Synthesis, crystal, and magnetic structures of the sodium ferrate (IV) Na4FeO4 studied by neutron diffraction and mdssbauer techniques

The alkali sodium ferrate (IV) Na4FeO4 has been prepared by solid-state reaction of sodium peroxide Na2O2 and wustite Fe1-xO, in a molar ratio Na/Fe = 4, at 400degreesC under vacuum. Powder X-ray and neutron diffraction studies indicate that Na4FeO4 crystallizes in the triclinic system P-1 with the cell parameters: a = 8.4810(2) Angstrom, b = 5.7688(1) Angstrom, c = 6.5622(1) Angstrom, alpha = 124.662(2)degrees, beta = 98.848(2)degrees, gamma = 101.761(2)degrees and Z = 2. Na4FeO4 is isotypic with the other known phases Na4MO4 (M = Ti, Cr, Mn, Co and Ge, Sn, Pb). The solid solution Na4FexCo1-xO4 exists for x = 0-1 and we have followed the evolution of the cell parameters with x to determine the lattice parameters of the triclinic cell of Na4FeO4. A three-dimensional network of isolated FeO4 tetrahedra connected by Na atoms characterizes the structure. This compound is antiferromagnetic below T-N = 16 K. At 2 K the magnetic cell is twice the nuclear cell and the magnetic structure is collinear (mu(Fe) = 3.36(12) mu(B) at 2 K). This black compound is highly hygroscopic. In water or on contact with the atmospheric moisture it is disproportionated in Fe3+ and Fe6+. The Mossbauer spectra of Na4FeO4 are fitted with one doublet (delta = -0.22 mm/s, Delta = 0.41 mm/s at 295 K) in the paramagnetic state and with a sextet at 8 K. These parameters characterize Fe4+ high-spin in tetrahedral FeO4 coordination. (C) 2002 Elsevier Science (USA).