Point defect formation, energetics

An alternative perspective on the subject of point defects to the continuum analysis advanced above is offered by atomic-level analysis. Perhaps the simplest microscopic model of point defect formation is that of the formation energy for vacancies within a pair potential description of the total energy. This calculation is revealing in two respects first, it illustrates the conceptual basis for evaluating the vacancy formation energy, even within schemes that are energetically more accurate. Secondly, it reveals additional conceptual shortcomings associated with... 

Catalytic applications of ceria and ceria-based mixed oxides depend primarily upon the nature and concentration of the defects present in the material. Although experimental techniques are available for the study of these defects, the characterization of their physical properties at the atomic level is often very difficult. The most important point defects in ceria are oxygen vacancies, reduced Ce centers and dopant impurities. The formation energy of such defects and the energetics of their mutual interactions within the bulk oxide have been the subject of several computational studies. 

Anyway, in this manner, we have built a thermodynamic bridge between defect properties, solid and liquid state , that is also mirrored in many semiempirical relationships (e.g. between enthalpy of defect formation and melting point). This, of course, is to be expected, since defect formation contains almost aU the relevant energetic and entropic information. Thus, it is understandable that t3q>ical binary... 

It is supposed that any unit of the chain may form a contact with any unit of another chain. Variations of parameters allow the kinetics of dissociation and association in the system to be controlled. Rate constants of formation and disappearance of one contact were estimated122. It is seen on the computer display screen that a strongly defect structures are formed first. In time, these structures go over to completely stretched ones. A completely stretched ladder form of the complex was found to be the most advantageous from the energetic point of view. 

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