Defect Classification

Homogeneous Point Defects
* Point Defects (0D)
* Missing atoms (vacancies) or extra atoms (self-interstitial) in a                     structure
* Vacancies are easier to form because it requires more energy to                 compress bonds than to spread them apart

Heterogeneous Point Defects
* Point Defects (0D)
* Interstitial- impurity atoms are between the lattice
* Substitutions- impurity atom where substance atom is expected

Linear Defects
* One Dimensional
* Edge dislocation- an extra plane of atoms is inserted into the lattice
-Denoted by an upside down “T” below plane of extra atoms
-Burger’s vector, b, denotes magnitude and direction of lattice                       distortion
-Burger’s vector is perpendicular to plane of extra atoms
-On the side of the extra atoms, there will be compression, and on the           side without the extra plane of atoms, there will be tension.
* Screw dislocation- atoms are one unit away from where they should be
-Burger’s vector, b, denotes magnitude and direction of lattice                      distortion
-Burger’s vector is parallel to extra plane of atoms
* Mixed dislocations- combinations of both edge and screw dislocations

Surface Defects
* Occur at surfaces, because the atoms on the surface are not bonded         to as many atoms as they could be
-Interfaces- grain boundaries
-Low angle grain boundaries
-High angle grain boundaries
-Twins: Mechanical and annealing
-Stacking faults- where more than one defect is stacked on top of                 another
-Phase boundaries
-Ferromagnetic domain walls: where the magnetic field varies from               grain to grain

Volumetric Defects
* Pores
* Cracks
* Inclusions
* Amorphous material
* Phase regions

Advertisements