Publicaciones: Nanocomposites Multifuncionales

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10

Sep 2018

Investigation of the order -disorder phase transition series in AuCu by in-situ temperature XRD and mechanical spectroscopy

Posted by / in Publicaciones 2019, Publicaciones Materiales Multifuncionales y Nanocomposites 2019, Publicaciones: Nanocomposites Multifuncionales, Últimas Publicaciones CINN / No comments yet

In-situ temperature XRD and mechanical spectroscopy were applied to study phase transitions in AuCu alloy from the disordered FCC state (A1). The phase transition temperature intervals were investigated upon heating and cooling using a rate of 1 K/min in order to be thoroughly determined. The following sequences of phase transitions were recorded upon continuous heating: A1->AuCuI ->AuCuII->A1 and on subsequent cooling: A1 ->A1þAuCuIþAuCuII ->AuCuIþAuCuII ->AuCuI. This transition sequences determine also temperature dependency of elastic and anelastic properties. Mechanical spectroscopy using a forced torsion pendulum shows a peak due to antiphase boundaries motion characterizing the orthorhombic phase AuCuII and a transient peak with the that appears in the tetragonal phase AuCuI together with the classical Zener peak in the A1 phase.

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13

Jun 2018

Synthesis, crystal structure, DFT (B3LYP/LanL2DZ) and photoluminescence study of new stanate (IV) based inorganic-organic hybrid

Posted by / in Publicaciones Materiales Multifuncionales 2018, Publicaciones Materiales Multifuncionales y Nanocomposites 2017, Publicaciones: Nanocomposites Multifuncionales / No comments yet

A novel interesting metal hybrid stanate compound, named as hexachlorostanate (II) 4.4′ bipyridinium and formulated as (C10H10N2) SnCl6, was synthesized at room temperature by slow evaporation and then characterized by a single X-ray diffraction, spectroscopic measurements, Scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence technique. It crystallizes in the space group C2/c with the following unit cell parameters: a = 17.9611 (13) Å, b = 12.9274 (5) Å, c = 7.6305 (6) Å and β = 117.860 (10) °. The structure can be described by the alternation of two different cationic-anionic layers. It consists of isolated [SnCl6] 2- octahedral anions and 4.4′ bipyridinium (C10H10N2) cations, which are connected via N-H⋯Cl hydrogen bonds forming a chain network. The Hirshfeld surface analysis was conducted to investigate intermolecular interactions and associated 2D fingerprint plots, revealing the relative contribution of these interactions in the crystal structure quantitatively. The optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of the present compound were theoretically examined by the DFT/ B3LYP method with the LanL2DZ basis set. The X-ray powder is in agreement with the X-ray structure. 13C NMR spectrum shows three signals, confirming the solid state structure determined by X-ray diffraction. Photoluminescence measurements showed a strong emission line at 2.95 eV associated with radiative recombinations of excitons confined within the [SnCl6] 2- which were investigated at room temperature.

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26

Apr 2018

Metastable phase in binary and ternary 12-carat gold alloys at low temperature

Posted by / in Publicaciones Destacadas, Publicaciones Materiales Multifuncionales 2018, Publicaciones: Nanocomposites Multifuncionales, Publications 2018, Últimas Publicaciones CINN / No comments yet

Low temperature phase transitions in 12-carat gold alloys have been investigated for binary Au-Cu and ternary Au-Cu-Ag compositions. The thermal analyses investigations using differential scanning calorimetry (DSC) and the dilatometry were performed in the 50–300 °C temperature range in order to detect the structural transformations. The thermal analyses were carried out on annealed samples at 700 °C for two hour followed by water quenching. They reveal an important new reaction for both used compositions and both thermal techniques confirm each other. This reaction has been assessed as pre-ordering reaction. SEM and STM imaging were performed on annealed samples at 700 °C for two hours and water quenched followed by a heating from room temperature up to the temperature of the new peaks obtained in the thermal study. The imaging reveals the relationship between the pre-ordering reaction and the surface aspect presented in the fact of dendrite precipitates. A series of SEM observation have been performed in order to follow the kinetic of the observed precipitates by the way of several series of heating up, from 140 to 220 °C for the binary composition and from 100 to 180 °C for the ternary composition. Furthermore, this study shows that the silver accelerates the ordering reaction.

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