A linear or one-dimensional defect around which some of the atoms are misaligned.  

A pure metal (consisting of only one type of atom) is impossible.  

Intentionally adding impurity atoms to impart specific characteristics to the material. 

Adding impurity results in the formation of a solid solution and/or a second phase. 

Solvent - material present in greater amount
Solute - material with minor concentration 

Substitutional and interstitial.

Impurity atoms substitute for host atoms.  The degree to which solute atoms dissolves into solvent is determined by atomic size factor (smaller difference more dissolve), crystal structure (must be same), electronegativity (small difference), valences (higher valency the higher metal will dissolve).
- Typically metals, but can also be ceramics (must have nearly same ionic size and charge as host)

Impurity atoms fill voids among host atoms.  
- The lower the atomic packing factors, the greater the voids (ie. NOT metals (which have high atomic packing factors)!).  
- Smaller atomic diameter of impurity, the greater the dissolution 
- Can be metals, and also ceramics 

In order for impurities to occur in ceramics: 
1) ionic size and charge of impurity must be similar to host ions
2) for an impurity ion having a diff charge, crystal must compensate for this difference in charge (neutrality must be maintained)

Both types of defects can be found in the crystalline regions of polymeric materials, similar to metals.  

Point defects in polymers can be similar to metals in crystalline regions of polymeric materials.  
- Chain ends considered defects (bc they're so chemically dissimilar to chain units). Vacancies are associated with chain ends.
- Additional defects can result from branches in polymer chain/chain segments that stick out. 

A linear defect that centers on the line is defined along the end of the extra half-plane of atoms (dislocation line)

Formed by shear stress (like trying to unscrew the crystal, results in shear stress)

Boundaries that have two dimensions and normally separate regions of the materials that have different crystal structures and/or crystallographic orientations. 

Boundary separating two small grains or crystals having different crystallographic orientations in polycrystalline materials.