CACAT KRISTAL (IMPERFECTION CRYSTAL)CITRA BUHATIKA 1021207015 Pascasarjana Kimia Universitas Andalas Padang, 2011

Types of Imperfectionsy Point defects

a. Vacancies b. Self-interstitial atoms c. Interstitial solute atoms d. Substitutional atoms y Line defects a. Dislocations y Area defects a. Grain Boundaries

Point Defects

Line DefectLinear Defects (Dislocations) Are one-dimensional defects around which atoms are misaligned, charaterized by a vector in the lattice called the Burgers vector b, a crystal vector, [uvw], which is a measure of the distortion of the lattice around the defect. y Edge dislocation: b to dislocation line y Screw dislocation: b || to dislocation line

- Edge Dislocation

- Screw Dislocation

- Mixed Dislocations

Area Defecty Grain Boundaries

- regions between crystals - transition from lattice of one region to that of the other - slightly disordered - low density in grain boundaries * high mobility * high diffusivity * high chemical reactivity

One case is a twin boundary (plane) Essentially a reflection of atom positions across the twin plane.

This is a type of coincidence-site boundary (atoms in the boundary are in lattice positions of both crystals

Low-angle boundary

Planar array of dislocations

TERIMA KASIH