, (1−x)(BiFe1-yLayO3)– xNaNbO3 with x = 0.25, 0.45 and y = 0.10, 0.20, are prepared by mixed oxide method. XRD analysis shows rhombohedral (hexagonal) structure at room temperature. The properties such as dielectric loss (tanδ) and dielectric constant (ϵr ) of all the samples are studied. A significant improvement in dielectric constants has been observed with the rise of Lanthanum (La) content. A dielectric anomaly above 350°C is observed for all the studied materials. Further, it is observed that ac conductivity (σ ac) spectrum obeys universal Jonscher’s power law. The variation of σ ac with inverse of temperature for all the samples is found to obey the Arrhenius equation. The formation of loop in polarisation verses electric field curve establishes the ferroelectric (FE) nature of all the studied samples. Current (I)-Electric Field (E) loops is studied to show the behaviour of domain switching.

Effect of co substitution of (Y, Mn) on electrical properties of bismuth ferrite

Using the method of solid-state reaction technique, (Y, Mn) modified Bismuth ferrite ferroelectric ceramic Bi0.8Y0.2(Fe0.5Mn0.5)O3 is prepared. The room temperature XRD analysis confirms the formation of a new single-phase compound with an orthorhombic crystal structure. The electrical properties are analyzed by the impedance analyzer. Through analysis, the dielectric behavior of the compound is explored in broad temperature and frequency span, which shows the strong temperature & frequency dependence characteristics of the compound. The high transition temperature of the parent bismuth ferrite compound (∼830 °C) markedly reduces to 370 °C when Y is substituted at A site and Mn at B site. Temperature-dependent behavior of conductivity and activation energy values estimated in different regimes are calculated from the temperature-dependent ac conductivity graphs, which suggests that the conduction process is of mixed type (i.e. ionic-polaronic and space charge generated from the oxygen ion vacancies). The ac conductivity spectrum obeys Jonscher’s universal power law.

Structure and Conductivity Correlation in NASICON Based Na3Al2P3O12 Glass: Effect of Na2SO4

Identifying the factors influencing the movement of sodium cations (Na+) in glasses accelerates the possible options of glass-based solid electrolyte materials for their applications as a promising electrolyte material in sodium-ion batteries. Nevertheless, due to the poor correlation between the structure and conductivity in glass materials, identifying the factors governing the conductivity still exists as a challenging task. Herein, we have investigated the DC-conductivity variations by correlating the structure and conductivity in sodium superionic conductor (NASICON) based Na3Al2P3O12 (NAP) glass (mol%: 37.5 P2O5—25.0 Al2O3—37.5 Na2O) due to the successive substitution of Na2SO4 for Al2O3. Structural variations have been identified using the Raman and magic-angle spinning nuclear magnetic resonance (MAS-NMR) (for 31P, 23Na, and 27Al nuclei) and conductivity measurements have been done using the impedance spectroscopy. From the ac-conductivity spectra, the correlations between mean square displacement (MSD) and dc-conductivity and between the Na+ concentration and dc-conductivity have also been evaluated. Raman spectra reveal that the increase in the Na2SO4 concentration increases the number of isolated SO42− sulfate groups that are charge compensated by the Na+ cations in the NAP glass. MAS-NMR spectra reveal that the increase in Na2SO4 concentration increases the concentration of non-bridging oxygens and further neither S-O-P nor S-O-Al bonds are formed. Impedance spectroscopy reveals that, at 373 K, the DC conductivity of the NAP glass increases with increasing the Na2SO4 up to 7.5 mol% and then decreases with the further increase. In the present study, we have shown that the mobility of sodium cations played a significant role in enhancing the ionic-conductivity. Further, we have shown that inter-ionic Coulombic interactions and the structural modification with the formation of SO42− units significantly influence the critical hopping length < R2 (tp)> of the sodium cations and consequently the mobility and the ionic conductivity. The present study clearly indicates that, based on the compositions, glass materials can also be treated as strong-electrolyte materials.

Investigation of temperature and frequency dependence of the dielectric properties of multiferroic (La0.8Ca0.2)0.4Bi0.6FeO3 nanoparticles for energy storage application.

In this work we synthesized the multifunctional (La0.8Ca0.2)0.4Bi0.6FeO3 material using a sol–gel process. Structural and morphologic investigations reveal a Pnma perovskite structure at room temperature with spherical and polygonal nanoparticles. A detailed study of the temperature dependence of the dielectric and electrical properties of the studied material proves a typical FE–PE transition with a colossal value of real permittivity at 350 K that allows the use of this material in energy storage devices. Thus, the investigation of the frequency dependence of the ac conductivity proves a correlated barrier hopping (CBH) conduction mechanism to be dominant in the temperature ranges of 150–170 K; the two observed Jonscher's power law exponents, s1 and s2 between 180 K and 270 K correspond to the observed dispersions in the ac conductivity spectra in this temperature region, unlike in the temperature range of 250–320 K, the small polaron tunnel (NSPT) was considered the appropriate conduction model.

