MSE Midterm 1 Set 5: Crystal Systems & Material Types

polymorphism

The ability of a COMPOUND or MOLECULE to exist in more than one form or crystal structure.

allotropy

The possibility of the existence of two or more different crystal structures for an ELEMENT

lattice parameters

The combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry.

crystal system

A scheme by which crystal structures are classified according to unit cell geometry. This geometry is specified in terms of the relationships between edge lengths and interaxial angles. There are seven different crystal systems.

Miller indices

A set of three integers (four for hexagonal) that designate crystallographic planes, as determined from reciprocals of fractional axial intercepts.

single crystal

A crystalline solid for which the periodic and repeated atomic pattern extends throughout its entirety without interruption.

grain

An individual crystal in a polycrystalline metal or ceramic.

polycrystalline

Crystalline materials composed of more than one crystal or grain.

grain boundary

The interface separating two adjoining grains having different crystallographic orientations.

anisotropic

Exhibiting different values of a property in different crystallographic directions.

“not equal in all directions”, asymmetric

isotropic

Having identical values of a property in all crystallographic directions. symmetrical