Question

Why does ZnO exhibit enhanced electrical conductivity on heating?

Answer 1

Zinc oxide on heating loses oxygen (being a gas) and thus left with only Zn2+ ions and free electrons. And due to the presence of free electrons ZnO shows electrical conductivity on heating
Eq ÷ ZnO → Zn2+ +1/2O2 + 2e-

Hope it helps...!

Answer 2

Zinc oxide (ZnO) has defects in the form of non-stoichiometry. When it is heated it changes colour due to the loss of oxygen and returns to its pure unstable metallic form in the colour yellow.

Now due to the presence of the electrons in the interstitial space the electrical conductivity of it increases. Zinc oxide otherwise has moderate electrical conductivity and is categorised as a semiconductor which is a soft metal and has low thermal expansion.