Virginie Hornebecq

Study of disorder in a tetragonal tungsten bronze ferroelectric relaxor: a structural approach

Electron diffraction analysis, nuclear magnetic resonance measurements, structure determinations and refinements were performed on two ferroelectric lead-containing ceramics (classical and relaxor), with tetragonal tungsten bronze structure, in order to investigate the origin of the relaxor behaviour in such compounds. In both compounds the lead atoms are found to be off-centred in the CN (coordination number) 15 (A2) site. The main difference between the two compositions is the proportion of lead in this site: in the relaxor composition, the A2 site is at least half occupied by lead atoms. Disorder in the repartition of lead and potassium atoms in the A1 (CN 12) and A2 sites was also studied via combinatorial calculations to correlate the evolution of the relaxor behaviour in the Pb5Ta10O30–Li10Ta10O30–K10Ta10O30 ternary system with composition. The combinatorial study demonstrated that the relaxor behaviour is enhanced by the disorder in cationic repartition.

Relaxations in new ferroelectric tantalates with tetragonal tungsten bronze structure

Abstract Ceramics belonging to the Pb5xK6(1−x)Li4(1−x)Ta10O30 solid solution were prepared and characterized by dielectric and a. c. impedance complex measurements. Two types of relaxations were observed: a relaxor behavior and an impedance relaxation. Characteristics of these two relaxations were studied and explained for a particular composition Pb3.75K1.50LiTa10O30.

Electrochemical Fabrication and Properties of Highly Ordered Fe-Doped TiO2 Nanotubes

Highly-ordered Fe-doped TiO(2) nanotubes (TiO(2)nts) were fabricated by anodization of co-sputtered Ti-Fe thin films in a glycerol electrolyte containing NH(4)F. The as-sputtered Ti-Fe thin films correspond to a solid solution of Ti and Fe according to X-ray diffraction. The Fe-doped TiO(2)nts were studied in terms of composition, morphology and structure. The characterization included scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, UV/Vis spectroscopy, X-ray photoelectron spectroscopy and Mott-Schottky analysis. As a result of the Fe doping, an indirect bandgap of 3.0 eV was estimated using Taucs plot, and this substantial red-shift extends its photoresponse to visible light. From the Mott-Schottky analysis, the flat-band potential (E(fb)) and the charge carrier concentration (N(D)) were determined to be -0.95 V vs Ag/AgCl and 5.0×10(19) cm(-3) respectively for the Fe-doped TiO(2)nts, whilst for the undoped TiO(2)nts, E(fb) of -0.85 V vs Ag/AgCl and N(D) of 6.5×10(19) cm(-3) were obtained.

Synthesis and structural characterization of new ruthenium(II) complexes and investigation of their antiproliferative and metastatic effect against human lung cancer (A549) cells

Reaction of 2-hydroxy-1-naphthaldehyde-4(N)-ethylthiosemicarbazone [H2-(Nap-etsc)] with [RuHCl(CO)(PPh3)3] conferred two entities, namely [Ru(H-Nap-etsc)Cl(CO)(PPh3)2] (1) and [Ru(Nap-etsc)(CO)(PPh3)2]·Cl (2). The new complexes were characterized using various spectroanalytical and X-ray crystallographic techniques. In this reaction the dual coordination behaviour (thiolate/thione) of the ligand was observed. It acted as NS bidentate monobasic and ONS tridentate monobasic in entities 1 and 2 respectively. The binding ability of complexes (1 and 2) to calf thymus DNA (CT DNA)/BSA has been explored by absorption and emission titration methods. The cytotoxic nature of the complexes was evaluated on human lung cancer cells, A549. Complexes induced apoptotic cell death via ROS hypergeneration and mitochondrial membrane damage. In addition these newly synthesized ruthenium complexes inhibited A549 cell migration, as evidenced by wound healing assay. The activity of the complexes was found to be very high by comparing with cisplatin, a conventional standard. The time dependent release of the complexes from porous system was investigated by taking mesoporous silica as the host material. It was shown that the main portion of the embedded complexes was released after 20 h and reached a maximum after 96 h.

Microcalorimetric investigation of high-surface-area mesoporous titania samples for CO2 adsorption.

