Question

What does F-centre mean in Chemistry?

Answer 1

F-centre:

• "The anionic sites occupied by unpaired electrons are called F-centres.
• Alkali halides such as Sodium chloride$\left(\mathrm{NaCl}\right)$ and Potassium chloride $\left(\mathrm{KCl}\right)$ show this type of defect.

Metal excess defect:

• The metal excess defect is produced due to the anionic vacancies and the presence of extra cations in the interstitial sites.
• Anionic vacancies are created when an alkali metal halide is heated with an alkali metal's atmosphere.
• This anion then diffuses to the crystal’s surface, where it joins freshly formed metal cations.

F-centre in a crystal is shown as: