Imperfections such as vacancies, interstitials, Schottky and Frenkel defects affect solid properties.
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Real crystals contain imperfections called defects, which are departures from perfect periodic order. Point defects include vacancies, where an atom is missing from its site, interstitials, where an extra atom sits between lattice sites, and substitutional impurities. Line defects, or dislocations, and surface defects also occur, and they strongly influence mechanical strength and plasticity. Defects change properties such as density, colour, electrical conductivity and reactivity, and they are often introduced deliberately. Doping is a controlled introduction of defects used to tune semiconductors.
Key ideas: Point defect concentration grows exponentially with temperature, roughly exp(-E/kT), so all crystals above 0 K have vacancies. Vacancies lower density slightly; interstitials usually raise it. Impurity defects cause colour in gems, for example Cr3+ in ruby. Dislocations enable plastic deformation, and work hardening increases their number.
Common mistakes and connections: A common error is claiming defects are always harmful; steel and semiconductors depend on them. Another is mixing up Schottky and Frenkel types. Non-stoichiometric compounds such as FeO, which is really Fe0.95O, arise from vacancies. Links to doping, ionic conductivity, metallurgy and colour centres.
Point defects include vacancies, interstitials and impurities; ionic solids show Schottky and Frenkel pairs that affect density and conductivity. The interactive lesson shows this as a live animation or chart.
Doping silicon with a small amount of phosphorus deliberately creates extra electrons, changing its conductivity in a controlled way.
Imperfections such as vacancies, interstitials, Schottky and Frenkel defects affect solid properties.
Crystal Defects is a advanced topic in States of Matter & Solutions. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in States of Matter & Solutions first: Crystal Systems, Bravais Lattices, X-ray Diffraction and Bragg's Law.
The next topics in States of Matter & Solutions are Schottky Defect and Frenkel Defect.
Yes. The interactive lesson includes a self-check question on Crystal Defects, and the States of Matter & Solutions quiz draws on every topic in this area.
Crystal Defects is topic 67 of 109 in States of Matter & Solutions.