F-centres are formed in $\mathrm{NaCl}$ crystal if it is heated with $\mathrm{Na}$ vapour. The above is due to
F-centres are formed in $\mathrm{NaCl}$ crystal if it is heated with $\mathrm{Na}$ vapour. The above is due to
Schottky defect
Dislocation defect
Metal excess defect
Metal deficiency defect
Solution
The crystal lattice has vacant anion sites, which are occupied by electrons. Anion sites occupied by electrons are called $\mathrm{F}$-centres ( $\mathrm{F}$ is abbreviated from Farbe, the German word for colour. These F-centres are associated with the colour of the compound and the more F-centres present, the greater the intensity of the coloration. F-centre containing solids are paramagnetic, photoconductors.