Multifunctional feature of double perovskite strontium iron vanadate for storage device

In this report, we have investigated the structure, vibration, optical, dielectric, transport and magnetic features of the double perovskite Sr2FeVO6. The structural investigation of the sample is done by incorporating X-ray diffraction (XRD) and scanning electron microscopic (SEM) technique at room temperature. The structural investigation suggests the formation of a single phase polycrystalline sample having monoclinic symmetry. The chemical composition and valence of the involved elements are investigated by incorporating the X-ray photoelectron spectroscopic (XPS) technique. The dual oxidation state of Fe is revealed through the XPS investigation. The vibrational property of the sample is analyzed through both Raman and FTIR spectroscopic methods. The various modes of vibrations such as symmetric, anti-symmetric and bending modes are illustrated through Raman and FTIR techniques. Analysis of optical spectrum and energy bandgap of the sample is done by UV–Visible spectroscopic technique. The bandgap (Eg = 2.88 eV) of the material is found suitable for photocatalytic activities. The dielectric spectrum of the sample is analyzed by investigating the variation of dielectric parameters, that is εr and tanδ, w.r.t frequency-temperature. The dielectric spectrum is found consistent with Maxwell-Wagner model. The electrical and transport activities in the material are investigated by analyzing the spectra of impedance, modulus and AC conductivity at varying frequencies and temperatures. The relaxation feature of the material is illustrated through impedance and modulus spectroscopic techniques whereas the significant contribution of hopping conduction mechanism is depicted through AC conductivity spectra. Finally, the ferromagnetic property of the material at room temperature is clarified through the hysteresis curve.

Influence of La doping on structure, AC conductivity and impedance spectroscopy of Ba2SnO4 Ruddlesden Popper oxide

A few compositions of (Ba1-xLax)2SnO4 with 0≤x≤0.10 have prepared via solid-state ceramic route followed by calcination at 1000 °C for 8 h. The preliminary phase of samples has analyzed using XRD and found to be crystallized into tetragonal structure up to 4 atoms %. The solubility limit of La at Ba-site has reconfirmed using FTIR and Raman analysis. The AC conductivity spectra of single-phase samples follow universal Jonscher's power law σac=σdc(1+(ffh)n). Further, the thermal dependence of dc conductivity (σdc) and hopping frequency (fh), indicating the presence of Arrhenius type charge transport in the samples. Ghosh scaling applied to σac of all temperatures found to superimpose on a single master curve, indicates the invariance of conduction mechanism. The impedance spectroscopy studies reflect the major contribution of grain in the conduction and relaxation process of all sample. Based on present study, the present material can be potentially used in semiconductor devices, UV-detector, and mixed ionic and electronic conductor (MIECs) by utilizing absorption states and thermo-curves as metastable state.

Hopping frequency and conductivity relaxation of promising chalcogenides: AC conductivity and dielectric relaxation approaches

Ag2S doped chalcogenide glassy systems have been characterised on the basis of AC conductivity and electric modulus formalism. Various nanophases such as Ag2Se, Te0.5 Se3.5 etc. and dislocation (defects) have been identified and their roles in the conduction process have been established. XRD analysis provides that incorporation of more Ag2S content in the present system should play important role to enhance the dislocation and to decrease the crystallite sizes. The Fourier transform infrared spectra (FT-IR) confirm the characteristic vibration of Ag–S at 500–650 cm−1, stretching vibrations of the O–H bond near 3400 cm−1 and bending vibrations of the adsorbed H2O molecules on the surface of Ag2S near 1600 cm−1. Composition dependent optical phonon frequency (ν0) and Debye temperature (θ D) have been estimated from FT-IR and it is noteworthy that θ D increases with Ag2S content in the compositions up to x = 0.1, but decreases for x = 0.2. This result suggests higher kinetic energy of the constituent atoms/molecules, which may refer to higher electrical conductivity due to polaron hopping. Correlated barrier hopping (CBH) model in its modified version has been found most suitable model to explore the conduction mechanism. Short time relaxation process may be considered to be trivially associated with conduction of polaron. universal scaling approach proposed by Ghosh and Pan has been adopted to interpret electrical relaxation process from time-temperature superposition principle. AC conductivity spectra at various temperatures exhibit a perfect overlap into a single master curve. This feature must be an indication of the temperature independent relaxation process. On the other hand, conductivity spectra of all the compositions at a particular temperature do not exhibit perfect overlapping into a single master curve. This result indicates that the relaxation dynamics of charge carriers (polarons) is strongly dependent on compositions.

