1,721,054 research outputs found
Local Chemical Environment of Pr3+ Substitutional Defects in Bulk and Nanocrystalline Gd3Ga5O12: A Joint EXAFS and Luminescence Study
No full textA joint approach using EXAFS (extended X-ray absorption fine structure) and luminescence results has been used to obtain information on the local structure and the electron-phonon coupling of the Pr3+ ion in bulk and nanocrystalline gadolinium gallium garnet samples. The nanocrystalline sample is prepared with a combustion synthesis, whereas the bulk sample is prepared by a sintering procedure using the nanocrystalline powders. EXAFS measurements show that the Pr-O distances are similar for the bulk and the nanocrystalline samples but a notable amount of static disorder in the first coordination sphere of the dopant is found to be present in the nanocrystalline sample. From the behavior of the emission line width and shift of a Pr3+ emission band as a function of the temperature, the electron-phonon coupling strength of the Pr3+ ion has been evaluated. The electron-phonon coupling strength results to be notably stronger for the nanocrystalline sample than for the bulk one. This behavior is attributed to the fact that the local surrounding of the Pr3+ ion is softer for the nanocrystalline sample than for the bulk one
Susceptibility and evidences of charge carriers interaction above T-c in Nd1.85Ce0.15CuO4+delta
No full textThe refiEXAFS station at the GILDA beamline (BM08) of ESRF
No full textThe experimental station for measuring X-ray absorption spectra in total reflection geometry operative at the GILDA CRG beamline of ESRF is described. The main features of the station are shown, namely: the possibility of detecting very small signals from thin (a few ML) samples, of depositing thin films under controlled conditions and thermal treating the samples in order to study dynamical processes. Case studies are reported in order to show the performances of the apparatus
Phase stability of high entropy oxides: A critical review
No full textAfter the discovery of the prototypical high-entropy oxide with formula Cu0.2Zn0.2Mg0.2Co0.2Ni0.2O, the research on these materials has shown a dramatic boost. While many studies were devoted to exploring their possible applications, only few addressed the effective reasons behind their stability. The possibility to achieve a single-phase structure is usually hastily attributed to configurational entropy. This resulted in an extensive misuse of the terms “entropy-stabilized oxides” and “high-entropy oxides”, often employed as synonyms. However, the effective role of entropy in the stabilization should be demonstrated for each system, and even for Cu0.2Zn0.2Mg0.2Co0.2Ni0.2O it is still under debate. Moreover, many effects concur to the stabilization, i.e. the relative concentration, the valence state and the ionic radii of the cations involved. We will here discuss the role of configurational entropy in the phase stability, considering the main classes of crystal structures and providing a guide to critically discern between entropy and non-entropy stabilized oxides
Probing the initial stages of solid-state reactions by total reflection EXAFS (reflEXAFS)
No full textThe effectiveness of reflEXAFS as a probe for the very initial stages of solid-state reactions has been investigated by studying the local chemical environment of Ni during the reaction of a 150 Å thick film of NiO deposited onto Al2O3. The reaction to give the spinel phase requires temperatures about 1000 °C, and reaction progress degrees could be obtained by increasing the firing time at high temperature. At lower temperatures (≅930 °C), a structural rearrangement in the NiO film could be detected, seemingly related to the process by which local chemical equilibrium is attained at the interface. This should be regarded as the very early stage of the solid-state reaction and therefore this experiment proves the feasibility of a reflEXAFS investigation on these aspects of solid-state chemistry
Localized and itinerant electronic states at the insulator-metal transition in Y1-xCaxVO3+delta: evidence from electric transport, magnetic properties and XAS spectroscopy
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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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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