CRYSTALLINE SOLIDS AND STRUCTURE OF METALS | LECTURE 2.1

three-dimensional pattern / unit cell

The smallest unit that shows the****** and arrangement of atoms is called a ***** .

Lattice parameters or cell parameters.

What are the collective terms for the lattice constants (a, b, c) and interaxial angles (α, β, γ) that define a unit cell?

Bravais lattices

Combinations of the four different types of unit cells and the seven crystal systems give rise to what are called the

14

How many Bravais lattices are there?

Isometric or cubic crystal system

Which crystal system is the most symmetric and occurs most often in nature?

Crystalline

What term describes materials where atoms are arranged in a periodic and orderly manner over large atomic distances?

Amorphous materials

What are materials called that lack the same long-range periodicity as crystalline materials?

Lattice

three-dimensional array of points that indicates the position of atoms or ions in a crystal structure?

easier

Materials with smaller atoms/particle size tend to crystallize ****.

promote

Slower cooling rates **** the formation of crystalline structure.

Unit cell

What is the smallest unit that shows the three-dimensional pattern and arrangement of atoms in a crystal structure?

The edge lengths of the unit cell

What do lattice constants correspond to in a unit cell?

interaxial angles

The angle measurements between a pair of the unit cell edges.

The seven crystal systems.

What do different combinations of lattice parameters give rise to?

Bravais lattices

What are the combinations of the four different types of unit cells and the seven crystal systems called?

What is the atomic packing factor (APF) for a Body-centered cubic (BCC) unit cell?

0.68

Which element naturally assumes a simple cubic unit cell at ambient conditions?

Polonium (Po)

atomic packing factor (APF)

defined as the volume of atoms in a unit cell divided by the total unit cell volume.

ρ=​nA/Vc​NA

What is the formula for theoretical density (ρρ) of metallic crystal structures?

Miller indices

What system is generally used to describe crystallographic points, directions, and planes?

Linear density

umber of atoms per unit length of a given direction.

Planar density

What is the term for the number of atoms per unit area on a plane?

single crysta

ormed when the periodic arrangement and order of the atoms and unit cells are perfect and extend throughout the material.

polycrystalline materials

made up of tiny single crystals known as grains.

Allotropy

property of a crystalline material to exist in more than one crystal structure.

Polymorphism

associated with crystalline materials that are composed of more than one element and exist in different crystal structures.