Electronic and optical properties of layered chalcogenide FeIn2Se4

We investigated the spectral-dependent dielectric function and temperature-dependent bandgap energy of layered chalcogenide FeIn₂Se₄ crystals. The critical-point energy and Lorentzian broadening were analyzed by fitting second-derivative spectra using the standard critical point model. The temperature effect of the bandgap energy was analyzed based on an analytical model considering both thermal lattice expansion and electron–phonon interactions. We also extensively analyzed the temperature dependence of absorption tails and identified their possible origins. The dielectric functions and absorption coefficient in the photon-energy range of 0.75–4.75 eV were obtained. The results also showed that optical phonon modes associated with the electron–phonon interactions could be closely related to the average phonon energy.     

Mössbauer studies of FeAl2O4 and FeIn2S4 spin glass spinels

Mössbauer experiments were performed on iron spinels in which spin-glass-like properties are observed. The spin glass character of FeIn₂S₄ cannot be considered as canonical due to the existence of a relaxation-time distribution nearT _g. A surprising first-order transition atT _g has been evidenced for FeAl₂O₄.     

Temperature and frequency dependence of AC electrical properties of Zn and Ni doped CoFe2O4 nanocrystals

Abstract

We have investigated the structure and the electrical properties of CoFe₂O₄, Ni_0.5Co_0.5Fe₂O₄ and Zn_0.5Co_0.5Fe₂O₄ nanoparticles, prepared through a chemical pyrophoric reaction technique. The study of the dielectric constant reveals evidence of Rabinkin and Novikova polarisation in the system. The increased value of the dielectric constant at low frequency is attributed to the presence of interfacial and dipolar polarisation in the system. The impedance for Zn_0.5Co_0.5Fe₂O₄ nanoparticles is found to decrease with increase in temperature, indicating the presence of a temperature-dependent electrical relaxation process in the system. Nyquist plots have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance. The activation energy is estimated from Nyquist plots, dc and ac conductivity data using the Arrhenius relation. This is indicating that the same type of charge carrier is responsible for the relaxation and the conduction processes in the system. Ac conductivity curves follow a double power law, as proposed by Jonscher. The conduction mechanism with temperature is mainly due to the large polaronic hopping in the system.     

AC electrical properties of proton irradiated EVA films

MeV ions passing through polymeric films modify their electrical, optical and thermal properties and these changes are related to changes in the chemical structure of the polymers. Ethylene vinyl acetate (EVA) films were irradiated with 3 MeV proton beam at different fluences of 10¹³, 10¹⁴ and 10¹⁵ ions/cm². AC electrical properties of pristine and irradiated samples were studied in the frequency range 100 Hz to 100 kHz by means of an LCR meter. There is an exponential increase in conductivity with log frequency and conductivity increases as fluence increases. The dielectric loss/constant is observed to change with the fluence. FTIR spectra reveals significant change in intensities of functional groups at a fluence of 10¹⁵ ions/cm² due to scissioning of polymer chains.     

Photoconductive properties of HgGa2S4

Mercury thiogallate, HgGa₂S₄ is a defect chalcopyrite semiconductor with the space group S₄² which offers a combination of attractive properties for applications.In order to obtain information about the electron states in the energy gap, photoconductivity measurements are performed in the 80–300 K range. Photoconductivity spectra show two peaks related to intrinsic and extrinsic excitation at about 410 and 500 nm, respectively; these maxima show a temperature dependence similar to the linear coefficient of the energy gap. Thermally stimulated currents have been studied by exciting the samples with intrinsic light at different temperatures. For all excitation temperatures a single TSC peaks were obtained. The analysis of TSC curves allowed one to estimate the kinetics of the trap emptying, trap energy distribution and thermal activation energy.A model for the level distribution in the semiconductor energy gap is suggested which in good agreement with the results of a previous photoluminescence study.     

