A new empirical model of glass formation in multicomponent systems

A new empirical model is proposed for the a priori determination of vitrification conditions of multicomponent systems. Based on the concept of antagonistic bonds, the model takes into account the contradictory effects of the glass modifier : i) generally highly ionic it tends to induce a recrystallization, ii) simultaneously it enhances the covalency of the glass former, increasing the polymerization of the species in the liquid phase and favoring the vitrification. The diagrams (enthalpy of formation of the glass modifier vs. polarizing power of the cation contained in the glass modifier) emphasize this double role. The model is applied to some oxychloride and fluoride glasses.     

Asymmetric silver to oxide adhesion in multilayers deposited on glass by sputtering

We have developed a wedge-loaded double-cantilever beam adhesion measurement set-up for thin films deposited on glass by sputtering. The test is described in details. Results on the Glass/sublayer/Ag/ZnO multilayer provide evidence that SnO₂ or TiO₂ perform better than ZnO as a sublayer. Then however, rupture within the multilayer shifts to the upper Ag/ZnO interface. The latter is shown to be tougher than the lower ZnO/Ag interface, an asymmetry due to non-equilibrium interfacial structures.     

Structural influence on charge-carrier lifetimes in TiO2 powders studied by microwave absorption

A set-up for contactless transient photoconductivity measurements on powders by the Time Resolved Microwave Photoconductivity (TRMC) method has been realized. These measurements have been used as a tool for the investigation of excess charge-carrier lifetimes in TiO₂ (anatase and rutile) powders. The influence of laser wavelength and intensity on TRMC decay shows the importance of the fast-recombination processes. The presence of a long time tail in the TRMC signals of the anatase modification of TiO₂ is attributed to quenching of this recombination by hole-trapping at the surface. The influence of surface treatment by ethanol and water on TRMC decay evidences that dominant effects are bulk recombination in rutile and surface trapping in anatase. The influence of doping in rutile shows that increasing the doping rate accelerates the decay whatever the doping type is. The doping element acts as an impurity favoring recombination by creation of structural defects. The influence of thermal treatment in anatase shows that increasing the thermal treatment temperature increases the lifetimes. High crystalline quality leads to long charge-carrier lifetimes. The results are discussed in view of their relevance for photocatalysis.     

Coupling between electrolysis and liquid-liquid extraction in an undivided electrochemical reactor: applied to the oxidation of Ce3+ to Ce4+ in an emulsion Part I. Experimental

The effect ofin situ simultaneous extraction of tetravalent cerium by an organic phase (di-2 ethylhexylphosphoric acid in kerosene) on the performance of an undivided batch electrochemical reactor using the Ce³⁺/Ce⁴⁺ system was investigated. The influence of the most important parameters (initial concentration of Ce³⁺, composition and volume percentage of the organic phase) were studied experimentally under potentiostatic control of the anode potential. A conversion factor of Ce³⁺ and extraction factor larger than 90% are obtained for the best operating conditions, but the presence of the organic phase and the necessity of avoiding oxygen gas evolution considerably reduce the operating anodic current densities. The transient cell behaviour and the final equilibrium state conditions are found to be in very good qualitative agreement with the conclusions of a preliminary study of the electrochemical kinetics of the Ce³⁺/Ce⁴⁺ system and extraction mechanisms of Ce⁴⁺ by the organic phase.This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

Designer Colloidal Layers of Disordered Plasmonic Nanoparticles for Light Extraction

Basic design rules are disclosed for broadband light‐extraction colloidal films formed with disordered ensembles of plasmonic particles. They are derived through the numerical study of a test‐bed geometry consisting of a low‐refractive index slab in air. Albeit simple, the geometry encompasses many physically effects encountered in real light‐emitting devices, including the pronounced absorption at the peak of the nanoparticles resonance spectrum, the anisotropy of the radiation diagram of nanoparticles in waveguides and unavoidable coherent multiple interferences that ruin the predictive strength of first‐order scattering models. How we can simultaneously take advantage of (1) the shape or size of the individual nanoparticles, (2) their transverse position with respect to the guiding photonic structure, (3) their concentration, and (4) the structural topology of the disorder ensemble are illustrated. Following this approach, a threefold enhancement in the extraction efficiency can be reached as compared to a film without plasmonic particles. It is also predicted that the extraction rapidly saturates and then decreases as the nanoparticle density increases, suggesting that best performance is achieved at low concentrations. Spectrally broad and directionally random far‐field radiation diagrams are additionally reported, which do not suffer from deterministic interferential behaviors observed at particular wavelengths and directionalities with periodic light‐extraction structures.