Maria Maddalena Carnasciali

Raman investigation of the composition and temperature-induced phase transition in (1-x)Pb(Fe2/3W1/3)O3-xPbTiO3 ceramics

The evolution with temperature of the Raman activity in the (1−x)Pb(Fe2∕3W1∕3)O3-xPbTiO3 solid solution with various compositions x∊(0,1) was investigated. By increasing x, a general evolution of the system from disordered relaxor to ordered ferroelectric state with typical lines also observed in other Pb-based relaxors were found. The Raman activity present at few hundred degrees above the Curie region confirms the thermal stability of the nanopolar ordered regions in a nonordered average cubic state. For all the examined samples, the position, intensity, or damping of a few Raman lines exhibit anomalies in a range of temperatures which was considered related to the Curie region. The range of Curie regions corresponding to each composition is in very good agreement with the shift of Curie temperature as a function of x found by previous dielectric investigations. Two sharp peaks in the Pb(Fe2∕3W1∕3)O3 spectra showed a maximum of their intensity at ≈500K. This behavior is interpreted as due to critical ch...

Synthesis and characterisation of superconducting RuSr2GdCu2O8

Abstract We report on the structural, electrical and magnetic properties of RuSr2GdCu2O8 samples made by systematic synthesis work so that they differ from one another in number of annealings and sintering temperature. Our aim is to highlight the different behaviours as a consequence of the thermal treatments. In particular, we deal with the onset of superconductivity in relation to the homogenisation process, and its influence on resistivity, structural and magnetic ordering. Finally, the problems related to the magnetic measurements due to the superimposition of different magnetic states are examined.

Evidence of the relaxor-paraelectric phase transition in Pb(Fe2/3W1/3)O3 ceramics

The transition relaxor-paraelectric in Pb(Fe2/3W1/3)O3 ceramics was studied by x-ray diffraction and Raman scattering at temperatures in the range of 85–800 K. For high diffraction angles (160° and 162°), a slight difference between the two phases was found. Raman spectra show an evolution with temperature with anomalies of bands of 848 cm−1 and 147 cm−1 (shift and intensity) in the Curie range of temperatures. This behavior is interpreted as an experimental evidence of perturbations of the nanopolar ordering related to the phase transition.

Correlations between Structural and Electronic Properties in the Filled Skutterudite Smy(FexNi1–x)4Sb12

A structural study of the filled skutterudite Smy(FexNi1-x)4Sb12 was performed by means of X-ray powder diffraction and μ-Raman spectroscopy with the aim to unveil the correlations between structural and electronic properties of this material and to favor the improvement of its thermoelectric performance. Samples were prepared by direct reaction of the elements at 1223 K, followed by quenching and subsequent sintering at 873 K; microstructure and composition of the obtained products were determined by SEM-EDS. The position of the boundary separating regions that obey hole- and electron-based conduction mechanisms was found by X-ray diffraction at x ≈ 0.63 and y ≈ 0.30, confirmed by measurements of room-temperature Seebeck coefficient, and discussed on the basis of crystallographic data. The presence of a discontinuity is observed in several structural and spectroscopic parameters at the p/n crossover; it is interpreted as associated with the change in the conduction mechanism. The role of the rare earth filling fraction in driving the structural response of the material is investigated too. The advantage of using X-ray diffraction and μ-Raman spectroscopy as aids in the study of electronic properties of this material is highlighted, as well as the complementarity of the two techniques.

1,3-Cycloaddition of Benzonitrile Oxides to Diazepines. I. 1-Ethoxycarbonyl-5-methyl-1,2-diazepine

Stable aryl nitrile oxides (1a-e) and 1ethoxycarbonyl-5-methyl-1,2-diazepine (2) undergo 1,3cycloaddition reactions to give isomeric 1,2,4oxadiazole (3), 4,5-dihydroisoxazole (4) and isoxazole (5) derivatives, the first one being in any case the most abundant product. Overall kinetics were measured at temperatures in the range 50-90°C, in 1,1,2,2tetrachloroethane and mixtures of the latter with DMF; rate coefficients for the parallel reactions were, thus, obtained. Substituent and solvent effects are discussed

