1,721,034 research outputs found
Order-/disorder phenomena of rare earth metal/calcium compounds
No full textSeltenerdmetall-/Calciumverbindungen sind aus strukturchemischer Sicht von großem Interesse. In Abhängigkeit von Ionenradien und Ladung der Seltenerdmetalle sind ausgeprägte Ordnungs-/Unordnungsphänomene für diese Verbindungen zu erwarten.
Nitride der Zusammensetzung (RxCa4−xNy)Bi2 mit R = La, Ce, Pr, und (EuCa2N0,74)Sn wurden Pulver synthetisiert. Während für die Verbindungen (RxCa4−xNy)Bi2 eine Teilordnung R/Ca bestimmt werden konnte, liegen Eu/Ca im kubischen Perowskit (EuCa2N0,74)Sn ungeordnet vor. Erstmalig wurde mit (EuCa2N0,74)Sn ein nitridischer inverser Perowskit dargestellt, in der das Seltenerdmetallion gemischtvalent vorliegt.From structure-chemical point of view rare earth metal/calcium compounds are of great interest. Distinctive order-/disorder phenomena are expected, depending on ionic radii and charge of the rare earth metal. Nitrides of the composition (RxCa4−xNy)Bi2 with R = La, Ce, Pr, and (EuCa2N0,74)Sn were synthesized. While a partial order R/Ca was determined for the compound (RxCa4−xNy)Bi2, no indication for Eu/Ca order was observed for the cubic Perovskite (EuCa2N0,74)Sn. The compound (EuCa2N0,74)Sn represents the first inverse Perovskite nitride with a mixed oxidation state of the rare earth metal
Synthesis and characterization of ternary and quaternary nitrides of the main group elements
No full textIm Rahmen dieser kumulativen Dissertation werden insbesondere die Nitride in Systemen der Art Erdalkalimetall - Tetrel - Stickstoff beleuchtet, sowie das kristallographische Computerprogramm Polynator vorgestellt.
Der Fokus liegt auf ternären Nitridogermanaten, Nitridosilicaten, sowie inversen Perowskiten. Letztere auch als Antiperowskite bekannt und treten hier mit Erdalkalimetallkationen, kleinen Nitridanionen und größeren Tetrelidanionen auf. Für diese Verbindungen werden Elpasolithartige Überstrukturen sowie drei vormals ganz unbekannte Vertreter beschrieben.
In Form von Silicid-Silicaten bzw. Germanid-Germanaten werden die ersten Verbindungen von Silicium und Germanium vorgestellt, die das jeweilige Element sowohl in seiner höchsten Oxidationsstufe +IV, als auch in seiner niedrigsten Oxidationsstufe -IV enthalten. Zudem werden unter anderem die ersten Nitridogermanate(III) vorgestellt, wobei ein neuartiges, ethananaloges Molekülanion gefunden wurde.
Das Programm Polynator dient zur Identifikation von Polyedern und anderen Baueinheiten in Kristallstrukturen, sowie zur quantitativen Analyse ihrer Geometrie, Symmetrie und Verknüpfungsmuster. Dabei macht es innovativen Gebrauch von dynamischen Modellen, die nicht nur eine bestimmte Form repräsentieren, sondern ein Kontinuum von verwandten Formen (zum Beispiel alle trigonalen Prismen). Es verfügt über eine graphische Benutzeroberfläche und ist in der Lage, CIF- XYZ- und MOL-Dateien einlesen
Synthesis, Characterization, <em>in-situ</em> and <em>ex-situ</em><em></em> High-pressure Behavior, Phase Transition and Properties of copper nitride, iron nitrides and iron Carbonitrides
No full textEs wurden phasenreine Precusoren von Kupfernitrid, Eisennitriden und Eisencarbonitriden synthetisiert und charakterisiert. Mit nachfolgenden in-situ Versuchen mit Synchrotronstrahlung in einer Diamantstempelzelle und ex-situ Versuchen in einer Vielstempel-Presse mit einem beheizten 2-stufigen Walker-Modul wurde das Hochdruckverhalten sowie mögliche Phasenumwandlungen untersucht. Kupfernitrid zeigt eine reversible Phasenumwandlung oberhalb von 5 GPa mit einer Hysterese von 2 GPa, die mit einer Halbleiter–Metall-Umwandlung ein hergeht. Mit Versuchen bei hohen Drücken und Temperaturen wurden in einer Vielstempel-Presse zum ersten Mal Eisennitrid-Einkristalle verschiedener Zusammensetzung aus dem weiten Homogenitätsbereich der Epsilon-Phase synthetisiert und charakterisiert. Die Synthese erfolgte entweder aus der Epsilon-Phase, aus ζ-Fe2N oder aus γ-Fe4N durch Phasenumwandlung und anschließender Kristallisation.Single phase precusors of copper nitride, iron nitrides and iron carbonitrides were synthesized and characterized. With subsequent in-situ experiments in a dimond anvil cell and synchrotron radiation and ex-situ experiments in a multi anvil device with a two-stage Walker-type module the hgih-pressure behavior as well as possible phase transitions are investigated. Copper nitride shows a reversible phase transition above5 GPa with a hysteresis of 2 GPa which is accompanied by a semiconducter to metal transition. Experiments at high pressures and high temperatures in a multi-anvil device leads for the first time to single crystals with various compositions in the large homogeneity range of the epsilon phase, which were synthesized and characterized. The synthesis started either from the epsilon phase, ζ-Fe2N or γ′-Fe4N via a phase-transition und subsequent crystallisation
