Thermal behavior of the amorphous precursors of the ZrO2–GaO1.5 system

The amorphous precursors of the ZrO2–GaO1.5 system on the ZrO2-rich side of the concentration range were prepared by co-precipitation from aqueous solutions of the corresponding salts. Thermal behavior of the amorphous precursors was monitored using differential thermal analysis (DTA), X-ray powder diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FE-SEM). Crystallization temperature of the amorphous precursors rose with an increase in the GaO1.5 content, from 405 °C (0 mol% GaO1.5) to 720 °C (50 mol% GaO1.5). The results of Rietveld refinements indicated that the maximum solubility of Ga3+ ions in the ZrO2 lattice (∼43 mol%) occurred in the metastable products obtained after crystallization of the amorphous precursors. Further thermal treatment caused a decrease of the solubility limits, which became negligible after calcination at 1100 °C. The results of Raman spectroscopy showed that the incorporation of Ga3+ ions partially stabilized the tetragonal polymorph of ZrO2, but could not stabilize its cubic polymorph. The incorporation of Ga3+ ions caused a linear decrease in the unit-cell volume of the ZrO2-type solid solutions, but the rate of the decrease turned out to be smaller than the rate obtained after the incorporation of bigger Fe3+ ions.