Elaboration de poudres de yig par coprecipitation

This paper deals with an original method for the preparation of ferrites with the garnet structure by coprecipitation.The different transformations of the coprecipitated hydroxide during heat treatment are studied and reported.YIG crystallization from amorphous oxide is significantly dependent of some parameters.However, pure homogeneous materials can be obtained at low temperature (800–850C) for Al substituted YIG Y₃Al_xFe_5–xO₁₂ with 0.5x1.

     

Deshydratation de l'alun d'ammonium

Dehydration of hydrated ammonium alum is a function of physical gaseous pressure. During dehydration, two kinds of partially dehydrated amorphous alum appears. These solids differ in texture and residual water composition.

     

Single-mode direct-ultraviolet-written channel waveguide laser in neodymium-doped silica on silicon

A waveguide laser with a neodymium-doped silica core is fabricated on a silicon substrate by a combination of flame hydrolysis deposition, solution doping, and direct UV writing. The neodymium-ion concentration is estimated to be approximately 8000 parts in 10(5). The propagation loss around 1.05 microns is < 0.8 dB/cm. Lasing in the range 1048-1056 nm and 1356 +/- 1 nm is observed. A slope efficiency of 33% for a high-reflectivity output coupler and a threshold of 4 mW of absorbed power for a 25% output coupler are measured for the 4F3/2-->4I11/2 transition.     

Deshydratation de l'alun d'ammonium

The formation of the two kinds of partially dehydrated amorphous alum can be explained by the water vapour gradient which appears within the sample during dehydration and by existence of a critical water pressureP _c at the reaction interface. The mechanisms of dehydration at “low” and “high” pressure are described.     

Synthese Basse Temperature Du Gallate De Zinc

The dependence of the firing conditions on the crystal structure formation of ZnGa₂ O₄ has been investigated. The effects of temperature and atmosphere were examined and gave evidence of the instability of the zinc gallate under a reducing atmosphere at temperatures above 600°C. A new preparation route has allowed to synthesize ZnGa₂ O₄ at low-temperature, right from 300°C, avoiding the decomposition of the matrix during the annealing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detection of foreign phases in doped a-alumina powders by thermoluminescence

The thermoluminescence (TL) after excitation by UV or X-rays radiation of doped a-alumina powders is investigated. In the case of zirconia, the alumina-zirconia composites present five of the characteristic peaks of zirconia at -170, -145, -90, 0 and 95°C. After a thermal treatment of mixed oxides, a new peak is observed at -35°C in TL. This peak reveals the presence of stabilized tetragonal zirconia in the material. In the case of calcium, the TL curves of a-alumina doped by calcium present a double peak around 110 and 130°C which can be attributed to the presence of the hibonite phase: CaAl₁₂O₁₉. Moreover, in the case of zirconia, by comparing this analysis with those realised by X-rays diffraction (XRD), it can be shown that the TL has one better limit of detection than the XRD. This revised version was published online in July 2006 with corrections to the Cover Date.