1,721,018 research outputs found
Dielectric properties of two phases of crystalline lutetium oxide
No full textHigh-dielectric constant oxides are the focus of intense current research. As a contribution to the rationalization of the search for candidate materials, we compare the dielectric properties obtained from first-principles linear-response calculations for two phases-the ground state bixbyite and the competing hexagonal structures-of the crystalline oxide Lu2O3. The dielectric constants of bixbyite is about 12 and that of hexagonal is about 19 (the electronic constant being about 4.5 in both cases). This difference is due almost exclusively to the vibrational properties, with minor or no influence of charge anomaly differences; as these are related mainly to oxygen vibrations, we argue that the dielectric properties of sesquioxides will be determined mostly by their preferred structure, i.e. they will be poorer for bixbyite (e.g. Y2O3) than for hexagonal (e.g. La2O3) sesquioxides. (c) 2004 Elsevier Ltd. All rights reserved
Energetics of transient enhanced diffusion of boron in Ge and SiGe
No full textWe study the energetics and migration of boron in Ge and ordered, Si-epitaxial Si0.5Ge0.5 via first-principles calculations, considering specifically the interstitial-mediated mechanism previously associated with B transient enhanced diffusion in Si. The temperature dependence of the migration length lambda of a B-interstitial complex is calculated from migration barriers and dissociation energies. In Ge, the migration length hardly depends on temperature, while in SiGe it is similar to that in Si, due to the preference of B for Si-like equilibrium sites and diffusion paths. The calculated solubility of B in Ge is similar to that in Si, about 1x10(19) cm(-3). In Si-epi strained SiGe the solubility is instead enhanced by two orders of magnitude, and in free-standing SiGe by one order of magnitude. The calculated activation energy for B diffusion in Ge (similar to4.5 eV) is considerably higher than in Si (similar to3.6 eV) and in our model SiGe, in accordance with recent experiments
Impurity-vacancy complexes and ferromagnetism in doped sesquioxides
No full textBased on hybrid density-functional calculations, we propose that ferromagnetism in the prototypical bixbyite sesquioxide In2O3 doped with Cr is due to Cr-oxygen vacancy complexes, while isolated Cr cannot support carrier-mediated magnetic coupling. Our proposal is consistent with experimental facts such as the onset of ferromagnetism in O-lean conditions only, the low or vanishing net moment in unintentionally doped material, and its increase upon intentional doping. © 2014 American Physical Society
Efficient thermoelectricity in Sr2Nb2 O7 with energy-dependent relaxation times
No full textWe evaluate theoretically the thermoelectric efficiency of the layered perovskite Sr2Nb2O7 via calculations of the electronic structure and transport coefficients within density-functional theory and Bloch-Boltzmann relaxation-time transport theory. The predicted figure-of-merit tensor ZT, computed with energy-, chemical potential-, and temperature-dependent relaxation times, has one component increasing monotonically from around 0.4 at room temperature to 2.4 at 1250 K at an optimal carrier density of around 2×1020cm-3, while the other components are small. The Seebeck coefficient is about 250 to 300 μV/K at optimal doping and reaches 800 μV/K at lower doping. We provide a python code implementing various approximations to the energy-dependent relaxation-time transport, which can be used to address different systems with an appropriate choice of material parameters
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
A three-order-parameter bistable magnetoelectric multiferroic metal
Full text linkUsing first-principles calculations we predict that the layered-perovskite metal Bi5Mn5O17 is a ferromagnet, ferroelectric, and ferrotoroid which may realize the long sought-after goal of a room-temperature ferromagnetic single-phase multiferroic with large, strongly coupled, primary-order polarization and magnetization. Bi5Mn5O17 has two nearly energy-degenerate ground states with mutually orthogonal vector order parameters (polarization, magnetization, ferrotoroidicity), which can be rotated globally by switching between ground states. Giant cross-coupling magnetoelectric and magnetotoroidic effects, as well as optical non-reciprocity, are thus expected. Importantly, Bi5Mn5O17 should be thermodynamically stable in O-rich growth conditions, and hence experimentally accessible
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
Dielectric properties of high-kappa oxides: Theory and experiment for Lu2O3
No full textWe present a combined experimental and theoretical analysis of the dielectric and vibrational properties of crystalline lutetium oxide in its ground-state bixbyite structure. The vibrational dielectric function of Lu2O3 thin films grown by atomic-layer deposition was studied by infrared transmission and reflection-absorption spectroscopies, selectively accessing transverse and longitudinal optical frequencies. The static dielectric constant is extracted analyzing the infrared response. We also present first-principles density-functional linear-response calculations, which are in close agreement with experiment, and provide insight into the microscopic nature of vibrational spectra and dielectric properties
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