Σdc Values Research Articles

Ac/dc conductivity and ML-based evaluation of electric characteristics of methylene blue solution

Utilizing a precision LCR meter, the complex permittivity ε*(f) of methylene blue (MB) solutions in distilled water (DW) was determined at various temperatures and concentrations in the lower frequency range from 20 Hz to 2 MHz. The complex ac conductivity σ*(f) of the liquid samples was calculated using ε*(f). DC conductivity, σdc of the samples was also calculated. The effect of changes in temperature and concentration on the σ*(f) and ε*(f) of solutions are examined. A solution of MB in DW, ranging from diluted to concentrated, greatly enhances the electrical conductivity σdc. The empirical Casteel-Amis (CA) formula was employed to fit the experimental σdc values at different concentrations. Accurate measurement of complex permittivity of liquid solutions over wide range of concentration at broad range of frequencies and temperature is laborious and uneconomical. Therefore, we performed the complex permittivity measurement of the aqueous solution of MB over a limited concentration and temperature range over 201 frequency point. Then we used this experimental data in CatBoost regression model to predict the dielectric properties at intermediate frequencies and various concentrations. This model was employed to assess the performance of material characteristics using R-squared score. The study demonstrated that the CatBoost regression model can predict material performance at intermediate frequencies and concentrations while decreasing measurement resource needs by 60 %.

Sodium Ion-Conducting Electrolytes Based on Chloroaluminate Ionic Liquids and δ-NaCl.

Sodium-containing ionic liquids are very promising candidates as ion-conducting materials in alternative to electrolytes based on lithium chemistry. Here we investigate a series of seven ionic liquids with formula (EMImCl/(AlCl3)1.5)/(δ-NaCl)x (0≤x≤0.74). The salt is comprised of a disordered form of NaCl prepared by metalorganic synthesis, which assures faster dissolution in high concentration. The vibrational investigation carried out by FT-IR spectroscopy in the medium IR region shed light on salt-IL interactions. The ionic conductivity was investigated by Broadband Electric Spectroscopy. The direct current conductivity (σdc) profiles versus the reciprocal temperature exhibited a Vogel-Tamman-Fulcher behavior indicating the assistance of micro-Brownian motions to ionic migration. The value of σdc at 25 °C for x=0.74 was found to be 1.2×10-2 S cm-1. Reversible deposition of Na and Al-containing species take place with high Coulombic efficiency (up to 97 %) and a high Na+ cation transport number (up to 0.95). The understanding of ionic speciation was investigated in comparison with aqueous acid-base systems exploring the benefits and limitations of such analogy. The role of a Grotthuss-type mechanism facilitating the exchange of chlorides between acidic catenated chloroaluminate species in anionic domains of the ILs is considered.

Hybrid Nanocomposites Based on Poly(3,6-dianiline-2,5-dichloro-1,4-benzoquinone): Synthesis, Structure and Properties.

Hybrid nanocomposites based on poly(3,6-dianiline-2,5-dichloro-1,4-benzoquinone) (PDACB) in salt form and graphene oxide (GO) have been obtained for the first time, and the significant influence of the preparation method on the composition and structure of nanocomposites and their functional properties has been demonstrated. Nanocomposites were prepared in three ways: via ultrasonic mixing of PDACB and GO; via in situ oxidative polymerization of 3,6-dianiline-2,5-dichloro-1,4-benzoquinone (DACB) in the presence of GO; and by heating a suspension of previously prepared PDACB and GO in DMF with the removal of the solvent. The results of the study of the composition, chemical structure, morphology, thermal stability and electrical properties of nanocomposites obtained via various methods are presented. Nanocomposites obtained by mixing the components in an ultrasonic field demonstrated strong intermolecular interactions between PDACB and GO both due to the formation of hydrogen bonds and π-stacking, as well as through electrostatic interactions. Under oxidative polymerization of DACB in the presence of GO, the latter participated in the oxidative process, being partially reduced. At the same time, a PDACB polymer film was formed on the surface of the GO. Prolonged heating for 4 h at 85 °C of a suspension of PDACB and GO in DMF led to the dedoping of PDACB with the transition of the polymer to the base non-conductive form and the reduction of GO. Regardless of the preparation method, all nanocomposites showed an increase in thermal stability compared to PDACB. All nanocomposites were characterized by a hopping mechanism of conductivity. Direct current (dc) conductivity σdc values varied within two orders of magnitude depending on the preparation conditions.

