Yttrium Oxide is mainly extracted from the mineral Xenotime (YPO₄). Its properties include high thermal stability and good transparency to infrared radiation. It has an affinity for oxygen and sulphur and is used as an additive to stabilise Zirconia and as a sintering aid in Sialons and silicon nitride. As an optical ceramic, it transmits well in the infrared range, from 1 to 8 microns wavelength. The high infrared transmission, together with good resistance to erosion and thermal shock, makes it ideal for protection domes for infrared sensors.