Unit 10 - crystal structures of ceramics

What are ceramics?

compounds of metalic and non metallic elements.

most frequently oxides, nitrides, carbides

What is the structure of ceramic materials?

ionic

positive cation, metal and negative anion, non metal

cations are much smaller so there is a close packing of the anions with the cations in the spaces

What is paulings rule for the structure of ceramics?

To maximise attraction and minimise repulsion, the cation is surrounded by the maximum positive of anions

the cations are located as far away from each other as possible

the structure must be electrically neutral

What is the coordination number?

the number of anions surrounding each cations

value depends on the ratio of radii, cations/ anions

interstitial atoms whose radii are slightly larger then the radius of the interstitial site enter and push the atoms slightly apart

atoms who radii are smaller them the hole are not stable

What is the NaCl structure?

FCC bravais lattice

cl anions are positioned in the fcc unit cell whilst the Na cation is located at the centre of the FCC edge

each atom has 6 nearest neighbours

What is the CsCl structure?

coordination number 8