Bismuth oxide is an inorganic oxide of bismuth, most commonly supplied as bismuth(III) oxide (Bi₂O₃). It appears as a yellow to pale yellow powder and is known for its high refractive index, strong dielectric properties, and low toxicity compared with other heavy metal oxides. Bismuth oxide exists in several polymorphic forms, with the α-phase being stable at room temperature. It is widely used in electronic ceramics, optical materials, pigments, and as a precursor for other bismuth compounds.