http://hdl.handle.net/2117/1312 2013-05-21T07:20:06Z http://hdl.handle.net/2117/18850 Title: Polymorphism in halogen-ethane derivatives: CCl3-CCl3 and ClF2C-CF2Cl Authors: Negrier, Philippe; Tamarit Mur, José Luis; Barrio Casado, María del; Mondieig, Denise Abstract: The polymorphism of hexachloroethane, Cl3C−CCl3, has been reinvestigated by means of X-ray and neutron scattering. The long time unknown structure of the intermediate phase II of Cl3C−CCl3 has been determined as monoclinic C2/m, with lattice parameters a = 17.9835(21) Å, b = 10.3642(11) Å, c = 6.3014(8) Å, and β = 94.410(5)° at 323 K, Z = 6. The polymorphism of 1,2-dichloro-1,1,2,2-tetrafluoro-ethane, ClF2C−CF2Cl, has also been investigated, and the structure of the intermediate phase II has been found to be orthorhombic (Cmca, Z = 4) with lattice parameters a = 6.305(4) Å, b = 10.177(12) Å, c = 8.714 (7) Å. The high-temperature phase I of ClF2C− CF2Cl has been found to be isomorphous with the orientationally disordered phase I of Cl3C−CCl3 (body centered cubic, Im3̅m), a consequence of the pseudospherical molecular shape of halogeno-ethane C2X6−nYn (X = Cl, Y = F) molecular crystals. The similarities of the intricate disorder of the intermediate phases II of both Cl3C−CCl3 and ClF2C−CF2Cl compounds are analyzed, together with the influence of the conformational disorder appearing in the last compound. 2013-04-17T10:40:00Z http://hdl.handle.net/2117/18803 Title: Crystal structure and solid-state properties of 3,4-diaminopyridine dihydrogen phosphate and their comparison with other diaminopyridine salts Authors: Mahe, N.; Nicolaï, B.; Allouchi, Hassan; Barrio Casado, María del; Do, Bernat; Céolin, René; Tamarit Mur, José Luis; Rietveld, Ivo B. Abstract: 3,4-Diaminopyridine is an active pharmaceutical ingredient for the treatment of Lambert−Eaton myasthenic syndrome (LEMS). It is 3,4-diaminopyridine dihydrogen phosphate that has become the active ingredient of choice. As part of a larger study for the development of this drug, solid-state studies have been carried out. At room temperature, the crystals are monoclinic (C2/c). Dihydrogen phosphate anions H2PO4 − form infinite chains parallel to the b axis, and these chains can be considered as macroanions (H2PO4)∞. The organic cations form hydrogen bonds with the macroanions bridging them together. A negative thermal expansion is observed along the [103] direction in the crystal, which coincides with the direction of chains of interchanging anions and cations. The crystal packing shows similarities with the hydrogen tartrate salt as illustrated by a Hirshfeld surface analysis. This phosphate and this tartrate salt are also the two diaminopyridine salts that have been selected for therapeutic use because of their appropriate physical properties. 2013-04-15T15:29:38Z http://hdl.handle.net/2117/18490 Title: Modeling of the effect of temperature, frequency, and phase transformations on the viscoelastic properties of AA 7075-T6 and AA 2024-T3 Aluminum Alloys Authors: Rojas Gregorio, José Ignacio; Crespo Artiaga, Daniel Abstract: The viscoelastic response of commercial aluminum alloys 7075-T6 and 2024-T3 as a function of temperature is presented. Experimental data are obtained with a dynamic-mechanical analyzer (DMA) at different loading frequencies and compared with the available transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) data. The effect of successive microstructural transformations (particle precipitation and redissolution) is revealed. An ana- lytical model is developed, which fits the mechanical response up to 573 K (300 C). The model takes into account the concentration of Guinier-Preston Zones (GPZ) and metastable precipi- tates ( g ¢ in AA 7075-T6 and h ¢ /S ¢ in AA 2024-T3), allowing us to determine the kinetic parameters of these transformations. The activation energies were previously obtained by sev- eral authors from DSC measurements and other techniques, showing considerable dispersion. The presented data, obtained with a completely different technique, allow us to reduce the uncertainty on these data and show the potential of DMA measurements in the study of microstructural transformations. 2013-03-22T12:31:18Z http://hdl.handle.net/2117/17756 Title: Uniaxial negative thermal expansion in crystals of tienoxolol Authors: Nicolaï, Beatrice; Rietveld, Ivo B.; Barrio Casado, María del; Mahé, Nathalie; Tamarit Mur, José Luis; Céolin, René; Guéchot, Christophe; Teulon, Jean-Marie Abstract: The thermal expansion of tienoxolol has been investigated by X-ray powder diffraction up to its melting temperature. The data indicate that the expansion is anisotropic and even negative in one direction of the unit cell. The supramolecular structure formed by hydrogenbonds reflects that of a trellis, which explains the observed behavior of tienoxolol crystals. 