Additives different crystallographic faces

Influence of additives on deposition at different crystallographic faces... 

Since every unit cell in the crystal lattice is identical to all others, it is said that the lattice can be primitive or centered. We already mentioned (Eq. 1.1) that a crystallographic lattice is based on three non-coplanar translations (vectors), thus the presence of lattice centering introduces additional translations that are different from the three basis translations. Properties of various lattices are summarized in Table 1.13 along with the international symbols adopted to differentiate between different lattice types. In a base-centered lattice, there are three different possibilities to select a pair of opposite faces, which is also reflected in Table 1.13. 

The earliest investigations of the crystal structure of cerium (Hull, 1921) indicated that cerium had both a face centered cubic (fee) and a hexagonal close-packed (hep with cl a = 1.62) structure at room temperature and one atmosphere. Subsequent studies revealed only the fee phase with a ==5.15 A, which today is identified as y-Ce (see table 4.2 for additional crystallographic data). About 25 years ago the a-Ce phase was identified by X-ray methods at both high pressure and room temperature (Lawson and Tang, 1949) and at low temperature and atmospheric pressure (Schuck and Sturdivant, 1950) to have a fee structure but with a = 4.83 A. The a phase, with a volume about 17% less than that of y-Ce, is also known as the collapsed fee phase. This large volume difference is also observed in dilatometric and volumetric studies of the a y transformation. 

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