Philippe Tailhades

Nanoenergetic Materials for MEMS: A Review

New energetic materials (EMs) are the key to great advances in microscale energy-demanding systems as actuation part, igniter, propulsion unit, and power. Nanoscale EMs (nEMs) particularly offer the promise of much higher energy densities, faster rate of energy release, greater stability, and more security (sensitivity to unwanted initiation). nEMs could therefore give response to microenergetics challenges. This paper provides a comprehensive review of current research activities in nEMs for microenergetics application. While thermodynamic calculations of flame temperature and reaction enthalpies are tools to choose desirable EMs, they are not sufficient for the choice of good material for microscale application where thermal losses are very penalizing. A strategy to select nEM is therefore proposed based on an analysis of the material diffusivity and heat of reaction. Finally, after a description of the different nEMs synthesis approaches, some guidelines for future investigations are provided.

RELATIONS BETWEEN MAGNETO-OPTICAL PROPERTIES AND REACTIVITY IN COBALT-MANGANESE FERRITE THIN FILMS AND POWDERS

Abstract Co-Mn spinel ferrites were prepared as submicron powders and thin films. Because of their finely divided state, these spinels could be oxidized at low temperatures to give novel cation-deficient ferrites. For these two material forms, the magneto-optical properties were found to be strongly dependent on the ferrite oxidation state. The highest coercivities and Faraday rotations were obtained when the ferrites were partially oxidized. These phenomena are attributed to the mechanical stress effect developed during the oxidation of the manganese ions. The properties of these ferrites could be of interest for magneto-optical recording applications. The first static recording tests were performed at 780 nm wavelength.

p-Type conducting transparent characteristics of delafossite Mg-doped CuCrO2thin films prepared by RF-sputtering

The growth of technologically relevant compounds, Mg-doped CuCrO2 delafossite thin films, on a quartz substrate by radio-frequency sputtering is reported in this work. The deposition, performed at room temperature, leads to a nanocrystalline phase with extremely low roughness and high density. Delafossite characteristic diffraction peaks were obtained as a function of the thermal treatment under primary vacuum. The electrical conductivity was optimized until 1.6 S cm−1 with an optical transmittance of 63% in the visible range by a 600 °C annealing treatment under primary vacuum applied for 4 h. The transport properties were analyzed by Seebeck and Hall measurement, integrated spectrophotometry and optical simulation. These measurements highlighted degenerated semiconductor behavior using a hopping mechanism with a high hole concentration (1021 cm−3) and a low mobility (0.2 cm2 V−1 s−1). The direct optical bandgap of 3.3 eV has been measured according to Taucs relationship. A refractive index of 2.3 at a wavelength of 1100 nm has been determined by spectroscopic ellipsometry and confirmed by two independent modellings of the optical transmittance and reflectance spectra. All these p-type TCO optoelectronic characteristics have led to the highest Haackes figure of merit (1.5 × 10−7 Ω−1) reported so far for such delafossite materials

Synthesis and Thermostructural Studies of a CuFe1−xCrxO2 Delafossite Solid Solution with 0 ≤ x ≤ 1

In this work, different CuFe(1-x)Cr(x)O(2) compositions with 0 <or= x <or= 1 were prepared by a standard solid-state reaction. These oxides crystallize with the delafossite structure. The phase stability and thermal behavior of the complete CuFe(1-x)Cr(x)O(2) solid solution was studied by thermogravimetric analysis and high-temperature X-ray diffraction experiments under an air atmosphere up to 1000 degrees C. For x = 0, CuFeO(2) is oxidized into the spinel (CuFe(2)O(4)) and copper monoxide (CuO) phases, whereas for x = 1, CuCrO(2) is thermally stable. For all of the intermediate compositions (0 < x < 1), complex oxidation, reduction, and phase transitions between delafossite and spinel have been observed. chromium tends to stabilize the stoichiometric delafossite phase, while iron favors the delafossite-to-spinel phase transition.

Synthesis and characterization of sub-micron size Co–Ni alloys using malonate as precursor

Sub-micron size

Oxidation mechanism of manganese-substituted magnetite

(0.2 - 0.6\mu m)

CuFe2O4 thin films: elaboration process, microstructural and magneto-optical properties

particles of

Submicron MnxCo1Fe2−xO4 spinel ferrites: Cationic distribution and reactivity

Co_1 - x Ni_x (0\leq x \leq1)

About the interesting properties of mixed-valence defect spinel ferrites for mass storage media

alloys have been synthesized by the polyol method using Co–Ni malonates as precursors but without using any protective agents such as PVP or any other surfactants. The synthesized alloys are found to be homogeneous. EDX analysis of the alloys showed particle-to-particle uniformity in composition. SEM showed largely non-agglomerated, almost spherical particles, with a fairly narrow size distribution. In the first reported effort of its kind, WAXS analysis was carried out to estimate the amounts of HCP and FCC phases present in pure Co and

Electrical conductivity study of oxidation process in manganese-substituted magnetites

Co_{0.8}Ni_{0.2}