Part 5: Defects & Amorphous Solids
No real crystal is perfect. Defects control many properties of materials, from mechanical strength to electrical conductivity and diffusion. Meanwhile, amorphous solids like glasses lack long-range order entirely, giving rise to unique optical and mechanical properties that make them indispensable in technology.
What You Will Learn
- βPoint defects: vacancies, interstitials, and substitutional atoms
- βSchottky and Frenkel defects in ionic crystals
- βLine defects: edge and screw dislocations
- βStrengthening mechanisms in metals and alloys
- βGlass transition, Zachariasen's rules, and glass composition
- βViscosity models: Arrhenius and Vogel-Fulcher-Tammann
Key Equations
Vacancy concentration
$$n_v = N\exp\!\left(-\frac{E_v}{k_BT}\right)$$
Arrhenius viscosity
$$\eta = \eta_0\exp\!\left(\frac{E_a}{RT}\right)$$
VFT equation
$$\eta = A\exp\!\left(\frac{B}{T - T_0}\right)$$
Schottky pair equilibrium
$$n_s = N\exp\!\left(-\frac{E_s}{2k_BT}\right)$$
Topics
5.1 Point and Line Defects
Vacancies, interstitials, Schottky and Frenkel defects, edge and screw dislocations, Burgers vectors, and strengthening mechanisms.
5.2 Amorphous Solids & Glasses
Glass transition, Zachariasen's rules, network formers and modifiers, viscosity models, optical properties, tempering and annealing.