1,721,072 research outputs found
Ferroelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 ceramics
Get PDFDifferent processing conditions and the effect of secondary phases on ferroelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT) are studied. Ceramic powders are prepared by solid state reaction and different sintering temperatures (temperatures between 1075 and 1150ºC) are analyzed. Finally, samples are characterized by X-ray diffraction, Raman microspectroscopy, Scanning Electron Microscopy, impedance spectroscopy, and density measurements. Through XRD patterns, the perovskite structure is stabilized; together with small peaks corresponding to a secondary phase associated with K2-xNaxTi6O13 phase. Moreover, the content of the secondary phase, d33 piezoelectric constant and dielectric properties increase with sintering temperature.Fil: Camargo, Javier Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Ramajo, Leandro Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Rubio Marcos, Fernando. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin
Influences of secondary phases on ferroelectric properties of Bi(Na,K)TiO3 ceramics
Get PDFThe effect of secondary phases on ferroelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT) is studied. Ceramic powders are prepared by the solid-state reaction method where the influence of different sintering temperatures is also studied. Then, samples are characterized by X-ray diffraction (XRD), Raman microspectroscopy, Scanning Electron Microscopy and impedance spectroscopy. Through XRD and Raman results,the perovskite structure is detected; together with small peaks corresponding to a secondary phase associated with a K2xNaxTi6O13-based phase. The secondary phases amount increases with the sintering temperature, yielding different combinations of K2xNaxTi6O13- and Bi0.5(Na1yKy)0.5 TiO3-based phases. Moreover, the content of the secondary phase improves the d33 piezoelectric constant and dielectric properties of BNKT ceramics. These results can benefit the understanding of BNKT ceramics and the expanding of their applications range.Fil: Ramajo, Leandro Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Camargo, Javier Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Rubio Marcos, Fernando. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentin
Dielectric and ferroelectric properties evolution of (1−x)(Bi0.5Na0.5TiO3)–xK0.5Na0.5NbO3 piezoceramics
No full textIn this work, piezoceramics of (1-x)(Bi0.5Na0.5)TiO3-x(K0.5Na0.5)NbO3, (1-x)BNT-xKNN, composition with x=0.01, 0.02, 0.03, 0.04, 0.05, 0.06 and 0.07 were prepared by a mechanochemically activated solid-state method. The structural phase formation and microstructural, dielectric and ferroelectric properties were studied. Although changes, in symmetry of the perovskite structure, were not detected with the composition (that is, from a perspective of its intrinsic properties), the microstructural evolution was strongly dependent on the content of the KNN phase (that is, based on its extrinsic properties). Specifically, KNN favoured the formation of a microstructure with cubic grains, typical morphology of the alkaline niobate ceramics. After KNN addition, both the maximum permittivity temperature and the long-range to short-range ordered transition temperature were reduced. Additionally, ferroelectric loops and strain deformation curves also reflect the long-range to short-range order evolution with KNN addition and temperature.Fil: Prado Espinosa, Fabiola Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Rubio Marcos, Fernando. Instituto de Cerámica y Vidrio de Madrid; EspañaFil: Ramajo, Leandro Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin
Revealing the role of cationic displacement in potassium-sodium niobate lead-free piezoceramics by adding W6+ ions
Get PDFThe effect of the structural modifications induced by the replacement of the B sites with W6+ ions in (K0.44Na0.52Li0.04)[(Nb0.86Ta0.10Sb0.04)1-xW5x/6]O3 lead free ceramics is investigated. Here we show the coexistence between a tetragonal symmetry (T) and an orthorhombic symmetry (O) in the perovskite structure, which is tuned by varying the doping level. In addition, this polymorphic behaviour is accompanied by the appearance of a secondary phase, which can be detected through XRD and Raman results. A correlation between the presence of both structural features and the W6+ content has been evaluated, and therefore this lead free system reveals a transition from a normal ferroelectric to a 'relaxor-like' ferroelectric due to the cation disorder in the perovskite-structure in doped samples. A large diffusivity value (γ) has been attained when the x value reached 0.05 owing to the involved O-T polymorphic phase, as well as due to the appearance of a secondary phase. The experimental proof makes clear that the role of the secondary phase is to capture the alkali ions of the (KNa)NbO3-based system, provoking a cation disorder in the perovskite-structure matrix. The significance of this work lies in evaluating whether such a material can benefit the understanding of (KNa)NbO3-based ceramics and the expansion of their application range.Fil: Ramajo, Leandro Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; ArgentinaFil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; ArgentinaFil: del Campo, A.. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Fernandez, J.F.. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Rubio Marcos, Fernando. Instituto de Ceramica y Vidrio de Madrid; Españ
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
New insights into the properties of KxNa(1-x)NbO3 ceramics obtained by hydrothermal synthesis
Get PDFDifferent reaction conditions for the hydrothermal synthesis of KxNa(1-x)NbO3 (KNN) were studied. Samples were synthesized at 190°C in a Teflon lined autoclave and the effects of different KOH/(KOH+NaOH) ratios (0 to 0.8) and total hydroxide concentration (2 to 8N) on the microstructural and electrical properties of KNN were analyzed. A sodium rich phase with a monoclinic structure has been obtained, in which the orthorhombic phase coexists as detected by X-ray diffraction. These analyses also revealed that the x value in the KxNa(1-x)NbO3 system gradually increases with the increasing KOH/(KOH+NaOH) ratio and total hydroxide concentration. Samples with higher potassium content showed higher density and improved electrical behavior. An exhaustive characterization by Confocal Raman Microscope allowed the observation of the ferroelectric domain structure in KNN ceramics. It was established that the grain boundaries constrain the 90º domain walls in order to reduce the stress accumulated by the orthorhombic and the monoclinic phase coexistence within the KNN grains.Fil: Ramajo, Leandro Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Misiones. Facultad de Ingenieria; ArgentinaFil: Rubio Marcos, Fernando. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Del Campo, Adolfo. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Fernandez, José F.. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Parra, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentin
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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