Morphological unit cell parameters

Irrespectively of the iron content, the applied synthesis procedure yielded highly crystalline microporous products i.e. the Fe-ZSM-22 zeolite. No contamination with other microporous phases or unreacted amorphous material was detected. The SEM analysis revealed that size and morphology of the crystals depended on the Si/Fe ratio. The ZSM-22 samples poor in Fe (Si/Fe=150) consisted of rice-like isolated crystals up to 5 p. On the other hand the preparation with a high iron content (Fe=27, 36) consisted of agglomerates of very small (<0.5 p) poorly defined crystals. The incorporation of Fe3+ into the framework positions was confirmed by XRD - an increase of the unit cell parameters with the increase in the number of the Fe atoms introduced into the framework was observed, and by IR - the Si-OH-Fe band at 3620 cm 1 appeared in the spectra of activated Fe-TON samples. 

The Mo2N-A X-ray diffraction powder pattern shows broad diffraction peaks, making slight variations of the a cubic unit cell parameter difficult to measure. Despite careful preparation the platelet morphology of the powder gives rise to preferential orientation and an increase in the 200 peak intensity relative to the 111 reflection (Figure 13.3). 

Space groups and unit-cell parameters are generally as taken from the published literature, but some have been transformed into alternative settings to maintain consistency within a group or to conform with traditional morphological descriptions. 

The convention of Miller indices is used to describe the planes within a unit cell. Miller indices are defined as the reciprocals of the intercept, which the plane makes with each of the three crystal axes. Each plane is denoted by three parameters h k and Planes which are parallel to a crystal axis are given the Miller index of 0 while planes formed in the negative direction are written with a bar over the number in the Miller index. The Miller index of a single specific plane is written within parentheses (hkl) whereas the Miller indices describing a whole family of faces are written with braces hkl. The faces that exist and define the crystal morphology are termed morphologically important and are commonly identified by the Miller indices of the planes represented by those faces. 

The crystal morphology (Fig. 4) and the dimension of the unit cell b parameter of 76.403 A lead to the conclusions that s... 

The morphology and habit exhibited by a crystal are controlled by a combination of the internal crystal structure of the unit cell and the external growth parameters. The morphology that is observed is in general a consequence of... 

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