In Class 12 Chemistry (The Solid State), point defects in crystals are an important topic. The Schottky Defect is one of the primary types of stoichiometric point defects found in ionic solids.
Interestingly, Silver Bromide (AgBr) is a unique ionic solid that shows both Schottky defects and Frenkel defects simultaneously.
A Schottky defect occurs when an equal number of cations (positive ions) and anions (negative ions) are missing from their normal lattice sites in an ionic crystal. Because an equal number of positive and negative charges leave, the electrical neutrality of the crystal is perfectly maintained.
This defect is typically shown by ionic compounds that have:
Since ions completely leave the crystal structure, the total mass of the crystal decreases while its volume remains the same. Therefore, a Schottky defect decreases the density of the substance.
Common examples of compounds showing Schottky defects include:
In a Schottky defect, ions completely leave the crystal (lowering density). In a Frenkel defect, the smaller ion (usually the cation) just moves from its normal site to an interstitial site within the crystal (so the density remains the same).
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