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nidhiyadav918... , asked a question
Subject: Chemistry , asked on 2/1/12

why are frenkel defects not found in pure alkali halides?

EXPERT ANSWER

Anand Singh ,Meritnation Expert added an answer
Answered on 3/1/12

The frenkel defect is favoured by a large difference in size between the positive and negative ions. The Metal cations are generally smaller than the anions which occupy the vacant lattice site or hole. 

In case of pure alkali halides, the frenkel defect is not common. because the the alkali metal cannot fit into the interstitial vacant positions due to their large sizes. 

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Vaibhav Pandey , From Krishna Public School , added an answer
Answered on 2/1/12

Frenkel defect is observed in those cases where sizes of the cations and anions are incomparable i.e, one is very small and the other is too large.Since alkali metals and hydrogen have almost similar sizes, it doesnot show frenkel defect

akshaypatra , added an answer
Answered on 8/1/12

because the the alkali metal cannot fit into the interstitial vacant positions 
due to their large sizes