Materials Chapter 3: Structure of Crystalline Solids

Midterm 1

crystalline

periodic and repeating 3D array of atoms, ions, or molecules (metals, many ceramics, some polymers)

amorphous / noncrystalline

no periodic arrangement (complex structures)

ordered structures

tend to be nearer to the minimum in bonding energy, more stable

minimized

bonds tend to form between particles such that there is 0 net force exerted on them and overall energy is ________.

N = Ni + Nf/2 + Nc/8

number of atoms per cubic unit cell

1

Number of atoms per SC

4

Number of atoms per FCC

2

Number of atoms per BCC

6

Number of atoms per HCP

coordination number

number of nearest neighbor or touching atoms

6

coordination number for SC

12

coordination number for FCC

8

coordination number for BCC

12

coordination number for HCP

APF

the fraction of a unit cell occupied by hard-sphere atoms or ions, measure of the packing efficiency of a unit cell

APF = N*(V_atom)/V_cell

APF formula

6*R²*c*sqrt(3)

V_cell for HCP

hexagonal structure

tetragonal structure

rhombohedral (trigonal) structure

orthorhombic structure

monoclinic structure

triclinic structure

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

metals > ceramics > polymers

density comparison for 3 material types

single crystals

the periodic arrangement of atoms (crystal structure) extends without interruption throughout the entire specimen.

polycrystalline

consisting of many crystalline parts that are randomly oriented with respect to each other

Px Py Pz

notation for points

[n1 n2 n3]

notation for lattice vector (direction)

<h k l>

notation for set or family of directions

(h k l)

notation for crystal plane / Miller indices

{h k l}

notation for set or family of planes

(h k i l); i = - (h + k)

notation for hexagonal lattice

anisotropy

property value depends on crystallographic direction of measurement, observed in single crystals