Zinc Oxide (ZnO)

Definition

Zinc oxide is an inorganic compound with the formula ZnO, known for its unique properties and versatility in various applications. It exists in several polymorphic forms, including wurtzite and zinc blende, and can function as a semiconductor, insulator, or catalyst. Its behavior can be influenced by defects and non-stoichiometry, which are crucial for understanding its performance in applications such as electronics and materials science.

5 Must Know Facts For Your Next Test

1. Zinc oxide exhibits both n-type and p-type conductivity depending on the presence of defects such as oxygen vacancies or zinc interstitials.
2. As a wide bandgap semiconductor (3.37 eV), ZnO is used in applications like UV light-emitting diodes (LEDs) and laser diodes.
3. The presence of defects can lead to non-stoichiometric compositions, affecting the optical and electrical properties of zinc oxide.
4. ZnO nanoparticles are extensively used in sunscreens and cosmetics due to their UV-filtering properties and low toxicity.
5. Zinc oxide's piezoelectric properties make it useful in sensors, actuators, and other electronic devices where mechanical strain is converted to electrical energy.

Review Questions

• How do defects in zinc oxide affect its electrical properties?
  • Defects in zinc oxide, such as oxygen vacancies or zinc interstitials, play a crucial role in determining its electrical properties. For instance, oxygen vacancies can introduce extra electrons into the conduction band, leading to n-type conductivity. Conversely, if zinc atoms are missing from the lattice, it may lead to p-type conductivity. These defects influence charge carrier concentration and mobility, ultimately impacting the performance of devices made from ZnO.
• Discuss how non-stoichiometry in zinc oxide influences its application as a semiconductor.
  • Non-stoichiometry in zinc oxide alters the ratio of zinc to oxygen in the compound, which significantly impacts its semiconducting properties. Variations in this ratio can lead to changes in the type of conductivity exhibited by ZnO—whether n-type or p-type—thereby affecting its behavior as a semiconductor. These changes also influence important characteristics such as carrier concentration, bandgap energy, and overall electronic performance in applications like LEDs and solar cells.
• Evaluate the implications of using zinc oxide nanoparticles in consumer products with respect to safety and environmental concerns.
  • The increasing use of zinc oxide nanoparticles in consumer products like sunscreens raises important safety and environmental concerns. While ZnO is considered relatively non-toxic compared to other nanoparticles, its small size allows for potential absorption by skin or inhalation, leading to uncertain health effects. Additionally, the release of these nanoparticles into the environment may impact ecosystems, particularly aquatic life, due to their reactivity and bioaccumulation potential. Thus, evaluating both benefits and risks is crucial for responsible use.

Related terms

Defects: Irregularities in the crystal structure of materials that can significantly affect their physical properties and performance.

Non-stoichiometry: A condition in which the proportions of elements in a compound deviate from the ideal stoichiometric ratio, often resulting in altered properties.

Semiconductor: A material that has electrical conductivity between that of a conductor and an insulator, often used in electronic devices.