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1.
A. Bianconi Y. Busby M. Fratini V. Palmisano L. Simonelli M. Filippi S. Sanna F. Congiu A. Saccone M. Giovannini S. De Negri 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):495-501
Here we report synthesis and characterization of high quality samples of the superconducting system Mg1−x
Al
x
B2, with a novel optimized preparation method, in a wide range of Al concentration. All the physical properties of the samples
can be tuned continuously with increasing Al content. We have characterized the samples for their structural, morphological
and magnetic properties with high resolution XRD, SEM-EDS and susceptibility measurements. We have prepared a large number
of Al doped MgB2 in the range 0<x<0.57. All the samples are bulk superconductors and the critical temperature show a smooth and regular behavior as a function
of x.
This work was supported by European project 517039 “Controlling Mesoscopic Phase Separation” (COMEPHS) (2005).
An erratum to this article can be found at 相似文献
2.
Costa A. Buffa G. Palmeri D. Pollara G. Fratini L. 《Journal of Intelligent Manufacturing》2022,33(7):1967-1989
Journal of Intelligent Manufacturing - It is well known that the processing parameters of selective laser melting (SLM) highly influence mechanical and physical properties of the manufactured... 相似文献
3.
In the paper the microstructural phenomena in terms of average grain size occurring in friction stir welding (FSW) processes are focused. A neural network was linked to a finite element model (FEM) of the process to predict the average grain size values. The utilized net was trained starting from experimental data and numerical results of butt joints and then tested on further butt, lap and T-joints. The obtained results show the capability of the AI technique in conjunction with the FE tool to predict the final microstructure in the FSW joints. 相似文献
4.
M. Fratini G. Campi L. Simonelli V. Palmisano S. Agrestini M. Filippi N. L. Saini A. Bianconi 《Journal of Superconductivity and Novel Magnetism》2005,18(5-6):671-674
The interstitial oxygen ordering in a La2CuO4+ y (y = 0.08) single crystal with a T c = 38 K has been investigated. We have studied the growth dynamics of the three dimensional (3D) ordered phase, called Q2, at different temperatures under X-ray illumination. The critical temperature T 0~334 K of the order-disorder transition for the Q2 phase has been determined. We have found that the illumination of the sample with a continuous polarized synchrotron radiation X-ray flux stimulates the oxygen ordering kinetics. The photoinduced ordering process shows a threshold characteristic of cooperative phenomena and its kinetics shows a temperature dependence that is controlled by the activation energy E A = 100 meV. 相似文献
5.
V. Palmisano S. Agrestini G. Campi M. Filippi L. Simonelli M. Fratini A. Bianconi S. De Negri M. Giovannini A. Saccone A. N. Fitch M. Brunelli I. Margiolaki 《Journal of Superconductivity and Novel Magnetism》2005,18(5-6):737-741
The thermal lattice expansion in the superconducting Mg1? x Al x B2 system (x = 0, 0.13, and 0.59) has been measured using high-resolution X-ray powder diffraction. An unusual large negative thermal expansion (NTE) appears for temperatures below T * = 60 K in the MgB2. The NTE effect increases in Mg0.87Al0.13B2 and disappears at high Al content in the Mg0.59Al0.41B2 where the temperature dependence of volume follows a standard Einstein model in the whole temperature range. The anomalous behavior of the thermal expansion provides a direct evidence in the physics of diborides for the relevance of the proximity to the 2.5 Lifshitz electronic topological transition where the Fermi surface of the σband changes from a two-dimensional (2D) to a three-dimensional (3D) topology. 相似文献
6.
Alessandro Ricci Michela Fratini Antonio Bianconi 《Journal of Superconductivity and Novel Magnetism》2009,22(3):305-308
We report the temperature-dependent x-ray powder diffraction of the FeAs-based superconductors in the range between 300 and
95 K. In the case of NdOFeAs we have detected the structural phase transition from the tetragonal phase, with P4/nmm space
group, to the orthorhombic phase, with Cmma space group, over a broad temperature range from 150 to 120 K, centered at T
0∼137 K. This transition is reduced, by about ∼30 K, by the internal chemical pressure going from LaOFeAs to NdOFeAs. On the
contrary, the superconducting critical temperature increases from 27 to 51 K going from LaOFeAs to NdOFeAs doped samples.
