9 research outputs found
Synthesis and characterisation of new MO(OH)2 (M = Zr, Hf) oxyhydroxides and related Li2MO3 salts
Two new solid MO(OH)2 (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P21/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling
New Solid Electrolyte Na 9 Al(MoO 4 ) 6 : Structure and Na + Ion Conductivity
International audienc
New Solid Electrolyte Na<sub>9</sub>Al(MoO<sub>4</sub>)<sub>6</sub>: Structure and Na<sup>+</sup> Ion Conductivity
Solid
electrolytes are important materials with a wide range of
technological applications. This work reports the crystal structure
and electrical properties of a new solid electrolyte Na<sub>9</sub>Al(MoO<sub>4</sub>)<sub>6</sub>. The monoclinic Na<sub>9</sub>Al(MoO<sub>4</sub>)<sub>6</sub> consists of isolated polyhedral [Al(MoO<sub>4</sub>)<sub>6</sub>]<sup>9–</sup> clusters composed of a
central AlO<sub>6</sub> octahedron sharing vertices with six MoO<sub>4</sub> tetrahedra to form a three-dimensional framework. The AlO<sub>6</sub> octahedron also shares edges with one Na1O<sub>6</sub> octahedron
and two Na2O<sub>6</sub> octahedra. Na3–Na5 atoms are located
in the framework cavities. The structure is related to that of sodium
ion conductor II-Na<sub>3</sub>Fe<sub>2</sub>(AsO<sub>4</sub>)<sub>3</sub>. High-temperature conductivity measurements revealed that
the conductivity (σ) of Na<sub>9</sub>Al(MoO<sub>4</sub>)<sub>6</sub> at 803 K equals 1.63 × 10<sup>–2</sup> S cm<sup>–1</sup>. The temperature behavior of the <sup>23</sup>Na
and <sup>27</sup>Al nuclear magnetic resonance spectra and the spin-lattice
relaxation rates of the <sup>23</sup>Na nuclei indicate the presence
of fast Na<sup>+</sup> ion diffusion in the studied compound. At <i>T</i><490 K, diffusion occurs by means of Na<sup>+</sup> ion
jumps exclusively through the sublattice of Na3–Na5 positions,
whereas Na1 and Na2 become involved in the diffusion processes (through
chemical exchange with the Na3–Na5 sublattice) only at higher
temperatures