Solid State Reactions Involving Oxides of Trivalent Cations

Area of Science:

• Materials Science
• Solid State Chemistry
• Inorganic Chemistry

Background:

• Double oxides of trivalent cations are crucial in materials science.
• Understanding their phase equilibria and structure types is essential for predicting material properties.
• Previous studies have explored various binary systems, but a comprehensive survey across a wide range of trivalent oxides was needed.

Purpose of the Study:

• To systematically investigate the phase equilibria and structure types of selected binary systems involving 8 different trivalent metal oxides.
• To correlate the stability of different crystal structures with the ionic radii of the constituent trivalent cations.
• To map the subsolidus phase relationships for numerous binary oxide systems.

Main Methods:

• Preparation of mixtures in 69 binary systems involving Al2O3, Ga2O3, Cr2O3, Fe2O3, Sc2O3, In2O3, Y2O3, and rare earth oxides.
• Heat treatment of the mixtures at various temperatures.
• Characterization of the resulting phases using X-ray diffraction techniques.

Main Results:

• Identified stability regions for various structure types, including rare earth oxide types (A, B, C), corundum, beta gallia, kappa alumina, garnet, and perovskite.
• The majority of A+3B+3O3 compounds were found to adopt the perovskite structure.
• Observed solid solution formation in garnet-type compounds containing gallia and phases similar to kappa alumina in Fe2O3-Al2O3 and Fe2O3-Ga2O3 systems.
• Established subsolidus phase equilibria for 79 binary systems based on experimental data.

Conclusions:

• The study successfully correlated cation radii with the stability of different crystal structures in binary trivalent metal oxides.
• The findings provide a valuable dataset for predicting and designing new materials with desired structural and potentially functional properties.
• The established phase diagrams serve as a foundation for further research into ternary and higher-order systems involving these oxides.