Exercise 2
Question 23
Explain the following terms with suitable examples:
(i) Schottky defect
(ii) Frenkel defect
(iii) Interstitials and
(iv) F-centres
1) Schottky defect – It was discovered by German scientist Schottky in 1930.It arise if some of the atoms or ions are missing from their normal lattice sites.the unoccupied lattice sites are called as lattice holes.Since the crystal is to remain electrically neutral,equal number of cations & anions are missing.
2) Frenkel defect – It was discovered by a Russian scientist Frenkel in 1926.It arises when an ion is missing from its normal position & occupies an interstitial site between the lattice points..in this case the crystal remains electrically neutral because the number of cations & anions remains the same.
3) Interstitials defect – When some constituent particles occupy vacant interstitial positions ,the crystal will have a interstitial defect.
4) F-centres – During an anion vacancy ,the electrons trapped in anion vacancies are called as F centres.It is originated from a german word farbenzenter which means colour centre.
