Bulk distortion energy, surface

The first term is related to the bulk distortion energy, determined by the elastic deformation and external bulk field interactions. The second term is the surface contribution of the limiting surface D. The actual director field can be obtained by minimizing the energy. In a simple sandwich cell geometry (see Figure 4.27), the director (n(r)) can be expressed with the tilt angle as Q = cos (n k)> where k is the unit vector of the surface normal. 

Brooks [10] assumed the crystal is isotropic and considered the formation of a vacancy as an equivalent to creating new surface, equal to the area of one unit cell, being approximately the spherical surface of the atomic volume. He also assumed that the surface tension of the hole would shrink the vacancy size by distorting the rest of the crystal elastically. Then, the for atomic vacancy formation inside a bulk solid equals the minimum of the sum of the increased surface energy and distortion energy,... 

Returning to more surface chemical considerations, most literature discussions that relate adhesion to work of adhesion or to contact angle deal with surface free energy quantities. It has been pointed out that structural distortions are generally present in adsorbed layers and must be present if bulk liquid adsorbate forms a finite contact angle with the substrate (see Ref. 115). Thus both the entropy and the energy of adsorption are important (relative to bulk liquid). The... 

The efficiencies of various metals for the recombination of H atoms are given in Table 8. In all cases, the recombination is first-order and the activation energy is less than 5 kJ mole 1. The fact that the state of anneal of the metal can alter 7 by a factor of ten [14] suggests that the reaction may occur on minority sites, rather than on a well-defined surface characterised by the intrinsic properties of the metal. This is certainly the explanation for the wide range of values reported for palladium. The extent of diffusion of H atoms into the bulk is also a complicating factor, making 7 dependent on the time of exposure to H atoms for palladium, this effect can be so gross as to result in distortion of the sample. 

Catalytic molecular surface species may undergo drastic changes in their structure in the presence of reactants. For example, polymeric clusters may transform into highly distorted monomeric species. A crystalline phase may become mobile at its Tammann temperature, as shown by Raman spectroscopy, and it may spread over oxide supports driven by the reduction of the overall surface free energy. Reactive environments trigger many structural transformations, exemplified by particle sintering, dispersion of bulk phases, segregation of surface species into bulk phases, and solid-state reactions between supported oxides and supports. 

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