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

Synthesis of mixed-valent α- and β-NaFe2O3 polymorphs under controlled partial oxygen pressure

“…The syntheses of all samples and subsequent X-ray diffraction measurements were successfully reproduced. It was reported that NaFe 2 O 3 slowly hydrolyzes in air [14]; therefore, all operation with initial mixtures and final compounds were performed under nitrogen. a-NaFeO 2 was synthesized by the reaction of a-Fe 2 O 3 (99.5%, Alfa Aesar) with a 20% stoichiometric excess of NaOH (98.8%, Mallinckrodt Chemicals) under O 2 flow at 500 1C for 48 h. Excess NaOH was removed by washing with anhydrous methanol in a nitrogen filled glovebox.…”

“…Peaks related to the b-Na x Fe 2 O 3 polymorph were absent in the SPXD pattern while the strongest peak of the Fe 3 O 4 admixture was at $ 0.1% of relative intensity level. Attempts to perform a Rietveld refinement using the literature structural model [14] were unsuccessful (w 2 E22). While peak positions and peak profile could be fitted adequately, there were substantial differences in peak intensities which did not change systematically with peak indices, indicating a problem with the structural model rather than preferred orientation.…”

“…From this data, it becomes obvious that the synthesis of NaFe 2 O 3 requires very careful control over oxygen stoichiometry. Since both the a-and b-NaFe 2 O 3 polymorphs were prepared earlier at distinct, but unknown pO 2 [14], the dependence of phase composition vs. pO 2 was studied in order to prepare the pure compounds.…”

“…Preparation methods and crystal structures of a-and bNaFe 2 O 3 were reported in the 1970s by El Balkhi et al [14,15]. For the synthesis of the NaFe 2 O 3 polymorphs, mixtures of NaFeO 2 , Fe 2 O 3 and Fe were sealed in ampoules and annealed at 1000 1C for 48 h. The a and b phases were originally prepared in sealed steel and Cu ampoules, respectively.…”

“…The only known example is b-NaFe 2 O 3 ; its crystal structure consists of double rock-salt layers of octahedrally coordinated iron (Fe 2 O 3 blocks) separated by Na ions (Fig. 1) [14][15][16][17]. Generally speaking, 3d metal compounds with b-NaFe 2 O 3 structures are expected to demonstrate different properties than their a-NaFeO 2 type counterparts due to the difference in M oxidation states as well as in the dimensionality of the 3d metal -oxygen blocks.…”