Microcrystal X-ray diffraction and NMR studies of thermal expansion properties of pure silica zeolites FER and a comparison with IFR

The mechanism of negative thermal expansion in a purely siliceous form of zeolite FER is compared with that of zeolite IFR. At first glance the materials seem to show vastly differing behaviour - FER shows positive thermal expansion LIP to a phase transition (similar to 400K) above which it is a negative thermal expansion, IFR is a negative thermal expansion material at all temperatures so far measured. A comparison of the two mechanisms is made and a series of rules' about the magnitude of negative thermal expansion is discussed.