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Powdered promethium oxide in a metal tray
|Molar mass||337.824 g/mol|
|Other cations||Neptunium(III) oxide|
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Promethium oxide exists in three major crystalline forms:
|Form||Pearson symbol||Space group||No.||a,b,c (nm)||β(deg)||Z||Density
|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.
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