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Influência dos íons Cu2+ nas propriedades ópticas dos pós de (Ca1-x Cux)TiO3 preparados por métodos químicos
(Universidade Federal de São Carlos, 2012-10-29) Oliveira, Larissa Helena de; Varela, José Arana; https://lattes.cnpq.br/1807399214239200; https://lattes.cnpq.br/1461337173265474
The influence of Cu2+ doping as well as the preparation methods on the structural, morphological and optical properties of (Ca1-xCux)TiO3 powders with (x= 0; 0,01; 0,02; 0,04 and 0,10) of Cu2+ were studied in this work. The copper ions has been chose to replace the A site in the CaTiO3 perovskite, by the fact that structural defects related to covalent character of Cu-O linkages are created in the CaTiO3 crystalline structure. This effect is able to change the polarization or charge density of CaO12 and TiO6 clusters in the matrix, influencing its optical properties. The studied systems were synthesized by the microwave assisted hydrothermal method (HM) and Polymeric precursor method (PPM). These powders were structurally and morphologically characterized by X-ray diffraction (XRD), Rietveld refinement, micro-Raman (MR) spectroscopy, volumetric gas adsorption of Brunauer, Emmett e Teller (BET) method and field emission scanning electron microscopy (FE-SEM). Finally, their optical properties were investigated by ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) measurements. XRD patterns, Rietveld refinement indicated that these crystals present a perovskite-type CaTiO3 orthorhombic structure and space group Pbnm. MR spectroscopy indicated the presence of strtuctural defects which are associated to the introduction of Cu2+ ions in the A site of the perovskite.The presence of structural defects which are able to modify the polarization and/or charge density into the lattice, influencing its optical properties. Moreover, the reduction in band gap (Egap) observed for these systems is also related to them. The defects and distortions into lattice at medium- and short-range on the [CaO12]/[TiO6] clusters promotes the structural order-disorder responsible for the intense PL properties of these systems. The powders morphology are also influenced by the experimental procedure employed in the systems preparation. These materials are promising candidates for future applications in optical devices.
Entre idas e vindas, entre ganhos e perdas: as trajetórias de camponeses brasileiros em vivências na fronteira boliviana com o Acre
(Universidade Federal de São Carlos, 2012-10-29) Silva, Diego Correia da; Valêncio, Norma Felicidade Lopes da Silva; https://lattes.cnpq.br/7161606146208875; https://lattes.cnpq.br/9335706646959912
The induced migration is a constitutive and persistent part of the Brazilian state strategies in the Amazon occupation process and, particularly, in the Acre occupation process as well. However, the incessant concentration of the means of production especially land and the local resistance movements apart has generated the expulsion of some groups to beyond the Brazilian border. These groups occupied the Bolivian side of the border as an alternative, even though precarious to keep their economical survival, without losing their social bond that links them to the acrian side. But to across the border between Acre and Bolívia was not the most painful experience of these groups, in terms of their identitary state as extractives, since these groups are confronted with a greater challenge that is their expulsion of the border as a means of national security and Bolivian sovereignty. With deadline to leave their homes, i.e., desterritorializate in a compulsory manner, these groups comprehend their nationality as a restrictive factor to production place in the Bolivian territory, and at the same time, they do not have any favorable factor to their reinsertion in the Brazilian territory, mainly in the Acre countryside. In this context, the objective of this dissertation is a sociological investigation about the trajectories and the subsequent socio-spatial vulnerabilization processes lived by the Brazilian peasants that nowadays occupy areas in the border between Bolívia and Acre. For this purpose, we present a sociological and qualitative research, whose procedures are the bibliography review about the politics of Amazon occupation, studies about the official data from multilateral organizations and Brazilian institutes involved with the topic, semistructured interviews and photo-documentation. The analysis of the results was divided in three parts, each one relative to one migratory movement: from Brazilian Northwest to Amazon (Trajectory 1); from Acre to Bolívia (Trajectory 2); and the return of the peasants to Brazil (Trajectory 3). Among the most important findings are the identification of regular regimes that affected the deterritorialization processes of the group, such as the lack of legitimacy of the right to ownership of land by peasants, and other unique traits, such as degradation resulting from identity tensions experienced in the bolivian context, which are being expelled.