BME2100 - Materials 1 Lecture 4 - Crystallographic Structures

These flashcards cover key concepts related to crystallographic structures, including crystalline materials, unit cells, atomic packing, single vs. polycrystalline materials, and the use of Miller indices.

What is a crystalline material?

A material in which the atoms are situated in a repeating or periodic array over large atomic distances.

What is the smallest repeat structure in crystal structures called?

Unit cell.

What types of metallic crystal structures are common?

Body Centred Cubic (BCC), Face Centred Cubic (FCC), and Hexagonal Close Packed (HCP).

What makes face-centered cubic (FCC) structures significant?

FCC structures allow for sufficient plastic deformation due to their configuration, allowing atoms to slip past each other easily.

Which materials typically exhibit a body-centered cubic (BCC) structure?

Lithium, alpha-iron, and tungsten.

What defines the packing factor in crystalline structures?

The fraction of space occupied by atoms in the unit cell.

What characterizes single crystal materials?

Single crystal materials have a periodic arrangement of atoms that extends without interruption throughout the entire specimen.

What is the difference between single crystal and polycrystalline materials?

Single crystal materials have a uniform orientation, while polycrystalline materials consist of many small crystals (grains) with various orientations.

What is anisotropy in material science?

Anisotropy refers to property values that depend on the crystallographic direction of measurement, typically observed in single crystals.

What are Miller indices used for in crystallography?

Miller indices are used to describe points, directions, and planes in a crystal lattice.

How are crystallographic directions typically expressed?

Crystallographic directions are expressed in square brackets, such as [u v w].

What is the formula for determining Miller indices for a plane?

1. Determine intercepts of the plane on the axes. 2. Take the reciprocals of these intercepts. 3. Normalize by multiplying by lattice parameters. 4. Reduce to the smallest integer values.

What does a family of directions or planes indicate in crystallography?

A family of directions or planes indicates all crystallographically equivalent directions or planes that have the same atomic spacing or packing.