Systèmes métaux alcalins–oxygène. 3ème Partie. Polymorphisme du monooxyde de potassium K2O

First order reversible transitions occur in potassium monoxide successively at 317 and 372 °C. These transitions have been observed by differential thermal analysis. The known form is γ-K 2 O, face-centered cubic, a = 6.436 Å. The new forms are β-K 2 O between 317 and 372 °C, primitive cubic, a = 12.125 Å and α-K 2 O from 372 °C to the melting point, rhombohedral, a = 12.543 Å, α = 91.47°. An order–disorder transformation occurs at 446 °C. It is at approximately this temperature that K 2 O begins to disproportionate into K 2 O 2 and K.