Electrical Properties of Pure and Modified Copper Tartrate Single Crystals

The present paper reports the electrical properties of pure and sodium modified copper tartrate single crystals. Single crystal growth of these materials followed by their characteristics has already been published somewhere else. Having achieved the growth of pure and sodium modified copper tartrate single crystals and established their basic characteristics, it is thought worthwhile to have an understanding of their electrical properties and their modification on replacement of some copper ions in the lattice of copper tartrate by sodium ions. The electrical properties are studied by measuring electrical conductivity in the temperature range from 80 to 300 K. The study reveals that conductivity is a function temperature in these crystals. Moreover both pure and modified copper tatrate single crystal are semiconducting but the conductivity of pure modified copper tatrate single crystal is more than that of pure a copper tatrate single crystal. The results have been explained in terms variable range hopping model.

Influence of Electrochemically Exfoliated Graphite Addition on the Dielectric Properties of Epoxy/Montmorillonite Nanocomposites

The influence of hydrophilic electrochemically exfoliated graphite (EEG) and hydrophobic reduced EEG (rEEG) on the electrical conductivity, dielectric properties, and high-frequency dielectric losses of epoxy-based composites with montmorillonite was described. It was confirmed, that the addition of EEG changes the low-temperature conduction mechanism. The electrical conductivity in composite with EEG and montmorillonite was described by correlated barrier hopping model, whereas for composites with montmorillonite and rEEG two models were used: non-overlapping small polaron tunneling and correlated barrier hopping. The addition of EEG drastically changes the activation energy of charge carriers motions from 2.68 to 0.83 eV, whereas the addition of rEEG only to 2.43 eV. Also composite with EEG was characterized by highest high-frequency dielectric losses.

The Effect of Alkaline Earth (Ba, Sr and Ca) Doped Iron Bismuth Glasses on The Structural, Thermoelectric and Electrical Properties

Glasses with nominal composition 70Bi2O3-30Fe2O3 and 10A-60Bi2O3-30Fe2O3 (mol%); (A = Ba, Sr and Ca) were prepared by the conventional melt quenching technique. X-ray diffraction (XRD) and Differential scanning calorimeter (DSC) confirm the amorphous nature of the glass samples. The iron-bismuth glasses show good solubility of alkaline earth elements ions. In temperatures range of 310–450 K, the dc conductivity of the glass samples containing alkaline earth elements enhanced. Glass sample containing Sr shows interesting electrical properties. All glass samples showed a transition from negative to positive Seebeck coefficient, this means that the conduction is mixed of electrons and holes charge carriers. The conduction mechanism of all samples obeys non-adiabatic small polaron hopping model of electron between iron ions. The calculated small polaron coupling constant, (γp) was found to be in the range of 10.25–17.28. Also, the calculated hopping mobility (µ) and carrier density (Nc) of glasses were in the range of 4.65\(\times {10}^{- 7}\)- 4.11\(\times {10}^{-3}\left({\text{c}\text{m}}^{2}{\text{V}}^{-1}{\text{s}}^{-1}\right)\) and 0.029-10 \(\left({\times {10}^{1 7}\text{c}\text{m}}^{-3}\right)\) at 333 K, respectively.

A well-posedness result for a system of cross-diffusion equations

This work’s major intention is the investigation of the well-posedness of certain cross-diffusion equations in the class of bounded functions. More precisely, we show existence, uniqueness and stability of bounded weak solutions under a smallness assumption on the intial data. As an application, we provide a new well-posedness theory for a diffusion-dominant cross-diffusion system that originates from a hopping model with size exclusions. Our approach is based on a fixed point argument in a function space that is induced by suitable Carleson-type measures.

Enhancement of Dielectric Responses and Conduction Properties of Zn-doped TiO2 for Energy Storage and Photosensitivity Applications

This work deals with the physical investigations on Zn-doped TiO2 synthesized via a solvent controlled non-aqueous sol–gel route. X-ray diffraction analysis indicated that TiO2 particles crystallized in both tetragonal anatase and rutile structures. FTIR analysis confirmed the insertion of Zn in TiO2 network, and revealed the presence of surface defects in the prepared powders, as proved by their porous morphologies. UV-visible absorption was performed to provide an insight into the band-gap variation in the Zn-doped TiO2 nanopowders as a function of Zn doping. On the other hand, the electrical properties were studied using complex impedance spectroscopy in the frequency range from 40Hz to 1MHz at temperature range 480-600K. The impedance plots are well fitted to an (R1//C1)-(R2//CPE1) equivalent circuit. As well, the correlated barrier hopping model (CBH) was proposed to describe the conduction mechanism. Finally, Photocatalytic activities of the Zn doped TiO2 nanoparticles were evaluated via the degradation of the rhodamine B (RhB) dye under UV light irradiation. The results showed enhanced performance by Zn-doping, compared to the undoped TiO2 nanoparticles.

