Síntese e caracterização de vidros e vitrocerâmicas no sistema V2O5 – Bi2O3 – Fe2O3

Abstract

Bismuth ferrite (BiFeO3) is a promising material and largely studied due to its combination of ferroelectric and ferromagnetic properties, with possible applications in sensors, actuators and memory storing devices. However, the synthesis of this material is problematic due to the frequent formation of undesired secondary phases. One line of study developed to try to solve this problem is the obtention of BiFeO3 from the crystallization of a glass matrix containing iron oxide and bismuth oxide. In this work the possibility of obtention of BiFeO3 from the glass system V2O5 – Bi2O3 – Fe2O3 was evaluated. The samples were prepared using several cooling methods to compare the results. Differential Scanning Calorimetry was employed on the vitreous samples to determine the glass transition temperature (Tg) and crystallization temperature (Tc), showing an increase in the characteristic temperatures and reduction of the vitreous stability with the increase of iron oxide. The vitreous samples were than heat treated in the crystallization temperature. X-Ray Diffraction (XRD) results were used to confirm the vitreous characteristic before heat treatment and the phases formed after the treatment. Rietveld refinements were also employed on the samples with 20% iron oxide to determine the crystalline percentage, cell parameters and mean particle size. The samples before and after treatment had 7,9% crystallinity and 72,4% crystallinity, respectively. The cell parameters obtained were similar to the theoretical values, indicating that iron stayed in the amorphous phase after treatment. Scherrer inference calculations yielded a mean particle size of 24,48nm. Fourier transform infrared spectroscopy(FTIR) and Raman spectroscopy measurements to evaluate the structural evolution of the samples. Voltage versus current measurements showed a non-linearity coefficient of 40,07 for the sample with 15% iron oxide.