With a density of 5.01g/cm³, it is insoluble in water/alkalis but soluble in acids. As an additive for steel/non-ferrous alloys, it enhances oxidation resistance (FeCr alloys: 0.5%–4% Y₂O₃), improves alloy performance (MB26, Al-Zr) and copper alloy conductivity/strength. It’s used in Si₃N₄ ceramics (6% Y₂O₃, 2% Al) for engine parts, Y-Al garnet for electron microscope screens, high-Y₂O₃ alloys (90% Gd₂O₃) for low-density/high-melting scenarios, fuel cell proton conductors, high-temp coatings, nuclear reactor diluents, and permanent magnet additives.