bcc ,fcc & hcp struc 2.pptx

BCC, FCC , HCP

1. Crystal structure of metals Atoms of a metal crystal are arranged in close-packed structures. Most pure metals naturally adopt one of these three closest packing arrangements 1)body-centered cubic (bcc), 2) face centered cubic, (fcc) 3)hexagonal close packed (hcp)

2. primitive unit cell/Simple cubic unit cell - , atoms are present at corners only. In a crystal lattice every corner is shared by eight adjacent unit cells. Therefore, only 1/8 of an atom belong to a particular unit cell. Since, there are 8 atoms present in a unit cell Therefore, total number of atoms in one unit cell  =8×1/8=1

3. Body Centred Cubic (bcc) Unit Cell – There are eight atoms at each corner and one atom present at the centre of body in a body centred cubic (bcc) unit cell. Atoms touches only along body diagonal of cube. Therefore, the number of atoms present in a Body Centred Cubic (bcc) Unit Cell 8 corners  ×1/8  atoms per corner  =8×1/8= 1 atom Body center atom  =1×1 =1 atom Hence, total number of atoms per unit cell =1+1 =2 atom

4. face centred cubic(fcc) unit cell,- there are eight atoms present at each corner of a cube and also centre of each of the faces of the cube Atoms touches only along face diagonal Therefore, number of atoms in an fcc unit cell - 8 corners  ×1/8  atoms per corner  =8×1/8= 1 atom 6 face centered atoms  ×1/2  atom per face  =6×1/2=3 Hence, total number of atoms per unit cell in a fcc unit cell  =1+3=4

5. hcp- The hcp structure is represented as an atom at each of 12 corners of the hexagonal prism( basal plane), 2 atoms at top and bottom face centre and 3 atoms in between the top and bottom face Total no of effective atoms per unit cell = 12×1/6+2×1/2+3 . =2+1+3 = 6 atoms per unit cell

6. Cordination no -Cordination no is the no of nearest atom which are directly surrounded a given atom. When the cordination no is larger the structure is more closely packed

7. Bcc

8. fcc

9. hcp

10. Cordination no