Promethium(III) oxide
Promethium oxide is a compound with the formula Pm2O3. It is the most common form of promethium.Promethium oxide exists in three major crystalline forms:
| Form | Pearson symbol | Space group | No. | a,b,c | β | Z | Density
|
| Cubic | cI80 | Ia | 206 | 1.099 | | 16 | 6.85 |
| Monoclinic | mS30 | C2/m | 12 | 1.422; 0.365; 0.891 | 100.1 | 6 | 7.48 |
| Hexagonal | hP5 | Pm1 | 164 | 0.3802; 0.3802; 0.5954 | | 1 | 7.62 |
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.
