A synchrotron powder diffraction study of Na-LTA

The charge density distribution of Na-LTA is obtained by the Maximum Entrop y Method (MEM) using synchrotron powder data. In the MEM map, all the compo nents; framework, cations and absorbed water molecules, are all clearly sho wn even if the site occupation is very low, say less than 10%, A powder dif fraction experiment is carried out by the transmission geometry with Imagin g Plate (IP) detector at BL-6A(2), PE In the analysis, a new method which i s a iterative use of Rietveld refinement and MEM is applied in order to imp rove a structure model used in Rietveld refinement An initial structure mod el used in Rietveld is just simple framework only. In the first Rietveld re finement, the agreement factor, RI, was very had i.e.37.4%. Following MEM a nalysis, however, gives the key information of how to improve next structur e model for Rietveld refinement Improvement of the structure model by the p resent method eventually lead to RI to be as low as 5.2%, which proves a gr eat success of the method. The present method may lead a drastic change of structural studies of zeolite compounds when it is applied to high resoluti on and high intensity synchrotron powder data.