Debye Temperature Evaluation for Secondary Battery Cathode of α-SnxFe1-xOOH Nanoparticles Derived from the 57Fe- and 119Sn-Mössbauer Spectra.

Debye temperatures of α-SnxFe1-xOOH nanoparticles (x = 0, 0.05, 0.10, 0.15 and 0.20, abbreviated as Sn100x NPs) prepared by hydrothermal reaction were estimated with 57Fe- and 119Sn-Mössbauer spectra measured by varying the temperature from 20 to 300 K. Electrical properties were studied by solid-state impedance spectroscopy (SS-IS). Together, the charge-discharge capacity of Li- and Na-ion batteries containing Sn100x NPs as a cathode were evaluated. 57Fe-Mössbauer spectra of Sn10, Sn15, and Sn20 measured at 300 K showed only one doublet due to the superparamagnetic doublet, while the doublet decomposed into a sextet due to goethite at the temperature below 50 K for Sn 10, 200 K for Sn15, and 100 K for Sn20. These results suggest that Sn10, Sn15 and Sn20 had smaller particles than Sn0. On the other hand, 20 K 119Sn-Mössbauer spectra of Sn15 were composed of a paramagnetic doublet with an isomer shift (δ) of 0.24 mm s-1 and quadrupole splitting (∆) of 3.52 mm s-1. These values were larger than those of Sn10 (δ: 0.08 mm s-1, ∆: 0.00 mm s-1) and Sn20 (δ: 0.10 mm s-1, ∆: 0.00 mm s-1), suggesting that the SnIV-O chemical bond is shorter and the distortion of octahedral SnO6 is larger in Sn15 than in Sn10 and Sn20 due to the increase in the covalency and polarization of the SnIV-O chemical bond. Debye temperatures determined from 57Fe-Mössbauer spectra measured at the low temperature were 210 K, 228 K, and 250 K for Sn10, Sn15, and Sn20, while that of α-Fe2O3 was 324 K. Similarly, the Debye temperature of 199, 251, and 269 K for Sn10, Sn15, and Sn20 were estimated from the temperature-dependent 119Sn-Mössbauer spectra, which were significantly smaller than that of BaSnO3 (=658 K) and SnO2 (=382 K). These results suggest that Fe and Sn are a weakly bound lattice in goethite NPs with low crystallinity. Modification of NPs and addition of Sn has a positive effect, resulting in an increase in DC conductivity of almost 5 orders of magnitude, from a σDC value of 9.37 × 10-7 (Ω cm)-1 for pure goethite Sn (Sn0) up to DC plateau for samples containing 0.15 and 0.20 Sn (Sn15 and Sn20) with a DC value of ~4 × 10-7 (Ω cm)-1 @423 K. This non-linear conductivity pattern and levelling at a higher Sn content suggests that structural modifications have a notable impact on electron transport, which is primarily governed by the thermally activated via three-dimensional hopping of small polarons (SPH). Measurements of SIB performance, including the Sn100x cathode under a current density of 50 mA g-1, showed initial capacities of 81 and 85 mAh g-1 for Sn0 and Sn15, which were larger than the others. The large initial capacities were measured at a current density of 5 mA g-1 found at 170 and 182 mAh g-1 for Sn15 and Sn20, respectively. It is concluded that tin-goethite NPs are an excellent material for a secondary battery cathode and that Sn15 is the best cathode among the studied Sn100x NPs.

