meu Orientador, pela dedicação, paciência e conhecimentos transmitidos. Por sua orientação de forma ímpar, sem a qual esse trabalho não teria atingido o ideal traçado.
In this work it has been developed a device, called electromagnetic induction furnace (EIF), which allow us to work at high temperatures ~ 1900 ° C and under dynamic vacuum equivalent to partial pressure of oxygen PO 2 ~ 10-10 atm. During the calibration experiments of the EIF, it was studied a binary compound of Y 2 O 3 with 3 mol% of ZrO 2 which was obtained by mixing oxides. The samples were processed by uniaxial pressing 50 MPa followed by isostatic pressing at 350 MPa for 10 minutes and submitted to sintering at temperatures above 1800 °C, resulting in transparency greater than 60% for wavelengths around 800 nm. After, a quaternary compound of BaTi 0.85 Zr 0.15 O was produced by mixing oxides and calcination at 1200 o C. Then the samples were shaped according to the same methodology of the Y 2 O 3 subsequently sintered between 1250 °C to 1400 °C, with 1 h and 3 h baseline. The samples prepared in the EIF were submitted to oxygen partial pressure of ~ 10-7 atm, while another samples set was sintered in a conventional electric furnace (CEF) with open atmosphere for comparison. Microstructural characterizations were performed by applying the techniques of X-ray diffraction, BET, EDS, SEM, and electrical characterization by impedance spectroscopy. In these characterizations were obtained powder particles of BaTi 0.85 Zr 0.15 O 3 with an average size of 110 nm. The average grain size in the microstructures ranged between 4 and 30 μm in the samples fabricated in CEF, but in the samples manufactured in EIF the size has been around 250 nm. For samples made in the CEF, the dielectric response of the grains showed the fulfillment of the Curie-Weiss law according to the bricklayer model made in the Zview program, but was observed dielectric anomaly on measurements of permittivity at temperatures higher than 96 o C. The material made in EIF does not showed ferroelectric behavior in the studied temperature range-243-137 °C, but was shown a typical behavior of varistor material. Considering the relationship between macroscopic and microscopic properties in the bricklayer model, the ferroelectricity and the dielectric anomaly variation are discussed at function of the grain size for samples made in CEF. Based on the model of Pike for varistors, the varistor behavior of the material made in EIF is discussed in terms of defects caused by low oxygen partial pressure ~ 10-7 atm.
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