Combined effect of MgO sintering additive and stoichiometry deviation on YAG crystal lattice defects

Abstract

This study aims to investigate the combined effect of the magnesium oxide (MgO) sintering additive and the deviations of the yttrium aluminum garnet (YAG) stoichiometry towards the excess of Al3+ and Y3+ on crystal lattice defects. YAG ceramic powders with an excess of aluminum (up to 4.79 mol.%) or yttrium (up to 2.87 mol.%) and various concentrations of the MgO sintering additive (from 0 to 0.2 wt%) were obtained using a two-stage co-precipitation method. The samples calcined at 1600 °C were studied by X-ray powder diffraction (XRD), scanning electron microscopy, diffuse reflectance, Raman and IR-spectroscopy. The cumulative analysis of theoretical calculations of the composition of the samples was performed based on a change in the lattice parameters. Experimental data obtained suggested that, depending on the YAG stoichiometry, magnesium can substitute both the dodecahedral positions of yttrium (in the case of aluminum excess), as well as the octahedral positions of aluminum (in the case of yttrium excess). The resulting substitution defects give pronounced absorption bands in the diffuse reflectance spectra. An increase in the concentration of introduced magnesium leads to a shift in the IR-transmission maximum of ≈620 cm−1 towards wave numbers increasing with an excess of aluminum and towards wave numbers decreasing with an excess of yttrium. In addition, when magnesium was introduced, a decrease in the intensity of incidental peaks in the Raman spectra was observed, which may be due to the relaxation of stresses due to a decrease in the number of intrinsic crystal lattice defects