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- ItemSomente MetadadadosInfluência Do Processamento Na Formação De Cerâmicas Eletrônicas Polifásicas E Suas Propriedades Elétricas(Universidade Federal de São Paulo (UNIFESP), 2017-12-08) Boaventura, Andre Luis [UNIFESP]; Antonelli, Eduardo [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)The general objective of this work was to investigate the influence of processing on the electrical properties (dielectric and piezoelectric) of ceramics of the barium-zirconate titanate system (BT+BZ) as well as the barium zirconate-titanate/barium calcium-titanate (BZT-BCT). Studies indicate that intrinsic and extrinsic factors influence the dielectric and piezoelectric properties of electronic ceramics. The methodology consisted in obtaining monophase materials of barium-zirconate titanate (BZT), calcium titanate (BCT), barium titanate (BT) and barium zirconate (BZ). New materials were made through mixture of calcined powders of BZT with BCT and BZ, forming polyphase ceramics of BZT-BCT and BT-BZ respectively. The ceramics were sintered at 1380 ºC at different times (10 min, 2h, 3h and 24h). The results showed that polyphase ceramics presented the phase coexistence in the temperature range studied, forming polymorphic phase behavior (PPB). The intrinsic and extrinsic factors were influenced by the stage of sintering. For the BZT-BCT polyphase system, the extrinsic factors (average grain size, texture, density, grain boundary) and intrinsic factors (coexistence of symmetries, polarization, tetragonal phase stabilization) increased because of the stages of sintering e and consequently improved the piezoelectric responses of this system. As for the polyphase system BT-BZ, the intrinsic factors (coexistence of symmetries and the stabilization of the cubic phase) increased because of the stages of sintering, while the extrinsic factors (average grain size, homogeneity and phase segregation) decreased because of the increase of stages of sintering. For sintered BT-BZ ceramics with a time interval of 10 mins, the balance between the intrinsic and extrinsic factors, caused the dielectric properties to be more stable than the single-phase solid solution (BZT). This result is a promising choice for the production of dielectric materials for the purpose of usage in the capacitors. Therefore, it was possible to demonstrate that the processing routes of the mixtures, BZT-BCT and BT-BZ formed polyphase materials with PPB, and that the time of stages influenced the intrinsic and extrinsic factors that led to the responses in the electrical, dielectric properties and piezoelectric properties of the ceramics investigated
- ItemSomente MetadadadosPreparação, Caracterização E Estudo Das Propriedades Dielétricas Dos Materiais Cerâmicos De Cacu3Ti4O12 Dopados Com Magnésio(Universidade Federal de São Paulo (UNIFESP), 2017-02-22) Arruda, Leonardo Goncalves [UNIFESP]; Antonelli, Eduardo [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Recently, CaCu3Ti4O12 (CCTO) has attracted significant attention due its high permittivity. Although it presents high value for tangent of loss, which has limited its utilization in technological industries. In this work, CCTO pure and doping with magnesium (Mg) were sintered by reaction ceramic powders solid reaction. The powders were initially characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), density by Archimedes and Impedance Spectroscopy (IS). The analysis with XRD showed that phase of CCTO were obtained in both sample. A displacement was observed at main peak of pure sample; however, the same result was not observed for the doped sample. Studies by SEM indicate that process growth and densification of the pure sample is related to the sintering time, however the same result is not observed for the doping sample. These results were associated with the fact that Cu and Mg had the same ionic radius. By the SI technique, it was verified that microstructure of the material is not able to explain the origin of GDC and that grain boundaries and grain are responsible for CCTO dielectric constant. Although the Internal Barrier Layer Capacitor (IBLC) model describes some presented results, it was inefficient in describing the electric behavior of the CCTO. After all, the IBLC model not be able explain the increase in the dielectric constant accompanied by the increase in the loss tangent. However, the Nanosized Barrier Layer Capacitor (NBLC) and grain domain models can better explain the electrical behavior of the samples. Since the essences of the two models are similar, they are based on planar defects. However, the NBLC presented with the best model to explain the electric response of the CCTO, as discussed.
- ItemSomente MetadadadosSíntese e estudo das transições de fases estruturais no sistema (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (BCZT) utilizando a associação de diferentes técnicas de caracterização(Universidade Federal de São Paulo (UNIFESP), 2019-07-31) Aredes, Rangel Graudiston [UNIFESP]; Antonelli, Eduardo [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Lead-free piezoelectric ceramics can demonstrate excellent properties when their compositions are projected with sequences of specific phase transitions and / or the coexistence of phases. It has been reported that some compositions of (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (xBCZT) may present phases coexistence (rhombohedral “R” and orthorhombic “O”) at room temperature. Besides, recent studies have observed the O phase as an intermediate phase before the tetragonal “T”-cubic “C” phase transitions. Herein, we study the xBCZT to verify if the experimental characterizations can detect R-O, O-T and T-C phase transitions and identify the physical anomalies that confirm the phases coexistence. The phase transitions were studied during a heating program for xBCZT and compared with pure BaTiO3 by dielectric spectroscopy, pyroelectric coefficient analyses, thermal analyses, linear expansion and powder X-ray diffraction. The interpretation of different responses allows us to conclude that the substitutions of Ca2+ for Ba2+ or Zr4+ for Ti4+ in the formulation xBCZT can result in two or more different solid solutions, belonging to the perovskite family, which coexist in the ceramic. The transitions of each one of the phases happen in a cooperative effect and, in some specific interval of temperatures, the break of the cooperative effect happens and make clear the phase coexistence.