2.1 Point Defects

• Point defects are caused due to deviations from the perfect atomic arrangement or stoichiometry. These could be missing lattice ions from their positions, interstitial ions or substitutional ions (or impurities) and valence electrons and/or holes.

• Usually, point defects in metals are electrically neutral whereas in ionic oxides, these are electrically charged.

• Ionic defects

  • Occupy lattice positions

  • Can be either of vacancies, interstitial ions, impurities and substitutional ions

• Electronic defects

• Deviations from a ground state electron orbital configuration give rise to such defects when valence electrons are excited into higher energy orbitals/ levels and lead to formation of electron or holes.

• Defects are present in most oxides and are easily understood. Hence most examples in the following section use examples of oxides.