Ceramics Week 2 Crystal rules and Thermodynamics

Radius ratio

r+/r-

Determines coordination number, where the ratio will fall in between limits required for certain polyhedrons

Pauling rule 1

Crystal only stable if cation in contact with each of its neighbouring anions.

Pauling rule 2

Charge neutrality. Total electrostatic bond strength reaching an anion in a polyherdron from all neighbouring cations should equal to the charge of the anion.

Pauling rule 3

Polyhedra in a structure tend to not share edges or faces. This is cause by sharing corners instead, cations can minimise repulsion between each other.

Fluorite structure

ROck salt structure