1,721,080 research outputs found
Silvia PALLECCHI, I mortaria di produzione centro-italica. Corpus dei bolli.
No full textDesy Philippe. Silvia PALLECCHI, I mortaria di produzione centro-italica. Corpus dei bolli. . In: L'antiquité classique, Tome 76, 2007. pp. 484-485
Silvia PALLECCHI, I mortaria di produzione centro-italica. Corpus dei bolli.
No full textDesy Philippe. Silvia PALLECCHI, I mortaria di produzione centro-italica. Corpus dei bolli. . In: L'antiquité classique, Tome 76, 2007. pp. 484-485
Uncollapsed LaFe2 As2 phase: Compensated, highly doped, electron-phonon-coupled, iron-based superconductor
No full textThe recently discovered LaFe2As2 superconducting compound, member of the 122 family of iron pnictide superconductors, becomes superconducting below TcGëê13K, yet its nominal doping apparently places it in the extreme overdoped limit, where superconductivity should be suppressed. In this work, we investigate the normal state of magneto- and thermoelectric transport and specific heat of this compound. The experimental data are consistent with the presence of highly compensated electron and hole bands, with Gê+0.42 electrons per unit cell just above Tc, and high effective masses Gê+3m0. The temperature dependence of transport properties strongly resembles that of conventional superconductors, pointing to a key role of electron-phonon coupling. From this evidence, LaFe2As2 can be regarded as the connecting compound between unconventional and conventional superconductors
Synthesis and magnetic properties of ZnFe2O4 obtained by mechanochemically assisted low-temperature annealing of mixtures of Zn and Fe oxalates
No full textThe mechanism of formation of zinc ferrite (ZnFe2O4) from ZnC2O4·1.8H2O–2FeIIC2O4·2H2O and ZnC2O4·1.8H2O–Fe2
III(C2O4)3·6H2O mixtures is investigated. By combination of TG and XRPD measurements it has been shown that microcrystalline ZnFe2O4 forms from physical mixtures after prolonged annealing at 1000 ◦C while nanocrystalline ZnFe2O4 powders are produced by mild annealing (1 h at 500 ◦C in air) of mechanically activated mixtures. The magnetic properties of ZnFe2O4 powders obtained from physical and from milled mixtures are compared
Synthesis and Structural Characterization of Sb-Doped TiFe2Sn Heusler Compounds
No full textTernary Heusler compounds form a numerous class of intermetallics, which include two families with general compositions ABC and AB2C, usually referred to as half- and full-Heusler compounds, respectively. Given their tunable electronic properties, made possible by adjusting the chemical composition, these materials are currently considered for the possible use in sustainable technologies such as solar energy and thermoelectric conversion. According to theoretical predictions, Sb substitution in the TiFe2Sn full-Heusler compound is thought to yield band structure modifications that should enhance the thermoelectric power factor. In this work, we tested the phase stability and the structural and microstructural properties of such heavily doped compounds. We synthesized polycrystalline TiFe2Sn1−xSbx samples, with x = 0, 0.1, 0.2 and 1.0 by arc melting, followed by an annealing treatment. The structural characterization, performed by x-ray powder diffraction and microscopy analyses, confirmed the formation of the pseudo-ternary Heusler structure (cF16, Fm-3m, prototype: MnCu2Al) in all samples, with only few percent amounts of secondary phases and only slight deviations from nominal stoichiometry. With increasing Sb substitution, we found a steady decrease in the lattice parameter, confirming that the replacement takes place at the Sn site. Quite unusually, the as-cast samples exhibited a higher lattice contraction than the annealed ones. The fully substituted x = 1.0 compound, again adopting the MnCu2Al structure, does not form as stoichiometric phase and turned out to be strongly Fe deficient. The physical behavior at room temperature indicated that annealing with increasing temperature is beneficial for electrical and thermoelectrical transport. Moreover, we measured a slight improvement in electrical and thermoelectrical properties in the x = 0.1 sample and a suppression in the x = 0.2 sample, as compared to the undoped x = 0 sample
Review on thermoelectric properties of transition metal dichalcogenides
No full textTransition metal dichalcogenides (TMDs) are considered an advantageous alternative to their celebrated two-dimensional (2D) van der Waals akin compound, graphene, for a number of applications, especially those requiring a gapped and possibly tunable band structure. Thermoelectricity is one of the application fields where TMDs could indeed outperform graphene, thanks to their lower thermal conductivity, large effective masses, valley degeneracy, varied and tunable transport properties, as well as sensitivity of their band structures and phonon spectra to confinement. Yet, despite promising theoretical predictions, thermoelectric properties of TMDs have not been extensively investigated so far and a clear assessment of TMDs as viable thermoelectric materials, based on experimental results, is still missing. In this paper, we review the experimental findings of literature on thermoelectric properties of TMDs, to sort out the countless combinations of chemical compositions, doping, off-stoichiometry and sample forms which could potentially result in optimized and possibly competitive thermoelectric properties. Based on the experimental data of literature, we simulate the performance of an all-TMD thermoelectric device for practical application as a micron sized cryocooler or power generator
Ink-jet printing and drop-casting deposition of 2H-phase SnSe2 and WSe2 nanoflake assemblies for thermoelectric applications
No full textThe development of simple, scalable, and cost-effective methods to prepare Van der Waals materials for thermoelectric applications is a timely research field, whose potential and possibilities are still largely unexplored. In this work, we present a systematic study of ink-jet printing and drop-casting deposition of 2H phase SnSe2 and WSe2 nanoflake assemblies, obtained by liquid phase exfoliation, and their characterization in terms of electronic and thermoelectric properties. The choice of optimal annealing temperature and time is crucial for preserving phase purity and stoichiometry and for removing dry residues of ink solvents at interflake boundaries, while maximizing the sintering of nanoflakes. An additional pressing is beneficial to improve nanoflake orientation and packing, thus enhancing electric conductivity. In nanoflake assemblies deposited by drop casting and pressed at 1 GPa, we obtained thermoelectric power factors at room temperature up to 2.2 × 10-4 mW m-1 K-2 for SnSe2 and up to 3.0 × 10-4 mW m-1 K-2 for WSe2
Thermal and voltage activated excess 1/f noise in FeTe0.5Se0.5 epitaxial thin films
No full textWe report on measurements of electric transport and voltage noise in FeTe0.5Se0.5 epitaxial thin films. Detailed structural investigations demonstrate the high quality of the samples, also testified by a superconducting transition temperature of 18 K, larger than the value observed for bulk compounds. An unusual dependence of the 1/f noise is found by varying the applied voltage and the temperature. Above a threshold voltage the 1/f noise shows a nonquadratic dependence on applied voltage with a temperature-dependent exponent. Conversely, at low voltages the 1/f noise amplitude follows always a quadratic law. In the superconductive transition region, a simple percolative model allows one to estimate the dimensionality of the system, which is found to be two-dimensional, with a critical exponent similar to values reported for other high-Tc superconductors. The experimental findings on noise properties give evidence of unusual transport processes, occurring in this new superconducting material, and can provide useful information on possible conduction mechanisms
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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