Effect of ionic liquid on structural, thermal and electrical transport properties of PVA-PVP based polymer blend electrolyte membrane

The present paper deals with the loading effect of ionic liquid (IL), 1-ethyl-3-methylimidazolium methylsulfate [EMIM][MS] on structural and electrical transport properties of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG)- salt, sodium methyl sulfate (MeSO4Na) based polymer blend electrolyte (PBE) films. The samples were prepared using conventional solution cast method. The x-ray Diffraction (XRD) result shows that PBE films has characteristic peak with broad halo appeared in the range 2θ = 19.95° to 22.72° reveals the amorphous nature (semi-crystalline).The % degree of crystalinity (X c ) of prepared IL based PBE films were found to decreases with increasing IL content. Fourier transform infrared (FTIR) in total attenuated reflectance (ATR) mode analysis reveals the interaction between the functional groups (C=O and O–H) of polymer electrolyte with the cation, EMIM+/anion of IL/salt. Thermogravimetric analysis (TGA) shows that IL based PBE samples decomposes in multistep and Td,onset/peak value decreases with IL loading. Sample containing 30 wt%IL shows optimum dc conductivity value ∼1.5 × 10−4 S cm−1 at 30 °C with minimum activation energy ∼0.21 eV. Logσ versus 1000/T plot for all PBE sample follow the Arrhenius type thermally activated process and activation energy decreased with increasing IL content in PBE films. Frequency dependent conductivity behavior for IL based PBE film follow the Jonscher’s power law with power law exponent, n value<1 (amorphous polymeric system). AC conductivity spectra and loss tangent spectra (tanδ) with respect to IL/temperature content scalled successfully. Dielectric relaxation behavior and conductivity relaxation were analyses with respect to IL content and temperature. Mobility, total number of charge/ion density, ion diffusivity was estimated. Ionic transference number (ITN) measurement (tion ∼0.98, tele ∼0.02) reveals that ions are principal charge carriers in present system. Linear sweep voltametry (LSV) and cyclic voltamerty (CV) measurements show that 30 wt%IL containing sample has electrochemical stability window (ESW) ∼±2.7volt and Faradic oxidation reduction peaks were observed, respectively.

Dielectric and magnetic behavior of Sr-modified vanadium based double perovskite

The Sr-modified vanadium-based double perovskite Ba1.5Sr0.5FeVO6 was synthesized by conventional solid solution casting procedure at an optimized temperature 1225 °C. The preliminary structural investigation was carried out through X-ray diffraction (XRD) and scanning electron microscope (SEM). Fourier transforms infrared (FTIR) technique was utilized to distinguish among the different modes of vibration of the elements in the compound. The band gap (2.76 eV) of the material was evaluated through the UV–Visible spectroscopy technique. Dielectric and related measurements were conducted through LCR meter in the frequency range (100 Hz–5 MHz) under the temperature range (25 °C-–500 °C). Room temperature dielectric constant (εr ~ 500) and tangent loss (tanδ ~ 0.08) at 10 kHz suggests material may be useful for multilayer capacitor and other storage devices. Non-destructive impedance spectroscopy (IS) techniques have been adopted for electrical characterization. In addition to the IS further electrical features have been investigated through ac and dc conductivity spectra . For magnetic behavior of the material (M-H) hysteresis was carried out at room temperature to investigate the magnetic properties of the material.

Effect of Bi substitution on nanostructural, morphologic, and electrical behavior of nanocrystalline La1-xBixNi0.5Ti0.5O3 (x = 0 and x = 0.2) for the electrical devices

Bi-substituted Ti–Ni perovskite of different compositions La1-xBixNi0.5Ti0.5O3 were elaborated utilizing the sol–gel method. TGA thermogravimetric and DSC calorimetric analysis was used to obtain the optimal sample formation temperature. XRD Results showing that samples have crystallized in the orthorhombic structure, belonging to the Pnma spatial group. The purity and morphology of nano-grains were investigated by EDX and SEM. Dc conductivity is specified by SPH model at high temperatures and VRH model at low temperatures. The AC conductivity spectra follow to Jonscher’s universal power law. The Ghosh scale law was investigated to understand the ionic dynamics of compounds. The estimated activation energy values from alternative conductivity and impedance verify that relaxation process and electrical conductivity can be associated with the same type of charge carriers. The equivalent electrical circuit was utilized for modeling the Nyquist data. The observed high conductivity values indicate that our samples may be suitable for applications in the electrical devices.

