
Promethium(III) oxide

Promethium(III) oxide is a compound with the formula Pm2O3. It is the most common form of promethium.
Crystal structure.
Promethium oxide exists in three major crystalline forms:
The low-temperature cubic form converts to the monoclinic structure upon heating to 750–800 °C, and this transition can only be reversed by melting the oxide. The transition from the monoclinic to hexagonal form occurs at 1740 °C.