3.4 Energy for the formation of a vacancy and number of vacancies — at equilibrium concentration

Energy supply to a crystal moves some of the atoms present at regular atomic sites in the interior of the crystal to the surface, so that vacancies are formed inside the crystal. If we supply energy to an ionic crystal, then either cation–anion pairs are moved to the surface [Schottky defect] or cations are moved to interstitial spaces [Frenkel defect], so that vacancies are formed inside the ionic crystal. We shall find the relation between number of vacancies and energy of formation of a vacancy in all the above cases.

(i) In metallic crystals: Let a crystal contains N number of atoms. The energy required to move an atom at a regular atomic site ...

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