L13Defects145s09

L13Defects145s09 - Lecture 13: Defects in Crystalline...

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Lecture 13, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : C&R §5.1-5.5; skim §5.7-5.10; OGC §21.5 Learning objectives: Categorize defects by dimensionality Point Line Planar Volume Recognize defects by type Vacancies Self interstitials Substitutional impurities Interstitial impurities Schottky Anion Frenkel Cation Frenkel • Know how to compute concentrations of intrinsic defects Know the rules for solid solution formation Lecture 13: Defects in Crystalline Materials
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Lecture 13, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Defects in Crystalline Solids Disruptions in the periodicity of the crystal structure Point defects Line defects Planar defects Volume defects (Atomic vibrations) Even small concentrations of defects may have major effects on properties Mechanical: dislocations & strain hardening in metals Electrical: doping in semiconductors Thermal: thermal conductivity of solid solutions Optical: color in gemstones
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Lecture 13, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Point Defects in Elemental Crystalline Solids [C&R §5.2] Intrinsic defects Vacancy Self-interstitial Extrinsic defects Substitutional impurity Interstitial impurity
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Lecture 13, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Point Defects in Ionic Compounds [OGC §21.5; C&R §5.3] Schottky defects (intrinsic) Anion vacancy Cation vacancy Form in proportion to the stoichiometry of the compound, e.g. a Schottky pair in compound MX Extrinsic defects Anion substitutional Cation substitutional Interstitial - + + OGC Figure 21.28
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Lecture 13, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Point Defects in Ionic Compounds [OGC §21.5] Point defects in ionic compounds Frenkel defects (intrinsic) Cation Frenkel pair Cation vacancy Cation interstitial Anion Frenkel pair Anion vacancy Anion interstitial OGC Figure 21.28
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Lecture 13, spring 2009 ENGR 145, Chemistry of Materials
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L13Defects145s09 - Lecture 13: Defects in Crystalline...

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