Otimização do processo de preparação e caracterização de cerâmicas do sistema Cu2O e Cu2O:Co3O4

Abstract

In this master's thesis, we present the studies related to the preparation and chemical and structural characterization of samples of the Cu2O and Cu2O:Co3O4 system, considering the potential doping of Cu2O with Co in the stoichiometry of (Cu1-xCox)2O, at the nominal concentrations of xN = 0.00; 0.01; 0.03; 0.05 and 0.07. Sample preparation was performed via conventional solid-state sintering for the Cu2O sample, and liquid phase sintering for the Cu2O:Co3O4 samples. The chemical characterization was carried out by scanning electron microscopy and measurements of energy dispersion X-ray spectroscopy, the structural analyses were performed using of X-ray diffraction and Rietveld refinement techniques, Raman scattering spectroscopy, and photoluminescence. We determined the sintering parameters leading to Cu2O single-phase samples. We verified that Co3O4 works as an additive that turns the sintering into the condition of liquid-phase sintering. The liquid-phase sintering leads to an increase of the volumetric mass density of the samples due to the elimination of the pores and the increase of the median grain diameter. We observed that unusually after cooling the Co-rich liquid-phase remains not crystalline, with a glassy structure even in the filled pores between the Cu2O grains. The photoluminescence results lead us to conclude that the Co was not incorporated into the Cu2O matrix, and that the liquid-phase sintering process leads to the formation of a higher density of structural vacancy defects. The increase of the volumetric mass density, of the median grain diameter, and the density of the point defects under the liquid-phase sintering allow us to infer a increase of the carrier mobility and density, optimizing the electrical transport properties of the Cu2O, potentially increasing the energetic conversion efficiency of photovoltaic cells based on this material.