Ordered structures are more ____ than random packing
Stable
Because closer to minimum bonding energy
Most metals are _______, while most ceramics and polymers are ____
Crystalline (except for glass, which is amorphous)
Amorphous or semi-crystalline
Coordination number
Number of nearest neighbours
Simple cubic: 6
FCC: 12
BCC: 8
HCP: 12
APF
Atomic packing factor. (Number of atoms in one cell x volume of one atom)/Volume of cell
Simple cubic: 0.52
FCC: 0.74
BCC: 0.68
HCP: 0.74
Densities in order
Metals > Ceramics > Polymers
Polymorphism / Allotropy
When same materials can have different structures depending on temperature, for example. Allotropy is term for metals.
Linear density / Planar density
Number of atoms centered on vector/ Length of vector
Number of atoms centered on plane/ Area of plane
Single crystals vs. Polycrystals
Material made up of one single crystal
Material made up of many crystals divided by grain boundaries. (most materials)
Anisotropic vs Isotropic properties
Anisotropic means that the property varies with direction. If grains are NOT randomly oriented (e.g. have a preferred direction) then anisotropic
Isotropic: Properties do not vary with direction. If the crystals are randomly oriented, then isotropic properties bc averages out in all directions.
Bragg’s law
Relationship between x-ray wavelength, interplanar spacing, angle of diffraction.
n(lambda) = 2d(hkl)sin(theta)