2013-02-14T10:53:07Z http://hdl.handle.net/2117/17573 Title: Molecular conformation in organic films from quantum chemistry ab initio calculations and second harmonic spectroscopy Authors: Macovez, Roberto; López, Núria; Mariano, Marina; Maymó Camós, Marc; Martorell Pena, Jordi Abstract: Identifying molecular species and conformations at surfaces is of interest for both catalytic and biointerfacial research. Here, we present an extinction and second harmonic spectroscopy study of films of crystal violet together with quantum chemistry ab initio calculations on several conformation geometries of this dye. By comparing experimental and theoretical data, we identify the molecular species responsible for the spectral resonances, and we ascribe the nonlinear optical generation to pyramidal conformers with nonzero dipolar hyperpolarizability. Our results, which are consistent with recent findings on alcohol solutions of the same dye, help to settle a long-standing debate and demonstrate that nonlinear second harmonic spectroscopy is a valuable tool for identifying and probing molecular conformation in interfacial systems. 2013-02-05T08:38:55Z http://hdl.handle.net/2117/17406 Title: Influence of a magnetic field applied during the quenching process on the spin density and nanoscale structure of an amorphous Fe-B ribbon Authors: Bonastre, J.; Suñol Martinez, Juan Jose; Bruna Escuer, Pere; Sato, K.; Santos, J.D.; Hernando, B. Abstract: The application of a magnetic field to the melt in the transverse direction of the wheel rotation during the solidification process induces magnetic anisotropy in amorphous magnetic ribbons. This procedure is here applied to a FeB amorphous alloy in order to check their influence on local electronic and nanoscale structure by comparing two samples (as quenched without field and field quenched). The existence of magnetic domains was showed via the Bitter technique. Mössbauer spectra analysis confirms an increase in the spin density (from 28 to 48%) in the applied field direction for the field quenched ribbon. Positron lifetime spectra analysis determines that at room temperature there is no influence on the nanoscale structure, but the annealing at 300 °C provokes the beginning of the nanocrystallization process in the field quenched sample while the samples as quenched without field remain fully amorphous. 2013-01-17T16:09:40Z http://hdl.handle.net/2117/17108 Title: SPHERS, Jïlich's high-flux neutron backscattering spectrometer at FRM II Authors: Wuttke, Joachim; Budwig, Alfred; Drochner, Matthias; Kämmerling, Hans; Kayser, Franz-Joseph; Kleines, Harald; Ossovyi, Vladimir; Pardo Soto, Luis Carlos; Prager, Michael; Richter, Dieter; Schneider, Gerald J.; Schneider, Harald; Staringer, Simon Abstract: SPHERES is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Jülich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 μeV, a dynamic range of ± 31 μeV, and a signal-to-noise ratio of up to 1750:1. 2012-12-12T09:30:05Z http://hdl.handle.net/2117/16940 Title: Spiral vortices between concentric cylinders Authors: Sánchez Umbría, Juan; Crespo Artiaga, Daniel; Marqués Truyol, Francisco Abstract: Spiral vortices appearing in Couette- Taylor flows are studied by means of numerical simulation. Transition curves from Couctte to spiral vortices for different radius ratios and wavenumbers have been calculated in order to test our technique. Critical Reynolds numbers, angular velocities and slopes of the spirals at the onset of the instability agree with previous results [1]. Non-linear solutions obtained by a pseudospectral collocation method are studied, and they show a weak net axial ftow. In arder to counteract this effect, which is absent in the usual experimental set-up, an axial pressure gradient has been included. This procedure has proved to be sufficient to make the axial flow negligible. The onset of a quasiperiodic flow for larger Reynolds numbers, corresponding to a secondary bifurcation is also presented. 2012-11-16T17:50:05Z http://hdl.handle.net/2117/16736 Title: Composition, nanostructure, and optical properties of silver and silver-copper lusters Authors: Pradell Cara, Trinitat; Pavlov, R.S.; Gutiérrez Repiso, Carolina; Climent Font, Aurelio; Molera Marimon, Judit Abstract: Lusters are composite thin layers of coinage metal nanoparticles in glass displaying peculiar optical properties and obtained by a process involving ionic exchange, diffusion, and crystallization. In particular, the origin of the high reflectance (golden-shine) shown by those layers has been subject of some discussion. It has been attributed to either the presence of larger particles, thinner multiple layers or higher volume fraction of nanoparticles. The object of this paper is to clarify this for which a set of laboratory designed lusters are analysed by Rutherford backscattering spectroscopy, transmission electron microscopy, x-ray diffraction, and ultraviolet-visible spectroscopy. Model calculations and numerical simulations using the finite difference time domain method were also performed to evaluate the optical properties. Finally, the correlation between synthesis conditions, nanostructure, and optical properties is obtained for these materials. 