Elaboration, étude structurale et analyse CHARDI et BVS d'une nouvelle variété β-Na₉Cr(MoO₄)₆de type alluaudite

Abstract

This alluaudite-type structure is constituted of infinite layers formed by links between M 2O10 (M = Cr1/Na1) dimers and MoO4 tetra­hedra. The Na+ and Cr3+ cations are located in the same genel site with, respectively, 0.25 and 0.75 occupancies. The layers are related by sharing corners with MoO4 tetra­hedra, resulting an in open three-dimensional framework with hexa­gonal-form cavities occupied by Na+ cations.

New Solid Electrolyte Na9Al(MoO4)6: Structure and Na+ Ion Conductivity

“…In comparison with Na 9 R(MoO 4 ) 6 (R = Fe, Sc, Cr), the alluaudite 7 related structure of monoclinic high temperature β-Na 9 Cr(MoO 4 ) 6 (space group C2/c) is constituted of infinite layers formed by links between M 2 O 10 (M = Cr/Na) dimers and MoO 4 tetrahedra. 39 Earlier high Na + ion conductivity was found in Na 9 Fe(MoO 4 ) 6 33 . However, the mechanism of ion transport was not determined.…”

“…The basic structural units of Na 9 R (MoO 4 ) 6 ( R = Fe or Sc) and low-temperature trigonal α-Na 9 Cr­(MoO 4 ) 6 (space group R 3̅ c ) are isolated polyhedral [ R (MoO 4 ) 6 ] 9– clusters composed of a central R O 6 octahedron sharing vertices with six MoO 4 tetrahedra to form an open framework in which the Na + cations are bound to the free vertices of the MoO 4 tetrahedra. In comparison with Na 9 R (MoO 4 ) 6 ( R = Fe, Sc, or Cr), the alluaudite related structure of monoclinic high-temperature β-Na 9 Cr­(MoO 4 ) 6 (space group C 2/ c ) is constituted of infinite layers formed by links between M 2 O 10 ( M = Cr/Na) dimers and MoO 4 tetrahedra . Previously, a high Na + ion conductivity was found in Na 9 Fe­(MoO 4 ) 6 .…”

Mechanism of Sodium-Ion Diffusion in Alluaudite-Type Na5Sc(MoO4)4 from NMR Experiment and Ab Initio Calculations

“…The ionic conductivity of these compounds (σ > 10 –3 S·cm –1 at 673–773 K, E a = 0.5–0.6 eV) , is comparable to that of Na 2+2 x Fe 2– x (SO 4 ) 3 and exceeds the corresponding values of isostructural orthophosphates Na 2 M 3 (PO 4 ) 3 (M 3 = GaMn 2 , GaCd 2 , InMn 2 , and FeMnCd) having σ ≈ 10 –5 S·cm –1 at 673 K and E a = 0.7–0.8 eV . Besides the above-mentioned compounds, alluaudite double molybdates of trivalent metals Na 5 R­(MoO 4 ) 4 (R = Sc and In) and Na 9 R­(MoO 4 ) 6 (R = Fe, Al, and Sc) − are also known as good sodium conductors.…”

“…Most of the studies of alluaudite molybdates have been devoted to their synthesis, crystal structure refinement, and electrophysical properties. − ,− ,− Much less consideration has been given to sodium transport mechanisms. Only recently, a microscopic mechanism of Na-ion diffusion was studied for Na 2+2 x Fe 2– x (SO 4 ) 3 , where the energy barriers were estimated for sodium-ion migration between different structural sites.…”

Synthesis, Structure, and Conductivity of Alluaudite‐Related Phases in the Na2MoO4–Cs2MoO4–CoMoO4 System

“…Orthophosphates and sulfates adopting the structure of alluaudite (Na, Ca)(Fe, Mn, Mg)(PO 4 ) 3 (space group C 2/ c, a = 12.004, b = 12.533, c = 6.404 Å, β = 114.4°, Z = 4) with open 3D frameworks and channels along the shortest c ‐axis and variable contents of sodium (lithium) and transition metal cations are considered as promising Na‐ or Li‐ion conductors or battery materials . The alluaudite‐type structure is also found for double molybdates Na 4–2 x M 1+ x (MoO 4 ) 3 ( M = Mg, Mn, Co, Ni, Cu, Zn, Cd; 0 ≤ x ≤ 0.50), K 4–2 x Cd 1+ x (MoO 4 ) 3 (0.14 ≤ x ≤ 0.38),[3d] Na 5 Sc(MoO 4 ) 4 , Na 5 In(MoO 4 ) 4 , β‐Na 9 Cr(MoO 4 ) 6 , as well as for triple molybdates K 0.4 Na 3.6 Co(MoO 4 ) 3 , KNa 5 Mn 3 (MoO 4 ) 6 , K 0.13 Na 3.87 Mg(MoO 4 ) 3 and double tungstates Na 4 Mg(WO 4 ) 3 and Na 5 Sc(WO 4 ) 4 . [3c] The crystal chemistry and compositions of the alluaudite‐type molybdates and tungstates was considered by us in.…”