Papers by Author: J. Dexpert-Ghys

Abstract: During the past few years, a pilot-scale spray pyrolysis set-up able to produce large quantities of submicronic powders (1kg/day) has been assembled in our laboratory. During the process, droplets of a precursor solution are dried and decomposed to the required compound. The presence of an additional soluble flux in the precursor solution permits to obtain agglomerate - free nanoparticles after washing the product. Therefore, pure zinc oxide nanoparticles have been successfully synthesized by adding lithium or sodium nitrates to the initial zinc nitrate solution. The nanoparticles have been characterized by X-ray diffraction, field-emission scanning electron microscopy, laser scattering size analyzer. The influence of the precursor solution composition and of the operating parameters on the morphology and the average size of ZnO nanoparticles is discussed.

Abstract: In Lead-cadmium fluorogermanate glasses (PbF2-CdF2-PbGeO3) the addition of metal fluorides to the base PbGeO3 glass leads to a decrease of the glass transition temperature (Tg) and to an enhancement of the ionic conductivity properties. Based on different spectroscopic techniques (19F NMR, Ge K-edge X-ryas absorption and Raman scattering) an heterogeneous glass structure is proposed at the molecular scale, which can be described by fluoride rich regions permeating the metagermanate chains. The temperature dependence of the 19F NMR lineshapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluoride mobility in these systems. Eu3+ emission and vibronic spectra are used to follow the crystallization process leading to transparent glass ceramics.