Optical and electrical properties of Li2WO4 compound

ABSTRACT

The preparation of the Li₂WO₄ compound was made by the solid–solid method under well-defined conditions of temperature, which has not been dealt with in the bibliography. The previous works have been focused on studying the structure and the conductivity of Li₂WO₄ compound, while our work aims to investigate this compound by X-ray diffractometer, DSC, SEM, impedance spectroscopy, and conductivity analysis. Moreover, the optical properties are also investigated. These measures allow us to confirm that the studied sample crystallizes in the monoclinic structure with the space group (P2/m) and the lattice parameters: a?=?7.49?Å b?=?8.31?Å, c?=?5.92?Å, α=γ=90° and β?=?96.81°. Li₂WO₄ compound presents a compact structure, wherein the presence of some porosity is noticed. The band gap and the Urbagh energies were determined from the optical measurement. The DSC study shows the presence of an endothermic peak at T?=?500?K, indicating the existence of a phase transition. With regards to the electrical properties, the grain and the grain boundary response was modeled by a series combination of two cells, each one of them is composed of a parallel combination of resistance (R) and constant phase element (CPE). The AC conductivity was carried out for a specific range of temperature and frequency, thus allowing the identification of the conductivity mechanism. For the same conditions, the electrical modulus was studied. The theoretical data help us to extract some remarkable results and to confirm the phase transition at T?=?500?K.     

Electronic properties of MgIn2S4 and CdIn2S4 by the self-consistent pseudopotential method

Summary The electronic properties of CdIn₂S₄ and MgIn₂S₄ are studied in the self-consistent local-density pseudopotential scheme based on hard-core atomic potentials. Our self-consistent calculation confirms the assumptions of previous empirical studies and provides for the lowestenergy gap values which agree with experimental data. The electron charge densities indicate that both sulphospinels are highly ionic. The two compounds have similar ground-state properties but different conduction bands. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

AC electrical properties study and equivalent circuit of a monovalent-mixed pyrophosphate

NaAgPbP₂O₇ was prepared with a solid-state reaction. The electrical properties were investigated by using impedance measurements in the frequency range from 200 Hz to 5 MHz with the TEGAM 3550 ALF automatic bridge monitored by a microcomputer between 581 K and 703 K. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit model. The conductivity data obey the universal power law. The conductivity in the material is due to the hopping of monovalent ions parallel to (001) plane.     

Synthesis and electrochemical properties of Li2S–B2S3–Li4SiO4

New Li⁺ ion-conductive glasses Li₂S–B₂S₃–Li₄SiO₄ were synthesized by rapid quenching, and they were transformed into glass ceramics by heat treatment. The heat treatment increased the ionic conductivities of the Li₄SiO₄-doped glasses, and the highest ionic conductivity observed in the system was 1.0 × 10^− 3 S cm^− 1 at room temperature. The glass ceramics were highly stable against electrochemical oxidation with a wide electrochemical window of 10 V.     

Equilibrium properties of the layer α-ZnIn2S4

Summary The ternary ZnIn₂S₄ is a semiconductor with a number of layerlike polytypes coordinated by both tetrahedral and octahedral bonds. The equilibrium properties of the α-phase are investigated self-consistently by using normconserving pseudopotentials. In particular we study in the Hellmann-Feynman scheme the relationship between atomic displacements and crystal stability by minimizing the forces acting on the anions. The resulting charge density maps are analysed and discussed. Work partially supported by Italian CNR through: Progetto finalizzato Sistemi informatici a Calcolo Parallelo under Grant n. 89.00006.69.     

Calculation of the optical properties of PbGa2S4 crystal

The high-frequency refractive index of PbGa₂S₄ crystal has been calculated using the Harrison bonding-orbital method. Satisfactory agreement between the calculation results and experimental data is obtained.     

