Influência da temperatura de tratamento térmico nas propriedades estruturais e ópticas de cristais de NiWO4

Abstract

In this work, we investigated the effect of heat treatment on the structural and optical behavior of NiWO4 crystals synthesized by coprecipitation followed by the hydrothermal method, with post-treatment at different temperatures. XRD patterns, Rietveld refinement and Raman spectra indicate that NiWO4 crystals have a wolframite-like monoclinic structure with a space group (P2/c) and a point symmetry group (C2h4). A preferential growth in the (011) planes was observed at 500 °C, confirmed by XRD, theoretical and documented, thus, crimped on the y-axis of partialst (W) tung event sequences for modeling unit cells/crystals10 in this temperature range in TGA and DSC. In Raman spectroscopy, the NiWO4 spectrum gradually changed in the spectra from its nanometer character and became a bulk material. The Egap values showed a tendency of temperature reduction with increasing heat treatment up to 500 °C (2.75 eV), increasing from there. Such alterations being confirmed in the colorimetric analysis, where from the temperature of 500 °C/2h the material acquired the yellow color and it becomes intended.