Hopping conduction mechanism and impedance spectroscopy analyses of La0.70Sr0.25Na0.05Mn0.70Ti0.30O3 ceramic

The perovskite sample La0.7Sr0.25Na0.05Mn0.7Ti0.3O3 (LSNM0.70T0.30) was produced via a solid-state route process. Impedance spectra of LSNM0.70T0.30 in the frequency interval [40Hz -1MHz] were studied at several temperatures [80K to 440 K]. The ac conductivity (σac) established that according to the Jonscher law. σac is described by Non-overlapping Small Polaron Tunneling model at low temperatures and Correlated Barrier Hopping model at high temperatures. From dc conductance analysis, conduction seems to be thermally activated, suggesting the existence of semiconductor process. Detailed investigation of impedance data revealed the non-Debye nature of the relaxation processes in the sample. In addition, Dielectric constant curves were applied to examine the relaxation dynamics of charge carriers. In fact, the Debye-like relaxation was performed on the basis of the polarization of spatial charges following Maxwell-Wagner model and Koop’s phenomenological theory.

Mechanisms of the energy transfer between thulium ions in tungstate and molybdate crystals

In this work, we investigated mechanisms of the energy transfer in Tm : KY(WO4)2, Tm : KLu(WO4)2 and Tm:NaBi(MoO4)2 crystals. Room-temperature absorption and emission spectra were used to determine microparameters of energy migration among thulium ions in the 3H4 and 3F4 excited states in the frames of Förster – Dexter theory. Parameters of cross-relaxation 3H4 + 3H6 → 3F4 + 3F4 and energy migration were obtained via analysis of luminescence decay 3H4 → 3F4 with a hopping model. The parameters describing excitation migration between thulium ions in 3H4 state obtained by two methods were in good agreement. It has been shown that the dipole-dipole mechanism of interaction is responsible for the efficient cross-relaxation process in the crystals under study. The results indicate that the energy migration between 3H4 enhances the cross-relaxation at thulium content more than ∼1.3–1.5 at. % in these laser materials. The obtained values of the migration parameters CDD exceed the values of the cross-relaxation parameters CDA, and the energy transfer in these materials can be described with the hopping model. An efficient cross-relaxation process leads to the relatively high efficiencies of the systems based on these crystals under pumping at 0.8 µm. The dominant process of energy migration between thulium ions in 3F4 excited state makes tungstate and molybdate crystals good candidates for the Ho3+ co-activation for laser generation at 2.1 µm. Parameters obtained in this study can be used for mathematical modeling of laser characteristics.

Influence of Zinc Oxide Nanoparticles on the Optical, Dielectric and Electromagnetic Interference Shielding Performance of Polystyrene Films

In the present work, Zinc oxide (ZnO) nanoparticles are synthesized using solvothermal technique. Polystyrene-ZnO (PS/ZnO) nanocomposite films are synthesized by solution casting procedure. PS/ZnO films are analyzed by XRD, FTIR and UV-Vis spectroscopic techniques. The addition of ZnO into the PS film is found to decrease the optical band gap (OBG) from 4.07 eV to 1.86 eV. Frequency dependence of dielectric constant (ε′), loss tangent (tanδ), ac conductivity (σac) and electromagnetic (EM) interference shielding effectiveness (SE) studies have been undertaken on the pure PS and PS/ZnO films. Insertion of ZnO into pure PS polymer matrix is found to enhance ε′, tanδ, σac, and SE considerably. The ε′ and tanδ were reduced with an enhancement in the frequency. σac of PS/ZnO nanocomposites was enhanced with rise in frequency and electrical conduction process in PS/ZnO film is in agreement with an electron-hopping model. EM interference SE is reduced with rise in the frequency. PS/ZnO films were proven as a favorable functional substance for the absorbing of EM waves at lower frequencies.