Ionic Bonds in Ceramic Material

The binding energy for ionic bonding varies from 150-370 kcal/mol, the same for metallic bond varies from 25-200 kcal/mol. The stiffness of a bond is related to the binding energy by the relationship S = (d²U / dr²), while the force between the atoms could be derived from the binding energy by evaluating
F= (dU / dr), where the binding energy for an ionic bond is defined by the relationship:

U= U₀ – q² / (4π ε₀ r) + B/rⁿ

Binding energy for a relatively weaker bond like Van der Walls bonding is defined as:

U = - A/r⁶ + B/r¹²

If you calculate the Force-deflection relationship for the two type of bonding you will get the figure below which clearly shows why ionic bonding has steeper force deflection relationship implying higher modulus of elasticity.