Schottky defect or small shot effect is named after a popular German physicist Walter H. In his model, he explains that the defect is formed in ionic crystals when oppositely charged ions leave their lattice sites which leads to the creation of vacancies. These vacancies are further created to maintain a neutral charge in the crystal. The model further explains that the surrounding atoms also move to occupy these vacancies. Typically, when the defect is found in non-ionic crystals it is referred to as lattice vacancy defect.
Definition: Schottky defect is a type of point defect or imperfection in solids which is caused by a vacant position that is generated in a crystal lattice due to the atoms or ions moving out from the interior to the surface of the crystal.
Yakov Frenkel, a Russian physicist was the person who discovered the Frenkel defect while conducting research on the molecular theory of the condensed state. This discovery was important as his model explained a defect in the molecule of crystalline solids where an atom or ion moved out of their own lattice site making it vacant while occupying another intermediary vacant site on the same crystal. The defect is also known as dislocation defect and it also clearly depicts both vacancy and self-interstitial defects.
Definition: A Frenkel defect is another form of a point defect which is created when an atom or cation leaves its original place in the lattice structure to create a vacancy while occupying another interstitial position within the solid crystal.