ZEOLITE-BETA - A DISORDERED STRUCTURE OF PSEUDO-OD TYPE

Single crystals of zeolite beta have been investigated for which X-ray photographs indicated disorder of the OD type. The X-ray intensities of the sharp reflexions were used for the refinement of the layer geom etry which originally was suggested for interpreting electron microsco py and X-ray experiments of disordered powder material. The refinement converged at R = 6.0% although averaging the intensities for symmetri cally equivalent reflexions gave R(int) = 2.8%. In addition the R-fact or increased as a function of sin theta/lambda. Because obviously the least-squares procedure did not compensate for the increase of the R-f actor by anisotropic or large isotropic temperature factors the follow ing corrections for the OD-model of the structure are suggested: becau se of local chemical bondings between atoms in subsequent layers the p ositions of the layers deviate slightly from where they are expected a ccording to OD theory. Because nevertheless there are sharp family ref lexions the layers have to be stacked in such a way that the disorder in the structure still is of the OD-type ''in average''.