Promethium(III) oxide
Pm oxide.jpg

Powdered promethium oxide in a metal tray
Kristallstruktur Indiumoxid.png

Cubic form

Hexagonal form
IUPAC name
Promethium(III) oxide
Other names
Promethium sesquioxide
3D model (JSmol)
  • InChI=1S/3O.2Pm/q3*-2;2*+3
  • [O-2].[O-2].[O-2].[Pm+3].[Pm+3]
Molar mass 337.824 g/mol
Melting point ~2320 °C[1]
Related compounds
Other anions
Promethium(III) chloride
Other cations
Neodymium(III) oxide, Samarium(III) oxide, Neptunium(III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.