Identificação da formação de titanato de bário a partir de mistura reacional calcinada em diferentes temperaturas via difração de raios X, espectroscopia fotoacústica e análise térmica

Abstract

Ferroelectric materials have been used in many areas of technology and science, because they have a large number of applications, such as sensors; transducers; capacitors; optical devices; among others. The search for new ferroelectric ceramics has been great. One of the most studied ferroelectric ceramic material is barium titanate (BT). There are several methods for production and characterization of barium titanate. In this work, ceramic powders of barium titanate were obtained by solid state reaction from reaction mixtures calcined at different temperatures between 400°C and 900°C. Three reaction mixtures were used: undoped; doped with 1%; and 5% doped with cerium dioxide (CeO2). The identification of the formation of BT, for the ceramic powders produced, was taken from three characterization techniques: X-ray diffraction (XRD); photoacoustic spectroscopy (PAS); and thermal analysis techniques. With the technique XRD diffraction patterns showed that complete formation of the barium titanate occurred after the calcination temperature of 700°C. For the sample not doped with cerium and calcined at 800°C, there was displacement of all diffraction peaks. In samples doped with cerium dioxide was no displacement of all diffraction peaks, comparing to undoped samples. It was also observed that the samples doped with 5% CeO2 and calcined at 700°C and 800°C, cerium dioxide residues were observed in the diffraction pattern. The absorption spectra were obtained with the technique PAS. It was possible to observe a large difference in absorption spectra in the samples calcined at 600°C and 630°C, indicating the formation of barium titanate at temperature of 630°C in the samples without doping of cerium dioxide. There was an enlargement in the absorption band above temperature of 600°C when the cerium dioxide was introduced into the matrix. It was also possible to determine the band-gap energy of the samples using the method of TAUC. With thermal analysis techniques, in particular by thermogravimetric technique (TG/DTG), has been proven that up to 400°C there was no formation of barium titanate. Once, in this calcination temperature there was the largest mass loss during the heating ramp. The onset of formation of barium titanate was observed from the calcination temperature of 500°C, as it has been found by the XRD and PAS techniques. Therefore, with the results presented, the identification of the formation of barium titanate calcined in reaction mixtures with the aid of the potentialities of the three techniques was demonstrated.