2.1 Crystal Structure I - Unit Cells
crystal lattice
A regular three-dimensional array of points in space associated with specific positions of atoms or molecules in a solid.
single crystal
A single, physically 3-D uniform solid with long-range order
lattice
A three-dimensional array of points associated with the positions of atoms or molecules
tin pest
An allotropic transformation of body-centered tetragonal white tin to diamond cubic gray tin due a decrease in temperature in which the metal crumbles into particles
grain
An individual crystal, usually referring one of many randomly oriented single crystals in a polycrystalline solid
polycrystalline
Composed of multiple crystals or grains
noncrystalline
Lacking long range atomic or molecular order
lattice parameters
The unit cell edge lengths and angles that define the unit cell geometry
cube
A 3-D geometric figure composed of orthogonal angles and equal axial lengths
face-centered cubic (FCC)
A crystal structure in which atoms are located at all corners and the centers of each face
body-centered cubic (BCC)
A crystal structure in which atoms are located at each corner and in the center of the unit cell
triclinic
A crystal structure in which none of the axial lengths or angles are equal or orthogonal
trigonal
A crystal structure in which the axial lengths and angles are all equal, but the angles are not orthogonal
monoclinic
A crystal structure in which the three edge lengths are unequal, and there are two orthogonal angles
hexagonal close-packed (HCP)
A crystal structure in which the unit cell is hexagonal and the stacking sequence of closed packed planes is ABAB...
tetragonal
A crystal structure in which two of the three edge lengths are equal, and all three angles are orthogonal
close packed direction
A direction in a crystal in which all the atoms are touching one another
crystal
A physically 3-D uniform solid with long-range order
close packed plane
A plane in a crystal in which all the atoms are touching one another
texture
A preferred crystallographic orientation of crystalline grains within a solid
crystalline
Having a periodic and repeating three-dimensional array of atoms
semicrystalline
Having both crystalline and amorphous regions within a solid, mainly occurring in polymers
anisotropic
Having different properties in different crystallographic directions
amorphous
Having no long-range order or crystalline structure
isotropic
Having the same properties in all crystallographic directions
Miller indices
Indices used to define the orientation of crystallographic planes
crystal system
Seven classes of crystal structures; cubic, hexagonal, rhombohedral, tetragonal, orthorhombic, monoclinc, triclinic
Bravais lattices
The 14 basic crystal structures
cube face
The area on a side of a cube
unit cell
The basic structural unit of a crystal structure
Bragg's law
The equation that specifies the condition for the diffraction of x-rays from a crystal
polymorphism
The existence of more than one form or crystal structure of a solid material
allotropy
The existence of multiple crystal structures for a material
grain boundary
The interface separating two adjacent grains with different crystallographic orientations in a polycrystalline solid
cube edge
The line along the edge of a crystal connecting two corners
face diagonal
The line connecting two corners of a face of a cube
body diagonal
The line that extends from one corner of a cube to the opposite corner
crystal structure
The manner in which atoms are regularly organized in space
theoretical density
The mass of the atoms in a unit cell divided by the volume of the unit cell
coordination number
The number of atoms touching a given atom in a crystal structure
diffraction
The symmetrical path change of an x-ray induced by its interaction with the atoms of a crystal
atoms per unit cell
The total number of atoms within one unit cell
atomic packing factor (APF)
Volume of hard-sphere atoms within a unit cell divided by total unit cell volume