Optical properties and CO_2 laser SHG with HgGa_2S_4

Optical properties and nonlinearity on phase-matching (PM) of two (yellow and orange) phase crystals were investigated in details. Damage threshold was determined in comparison with middle infrared (IR) crystal at identical experimental conditions. Second harmonic generation (SHG) of 30 ns TEA CO2 laser pulses was realized with 5% efficiency in energy and 6.9% in peak power.     

Improved interfacial and electrical properties of GaSb metal oxide semiconductor devices passivated with acidic （NH4）2S solution

Surface passivation with acidic(NH4)2S solution is shown to be effective in improving the interfacial and electrical properties of HfO2/GaSb metal oxide semiconductor devices. Compared with control samples, the samples treated with acidic(NH4)2S solution show great improvements in gate leakage current, frequency dispersion, border trap density, and interface trap density. These improvements are attributed to the enhancing passivation of the substrates, according to analysis from the perspective of chemical mechanism, X-ray photoelectron spectroscopy, and high-resolution cross-sectional transmission electron microscopy.     

The electrical properties of Cu2Te

The conductivity, Hall effect, and thermo-emf are reported for thin films and polycrystalline bulk specimens of Cu₂Te, which is found to be an impurity semiconductor whose forbidden band has a width of 0.9–1.0 eV. The compound dissociates on vacuum evaporation, so it is very difficult to produce thin films.I am indebted to Professor D. N. Naskedov for his interest and for valuable comments.     

Impact of ethylene carbonate on electrical properties of PVA/(NH4)2SO4/H2SO4 proton-conductive membrane

A new proton-conductive membrane (PCM) based on poly (vinyl alcohol) and ammonium sulfate (NH₄)₂SO₄ complexed with sulfuric acid and plasticized with ethylene carbonate (EC) at different weight percent were prepared by casting technique. The structural properties of these electrolyte films were examined by XRD studies. The XRD patterns of all the prepared polymer electrolytes reveal the amorphous nature of the films. ac conductivity and dielectric spectra of the electrolyte were studied with changing EC content from weight 0.00 to 0.75 g. A maximum conductivity of 7.3 × 10⁻⁵ S cm⁻¹ has been achieved at ambient temperature for PCM containing 0.25 g of ethylene carbonate. The electrical conductivity σ, dielectric constant ε′ and dielectric loss ε″ of PCM in frequency range (100 Hz to 100 KHz), and temperature range (300–400 K) were carried out. Measurement of transference number was carried out to investigate the nature of charge transport in these polymer electrolyte films using Wagner’s polarization technique. Transport number data showed that the charge transport in these polymer electrolyte systems was predominantly due to ions. The electrolyte with the highest electrical conductivity was used in the fabrication of a solid-state electrochemical cell with the configuration (Mg/PCM/PbO₂). Various cell parameters ldensity, and current density were determined. The fabricated cells gave capacity of 650 μAh and have an internal resistance of 11.6 kΩ.     

4H-SiC n-MOSFET的高温特性分析

通过考虑迁移率和阈值电压随温度的变化关系，模拟分析了4H-SiC n-MOSFET高温下的电学 特性，模拟结果与实验有较好的符合.并进一步讨论了主要结构参数和工艺参数对高温电特 性的影响及其最佳取值. 关键词： n-MOSFET 4H-SiC 迁移率 阈值电压     

Heating of magnons by hot charge carriers and electrical properties of HgCr2Se4

Strong variations of the conductivity and the Hall coefficient as a function of the magnetic and electric field strengths are discovered in the ferromagnetic semiconductor HgCr₂Se₄. The nature of these phenomena is discussed in connection with its electronic structure and the strong interaction between the electric and magnetic subsystems in this magnetic semiconductor. The results can be interpreted within a model of ordinary semiconductors with consideration of the strong electron-magnon interaction specific to magnetic semiconductors, the heating of magnons by hot charge carriers, and the trapping of charge carriers (the formation of ferrons) due to the s-d exchange interaction. Fiz. Tverd. Tela (St. Petersburg) 39, 664–667 (April 1997)