Answer: Impurity defect with cation vacancies.
- A Frenkel defect, where a cation migrates into an interstitial lattice site
- B Schottky defect, where equal numbers of cation and anion vacancies appear together
- C Interstitial defect caused by extra atoms squeezing into lattice gaps
- D Impurity defect with cation vacancies
Correct answer: D. Impurity defect with cation vacancies
Explanation: Sr²⁺ replaces two Na⁺ but occupies only one site; to maintain electrical neutrality, one Na⁺ site becomes vacant. This creates a cation vacancy impurity defect.
The three cubic unit cells: Simple Cubic has atoms only at corners; Body-Centred adds one atom at the centre; Face-Centred adds one atom at the centre of each of the 6 faces, giving the highest packing efficiency.
Concept context
Explore the ordered world of crystalline solids: unit cells, packing, defects, and how structure determines electrical and magnetic properties.