RESUMEN
Fast cation transport in solids underpins energy storage. Materials design has focused on structures that can define transport pathways with minimal cation coordination change, restricting attention to a small part of chemical space. Motivated by the greater structural diversity of binary intermetallics than that of the metallic elements, we used two anions to build a pathway for three-dimensional superionic lithium ion conductivity that exploits multiple cation coordination environments. Li7Si2S7I is a pure lithium ion conductor created by an ordering of sulphide and iodide that combines elements of hexagonal and cubic close-packing analogously to the structure of NiZr. The resulting diverse network of lithium positions with distinct geometries and anion coordination chemistries affords low barriers to transport, opening a large structural space for high cation conductivity.
RESUMEN
Argyrodite is a key structure type for ion-transporting materials. Oxide argyrodites are largely unexplored despite sulfide argyrodites being a leading family of solid-state lithium-ion conductors, in which the control of lithium distribution over a wide range of available sites strongly influences the conductivity. We present a new cubic Li-rich (>6 Li+ per formula unit) oxide argyrodite Li7SiO5Cl that crystallizes with an ordered cubic (P213) structure at room temperature, undergoing a transition at 473 K to a Li+ site disordered F4Ì 3m structure, consistent with the symmetry adopted by superionic sulfide argyrodites. Four different Li+ sites are occupied in Li7SiO5Cl (T5, T5a, T3, and T4), the combination of which is previously unreported for Li-containing argyrodites. The disordered F4Ì 3m structure is stabilized to room temperature via substitution of Si4+ with P5+ in Li6+xP1-xSixO5Cl (0.3 < x < 0.85) solid solution. The resulting delocalization of Li+ sites leads to a maximum ionic conductivity of 1.82(1) × 10-6 S cm-1 at x = 0.75, which is 3 orders of magnitude higher than the conductivities reported previously for oxide argyrodites. The variation of ionic conductivity with composition in Li6+xP1-xSixO5Cl is directly connected to structural changes occurring within the Li+ sublattice. These materials present superior atmospheric stability over analogous sulfide argyrodites and are stable against Li metal. The ability to control the ionic conductivity through structure and composition emphasizes the advances that can be made with further research in the open field of oxide argyrodites.
RESUMEN
The title compound, sodium chromium/aluminium molybdenum/aluminium dodeca-oxide, Na0.72Cr0.48Al1.74Mo2.77O12, was prepared by solid-state reaction. Its crystal structure is related to NaSICON-type compounds. The framework is built up from M1O6 (M1 = Cr/Al) octa-hedra and M2O4 (M2 = Mo/Al) tetra-hedra inter-connected by corners. The three-dimensional framework contains cavities in which sodium cations are located. Two validation models (BVS and CHARDI) were used to confirm the proposed structural model. The mobility of Na+ ions in the structure has been investigated by theoretical means.
RESUMEN
The title compound, nonasodium chromium(III) hexakis[molybdate(VI)], ß-Na9CrMo6O24, was prepared by solid-state reactions. This alluaudite-type structure is constituted of infinite layers formed by links between M 2O10 (M = C/Na) dimers and MoO4 tetra-hedra. The Na(+) and Cr(3+) cations are located in the same site with, respectively, 0.25 and 0.75 occupancies. The layers are connected to each other through MoO4 sharing corners, resulting an in open three-dimensional framework with hexa-gonal-form cavities occupied by Na(+) cations. The proposed structural model is supported by charge-distribution (CHARDI) and bond-valence-sum (BVS) analysis. All atoms are on general positions except for one Mo, two Na (site symmetry 2) and another Na site (site symmetry -1). A comparison is made with the similar structures Na4Co(MoO4)3, Na2Ni(MoO4)2, Cu1.35Fe3(PO4)3 and NaAgFeMn2(PO4)3.