STUDY OF THE INFLUENCE OF VARIATIONS IN THE PHASE COMPOSITION ON THE DIELECTRIC PROPERTIES OF FERROELECTRIC CaTiO<sub>3</sub> CERAMICS DOPED WITH Y<sub>2</sub>O<sub>3</sub>

The study of the relationship between the effect of phase composition variation on the dielectric characteristics of ferroelectric ceramics is one of the most important fundamental questions, the answer to which will allow us to determine the potential of using ferroelectrics in microelectronic applications and the creation of alternative energy sources (solid oxide fuel cells). The purpose of this study is to explore the effect of the Y2O3 dopant on the phase formation processes and the properties of the synthesized ferroelectric ceramics of calcium titanate, as well as to establish the connection between the influence of the formation of impurity phases on the change in the dielectric properties of ceramics. According to the data of X-ray phase analysis, it was found that the addition of Y2O3 with a concentration above 0.15 M leads to the formation of an orthorhombic CaY2O4 phase in the ceramic structure, the weight contribution of which increases with the dopant concentration growth. An analysis of the dependence of the specific electrical conductivity (σDC) with varying dopant concentration showed that the maximum value of σDC is achieved at dopant concentrations of 0.05 M, which leads to structural ordering due to the effect of adding yttrium oxide acting as a stabilizer, as well as the formation of impurity donor conductivity in the structure. An analysis of the dependence of the specific electrical conductivity (σDC) from dopant concentration was carried out. It has been established that the maximum value of σDC is achieved at a dopant concentration of 0.05 M. This is explained by structural ordering due to the addition of a stabilizer – yttrium oxide, as well as the formation of impurity donor conductivity in the synthesized sample. At the same time, the established dependences of the change in dielectric characteristics are in good agreement with the change in the phase composition, and an increase in the concentration of charge carriers due to the introduction of a donor impurity in the form of Y3+ leads to the appearance of volume-charge polarization in ceramics.

Fabrication and characterizations of nanocomposite flexible films of ZnO and polyvinyl chloride/poly(N-vinyl carbazole) polymers for dielectric capacitors

Polymer-based energy storage has recently attracted the attention of researchers. Herein, via the sol–gel method, we prepared zinc oxide nanoparticles (ZnO NPs), as nanofiller up to 5 wt% filling levels, and a host polymeric blend matrix of polyvinyl chloride (PVC) and poly (N-vinyl carbazole) (PVK) were taken to synthesize nanocomposite films via the solution casting. The ratio of PVC: PVK was 90:10 wt%. The X-ray diffraction (XRD) results indicated that the prepared nanocomposite films’ crystallinity decreased as ZnO NPs content increased; it decreased from 54.23 to 22.14 %. The scanning electron microscope (SEM) micrographs revealed good miscibility of the prepared PVC/PVK blend and the homogeneous distribution of ZnO NPs within the host blend matrix. The thermal stability of the prepared nanocomposites was studied through the TGA technique, and the thermal activation energy was calculated using the Coats-Redfern method. In the optical results, the optical absorption spectra revealed that the energy gap for the allowed direct transition reduced under adding ZnO NPs; it reduced from 3.61 eV for the pure PVC/PVK blend to 2.96 eV for the nanocomposite film with ZnO nanofiller content of 5 wt%. AC conductivity experiments revealed that the electrical/dielectric properties of the nanocomposite films get enhanced by increasing the ZnO NPs content. Following the incorporation of the ZnO NPs, the AC electrical conductivity (σac), dc electrical conductivity (σdc), dielectric constant (ε′), and dielectric loss (ε″) values of PVC/PVK/ZnO nanocomposite films get improved; the σdc values increased from 6.46 × 10−16 S/cm for the blend PVC/PVK matrix to 3.63 × 10−13 S/cm for nanocomposites with ZnO NPs content of 5 wt%. Additionally, both ε′ and ε″ values increased while increasing the ZnO NPs content. These findings could suggest that the prepared PVC/PVK/ZnO nanocomposite films could be a promise for the applications of dielectric energy storage polymer-based capacitors.

Reformed dielectric features in single phase orthorhombic nickel vanadate complex oxides and the significance of the lattice dynamics in the optoelectrical features

