Promethium(III) oxide


Promethium 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:
FormPearson symbolSpace groupNo.a; b; c βZDensity
CubiccI80Ia2061.099166.85
MonoclinicmS30C2/m121.422; 0.365; 0.891100.167.48
HexagonalhP5P''m''11640.3802; 0.3802; 0.595417.62

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.