Poly(4,4'-oxydiphenylene-oxydiphthalimide) (POO) was thermally treated at 773 K for 1, 15 and 60 minutes under argon atmosphere resulting in free-standing films with intermingled characteristics between polymer and carbon-rich derivatives. Degradative thermal analysis performed by pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS) revealed CO 2 among the major products of thermal decomposition which according to electron paramagnetic resonance (EPR) passed through a radical process. X-ray diffraction (XRD) revealed thermal treated samples with semicrystalline organization that was attributed to the development of lamellae structure. Moreover, Atomic force microscopy (AFM) showed an increase in the roughness of the samples that acquired pronounced roughcast-like surface. Hence, there was an enhancement of mechanical strength and dielectric permittivity. From the data collected a mechanism of thermal decomposition was proposed.
The dielectric, pyroelectric and ferroelectric properties of bilayered BaTiO3/BaTi0.8Zr0.2O3 ceramics are described and correlated with their microstructure. Different sintering times are employed to change the microstructure and promote interdiffusion between the layers. The effects of constrained sintering on both compositions are analyzed and their properties are compared to that of single phase BaTiO3 and BaTi0.8Zr0.2O3 ceramics. The results show that, at sintering times until 2 hours, the bilayer properties are predominantly affected by the presence of residual stresses. Only after 4 hours sintering, the properties are predominantly affected by interdiffusion between the layers.
Validity of mixture rule for dielectrics in series configuration and the correlation between microstructure and electrical properties in bilayered BaTiO 3 /BaTi 1-x Zr x O 3 ceramics were studied. Samples were obtained from BaTi 1-x Zr x O 3 (BTZx) nanopowder synthesized by the polymeric precursor technique and had their microstructure, dielectric, piezoelectric and ferroelectric properties investigated.These bilayered ceramics properties were compared to the properties of homogeneous BTZx samples. And, also, the former's electrical permittivities were compared with the predictions of the simple mixture rule. According to the results, the microstructures of the layers do not differ from the microstructure of the corresponding homogeneous BTZx ceramic. And pyroelectric coefficient measurements show that the electrical properties of the interface do not contribute to the functional properties of the bilayered samples. Nevertheless, on increasing Zr 4+ , the agreement between the experimental and the predicted permittivity of the 1 thimaral@ursa.ifsc.usp.br 2 bilayered ceramics is gradually reduced, mainly at temperatures where the permittivity is governed by the response of the layer containing Zr 4+ . As a mechanical joint between the layers, the interface induces stresses during sintering due to thermal mismatch between compositions, thereby affecting the bilayer's electrical properties. Our results show that mechanical interface effects compromise the functional properties of layered ferroelectric ceramics.
Aos amigos do IFSC, pelas conversas, pela SIFSC e por várias discussões.Aos amigos do IF-UFG pela grande amizade forjada durante os anos de graduação.
Aos membros do Grupo de Crescimento de Cristais e Materiais
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