Crystallography Flashcards
What is a space lattice
A space lattice is an infinite array of points in three dimensions in which every point has the same surrounding identical to that of every other point in the array.
What is a unit cell
A unit cell is the smallest unit which, when repeated in space indefinitely, will generate a space lattice.
It is thus the smallest volume that will describe the structure of amaterial.
How many distinguishable ways in how many dimensions and how many crystal systems
14 spaces lattices and seven crystal systems in 3 dimensions
what are the seven crystals systems
cubic, tetragonal, orthorhombic, rhombohedral, hexagonal, monoclinic, triclinic
what are the four crystalline imperfections
point, line, surface and volume
describe point imperfections
imperfections found in point-like regions of
the crystal. Typically range from one to two atomic diameters in size and exist in three common forms:
Vacancy
Substitutional impurity
Interstitial impurity
describe line imperfections
These comprise imperfections that cause lattice distortion centered around a line.
Line dislocations are created during solidification or by plastic deformation of crystalline structures.
They are one dimensional and are best understood by referring to two limiting straight-line types:
Edge dislocation
Screw dislocation
describe edge dislocations
Edge dislocations are created when an extra half plane of atoms are inserted into a crystal structure.
They are represented by a T-shaped symbol, either erect or inverted depending on whether the incomplete plane starts from the top or the bottom of the crystal.
These symbols are known as positive and negative edge dislocations respectively.
Describe screw dislocation
These dislocations are formed when an upward or downward shear stress is applied to a crystal which has been separated by a cutting plane.
What are surface imperfections
Surface imperfections are regions of distortion that lie about the surface, having a thickness of few atomic diameters. Examples of such imperfections are the external surface of the crystal itself and the grain boundaries of the crystal.
What is a mixed dislocation
known as a combination of line + screw dislocations
