Porotectosilicate Structure Determination from Model Building

Abstract

AbstractPorotectosilicates are a class of siliceous crystalline materials which includes both zeolites and materials which resemble zeolites in crystal structure, but may or may not have ion exchange capability. The framework structures of these porotectosilicates are comprised of “T” atoms tetrahedrally coordinated to oxygen, where “T” can be Al, Si or any other element capable of isomorphous substitution for silicon. The occurrence of small crystals and the additional problems introduced by the presence of stacking faults and crystal twinning make structure determination of porotectosilicates by conventional approaches difficult.The industrial significance of these materials has led to the development of a technique which permits the determination of their structure. The method involves the construction of appropriate hypothetical models, a DLS refinement followed by computation of a Smith plot for comparison with the experimental powder pattern. Model crystal structures may now be refined using the Rietveld technique. It is expected that this technique will contribute significantly to the solution of porotectosilicate structures which are difficult--if not impossible--to establish by other techniques.