Chemical compound

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:[1]

Form Pearson symbol Space group No. a,b,c (nm) β(deg) Z Density
Cubic cI80 Ia3 206 1.099 16 6.85
Monoclinic mS30 C2/m 12 1.422; 0.365; 0.891 100.1 6 7.48
Hexagonal hP5 P3m1 164 0.3802; 0.3802; 0.5954 1 7.62

*a, b and c are lattice parameters, Z is the number of formula units per unit cell, density is calculated from X-ray data.

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.


  1. ^ a b Chikalla, T. D.; McNeilly, C. E.; Roberts, F. P. (1972). "Polymorphic Modifications of Pm2O3". Journal of the American Ceramic Society. 55 (8): 428. doi:10.1111/j.1151-2916.1972.tb11329.x.