PREPARATION AND CHARACTERIZATION OF SOME NEW COMPOUNDS WITH NASICON-TYPE STRUCTURES

The new compounds CuTiZrP3O12, NbSnP3O12, FexTaTiP3O12 x <0.33) and SnxTaTiP3O12 (x <0.5) have been prepared and characterized by X-ray powder diffraction. The lattice parameters are compared with those of related compounds. The copper K-edge extended X-ray absorption fine structure (EXAFS) indicates that Cu+ ions in materials of composition Cu+M24+P3O12 are displaced along [001] from the centre of an octahedral interstitial site. The incorporation of iron and tin as Fe2+ and Sn2+ within the three dimensional interspace of compounds of the type M5+M4+P3O12 is discussed in terms of the amenability of pentavalent cations in the host lattice to reduction to a lower oxidation state, which is stable in octahedral oxygen coordination.