Theory of point defect energetics: A review

The energetics of point defects provide the controlling factor in determini ng the atomistic mechanisms in a wide range of solid state processes. We pr esent here a pedagogical overview of the development of the continuum, quas i-lattice and lattice theories for different classes of point defects and m aterials. Varied approaches were followed in the past in modelling the rele vant perfect crystals for interatomic forces for nonionic solids and model potentials for ionic materials. The earliest continuum approaches are those of Eshelby and Jest for treating point defects as elastic and dielectric s ingularities. These were followed by semicontinuum Mott-Littleton technique s and the Kanzaki defect force techniques in application to charged and neu tral defect species. However the importance of a correct assessment of the dielectric polarization and the anharmonicity of the forces in the evaluati on of the enthalpies and volumes have been well documented. Numerical compu tations of the enthalpies are seen to be sensitive to the choice of potenti al parameters and polarization models to varying degrees. While the theoret ical picture is relatively clear in the case of the simpler materials with a near-ideal pure disorder, materials with mixed type of point defect disor ders call for a more challenging simulation of defect environments which am ong other things should take into account the strong inhomogeneities of def ect fields. The paper gives an overview of the evolution covering the highl ights of these developments.