Dielectric relaxation and variable range hopping conduction in sol-gel auto combustion derived La0.7Bi0.3Fe0.5Mn0.5O3 manganite

In the present work, the polycrystalline La0.7Bi0.3Fe0.5Mn0.5O3 maganite was synthesized by sol-gel auto-combustion method. The room temperature X-ray powder diffraction pattern confirmed the orthorhombic phase of the sample with pbnm space group. Frequency and temperature dependent electric modulus and impedance spectroscopic analyses revealed two electro-active components of the material characterized by highly resistive grain boundaries and comparatively conducting grains, respectively. The normalized scaling behavior of modulus plots divulged the temperature independence of the dynamic process in electro-active regions. The fitting of impedance data by the equivalent circuit (RG||QG) + (RGB||QGB) was applied to explore the physical parameters associated with grains and grain boundaries. The dispersion in dielectric permittivity and loss factor at lower frequencies attributed to the space charge polarization were observed. The electrical conductivity obeyed Mott’s T1/4 law and the slope of frequency dependent AC conductivity spectra changed due to multiple activation barriers and active traps, consistent with the variable-range hopping conduction in the material.

Structural, thermal, and ion dynamics studies of PVA-CS-NaI-based biopolymer electrolyte films

A series of biopolymer blend electrolytes (BPBEs) based on ((100-x)PVA-xCS)-NaI, viz. BPBE-1 to BPBE-5 (x = 10, 20, 30, 40, 50 in wt%), respectively, were prepared using solution cast technique. Prepared samples have been characterized using XRD, ATR-FTIR, TGA, and AC impedance spectroscopic techniques. ATR-FTIR results reveal the interactions between the constituents of PVA/CS with salt, NaI. XRD results show the semi-crystalline nature of PVA-CS polymer blend and %degree of crystallinity (Xc) was found to be minimum for sample BPBE-1. TGA and its 1st derivative (DTGA) results show that BPBE films decompose in multi-steps. The decomposition temperature peak (Td, peak) associated with CS-PVA polymer blend and the interactions between CS-PVA-NaI have been discussed using TGA analysis. Temperature-dependent dc conductivity (σdc) and relaxation frequency (fr) follow the Arrhenius type mechanism. The optimum σdc ~ 1.2 × 10−5 S/cm at 30 °C was received for sample, BPBE-1. The ac conductivity spectra for all samples follow the Jonscher’s power law (JPL). Dielectric permittivity and electric modulus studies have also been done for understanding the charge storage properties and conductivity relaxation. Ionic transference number (ITN) measurement has been carried out for knowing the ionic/electronic nature of charge species. Cyclic voltammetry (CV) measurement has been done to study the electrochemical behavior of the optimized sample.

Effect of TiO2 Nano-Filler on Electrical Properties of Na+ Ion Conducting PEO/PVDF Based Blended Polymer Electrolyte

Nanocomposite polymer electrolyte (NCPE) films based on a blend of two polymers poly (ethylene oxide) (PEO) and poly (vinylidene fluoride) (PVDF) complexed with sodium perchlorate (NaClO4) salt and Nano-filler titanium dioxide (TiO2) (i.e., (80 wt% PEO/20 wt% PVDF) + 7.5 wt% NaClO4 + x wt% TiO2 where x = 3, 6, 9, 12, 15, and 18) were prepared and characterized as potential candidates for battery applications. Electrochemical impedance spectroscopy (EIS) has been employed between the frequencies 10 Hz and 4 MHz to investigate electrical, dielectric and electric modulus properties of the prepared NCPE films. Effect of TiO2 Nano-filler concentration on the structural, ionic conductivity, and dielectric relaxation has been studied. The AC conductivity of the NCPE films at high frequencies obeys Jonscher’s power law. The values of DC ionic conductivity calculated by fitting the AC conductivity spectra to the best fit of Joncher’s power law are consistent with the values of DC ionic conductivity calculated from the bulk resistance (Rb) of the NCPE films. The ionic conductivity that depends on temperature follows the Arrhenius rule between the temperatures 298 and 328 K. The maximum ionic conductivity at ambient temperature 8.75 × 10–5 S/cm was obtained for (80 wt% PEO/20 wt% PVDF) + 7.5wt% NaClO4 + 15 wt% TiO2 NCPE film and it is attributed to the decrease in crystallinity. Using Wagner’s polarization technique ionic transport numbers of various NCPE films were measured.

Carrier transport and electron–lattice interactions of nonlinear optical crystals CdGeP2, ZnGeP2, and CdSiP2

Terahertz time-domain spectroscopy is employed to investigate temperature-dependent properties of bulk chalcopyrite crystals ( C d G e P 2 , Z n G e P 2 , and C d S i P 2 ). The complex spectra provide refraction and absorption as a function of temperature, from which electron–phonon coupling and average phonon energies are extracted and linked to the mechanics of the A- and B-site cations. AC conductivity spectra provide carrier densities and electron scattering times, the temperature dependence of which are associated with unintentional shallow dopants. Temperature dependence of the scattering time is converted into carrier mobility and modeled with microscopic transport mechanisms such as polar optical phonon, acoustic phonons, deformation potential, ionized impurity, and dislocation scattering. Hence, analysis links the terahertz optical and electronic properties to relate microscopic carrier transport and carrier–lattice interactions.