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Schottky defect also exists in pair to maintain electroneutrality. Therefore, it generates equal number of cation and anion vacancies. In case of doping of NaCl by CdCl 2 , CI – ions enter Cl – ions site in NaCl while Cd 2+ displace Na + . In doping so, one positive charge becomes extra. Therefore one Na + is displaced so as to maintain electro-neutrality. That is doing only cation vacancies exist.

Schottky defects generate an equal number of cation and anion vacancies while doping produces only cation vacancies and not anion vacancies. Why?

Schottky defect also exists in pair to maintain electroneutrality. Therefore, it generates equal number of cation and anion vacancies. In case of doping of NaCl by CdCl₂, CI^– ions enter Cl^– ions site in NaCl while Cd²⁺ displace Na⁺. In doping so, one positive charge becomes extra. Therefore one Na⁺ is displaced so as to maintain electro-neutrality. That is doing only cation vacancies exist.

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Pure silicon is an insulator. Silicon doped with phosphorus is a semi-conductor. Silicon doped with gallium is also a semiconductor. What is the difference between the two doped silicon semi-conductor?

How would you account for the following:
Schottky defects lower the density of related solids.

Examine the illustration of a portion of the defective crystal given below and answer the following questions:
(i) What are these types of vacancy defects called?
(ii) How is the density of a crystal affected by these defects?
(iii) Name one ionic compound which can show this type of defect in the crystalline state.
(iv) How is the stoichiometry of the compound effected?

How would you account for the following:
Frenkel defects are not found in alkali metal halides.

The Solid State

Schottky defects generate an equal number of cation and anion vacancies while doping produces only cation vacancies and not anion vacancies. Why?