Metal Excess Defect in Zinc Oxide ZnO

The video tutorial explains the concept of metal excess defect, which occurs when excess cations and free electrons occupy interstitial positions in a crystal to maintain electrical neutrality. This defect imparts color to the crystal and enhances its electrical conductivity. The tutorial uses zinc oxide as an example, describing how it changes color from white to yellow upon heating due to the movement of zinc ions and free electrons. When light falls on these heated crystals, the free electrons absorb and emit yellow light, causing the yellow coloration.

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