V(1-x)2Ni3xO5-δ compounds are prepared by high-temperature solid-state reactions for mole fractions x = 0.04, 0.05, and 0.06. Micro-Raman spectrum with an excitation wavelength of 540 nm reveals 12 well-resolved phonon modes corresponding to the orthorhombic alpha-polymorphic phase of Vanadium Pentoxide and an extra vibrational mode excited by the tetravalent vanadium cation. A sharp absorption edge is observed from 500 nm to 650 nm in the diffuse reflectance spectrum with the rate of absorption increasing slightly, directly proportional to the x value. Kubelka-Munk plots reveal band gap reduction due to the negative Moss-Burstein shift that is attributed to the Ni2+ occupancy at the lattice sites creating electron deficiency. Frequency-dependent AC conductivity, studied in the frequency range 1 KHz to 1 MHz at room temperature exhibited DC-like conductivity in the low-frequency region, and the Jonsher Power Law fit gives the σdc values increasing with Ni ion concentration. AC conductivity at 1MHZ shows an elevation from 1.6 × 10−03 Sm−1 through 4.8 × 10−03 Sm−1 reaching 13.6 × 10−03 Sm−1 by increasing the concentration of Ni2+ ions. The dielectric constant at 250 °C, is observed to increase from 395, through 1447 to 2614, for mole fractions 0.04,0.05 and 0.06 respectively making this multivalent vanadate system a potential candidate for optoelectric and solid oxide fuel cell applications.

IONIC CONDUCTIVITY AND THERMAL STABILITY OF BiF<sub>3</sub> CRYSTALS

The temperature dependence of the ionic conductivity σdc(T) and thermal stability of BiF3 crystals with the structure of orthorhombic β-YF3 (sp. gr. Pnma, a = 6.5620(1) Å, b = 7.0144(1) Å, c = 4.8410(1) Å, V/Z = 55.71 Å3), grown from melt by the vertical directional crystallization technique have been investigated. The electrical characteristics of BiF3 are obtained from impedance measurements in the temperature range of 360−540 K. The σdc value at T = 500 K and the ion transport activation enthalpy ΔHa are found to be 2.5 × 10−5 S/cm and 0.48 ± 0.05 eV, respectively. The ΔHa value for the crystal studied is smaller by a factor of 1.4 in comparison with the isostructural rare-earth (Tb, Ho, Er, Y) trifluorides, which is due to the high electronic polarizability and large ionic radius of Bi3+ cations. It was found that BiF3 crystals are thermally stable at temperatures up to 550−600 K; at higher temperatures degradation was observed due to the sublimation and pyrohydrolysis of this material. The formation of oxofluoride phases is responsible for the detected conductivity jump in the dependence σdc(T) at T ∼ 600 K.

Crystallization kinetics and structural studies of Li1.25Al0.5Ge1.5P2.75Mo0.25O12 (LAGPM) glass/glass-ceramics based solid state electrolyte

The crystallization kinetics and structural behaviour of Li1.25Al0.5Ge1.5P2.75Mo0.25O12 (LAGPM) glass/glass-ceramics system have been investigated. Glass was prepared by melting the calcined initial charges at 1450 °C using conventional quenching technique. From model free crystallization kinetics, the value of activation energy obtained was 165 kJ mol−1. The nature of nucleation and the dimension of growth of the NASICON crystal were estimated from the kinetics parameters. This glass was converted to glass-ceramics using suitable heat schedule as per DTA data. X-ray diffraction analysis confirmed the formation of desired NASICON phase along with AlPO4 as minor phase. Raman spectroscopy and EXAFS studies showed that molybdenum ions moved to the desired tetrahedral sites in glass-ceramic. The dimension of the crystal growth was clearly seen in SEM image of LAGPM glass-ceramics sample. Impedance spectroscopy was carried out to evaluate the dc ionic conductivity (σdc) of LAGPM glass-ceramics based solid electrolyte. The value of σdc evaluated from the Nyquist plot was found as ∼4.64 × 10−4 S.cm−1 at room temperature.

Механизм электропереноса в суперионном проводнике Sr-=SUB=-0.7-=/SUB=-La-=SUB=-0.15-=/SUB=-Lu-=SUB=-0.15-=/SUB=-F-=SUB=-2.3-=/SUB=- со структурой флюорита

The ionic conductivity of the superionic conductor Sr0.7La0.15Lu0.15F2.3 with the fluorite-type structure (type CaF2, sp. gr. Fm-3m) had measured by the impedance spectroscopy in the temperature range 385–794 K. Bulk crystals of a three-component solid solution (lattice parameter a = 5.7726(1) A) had obtained from the melt by the directed crystallization technique. Temperature dependence ionic conductivity σdc(T) satisfies the Arrhenius–Frenkel equation with the activation enthalpy of the electrical conductivity Hσ = 0.706 ± 0.05 eV. The value of σdc is 1.5 10–5 S/cm at 500 K. Based on the analysis of electrophysical and structural studies of fluorite-type solid solutions in SrF2–LaF3 and SrF2–LuF3 systems, the microscopic model of ion transport in the Sr0.7La0.15Lu0.15F2.3 crystal was proposed. The concentration and mobility of charge carriers were calculated: nmob = 7.8 × 1020 cm–3 and μmob = 1.2 × 10–7 cm2/Vs at 500K.

