A powder neutron diffraction study has been carried out on dehydrated sodium zeolite ZK-4 (Na9Al9Si15O48). No superlattice reflections resulting from Si,Al ordering in the tetrahedral sites could be detected, in contrast to its less siliceous analogue, zeolite-A ( Si Al∼1.0); the space group is Pm3m and the cubic cell constant, a=12.1907(8) A ̊. The mean TO bond length (1.652 Å) is in excellent agreement with that expected for a zeolite with the above chemical formula (1.653 Å). The principal sodium location is in the centre of the six-ring window (Na(1)O(3)=2.311(8) Å). Additional peaks were observed in difference Fourier calculations, probably resulting from decomposition of the organic template, or slight dealumination of the framework. Gross deviations from the ideal Gaussian peak shape are observed in the neutron powder pattern. These are modelled by using a Voigt function and a new treatment for asymmetry, reducing the RwPr factor from 19.7% to 12.6%. This leads to significant changes in some of the profile parameters, but, apart from an improvement in precision, the atomic coordinates are essentially unchanged. © 1986.
