1.6 Ionically Bonded Ceramic Structures

• Most of the ceramic materials are compounds with anions and cations with different electronegativities. Hence, when these ions are brought together, they form a very strong ionic bond.
  
  
• Typically, since anions are bigger in size than cations, anions tend to form the base lattice and cations fill in the interstices.
  .
• However, it is not so simple. As there is an involvement of two different types of ions to form a crystal structure, there are certain rules or say guidelines which need to be followed to give rise to a stable crystal structure. These rules are called Pauling’s rules.
  
  
• Based on these rules, typically ceramic structures are based on anions forming the base lattice and cations occupying the interstices in them. Fortunately, most ceramic compounds are completely or partially ionically bonded and happen to be based on either of FCC or HCP packing of anions. As a result, we can categorize the structures of most ceramic materials into following categories

  • Compounds based on cubic closed packing (CCP or FCC) of ions

  • Compounds based on hexagonal closed packing (HCP) of ions

  • Other structures with some deviations from above two.