THE CRYSTAL-STRUCTURE OF A NONSTOICHIOMETRIC NASICON
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abstract
The crystal structure of a nonstoichiometric NASICON prepared from a hydrothermally synthesized precursor phase was solved by means of X-ray powder and neutron powder diffraction methods. The NASICON phase is monoclinic with unit cell parameters, from Rietveld refinement of the neutron data, of a = 15.6209(8), b = 9.0326(5), c = 9.2172(5) A , = 123.67(1), V = 1082.5 A 3. The space group is C2/c with Z = 4. The structure is essentially that proposed earlier by Hong, but the nonstoichiometry results from replacement of part of the Zr4+ by Na+. Refinement of site occupancies coupled with the requirement of overall charge balance yields the formula Na2.88(Na0.32Zr1.68)Si1.84P1.16O11.54 which also agrees well with analytical data. Only 20% of the Na1 sites are occupied, but 80% of the Na3 sites are filled. This structure provides a framework from which to rationalize the many reports in the literature that NASICON can only be prepared with difficulty by high temperature solid state reactions. 1985.
