Yttrium oxide is Y2O3. It is an air-stable, white substance. Yttrium oxide is used as a common starting material for both material science as well as inorganic compounds.

In material science

It is the most important yttrium compound and is widely used to make YVO4 europium and Y2O3 europium phosphors that give the red color in color TV picture tubes. Yttrium oxide is also used to make yttrium-iron-garnets, which are very effective microwave filters.

In its most important application, Y2O3 is used to make the high temperature superconductor YBa2Cu3O7, known as "1-2-3" to indicate the ratio of the metal constituents:

0.5 Y2O3 + 2 BaO + 3 CuO + 0.25 O2 ? YBa2Cu3O7

This synthesis is typically conducted at 800 °C.

Yttrium oxide is an important starting point for inorganic compounds. For organometallic chemistry it is converted to YCl3 in a reaction with concentrated hydrochloric acid and ammonium chloride.