2012-10-16T17:09:04Z http://hdl.handle.net/2117/16161 Title: Overall stability for the ibuprofen racemate: experimental and topological results leading to the pressure-temperature phase relationships between its racemate and conglomerate Authors: Rietveld, Ivo B.; Barrio Casado, María del; Do, Bernard; Tamarit Mur, José Luis; Céolin, René Abstract: Enantiomer resolution is much sought after for pharmaceutical applications, because many optically active drug molecules have only one pharmaceutically active enantiomer. Although it is always possible to force separation, it will come at a cost. The present method, based on thermodynamics, provides a relatively easy approach to investigate whether separation can be thermodynamically spontaneous. A topological phase diagram of the binary enantiomer system at 0.5 mol-fraction is constructed as a function of temperature and pressure after analysis of pressure and heat related quantities. It is demonstrated that for ibuprofen, an optically active analgesic, the racemate is the only stable solid form; the phase relationship between the racemate and the conglomerate is analogous to dimorphism with overall monotropy in pure chemical compounds. 2012-06-29T10:38:45Z http://hdl.handle.net/2117/15765 Title: Emergence of glassy-like dynamics in an orientationally ordered phase Authors: Romanini, Michela; Negrier, Philippe; Tamarit Mur, José Luis; Capaccioli, Simon; Barrio Casado, María del; Pardo Soto, Luis Carlos; Mondieig, Denise Abstract: The dynamics of a simple rigid pseudoglobular molecule (2-adamantanone) has been studied by means of dielectric spectroscopy and examined under the constraints imposed by the space group of the crystal structure determined by x-ray powder diffraction. The low-temperature monoclinic structure of 2-adamantanone, with one molecule per asymmetric unit (Z'= 1), displays a statistical intrinsic disorder, concerning the site occupancy of the oxygen atom along three different sites. Such a physically identifiable disorder gives rise to large-angle molecular rotations which inherently lead to time-average fluctuations of the molecular dipole, thus contributing to the dielectric susceptibility. The dielectric spectra for the low-temperature “ordered” phase displays a universal feature of glassy-like materials, i.e., coexistence of α- and β-relaxation processes. The former is clearly identified with the strongly restricted reorientational motions within the long-range “ordered” crystalline lattice. The latter, never observed before in fully translationally and highly orientationally ordered phases, displays all the properties of an original Johari-Goldstein β-relaxation, in spite of the strong character of this glass-like phase. These findings can be explained according to the coupling model, applied to such “ordered” phases. 2012-04-26T10:29:38Z http://hdl.handle.net/2117/15531 Title: Polymorphism in halogen-ethane derivatives: CCl3-CF2Cl and CF3-CF2Cl Authors: Negrier, Philippe; Barrio Casado, María del; Tamarit Mur, José Luis; Pardo Soto, Luis Carlos; Mondieig, Denise Abstract: Molecular crystals of halogen–ethane derivatives C2X6–nYn (X = Cl, Y = F) are known to display order–disorder phase transitions involving changes of the translational, orientational, and conformational order. The appearance of a high-temperature orientationally disordered phase with a high symmetry lattice is expected for this set of compounds in view of their “pseudospherical” molecular geometry. In this work, we present a study of polymorphism of the compounds 1,1,1,2-tetrachloro-2,2-difluoroethane (CCl3–CF2Cl) and 1-chloro-1,1,2,2,2-pentafluoroethane (CF3–CF2Cl), in which conformational disorder is not present, by combining neutron (D2B and D1B instruments at the Laue-Langevin Institute) and X-ray scattering experiments. We show that despite the close molecular shapes and molecular structures of both compounds, strong differences concerning the disorder appear in the low-temperature phase. The low-temperature phase for CF3–CF2Cl is found to be fully ordered, with a monoclinic P21/n structure (Z = 4), while that of CCl3–CF2Cl is found to be orthorhombic Pmna (Z = 4) with a disorder concerning one Cl and one F sites, each one with a fractional occupancy of 50%. Details related to the high-temperature orientationally disordered phases (both body-centered-cubic) are also given. 