Lecture – 6 & 7
Atomic
arrangements,
Directions and
Planes, Linear and
Planar Densities
Md. Fakhrul Islam
Crystallographic Plane in FCC : (100)
Crystallographic Plane in FCC : (110)
Crystallographic Plane in FCC : (111)
Determination of FCC Unit Cell Volume
From the right triangle on the face
Computation of the Atomic Packing Factor for FCC
FCC : Linear Density [110]
FCC : Linear Density [111]
Determination of BCC Unit Cell Volume
Centre and corner atoms touch one another along cube diagonals,
and unit cell length a and aomic radius R are related through
BCC : Planar Density (100) Plane
BCC : Planar Density (110) Plane
Crystal System
Below is a unit cell for a hypothetical metal
(a) The unit cell belongs to the tetragonal crystal system
since a=b=0.30 nm, c=0,40nm, and a=b=g=90o.
(b) The crystal structure would be called body-centered
tetragonal.
(c) As with BCT, n=2 atoms/unit cell,
(a) To which crystal system does this unit cell belong?
(b) What would this crystal structure be called?
(c) Calculate the density of the material, given that its
atomic weight is 141 g/mol.
Determine the indices for the directions shown in the following cubic unit cells:
Determine the Miller indices for the planes shown in the following unit cells:
Determination of HCP Unit Cell Volume
For the HCP crystal structure, show that the ideal c/a ratio is 1.633
Basal Plane in the Hexagonal unit cell
Crystallographic Plane in HCP
HCP : Planar Density
Thanks