Face-cubic anisotropy

Although the correlation between ionic porosity and diffusivity is imperfect, there is a rough trend that oxygen diffusivity in the minerals increases with increasing IP. The trend is useful in qualitative estimation of closure temperature (among other applications). Extending the relation to metallic systems, one prediction is that diffusion in face-centered cubic structure (25.95% free space) is slower that that in body-centered structure (31.98% free space) of the same metal composition. To avoid the issue of anisotropy, it would be worthwhile to reexamine the relations between diffusivity and ionic porosity using only isometric minerals. 

Although the Prussian blue phases exhibit remarkable magnetic properties, their face-centred cubic structures mean that no magnetic anisotropy can be expected. 

The structure of cubic boron nitride is of the zincblende (or sphalerite) type which is similar to that of diamond and p-SiC and is characterized by extremehardness and excellent chemical resistance. It is shown in Fig. 12.3. Note the similarity with Fig. 7.1 of Ch. 7. This structure is relatively simple in the sense that it is essentially isotropic, in contrast with the pronounced anisotropy of hexagonal boron nitride. It can be visualized as a stacking of puckered infinite 111 layers or as two face-centered interpenetrating cubic sublattices, one consisting entirely of boron atoms and the other entirely of nitrogen atoms.I l... 

One particular type of cubic structure, the zinc blende structure found in several important compound ceramic semiconductors such as GaAs and InP, has been known to exhibit a particular type of composition hardness anisotropy first noted more than 40 years ago when it was christened hardness polarity. This effect is seen on (111) and (ITT) faces of the group Ill-group V ceramics, of which GaAs is the most investigated. The hardness difference is ascribed initially to the fact that these two planes are formed either by... 

The most striking feature of the collected data in the tables in this chapter and in Chapter 6 on anisotropic indentation hardness values for crystalline ceramics is its dependence on the relevant active slip systems. This has been extended by observation to encompass materials beyond ceramics. Thus, the nature of anisotropy for a soft, face-centered cubic metal may be the same as for hard, covalent cubic crystals like diamond, since they both have lll (lTo) slip systems. Consequently it is natural that, in order to develop a universal model, we should first look for explanations based on mechanisms of plastic deformation. 

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