HIGH-TEMPERATURE ANOMALY OF THE ANIONIC CONDUCTIVITY IN LaF<sub>3</sub> CRYSTALS

The anionic electrical conductivity σdc(T) of the superionic LaF3 conductor single crystal has been studied by impedance spectroscopy in a wide (312–1073 K) temperature range. Electrical measurements in a protective nitrogen atmosphere have been carried out. It is shown that the σdc values change from 1.5 × 10–5 to 7 × 10–2 S/cm (by a factor of ~5 × 103) in the investigated temperature range. A high-temperature anomaly of the σdc(T) dependence has been found at T0 ≈ 970 K, which is apparently indicative of the onset of a diffuse (Faraday) phase transition in the LaF3 tysonite structure.

Utilization study on red brick waste as novel reinforcing and economical filler for acrylonitrile butadiene rubber composite

Red brick waste (RBW) powder was used as a reinforcing filler for acrylonitrile butadiene rubber (NBR) for preparing eco-friendly composites. The main constituent of this waste is silica which is considered to be one of the traditional fillers used in the rubber industry. So it was worthwhile to get (RBW) in a suitable manner by using this waste as a filler for NBR. Physicomechanical properties were evaluated, including tensile strength, elongation at break, hardness shore A, and change in mechanical properties after thermal-oxidative aging for seven days at 90 °C. In addition, equilibrium swelling in toluene for prepared composites was also included. Moreover, cross-linking density was measured according to Flory Rehner's equation. From physicomechanical measurements, it is observed that the tensile strength and hardness (shore A) increased with increasing the waste filler content because of the red brick filler's stiffness. In contrast, the elongation at break and equilibrium swelling degree decreased with increasing the waste filler content. The morphology of the polymeric composites was monitored using a scanning electron microscope which reflects the uniform distribution of the filler inside the NBR matrix. The electrical and magnetic properties of NBR/RBW composites were evaluated. The electrical measurements revealed that the values of ε′ increase by increasing red brick waste while ε'' decreases by increasing filler content. The dc conductivity σdc values lie in the order of 10–11 S/cm. This finding recommends that such composites could be used for insulation and antistatic applications. In addition, the magnetic measurements show superparamagnetic behavior in NBR/RBW composites. Therefore, the obtained composites be used as electromagnetic composites based on electrical and magnetic measurements.Graphical

Dielectric characterization of the BiFe0.5Cr0.5O3 ceramics

Dielectric properties of the BiFe0.5Cr0.5O3 ceramics synthesized under high pressure were investigated in a broad frequency range (20 Hz – 1 GHz) between 200 and 500 K. It was revealed that the ceramics exhibit electrical conductivity above 300 K. Below 300 K, a dielectric dispersion caused by ferroelectric domains was observed. It was found that the conductivity follows the Almond–West law, which allowed us to determine a DC contribution (σDC). From the σDC values obtained at different temperatures, the activation energy (EA = 0.302 ± 0.006 eV) was calculated using the Arrhenius law.

DC conductivity, optical properties and Judd-Ofelt evaluation of 20Li2O-xBi2O3-(78-x)TeO2-1Er2O3-1Ag mixed ionic-electronic glasses

