Structural investigation of the Na–Fe–Mo–O system

Abstract

Four new crystalline structures within the Na-Fe-Mo-O system are reported: sodium tetrairon pentamolydate (1), NaFe(4)(MoO(4))(5), alpha-sodium diiron trimolybdate (2), alpha-NaFe(2)(MoO(4))(3), beta-sodium diiron trimolybdate (3), beta-NaFe(2)(MoO(4))(3), trisodium diiron trimolybdate (4), Na(3)Fe(2)(MoO(4))(3). All these structures belong to orthomolybdate class of compound and are described as networks of [FeO(6)] octahedra and [MoO(4)] tetrahedra. They are compared with each other and with other related structures.

Orthomolybdates in the Cs–FeII,III–Mo–O System: Cs4Fe(MoO4)3, Cs2Fe2(MoO4)3 and CsFe5(MoO4)7

“…A nearly phase-pure polycrystalline sample of CsFe 5 (MoO 4 ) 7 was obtained, according to X-ray powder diffraction (see Figure 10), by synthesis in dynamic vacuum with a steplike temperature increase up to a final temperature of 973 K over 20 h. Less than 2 % (w/w) monoclinic α-FeMoO 4 (space group C2/m) was detected as an admixture, which is antiferromagnetic below 35 K. [14] The temperature dependencies of magnetization (Figure 11a) of CsFe 5 -(MoO 4 ) 7 show a difference between zero-field-cooled (ZFC) and field-cooled (FC) measurements below 10 K, which is attributed to the onset of a ferro-or ferrimagnetic ordering. α-FeMoO 4 does not contribute to these observed magnetic properties of CsFe 5 (MoO 4 ) 7 .…”

“…[2][3][4] Due to the rather weak bonding of the alkaline ions, high ionic conductivity is often observed for these compounds at elevated temperature. These molybdates might also be considered as intercalation materials, because the channels are only partially occupied and can host additional alkaline ions such as Li + or Na + , which can be inserted into the 7 orders magnetically with a ferromagnetic component at T C = 10 K, proposed as a canted antiferromagnet. Its antiferromagnetic structure at 0 T was described by combination of two propagation vectors k = (1/2, 0, 0) and k = (0, 0, 0) with magnetic moments of 2.6, 1.6 and 3.5 μ B for three independent Fe sites.…”

“…For example, four orthomolybdate phases with three-dimensional networks of MoO 4 tetrahedra and FeO 6 octahedra and different connectivity schemes are reported for the Na x Fe y (MoO 4 ) z system that have not been found for other 3d cations: NaFe 4 (MoO 4 ) 5 , α-NaFe 2 (MoO 4 ) 3 , β-NaFe 2 (MoO 4 ) 3 and Na 3 Fe 2 (MoO 4 ) 3 . [7] For the latter one, the unusual combination of oxidation states Fe III /Mo V was postulated. In the Ag-Fe II,III -Mo-O system, AgFe 2 (MoO 4 ) 3 was found isostructural to α-NaFe 2 (MoO 4 ) 3 .…”

Scheme of orthomolybdates, KxCoy(MoO4)z

“…The proposed scheme of K-Co-orthomolybdates is compared with the reported one for Na-Fe-orthomolybdates [5]. Up to now only the alluaudite-type phase has been found in both systems.…”

“…The only known quarternary phase in this system, which is not an orthomolybdate, is K 10 CoMo 7 O 27 [5].…”