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ECE331 Wi11 lecture 6

ECE331 Wi11 lecture 6 - LAST TIME Equilibrium Concentration...

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LAST TIME : Equilibrium Concentration: P i t D f t Equilibrium concentration varies with temperature! Point Defects No. of defects Activation energy N v N = exp Q v k T No. of potential defect sites. Temperature Boltzmann's constant (1.38 x 10 -23 J/atom-K) (8.62 x 10 -5 eV/atom-K) Each lattice site is a potential is a potential vacancy site
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Today, start with Impurities in Solids Impurities also form a type of point defect, but they are “extrinsic” (as opposed to “intrinsic” in origin) Substitutional impurity : when an impurity atom exactly replaxes (substitutes) for a host atom in the crystal Interstitial impurity : when an impurity atom resides at an interstitial location in the crystal
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Impurities in Solids Two outcomes if impurity (B) added to host (A): (1) Solid solution of B ( solute ) in A ( solvent ) (random dist. of point defects) OR Substitutional solid soln. (e g Cu in Ni ) Interstitial solid soln. (e g C in Fe ) (e.g., in (e.g., in Ideal solid solution: Impurities do not alter crystal structure of host solid material
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