The FeAs layers in all undoped “1111” and “122” systems suffer a tensile misfit strain. The tensile misfit strain is reduced
in “1111” and in “122” samples and at optimum doping the misfit strain is close to zero. This result shows that the normal
striped orthorhombic Cmma phase competes with the superconducting tetragonal phase. In the orthorhombic clusters the charges
can move only along the stripes in the b direction and are localized by the magnetic interaction. 相似文献
7.
Gianluca Buffa Davide Campanella Livan Fratini Fabrizio Micari 《International Journal of Material Forming》2016,9(5):613-618
Friction Stir Extrusion is a novel technique for direct recycling of metal scrap. In the process, a dedicated tool produces both the heat and the pressure to compact and extrude the original raw material, i.e., machining chip, as a consolidated component. A proper fixture was used to carry out an experimental campaign on Friction Stir Extrusion of AZ31 magnesium alloy. Variable tool rotation and extrusion ratio were considered. Appearance of defects and fractures was related to either too high or too low power input. The extruded rods were investigated both from the metallurgical and mechanical points of view. Tensile strength up to 80 % of the parent material was found for the best combination of process parameters. A peculiar 3D helical material flow was highlighted through metallurgical observation of the specimens. 相似文献
8.
M. Geiger F. Micari M. Merklein L. Fratini D. Contorno A. Giera D. Staud 《International Journal of Machine Tools and Manufacture》2008,48(5):515
To develop steel aluminium-tailored hybrids in a butt joint for sheets in a thickness of about 1 mm conventional Friction Stir Welding is not feasible due to a high distortion of the welded specimen. Contrary to Friction Stir Welding the tool used for Friction Stir Knead Welding has no pin wherefore higher welding speeds can be realised. Due to the fact that this is a newer process, applied for patent in 2005, the cut contours of the edges and their variations have to be optimised by numerical analysis to transfer a maximum of load in order to improve the formability. The examined materials in this paper are steel DC04, as well as the aluminium alloys AA5182 and AA6016 in sheet thicknesses of 1 mm. Accompanying experimental investigations, as tensile tests, will evaluate the quality of the welding mechanism. As the mechanics of the new welding technology is not fundamentally investigated until now, metallographic investigations are performed, and additionally micro hardness measurements are carried out to verify the changes in the hardness distribution in the welding zone after stirring and welding. 相似文献
9.
A. Forcellese L. Fratini F. Gabrielli F. Micari 《Journal of Materials Processing Technology》1996,60(1-4):225-232
The effects of the punch nose radius and sheet thickness on the elastic springback and residual stresses in the 90° V-punch and U-die bending process of AA 5083 aluminium alloy have been extensively studied by numerical simulations based on the finite element method. The results show that, irrespective of the sheet thickness and punch stroke, the springback ratio is not affected by the punch nose radius. Such results are in excellent agreement with the experimental ones obtained in similar conditions. As far as punch nose radius effects on the residual stresses are considered, significant differences were observed between residual stresses predicted with different nose radii. In particular, the shifting of the neutral layer and increase in the magnitude of the residual stresses predicted by the FEM code were found with decreasing punch nose radius. 相似文献
10.
D. Innocenti A. Ricci N. Poccia G. Campi M. Fratini Antonio Bianconi 《Journal of Superconductivity and Novel Magnetism》2009,22(6):529-533
The phase separation between a striped polaron liquid at the particular density and a high density polaron liquid is described
by a modified Van der Waals scheme. The striped polaron liquid represents the pseudo gap matter or Wigner-like polaron phase
at 1/8 doping in cuprate superconductors. The model includes the tendency of pseudo-Jahn-Teller polarons to form anisotropic
directional bonds at a preferential volume with the formation of different “liquid phases”. The model gives the coexistence
of a first low density polaron striped liquid and a second high density liquid that appears in cuprate superconductors for
doping larger than 1/8. We discuss how the strength of anisotropic bonds controls the variation the phase separation scenarios
for complex systems in the presence of a quantum critical point where the phase separation vanishes. 相似文献