20Li2O-xBi2O3-(78-x)TeO2-1Er2O3-1Ag glass system was prepared by melt quenching, and its DC conductivity, optical and spectroscopic properties were investigated. Its amorphous nature was confirmed by x-ray diffraction analysis. Results showed that DC conductivity σdc initially increased at x < 7 mol% and then decreased to a minimum at x = 11 mol% Bi2O3. UV–vis–NIR absorption spectra indicated six transition bands centered at 1496, 979, 799, 653, 544, and 521 nm corresponding to 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, and 2H11/2 Er3+ transitions, respectively. Analysis on optical absorption edge by Tauc’s plot revealed maximum in direct Eoptd(3.609 eV) and indirect optical energy bandgap Eopti(3.259 eV) at x = 11 mol%. Judd–Ofelt intensity parameter Ω2was calculated from optical absorption data to describe the intensity of electron transitions within the 4 f shells of Er3+ ions in the glasses. A minimum Ω2 was obtained at x = 11 mol%. The minimum values of σdc and Ω2 at x = 11 mol% are related to the presence of high bridging oxygen in the mixed ionic-electronic region that influences the symmetry of surrounding Er3+ ions.

Влияние изо- и гетеровалентных замещений катионов на суперионный фарадеевский переход во флюоритовой модификации &amp;beta;-PbF-=SUB=-2-=/SUB=-

The influence of isovalent substitutions of Pb2+ by Cd2+ and heterovalent substitutions of Pb2+ by Sc3+ on a superionic Faraday transition in Pb1 – xCdxF2 (x = 0.33) and Pb1 – x ScxF2+x (x = 0.1) solid solutions based on the fluorite-type modification β-PbF2 with sp. gr. Fm¯3m has been studied. The Faraday phase transition can be characterized by the temperature Tλ corresponding to maximum on the heat capacity curve and temperature Tα corresponding to the beginning of the structural disorder anion sublattice. Both of these temperatures are found on the temperature conductivity dependence σdc(T ) of β-PbF2, Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1 crystals. The values of Tλ and Tα in solid solutions compared with β-PbF2 matrix (Tλ = 715 ± 10K, Tα = 597 ± 12 K) decrease by 100–110 and 30–45 K for Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1, respectively. Decreasing of temperature Tλ leads to an increase in temperature interval of existence of the superionic state. For T &gt; Tλ the anionic conductivity of fluorite-type Pb0.67Cd0.33F2, Pb0.9Sc0.1F2.1, and β-PbF2 crystals reaches anomalously high values of σdc = 1–2 S/cm (873 K) at an ion transfer activation enthalpy equals to Hσ = 0.3 eV.

Optical and electronic properties of iodine and bromine doped chirality enriched (12,1) and (13,2) single-walled carbon nanotubes

We present transmission measurements on chirality enriched semiconducting (12,1) and (13,2) single-walled carbon nanotubes (CE-s-SWCNTs) and CE-s-SWCNTs doped with iodine (I2@CE-s-SWCNTs) and bromine (Br2@CE-s-SWCNTs) in wide frequency range from 0.1 to 40 THz. The real part of the optical conductivity σreal(ω) was fitted using Drude-Lorentz model. The Drude (D) term in the CE-s-SWCNTs was attributed to the presence of metallic tubes traces in the sample. The D/scattering rate(γD) ratio was increased by a factor of 1.13 and 2.35 with iodine and bromine p-doping, respectively. This increase was compensated by large increase in D term leading to an increase in the optical conductivity at the DC limit (σDC), growing from 186 Ω−1cm−1 for the CE-s-SWCNTs to 203 and 426 Ω−1cm−1 for the I2@CE-s-SWCNTs and Br2@CE-s-SWCNTs, respectively. In addition, the plasmon peak was shifted to higher frequencies and gains more spectral weight with doping. The calculated optical parameters determine that iodine and bromine create acceptor levels above the top of the CE-s-SWCNTs valence band by 0.04 and 0.08 eV, respectively, shifting the Fermi level. The high σDC value of the Br2@CE-s-SWCNTs is due to the higher electronegativity of bromine which enables removal of more electrons from the valence band of CE-s-SWCNTs to bromine acceptor levels.

Structural, thermal and dielectric studies of mixed spinel CoFe2O4

In the present work, the phase development and dielectric response of polycrystalline CoFe2O4 has been studied as a function of temperature. The CoFe2O4 was synthesized by solid state reaction technique. The thermal activation of the reactions between precursors were studied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) to optimize the calcination temperature. The structural studies performed by X-ray diffraction followed by Rietveld refinement shows that CoFe2O4 crystallize in cubic Fd-3 m, conforming to a mixed spinel structure (Co0.95Fe0.05) (Fe0.975Co0.025)2O4. The dielectric studies show a low frequency dispersion, predominantly associated with the Maxwell-Wagner polarization. The real part of ac conductivity, σ' shows a change of ~ 4 orders in magnitude and follows the modified Jonscher’s law. The derived values of σdc, comply with Arrhenius behavior with the activation energy of ~ 0.382 eV. The values of exponents range from 0 to 1, indicating the conductivity in measured range is dominated by hopping of charge carriers.

