Defects in Solids

Abstract

In a perfect solid, atoms, molecules, or ions are arranged in a three-dimensional lattice. The removal of any particle from that needs the overcome of the lattice force. Therefore, the perfect lattice of a solid is an ideal state. The real solid is imperfect respectively the arrangement of the particles (disorder in arrangement), the different orientation (orientation disorder), and not uniform in vibration and rotation (movement disorder). Most important for different properties like mechanical and electrical behavior is the nonideal arrangement of the lattice building blocks. According to the extension, it can be distinguished in three-, two-, one-, and zero-dimensional disorder, respectively. Most important for the understanding of electrical conductivity as well as for the diffusion in solids is the zero-dimensional disorder (point defects). From the view of thermodynamics, the generation of defects in solids is understandable. Only at temperature 0 K, the lattice is perfect; that means all particles take their normal positions and the entropy is zero. Due to the entropy effect, the amount of defects increases with increasing temperature and therefore the Gibbs energy is diminished. At a certain concentration of defects, the free energy increases because of the forming of defects has no influence on the entropy. Those defects which are formed without changing of stoichiometry and arise from the solid system itself according to the thermodynamic conditions are called as intrinsic defects or sometimes as stoichiometric defects. According to the place in the lattice, atoms, ions, or molecules move from their normal positions in the lattice into free spaces of the lattice between particles into the so-called interstitials (Frenkel defects) or to the surface (Schottky defects)