New double molybdate Na{sub 9}Fe(MoO{sub 4}){sub 6}: Synthesis, structure, properties

A new double molybdate Na{sub 9}Fe(MoO{sub 4}){sub 6} was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, X-ray fluorescence analysis, Mossbauer and dielectric impedance spectroscopy. Single crystals of Na{sub 9}Fe(MoO{sub 4}){sub 6} were obtained and its structure was solved (the space group R3{sup ¯}, a=14.8264(2), c=19.2402(3) A, V=3662.79(9) A{sup 3}, Z=6, R=0.0132). The structure is related to that of sodium ion conductor II-Na{sub 3}Fe{sub 2}(AsO{sub 4}){sub 3}. The basic structure units are polyhedral clusters composed of central FeO{sub 6} octahedron sharing edges with three Na(1)O{sub 6} octahedra. The clusters share common vertices with bridging MoO{sub 4} tetrahedra to form an open 3D framework where the cavities are occupied by Na(2) and Na(3) atoms. The compound melts incongruently at 904.7±0.2 K. Arrhenius type temperature dependence of electric conductivity σ has been registered in solid state (σ=6.8×10{sup −2} S cm{sup −1} at 800 K), thus allowing considering Na{sub 9}Fe(MoO{sub 4}){sub 6} as a new sodium ion conductor. - Graphical abstract: A new double molybdate Na{sub 9}Fe(MoO{sub 4}){sub 6} was synthesized and structurally characterized, its physicochemical properties were studied. Display Omitted - Highlights: • A new compound Na{sub 9}Fe(MoO{sub 4}){sub 6} wasmore » synthesized as ceramics and single crystals. • Na{sub 9}Fe(MoO{sub 4}){sub 6} structure is related to that of sodium-ion conductor II-Na{sub 3}Fe{sub 2}(AsO{sub 4}){sub 3}. • Physicochemical properties of the compound were studied. • Arrhenius plot for conductivity showed 6.8×10{sup −2} S cm{sup −1} at 800 K, E{sub a}∼0.8 eV. • Thus, Na{sub 9}Fe(MoO{sub 4}){sub 6} may be considered as a new sodium ion conductor.« less