Cottrell atmosphere

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The concept of Cottrell atmosphere was introduced by Cottrell and Bilby in 1949 to explain certain dynamic instabilities observed in plastically deformed materials.

In crystalic structures, a foreign atom or impurity has lower energy in dislocation than in the center of the crystal. The foreign atoms are thus "attracted" by the dislocations. They move to the positions with lower energy and form Cottrell atmosphere around dislocations. This makes the movement of dislocations more difficult.