Préparation et propriétés d'un oxyde de sodium-fer(II,III): NaFe2O3

This compound is prepared, within sealed metallic tubes at 1000°C, through different reactions between components of the FeFe₂O₃NaFeO₂ system. It is black and weakly hygroscopic and gives two forms, α and β, according to oxygen pressure values.The examination of a crystal of the α form leads to a trigonal cell (space group $\text{R3m, R}\text{3}\text{m}$ or R32) with a = 3.047 Å and c = 31.04 Å for the hexagonal cell (Z = 4). The structure is described as a stacking of alternate cationic and anionic planes with a succession of 12 cationic planes: 3 × FFMM (F, plane including Fe; M, mixed plane including $\text{2}\text{3}\text{Na}\text{+}\text{1}\text{3}\text{Fe}$).α-NaFe₂O₃ is paramagnetic above 94°K with μ_eff = 5.40; it is a semiconductor, n type, with E = 0.18 eV. Above 1050°C it dissociates into NaFeO₂ and sodic wustite, which oxidizes easily.The β form is probably a polytype with a hexagonal cell (a = 3.045Å, c = 15.55 Å) with six cationic planes.