Síntese e caracterização estrutural, morfológica, óptica e térmica do niobato de cério hiperestequiométrico (CeNbO4,25) obtido por reação em estado sólido

Abstract

This dissertation describes the synthesis of CeNbO4.25 via solid-state reaction under ambient atmosphere, investigated using multiple characterization techniques. High-purity cerium oxide (CeO2) and niobium oxide (Nb2O5) samples were homogenized at a 1:1 Ce/Nb molar ratio and subjected to high-energy ball milling (HEBM) with a constant ball-to-powder ratio (BPR) of 7.6:1 in a vibratory mill for 15 hours. During the process, the samples were monitored and characterized by X-ray diffraction (XRD) at each milling stage, followed by phase identification and structural refinement using the Rietveld method (RM). The sample obtained from the final milling stage was analyzed by differential scanning calorimetry (DSC) and thermally treated at 700 °C, 950 °C, and 1200 °C, remaining at each temperature for periods of one and eight hours of exposure. Characterization of the sample calcined at 950 °C for eight hours, by XRD, Raman spectroscopy (RS), and UV-Vis diffuse reflectance spectroscopy, revealed the formation of a pure monoclinic hyperstoichiometric cerium niobate phase (CeNbO4.25) at room temperature. Using Brown’s bond valence model, the oxygen hyperstoichiometric value was estimated for the phase calcined at 1200 °C for 8h.