1,720,990 research outputs found
Rietveld refinement using Debye-Scherrer film techniques
No full textThe advent of modern diffractometers has overcome the old film techniques that were used during the past years. One reason is that computer-controlled diffractometers made available data in a formal ready for the analyses, and the intensities obtained do not suffer for non-linear correction and are very much reliable. The Rietveld method also is established on data obtained from Bragg-Brentano diffractometers equipped with scintillation detectors. However recently, a need for speeding up the analyses is growing, and several experiments have been made to use position-sensitive detectors or energy dispersive detectors for data collection. Very little effort has been involved to resume the old film techniques, coupled with microphotometer systems, that can be used potentially as low cost position sensitive detectors. The film method can be easily improved by simple collection strategies and arrangement on the film-scanning side. The Rietveld method has be successfully applied to the data obtained by the Debye-Scherrer film-technique for structure refinement of a corundum and a quartz samples. A comparison with the results obtainable by a standard Bragg-Brentano diffractometer has been made. Another advantage of the present measurement method is that slight preferred orientations can be easily corrected by rotating the capillary sample holder.The advent of modern diffractometers has overcome the old film techniques that were used during the past years. One reason is that computer-controlled diffractometers made available data in a format ready for the analyses, and the intensities obtained do not suffer for non-linear correction and are very much reliable. The Rietveld method also is established on data obtained from Bragg-Brentano diffractometers equipped with scintillation detectors. However recently, a need for speeding up the analyses is growing, and several experiments have been made to use position-sensitive detectors or energy dispersive detectors for data collection. Very little effort has been involved to resume the old film techniques, coupled with microphotometer systems, that can be used potentially as low cost position sensitive detectors. The film method can be easily improved by simple collection strategies and arrangement on the film-scanning side. The Rietveld method has be successfully applied to the data obtained by the Debye-Scherrer film-technique for structure refinement of a corundum and a quartz samples. A comparison with the results obtainable by a standard Bragg-Brentano diffractometer has been made. Another advantage of the present measurement method is that slight preferred orientations can be easily corrected by rotating the capillary sample holder
Materials and technological aspects of gilded buckles from a North Eastern Medieval Italian context
No full textThis study concerns the archaeometric characterization
of two artefacts from the medieval site of San Rocco
(Castelfranco Veneto, Italy). Both of them belong to a larger
set of metallic objects, some being part of tomb ornaments
belonging to two very well distinct periods of frequentation
of the site. Both items are buckles and they have been selected
as representative of two very well-known and established
typologies. The older one, at the end of the sixth—
beginning of the seventh century AD, is made of silver, although
relicts of gold have been found. A number of relevant
counterparts of this item have been found in different
sites of the Longobard Italy. The main body of the second
artefact (second half of the fourteenth century AD) consists
of a bent strip of a copper rich alloy, coated on one side
with a nearly continuous, decorated, gold layer. This is a socalled
lyre-buckle, with a widespread diffusion not only in
Italian, but also North European contexts. From the results
of the analyses carried out using low-vacuum scanning electron
microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometry, information on manufacturing, gilding
technology and materials have been obtained that will be an
useful benchmark for the archaeometric characterization of
similar items from selected collections. In this way, the already
established typological affinity of these two classes
of items will be extended to technological and materials aspects,
also
Combining XRD and XRF analysis in one Rietveld-like fitting
No full textX-ray diffraction (XRD) and X-ray fluorescence (XRF) are widely used analytical techniques for materials characterization; the information they provide can be considered complementary, as the former is mostly used to obtain crystallographic information and analyze phase content, whereas the latter is sensitive to elemental composition. Many researchers and technologists working in a variety of application fields already use them together in some sort of a “combined” approach, by separately performing XRD and XRF data collection and analysis on the same sample and then comparing the analytical results obtained to integrate and complement the respective analytical information. In this work, we propose a true combined approach to merge both XRD and XRF data acquisition and analysis. Custom analytical X-ray instrumentation has been developed to perform the simultaneous data acquisition, by using a single X-ray source and dedicated detectors to collect the diffracted and fluorescent X-ray photons from the same sample volume. Additionally, a combined XRD/XRF data analysis methodology has been implemented by extending Rietveld based code to incorporate the full pattern fitting of XRF spectra starting from the phases instead of a simple matrix elemental composition. We report two analytical examples from different application fields to better illustrate the capabilities of the proposed approach
