Jean-Pierre Levy

Anion deficiency in iron perovskites: The SrxNd1−xFeO3−y solid solution I: 0,6 < x < 0,8

Abstract Electron Microscopy and Diffraction of samples of the above solid solution indicate that samples reduced in Argon at 1350 C, although appearing cubic to X-ray Diffraction, have a tetragonal cell which is a superstructure of the perovskite cell. The supercell has the dimensions: 2a p xa p xa p . The doubling of one of the perovskite cell axes appears at random in the a, b or c directions within the same crystal. Such a structural situation originates the existence of a microdomain texture ; the domains are randomly intergrown in the three dimensions.

Structural evidence in 2-amino-5-nitropyridinium halides (Cl–, Br–) of herringbone motifs favourable to efficient quadratic non-linear optical properties

2-Amino-5-nitropyridinium halides have been synthesized and their crystal structures determined. The structures of acentric phases reveal networks of non-linear chromophores arranged in herringbone motifs. Their secondharmonic generation responses vary in magnitude between that of 3-methyl-4-nitropyridine N-oxide and 2-methyl-2,4-dinitrophenyl aminopropanoate molecular compounds. Chained anions screen favourably the interactions between the non-linear cations in acentric phases, while the reverse situation is observed in the centric phase of 2-amino-5-nitropyiridinium bromide built up with open pseudo-hexagonal anionic layers.

Hydrothermal and flux synthesis of LiMnO compounds: Crystal growth of LiMnO2 and Li2MnO3

Abstract Under hydrothermal conditions (100 MPa, 875 K), Mn oxides react with LiOH to form MnO, LiMnO 2 , Li 2 MnO 2 , Li 2 MnO 3 and/or Li 3 MnO 4 , depending on the prevailing redox conditions. Millimetre-size crystals of LiMnO 2 and Li 2 MnO 3 were obtained. Li 2 MnO 3 was also formed by reacting Mn 2 O 3 or MnO 2 with molten LiOH or LiCl at atmospheric pressure. Crystals of Li 2 MnO 3 up to 3×2×0.1 mm 3 were grown from a LiCl flux. Li 2 MnO 3 , which contains Mn 4+ ions, is thermally stable up to at least 1373 K.

Anchorage of 4-nitropyridine N-oxide, an optically non-linear entity, onto CdCl2 and CdI2 host matrices

The syntheses and crystal structures of bis(4-nitropyridine N-oxide)cadmium chloride and bis(4-nitropyridine N-oxide)cadmium iodide dihydrate are reported. The cadmium chloride complex exhibits a second-harmonic generation signal (SHG) of the same magnitude as that of KTiOPO4(KTP). The CdCl2 polymeric chains host the 4-nitropyridine N-oxide molecules through short Cd–O bonds, suggesting an extension of the π molecular orbital of the guest molecule through a O—Cd—O bridge.

Two 4‐nitropyridine N‐oxide adducts: (C5H4N2O3)2.AgNO3 and (C5H4N2O3)2.Co(NO3)2.4H2O

Two new addition compounds of the optically nonlinear molecule 4-nitropyridine N-oxide (NPO) have been synthesized and characterized: bis(4-nitropyridine N-oxide)silver nitrate and bis(4-nitropyridine N-oxide)cobalt nitrate tetrahydrate. Their structural features are described and compared, in particular the arrangement of the NPO molecules, the type of linkage in the inorganic entities (the cationic polyhedra and the nitrate anions) which make up the host matrice for the organic molecules and the hydrogen-bonding scheme contributing to the packing cohesion. Certain characteristics of both these centrosymmetric structures are also discussed with respect to some non-linear optical NPO derivatives

SFG Study of Thiocyanate Ion Adsorption onto Polycrystalline Au Electrode and Electrodeposited Metallic Thin Films

The sum frequency generation (SFG) characteristics of thiocyanate ions adsorbed on polycrystalline gold electrodes and on electrodeposited cobalt and nickel films are presented. The aim of this study is to compare the ion adsorption behavior on these metals by studying the CN stretching mode variations. In the cobalt-containing solution, a transition in the band frequency potential dependence between the naked gold surface and the cobalt-covered one has been evidence for potentials more positive than the one required for bulk cobalt deposition, suggesting that an anion-induced underpotential deposition process is taking place. The change of the SFG spectrum shape, the higher slope value of the band potential dependence, and the lower band frequency value observed on the bulk electrodeposited Co and Ni films suggest differences in the interaction strength, related to the d band filling of the substrate, and in the adsorption geometry of thiocyanate ions on these metals compared to the gold surface.

Crystal structure of bis(4-methoxypyridine-N-oxide) dichlorocopper, (C6NO2H7)2(CuCl2)

Source of material: Crystals have been prepared by dissolving 4/1000 mole of copper chloride dihydrate in 4cc of aqueous solution containing 4/1000 mole of MPO. During slow evaporation at room temperature crystals have grown. In view to design optically nonlinear crystals, the anchorage of MPO molecules onto transition-metal host matrices has been performed. The connections between MPO and CuCl2 entities through oxygen-metal bonds lead to the formation of a (MPO^CuCh centrosymmetrical motif. The MPO and CUCI2O2 planes are nearly perpendicular. The bond angle values around Ol suggest a sp hybridization.

The ASHA model: An alternative to the Markovian approach to housing vacancy chains: An application to the study of population in Lille (Nord, France)

This article proposes an alternative method to Markovian approaches through the housing systems analysis (ASHA) model. Its objective is to simulate the impact of the housing stock on population redistribution at a given scale and duration, by modelling the processes whereby residential mobilities are linked, initiated either by a change in the housing stock, or by a movement of housing releases that does not lead to a dwelling being occupied within the study area. The model takes into account the mobilities specific to each household category, in terms – for example – of social position, age, size or the dwelling occupied. It provides information on trends in the population structures of the different housing types brought about by vacancies-reoccupancies. The article begins by describing the model’s theoretical foundations (filtering process and housing vacancy chains) and conception. It then goes on to present, through the example of the city of Lille (Nord, France), a method of data classification that allows comparative analysis suited to the application of the ASHA model. Next, it illustrates the model’s analytical scope and the way it can be used to understand the organisation of a housing system. Finally, drawing on a number of examples (family accommodation, gentrification, housing programmes), it sets out the model’s operational utility and the way local managers can use it to understand and anticipate the impact of housing policy on the urban population.