Admittance spectroscopy study of NiGe contact on GeSn

Conference (2011)

The direct gap semiconductor germanium tin (GeSn) is an attractive material for next-generation devices in nanoelectronics as well as in photovoltaic applications. However, its detailed electronic ... [more ▼]

The direct gap semiconductor germanium tin (GeSn) is an attractive material for next-generation devices in nanoelectronics as well as in photovoltaic applications. However, its detailed electronic properties have not yet been clearly understood. Recently, admittance spectroscopy has become a popular analytical tool in materials research and development because it involves a relatively simple electrical measurement whose results may establish accurate characteristics of materials. The aim of this work is to study the effects of the annealing temperature on the electrical nature (rectifying or non-rectifying) of the metal contact by admittance spectroscopy. A numerical method, which is based on the solution of the basic semiconductor equations, is applied to simulate the material structure. From the calculation of microscopic quantities such as the modulated carrier concentrations and current densites, we can compute the theoretical admittance and impedance curves as function of frequency and external parameters (temperature and steady-state voltage) and then extract information on the electrical properties of the heterostructure. By a detailed investigation of the impact of microscopic parameters such as the dopant concentrations and the metal barrier height on the electrical characteristics, our objective is to understand the mechanisms of charge transport between the two electrodes. [less ▲]

Thermoelectric properties of n-type Ca1-xDyxMn1-yNbyO3-delta compounds (x=0, 0.02, 0.1 and y=0, 0.02) prepared by spray-drying method

in Journal Of Alloys And Compounds (2011), 509(29), 7710-7716

We report the high temperature thermoelectric properties of Ca1-xDyxMn1-yNbyO3-delta (x = 0, 0.02, 0.1 and y = 0, 0.02) synthesized by spray-drying method. A maximum power factor (PF) value of 2.65 mu WK ... [more ▼]

We report the high temperature thermoelectric properties of Ca1-xDyxMn1-yNbyO3-delta (x = 0, 0.02, 0.1 and y = 0, 0.02) synthesized by spray-drying method. A maximum power factor (PF) value of 2.65 mu WK-2 cm(-1) is obtained at 1100 K for CaMn0.98Nb0.02O3-delta. This represents an improvement of about 75% with respect to undoped CaMnO3-delta sample at the same temperature. We also provide a complete structural characterization of the samples. (C) 2011 Elsevier B.V. All rights reserved. [less ▲]

Characterization of surface and porous properties of synthetic hybrid lamellar silica

in Journal of Non-Crystalline Solids (2011), 357

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric ... [more ▼]

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow-slit like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of the specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g makes these lamellar silicas interesting materials for catalysis applications. [less ▲]

Vanadium oxide-based mesoporous films as positive electrode material in Li-ion batteries

Conference (2010)

Improvement of the thermoelectric properties of [Bi1.68Ca2O4-delta](RS)[CoO2](1.69) cobaltite by chimie douce methods

in Journal of Solid State Chemistry (2010), 183(6), 1252-1257

[Bi1 68Ca2O4 delta](RS)[CoO2](1 69) has been obtained by different chimie douce methods and uniaxially or isostatically pressed The influence of these parameters on the thermoelectric properties has been ... [more ▼]

[Bi1 68Ca2O4 delta](RS)[CoO2](1 69) has been obtained by different chimie douce methods and uniaxially or isostatically pressed The influence of these parameters on the thermoelectric properties has been investigated. Contrary to the Seebeck coefficient, which remains unchanged, the electrical conductivity is greatly modified In particular, spray-drying synthesis followed by uniaxial pressing results in an electrical conductivity two times larger than in the case of conventional solid state synthesis. Our results suggest that a narrow particle size distribution is beneficial to the thermoelectric properties of the layered compounds. The spray-drying technique seems to be promising to Improve the electrical conductivity of layered materials. Moreover, this method presents other advantages (homogeneous samples and less energetic processing) which could be interesting to the future manufacturing of thermoelectric devices (C) 2010 Elsevier Inc. All rights reserved [less ▲]

Effect of annealing temperatures on properties of sol-gel grown ZnO-ZrO2 films

in Crystal Research And Technology (2010), 45(11), 1154-1160

Mixed ZnO-ZrO2 films have been obtained by sol-gel technology. By using spin coating method, the films were deposited on Si and glass substrates. The influence of thermal annealings (the temperatures vary ... [more ▼]