Mesoporous titania powders were synthesized using the triblock copolymer F127 (PEO(106)PPO(70)PEO(106)) as a surfactant template. Two different procedures (ammonia and/or low-temperature treatment at 393 K) were successfully applied to stabilize the mesoporous structure, resulting in significantly increased surface areas and pore volumes with respect to those of the untreated titania powders. Three of these samples were chosen for further investigation by adsorption microcalorimetry. These samples are characterized by high surface areas (varying between 340 and 141 m (2) g (-1)) and a varying degree of crystallization (anatase phase). The samples were compared to nanosized anatase particles treated to 873 K. The adsorption microcalorimetry was carried out using nitrogen and carbon dioxide at 77 and 303 K, respectively, to gain complementary information about the surfaces. Nitrogen at 77 K showed, for the three samples, adsorption enthalpies at low coverage of similar values, approximately -19 to -22 kJ mol (-1), indicating that the probe gas interacts with similar energetic surface sites. Two distinct energetic regions are observed, the first of which increases with increasing pretreatment temperature, which can be related to increased sample crystallinity. The adsorption of carbon dioxide at 303 K showed high adsorption enthalpies (up to approximately 65-80 kJ mol (-1)), highlighting strong interactions of the carbon dioxide with the titania surface at low pressures. Finally, the CO(2) adsorption properties of the titania samples (adsorbed amount and enthalpies of adsorption) are compared with those of other nanosized adsorbents. This comparison shows the potentiality of mesoporous titania powders for the adsorption of CO(2).

Self-assembled liquid crystalline nanoparticles as an ophthalmic drug delivery system. Part II: optimization of formulation variables using experimental design

Abstract In the field of keratoconus treatment, a lipid-based liquid crystal nanoparticles system has been developed to improve the preocular retention and ocular bioavailability of riboflavin, a water-soluble drug. The formulation of this ophthalmic drug delivery system was optimized by a simplex lattice experimental design. The delivery system is composed of three main components that are mono acyl glycerol (monoolein), poloxamer 407 and water and two secondary components that are riboflavin and glycerol (added to adjust the osmotic pressure). The amounts of these three main components were selected as the factors to systematically optimize the dependent variables that are the encapsulation efficiency and the particle size. In this way, 12 formulas describing experimental domain of interest were prepared. Results obtained using small angle X-rays scattering (SAXS) and cryo-transmission electron microscopy (cryo-TEM) evidenced the presence of nano-objects with either sponge or hexagonal inverted structure. In the zone of interest, the percentage of each component was determined to obtain both high encapsulation efficiency and small size of particles. Two optimized formulations were found: F7 and F1. They are very close in the ternary phase diagram as they contain 6.83% of poloxamer 407; 44.18% and 42.03% of monoolein; 46.29% and 48.44% of water for F7 and F11, respectively. These formulations displayed a good compromise between inputs and outputs investigated.

Perturbation induced formation of a 3D-network of microcrystals producing soft materials

Toluene and 1-chloronaphthalene immobilization was observed when perturbing stimuli such as agitation or ultrasound are applied during the cooling of a hot supersaturated solution of the rigid dinitroxide bTbk. X-Ray diffraction and cryo-SEM on gels and solid samples (crystal, powder) confirmed the pivotal role of clathrate type microcrystals in the solvent immobilization process.

Bottom-up solution chemistry approaches for nanostructured thermoelectric materials

Despite recent progress in the development of the thermoelectric power factor, improvement in the efficiency of thermoelectric materials remains limited. Over the past decade, almost all the significant advances have been made by the development of nanostructured materials. Both theoretical studies and experimental results bring out three main avenues of research for optimizing the engineering of these materials: (i) quantum confinement, (ii) phonon-blocking/electron transmitting and (iii) electron filtering barrier structures. The optimization of one or several of these parameters is dependent on the design of the materials that are very complex to synthesize and, for this reason, many of the studies remain merely of theoretical interest. A material allowing the optimization of all of these parameters is thus proposed. It is based on a nanostructured material (starting from a mesoporous matrix), within which it is possible to control the size and spacing of nanoparticles. In addition, some confined bismuth nanoparticles in this type of structure transform to a cubic phase, making it possible to avoid orientation problems related to the effective masses.

Organic multishell isostructural host-guest crystals: fullerenes C-60 inside a nitroxide open framework

The dinitroxide biradical crystallizes forming hexagonal open frameworks with one-dimensional corrugated channels filled with crystallization solvent. The large pockets constitutive of the channels allowed the inclusion of C(60) in the paramagnetic network. The rapidity and high fidelity of crystal growth were used to prepare isostructural multilayer host-guest crystals successively stained with C(60).

Wide Frequency Range Dispersion and Relaxations in Ceramics of the K6Li4Ta10O30–Pb5Ta10O30 System

Dielectric and impedance measurements were performed on ceramics with composition Pb 5x K 6(1-x) Li 4(1-x) Ta 10 O 30 , in wide frequency and temperature ranges, 10 1 to 10 9 Hz and 100 to 650 K, respectively. At low frequency and low temperature, a relaxor behavior is found for compositions corresponding to x > 0.70. Moreover, two other relaxations are observed: an ionic conduction relaxation at low frequency and high temperature and a network relaxation at high frequency and low temperature. The former is explained on the basis of the motion of Li + cations in sites of coordination number 9 and the latter on the basis of correlation chains.