Structural, electrical conductance and complex impedance analysis of (Nd1−xCex)0.7Sr0.3MnO3 (0≤x≤0.20) perovskite

International audiencePolycrystalline samples of (Nd1−xCex)0.7Sr0.3MnO3 (x=0, 0.10 and 0.20) were prepared by a high-temperature solid-state reaction technique. The X-ray diffraction study has shown that all the samples exhibit a single phase with orthorhombic structure (space group Pnma). From the resistivity data, it is found that all the samples show metal to semiconductor transition and the transition temperature decreases with the Ce doping. The complex impedance has been investigated in the temperature range 80–320 K and in the frequency range 40 Hz–1 MHz. AC conductance analyses indicate that the conduction mechanism is strongly dependent on temperature and frequency. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The activation energies obtained from the conductance is slightly higher than that from time relaxation analyse

Electrical conductivity and complex impedance analysis of La0.7-xNdxSr0.3Mn0.7Ti0.3O3 (x≤0.30) perovskite

International audiencePolycrystalline samples La0.7-xNdxSr0.3Mn0.7Ti0.3O3 (x= 0.10; 0.20 and 0.30) were prepared by a high-temperature solide-state reaction technique. The X-ray diffraction shows that all the samples crystallize in the orthorhombic structure, Pbnm space group, with presence of a minor unreacted Nd2O3. The electrical response was studied by impedance complex spectroscopy over a broad frequency range (40-100 MHz) at room temperature. The values of ac conductivity for all samples were fitted by the Jonscher law σ ( ω ) = σ dc + A ω s . For x= 0.10 and 0.20, hopping occurs between neighboring sites, whereas for x=0.30 the hopping process occurs through longer distance. Complex impedance plots exhibit semicircular arcs described by an electrical equivalent circuit, which indicates that the Nd-doped compounds obey a non-Debye relaxation proces

Towards sustainable, solution-processed organic field-effect transistors using cashew gum as the gate dielectric

To realize low-cost, environmentally friendly electronic devices and circuits, there is currently a strong trend to explore plant-based dielectric materials because they can be responsibly sourced from agricultural or forest vegetation, are generally water-soluble, and possess good electrical insulator properties. In this contribution, organic field-effect transistors (OFETs) using a biopolymer dielectric obtained from exudates of Anacardium occidentale Linn. trees, namely, cashew gum (CG), are reported. To characterise the physical and dielectric properties of the gum, thin films and metal-insulator-metal (MIM) capacitors were prepared and characterized. To evaluate the material’s performance in OFETs, bottom-gate top-contact (BGTC) p-channel poly [3,6-di(2-thien-5-yl)-2,5-di(2-octyldodecyl)-pyrrolo (3,4-c)pyrrole-1,4-dione) thieno (3,2-b) thiophene]:polymethyl methacrylate (DPPTTT:PMMA) transistors were engineered and studied. The fabricated MIM capacitors display a comparatively high areal capacitance of 260 nF/cm2 at 1 kHz for 130 nm thick films. As a result, the solution-processed DPPTTT:PMMA OFETs favourably operate at 3 V with the average saturation field-effect mobility equal to 0.20 cm2/Vs., threshold voltage around −1.4 V, subthreshold swing in the region of 250 mV/dec, and ON/OFF current ratio well above 103. As such, cashew gum emerges as a promising dielectric for sustainable manufacturing of solution-processed organic FETs

Optical and electrical properties of porous silicon impregnated with congo red dye

Incorporation of molecules into porous silicon (PS) matrix is of particular interest for potential utilization in hybrid organic-semiconductor devices. In this study, the incorporation of Congo Red molecules inside luminescent PS layers was investigated. The resulting structures have been characterized by Fourier Transformer Infrared (FTIR) and photoluminescence (PL) techniques. Based on these characterizations, the infiltration of dye molecules into the porous matrix has been proved. The recuperated PL signal was more important than that of porous silicon alone. A nonradiative excitation transfer due to dipolar interactions was evidenced from the effect of the CR concentration on the PL emission which was also confirmed by FTIR spectroscopy. It was found that the formed composite displays an efficient and stable PL. Preliminary characterizations of the electrical properties of the resulting nanocomposite structure have been also performed. The current-voltage (I-V) characteristics of CR-PS/p-Si were measured at the room temperature (300 K). To study the effect of illumination on CR-PS/p-Si composites, the measurement has been performed in dark and under illumination, at room temperature. The diode characteristics including zero-bias barrier height (ΦB0), ideality factor (n), and series resistance (Rs) were calculated at room temperature in dark and under illumination. The obtained results have shown that these characteristics are largely affected by illumination. The incorporation of dye molecules in porous silicon matrix enhanced photovoltaic properties of resulting structures. © 2013 AIP Publishing LLC

Structural, elastic, optical and dielectric properties of Li0.5Fe2.5 O4 nanopowders with different particle sizes

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Magnetic and optical properties, electrical behavior and conduction mechanism study by CBH model of Cu(HAsO3)·Te(OH)6 compound