Topics on the preparation of HTSC via solid state reaction and melting process

The problems of the preparation of High Temperature Superconductors by sintering and melting are examined. Results of the thermal properties of the total substitution of Yttrium by a rare earth element are reported. The process of fabrication of HTSC after high temperature decomposition is indicated. The results of first characterisation are also reported.ZusammenfassungProbleme der Herstellung von Hochtemperatur-Supraleitern durch Sinter- und SchmelzvorgÄnge wurden untersucht.Es werden Resultate der thermischen Auswirkungen der vollstÄndigen Substitution von Yttrium durch Seltenerdelemente wiedergegeben. Der Prozess einer Herstellung von HT-Supraleitern nach thermischer Zersetzung im Bereich hoher Temperatur wird beschrieben, und es werden Resultate erster Charakterisierungen mitgeteilt.

Search for new superconducting oxides in M4Pn2O phases (M=Ca, Sr, Ba and Pn=As, Sb, Bi)

Abstract All the high- T c oxide superconducors known to date are copper-based oxides (cuprates) in the layered perovskite crystal structures that contain a planar network of copper and oxygen (CuO 2 plane). In searching for possible new superconducting metal oxides without Cu ions, we have examined the layered tetragonal pnictides M 4 Pn 2 O (M=Ca, Sr, Ba and Pn=As, Sb, Bi) because their structures are considered as an anti-perovskite with alternate stacking of two kinds of layers; conducting M 2 Pn 2 block layers sandwiched by insulating perovskite-based M 2 O layers. Compounds were prepared by melting stoichiometric amounts of the components in tantalum tube all sealed under an argon atmosphere. The samples have been characterised by scanning electron microscopy, powder X-ray diffraction (XRD), metallographic examination and electrical resistivity. For these stoichiometric compounds no superconductive transition is observed.

8-Chloro-6-phenyl-4H-[1,2,4]­triazolo­[4,3-a][1,5]­benzodiazepin-5(6H)-one

The title compound, C16H11ClN4O, is an anticonvulsant agent. In the crystal, a particularly short C—H⋯N intermolecular hydrogen bond is noted [H⋯N 2.22 (2) A]. The diazepine ring has a boat conformation.

A Characterisation Study on Modern Bronze Sculpture: The Artistic Patinas of Nado Canuti

ABSTRACT Artistic patination is a traditional colouring technique for metal sculpture, employed by artists in ancient and modern times for aesthetic purposes. Today, knowledge of the artistic value and the chemistry of this superficial chromatic layer, called ‘artistic patina’, can be successfully acquired through a close collaboration between living artists, foundry artisans, and scientists. Starting from several interviews with the Italian artist Nado Canuti and foundry artisans, specific information was gathered about patination methods and the artist’s attitude towards materials restoration. Afterwards, the patinas most used by Canuti were reproduced to study their nature before any ageing or degradation. Their chromatic values, morphologies, and compositions were studied employing a range of techniques such as colour measurements, scanning electron microscopy with energy dispersive X-ray spectroscopy, and micro-Raman spectroscopy. The collected data revealed the formation of main compounds (cuprite, cassiterite, rouaite, chalcocite, isocubanite, and ferroxyhite) and additional compounds (atacamite and CN-containing compound). The scientific results, as well as the artist’s statements concerning the patinas’ significance, maintenance, and conservation, will contribute towards the future care and preservation of Canuti’s sculptures.

Ionic conductivity and local structural features in Ce1-xSmxO2-x/2

Sm-Doped ceria is one of the most promising materials to be used as electrolyte in solid oxide fuel cells due to its remarkable ionic conductivity values in the intermediate temperature range. Transport properties and local structural features of Ce1-xSmxO2-x/2 (0.1 ≤ x ≤ 0.7) were studied by an impedance/μ-Raman spectroscopy coupled approach up to 1073 K. Results suggest that C-based nanosized defect clusters are responsible for the drop in ionic conductivity observed even at x = 0.2, i.e. at a Sm content lower than necessary to allow C domains to reach the percolation threshold through crystallites. Moreover, within the fluorite-type compositional region, with increasing the Sm content, defect clusters undergo a rearrangement resulting in the enlargement of C-based domains rather than in the increase of their number; at higher x, on the contrary, both the size and amount of C domains increase in parallel.