SOL ; Metal Excess Defect
(i) By Anion Vacancy In this defect one or more anions are missing from their lattice sites leaving behind holes which are occupied by electrons to maintain the electrical neutrality of the crystal. This defect has similarity with Schottky defect.
(ii) By Presence Of Extra Cations At The Interstitial Sites This defect is observed when an extra cation is present at one interstitial site and electron at other interstitial site. The crystal remain electrically neutral. This defect has similarity with Frenkel defect.
Consequences Of Metal Excess Defect
(i) The crystal with metal excess defect are conducting due to the presence of electrons. However conductivity is very low therefore act as n type semiconductor.
(ii) The crystal with metal excess defect are paramagnetic due to free electrons.
(iii) The crystal with metal excess defect are generally coloured due to free electrons.
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