Crystals and Crystallography

What is a crystalline material?

Solids with an ordered structure

What is a amorphous material?

Solids without an ordered structure

What is a unit cell?

The minimum number of atoms to represent the repetitive pattern

What are the 3 types of unit cell?

• Hexagonal close packing (HCP)

• Face centred cubic packing (FCC)

• Body centred cubic (BCC)

How to draw a unit cell of hexagonal close packing (HCP)

Packing Structure = ABABAB

How to draw a unit cell of face centred cubic packing (FCC)

Packing Structure = ABCABC

How to draw a unit cell of body centred cubic (BCC)

Packing Structure = Not relevant, as it's not considered to be a close-packed structure like FCC or HCP (i.e. has close-packed directions but lacks close-packed planes

What is polymorphism/allotropy?

When materials can have more than one crystal structure (i.e. structure changes with temperature)

Examples of planes of atoms within a unit cell

Crystal direction for A[110]

Crystal direction for B[011]

Crystal direction for D[1̅10]

Which brackets are used for a family of directions?

<>

( i.e. <110> )

Crystal plane for (010)

Crystal plane for (020)

Which brackets are used for a family of planes?

{}

( i.e. {110} )