Susagna Ricart

Nanoscale strain-induced pair suppression as a vortex-pinning mechanism in high-temperature superconductors

Boosting large-scale superconductor applications require nanostructured conductors with artificial pinning centres immobilizing quantized vortices at high temperature and magnetic fields. Here we demonstrate a highly effective mechanism of artificial pinning centres in solution-derived high-temperature superconductor nanocomposites through generation of nanostrained regions where Cooper pair formation is suppressed. The nanostrained regions identified from transmission electron microscopy devise a very high concentration of partial dislocations associated with intergrowths generated between the randomly oriented nanodots and the epitaxial YBa(2)Cu(3)O(7) matrix. Consequently, an outstanding vortex-pinning enhancement correlated to the nanostrain is demonstrated for four types of randomly oriented nanodot, and a unique evolution towards an isotropic vortex-pinning behaviour, even in the effective anisotropy, is achieved as the nanostrain turns isotropic. We suggest a new vortex-pinning mechanism based on the bond-contraction pairing model, where pair formation is quenched under tensile strain, forming new and effective core-pinning regions.

Quatsomes: Vesicles Formed by Self-Assembly of Sterols and Quaternary Ammonium Surfactants

Thermodynamically stable nanovesicle structures are of high interest for academia and industry in a wide variety of application fields, ranging from preparation of nanomaterials to nanomedicine. Here, we show the ability of quaternary ammonium surfactants and sterols to self-assemble, forming stable amphiphilic bimolecular building-blocks with the appropriate structural characteristics to form in aqueous phases, closed bilayers, named quatsomes, with outstanding stability, with time and temperature. The molecular self-assembling of cholesterol and surfactant cetyltrimethylammonium bromide (CTAB) was studied by quasi-elastic light scattering, cryogenic transmission electron microscopy, turbidity (optical density) measurements, and molecular dynamic simulations with atomistic detail, upon varying the cholesterol-to-surfactant molar ratio. As pure species, CTAB forms micelles and insoluble cholesterol forms crystals in water. However, our molecular dynamic simulations reveal that the synergy between CTAB and cholesterol molecules makes them self-assemble into bimolecular amphiphiles and then into bilayers in the presence of water. These bilayers have the same structure of those formed by double-tailed unimolecular amphiphiles.

Acid anhydrides: a simple route to highly pure organometallic solutions for superconducting films

The presence of impurities in the precursor metal carboxylate solutions for the preparation of epitaxial thin films by metal organic decomposition (MOD) is substantially avoided by the use of acid anhydrides. In particular, trifluoroacetic anhydride (TFAA) was used for the synthesis of the starting Y, Ba and Cu trifluoroacetates used in YBa2Cu3O7?x (YBCO) preparation by the MOD process. In this way, highly stable organometallic precursors and a short pyrolysis process could be used leading to YBCO films with high critical currents (Jc ?2?4?MA?cm?2 at 77?K). Furthermore, the reproducibility of the results has been ascertained.

Deposition of photocatalytically active TiO2 films by inkjet printing of TiO2 nanoparticle suspensions obtained from microwave-assisted hydrothermal synthesis

In this paper, we present an inkjet printing approach suited for the deposition of photocatalytically active, transparent titanium oxide coatings from an aqueous, colloidal suspension. We used a bottom-up approach in which a microwave-assisted hydrothermal treatment of titanium propoxide aqueous solutions in the presence of ethylenediaminetetraacetic acid and triethanolamine was used to create suspensions containing titania nanoparticles. Different inkjet printing set-ups, electromagnetic and piezoelectric driven, were tested to deposit the inks on glass substrates. The presence of preformed titania nanoparticles was expected to make it possible to reduce the heating temperature necessary to obtain the functionality of photocatalysis which can widen the application range of the approach to heat-sensitive substrates. We investigated the crystallinity and size of the obtained nanoparticles by electron microscopy and dynamic light scattering. The rheological properties of the suspensions were evaluated against the relevant criteria for inkjet printing and the jettability was analyzed. The photocatalytic activity of the obtained layers was analyzed by following the decomposition of a methylene blue solution under UV illumination. The influence of the heat treatment temperature on the film roughness, thickness and photocatalytic activity was studied. Good photocatalytic performance was achieved for heat treatments at temperatures as low as 150 °C, introducing the possibility of using this approach for heat-sensitive substrates.

