Crystalline Structure Flashcards
What are crystalline materials?
-Metals
-Atoms arranged in 3D periodic arrays
-Many ceramics
-Some polymers
What are non crystalline materials?
-Atoms with no periodic arrangement
-Complex structures
These are known as amorphous
What is a unit cell?
the smallest unit of volume representing the crystal structure of the material
What are the types of unit cell?
-Cubic: a=b=c
-Hexagonal: a=b=|c
-Tetragonal: a=b=|c
-Rhombohedral a=b=c
-Orthorhombic a=|b=|c
What is a simple cubic crystal?
-Centres of atoms located at the 8 corners of a cube
-Rare due to low packing density
-Close packed directions are cube edges
What is crystal structure?
-A unique arrangement of atoms
-Most elements crystallise to form
+Body centred cubic (BCC)
+Face centred cubic (FCC)
+Hexagonal close packed(HCP)
What is a body centred cube?
-Axial lengths are equal
-2 atoms per unit cell
-R=sqrt a/4
What is a face centred cubic?
-Atoms located at 8 cube corners and at the centred of the 6 faces
-Axial lengths are equal
-sqrt 2a=4R
What is hexagonal close packed?
-6 atoms per unit cell
-Axial lengths are not equal
-a=2R
What is a single crystal?
When the periodic arrangement of atoms extends throughout the entire specimen
What is the diffraction phenomenon?
It is the result of radiation being scattered by a regular array of scattering centres whose spacing is about the same as the wavelength of radiation
What is the diffraction angle?
2𝞱