2012-03-09T08:56:42Z http://hdl.handle.net/2117/15081 Title: Surface hubbard U of alkali fullerides Authors: Macovez, Roberto Abstract: Wereport a combined photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES) study of distilled, phase pure films of C60 and the monomeric fullerides Cs6C60, Cs4C60 and fcc RbC60. The separation between the highest energy PES and lowest energy IPES features, which is a measure of the barrier to hopping, is 1.45 eV in Cs4C60 and 0.7 eV in RbC60. This difference is large enough to explain, in a correlated electron picture, the reported differences in electronic mobility between the two stoichoimetries. From the PES-IPES energy separation, the value of the Hubbard U is estimated to be 1.5 eV in closed-shell C60 and Cs6C60, while in Cs4C60 and RbC60 such value is reduced to∼1 and 0.7 eV, respectively. This trend can be only partially understood taking into account the different molecular polarizability and crystal structure of the various stoichiometries. The relatively low values found for open-shell compounds indicate that the bulk Hubbard U is smaller in open-shell fullerides than usually believed, which might help explain superconductivity and the observation of spin-singlets in odd-stoichiometry fullerides. 2012-02-13T10:00:24Z http://hdl.handle.net/2117/14970 Title: Effects of internal molecular degrees of freedom on the thermal conductivity of some glasses and disordered crystals Authors: Davydova, N. A.; Baran, J.; Jezowski, A.; Krivchikov, A.I.; Korolyuk, O.A.; Sharapova, I.V.; Tamarit Mur, José Luis; Bermejo, F.J.; Pardo Soto, Luis Carlos; Rovira Esteva, Muriel; Ruíz Martín, María Dolores Abstract: The thermal conductivity κ(T ) of the fully ordered stable phase II, the metastable phase III, the orientationally disordered (plastic) phase I, as well as the nonergodic orientational glass (OG) phase, of the glass former cyclohexanol (C6H11OH) has been measured under equilibrium vapor pressure within the 2–200 K temperature range. The main emphasis is here focused on the influence of the conformational disorder upon the thermal properties of this material. Comparison of results with those regarding cyanoclyclohexane (C6H11CN), a chemically related compound, serves to quantify the role played by the terminal groups -OH and -CN on the phonon scattering processes. The picture that emerges shows that motions of such groups do play a minor role as scattering centers, both within the low-temperature orientationally ordered phases as well as in the OG states. The results are analyzed within the Debye-Peierls relaxation time model for isotropic solids comprising mechanisms for long-wave phonon scattering within the OG and orientational ordered low-temperature phases, as well as others arising from localized short-wavelength vibrational modes as pictured by the Cahill-Pohl model. By means of complementary neutron and Raman scattering we show that in the OG state the energy landscapes for both compounds are very similar. 2012-02-06T13:24:55Z http://hdl.handle.net/2117/14858 Title: Determination of wind speed and associated loads over the sports facility collapsed during the severe windstorm of 24 January 2009 in Sant Boi de Llobregat (Barcelona) Authors: Mazón Bueso, Jordi; Crespo Artiaga, Daniel; Pino González, David Abstract: The severe windstorm of 24 January 2009, caused by an explosive cyclogenesis, affected coastal and precoastal areas of the northeast of the Iberian Peninsula, where damages were numerous and significant, both in urban areas and in forests. One of the most important effects was the collapse of a sports facility in Sant Boi de Llobregat (10 km southwest of Barcelona), killing four children. The objective of this study is to estimate the wind speed over the sports facility and calculate the suction of the wind on the roof of the building, and the consequent collapse of the walls. To get a first approximation, a simulation of the episode around the time of maximum wind gust was inspected using the mesoscale model MM5. In the second part, the damage around the collapsed facility was analyzed, with which we note the fact that a truck was dragged and knocked over by the wind. This analysis allows for the conclusion that, in conjunction with the maximum wind gust, there was a sudden and very local shift in the wind, which caused the gust to hit the building head on. Based on this observation, the wind speed on surface and at 7 m (roof of the building) was estimated, and the suction of the wind was calculated 2012-01-27T17:27:48Z