Question

can anyone help me in explaining the metal excess defect in Non stoichiometric defects? i fail to understand it

Answer 1

Non-stoichiometric defects are compounds which contain the combining elements in a ratio different from that required by their stoichiometric formula. The solids with metal excess defect contain metal in excess to the stoichiometric ratio. Such defect is caused due to either of the following reasons:
1. Metal excess Defect due to Anionic Vacancies:
     In this, negative ions may be missing from their lattice sites leaving holes in which the electrons remain entrapped to maintain the electrical neutrality.
2. Metal excess defect due to the presence of extra cations at interstitial sites:
     In this case, there are extra positive ions occupying interstitial sites and the electrons in another interstitial sites to maintain electrical neutrality. The defect may be visualized as the loss of non-metal atoms which leave their electrons behind. The excess metal ions occupy interstitial positions.