MSE2001H_4_1

MSE2001H_4_1 - 1 Chapter 4 Point Defects and Diffusion...

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1 • Introduction • Point Defects • Impurities • Solid State Diffusion Chapter 4 Point Defects and Diffusion
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2 Introduction- Defects and Impurities Number of Fe atoms in 1 cm 3 . For BCC Fe, one unit cell with a=0.287 nm has two Fe atoms. Considering such huge number of atoms, it should not be surprising that some mistakes happen in the atomic arrangement. 22 3 10 46 . 8 1 # × = cm in atoms Fe of Types mistakes Point defects Linear defects Planar defects
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3 Are these defects undesirable? Introduction- Defects and Impurities What effect do the defects have on properties of materials? Can we control the defects for our purpose? Questions Example) semiconductor
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4 Point Defect defined as an imperfection that involves a few atoms at most V: vacancy in which an atom is missed I: interstitial in which an extra atom gets in (wrongly)
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5 Point Defects Δ G = Δ H - T Δ S Perfect crystal Enthalpy Perfect crystal is favorable. Entropy Perfect crystal is unfavorable. Why does the nature choose imperfect one?
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This note was uploaded on 06/29/2009 for the course MSE 2001 taught by Professor Tannebaum during the Spring '08 term at Georgia Tech.

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MSE2001H_4_1 - 1 Chapter 4 Point Defects and Diffusion...

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