The copper hydrogeno-arsenite tellurate material (CuAsTe) was synthesized and its magnetic properties were investigated. Thermal analyses revealed that no mass loss was recorded before 480 K. Additionally, in this current work, electrical properties based on the impedance measurements were determined. The complex impedance diagram at different temperatures demonstrated a single semicircle, implying that the response originated from a single capacitive element corresponding to the grains. The thermal evolution of the conductivity ¿dc displayed an Arrhenius type behavior and suggested that this material is an ionic protonic conductor at high temperature whereas the ¿ac conductivity was indicative that the conduction mechanism is ensured by the correlated barrier hopping (CBH) model. The variation of M¿ versus frequency proved to be a thermally activated dielectric relaxation process. Notably, we specified determined the direct optical band gap Eg = 2.3 eV in order to characterize the optical properties.This work is supported by the Ministry of the Higher Education and Research of Tunisia and Spanish MINECO MAT2013-40950-R and ERDF for financial support. We are deeply grateful to Dr. Mohammed Said Abdelbaky from the faculty of chemistry university of Oviedo Spain for his constant support as far as different manipulations are concerned. We are equally indebted the English teacher Jawaher Zekri from the faculty of sciences of Sfax for her constant help concerning the language correction

Structural, optical and dielectric properties of Cu1.5Mn1.5O4 spinel nanoparticles

In this study, a Cu1.5Mn1.5O4 spinel was successfully synthesized by a sol-gel method at 500 °C for 5 h and characterized by different techniques. X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectroscopy and Raman spectroscopic analyses confirmed the formation of a spinel cubic structure with the Fd3̄m space group. The SEM proves that the grain size of our compound is of the order of 48 nm. Crystallite sizes determined from three estimates are closer to the grain size obtained from the SEM, indicating the single domain nature of the sample. The optical properties of UV-visible spectroscopy for our sample showed that the gap value is equal to 3.82 eV, making our compound a good candidate for optoelectronic applications. For electrical properties, impedance spectroscopy was performed at a frequency range of 40 ≤ frequency ≤ 106 Hz. This suggested hoping conduction due to three theoretical models. The latter can be attributed to the correlated barrier hopping (CBH) model in region I, overlapping large polaron tunneling (OLPT) in region II and non-overlapping small polaron tunneling (NSPT) mechanism in region III. One dielectric relaxation is detected from the dielectric impedance and modulus, attributed to grain contributions. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance at different measuring temperatures

Hydrogen doped BaTiO3 films as solid-state electrolyte for micro-supercapacitor applications

International audienceSolid electrolytes are important part of all-solid state energy systems that store electrical energy on the chip. They allow a direct incorporation of micro-storage component with simple device architecture while operating at higher temperatures compared to liquid electrolytes. However, solid electrolytes are usually deposited at high temperatures, exceeding the thermal budget of current semiconductor technology. Herein, we report on the synthesis of high performance BaTiO3:H films as solid state electrolyte in which we incorporate protons during a room temperature RF sputtering process. Drastic changes occur on chemical, structural and electrical properties of the films when they accommodate highly mobile and reactive protons. BaTiO3:H films have well-defined crystalline phases and display an optical bandgap which decreases by increasing the HMR in the sputtering gas. In addition, these films show two relaxation processes. The first, thermally activated with an energy around 0.5 eV, emerges at low temperature due to the proton diffusion within the oxide material. The diffusion of positively charged oxygen vacancies by overcoming an energetic barrier of about 1.1 eV yields to a second relaxation which takes place at relatively high temperature. By using carbon nanowalls as high effective area bottom electrode, we anticipate a large specific capacitance

Carbon Nano-Fiber/PDMS Composite Used as Corrosion-Resistant Coating for Copper Anodes in Microbial Fuel Cells

The development of high-performance anode materials is one of the greatest challenges for the practical implementation of Microbial Fuel Cell (MFC) technology. Copper (Cu) has a much higher electrical conductivity than carbon-based materials usually used as anodes in MFCs. However, it is an unsuitable anode material, in raw state, for MFC application due to its corrosion and its toxicity to microorganisms. In this paper, we report the development of a Cu anode material coated with a corrosion-resistant composite made of Polydimethylsiloxane (PDMS) doped with carbon nanofiber (CNF). The surface modification method was optimized for improving the interfacial electron transfer of Cu anodes for use in MFCs. Characterization of CNF-PDMS composites doped at different weight ratios demonstrated that the best electrical conductivity and electrochemical properties are obtained at 8% weight ratio of CNF/PDMS mixture. Electrochemical characterization showed that the corrosion rate of Cu electrode in acidified solution decreased from (17 ± 6) × 103 μm y−1 to 93 ± 23 μm y−1 after CNF-PDMS coating. The performance of Cu anodes coated with different layer thicknesses of CNF-PDMS (250 µm, 500 µm, and 1000 µm), was evaluated in MFC. The highest power density of 70 ± 8 mW m−2 obtained with 500 µm CNF-PDMS was about 8-times higher and more stable than that obtained through galvanic corrosion of unmodified Cu. Consequently, the followed process improves the performance of Cu anode for MFC applications