Chapter 4.2

Chapter 4.2 - Point Defects: Vacancies Vacancy = absence of...

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6 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals How many vacancies are there? Vacancy = absence of an atom from its normal location in a perfect crystal structure Point Defects: Vacancies Vacancies are always present in crystals and they are particularly numerous at high temperatures, when atoms are frequently and randomly change their positions leaving behind empty lattice sites ( vacancies ). Statistical thermodynamics predicts that the number of vacancies, N v , have very strong dependence on temperature, T, and can be estimated using the Boltzmann distribution: where N s is the number of regular lattice sites, k B is the Boltzmann constant, Q v is the energy needed to form a vacant lattice site in a perfect crystal, and T the temperature in Kelvin ( note, not in o Cor o F ). = T k Q exp N N B v s v
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7 MSE 2090: Introduction to Materials Science Chapter 4, Defects in crystals Note, that the above equation gives the lower end estimation of the number of vacancies in real materials, a
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This note was uploaded on 02/14/2012 for the course MSE 2090 taught by Professor Leoindzhiglei during the Fall '10 term at UVA.

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Chapter 4.2 - Point Defects: Vacancies Vacancy = absence of...

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