Indium oxide

Indium oxide is a compound of indium and oxygen, In₂O₃. It's a pale yellow powder that doesn't dissolve in water. As a thin film it is nearly transparent and conducts a little, which makes it a natural base for clear electrodes.

Indium itself is scarce and almost never mined for its own sake. It's recovered as a byproduct of refining zinc ores, where it occurs in tiny amounts. The refined metal is turned into oxide either by dissolving it in acid, precipitating indium hydroxide and heating that until the water is driven off, or by burning the metal in oxygen. For sputtering targets, the powder must be very fine and very pure.

Its main job is as about 90% of indium tin oxide. Mixed with tin dioxide and fired into targets, it becomes the clear conducting film inside almost every LCD and touchscreen. Because indium supply is limited and only part of each target ends up on the glass, factories recycle used targets carefully. Researchers have tried replacements such as silver nanowires and graphene, but ITO remains the standard.