# Ch05 2

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CHAPTER 5: IMPERFECTIONS IN SOLIDS ISSUES TO ADDRESS... • What types of defects arise in solids? • Can the number and type of defects be varied and controlled? • How do defects affect material properties? • Are defects undesirable? • How do point defects in ceramics differ from those in metals? • In ceramics, how are impurities accommodated in the lattice and how do they affect properties? 1 TYPES OF IMPERFECTIONS • Vacancy atoms • Interstitial atoms • Substitutional atoms Point defects • Dislocations Line defects • Grain Boundaries Area defects 2 POINT DEFECTS • Vacancies: -vacant atomic sites in a structure. Vacan distortion of planes • Self-Interstitials: -"extra" atoms positioned between atomic sites. distortion of planes selfinterstit 3 EQUIL. CONCENTRATION: POINT DEFECTS • Equilibrium concentration varies with temperature! No. of defects Activation energy −Q  ND= exp  D   kT  N No. of potential Temperature defect sites.Boltzmann's constant (1.38 x -23 10 J/atom K) -5eV/at (8.62 x10 om K) Each lattice site is a potential vacancy site 4 MEASURING ACTIVATION ENERG Y • We can get Q from an experiment. • Measure this... • Replot it... ND ln N 1 slope -QD/k 1/T 5 ESTIMATING VACANCY CONC. • Find the equil. # of vacancies in 1m of3 Cu at 1000C. • Given: 0.9eV/atom −  N Q D   -4 =exp  D  N = 2.7 · 10 k T 1273K 8.62 -5 x eV/atom-K 10 N 3= 8.028 3 x sites ...
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