Mixed ZnO-ZrO2 films have been obtained by sol-gel technology. By using spin coating method, the films were deposited on Si and glass substrates. The influence of thermal annealings (the temperatures vary from 400 degrees C to 750 degrees C) on their structural properties has been studied. The structural behavior has been investigated by the means of XRD and FTIR techniques. The results revealed no presence of mixed oxide phases, the detected crystal phases were related to the hexagonal ZnO and to crystalline ZrO2. The sol-gel ZnO-ZrO2 films showed polycrystalline structure with a certain degree of an amorphous fraction. The optical transmittance reached 91% and it diminished with increasing the annealing temperatures. The optical properties of the sol-gel ZnO-ZrO2 films, deposited on glass substrates are excellent with high transparency and better then those of pure ZrO2 films, obtained at similar technological conditions. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [less ▲]

Vanadium oxide-based mesoporous films as positive electrode material in Li-ion batteries

Conference (2009)

Grain boundary effects in bulk colossal magneto resistive (CMR) manganites and manganite/insulator composites: electrical and magnetic properties

in Journal of Optoelectronics and Advanced Materials [= JOAM] (2009), 11(9), 1115-1121

In the first part of this paper, we discuss the effects of grain boundaries on the properties of bulk colossal magnetoresistive (CMR) manganites We compare the electrical resistivity and AC magnetic ... [more ▼]

In the first part of this paper, we discuss the effects of grain boundaries on the properties of bulk colossal magnetoresistive (CMR) manganites We compare the electrical resistivity and AC magnetic susceptibility of perovskite La-Ca-Mn-O samples with the same nominal stoichiometry but differing in their microstructure (i) a single grain sample, (ii) a sample containing two grains and (iii) a polycrystalline sample Emphasis is placed on information that can be deduced from the measurements in each case In the second part of the paper, we report the data measured on composite samples containing a CMR phase (La-Ca-Mn-O) and an insulating phase (Mn3O4) The results are discussed in the framework of percolation theory We show how the grain boundaries affect the electrical properties of these materials, and we highlight the crucial role of geometric (demagnetization) effects on the resistance vs magnetic field measurements [less ▲]

Rapid synthesis of submicron crystalline barium zirconate BaZrO3 by precipitation in aqueous basic solution below 100 degrees C

in Journal of the European Ceramic Society (2009), 29(8), 1457-1462

Pure crystalline BaZrO3 powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH- concentration ([NaOH] = 20 mol/l ... [more ▼]

Pure crystalline BaZrO3 powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH- concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (similar to 80 degrees C), after a short reaction time (15 min) and without requiring any precaution to avoid the presence of CO2. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba + Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba + Zr] = 1 mol/l, reaction time= 15 min) yields a sub-micron precipitate with excellent densification behaviour. Corrosion tests in BaO-CuO melt show that similar to 98% dense BaZrO3 obtained by sintering at 1650 degrees C for 13 h could be used for crucibles in the synthesis of YBa2Cu3O7 superconducting single crystals. (C) 2008 Elsevier Ltd. All rights reserved. [less ▲]

Interactions in YBa2Cu3O7-x aqueous suspensions

in Materials Chemistry & Physics (2009), 116(2-3), 368-375

Surface charging mechanism of YBa2Cu3O7-x (YBCO) particles in water has been investigated in order to understand their colloidal behaviour and stabilise concentrated suspensions. A broad study relating ... [more ▼]

Surface charging mechanism of YBa2Cu3O7-x (YBCO) particles in water has been investigated in order to understand their colloidal behaviour and stabilise concentrated suspensions. A broad study relating the suspension parameters (pH and zeta potential) vs. the conditions of the suspension performance (atmosphere and time) has been shown and discussed. The zeta potential values remain positive in all the pH range for the highest powder concentration studied (10 g l(-1)), evidencing a large influence of the solid content in the particle charge. The chemistry of YBa2Cu3O7-x in water has been studied through the chemical analysis of the supernatant by inductively coupled plasma (ICP), and the surface analysis of the particles by X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). The presence of BaCO3, CuO, and the hydrolysed Ba species, such as Ba(OH)(2) and Ba(OH)(+), at the particles surface has been evaluated as a function of the powder concentration. Based on these analyses, the dependence of the colloidal behaviour of YBCO on the presence of Ba soluble species has been determined. A stabilisation mechanism for YBCO particles in aqueous suspension focus on the powders deleterious minimization was proposed. (C) 2009 Elsevier B.V. All rights reserved. [less ▲]