RIETVELD REFINEMENT RESULTS ON 3 NONSTOICHIOMETRIC MONOCLINIC NASICONS

The results of three powder Rietveld refinements of monoclinic NASICONs, prepared by different methods, are examined. Neutron TOF (time of flight) data were collected on two samples: a sol-gel prepared NASICON was found to have the formula Na//3Zr//1//. //9//3Si//2PO//1//1//. //8//6 and a reheated commercially available NASICON a formula of Na//3//. //1//7Zr//1//. //9//3Si//1//. //9P//1//. //1O//1//2. Following the neutron study on a nonstoichiometric hydrothermally prepared NASICON we prepared the same nonstoichiometric phase by sol-gel methods and X-ray Rietveld analysis yielded the formula Na//3//. //2Zr//1//. //6//8Si//1//. //8//4P//1//. //1//6 O//1//1//. //5//4. These differences in stoichiometry are accompanied by structural differences such as Si/P segregation and variations in cavity occupancy by Na** plus . It is proposed that the method of preparation is largely responsible for the observed differences.