Imperfections in Ceramics

The expression defect structure is often used to designate the types and concentrations of atomic defects in ceramics. Because the atoms exist as charged ions, when defect structures are considered, conditions of electroneutrality must be maintained. Electroneutrality is the state that exists when there are equal numbers of positive and 

The ratio of cations to anions is not altered by the formation of either a Frenkel or a Schottky defect. If no other defects are present, the material is said to be stoichiometric, stoichiometry Stoichiometry may be defined as a state for ionic compounds wherein there is the exact 

Figore 12.20 Schematic representation of an Fe vacancy in FeO that results from the formation of two Fe ions. 

Concept Check 12.2 Can Schottky defects exist in K2O If so, briefly describe this type of defect. If they cannot exist, then explain why. 

The eqnflibrinm numbers of both Frenkel and Schottky defects increase with and depend on temperature in a manner similar to the number of vacancies in metals (Equation 4.1). For Frenkel defects, the nnmber of cation-vacancy/cation-interstitial defect pairs (Af ) depends on temperatnre according to the following expression  

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