Question

The crystal AB (rock salt structure) has molecular weight 6.023y u. where, y is an arbitrary number in u. If the minimum distance between cation and anion is y1/3 nm and the observed density is 20 kg/m³ . Find the (a) density in kg/m³ and (b) type of defect. 

Answer 1

 (a) In rock-salt like crystal AB, there are four AB units per unit cell. Therefore, density (d) is

(b) Since, observed density is greater than expected, theoretical density, there must be some excess metal occupying interstitial spaces. This type of defect is known as metal excess defect.