Silver doping in lanthanum manganite materials: structural and electrical properties

Ag-doped LaMnO3 nanoparticles have been synthesized through sol–gel process using citric acid as a chelating agent. Silver effect on physicochemical properties was studied. The physicochemical properties and electrical performance of the obtained materials were also investigated, using thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. Thermogravimetric analysis shows that for the studied materials a decomposition stage between 3.7% and 4.1% can be observed, and mass increases from the LMN-Ag1 to the LMN-Ag3 sample. Also, in all those three situations an endothermic process with a maximum around 600 °C is observed. The diffractograms of the perovskite materials showed single-phase crystalline with high purity and rhombohedral structure with R-3c space group. The electrical measurements show that the conductivity spectrum is formed by both the static component σDC corresponding to the low frequencies and the component σAC corresponding to high frequencies. The values of σDC of samples are significantly influenced by the silver ions concentration.

Polyaniline co-doped with dodecyl benzene sulfonic acid and zwitterionic-based ionic liquids prepared by inverse emulsion polymerization

Sulfonate zwitterionic ionic liquids with methyl-imidazolium (mim.ZIL) or triphenylphosphonium (PPh3.ZIL) as the cations were mixed with dodecylbenzenesulfonic acid (DBSA) and used as co-doping agent for the synthesis of polyaniline (PANI) by inverted emulsion polymerization approach in toluene medium. The ZIL-DBSA combination resulted in PANI with higher DC conductivity (σDC) values and the better response was obtained with mim.ZIL/DBSA in a molar ratio of 1.0, with σDC corresponding to around 8 S cm−1. The presence of cetyl trimethylammonium bromide (CTAB) during the synthesis caused an additional improvement of the conductivity, reaching values as high as 16.3 and 14.0 for PANI prepared in the presence of mim.ZIL and PPh3.ZIL, respectively. Electromagnetic interference shielding effectiveness (EMI SE) of PANI samples prepared with different conditions was also investigated in the X-band frequency range. An improved EMI SE, with electromagnetic attenuation of -55 dB was observed for PANI sample prepared in the presence of CTAB and mim.ZIL/DBSA in a molar ratio of 1.0.

Charge transport by global protonic conductivity and relaxational dynamics over hydrogen bonds in Fe2+Fe3+3.2(Mn2+,Zn)0.8(PO4)3(OH)4.2(HOH)0.8

This study deals with the charge transport by protons over hydrogen bonds (HBs) in a rockbridgeite-type compound, Fe2+Fe3+3.2(Mn2+,Zn)0.8(PO4)3(OH)4.2(HOH)0.8. Its dielectric response in a wide frequency range of 1 Hz – 3 GHz from 30 K to 500 K can be traced back to structural properties of this phosphatic oxyhydroxide, revealed by Rietveld refinements using neutron powder diffraction data. The probable charge transport paths for protons are proposed, based on the honeycomb-like distribution of their neutron scattering length densities reconstructed by the Maximum-Entropy Method. Two distinctly decoupled proton dynamic processes occur in this system: at high temperatures, global protonic transport is thermally activated over an energy barrier (EB) of 0.49 eV, showing a dc conductivity (σdc) value of about 10-4 Ω-1 cm-1 at 500 K. The temperature-dependency of σdc becomes weaker at decreased temperatures, indicating the possible onset of proton tunneling-dominated charge transport. At low temperatures, relaxational proton hopping within double-well potentials in HBs is thermally activated with EB = 0.62 eV. An extremely fast relaxation time of ~50 ps at 250 K continuously slows down to ~1 ms at 150 K, pointing to the approach of an orientational proton-glass state at about 125 K. Isosurfaces of bond valence energy landscape maps of H+ at 0.49 eV clearly evidence the honeycomb-shaped route for the protonic conductivity at 393 K.