Читать книгу Earth Materials - John O'Brien - Страница 121

Point defects involve individual atoms and therefore do not have longer range extent; they are considered to be zero‐dimensional defects. Many types of point defects exist, and they are important in explaining the properties of minerals as well as other materials that include steel, cement, glass products, semiconductors, and superconductors. These include the following:

1 Substitution defects (Figure 4.32b) form when anomalous ions of inappropriate size and/or charge substitute for ions of appropriate size and/or charge in a structural site. These anomalous ions tend to distort the crystal lattice locally and to be somewhat randomly distributed within the crystal lattice.

2 Interstitial defects (Figure 4.32c) occur when anomalous ions occupy the spaces between structural sites. Such “extra” ions are trapped in the interstices between the “normal” locations of ions in the crystal lattice.

3 Omission defects (Figure 4.32d) form when structural sites that should contain ions are unoccupied. In such cases, ions that should occur within the ideal crystal structure are omitted from the crystal lattice leaving a “hole” in the ideal crystal structure.