Stoichiometric Defects

Defects in Solid

Crystalline solids are formed by the well-ordered replication of a volumetric number of unit cells in all directions. An ionic crystal that consists of a single unit cell with identical lattice points throughout the crystal is known as an ideal crystal. Regardless of whether such ideal crystals exist only at absolute zero (0K) temperature. At any temperature above 0 K, the crystals are somewhat out of a completely arranged arrangement. I...

Types of Defects

The defects are of two types:...

Point Defect in Solid

When crystallisation occurs quickly, point defects arise, preventing a perfect crystal structure from forming. It should be noted, however, that even during a slow crystallisation, there exist defects. Point Defects can be divided into three categories....

Stoichiometric Defects

Stoichiometric compounds are those in which the number of positive and negative ions is in the ratio indicated by their chemical formulas. For the sake of simplicity, we can consider AB-type compounds that have an equal number of A+ and B– ions. Defects in these types of compounds are called stoichiometric defects. Generally, two types of defects are observed in these compounds....

Schottky Defect

The Schottky defect arises if some of the atoms or ions are missing from their normal lattice sites. The lattice sites which are abortively are called lattice vacancies or holes. So far as the crystal has to be electrically neutral, an equal number of cations and anions are missing. The ideal AB crystal is shown above. Presence of two holes one due to missing cation and the other due to missing. It is parring excellence a vacancy defect in ionic solids....

Frenkel Defect

The Frenkel defect occurs when an ion disappears from its normal state and occupies an interstitial site between lattice points. The existence of a hole due to a missing cation from its normal position and occupying the interstitial position is shown. In this case, also, the crystal remains electrically neutral because the number of anions and cations remains the same This defect is also known as an interstitial defect. It creates vacancy defects. It has its original position and an interstitial defect in its new location....

Non-Stoichiometric Crystals Defects

Non-stoichiometric defects unsettle the stoichiometry of solids. The ionic sites occupied by unpaired electrons are called F-centers (Farbenzenter or colour centre). They impart colour to alkali metal halide crystals. The colours are produced by the excitation of these electrons when they absorb energy from visible light falling on the crystal. Excess of Na turns NaCl crystals yellow, excess of Li makes LICI pink, and excess of potassium turns KCl crystals purple....

FAQs on Point Defects

Q1: What is a Point Defect?...