Module 1: Structure of Ceramics
  Interstices in Structures
 


     1.4 Interstices in Structures

  • Since the unit cell is not completely packed as packing efficiency in the previous structures is less than 100%, there are empty spaces inside which are called as interstices.

  • These interstices are very useful because there can contain smaller atoms which modify the properties of materials tremendously, such as Carbon (C) in Iron (Fe) makes steel and makes iron stronger.
      1.4.1 Interstices in FCC Structure

  • Tetrahedral Interstices

    • 2 per atom

  • Octahedral Interstices

    • 1 per atom

Figure 1.19 Interstices in a FCC structure

So, by simple geometry, you can also estimate the size of the largest interstitial atom that would fit in these interstices without distorting them.
rtet = 0.225* r
rtet = 0.225* r

1.4.2 Interstices in BCC Structures

Figure 1.20 Interstices in a BCC structure