Promethium(III) oxide

Promethium(III) oxide

Powdered promethium oxide in a metal tray
Cubic form
Hexagonal form
Names
IUPAC name Promethium(III) oxide
Other names Promethium sesquioxide
Identifiers
CAS Number	12036-25-8
Properties
Chemical formula	Pm2O3
Molar mass	337.824 g/mol
Melting point	~2320 °C[1]
Structure
Crystal structure	Cubic
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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Infobox references

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 (g/cm^3)
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.

References

1. 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.