What are point defects in crystals?
Point defects are lattice defects of zero dimensionality, i.e., they do not possess lattice structure in any dimension. Typical point defects are impurity atoms in a pure metal, vacancies and self-interstitials.
What types of defects arise in solids?
Point, Line, and Area defects arise in solids. The number and type of defects can be varied and controlled (e.g., T controls vacancy conc.) Defects affect material properties (e.g., grain boundaries control crystal slip).
What is Schottky defect example?
Examples. This type of defect is typically observed in highly ionic compounds, highly coordinated compounds, and where there is only a small difference in sizes of cations and anions of which the compound lattice is composed. Typical salts where Schottky disorder is observed are NaCl, KCl, KBr, CsCl and AgBr.
Why does density decrease in Schottky defect?
Schottky defects is a vacancy defect which lowers the density of the solid crystal.In this an equal number of cation and anion is missing from the interstitial site and this leads to the lowering of the density.
What happens to density in Frenkel defect?
Frenkel defect contains ionic crystals where the anion is larger than the cation. Both anion and cation leave the solid crystal. The density of the solid decreases. Density remains the same.
Does density change in Schottky defect?
In Schottky defect, certain cations and anions are missing from the crystal lattice. Therefore, the density of the crystal decreases.
What is a self interstitial?
Self-interstitial defects are interstitial defects which contain only atoms which are the same as those already present in the lattice.
What is interstitial position?
Interstitial Site. interstitial site: a position between the regular positions in an array of atoms or ions that can be occupied by other atoms or ions.
What is F Centre defect?
An F-center, Farbe center or color center (from the original German Farbzentrum, where Farbe means color and zentrum means center) is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more unpaired electrons.
What are the consequences of Schottky defect?
Consequences of Schottky defect: Density of the crystal decreases. The crystal begins to conduct electricity to small extent by ionic mechanism. The presence of too many voids lowers the lattice energy or the stability of the crystal.
Why are there stoichiometric defects?
Solution : Stoichiometric defects are so called because they do not alter the stochiometry of the crystal in both Schottky and Frenkel defects. They are called intrinsic defects because it is due to the deviation from regular arrangement of constituent particles with in the crystal and no external substance is added.
Which is not stoichiometric defects?
Non-stoichiometric defects: The defects which disturb the stoichiometry of the compounds are called non-stoichiometry defects. These defects are either due to the presence of excess metal ions or deficiency of metal ions.
What are metal excess defects?
A metal excess defect is one of the defects seen in the crystal structures. These are the non-stoichiometric inorganic solids that contain constituent elements in non-stoichiometric ration because of the defects in their crystal structures.
What does stoichiometry mean?
Stoichiometry is exactly that. It is the quantitative relation between the number of moles (and therefore mass) of various products and reactants in a chemical reaction. Chemical reactions must be balanced, or in other words, must have the same number of various atoms in the products as in the reactants.