Imperfections in Solids - I

Defects in Non-Stoichiometric Compounds: The compounds in which the ratio between numbers of anions to number of anions is not equal to ratio indicated by the formula.

• Metal Excess Defect
• Metal Deficiency Defect.

a. Metal Excess Defect: In these compounds there is an excess of cations along with the electrons occurs.   

i. Anion Vacancy:

⇒ This free electron center is called F-centre.

⇒ Due to this only these compounds exhibits colour.

ii. Interstitial cation:

⇒ In this one of the cation will present at the interstitial position and which is stabilized by the electron at interstitial position.

⇒ In this the number of cations are not equal to the number of anions. 

b. Metal Deficiency Effect:

i. Cation Vacancy: One cationic space is empty instead of that a positive cation will present in order to maintain the electrical neutrality.

ii. Interstitial Anion: In this defect the anion occupies interstitial position and one of the cation will be in its +2 oxidation state.