Organo-modified silica aerogels and implications for material hydrophobicity and mechanical properties

Two types of organo-modified silica gels, with the organic groups trimethoxymethylsilane (TRIMOS) and 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), have been synthesized. The wet gels were dried by supercritical evacuation of the solvent. The materials with enhanced performance were those hybridized with TRIMOS and dried above the critical conditions of methanol. Such aerogels were found to be hydrophobic with mechanically improved properties whilst still maintaining the characteristic transparency of pure silica aerogels. The condensation degree and the number of superficial hydroxyl groups were determined from solid-state 29Si-NMR spectroscopy. Mechanical properties were measured using nanoindentation.

Chemical solution deposition using ink-jet printing for YBCO coated conductors

This paper reports the successful application of ink-jet printing to the deposition of both continuous coatings and multi-filamentary structures of YBCO. Stable inks have been prepared using both the established TFA-MOD route and novel fluorine-free precursors with appropriate rheological properties for ink-jet printing. Continuous and well textured coatings with lengths exceeding 100?m and a thickness of 0.5??m have been deposited by electromagnetic ink-jet printing from TFA precursors on LZO-buffered Ni?W substrates and samples have achieved a Jc around 1.5?MA?cm?2 (self-field, 77?K). On single crystal substrates, continuous coatings and multi-filamentary structures have been deposited using piezoelectric ink-jet printing both from TFA-?and water-based precursors, achieving Jc values up to 3?MA?cm?2.

Conjugate additions to alkynylalkoxycarbenemetal (Cr or W) complexes

Abstract The addition of different nucleophilic compounds (aliphatic and aromatic alcohols, thiols and phosphines) to alkynylalkoxycarbene complexes has been studied. The reaction with smaller nucleophiles proceeds readily and regioselectively at the β-carbene position. With more substituted nucleophiles the reaction rate slowed down considerably. Addition of a catalytic amount of DBU (1,8-di-azabicyclo[5.4.0]undec-7-ene]) speeded up the reaction and improved the E/Z ratio.

Enhanced Vortex Pinning in YBCO Coated Conductors With BZO Nanoparticles From Chemical Solution Deposition

We present our latest results on the growth of chemical solution deposited YBa₂Cu₃O₇ - BaZrO₃ nanocomposites on metallic substrates. All chemical ^TFAYBCO-BZO/^MODCZO/^ABADYSZ/SS tapes with J_c(77K,sf) = 1.7 MA/cm² have been achieved with weaker field dependence of J_c than that of standard ^TFAYBCO tapes. Angular resolved measurements show isotropic enhancement of vortex pinning due to the presence of randomly oriented BZO nanoparticles in the YBCO matrix. Chemical routes are thus a promising way to efficiently increase vortex pinning in coated conductors and improve their capabilities for high field applications.

The nickel-catalyzed carbonylative cycloaddition of allyl halides and acetylenes: an efficient tool for cyclopentane annelation.

From a practical synthetic point of view, the nickel-mediated carbonylative cycloaddition of alkynes and allyl halides is a straightforward method for obtaining the cyclopentane skeleton in high yields and with controlled stereochemistry, especially when considering the efficiency of the intermolecular version of the reaction. The efforts to make the previously stoichiometric process catalytic in nickel, after experimental mechanistic observations, are reported herein. The unexpected intervention of iron as a reductant and the isolation of a final dimeric species that exhibits interesting tautomeric behavior are also presented. An extension of the reaction to new substrates has led to the conclusion that, although the steric and electronic effects of the alkyne substituents are generally irrelevant in relation to the adducts and their yields, those of the allylic counterpart may have a significant influence on the outcome of the reaction. However, the presence of the amine moiety in the alkyne completely inhibited the reaction. The feasibility of a multicentered reaction was verified with a triacetylene in which up to 12 bonds were created at once and in good yield.

Neutron and X-ray diffraction study of ferrite nanocrystals obtained by microwave-assisted growth. A structural comparison with the thermal synthetic route. Corrigendum

Corrigendum to J. Appl. Cryst. (2014), 47, 414–420.