Question

$ZnO$ is white when cold and yellow when heated. It is due to development of:

• A. Frenkel defect
• B. metal excess defect
• C. Schottky defect
• D. metal deficiency defect

Answer 1

The correct option is B metal excess defect

$ZnO$ turns yellow on heating as $Z{n}^{2+}$ ions move in interstitial sites and electrons also get entrapped in nearby interstitial sites to maintain electrical neutrality. As extra $Z{n}^{2+}$ ions are present in interstitial sites thus, it is metal excess defect.