Navegando por Palavras-chave "Thermal Expansion"

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    Síntese 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.