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
New ternary nitrides – chemical structure and physical properties
No full textLanthanid-Übergangsmetall-Nitride können aufgrund starker kovalenter Bindungsanteile zwischen Übergangsmetall und Stickstoff oft als Nitridometallate beschrieben werden. Ce2[CrN3] konnte als mikrokristallines Pulver synthetisiert und strukturchemisch charakterisiert werden. Nach Untersuchungen zur elektronischen Struktur und magnetischen Suszeptibilität sowie Ergebnissen von Ce-LIII-Kantenspektroskopie kann Cer die Oxidationsstufe IV zugeordnet werden. Ce2[CrN3] ist damit als Nitridochromat(I) anzusehen.
Die Synthese von Li8EN2 (E = Se, Te) gelang über Festkörperreaktionen aus Li3N und Li2E. Nach der strukturchemischen Charakterisierung auf Grundlage von Röntgen- und Neutronenbeugungsdaten kann die Anionenteilstruktur als hierarchische Variante der kubischen Laves-Phase beschrieben werden. Neutronen- (3 – 300 K) und Röntgenbeugungsexperimente mit Synchrotronstrahlung (298 – 1000 K) zeigen keine Hinweise auf Phasenumwandlungen. Trotzdem belegen 7Li-NMR-spektroskopische Untersuchungen eine Mobilität der Li-Ionen oberhalb Zimmertemperatur.Lanthanide transition metal nitrides can often be described as nitridometalates due to strong covalent interactions between the transition metal and nitrogen. Ce2[CrN3] was synthesized as a microcrystalline powder, and its structure was determined. After investigation of the electronic structure and magnetic susceptibility as well as results from edge-spectroscopy at the Ce-LIII threshold, cerium can be assigned the oxidation sate IV. Thus, Ce2[CrN3] is a nitridochromate(I).
The synthesis of Li8EN2 (E = Se, Te) succeeded by a solid state reactions from Li3N and Li2E. Structural characterization using X-ray and neutron diffraction data reveals that the anionic substructure can be described as hierarchical variant of the cubic Laves phase. Neutron (3 – 300 K) and X-ray diffraction using synchrotron radiation (298 – 1000 K) show no indications for phase transitions. Nevertheless, 7Li-NMR-spectroscopic investigations support a mobility of lithium ions
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
Oxonitridosilicate chlorides-synthesis, single-crystal X-ray and neutron powder diffraction, chemical analysis and properties of Ln(4) Si4O3+N-x(7-x) Cl1-xOx with Ln = Ce, Pr, Nd and x approximate to 0.2
No full textThe isotypic oxonitridosilicate chlorides Ln(4)[Si4O3+xN7-x]Cl1-xOx with Ln = Ce, Pr, Nd and x approximate to 0.2 were obtained by the reaction of the respective rare-earth metals, their oxides and chlorides with "Si(NH)(2)" in a radiofrequency furnace at temperatures around 1800 degrees C, using CsCl as a flux. The crystal structures were determined by single-crystal X-ray diffraction (P2(1)3, no. 198, Z = 4, Cc: a = 10.4461(12)pm, R1 = 0.0524; Pr: a = 10.3720(12)pm, R1 = 0.0415; Nd: a = 10.3618(12) pm, R1 = 0.0257) and found to be isotypic with Ce-4[Si4O4N6]O. In order to characterize the incorporation of chlorine into the structure, the crystallographic site occupation factors of O, N and Cl were determined by neutron powder diffraction. Furthermore, these results were substantiated by the chemical analyses for Pr-4[Si4O3+xN7-x]Cl1-xOx and electron microprobe analyses for all of the synthesized oxonitridosilicate chlorides. Temperature-dependent magnetic Susceptibility measurements of the cerium and the praseodymium compound indicate Curie-Weiss behavior with experimentally determined magnetic moments of 2.15(5) mu(B)/Ce and 3.50(5) mu(B)/Pr, respectively. No magnetic ordering could be detected down to 2 K. The 4f(I) of cerium has been confirmed by XAS measurements
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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