Preferential site occupation

According to an analysis performed by Ferro and Cacciamani (2002), the preferential site occupancies observed in MgCu2-type phases are summarized in Table 3.8. The atoms preferentially present in each site type are indicated. 

Table 3.8. cF24-MgCu2 type Laves phases, (preferential site occupancies). 

S.4.3.4 Order-disorder transformations. The previous examples considered strict site preference for the components in sublattice phases. For example, in the (Cr, Fe)2B compound, B is not considered to mix on the metal sublattice, nor are Cr and Fe considered to mix on the B sublattice. This strict limitation on occupancy does not always occur. Some phases, which have preferential site occupation of elements on different sublattices at low temperatures, can disorder at higher temperatures with all elements mixing randomly on all sublattices. 

Investigations on the pseudobinary systems of RB5 compounds with Th have revealed a number of extraordinary effects such as preferential site occupation... 

The reason for preferential axial site occupancy by mono-dentate ligands is probably related to results of recent CNDO calculations on [Co CO) ] (15) which show that the axial carbonyls are least involved in back-bonding. Extrapolation to Rh - and Ir -derivatives seems reasonable and finds some support from n.m.r. measurements, which show that the n.m.r. chemical shift of the axial carbonyl is always at higher field than the radial carbonyl in both rhodium (16) and iridium derivatives. (12)... 

Figure 4 illustrates some of the defect sites that must exist in the polymeric superstructures of the 5NPE c [CBPQ T ] and 5NP c [CBPQT ] crystals. Since 5NPE is not a HMW polymer, a mixture of discrete pseudorotaxanes sum to a lattice with 1/6 DNP site vacancy. Although the vacancy can occur either inside (Fig. 4a) or alongside (Fig. 4b) CBPQ F, the structure refines to site occupancy factors of 0.900 and 0.767 for encircled and unencircled DNP units, respectively, indicating that almigside DNP units are preferentially vacated over encircled ones.

Preferential occupation of / edge/defect sites by atomic O/N... 

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