Characterization of nanograined powder samples using the Rietveld method applied to electron diffraction ring patterns
Full text linkA full-pattern fitting procedure based on the Rietveld method was applied to electron diffraction ring patterns of a two-phase system, exhibiting the co-presence of zinc sulfide (sphalerite) and zinc oxide (Wurtzite). Bright and dark field (DF) images reveal the presence of micrometric aggregates, composed of quasi-spherical nanosized crystallites. These conventional transmission electron microscopy imaging methods provide a general morphological characterization of the specimens although, in the present case, they are not suitable for a detailed characterization of the microstructural features of the analyzed samples. Owing to the overlap and broadening of the diffraction rings of the two phases, DF images cannot provide a satisfactory picture of the individual crystallites of each single phase. To overcome this limit, the mentioned Rietveld approach was applied to model the electron diffraction data. The crystalline domain size and relevant shapes for both phases were successfully evaluated using the proposed methodological approach. The excellent results obtained in the microstructural characterization of the nanostructured multiphase samples demonstrate the capability of this technique, that may represents a fully quantitative method for the routine characterization of crystalline nanomaterials
Highly crystalline strontium ferrites SrFeO3-δ: an easy and effective wet-chemistry synthesis
No full textThe synthesis of strontium ferrite SrFeO3−δ has been explored through wet-chemistry methods in order to optimize a quick, easy and reproducible method to obtain the perovskite in pure crystalline form with a high yield. Among the three investigated synthetic paths, (i) coprecipitation of hydroxides, (ii) coprecipitation of oxalates and (iii) polyol-assisted coprecipitation, only the second one was effective in obtaining the desired perovskite modification as a single phase. The products were analyzed by means of powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), to determine the crystalline structure and the chemical composition of the sample surface, respectively, and to optimise the synthetic process. Pure samples were further characterised by means of inductively coupled plasma (ICP-AES) analysis, nitrogen adsorption, elemental analysis, temperature programmed reduction (TPR) and Mössbauer spectroscopy.Due to their important and diverse properties, mixed transition metal oxides having perovskite crystal structures have long been object of academic studies and technological applications. In this framework, strontium ferrite SrFeO3-x holds particular interest due to its capability to act as both an electronic and ionic conductor at high temperatures (oxygen ions migrate through vacancies in its crystal structure) and thus employable both in fuel cells (as an electrode) and in oxygen concentrating devices. Moreover this compound is also endowed with remarkable magnetic and catalytic properties. In this work, the perovskite SrFeO3-x has been obtained through an easy, reproducible and cost-effective wet-chemistry coprecipitation route. Firstly, three synthetic paths have been explored: i) coprecipitation of hydroxides from an aqueous solution, ii) coprecipitation of oxalates from an aqueous solution and iii) polyol-assisted coprecipitation. Products of all three synthetic paths were analyzed by means of powder X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) to determine the crystalline structure and the chemical composition of the sample surface and to optimize the synthetic process. These analyses revealed that only the coprecipitation of oxalates was effective in obtaining the desired perovskite modification as a single phase. Pure samples were further characterized by means of Inductive Coupled Plasma (ICP-MS) analysis, nitrogen adsorption, elemental analysis, temperature programmed reduction (TPR) and Mössbauer spectroscopy. In particular, Mössbauer spectroscopy was used to analyze the oxidation states and magnetic properties of the iron atoms contained in the sample, thus also allowing to estimate the correct oxygen content
Characterization of the mistura alloy used for Venetian sesino coins: 16th century
No full textThe information provided by material investigations on ancient coins is interesting in many respects, as concerns the archaeological and historical research. In this study a set of Venetian sesino coins, minted over a period ranging from 1554 until 1605, have been investigated in order to shed light on some aspects of the so‐called mistura (mixture) alloy. The widespread diffusion of these relatively low‐value coins of the Venetian Republic, commonly used in commercial transactions in the second half of 16th century, also outside the territories of the Republic, makes them an important proxy to be used in the reconstruction of the political and historical events of the period. The specific issue of the actual composition of the mistura alloy is herewith addressed for the first time, using a combined approach based on X‐ray fluorescence and X‐ray diffraction nondestructively applied to the analysis of the samples. It turns out that the mistura alloy, traditionally regarded as a Cu‐Ag two phase alloy, over the latest period of circulation of the sesino coins, was actually made of copper only, still containing minor concentrations of lead, to be regarded as an impurity of the alloy and not as an intentional addition
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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